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Climate warming and heavy livestock grazing are known to have great impacts on alpine ecosystems. However, it is still unclear how plant belowground biomass, soil carbon, and nitrogen respond to climate warming and heavy livestock grazing at different soil depths in these alpine ecosystems. The aim of this research was to investigate the individual and combined effects of warming and clipping on plant and soil properties in an alpine meadow ecosystem. Here, we report the results from a manipulation experiment, which has been running in the Qinghai-Tibetan Plateau (QTP) since 2010. Infrared radiators were used to simulate year-round warming starting in July 2010, while clipping was performed once a year in October to mimic the local heavy livestock grazing beginning from 2011. The experiment, including 3-year warming and 2-year clipping, was a randomized block design which consisted of five replications and four treatments: control (CK), warming without clipping (W), clipping without warming (C), and warming combined with clipping (W × C). Plant and soil properties were determined in the growing season of the alpine meadow in 2012 and 2013. The W treatments induced the downward transport of soil moisture to deeper layers. The drought caused by the downward transport of soil moisture in upper layers altered the allocation of plant belowground biomass at various soil depths. The relative effects on plant belowground biomass, organic carbon, activated carbon, and total nitrogen were also observed in deeper soil layers in W, C, and W × C. Therefore, the allocation of plant belowground biomass to deeper layers likely modified the distribution of organic carbon, activated carbon, and total nitrogen in soil of the alpine meadow in the QTP. [ABSTRACT FROM AUTHOR]

Nitrogen (N) availability is projected to increase in a warming climate. But whether the more available N is immobilized by microbes (thus stimulates soil carbon (C) decomposition), or is absorbed by plants (thus intensifies C uptake) remains unknown in the alpine meadow ecosystem. Infrared heaters were used to simulate climate warming with a paired experimental design. Soil ammonification, nitrification, and net mineralization were obtained by in situ incubation in a permafrost region of the Qinghai-Tibet Plateau (QTP). Available N significantly increased due to the stimulation of net nitrification and mineralization in 0-30 cm soil layer. Microbes immobilized N in the end of growing season in both warming and control plots. The magnitude of immobilized N was lower in the warming plots. The root N concentration significantly reduced, but root N pool intensified due to the significant increase in root biomass in the warming treatment. Our results suggest that a warming-induced increase in biomass is the major N sink and will continue to stimulate plant growth until plant N saturation, which could sustain the positive warming effect on ecosystem productivity. [ABSTRACT FROM AUTHOR]

Climate warming and overgrazing are inducing degradation of the alpine meadow ecosystem on the Qinghai-Tibetan Plateau. The Plateau is an important pastoral region in China and controversy surrounds the estimated carbon release occurring in this region of the world. Nevertheless, little comprehensive research analyzing land degradation has been conducted involving multiple factors in this region. Using two years of observational data, we compared differences in air temperature and relative humidity, soil temperature and moisture, soil texture, soil bulk density, soil organic carbon, soil respiration, vegetation height, coverage and biodiversity, above- and below ground biomass between moderately degraded and intact alpine meadow, and analyzed their relationships. The results show that the main process occurring during degradation was that Spenceria species and weeds with deep roots and a relatively high ability to resist drought replaced Kobresia species that previously exhibited high vegetation coverage and low vegetation height in alpine meadows of the Qinghai-Tibetan Plateau; these changes fundamentally affected corresponding changes in soil physical, chemical and thermal characteristics of the meadows. The change of vegetation species is believed to be the result of drought in the shallow soil of this habitat and is controlled by temperature and precipitation. The results suggest that a good collocation between temperature and precipitation is beneficial to the development of the alpine meadows; conversely, a poor pairing of temperature and precipitation not only causes the degradation of alpine meadows, it can even continually intensify the process by creating a vicious circle involving changes in soil physical, chemical, thermal and hydraulic conditions. [ABSTRACT FROM AUTHOR]