Sulfur in Plants: An Ecological Perspective: 6 (Plant Ecophysiology)

Details about the different procedures for fractionating different S forms are given by Eriksen et al. Sulfate released from labile S fractions and microbial biomass is important for the S nutrition of crops. A soil feature, which affects the plant-available S pool is soil texture. A relative increase of the sulfate-ester pool with decreasing particle size indicates a protection of organic S from mineralization Eriksen et al. This hypothesis is supported by the findings of Anderson et al.

These findings are in agreement with those of Bettany et al. The largest scale reflects differences between soil types, the lowest scale that within a single field. Examples for differences in S speciation for different soil types are given in Table 1. Notably the proportion of carbon-bonded S can be lower than 0. The plant-available sulfate content varied between 1. It has been outlined previously that inorganic sulfate content is of prime relevance for the plant S supply. S transformation processes are dynamic and the high spatio-temporal variability of sulfate reflects this Figure 1, Schnug and Haneklaus ; Bloem et al.

Spatio-temporal variability of the sulfate contents in different soil layers on two soil types. Adapted from Bloem et al. The variability of sulfate concentrations within one field can be as high as variations between different soil types in different climatic areas Table 1, Schnug and Haneklaus This high spatio-temporal variation of plant-available sulfate concentrations under humid conditions was shown to be closely related to soil physical and hydrological parameters Bloem Severe S deficiency in crops can occur on all soil types and is generally exacerbated by high yields, soils with a light soil texture, high permeability and low organic matter content, sites poorly connected to capillary ascending groundwater, leaching; reduced root growth and rooting intensity in acid soils, soil compaction, or low soil temperatures.

In addition to the spatial variability, rapid temporal changes in soil sulfate are Sulfur Interactions in Crop Ecosystems 29 a causal reason for a lack of relationship between soil analytical data and plant S status or crop yield Schnug and Haneklaus Allelochemicals are secondary compounds, which affect plants, soil microorganisms, insects, and herbivores. S-containing allelochemicals are closely related to adaptations of the plant rhizosphere to changes in the S supply as they influence soil microorganisms and other plants. Root exudates may directly affect seed germination of another plant, either by promoting the process, or inhibiting it Curl and Truelove The allelopathic effect of plants from the orders Cruciferae, Resedaceae, and Capparidaceae on weeds and soil-borne diseases usually focusses on the release of volatile isothiocyanates ITCs.

The degradation of glucosinolates GSLs by myrosinase delivers not only ITCs, but also organic cyanides, nitriles, oxazolidinethiones, and ionic ITCs all of which have allelopathic potential Brown and Morra ; Mizutani Myrosinase activity was proven on fields where Brassica species were grown Borek et al. At lower concentrations hirsutin proved to have an inhibitory effect exclusively on noncruciferous crops Kawabata et al.

ITCs may interfere with seed enzymes Drobnica et al. Basically, ITCs were shown to inhibit germination and growth of both, monocotyledonous and dicotyledonous plants Petersen et al. In pot experiments, Norsworthy and Meehan a, b found the sensitivity of Panicum texanum, Digitaria anguinalis, Senna otusifolia, and Amaranthus palmeri, Ipomoea lacunose, and Cyperus esculentus to be related to chemical structure and concentration of ITCs.

Under field conditions mustard, summer and winter oilseed rape were mixed at flowering after mowing with the soil to test their effect on seed germination Haramoto and 30 S. These authors could not verify any significant effect of Brassica crops on the delay of seed germination by weeds when compared to non-Brassica cover crops. GSLs may be released by root exudates of living plants and exert their allelopathic effects. Another option is their degradation after decomposition of separated plant parts or harvest residues. Their effect on soil-borne pathogens is summarized by the term and phenomenon of biofumigation.

Biofumigation might advance to a promising and ecologically sound alternative for crop protection if its efficiency can be directed. The toxicity of ITCs is based on their nonspecific, irreversible interactions with sulfhydryl groups, disulfide bonds, and amino groups of proteins and amino acids; thiocyanates interfere with the tertiary structure of proteins through electrostatic interaction Brown and Morra For aliphatic ITCs Sawar et al. Distribution of S species in the upper layers of different soils.

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Schnug The fungicidal or fungitoxic effect depended on the ITC concentration in agar and headspace, respectively Sawar et al. The lowest fungitoxic concentration on Gaeumannomyces graminis was 1. The results of these experiments showed that the toxicity of ITCs was different when incorporated into agar, or released in gaseous form. Compared to aliphatic ITCs, aromatic ITCs had a higher toxicity in agar than in gaseous form because of different vapor pressures Sawar et al. In comparison, allyl-ITC had a half-life of only 20 to 60 h in soils Borek et al. Another impairment of the efficacy occurs when GSL-containing plant material is used instead of pure chemicals.

Myrosinase concentration in plant tissue was sufficient for degradation of GSLs and supplementing additional myrosinase yielded no higher fungitoxicity Lazzeri et al. Soil moisture content and a sufficient decomposition of the plant material were obviously major limiting factors for the release of ITC Morra and Kirkegaard Another limiting factor might rely on the reaction of ITCs with inherent plant proteins and amino acids Warton et al. The efficacy of plant materials to yield a fungitoxic or fungistatic effect was related to crop type.

Not only vegetative, but also generative plant material had a fungitoxic effect. Seed meal of mustard inhibited completely mycelial growth of R. A significant decline was found after 8 h, which underlines the narrow time slot for a phytosanitary effect of ITCs. In addition, microbial degradation in soils decreased the allyl-ITC concentration. A higher allyl-ITC concentration was found on a more sandy soil, which the authors attributed to a presumably lower adsorption to the organic matter fraction Price et al.

