Mobilization of Labelled Organic Sulfur in Rhizosphere of Rape and Barley and in Non-Rhizosphere Soil

Abstract

Rape is known to require more sulfur (S) than is necessary for the secondary metabolite synthesis. It is hypothesized that its coarse root system harbors more homogenous microbial biomass specific for sulfur immobilization=remobilization. In a growth chamber experiment, this work examined the ability of rape and barley to take up the labile 35 S (including 35 S-SO 4 2À and 35 S-organic extracted by hot water). For that, the endogenous compounds of soil organic matter were previously labeled with 35 S-SO 4 2À for three months prior to plant growth. The use of ''rhizobag'', a polyamide bag, easily allows the separation of rhizosphere from non-rhizosphere soil. In order to simulate the high input agrosystems, the soil received just before sowing, a unique dose of 76.9 mg N kg À 1 soil as ammonium nitrate and three levels of S (20.4, 30.8, and 61.5 mg kg À 1 soil) as MgSO 4 . Despite the dilutions made by levels of additional S-SO 4 2À , the results showed an increase in 35 S uptake by rape in contrary to barley, which showed a progressive decrease with increasing S-SO 4 2À dilutions. The mean percentage values of total 35 S taken up by rape were higher than barley (8.9, 22.2, and 28.2% at day 20, 42, and 56 after sowing vs. 3.7, 17.1, and 21.8% respectively). Correlated to 35 S-uptake, significant coefficient was found with the 35 S-SO 4 2À (0.78, p < 0.01), and 35 S extracted by hot water at 70 C for 18 h in rape rhizosphere (r 2 ¼ 0.75, p < 0.05) but not in barley. Similarly, significant correlation coefficient was observed between soil arylsulfatase and root 35 S uptake of rape (r 2 ¼ 0.79, p < 0.01) but not of barley. These results clearly showed the higher capacity of rape rhizosphere in regulating via the arylsulfatase activity the uptake of 35 S-endogenous compounds.

Effects of low‐molecular‐weight organic compounds on sulphur immobilization and re‐mineralization and extraction of immobilized sulphur by hot‐water and acid hydrolysis

“…The proportion of HW‐S related to immobilized S was substrate and soil dependent. In addition, our previous studies using calcareous arable soil sampled from the same experimental site, showed that plants requiring large amounts of S, such as rape and ryegrass, are able to deplete S from the HW‐S pool when the soil solution is sulphate‐S‐deficient (Vong et al , 2002, 2004, 2007). The results show that hot‐water extractable S is an active pool that is indicative of labile soil organic S readily available for plants.…”

The Effect of Sulfur Nutrition on Plant Glucosinolate Content: Physiology and Molecular Mechanisms

“…It is currently standard agricultural practice to fertilise Brassica crops with sulfur to enhance yield (reviewed in Walker and Booth, 2003), since even mild sulfur shortages can result in reduced yield and quality of Brassicaceae without the appearance of visible symptoms. Under natural conditions, the high amounts of sulfur required by Brassicaceae may be supplied by the complement of soil microorganisms associated with their roots, which oxidise elemental sulfur to sulfate, thiosulfate, and tetrathionate (Grayston and Germida, 1991;Vong et al, 2002). Of 273 bacterial isolates found in the rhizosphere of oilseed rape, 90 % were able to oxidise elemental sulfur (Grayston and Germida, 1991).…”

“…Of 273 bacterial isolates found in the rhizosphere of oilseed rape, 90 % were able to oxidise elemental sulfur (Grayston and Germida, 1991). After 35 S-labelled sulfate was applied to the rhizosphere, the roots of Brassica napus took up significantly more sulfate than did barley roots (Vong et al, 2002).…”

Defining composition and function of the rhizosphere microbiota of barley genotypes exposed to growth-limiting nitrogen supplies

“…For instance, ammonium and sulphur were significantly more abundant in heat-treated samples compared to ‘native’ soils. Studies conducted with a modern barley variety revealed that an increased level of sulphate in the rhizosphere inhibits the rhizospheric arylsulfates activity [42], i.e., the enzyme catalysing the hydrolysis of sulphate esters into mineral forms available for plant uptake [43]. Conversely, a microbiota better adapted to nitrogen and sulphur metabolism, such as the one associated with the Desert genotype, may offset this mineral imbalance contributing to a more efficient plant sulphur uptake in the barley rhizosphere and, at least in part, to the observed growth phenotype.…”