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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]

The mid-domain effect (MDE) explains altitudinal patterns of species diversity of mountainous plants at different elevations. However, its application is limited by the species life form and family flora in different layers of plant communities. To verify the MDE hypothesis at the plant community level, we chose a mountain with representative characteristics of the study area in the east of the Loess Plateau, China, such as obvious elevation (from 1324 to 2745 m) and latitude (from 36° 23′ to 39° 03′) gradients and considerable vegetation types (mainly coniferous and broad-leaved forests). We measured the life forms, families, and species diversity indices of tree, shrub, and herb communities along different elevations. We determined that the family numbers of the herb and shrub communities presented unimodal patterns across an altitudinal gradient, and the highest values occurred at intermediate elevations. The importance values of dominant families in the shrub and tree communities presented unimodal patterns, but the lowest values occurred at intermediate elevations. The species diversity indices of the herb, shrub, and tree communities conformed to unimodal change patterns following an altitudinal gradient, but the greatest diversity occurred at high, low, and intermediate elevations, respectively. At higher elevations, forbs and grasses grew well, whereas sedges grew well at lower elevations. Responses of different tree life forms to the altitudinal gradient were greater for evergreen coniferous tree species than for deciduous coniferous and deciduous broad-leaved tree species. We concluded that the MDE hypothesis of species diversity for mountainous plants is influenced greatly by the community life form and family at the plant community level in a temperate semi-arid region of the Loess Plateau, China. This conclusion tested and modified the MDE hypothesis and may be valuable for fueling prediction of biodiversity models and for the comparison with similar studies in arid and semi-arid mountainous regions. [ABSTRACT FROM AUTHOR]

• Soil elements had effects on carabids diversity, composition, morphometric traits. • Soil Zn, N, Ca and Mn elements were predominantly related to assemblage composition. • Soil elements had larger effects on species body wide, profemora and protibia length. • Mg, Mn, N and pH value were main reason for the variability of morphometric traits. Industrial and agricultural activities result in the direct release of contaminants into soil, which alters and destructs the habitats of soil biota. Clarifying the effects of soil contamination on soil organisms can provide a theoretical basis for the conservation of soil organisms. In this study, 3 nonmetal elements (total C, total N, total P), 5 light metal elements (total K, Ca, Mg, Al, Na), 5 heavy metal elements (Fe, Hg, Pb, Mn, Zn) and soil pH, and 18 morphological traits of carabid species were analysed to explore the responses of spatial variation of species diversity, community composition and morphometric traits to differences of soil chemical properties in four sites (Cement Plant, Coal Coking Plant, Village and Nature Reserve) in Gujiao City, the largest coking coal production city of China. In total, 1095 carabid beetles representing 59 species were recorded, with the greatest richness and activity abundance of ground beetles were found in Cement Plant and the largest species diversity was found in Coal Coking Plant, Nature Reserve contained carabid assemblages distinct from the other three sites. As for species distribution, 14 soil chemical properties could be associated with 43.2% of the observed variation, with soil Zn, N, Ca and Mn being the most important in explaining the spatial variation of the species. Changes in the type of economic activity had a significant influence on the 18 morphometric traits of carabid species, species of Coal Coking Plant and Nature Reserve had larger morphological traits than the other two sites. Variations in morphometric traits showed a significant correlation with soil chemical properties, especially body wide and profemora length, with 14 soil factors explaining more than 60% of their variance. Soil Mg, Mn, total N and pH value contributed the most in explaining morphometric traits variability of ground beetles. In summary, changes in soil chemical properties due to industrial and agricultural activities have led to carabid species diversity, community and morphometric traits changes. Soil health management is prerequisites that contribute to conserve soil biodiversity and function in industrial areas. [ABSTRACT FROM AUTHOR]

Researchers frequently discuss spatial distribution patterns of species diversity and biomass together with their correlations along geographical gradients. Typical subalpine meadows occur widely on the east of the Loess Plateau, China; here, we selected nine mountains belonging to four mountain systems from north to south on the east of the plateau. We analyzed five latitudinal and longitudinal gradients together with six elevational gradients to study the spatial distribution patterns of species diversity (including α, β, and γ diversity) and biomass plus with their relationships at various scales. Results showed that (1) for diversity, α-Diversity manifested unimodal variation patterns in horizontal spaces, peaking at high latitude and low longitude. However, α-diversity was not sensitive to elevation in vertical spaces and tended to decrease with increasing elevation. With increased latitude, longitude, and elevation, β-Diversity diminished; meanwhile, the rate of species turnover decreased and the similarity of community composition enlarged. γ-Diversity demonstrated quadratic function changes that were initially incremental and then decreased with increasing longitude, elevation, and latitude from 37.5° to 40°. In general, β-diversity had positive correlation with γ-diversity and negative correlation with α-diversity, which conformed to the function of β = γ/α. (2) For biomass, changes of aboveground biomass (AB) were more obvious along latitudinal gradients, whereas variations of belowground biomass (BB) had smaller differences along longitudinal and latitudinal gradients. More biomass was allocated to BB toward the north and east, whereas root-to-shoot ratio (R/S) was more evident at greater latitude than greater longitude. With increased elevation, more biomass was also allocated to BB, and the relationship of biomass to elevation was closer in AB. In short, the relation of biomass allocation tended to belowground plant parts with different geographical scales. (3) Species diversity had the strongest positive influence on AB. The Patrick and Shannon indices had correlations of power functions with AB and R/S, respectively, indicating that an allometric model could be used to model relationships between species diversity and biomass. In conclusion, the unique geomorphological structures with a series of basins between mountain systems on the east of the Loess Plateau, meant that subalpine meadows were mostly distributed along latitudinal directions, so the spatial distribution of species diversity and biomass was more evident along latitudinal gradients, and thus the response of aboveground biomass was more sensitive to variations of spatial gradients and species diversity. [ABSTRACT FROM AUTHOR]