Under field conditions Smith et al. This effect coincided with root decay and a reduced content of intact GSLs at maturity Kirkegaard et al. Under field conditions, radish showed resistance against Meloidogyne javanica and Meloidogyne arenaria that was comparable to resistant fodder sorghum, while Brassica crops also reduced reproduction of these nematodes Pattison et al. The contribution of ITCs from Raphanus sativus to this resistance remains uncertain. The nematicidal effect of individual GSLs and their degradation products on Meloidogyne incognita and Globodera rostochiensis was tested in vitro Buskov et al.

ITCs differed in their nematicidal effect by factor ; their efficacy was usually higher when exposure time was exalted Lazerri et al. Research in the field of biofumigation has shown that GSL content and pattern vary in relation to plant species, plant part, growth stage, and S supply. The potency of ITCs was found to be distinctly higher under laboratory than field conditions if at all.

Soils are open systems with a much higher volume than that of sealed containers in the lab, resulting putatively in a lower ITC concentration in the headspace of pathogens. Additional obstacles under field conditions are that the incorporation of the break crop is not homogenous; the GSL content is lower in plant residues than in younger plant material and degradation of GSLs is incomplete as it requires mechanical disruption to destroy cell structures and sufficient water for a sufficiently high myrosinase activity.

A solution to these problems might be a functional biofertilizer, which consists of material from different plants with highest concentrations of GSLs releasing most biocidal ITCs. The S demand of agricultural crops may be as low as 1 kg S t—1 for sugar beet and as high as 17 kg S t—1 for Brassica crops Haneklaus et al.

In physiological terms the S requirement is equivalent to the rate of S uptake, reduction and metabolism needed per gram plant biomass produced over time and can be expressed as mg S g—1 plant day—1 Haneklaus et al. When a plant is in the vegetative growth period, the S requirement Srequirement can be calculated as follows De Kok et al.

The RGR can be calculated by: When all other essential plant nutrients are sufficiently supplied and abiotic growth conditions are optimum, the S requirement of different crop species varies between 0. Generally, the major proportion of the sulfate taken up is reduced and metabolized into organic compounds, which are essential for structural growth. However, in some plant species a large proportion of S is present as sulfate.

Here, organic S content may be a better parameter for the calculation of S requirement Haneklaus et al. Restricted root growth can, for instance regularly be found on headlands Sulfur Interactions in Crop Ecosystems 35 due to soil compaction. Here, symptoms of S deficiency regularly appear first. Reduced root growth limits the ability of the plant to explore the soil spatially for available S and hampers its access to S resources in subsoil water Bloem et al.

Under humid conditions, sulfate can be leached from the root zone due to precipitation in autumn particularly on light soils, so that young plantlets do not have access to sulfate-rich capillary ascending water or groundwater. Although crops with a high S demand, such as oilseed rape, have a coarse root system which favors microbial activity and microbially-mediated degradation of ester-bonded S, this morphological modification alone might not deliver sufficient amounts of sulfate to satisfy the S demand.

Whenever S supply is insufficient, this will result in the occurrence of macroscopic S deficiency symptoms, even during the very early growth stages.

Sulfur in Plants – an Ecological Perspective is the 6th volume in the Plant in the plant sulfur field in the context of plant ecology and physiology. The. Combining an ecosystems approach with new insights at the molecular and biochemical level, this book presents the Sulfur and plant ecology: a central role of sulfate transporters in responses to sulfur availability . Series Title: Plant Ecophysiology; Series Volume: 6; Copyright: ; Publisher: Springer Netherlands.

An increasing problem in agriculture is the enhancement of S deficiency where Tebuconazol was applied as a fungicide, as it apparently reduces not only the growth of the aboveground vegetative plant parts, but also reduces root depth and density Bloem et al. Apparently this effect is also consistent in crop rotation. Lange showed that S fertilization to leguminous crops significantly increased shoot, root, and nodule biomass of alfalfa, crimson clover, and faba bean; in the case of peas this effect was significant for shoot and nodule biomass Figure 2.

The improved root growth due to S fertilization yielded a higher number of nodules, while nodulation itself was not affected Scherer and Lange ; Lange These results strengthen the significance of a sufficient S supply in intensive farming as root growth may be inhibited and thus the risk of S deficiency enhanced. In S-deficient legumes, N that was fixed in nodules was not assimilated which caused disturbance of protein synthesis and finally resulted in the appearance of macroscopic symptoms of S deficiency Lange Yield components During the very early growth stages of winter cereals, severe S deficiency caused an irreversible reduction of generative yield components Haneklaus et al.

Such severe disorder could only be counterbalanced by S fertilization prior to tillering Haneklaus et al. The S nutritional status had the strongest effect on the number of kernels per ear. Cereal plants obviously retain the number of 36 S. Schnug inflorescence bearing culms at the expense of grain setting under conditions of S deficiency. The S rate significantly influenced the number of pods per plant and seeds per pod of oilseed rape under greenhouse conditions Schnug When the N supply was low, S fertilization had no effect on the number of pods and number of seeds per pod.

When the N supply was high, S fertilization nearly doubled the number of seeds per pod. Neither variations in the N, nor in the S supply had a significant influence on the thousand grain weight TGW. Asare and Scarisbrick could verify no significant influence of S fertilization on TGW of oilseed rape under field conditions, either. In contrast, Shukla et al. Influence of S fertilization on shoot and root biomass, and number of nodules of alfalfa, crimson clover, faba bean, and pea.

