No abstract

Livestock grazing activities potentially alter ecosystem carbon (C) and nitrogen (N) cycles in grassland ecosystems. Despite the fact that numerous individual studies and a few meta-analyses had been conducted, how grazing, especially its intensity, affects belowground C and N cycling in grasslands remains unclear. In this study, we performed a comprehensive meta-analysis of 115 published studies to examine the responses of 19 variables associated with belowground C and N cycling to livestock grazing in global grasslands. Our results showed that, on average, grazing significantly decreased belowground C and N pools in grassland ecosystems, with the largest decreases in microbial biomass C and N (21.62% and 24.40%, respectively). In contrast, belowground fluxes, including soil respiration, soil net N mineralization and soil N nitrification increased by 4.25%, 34.67% and 25.87%, respectively, in grazed grasslands compared to ungrazed ones. More importantly, grazing intensity significantly affected the magnitude (even direction) of changes in the majority of the assessed belowground C and N pools and fluxes, and C : N ratio as well as soil moisture. Specifically,light grazing contributed to soil C and N sequestration whereas moderate and heavy grazing significantly increased C and N losses. In addition, soil depth, livestock type and climatic conditions influenced the responses of selected variables to livestock grazing to some degree. Our findings highlight the importance of the effects of grazing intensity on belowground C and N cycling, which may need to be incorporated into regional and global models for predicting effects of human disturbance on global grasslands and assessing the climate-biosphere feedbacks.

Some soluble phosphate salts, heavily used in agriculture as highly effective phosphorus (P) fertilizers, cause surface water eutrophication, while solid phosphates are less effective in supplying the nutrient P. In contrast, synthetic apatite nanoparticles could hypothetically supply sufficient P nutrients to crops but with less mobility in the environment and with less bioavailable P to algae in comparison to the soluble counterparts. Thus, a greenhouse experiment was conducted to assess the fertilizing effect of synthetic apatite nanoparticles on soybean (Glycine max). The particles, prepared using one-step wet chemical method, were spherical in shape with diameters of 15.8 ± 7.4 nm and the chemical composition was pure hydroxyapatite. The data show that application of the nanoparticles increased the growth rate and seed yield by 32.6% and 20.4%, respectively, compared to those of soybeans treated with a regular P fertilizer (Ca(H2PO4)2). Biomass productions were enhanced by 18.2% (above-ground) and 41.2% (below-ground). Using apatite nanoparticles as a new class of P fertilizer can potentially enhance agronomical yield and reduce risks of water eutrophication.

No abstract

Natural polyphenols may play an important role in aluminum detoxification in some plants. We examined the interaction between Al(3+) and the purified high molecular weight polyphenols pentagalloyl glucose (940 Da) and oenothein B (1568 Da), and the related compound methyl gallate (184 Da) at pH 4 and 6. We used spectrophotometric titration and chemometric modeling to determine stability constants and stoichiometries for the aluminum-phenol (AlL) complexes. The structures and spectral features of aluminum-methyl gallate complexes were evaluated with quantum chemical calculations. The high molecular weight polyphenols formed Al3L2 complexes with conditional stability constants (β) ∼ 1 × 10(23) at pH 6 and AlL complexes with β ∼ 1 × 10(5) at pH 4. Methyl gallate formed AlL complexes with β = 1 × 10(6) at pH 6 but did not complex aluminum at pH 4. At intermediate metal-to-polyphenol ratios, high molecular weight polyphenols formed insoluble Al complexes but methyl gallate complexes were soluble. The high molecular weight polyphenols have high affinities and solubility features that are favorable for a role in aluminum detoxification in the environment.