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Plant biomass reveals the productivity and stability of a biotic community and is extremely sensitive to climate warming in permafrost regions, such as the Qinghai-Tibetan Plateau (QTP) in China. However, the response of the plant biomass of different functional groups to rising temperatures in such alpine zones remains unclear. Here, infrared radiators were used to simulate year-round warming on the QTP from 2011 to 2018. During the 8-year warming experiment, air temperature increased by 0.16 °C, while humidity tended to increase by 0.27 % at 20 cm above the ground. However, the rate of the increase in air temperature declined with an increasing number of years. Soil temperature and moisture increased by 1.28 °C and 3.61 %, respectively, on average from 0 to 100 cm below the ground, and the increment of soil moisture tended to rise with increasing depth. At the depths from 0 cm to 20 cm below the ground, soil organic carbon and total phosphorus tended to decrease by 0.79 g/kg and 0.04 g/kg, respectively, while soil total nitrogen tended to increase by 0.04 g/kg. Plant biomass had non-significant responses to warming, but the variation among different plant functional groups was greatest for forbs with the increment being 12.50, 147.97, and 160.47 g/m2 for plants aboveground, belowground, and total biomass, respectively. The ratios of plant total biomass tended to decrease by 2.29 %, increase by 0.60 %, and increase by 1.70 % for grasses, sedges, and forbs, respectively, so warming greatly decreased the proportion of grasses and increased the proportion of forbs in community. Warming weakened the positive correlation of grass biomass with soil temperature and enhanced the negative correlation of grass biomass with soil N and P content, along with weakening the positive correlation of sedge biomass with soil moisture and N content, while enhancing the negative correlation between sedge biomass and soil temperature. Meanwhile, forb biomass was greatly increased by soil temperature in the effects of warming. In conclusion, the 8-year warming produced negative effects on grasses and sedges by increasing soil temperature and N content and thus promoted the growth of forbs, which might induce a shift toward forbs in this community. [Display omitted] • Infrared radiators were used to simulate a year-round warming experiment on a frozen area over 8 years. • The melt of frozen soil caused an increment of soil moisture in deep layers under the 8-year warming. • The increment of soil moisture induced downward transport of soil nutrients and root biomass to deep layers. • The transport of soil nutrients and root biomass altered plant composition among different functional groups. • Eight-year warming might induce shift toward forbs by increasing soil temperature and nitrogen content. [ABSTRACT FROM AUTHOR]

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]

• Spatial patterns of warming effects are explored for mountainous grasslands in forest. • Warming experiments were conducted to explore spatial patterns along latitudinal and altitudinal gradients. • Corresponding responsiveness of air and soil temperature to warming was dependent on elevation and latitude. • Warming reinforced the relationship of vegetation with moisture and promoted its dependence on moisture. • Moisture increment induced by rainfall might weaken the effects of warming on soil and its relation with vegetation. As climate warming is more obvious in high mountains, the spatial patterns of mountainous vegetation responding to climate warming are expected to become a new aspect in forest ecosystem research. However, we do not know how spatial patterns of vegetation in mountainous regions respond to climate warming, and we also do not know what will happen to the patterns when rainfall occurs. Here, we conducted warming experiments to explore the variation pattern of the response of the herbaceous community to experimental warming along latitudinal and altitudinal gradients in mountainous forests of the Loess Plateau. In low and high warming amplitudes, air temperature increased by a maximum of 0.86 °C and 2.83 °C, respectively; the response of air temperature was obviously affected by elevation, whereas air humidity was not sensitive to warming. When rainfall occurred, warming produced decreases in soil temperature by a maximum of 0.56 °C and 0.61 °C in low and high warming amplitudes, respectively; soil temperature was evidently affected by latitude; and soil moisture was insensitive to warming. That was, the corresponding responsiveness of air and soil temperature was dependent on elevation and latitude, and a sudden increase in soil moisture caused by rainfall influenced the effects of warming on soil temperature. Warming also increased plant height and coverage, but plant density and frequency did not respond to warming, thus leading to insignificant changes for importance values of grass, sedge, and forb. Moreover, plant richness and Simpson indices increased in low-amplitude warming and decreased in high-amplitude warming, but the Pielou index was insensitive to warming. The responsiveness of these plant factors decreased with latitude and increased with elevation. Correlations tended to be enhanced by warming among vegetation, temperature (air temperature and soil temperature), and moisture (air humidity and soil moisture); the correlation among vegetation, air humidity, and soil moisture increased relatively rapidly in response to warming. With soil moisture increasing, plant height diminished and species diversity enlarged in warming, demonstrating that moisture increase caused by rainfall modified warming effects on vegetation. In regions with water deficits as the Loess Plateau, warming reinforced the relationship of vegetation with water and thus promoted its dependence on water. Warming could be controlled in a certain range and thus exerted positive effects on vegetation and facilitated plant community development. In regions where water is the limiting factor, warming effects were largely influenced by rainfall; the moisture increment induced by rainfall might weaken warming effects on soil and its correlation with vegetation. [ABSTRACT FROM AUTHOR]