Seasonal grazing is a common alternative to the rest-rotation grazing management regime. Although that research has been extensive on the impacts of grazing on soil organic carbon (SOC) and nitrogen (N) sequestration, there is limited understanding of the regulatory mechanisms of plant productivity and species on SOC and N sequestration under seasonal grazing. To address this problem, the response of plant properties was quantified in five different seasonal grazing regimes (no grazing control, continuous grazing, early summer and late summer grazing, mid summer and early autumn grazing, late summer and mid autumn grazing) in a semi-arid grassland of North China between 2012 and 2018. The results indicated that early summer and late summer grazing had little damage to the plant communities but reduced the SOC and N sequestration in the 10-20 cm layer, while mid summer and early autumn grazing maintained a relatively high plant productivity but resulted in the losses of SOC and N sequestration in the 0-20 cm layer. The late summer and mid autumn grazing regime enhanced SOC and N sequestration in the 0-20 cm layer by producing higher yields of Stipa krylovii and root biomass. The improved biomass of S. krylovii and roots is an indicator of soil quality evolution in the context of grazing management. It is therefore proposed that the late summer and mid autumn grazing regime, including a two-month rest period, is likely to be a beneficial strategy to conserve both plant communities and soil nutrients for sustainable management of the studied grassland.

There is no knowledge of winter plant phenology and its controlling factors on the Qinghai-Tibetan Plateau (QTP). Thus, we conducted a 4 year winter phenology and growth dynamics study in the alpine meadow on the eastern QTP. From November 2013 to March 2017, the phenology of the 'winter-growth' and 'winter-green' species was recorded every 5 d. In November-February from 2014 to 2015, the above-ground biomass (AGB) in random plots was calculated to distinguish different growth patterns among winter growing species. The percentage of winter abundance relative to the summer population for forbs and the percentage of absolute coverage for grasses (W/S) were calculated to describe the importance of the winter population to the summer population. The soil moisture (SM) and soil temperature (ST) were used to explore the controlling factors on the AGB. Pearson's correlation analysis between winter phenology data and environmental variables, including air temperature (T-air), snow cover fraction (SCF), SM and ST, was used to investigate the factors affecting winter phenology during November-February from 2014 to 2017. There were 107 species in total in the sites, including ten 'winter-growth' species and four 'winter-green' species. Among the 'winter-green' species, Festuca ovina and Deschampsia cespitosa were the dominant species in the sites. The 'winter-growth' species grew new leaves or ramets or transitioned to reproductive growth. Gentiana spathulifolia even flowered in winter. 'Winter-growth' made important contributions to the annual AGB, e.g. winter growth of G. spathulifolia accounted for 23.26 % of its annual AGB, while 14.74 % of the annual AGB of G. crassuloides was from winter growth. In addition, winter warming and snowfall reduction under global climate change on the eastern QTP may decrease the AGB increment of the 'winter-growth' and delay the green-up onset date of 'winter-green' species. Also, winter warming and snowfall reduction may advance the first flowering date of 'winter-growth' species. In contrast to previous views that plants on the QTP were generally considered to remain dormant in winter, our study revealed that alpine meadow plants had strong winter growth which suggested the importance of re-evaluating the dynamics of ecosystem function of alpine meadow, including its contribution to the global carbon balance. It was also shown that soil moisture availability is more important than warmer temperature in controlling the green-up onset of 'winter-green' species on the eastern QTP, which contrasts with the traditional view that warmer winters could advance green-up. As snowmelt is the only source of soil water in winter, the prediction of the green-up trend may be further complicated by snowfall variation in winter.