Adapted from Lange Sulfur Interactions in Crop Ecosystems 37 Investigations on the timing of S fertilization and initiation of S deficiency in oilseeds, revealed that in both cases a close and significant relationship existed between duration of S deficiency and all yield components number of branches, number of pods per plant, number of seeds per pod, seed and straw yield except TGW Schnug A comparison between single and double low varieties showed that the double low cultivars had reduced components of yield structure consistently more than did the single low varieties Schnug An assessment of the differential effect of the point of timing when S deficiency affected plant growth revealed that components of yield structure were more reduced when S deficiency occurred later during growth.

From the viewpoint of plant production the area-related seed yield was reduced equally by both scenarios Schnug Influence of timing of S application, under conditions of severe S deficiency, on kernel weight, ear number, kernels per ear, and on grain and straw yield of wheat in comparison to a sufficiently supplied crop. Adapted from Haneklaus et al. Rhizoctonia solania Gaeumannomyces graminisa Fusarium oxysporuma Pythium irregularea Rhizoctonia solania Sclerotinia sclerotioruma Sclerotium cepivoruma 41 isolates of bacteriab 75 isolates of fungi and oomycetesb Bipolaris sorokinianab Fusarium graminearumb Gaeumannomyces graminisb Pythium irregulareb Rhizoctonia solanib Fusarium oxysporumb Fusarium oxysporumb Leptosphaeria maculansb Globodera rostochiensisb Globodera rostochiensisb Effect inhibition of mycelial growth and germination of encysted zoospores reduced disease severity retardation of mycelial growth retardation of mycelial growth vegetative material inhibition by mustard seed meal 25 mg inhibition of mycelial growth by mustard shoots mg and seed meal 5 mg retardation of mycelial growth vegetative material inhibition by mustard seed meal 25 mg inhibition of mycelial growth; effect decreased with age of mycelium inhibition of germination of chlamydospores Ref.

Schnug Pathogen Aphanomyces euteichesa 38 Table 2. Influence of ITCs on soil-borne fungal pathogens, bacteria, and nematodes under laboratory conditions. Sulfur Interactions in Crop Ecosystems 39 Table 3. Influence of excessive S supply on yield components and selected plant characteristics. Schnug In sunflower, S deficiency delayed floret initiation and anthesis, but not maturity under controlled growth conditions Hocking et al.

Additionally, the number of seeds per plant and TGW were reduced. The authors concluded that a sufficient S supply before floret initiation is important for initiating a maximum number of florets and thus potential seeds. S uptake runs more or less parallel to biomass development and is proportional to seed yield. Oilseed rape for instance may take up about one-third of its total S demand before winter resting. Usually, under conditions of S deficiency, S fertilization significantly increases vegetative and generative plant biomass production. Lack of response is often related to experimental conditions such as site and climatic conditions Kowalenko Growing leguminous crops such as soybean, which have been previously multiplied on S-deficient soils, increases the susceptibility of young plantlets against an insufficient S supply, as the proportion of Scontaining storage proteins is reduced Hitsuda et al.

S deficiency in the vegetative stage reduced biomass Randall and Wrigley and a lower plant dry matter of sunflower was closely related to the N supply in such a way that no impact was found at a low N input, however, severe losses were recorded when the N supply was high Hocking et al. The influence of S deficiency on vegetative and generative yield has been studied in detail for agricultural crops and is comprehensively summarized for instance by Pedersen et al. Plant growth under excessive S availability While numerous studies have investigated the influence of S fertilization on crop productivity under limiting conditions, the impact of excessive S input in temperate regions has only been dealt with sporadically.

An exception is the influence of atmospheric S pollution on plant growth. In comparison, extremely high S rates are applied, for instance, in desert agriculture for the amelioration of salinity and alkalinity, and in the course of cultivating post-mining land Table 3. S is commonly considered as being highly biocompliant such that excess S neither diminishes productivity, nor impairs quality of the plant products. There are, however, indications that overrated S fertilization may Sulfur Interactions in Crop Ecosystems 41 reduce crop yield and that this effect is related to crop type Table 3.

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A major handicap of a proper attribution of effects to an excessive S rate Table 3 is the lack of information about other growth limiting factors, antagonistic effects with other essential plant nutrients, and the S nutritional status itself. Even more important than detrimental effects of an excess S supply on crop parameters is a possibly detrimental effect on animal health.

Prominent examples of adverse effects of high S intake on ruminants are polioencephalomalacia, a neurological disorder and haemolytic anaemia Stoewsand ; Gould et al. The risk of polioencephalomalacia exists when grass which contains more than 0. Excess S may cause a premature leaf fall Motavalli et al. Even a uniform application rate of kg ha—1 S causes site-specifical yield increases and depressions as was shown for forage grass Kowalenko These results fit to the observations of Donald and Chapman who found indications of S toxicity at rates of kg ha—1 S to grass and clover.

This growth-depressive effect was observed at total S concentrations of about 6—9 mg g—1 S dry weight at silking stage. Other reports from McKeown and Bakker and Sanderson delivered contradictory results. Cabbage yield decreased when S rates exceeded 55 kg ha—1 S; this effect was not significant for the harvest products of broccoli though biomass production was reduced 8—10 times McKeown and Bakker In contrast, S rates of up to kg ha—1 S proved to be compliant for broccoli Sanderson In both experiments the S source was gypsum so that a Ca effect might be excluded.