Varying patterns of plant community diversity along geographical gradients are a significant topic in biodiversity research. Here, to explore the integrated effects of latitude and altitude on the plant community diversity in a mountainous ecosystem, we set Guancen Mountain in the northern section, Guandi Mountain in the middle section, and Wulu Mountain in the southern section of the Lvliang Mountains as study areas, and the plant community diversity (basal diameter and height of tree and species diversity indices of shrub and herb) was measured horizontally at different latitude gradients and vertically at different altitude gradients in late July 2015. The results showed that (1) the trees were taller and wider at the middle latitude and higher altitude with a stronger spatial heterogeneity in the structures along the latitudinal and altitudinal gradients. The evergreen tree growth preceded that of the deciduous trees in the higher latitude and lower altitude regions, whereas the deciduous tree growth preceded that of the evergreen trees in the middle latitude and higher altitude regions. (2) Shrubs and herbs tended to grow well in the lower latitude and middle-lower altitude regions. The shrubs had a larger species diversity at lower latitude and lower altitude, but the species diversity of the herbs was not sensitive to the influences of the latitudinal and altitudinal gradients. With the latitude and altitude increasing, perennial herbs tended to grow well at higher latitude and higher altitude, while annual herbs tended to thrive at the middle latitude and lower altitude. In conclusion, environmental deviations caused by latitudinal and altitudinal gradients had great influences on the spatial distributions of the plant community diversity in the Lvliang Mountains. [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]

Responses of ecosystem carbon (C) fluxes to human disturbance and climatic warming will affect terrestrial ecosystem C storage and feedback to climate change. We conducted a manipulative experiment to investigate the effects of warming and clipping on soil respiration (Rs), ecosystem respiration (ER), net ecosystem exchange (NEE) and gross ecosystem production (GEP) in an alpine meadow in a permafrost region during two hydrologically contrasting years (2012, with 29.9% higher precipitation than the long-term mean, and 2013, with 18.9% lower precipitation than the long-tem mean). Our results showed that GEP was higher than ER, leading to a net C sink (measured by NEE) over the two growing seasons. Warming significantly stimulated ecosystem C fluxes in 2012 but did not significantly affect these fluxes in 2013. On average, the warming-induced increase in GEP (1.49 µ mol m−2s−1) was higher than in ER (0.80 µ mol m−2s−1), resulting in an increase in NEE (0.70 µ mol m−2s−1). Clipping and its interaction with warming had no significant effects on C fluxes, whereas clipping significantly reduced aboveground biomass (AGB) by 51.5 g m−2 in 2013. These results suggest the response of C fluxes to warming and clipping depends on hydrological variations. In the wet year, the warming treatment caused a reduction in water, but increases in soil temperature and AGB contributed to the positive response of ecosystem C fluxes to warming. In the dry year, the reduction in soil moisture, caused by warming, and the reduction in AGB, caused by clipping, were compensated by higher soil temperatures in warmed plots. Our findings highlight the importance of changes in soil moisture in mediating the responses of ecosystem C fluxes to climate warming in an alpine meadow ecosystem. [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]

Recent studies found that the largest uncertainties in the response of the terrestrial carbon cycle to climate change might come from changes in soil moisture under the elevation of temperature. Warming-induced change in soil moisture and its level of influence on terrestrial ecosystems are mostly determined by climate, soil, and vegetation type and their sensitivity to temperature and moisture. Here, we present the results from a warming experiment of an alpine ecosystem conducted in the permafrost region of the Qinghai-Tibet Plateau using infrared heaters. Our results show that 3 years of warming treatments significantly elevated soil temperature at 0-100 cm depth, decreased soil moisture at 10 cm depth, and increased soil moisture at 40-100 cm depth. In contrast to the findings of previous research, experimental warming did not significantly affect NH4+-N, NO3−-N, and heterotrophic respiration, but stimulated the growth of plants and significantly increased root biomass at 30-50 cm depth. This led to increased soil organic carbon, total nitrogen, and liable carbon at 30-50 cm depth, and increased autotrophic respiration of plants. Analysis shows that experimental warming influenced deeper root production via redistributed soil moisture, which favors the accumulation of belowground carbon, but did not significantly affected the decomposition of soil organic carbon. Our findings suggest that future climate change studies need to take greater consideration of changes in the hydrological cycle and the local ecosystem characteristics. The results of our study will aid in understanding the response of terrestrial ecosystems to climate change and provide the regional case for global ecosystem models. [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]