Sulphur is an essential nutrient for all living organisms. However, S deficiency was rare before the 1990s, due to the presence of S in fertilisers and atmospheric deposition. Over the last decade the S balance has shifted toward deficit as a result of decreased S pollution, increased use of non S-containing fertilisers and increased crop yields. Long-term monitoring of S deposition at both Rothamsted and Woburn allowed us to detect the early signs of a potential S deficiency at the beginning of the 1990s (Fig. 25). Since then our research on S has intensified, encompassing both fundamental and applied aspects of crop S nutrition and the S cycling.
Arsenic in rice is derived from the soil matrix that sustains it. Paddy field biogeochemistry leads to excessive arsenic mobilization and subsequent assimilation by rice (see Chap. 5 ), though arsenic has to be present in the first...
Nickel uptake and cellular compartmentation were investigated in three Ni hyperaccumulators: Alyssum bertolonii (Desv), Alyssum lesbiacum (Candargy) and Thlaspi goesingense (Hálácsy). The three species showed similar hyperaccumulation of Ni, but T. goesingense was less tolerant to Ni than the two Alyssum species. An addition of 500 mg Ni kg(-1) to a nutrient-rich growth medium significantly increased shoot biomass of all three species, suggesting that the Ni hyperaccumulators have a higher requirement for Ni than normal plants. Energy-dispersive X-ray microanalysis (EDXA) was performed on frozen-hydrated tissues of leaves (all species) and stems (Alyssum only). In all species analysed, Ni was distributed preferentially in the epidermal cells, most likely in the vacuoles, of the leaves and stems. In stems, there was a second peak of Ni in the boundary cells between the cortical parenchyma and the vascular cylinder. The non-glandular trichomes on the leaf surfaces of the two Alyssum species were highly enriched with Ca, but contained little Ni except in the base. In the leaves of T. goesingense, the large elongated epidermal cells contained more Ni than the cells of the stomatal complexes. The role of cellular compartmentation in Ni hyperaccumulation is discussed.
We investigated the influence of soil properties on Ni toxicity to barley root and tomato shoot growth, using 16 European soils. The effective concentration of added Ni causing 50% inhibition (EC50) ranged from 52 to 1929mgkg−1 and from 17 to 920mgkg−1 for the barley and tomato test, respectively, representing 37- and 54-fold variation among soils. Soil cation exchange capacity was the best single predictor for the EC50. The EC50 based on either the Ni concentration or free Ni2+ activity in soil solution varied less among soils (7–14 fold) than that based on the total added Ni, suggesting that solubility of Ni is a key factor influencing its toxicity to plants. The EC50 for free Ni2+ activity from the barley test decreased with increasing pH, indicating a protective effect of protons. The results can be used in the risk assessment of Ni in the terrestrial environment.
This study investigated the variation of nitrogen to sulphur ratios in rapeseed (N/S)t and in rapeseed protein (N/S). Under S‐sufficient conditions the (N/ S)t ratios varied considerably between different varieties, with low glucosinolate varieties having higher ratios than high glucosinolate varieties. In contrast, (N/S)p remained relatively constant at about 11.5 for all varieties tested, though significant effects of N and S nutrition on the (N/S) ratio were present. The ratio increased in the S‐deficient samples. Results of yield responses to S fertilizer and (N/S)(from six field experiments were used to see if (N/S)t could indicate the S status of the crop. Although yield losses due to S shortage tended to occur when (N/S)t was greater than 10, the relationship was not sufficiently reliable for use in diagnosis.
Elemental sulfur (S) highly enriched in the stable isotope 34S (90 atom %) was converted quantitatively to sulfate and used as a tracer to investigate S uptake and distribution in wheat (Triticum aestivum L. cv. Axona). The 34S label was fed to wheat for 24 h at different growth stages in hydroponic culture. The 34S abundance in plant samples was determined using a continuous flow elemental analyzer coupled with an isotope ratio mass spectrometer. The unlabeled plant tissues showed very similar S isotope composition to the S source used in the nutrient solution, whereas labeled plants contained 0.43–18.88 atom % excess 34S over the background. Total amounts of the 34S label in the whole plants did not differ significantly between those harvested immediately after the labeling period and those harvested at anthesis. Stems and roots were the main contributors of the 34S label to ears up to the anthesis stage. This study shows that highly enriched 34S can be reliably used in plant nutrition studies.
