Table_2_Soil Moisture and Soluble Salt Content Dominate Changes in Foliar δ13C and δ15N of Desert Communities in the Qaidam Basin, Qinghai-Tibetan Plateau.XLSX

Changing precipitation and temperature are principal drivers for nutrient cycling dynamics in drylands. Foliar isotopic carbon (C) and nitrogen (N) composition (δ13C and δ15N) are often used to describe the plant’s water use efficiency and nitrogen use strategy in plant ecology research. However, the drivers and mechanisms under differential foliar δ13C and δ15N among plant species and communities are largely unknown for arid high-elevation regions. This study collected 462 leaf samples of ten top-dominant plant species (two or three replicates per species) across 16 sites in 2005 and 2010 to measure the community-weighted means (CWMs) of foliar δ13C and δ15N, northeastern Qaidam Basin, Qinghai-Tibetan Plateau. Our results showed that the CWM of foliar δ15N was higher in 2005 than in 2010 and was lower in the warm-dry season (July and August) than the cool-wet one (June and September) in 2010. Similarly, the CWM of foliar δ13C was higher in 2005 than in 2010, but no difference between warm-dry and cool-wet seasons in 2010. C4 plants have higher δ13C and generally grow faster than C3 species under warm-wet weathers. This might be why the CWM of foliar δ13C was high, while the CWM of foliar δ15N was low in the wet sampling year (2010). The general linear mixed models revealed that soil moisture was the most critical driver for the CWM of foliar δ15N, which explained 42.1% of the variance alone. However, the total soluble salt content was the crucial factor for the CWM of foliar δ13C, being responsible for 29.7% of the variance. Growing season temperature (GST) was the second most vital factor and explained 28.0% and 21.9% of the variance in the CWMs of foliar δ15N and δ13C. Meanwhile, remarkable differences in the CWMs of foliar δ15N and δ13C were also found at the species level. Specifically, Kalidium gracile and Salsola abrotanoides have higher foliar δ15N, while Ephedra sinica and Tamarix chinensis have lower foliar δ15N than other species. The foliar δ13C of Calligonum Kozlov and H. ammodendron was the highest among the ten species. Except for the foliar δ13C of E. sinica was higher than Ceratoide latens between the two sampling years or between the cool-wet and warm-dry seasons, no significant difference in foliar δ13C was found for other species. Overall, the CWMs of foliar δ15N and δ13C dynamics were affected by soil properties, wet-dry climate change, and species identity in high-elevation deserts on the Qinghai Tibetan Plateau.

降水与气温变化是旱地生态系统养分循环动态的核心驱动因子。在植物生态学研究中，叶片同位素碳（C）与氮（N）组成（δ13C和δ15N）常被用于阐释植物的水分利用效率与氮利用策略。然而，针对干旱高海拔区域，不同植物物种及群落间的叶片δ13C、δ15N差异的驱动因子与作用机制仍不明晰。本研究于2005年与2010年在青藏高原柴达木盆地东北部的16个样点采集了10种优势植物的462份叶片样本（每个物种设置2~3次生物学重复），以测定叶片δ13C与δ15N的群落加权均值（community-weighted means, CWMs）。研究结果显示，2005年的叶片δ15N群落加权均值高于2010年；2010年暖干季（7、8月）的该均值低于凉湿季（6、9月）。类似地，2005年的叶片δ13C群落加权均值同样高于2010年，但2010年暖干季与凉湿季的该均值无显著差异。C4植物的δ13C值更高，且在暖湿气候下的生长速率普遍快于C3植物，这或许可解释为何湿润采样年（2010年）的叶片δ13C群落加权均值较高，而叶片δ15N群落加权均值较低。广义线性混合模型（general linear mixed models）分析表明，土壤含水量是影响叶片δ15N群落加权均值的最关键驱动因子，单独可解释42.1%的变异；而总可溶性盐含量则是调控叶片δ13C群落加权均值的核心因素，可解释29.7%的变异。生长季气温（growing season temperature, GST）为第二重要的影响因子，分别可解释叶片δ15N与δ13C群落加权均值28.0%和21.9%的变异。同时，物种水平上的叶片δ15N、δ13C群落加权均值也存在显著差异。具体而言，细叶盐爪爪（Kalidium gracile）与松叶猪毛菜（Salsola abrotanoides）的叶片δ15N值高于其余物种，而草麻黄（Ephedra sinica）与中国柽柳（Tamarix chinensis）的叶片δ15N值则低于其他物种。10个供试物种中，科氏沙拐枣（Calligonum kozlovii）与梭梭（Haloxylon ammodendron）的叶片δ13C值最高。在两个采样年或凉湿季与暖干季的对比中，仅草麻黄的叶片δ13C值高于Ceratoide latens，其余物种的叶片δ13C值均无显著差异。总体而言，青藏高原高海拔荒漠中，叶片δ15N与δ13C的群落加权均值动态受到土壤属性、干湿气候变化以及物种特性的共同调控。