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Aims: Litter decomposition is a crucial component of nutrient recycling. Short-term nitrogen (N) deposition has been shown to influence litter decomposition in temperate steppe with significant variability due to differences in atmospheric N deposition, species identity, and experimental duration. Therefore, the effect of N addition, especially long-term, on litter decomposition in alpine grassland still needs further investigation. Methods: To address these knowledge gaps, we examined the influence of long-term N addition on litter decomposition, taking advantage of a field experiment with five N addition levels (0, 10, 30, 90, and 150 kg N ha−1 yr−1) with a meta-analysis, which has been running for 11 years in an alpine grassland, Northwest China. Results: Long-term N addition consistently decreased litter decomposition rates, and N negative effect became stronger with the increasing N addition rates. Reduced litter decomposition rates were related to lower soil enzymes activities. Litter decomposition rates were strongly correlated with litter quality, but weakly correlated with soil quality, but which suggested that litter quality and soil quality played important role in regulating litter decomposition. Furthermore, a regional meta-analysis revealed that N addition accelerated litter decomposition when all data were averaged. Although N addition indirectly increased litter decomposition, it had no direct effect on decomposition. However, the direction and degree of the direct effect of N on litter decomposition were regulated by N addition rate, experimental duration and form of N fertilizer. Conclusions: Overall, these results demonstrated that long-term N addition decreased litter decomposition and N negative effect increased over time. [ABSTRACT FROM AUTHOR]

Aims Litter is frequently buried in the soil in alpine grasslands due to grassland degradation, serious rodent infestation and frequent strong winds. However, the effects of various litter positions on litter decomposition rates and nutrient dynamics under nitrogen (N) enrichment in such areas remain unknown. Methods A field experiment was performed in the alpine grasslands of northwest China to investigate the influence of litter position (surface, buried in the soil and standing) and N enrichment on litter decomposition, using data from two dominant grass species (Festuca ovina and Leymus tianschanicus) in control and N-enriched plots. Important Findings Litter decomposition rates were much faster in buried litter and slower in standing litter than in surface litter. N enrichment significantly affected litter quality and then influenced decomposition. But no significant differences in litter mass remaining were observed between control and N-enriched soil burial. These results indicated that N enrichment significantly affected litter decomposition by changes in litter quality. In addition, all litter exhibited net carbon (C) and phosphorus (P) release regardless of treatments. Litter exhibited net N accumulation for litter from the control plots but showed N release for litter from N enrichment plots. These suggested that litter decomposition can be limited by N and N enrichment influenced N cycling of litter. Current study presented direct evidence that soil buried litter exhibited faster mass loss and C release, and that soil burial can be a candidate explanation why litter decomposes faster than expected in dryland. [ABSTRACT FROM AUTHOR]

Astragalus mongholicus Bunge (A.M.B), Potentilla anserina (A.P), Festuca ovina (F.O) The original article has been corrected. The original article can be found online at https://doi.org/10.1007/s11104-022-05537-8. [Extracted from the article]

Quantifying the similarities and differences in atmospheric nitrogen (N) deposition between different ecosystems is important to develop effective measures to reduce air pollution and maintain biodiversity. Here we show that the constitution of N deposition differed significantly between a grassland and a desert ecosystem in Northwestern China. Flux of bulk (wet plus part of dry deposition) and dry (gaseous NH 3 and NO 2) deposition were continuously monitored from 2018 to 2020. The grassland and desert sites had similar amount of total N deposition, being 7.29 and 6.33 kg N ha−1 yr−1, respectively. However, N deposition at the grassland was dominated by the bulk deposition (4.44 kg N ha−1 yr−1, 61% of the total N deposition), whereas that at the desert was dominated by dry deposition (4.20 kg N ha−1 yr−1, 66% of total deposition). The desert had greater ambient concentrations of NH 3 (3.66 μg N m−3) and NO 2 (1.52 μg N m−3) than the grassland (2.73 μg NH 3 –N m−3 and 0.72 μg NO 2 –N m−3). The amount of reduced N deposition (NH 4 + and NH 3) was around 3 times of that of oxidized N deposition (NO 3 − and NO 2) in both ecosystems. The N deposition rates in both ecosystems have exceeded the critical load for the fragile ecosystems (5–10 kg N ha−1 yr−1), highlighting the importance of reducing N emission sources that are related with anthropogenic disturbance. [Display omitted] • The boundary of Tarim Basin and Tibet Plateau has relatively low N deposition. • Bulk and dry deposition dominated in grassland and desert, respectively. • The reduced/oxidized N ratio in N deposition was close to 3 in both ecosystems. • N deposition exceeded the minimum critical load value for sensitive ecosystems. [ABSTRACT FROM AUTHOR]

• N enrichment enhanced foliar N, P concentration and N:P, but decreased NRE and PRE. • N enrichment notably changed plant N and P coupling in mature foliar. • NRE could regulate foliar N and P coupling under N enrichment. • Ambient N deposition notably affected foliar nutrient status and resorption. A meta-analysis was preformed to reveal how environmental and experimental factors alter the effects of N enrichment on the concentrations and stoichiometry of N and P in both mature and senesced foliage and nutrient resorption, with published studies from Chinese grasslands. N enrichment, when averaged across the studies, significantly increased the mature leaf N, P and N:P by 27.89%, 2.55% and 20.85%, respectively. The N, P and N:P ratio for senesced foliage under N enrichment increased by 41.35%, 3.28% and 20.11%, respectively, but N enrichment significantly decreased the leaf N resorption efficiency (NRE) and P resorption efficiency (PRE) by 6.85% and 3.41%, respectively. They were significantly controlled by the rates of addition of N, humidity index and the ratio of N addition rates to ambient N deposition, which suggested that ambient N deposition can indirectly influence plant internal nutrient cycling in this system. The effects of N enrichment on the N, P, stoichiometry and nutrient resorption in plants varied greatly among the types of grassland. In addition, the rates of N addition, forms of N application, experimental duration and application frequency of N had different effects on the leaf nutrient status. Specifically, the response of a critical threshold value of leaf P to N addition is 50–100 kg N ha−1 year−1, at which range with a shift from negative to positive impacts. Moreover, the addition of N significantly changed N and P coupling in mature leaves but not of senesced leaves, which were primarily regulated by N enrichment impacts on nutrient resorption. Our findings suggest that N enrichment significantly affected the status of leaf nutrients and then altered plant internal nutrient cycling across the grasslands of northern China. [ABSTRACT FROM AUTHOR]