Using a different S source it might be possible that excessive S rates induce Ca deficiency as was shown for tomatoes in hydroponics, which revealed blossom end, rot symptoms Lopez et al. In further experiments, S fertilizer rates of 45—90 kg ha—1 S reduced cabbage yield with the head size being affected in particular Rhoads and Olson ; in the pot experiments of Blankenburg a change of the S supply from sufficient to excess resulted in a reduction of head and floret yield of cabbage and broccoli by Schnug Disproportionate S rates significantly reduced shoot biomass of beans in a pot experiment with the S concentration in the leaf tissue more than doubled with values of 1.

The effects of extreme S applications when used in desert agriculture are also not consistent Table 3. For pawpaw, Picchioni et al. In comparison, stems of tomato plants were thinner, leaves darker green and smaller when grown under excessive S and symptoms became more pronunced with plant age and affected the aboveground biomass more than root growth Cerda et al. Relative increases in organic S concentrations in different plant parts, for instance from 0. Critical nutrient values and ranges For the evaluation of S nutritional status and prognosis of crop yield, different S species such as organic S, sulfate, total S, and the N: S ratio of various plant parts are determined, usually during the vegetation period and results are interpreted by employing diverse statistical approaches.

It is the large variation in experimental conditions and mathematical procedures which make it more or less impossible to compare results from different experiments Haneklaus et al. Thus the main objective, the reliable deduction of critical values is confronted with major limitations. Important threshold markers for the S supply are: A comprehensive overview of crop-specific deficiency and sufficiency ranges of S supply has been compiled by Haneklaus et al. Threshold values for total S concentrations mg g—1 S, d. A first hint of possible metabolic dysfunctions comes from the fact that excessive S supply to tomatoes induces Ca deficiency which becomes visible as blossom end rot Cerda et al.

Sulfur in Plants: An Ecological Perspective

The reactivity of the enzyme serine acetyltransferase, which catalyzes the first reaction in the biosynthesis of cysteine from serine was regulated by Cadependent protein kinase phosphorylation in soybean Liu et al. Additionally, pool sizes of ascorbic acid and GSH, and functional and regulatory interactions between them might be involved in growth inhibition under excessive S stress; a similar mode of action was proposed for boron deficient plants Lukaszewski and Blevins Thus it might be possible that under excessive S stress crosstalk between Ca and S metabolic pathways hampers S homeostasis and thus unfolds its toxic effects.

The identification of genes that govern the plant ionome might elucidate the mechanisms controlling S accumulation. The S nutritional status of crops has a significant influence on the nutritive value and sensory features of Sulfur Interactions in Crop Ecosystems 45 plant products. S-containing flavor compounds are, for example, cysteine in fruits Shankaranarayana et al.

The influence of S fertilization on secondary S-containing compounds has been comprehensively summarized by Haneklaus et al. Cysteine and methionine Vegetable proteins have been recognized as being of lower nutritional value than animal proteins. The reason is the imbalanced cysteine to methionine ratio rather than the lower S content per gram of protein Massey , see above.

A significant relationship between S supply and S-containing amino acids exists only under extreme S deficiency where macroscopic symptoms are visible Haneklaus et al. Under conditions of S deficiency, firstly a decrease of S-containing amino acids in proteins is found Schnug As the amino acid composition is genetically determined this effect is, however limited, and thereafter the total protein content will be reduced Schnug The transition point to a reduced protein content matches the appearance of severe S deficiency symptoms Schnug An insufficient S supply in the vegetative stage reduced biomass, the amino acid composition was only slightly influenced, however significant changes were observed in generative parts Randall and Wrigley The authors attributed this to the fact that leaf proteins are mainly functional, while seed proteins are mainly for storage.

Eppendorfer and Eggum found the biological value of proteins in potatoes reduced from 94 to 55 by S deficiency at high N supply and from 65 to 40 and 70 to 61 in kale and field beans, respectively. Whilst the essential amino acid concentrations declined due to S deficiency, the content of amino acids of low nutritional value, such as arginine, asparagines, and glutamic acid, increased Eppendorfer and Eggum The final influence of the S nutritional status is closely related to the N supply and they should therefore be assessed together.

At low N supply, S deficiency increased the starch content in vegetative parts of kale and ryegrass, and seeds of oilseed rape, while this effect was not found at high N input. At high N levels, S deficiency reduced the methionine content in vegetative tissue of kale and ryegrass more severely than the cysteine 46 S.

Schnug content, whereas in seeds of oilseed rape and field bean the cystine content was more strongly reduced Eppendorfer and Eggum The composition of seeds reflects an adaptation of plants to the S supply. Species with a low TGW, such as oilseed rape, typically rely on oil and fat as energy sources for the embryo. The total protein content of their seeds is uniform and more or less independent of the S supply.

An increase of cysteine and methionine in total protein from about 0. Adaptation of the metabolic sink to the S supply is maintained solely by the number of seeds produced Schnug and Haneklaus The endosperm of cereals which has a distinctly higher TGW, consists mainly of carbohydrates as the main energy reserve. S deficiency impairs the baking quality of wheat before crop productivity is reduced and a lack of protein or S could partly be compensated by increased concentrations of either compound Haneklaus et al.

The supply before anthesis is critical for wheat grain yield and quality as results of Haneklaus and Schnug , Haneklaus et al. So, the S content of plants deprived of S from start of anthesis equaled that of plants fully supplied with S throughout the vegetation period, whereby sulfate was derived presumably from uptake by roots and GSH translocation from flag leaves Anderson and Fitzgerald In legumes, which have a high TGW, the cotyledons have a major storage function, whilst the proportions of embryo and endosperm are minor.

Under conditions of S deficiency these plants reduce the amount of the S-rich fractions. In pea seeds, legumin-type globulin proteins contained a higher proportion of S-containing amino acids than vicilin-type globulins Randall et al. Extreme S deficiency yielded a decrease in the legumin content, whilst both increases and reductions were found when S was excessively applied to different genotypes Randall et al.

