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Nitrogen (N) deposition is considered to be an important source of atmospheric N 2 O emission. Although N deposition simulated experiments have been conducted in grassland, forest and arctic tundra, the effect of long-term N deposition on N 2 O emission is not well understood in alpine grassland. To assess the response, a 9-yr N addition experiment was conducted in an alpine grassland of the Tianshan Mountains of Central Asia, to characterize the relationship between N 2 O emission and N application rate. An N addition rate of 10 kg N ha−1 yr−1 had no significant effect on N 2 O, while increases in N 2 O emission were clearly observed with N deposition of up to 30 kg N ha−1 yr−1 with a low emission factor (EF). The average N 2 O emission factor was 0.19% (range: 0.03%–0.42%), lower than the current IPCC default value of 1%. Nitrogen application significantly increased soil accumulated N 2 O emission throughout the growing season from 2013 to 2017, showing an increasing tendency in N 2 O emission with time. Depending on the amount and duration of N application, the interannual variability was 48.55%, 27.56%, 15.12% and 10.16% at the control (no N addition), 10, 30, 90 kg N ha−1 yr−1 plots, respectively. These would help to refine the accuracy of N 2 O mitigation protocols with insignificant N 2 O promotion under double present N deposition scenarios in alpine grassland. • N 2 O emissions increased quickly with N input ≥30 kg N ha−1 yr−1. • The longer N was added and the larger N addition effects on N 2 O emission appeared. • The current IPCC EF should be re-estimated for non N-saturation alpine grasslands. [ABSTRACT FROM AUTHOR]

[Display omitted] • Soil organic C remains the most important indicator for soil quality assessment. • The nonlinear scoring and weighted additive integration method is the best SQI tool. • The soil quality in the wheat-maize and vegetable systems is higher than that in the cotton system. • High soil quality depends on high inputs of straw residues, organic and inorganic fertilizers. • Application of agrochemicals decreases soil quality. Soil quality on smallholder farms is progressively declining due to inappropriate land management and agricultural inputs. Assessing soil quality at the field scale and evaluating the contributions of agricultural inputs to soil quality is therefore important in the formulation of policies and technologies for improving the land management practices of smallholders. The objectives of this study were to analyze the effects of smallholder agricultural inputs (fertilizer input, agrochemical input, organic fertilization and straw incorporation) on soil quality under three dominant planting patterns (wheat-maize, vegetable and cotton) in Quzhou County on the North China Plain. Six soil indicators (soil organic carbon, available zinc, fungal species richness, carbon pool activity, total chromium content and acid phosphatase activity) were identified as the minimum dataset (MDS). The SQI calculated using nonlinear weighted additive integration (SQI-NLWA) had the best discrimination under different planting patterns. The SQIs in the wheat-maize and vegetable systems were significantly higher than those in the cotton system. The overall spatial pattern of soil quality was related to the distribution of the planting patterns throughout the county. Organic fertilization, fertilizer input and straw incorporation increased the SQI, while agrochemical input decreased the SQI. Our study provides a quantitative tool for assessing soil quality at the field-scale and creatively analyzes the effects of smallholder agricultural inputs on soil quality. Our findings suggest that resource input and allocation determine soil quality and agricultural sustainability in smallholder-dominated agricultural systems. [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]