Increasing rates of long-term nitrogen deposition consistently increased litter decomposition in a semi-arid grassland.

The continuing nitrogen (N) deposition observed worldwide alters ecosystem nutrient cycling and ecosystem functioning. Litter decomposition is a key process contributing to these changes, but the numerous mechanisms for altered decomposition remain poorly identified. We assessed these different mechanisms with a decomposition experiment using litter from four abundant species (Achnatherum sibiricum, Agropyron cristatum, Leymus chinensis and Stipa grandis) and litter mixtures representing treatment-specific community composition in a semi-arid grassland under long-term simulation of six different rates of N deposition. Decomposition increased consistently with increasing rates of N addition in all litter types. Higher soil manganese (Mn) availability, which apparently was a consequence of N addition-induced lower soil pH, was the most important factor for faster decomposition. Soil C : N ratios were lower with N addition that subsequently led to markedly higher bacterial to fungal ratios, which also stimulated litter decomposition. Several factors contributed jointly to higher rates of litter decomposition in response to N deposition. Shifts in plant species composition and litter quality played a minor role compared to N-driven reductions in soil pH and C : N, which increased soil Mn availability and altered microbial community structure. The soil-driven effect on decomposition reported here may have long-lasting impacts on nutrient cycling, soil organic matter dynamics and ecosystem functioning.

[Semen quality of infertile men carrying hepatitis B virus].

OBJECTIVE: To study the semen parameters of infertile men carrying hepatitis B virus (HBV) and the influence of HBV infection on semen quality. METHODS: We collected the semen samples from 782 infertility males aged 25－35 years old. According to the results of serological examinations, we divided the patients into groups A (HBsAg, HBeAb and HBcAb positive, n = 286), B (HBsAg, HBeAg and HBcAb positive, n = 230) and C (non-HBV control, n = 266), and comparatively analyzed the routine semen parameters, sperm acrosin activity, sperm DNA fragmentation index (DFI) and high DNA stainability (HDS) among the three groups of patients. RESULTS: Compared with the patients of groups B and C, those of group A showed markedly decreased sperm concentration (ï¼»88.20 ± 82.62ï¼½ and ï¼»89.29 ± 53.80ï¼½ vs ï¼»71.49 ± 60.03ï¼½ ×106/ml, P<0.05), progressively motile sperm (PMS) (ï¼»34.88 ± 15.60ï¼½% and ï¼»37.82 ± 13.63ï¼½% vs ï¼»30.70 ± 14.79ï¼½%, P<0.05), sperm motility (ï¼»45.77 ± 16.58ï¼½% and ï¼»48.16 ± 14.03ï¼½% vs ï¼»42.67 ± 17.23ï¼½%, P<0.05), sperm viability (ï¼»82.55 ± 7.55ï¼½% and ï¼»85.26 ± 6.39ï¼½% vs ï¼»81.07 ± 10.19ï¼½%, P>0.05) and morphologically normal sperm (MNS) (ï¼»6.93 ± 4.45ï¼½% and ï¼»7.27 ± 4.43ï¼½% vs ï¼»5.72 ± 3.47ï¼½%, P<0.05), with sperm concentration, PMS, sperm motility, sperm viability and MNS remarkably lower in group B than in C. Sperm acrosin activity was significantly reduced in group A in comparison with groups B and C (ï¼»57.07 ± 26.38ï¼½ vs ï¼»63.03 ± 28.75ï¼½ and ï¼»78.00 ± 33.49ï¼½ µIU/106, P<0.01), remarkably lower in group B than in C (P<0.01). The sperm DFI and HDS, however, were markedly higher in group A than in B (ï¼»14.79 ± 9.46ï¼½% vs ï¼»12.95 ± 7.29ï¼½% and ï¼»11.60 ± 5.98ï¼½%, P<0.05; ï¼»9.62 ± 6.20ï¼½% vs ï¼»8.43 ± 4.72ï¼½% and ï¼»8.41 ± 4.59ï¼½%, P<0.05), and both higher in group B than in C. CONCLUSIONS: Semen quality is lower in infertile men carrying HBV and therefore HBV infection is one of the causes of male infertility.