Indicator of climate variability:low treeline displacement in arid valleys of mountain areas,China

As climate change intensifies,finding an ecological indicator to quickly and accurately reflect the impact on mountain ecosystems is necessary.The low treeline/timberline,highly sensitive to climate variability and changes significantly within 5–10years,provides a new way to study the response to regional climate variability.This study explored the distribution and vertical displacement patterns of the low treeline in the Upper Minjiang River of China,using SPOT remote sensing images in 1999 and 2013and long-term positional observations.Using the Geodetector model,the study investigated the dominant climatic factors influencing the low treeline displacement.The results showed that the low treeline was located at 1700–3200 m elevation on sunny slopes(southeast,south,southwest,and west slopes)with slopes over 25°.From 1999 to 2013,the low treeline moved downward by 6 m from 2561±264m to 2555±265 m,along with a warm–humid climate tendency.The downward displacement was greater on slopes over 25°and shady slopes(-20 m and-10 m,respectively)than on slopes≤25°and sunny slopes.Additionally,the downward was greater in the warm and humid Zagunao River Basin(-15 m)compared to the arid valley center(-7 m)and the cold Heishui River Basin(-3 m).Meanwhile,the low treeline displacement correlated negatively with precipitation and relative humidity variations at the significance level of 0.05,with correlation coefficients of-0.572and-0.551,respectively.Variations in relative humidity and temperature significantly affected the spatial differentiation of low treeline displacement with influencing power of 0.246(p=0.036<0.05)and 0.183(p=0.032<0.05),respectively.Thus,the low treeline is a moisture-limited line,and its formation and variation are closely related to regional water–heat balance.The study clarifies the indicative value of the low treeline for climate variability in mountain areas and can provide references for ecological restoration in arid valleys.

Increased contribution of microbial necromass to soil organic carbon in solar farms on the Tibetan Plateau

Solar farms have been rapidly expanding on the Qinghai-Tibetan Plateau.However,the effects of photovoltaic arrays on the contribution of microbial necromass carbon(MNC)to soil organic carbon(SOC),along with the underlying mechanisms,remain unclear.To address this,we collected soil samples from the top 20 cm in under-panel,inter-panel and control plots at five solar farms constructed between 2012 and 2014 in the dry Yarlung Tsangpo and Lhasa River valleys on the Qinghai-Tibetan Plateau.We determined SOC,fungal and bacterial necromass and relevant soil properties.We found that the concentration of MNC in the under-panel plots(3.93±0.79 mg g-1)was significantly higher compared to the control plots(2.28±0.79 mg g-1)across all five solar farms.The proportion of MNC to SOC in the under-panel plots(34.7±2.4%)was also significantly higher than that in the control plots(27.5±1.4%).Specifically,the contribution of fungal necromass to SOC in the under-panel plots(26.4±2.2%)was significantly larger than that in the control plots(19.7±1.6%),while the increase in the bacterial necromass proportion was insignificant.Partial least squares structural equation modeling(PLS-SEM)indicated a significant and positive effect of increased soil moisture in the under-panel plots on the proportion of fungal necromass to SOC.These results highlight that beyond their economic benefits,solar farms in the arid regions on the Qinghai-Tibetan Plateau can enhance soil C sequestration by improving soil moisture and promoting microbial necromass accumulation.