Excess S was accumulated as sulfate and the nonprotein amino acid Smethylcysteine in lupin and peas Randall and Wrigley A sufficient S supply before floret initiation proved to be nevertheless important for inserting maximum number of florets in sunflower Hocking et al. Schroeder suggested that a sufficient S supply during seed filling might contribute to a significant improvement of the nutritive value of peas. TGW, protein, and fat content of oilseed rape seeds were only affected by the S supply under conditions of extreme S deficiency Schnug , otherwise no significant influence could be verified under field conditions Schnug ; Asare and Scarisbrick In contrast, Eppendorfer and Eggum and Shukla et al.

S deficient sunflower plants produced seeds with a lower TGW, while the oil content was not influenced Hocking et al. Crosstalk between S and N metabolic pathways will not only influence yield structure, biomass development, and dry matter composition, but also N-use efficiency of agricultural crops. Under conditions of S deficiency, nitrate and non-S-containing amino acids accumulate which may reduce the nitrate reductase activity Srivastava ; Schnug Can J Plant Sci Can J Soil Sci The nature and distribution of forms of carbon, nitrogen and sulfur.

Soil Sci Soc Am J Isothiocyanates released from Brassica roots inhibit growth of the take-all fungus. Field Crops Res Grauer, Beuren, Germany Bloem E Schwefel-Bilanz von Agraroekosystemen unter besonderer Beruecksichtigung hydrologischer und bodenphysikalischer Standorteigenschaften. FAL Agric Res Plant Sulfur Research in Europe. Comm Soil Sci Plant Anal J Plant Nutr J Agric Food Chem J Plant Nutr 7: Soil Biol Biochem J Natl Cancer Inst Advanced Series in Agricultural Sciences.

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Biol Fertil Soils Molecular, Biochemical and Physiological Aspects. Adv Hortic Sci 7: Commun Soil Sci Plant Anal Wiley, New York, pp — Eppendorfer WH, Eggum BO Dietary fibre, sugar, starch and amino acid content of kale, ryegrass and seed of rape and field beans as influenced by Sand N-fertilization.

Crop production is often driven by nitrogen, but inadequate sulfur will influence nitrogen utilization, yield, and more subtly, quality. The contribution of mineralization to the S supply of plants is only small with about 1. An increase of cysteine and methionine in total protein from about 0. T Brit Mycol Soc The glutathione content is closely related to the S nutritional status in such a way that an S application rate of kg S ha—1 increased the glutathione content by about 65 nmol g—1 dry weight in leaves of oilseed rape and asparagus spears Haneklaus et al.

Plant Foods Human Nutr Z Lebensmittel Untersuchung Forsch Molecul Diagn Ther Aust J Agric Res J Agron Crop Sci Can J Microbiol Soil Sci Plant Nutr Evaluation of the relative importance of genetics and environment including sulphur fertilisation. Sulphur in Agric Relations between sulphur and protein content and loaf volume. J Plant Nutr Soil Sci Asp Appl Biol Effects on weed and crop establishment.

Appl Microbiol Biotechnol Commun Soil Sci Plant Anal 15— J Nanjing Univ Natural Sci Water Air Soil Pollut Agric Biol Chem Grass Forage Sci Variation in glucosinolate profiles of diverse field grown Brassicas. Austr J Agric Res Eur J Agron Cancer Epidemiol Biomarkers Prev 9: Ind Crop Prod New Zealand J Agric Res Biol Fert Soils J Biol Chem Root growth inhibition in boron-deficient or aluminium-stressed squash may be a result of impaired ascorbate metabolism.

Arch Gerontol Geriatr T Brit Mycol Soc Crit Rev Plant Sci Annu Rev Pharmacol Toxicol Int J Pest Manag IV effects of sulfur, phosphorus, potassium and magnesium deficiencies. Aust J Plant Physiol 6: Adv Cereal Sci Technol 8: J Hortic Sci Biotechnol Effect of environment and ontogeny on glucosinolate production and implications for screening. III In vitro toxicity of isothiocyanates to soil-borne fungal pathogens.

Plant and Soil Glucosinolates — fundamental, environmental and agricultural aspects. Schnug Schnug E Significance of sulphur for the quality of domesticated plants. J Sci Food Agric J Soil Sci J Crop Prod 5: Arvense Ann Agric Res 9: Indian J Hort Food Chem Toxicot Page AL et al. J Environ Qual Animol Feed Sci Techn Biosynthesis of sulfur-containing acids in asparagus. Agric Food Chem Differences in chemical composition of seed and seedlings exudates.

J Chem Ecol Soils in Chinese 5: Commun Soil Sci Plant Anal in press. Z Pflanzenernaehr Bodenk Unfortunately, this seems to have masked the basic fact that sulfur is an essential nutrient element for all plants including forest trees, and that sulfur compounds play crucial roles in the defence of trees against environmental stress factors.

The main distinguishing feature of forest ecosystems is the dominance of the tree life-form, and whilst the biochemistry of sulfur metabolism in tree cells is not fundamentally different from plant cells in general principles laid out elsewhere in this volume , modifications of wholeplant metabolism related to the typical biology of trees, for example long life spans, long internal transport distances, and large volumes of woody tissues, are significant.

