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Background and aims\ud \ud Litter decomposition is a critical process in terrestrial ecosystems and understanding the effects of soil fertility on the litter decay rate is of great ecological relevance. Here we test the hypothesis that N transfer from soil to litter will promote the decay rate of N poor but not N rich litter types.\ud \ud Methods\ud \ud Ten organic substrates, encompassing a wide range of biochemical quality in terms of C/N and lignin/N ratios, were decomposed in microcosms over three soil types with different N content, but inoculated with the same microbiome. Organic substrates were characterized for mass loss, C and N content to assess N transfer from soil to litter.\ud \ud Results\ud \ud The decay rate response to soil fertility was related to their initial N content: positive for substrates with little initial N content and not significant for N rich plant residues. A significant N transfer, generally larger from N rich soil to N poor substrates, was found. Litter C/N and lignin/N ratios showed variable relationships with the litter decay according with the soil fertility gradient, with positive and negative correlations in N rich and N poor soils, respectively.\ud \ud Conclusions\ud \ud Our study demonstrated that the decomposition of N rich litter proceeded irrespective of soil fertility while the decay rate of N poor substrates, either lignin poor or rich, was controlled by soil fertility likely as a result of N transfer. Litter C/N and lignin/N ratios were reliable indicators of litter quality to predict their decay rate in N poor soil, but not in N rich soils

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Arsenic (As), a class one carcinogen, reflects a disastrous environmental threat due to its presence in each and every compartment of the environment. The high toxicity of As is notably present in its inorganic forms. Irrigation with As contaminated groundwater in rice fields increases As concentration in topsoil and its bioavailability for rice crops. However, most of the As in paddy field topsoils is present as As(III) form, which is predominant in rice grain. According to the OECD-FAO, rice is the second most extensively cultivated cereal throughout the world. This cereal is a staple food for a large number of populations in most of the developing countries in sub-Saharan Africa, Latin America, South and South-east Asia. Rice consumption is one of the major causes of chronic As diseases including cancer for Asian populations. Thus, this review provides an overview concerning the conditions involved in soil that leads to As entrance into rice crops, phytotoxicity and metabolism of As in rice plants. Moreover, the investigations of the As uptake in raw rice grain are compiled, and the As biotransfer into the human diet is focused. The As uptake by rice crop represents an important pathway of As exposure in countries with high rice and rice-based food consumption because of its high (more than the hygienic level) As levels found in edible plant part for livestock and humans.

Plant invasions can have relevant impacts on biogeochemical cycles, whose extent, in Mediterranean ecosystems, have not yet been systematically assessed comparing litter carbon (C) and nitrogen (N) dynamics between invasive plants and native communities. We carried out a 1-year litterbag experiment in 4 different plant communities (grassland, sand dune, riparian and mixed forests) on 8 invasives and 24 autochthonous plant species, used as control. Plant litter was characterized for mass loss, N release, proximate lignin and litter chemistry by 13C CPMAS NMR. Native and invasive species showed significant differences in litter chemical traits, with invaders generally showing higher N concentration and lower lignin/N ratio. Mass loss data revealed no consistent differences between native and invasive species, although some woody and vine invaders showed exceptionally high decomposition rate. In contrast, N release rate from litter was faster for invasive plants compared to native species. N concentration, lignin content and relative abundance of methoxyl and N-alkyl C region from 13C CPMAS NMR spectra were the parameters that better explained mass loss and N mineralization rates. Our findings demonstrate that during litter decomposition invasive species litter has no different decomposition rates but greater N release rate compared to natives. Accordingly, invasives are expected to affect N cycle in Mediterranean plant communities, possibly promoting a shift of plant assemblages.

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