Strong and rapid responses of soil microbial respiration to pulses, such as those from available soil organic matter (SOM) or water input from precipitation (especially in arid areas), are common. However, how soil microbes utilize new SOM inputs and the effects that temperature may have on their activities are unclear owing to the limitation in the application of traditional isotopic techniques at minute scales. In the present study, we developed a system of measuring ¹²CO₂ and δ¹³C minutely and synchronously under controlled incubation temperatures, i.e., for 48 h at 7, 10, 15, 20, and 25 °C, to explore the carbon utilization strategies of soil microbes. We measured the respiration rates of soil microbes in response to different carbon sources, i.e., added glucose (Rg) and initial SOM (Rs), as well as the total respiration rate (Rt). All responses were rapid and characterized by unimodal curves. Furthermore, the characteristic values of these curves, such as the maximum of rate (R-max), the time required to achieve R-max, and the ratio of the duration of R-max to that of 1/2 R-max, were all dependent on incubation temperature. Interestingly, temperature greatly influenced the strategy that microorganisms employed to utilize different carbon sources. The effects of temperature on the intensity of the microbial respiratory response and the ratio of Rg/Rs are important for evaluating the effect of land-use changes or variations in seasonal temperature on SOM turnover and should be considered in ecological models in future studies.

Evapotranspiration is the key driving factor of the earth’s water cycle, and an important component of surface water and energy balances. Therefore, it also reflects the geothermal regulation function of ecohydrological process. The Qinghai-Tibet Plateau is the birthplace of important rivers such as the Yangtze River and the Yellow River. The regional water balance is of great significance to regional ecological security. In this study, ARTS, a dual- source remote sensing evapotranspiration model developed on a global scale, is used to evaluate the actual evapotranspiration (ET) in the Qinghai-Tibet Plateau from 1982 to 2014, using meteorological data interpolated from observations, as well as FPAR and LAI data obtained by satellite remote sensing. The characteristics of seasonal. interannual and dynamic changes of evapotranspiration were analyzed. The rates at which meteorological factors contribute to evapotranspiration are calculated by sensitivity analysis and multiple linear regression analysis, and the dominant factors affecting the change of evapotranspiration in the Qinghai-Tibet Plateau are discussed. The results show that: (1) The estimated values can explain more than 80% of the seasonal variation of the observed values (R² = 0.80, P < 0.001), which indicates that the model has a high accuracy. (2) The evapotranspiration in the whole year, spring, summer and autumn show significant increasing trends in the past 30 years, but have significant regional differences. Whether in the whole year or in summer, the southern Tibetan Valley shows a significant decreasing trend (more than 20 mm per 10 years), while the Ali, Lhasa Valley and Haibei areas show increasing trends (more than 10 mm per 10 years). (3) Sensitivity analysis and multiple linear regression analysis show that the main factor driving the interannual change trend is climate warming, followed by the non-significant increase of precipitation. However, vegetation change also has a considerable impact, and together with climate factors, it can explain 56% of the interannual variation of evapotranspiration (multiple linear regression equation R² = 0.56, P < 0.001). The mean annual evapotranspiration of low-cover grassland was 26.9% of high-cover grassland and 21.1% of medium-cover grassland, respectively. Considering significant warming and insignificant wetting in the Qinghai-Tibet Plateau, the increase of surface evapotranspiration will threaten the regional ecological security at the cost of glacial melting water. Effectively protecting the ecological security and maintaining the sustainable development of regional society are difficult and huge challenges.

Ecosystem services are spatially heterogeneous and temporal variability, which results in trade-offs, synergies and neutrality. The trade-off is a key problem in ecosystem management and requires optimized decision-making research. This paper reviews methods for identifying trade-offs and suggest future model developments. We conclude that (1) ecosystem service assessment depends on quantitative indicators and its modeling; (2) scenario analysis, multi-objective analysis and production possibility boundary are an effective means of ecosystem service trade-off decision-making; (3) future research needs to strengthen ecosystem service supply and demand flow and assist decision-making ecosystem mapping. Finally, integrated models should be developed to simulate and diagnose different scenarios and to optimize measures in land and ecosystem management for sustainability.