The inhibition effect of tea polyphenols on soil nitrification is greater than denitrification in tea garden soil.

Tea polyphenols are the most widely distributed class of secondary metabolites (Camellia sinensis) and account for a considerable proportion of the pruning residues of tea. A large amount of tea polyphenols have fallen down over soil with prunning residues every year. However, the effect of tea polyphenols on soil nitrogen cycle, especially the denitrification process and its related microbial communities, remains unclear. Epigallocatechin gallate (EGCG), the most abundant component of tea polyphenols, was selected to simulate the effects of tea polyphenols on soil nitrification, denitrification, related functional genes and microbial community. The results indicated that addition of EGCG can significantly (p < 0.05) inhibit soil nitrification. Copy numbers of bacterial and archaeal ammonia monooxygenase genes (amoA) decreased as EGCG concentration increased. Further, the ammonia oxidisers exhibited a significantly (p < 0.05) greater niche differentiation under the effect of EGCG compared with the control treatment (no EGCG addition). However, the inhibition effect of EGCG over soil denitrification was most significant at 34 and 36 day of incubation period, and such inhibitory effect was more apparent on nitrification compared with denitrification. EGCG addition increased the diversity of bacterial community. The composition of bacterial community was significantly altered and community variation was primary explained by EGCG, NH4+-N, NO3--N, soil organic carbon contents and potential denitrification rates. EGCG addition significantly increased relative abundance of Proteobacteria and Bacteroidetes phyla whereas decreased Actinobacteria. Overall, tea polyphenols can inhibit soil nitrification to a larger extent than denitrification by reducing the abundance of microorganisms carrying the related functional genes. Our results can serve as important basis of reducing the nitrogen pollution risk in tea orchards and could be considered as a powerful natural nitrification inhibitor to reduce the environmental risks caused by unreasonable nitrogen fertiliser adaptation.

Foliage application of selenium and silicon nanoparticles alleviates Cd and Pb toxicity in rice (Oryza sativa L.).

Direct discharge of untreated industrial waste water in water bodies and then irrigation from these sources has increased trace metals contamination in paddy fields of southern China. Among trace metals, cadmium (Cd) and lead (Pb) are classified as most harmful contaminants in farmland to many organisms including plants, animals and humans. Rice is a staple food which is consumed by half population of the world; due to longer growth period it can easily absorb and accumulate the trace metals from soil. The objective of study was to check the efficacy of Se and Si NPs (nanoparticles) alone or in combination on metals accumulation and Se-fortified rice (Oryzasativa L.) production as their efficiency remained untested. Alone as well as combined application of Se- and Si-NPs (5, 10 and 20 mg L-1) was achieved along with CK. All the treatments significantly reduced the Cd and Pb contents in brown rice, except CK, Se3, Si1 and Se1Si3. Combined application of Se and Si (Se3Si2) was more effective in reducing the Cd and Pb contents by 62 and 52%, respectively. In addition, foliar application of both NPs improved the rice growth and quality by increasing the grain yield, rice biomass, and Se contents in brown rice. Highest concentration of Se (1.35 mg kg-1) in brown rice was observed with combined application of Se- and Si-Nps (Se3Si2). Selenium speciation revealed the presence of organic species (74%) in brown rice. The combinations of different doses of Se- and Si-Nps are the main determining factor for total concentration of metals in grains. These results demonstrate that foliage supplementation of Se and Si-Nps alleviate the Cd and Pb toxicity by reducing the metals' concentration in brown rice. Additionally foliage supplementation improved the nutritional quality by reducing the phytic acid contents in rice grains.