This chapter, therefore aims to characterize those ecophysiological aspects of sulfur metabolism that set trees and forests apart from agricultural and other ecosystems dominated by short-lived herbaceous plants. Plants normally take up sulfur from the soil and subsequently reduce it if taken up in a higher oxidation state than -II, e. Tausz sulfur compounds, and distribute it into all organs Figure 1. Reduction, incorporation, and distribution of S do not necessarily happen in this sequence, because the extent to which the different reactions operate depends on the tissue and organ, seasonal variation, environmental conditions, and the growth form.

In particular the distribution and cycling of S in trees is different from herbaceous plants, because trees have to redistribute their resources depending on the seasonal cycles, have access to large volumes of potential storage tissues in their stems and the transport distances are considerably longer than in herbaceous plants.

Inorganic sulfur is mainly present as sulfate, because sulfite and sulfide are metabolized at high rates and their tissue concentrations are usually kept very low. Total S contents and the ratio of inorganic to organic S in tree tissues may vary according to the species, the tissue type, environmental conditions, developmental stage, seasonal fluctuations, and supply with S and other nutrients.

As for most nutrients, deciduous foliage has a higher S content on a dry weight basis, which simply reflects the fact that it contains less sclerenchymatic elements and cell wall material Table 1. Total S contents in foliar tissues are used in diagnosis of nutritional deficiencies and as an indication for an overoptimal S supply due to airborne S input. For example, values above 1. Sulfur uptake in trees As for most plants, the normal sulfur source for trees is sulfate taken up from the soil via fine roots. Sulfate uptake into the roots and loading into the xylem proceeds via specific, energy dependent transporters, which are Sulfur in Forest Ecosystems 61 well characterized on the molecular level for herbaceous plants, where at least 14 different forms exist in Arabidopsis for example Chapter 1, Hawkesford Analysis of the poplar genome indicates a similar large gene family.

Functional analysis of sulfate uptake kinetics into the roots identified at least two distinct root uptake systems in trees Populus, Fagus, Quercus , a high affinity and a low affinity system. Feedback regulation of root sulfate uptake by phloem translocated glutathione as shown for herbaceous plants was not corroborated for trees Populus. Cross regulation by N availability, probably by O-acetylserine, the substrate of sulfur incorporation into amino acids, seems also important Herschbach and Rennenberg Foliage Stem Roots Picea abies 32 17—43 1 Fagus sylvatica 52 37—70 1 37 32—42 2 45 40—49 2 Eucalyptus spp.

The roots refer to mixed samples of the total root systems. In a forest ecosystem, the role of mycorrhiza, the symbiosis between tree roots and fungi, on tree sulfur nutrition needs to be taken into account. Mycorrhiza can improve the nutritional state of plants and virtually all forest trees are partners in mycorrhiza. However, mycorrhiza associations do not improve sulfur uptake in trees shown for Populus, Quercus, and Picea , although mycorrhized trees can become more resistant to short-term 62 M. Tausz sulfur starvation Herschbach and Rennenberg Even though mycorrhiza may not increase uptake rates, the pathway of sulfate into the plant will be different from non-mycorrhized plants.

At least in ectomycorrhiza, the predominant mycorrhiza-form of many forest trees, roots have little plant tissue available outside of a dense fungal mantle, which is near-impenetrable for sulfate. This means that uptake must proceed through the fungal hyphae, and potentially different regulatory mechanisms may apply Taylor and Peterson Some relationships between tree sulfur metabolism and tree— environment interactions. Ecophysiological functions of sulfur compounds are marked by grey boxes, main long-distance transport forms are underlined,? Sulfur in Forest Ecosystems 63 Whole tree regulation of sulfur metabolism A number of in-depth studies reviewed by Rennenberg and Herschbach ; Herschbach and Rennenberg compared sulfur nutrition of the deciduous broad leaf species, beech Fagus sylvatica , to the evergreen conifer, spruce Picea abies , and found appreciable differences related to the different life cycles of these trees Rennenberg and Herschbach The evergreen Picea abies takes up sulfate, transports it into the canopy, where it is reduced mainly in older needles.

Young needles or buds have only low activities of the enzymes of sulfur reduction and receive reduced sulfur, imported as glutathione, from older needles. Glutathione is exported at high rates from older needles during the night, and translocated in xylem and phloem towards the younger needles, where it may support day and night protein synthesis.

Reduced sulfur requirements of the organs below the canopy may be met by root sulfur reduction, as reduced sulfur compounds are found in appreciable amounts in the xylem sap of the trunk Kostner et al. However, under exceptional conditions, for example with high S uptake from the atmosphere directly into the foliage, spruce trees seem capable of transporting organic sulfur compounds most probably glutathione from the needles into the roots Tausz et al.

In deciduous beech, in contrast, sulfur nutrition of the developing leaf tissues at bud break is supported by both reduced organic sulfur in form of thiols mainly cysteine and some glutathione and sulfate supplied in the xylem. Cysteine seems to originate mainly from storage proteins in the trunk, which accumulate during the vegetation period through import of glutathione and sulfate rather than cysteine from leaves into the trunk.

Such damage and dieback can be directly 64 M. Tausz attributed to acute toxic effects of SO2 on trees Pfanz and Beyschlag , with conifers being highly susceptible. Emission control technologies decreased atmospheric SO2 concentrations in many regions of the world e. However, SO2related problems may still persist in some regions of Europe cf. In addition to direct toxic effects of the gas, atmospheric SO2 is oxidized to sulfate, which is then deposited into forest ecosystems via precipitation.

