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Rare species can switch between abundant and rare, respond to various external disturbances, enhance community resilience, and reduce the lag in ecosystem recovery. However, the impact of N enrichment on microbial community dynamic changes in rare species during the growing season is still poorly understood. To clarify which taxa contribute most to the community variation under N enrichment and whether the responses of these taxa vary at different periods of the growing season, we set up a 6-years multi-level field N addition experiment in an alpine meadow on the Tibetan Plateau. The variation in soil bacterial community diversity, composition, species interactions, and assembly process of different abundance profiles were investigated in the early, mid, and late-growing seasons. Approximately 80% of bacteria were classified as rare taxa (including permanently and conditionally rare taxa). The influence of N enrichment on the bacterial community was seasonally dependent. Bacterial community diversity and composition dissimilarity significantly increased only in the early growing season, especially in permanently rare taxa and conditionally rare taxa, but remained stable in the mid-and late-growing seasons. Seasonal fluctuations led to a shift in community composition, and conditionally rare taxa were the primary component of seasonal variation in community composition. Simultaneously, microbial network complexity and stability gradually increased over time, as evidenced by decreased modularity and vulnerability and increased robustness, clustering coefficient, connectivity, and keystone nodes. The assembly of conditionally rare taxa showed a significant difference under N addition, presented as decreased drift and increased dispersal limitation, which are closely related to the composition of the entire bacterial community. Our findings emphasize that the conditionally rare taxa decisive contribute to changes in the bacterial community under N enrichment, but seasonal fluctuations can make bacterial communities resistant to the influence of N enrichment. [ABSTRACT FROM AUTHOR]

The plateau pika ( Ochotona curzoniae ) is considered a keystone species on the Qinghai–Tibetan Plateau (QTP). Under a moderate burrow density condition, we investigated plant community and soil properties surrounding pika's burrows in comparison to the control sites (without pika's burrows) in an alpine meadow ecosystem. The results demonstrated that plant biomass, especially aboveground biomass around pika's burrow, was improved. The contents of available soil nutrients around the pika's burrow were improved as well. The highest aboveground biomass and highest contents of NH 4 -N, available phosphorus and available potassium was detected at the back of the burrow. The compositions of plant community were not changed significantly around the pika burrow, excluding at the front of the burrow. Our findings revealed that the activities of plateau pika can improve the production of alpine meadow and increase the soil fertility at individual burrow level when the burrow density was not out of control. [ABSTRACT FROM AUTHOR]

Atmospheric concentrations of nitrous oxide (N 2 O) have increased over the last 150 years due to human activities. Soils are important source of N 2 O where its production is largely regulated by biological processes. Nitrogen (N) deposition can alter the processes of autotrophic nitrification and denitrification, thus affecting the rate and direction of the soil N 2 O exchange with the atmosphere. It is obvious that atmospheric N deposition has influenced a dry alpine meadow in the Qinghai–Tibetan Plateau (QTP). Therefore, we investigated the effects of N deposition on the annual N 2 O emissions in an alpine meadow of the QTP. The N 2 O flux was measured for 2 years using static chambers and gas chromatography methods at four treatments (N0, background level; N7, add 7 kg N ha −1  yr −1 ; N20, add 20 kg N ha −1  yr −1 ; N40, add 40 kg N ha −1  yr −1 ). We found that high N deposition increased the N 2 O flux, not only in the growing season but also in winter and the spring thaw period. The average annual N 2 O fluxes at N0 and N40 plots were 3.1 and 6.1 μg m −2  h −1 , respectively. Compared with N0, the average annual N 2 O fluxes increased at N7, N20, and N40 plots by 13.7%, 47.6%, and 98.7%, respectively, the N 2 O fluxes in N40 plots increased by 113.6%, 41.6%, and 78.7% during the growing season, winter and spring thaw period, respectively. The emission of N 2 O during the growing season, winter and spring thaw period accounted for 63.2%, 29.9% and 6.9% of annual total emission of N 2 O, respectively. The N 2 O flux correlated significantly with air temperature, soil temperature, soil water content, total nitrogen, total organic carbon, and soil NH 4 + –N content in the alpine meadow. [ABSTRACT FROM AUTHOR]

Nitrogen (N) deposition-induced N input in alpine meadow soils may affect the soil exchange of methane (CH 4) with the atmosphere. The quantities and spatiotemporal variation in CH 4 uptake remain largely unknown for this ecosystem on a global scale. Previous studies regarding CH 4 flux have mainly focused on the growing season in alpine meadows. Thus, the impact of N deposition on the non-growing season uptake of CH 4 is unknown. In this study, we investigated the effects of N deposition on CH 4 uptake during both the growing and non-growing seasons in an alpine meadow on the central Qinghai-Tibet Plateau (QTP). The CH 4 fluxes were measured using static chambers and gas chromatography in four N deposition treatment areas (Control; N7, 7 kg N ha−1 yr−1; N20, 20 kg N ha−1 yr−1; N40, 40 kg N ha−1 yr−1) from May 2015 to August 2018. Our results showed that alpine meadow soils acted as CH 4 sinks throughout the year. N deposition significantly decreased CH 4 uptake fluxes (P < 0.05) and the annual mean CH 4 uptake fluxes declined at N deposition levels of 7, 20, and 40 kg N ha−1 yr−1 by 12.3%, 14.4%, and 20.5%, respectively, compared with that of the control. Annual CH 4 uptake was significantly correlated with total annual precipitation, mean annual air temperature, and N deposition rate. Annual cumulative CH 4 uptake in the four treatments across 3 years was 75.1 mg C m−2, where approximately 40% of the total annual CH 4 uptake occurred during the non-growing season. Our results showed that CH 4 uptake in the non-growing season cannot be ignored when estimating annual uptake of CH 4 because of the large CH 4 uptake during the non-growing season in the alpine meadow on the QTP under N deposition conditions. Contribution of different seasons to the annual cumulative CH 4 uptake in an alpine meadow on the Qinghai-Tibet Plateau. N7, N20, and N40 represent 7, 20, and 40 kg N ha−1 yr−1 nitrogen deposition, respectively. GSC = growing seasonal cumulative CH 4 uptake, NGSC = non-growing seasonal cumulative CH 4 uptake, AC = annual cumulative CH 4 uptake. Unlabelled Image • We investigated effects of N deposition on CH4 uptake in an alpine meadow on QTP. • N deposition significantly decreased CH4 uptake. • CH4 uptake in non-growing season accounted for about 40% of annual CH4 uptake. • CH 4 uptake was regulated by precipitation, air temperature and N deposition rate. [ABSTRACT FROM AUTHOR]