Atmospheric sulfate deposition can also have direct effects on trees, but even more significant effects on the forest ecosystem level e. It is worth noting that due to generally high atmospheric sulfur deposition, forest ecosystems deficient in sulfur have formerly only been described from remote areas in the northwestern United States, in Australia, and in East Africa Johnson and Mitchell On the other hand, due to high leaching loss rates of sulfur from soil parent materials, atmospheric sulfur seems to be the major sulfur source for all forest ecosystems, even those in low sulfur input areas Johnson and Mitchell While their concentrations are low in the range of pl l—1 in remote rural areas, they can be substantially higher in the vicinity of industrial both primary and secondary and volcanic activities.

All sulfurous gases are taken up by trees mainly via stomata, but the mechanisms limiting their uptake rates are different for oxidized SO2 and reduced H2S gases. Due to the fast decomposition of SO2 in the aqueous phase of mesophyll cell walls forming sulfuric acid , internal concentrations are close to zero, hence the concentration gradient driving its uptake is only dependent on the outside concentration, and uptake rates increase linearly with increasing concentration De Kok and Tausz , Chapter 5.

Uptake rates of H2S, on the other hand, show saturation at high outside concentrations, which suggests a limitation by internal metabolic processes. O-acetylserine thiol lyase, the enzyme responsible for incorporating sulfide Sulfur in Forest Ecosystems 65 into cysteine, seems to be the rate limiting step De Kok and Tausz , Chapter 5.

If sulfide accumulates in leaves, it may be re emitted as H2S following the equilibrium between dissolved sulfide and H2S at the liquid—gas interface Chapter 5. While this is not directly measurable under H2S exposure but possibly contributes to the saturation of uptake rates , H2S reemission from tree foliage has been demonstrated after SO2 exposure or from excess sulfur in the soil, and even in absence of excess sulfur.

H2S release has been regarded as a means of rapidly adjusting the sulfur assimilation rates to changing needs, which might be of particular importance in trees Hogan and Rennenberg Metabolic processes may also limit the potential uptake rates of volatile organic sulfur compounds Geng and Mu ; Kesselmeier et al. Under field conditions with ambient atmospheric concentrations of these gases, forests and trees are sources for DMS and methylmercaptane, but can be both sources and sinks for COS and CS2, depending on the species Xu et al.

Although stomata are considered relatively impenetrable to aqueous ion uptake; trees exposed to sulfate-containing acid mist exhibited higher foliar sulfate concentrations. It is assumed that uptake is possible through the incomplete cuticles in young leaves. Interestingly, such foliar absorbed sulfate accumulates in the apoplast, whereas excess sulfate from soil uptake and other processes is usually located in vacuoles Sheppard Effective concentrations, which may cause chronic injury, can be as low as 10 nl l—1 for SO2 and 30 nl l—1 for H2S Posthumus , Chapter 5. Acute injury to sensitive plants has been observed at concentrations as low as 30 nl l—1 for SO2, but only at much higher concentrations of nl l—1 for H2S Posthumus Due to its prevalence in forest decline issues, SO2 effects on trees have been intensively studied and many countries have derived air quality standards to protecting forest trees.

Much less is known about the effects of H2S on trees, and hardly any data exist on the effects of other sulfurous gases on trees. Trees incorporate sulfur from atmospheric sources into their normal sulfur metabolism and hence can use sulfurous gases as sulfur sources Figure 1. Under elevated SO2, trees accumulate high levels of sulfate in leaves, which is widely used as a diagnostic tool similarly to total sulfur 66 M.

Labeling experiments with spruce showed that the major part of sulfate accumulation comes directly from the SO2 Tausz et al. Furthermore, sulfite can also be channelled into the sulfur-reduction pathway leading to increases in reduced sulfur such as glutathione albeit quantitatively at a much lower level than sulfate accumulation and organic sulfur.

H2S, on the other hand, can be incorporated in organic compounds without prior reduction, leading to marked increases in glutathione content. However, part of the sulfur still shows up as increased sulfate, which has to be produced by oxidations Tausz et al. Both H2S and SO2 are used to synthetize organic sulfur compounds thus decreasing the utilization of soil sulfate.

It seems, however, that contrary to herbaceous plants, trees do not respond with a strong decrease of root sulfate uptake, possibly indicating a relatively poor canopy—root signaling in trees Herschbach ; Tausz et al.

Sulfur in plants: an ecological perspective

It seems surprising that after many decades of concern and research on SO2 effects on trees, aspects of the toxicity mechanisms are still unclear. Acute injury, which encompasses a number of morphological, cytological, and physiological effects Hogan and Rennenberg may be caused by severe acidification brought about by the formation of sulfuric acid upon contact of SO2 and water, by toxic levels of sulfite in the cells or by the superoxide-mediated free radical chain oxidation of sulfite to sulfate De Kok Furthermore, acidic reactions on the leaf surface may lead to direct cation leaching from the foliage and disturb the nutrient element balances Hogan and Rennenberg Some hypotheses have been put forward to explain chronic SO2 injury: In this respect, the disturbance of glutathione metabolism has been put forward as a crucial factor, because glutathione is a central regulator of cell metabolism, stress responses, and gene expression De Kok and Tausz , see below.

A specific effect of sulfate-containing acid mist on tree frost hardiness has been described and it is hypothesized that apoplastic sulfate accumulation, which specifically occurs upon direct sulfate uptake into the foliage, Sulfur in Forest Ecosystems 67 leads to plasma membrane dysfunctions and so exacerbates susceptibility to frost Sheppard Ecosystem effects of atmospheric sulfur on forests Sulfur input — as gaseous SO2 or sulfate in mist or precipitation, can have acidifying effects not only on tree tissues, but on the whole forest ecosystems including the soils, which is thought to have contributed to various forest damage and decline events Guderian Soil acidifycation can mobilize nutritional cations Ca, Mg, K , which can be leached from the ecosystem and lead to symptoms of mineral deficiencies.

Apart from disturbances of the nutritional cycles, a number of further negative effects of soil acidification on ecosystem health, such as the disturbance of mycorrhiza communities, have been described Guderian Hence, critical levels for sulfate inputs into forest ecosystems have been defined to guarantee the long-term steady state conditions of ecosystems de Vries A large-scale survey of European forests showed clear correlations between exceeding of these critical loads and soil pH values, indicating that the problems relating to forest ecosystem effects are not over in Europe Augustin et al.

A number of low-molecularweight sulfur metabolites are involved in plant defence and have collectively been named sulfur-containing defence compounds SDCs; Rausch and Wachter , Figure 1. Sulfur-containing defence compounds include multifaceted primary metabolites such as glutathione and its derivatives e. Glutathione and the cellular redox balance In addition to its role as a long-distance transport form of reduced sulfur, glutathione plays multiple roles in tree—environment interactions and defence.

It functions as an antioxidant and as a redox buffer to protect tissues from reactive oxygen species ROS produced under abiotic and biotic stress Tausz In this role it has been suggested as a general redox sensor and signaling agent in plant cells Meyer and Hell As a substrate in the glutathione S-transferase conjugation reaction it 68 M. Moreover, it is the substrate for phytochelatin synthesis, which serves to complex and detoxify heavy metals in plants Rauser Responses of the foliar glutathione system of two apple Malus domesticus cultivars to progressing drought.

Trees under stress seem to generally require and synthesize higher concentrations of glutathione, underlining the central role of this compound in plant cells under stress Tausz However the results seem to be highly inconsistent. There is a tendency towards increased glutathione levels at the early stage of the stress response, which can be interpreted as an acclimation effect to increase resistance.

With increasing stress levels, glutathione concentrations decrease with the degradation of the system just before cell and tissue death occurs Figure Sulfur in Forest Ecosystems 69 2. The glutathione redox state responds quickly to the onset of stress, which is thought to trigger an array of defensive responses Mullineaux and Rausch However, further and probably less controlled oxidation of the glutathione pool occurs in relation to destructive processes. Sampling at different points of this stress response without taking into account the dynamic nature can give inconsistent results Tausz et al.

It seems surprising that the role of glutathione in stress responses and resistance of trees is still not fully understood, given that transgenic trees with manipulated glutathione metabolism have been available for more than a decade Herschbach and Kopriva A number of transgenic approaches succeeded in producing poplar trees with elevated glutathione levels, and some of those trees were apparently more resistant to xenobiotics Gullner et al.

Hence, higher glutathione concentrations may easily translate to higher detoxification capacity. In contrast, higher glutathione status did not improve tree resistance to other types of stress, e. It has to be taken into account that the role of glutathione in response to oxidative stress is a multifaceted one, and glutathione is only one part of a complex network of antioxidants, enzymes, and redox balances Tausz It is not surprising that manipulation of only one element cannot increase the efficiency of the whole system. Up to now it has been found in a number of species from different families, among them the tree species Theobroma cacao Sterculiaceae.

Sulfur is a potent fungicide and local concentrations were considered effective. The pathway of elemental sulfur formation is uncharacterized, although first results link it to increased levels of glutathione and sulfate, and a high sulfur supply seems to be a prerequisite for this to occur Cooper There is currently no further 70 M. Tausz information available as to whether elemental sulfur is of significance in other tree species or forest ecosystems. Secondary sulfur compounds, such as glucosinolates, alliins, or derivatives induced upon attack phytoalexins are being intensively investigated with respect to protective effects against predators and parasites in crops Bloem et al.

A number of sulfur-containing secondary metabolites can be found in tree or shrub species. Examples include glucosinolates in the horticulturally important Carica papaya Caricaceae; Rodman et al. No information on the potential roles of sulfur containing secondary metabolites in forest tree—pathogen interactions is currently available. It has been shown that the activity of cysteine-desulfhydrase, an enzyme potentially responsible for the release of H2S, is elevated upon infestation Brassica napus with a pathogen Bloem et al.

Furthermore, today's molecular tools are far more sophisticated than any previous techniques, thus allowing unprecedented progress in study of the physiology, cell biology and molecular biology of sulfur. In this book, edited by two renowned experts in the field, the advances of the past decade are summarized and synthesized to elucidate the current state of knowledge of plant sulfur research.

Twenty researchers who study plant sulphur nutrition have done an excellent job of discussing some of the most topical aspects in the plant-sulfur field in the context of plant ecology and physiology. The book consists of ten chapters and each one can be read in isolation. The chapters typically start with a very short introduction that raises a few important questions, which is followed by an extensive review of the relevant literature. The editors have chosen a style very similar to that of a review article, describing many experimental details of the corresponding original publications.

Furthermore, chapters include comprehensive reference sections. We live in a scientific age and modern research and literature are very dynamic, so it is difficult to publish a book with the most recent references included. I am impressed that all the chapters include many papers published in and that more historic information is carefully selected with respect to relevance. Chapter 1 sets the scene with a short introduction covering a brief historical overview and gives some basic definitions.

Chapter 2 provides an overview of various aspects of the adaptation of crop plants to changes in sulfur supply. Chapters 3 and 4 deal with the ecophysiological aspects of sulfur metabolism that contribute to the characterization of forest ecosystems and marine environments, respectively. Chapter 5 focuses on the impact of atmospheric sulfur gases on plants. Chapter 7 discusses the effect of sulfur on the capability of plants to cope with various oxidative stresses and on the efficiency of antioxidative defence systems.