Leaves constitute a vital bottleneck in whole-plant water transport, and their water strategies are key determinants of plant competition and productivity. Nonetheless, our knowledge of leaf water strategies predominantly stems from single perspectives (i.e., hydraulic, stomatal or economic traits), severely limiting our capacity to comprehensively predict plant vulnerability and sustainability, especially under drought-stress conditions. Here, we examined the leaf hydraulic, stomatal and economic traits of three coexisting shrub species (i.e., Haloxylon ammodendron (C.A. Mey.) Bunge., Calligonum mongolicum Turcz. and Nitraria sphaerocarpa Maxim.) in the Badain Jaran desert-oasis ecotone to comprehensively evaluate their water strategies and drought adaptation mechanisms. The results demonstrated that these three shrubs exhibited significant differences in leaf hydraulic vulnerability, osmoregulatory capacity, stomatal behavior and economic traits. Nonetheless, these traits remain tightly related to guarantee their survival. Interestingly, two distinct interaction mechanisms between stomatal and hydraulic regulation were identified among the three shrubs with varying stomatal sensitivity. Specifically, N. sphaerocarpa and H. ammodendron employed relatively lower isohydric stomatal behavior, characterized by a synergistic decrease in vapor-phase water loss as liquid-phase water transport decreased during severe atmospheric drought. Conversely, C. mongolicum adopted higher isohydric stomatal behavior, rapidly reducing vapor-phase water loss during initial drought stress to compensate for its more vulnerable liquid-phase water transport system. Notably, all three shrubs presented risky leaf water strategies with negative hydraulic safety margins. Among them, the hydraulic dysfunction risk was lowest for C. mongolicum, followed by N. sphaerocarpa and H. ammodendron. Overall, our findings are anticipated to offer valuable insights for afforestation initiatives and ecological conservation efforts in desert-oasis ecotones that function as critical shelterbelts.

The Tibetan Plateau (TP), one of the most climate-sensitive regions in the world, has experienced significant warming and wetting in recent decades, which is widely recognized has promoted vegetation greening. However, a paradoxical phenomenon has been observed: during the growing seasons, vegetation greenness negatively correlates with precipitation across large areas of the TP. The underlying causes of this counterintuitive relationship remain unclear. In this study, we investigated this unexpected correlation relationship, using remotely sensed normalized difference vegetation index (NDVI) data, meteorological station observations, and several hydrometeorological datasets. First, we explored inter-annual variations in NDVI and precipitation on the TP during the growing seasons over the last four decades. Second, we examined the correlations between NDVI and precipitation in the growing seasons. Our analyses showed that from June to September, NDVI exhibited a significant (p < 0.05) positive correlation with precipitation in 3.04% - 10.9% of the vegetated area of the TP, whereas a significant negative correlation was observed in 3.02-6.03% of the vegetated area. Over half of the vegetated area showed negative correlations in July-September. Focusing on negatively correlated regions, we employed the structural equation model to explore the mechanisms causing this paradoxical relationship. Our findings suggest that the negative relationship between vegetation greenness and precipitation is primarily driven by a reduction in solar radiation associated with increased precipitation. During the growing season, higher precipitation levels led to lower solar radiation, which negatively impacted vegetation growth. These findings improve our understanding of vegetation-climate interactions in this climate-sensitive region.

ABSTRACTDesert plant communities play an irreplaceable role in maintaining the ecological balance of arid areas. Understanding the spatial distribution pattern of desert plant diversity and its environmental response mechanism is particularly important for the protection of regional biodiversity, and combining phylogenetic information can provide more in‐depth insights. To this end, this study conducted a survey of desert plant communities along the southeast to northwest direction of the Hexi Corridor, revealing the variation patterns of species and phylogenetic diversity (PD) indicators along longitude, latitude, and altitude, and explored the driving factors of these patterns in combination with geographical, climatic, and soil factors. The results showed that the changes in species diversity (Shannon–Wiener and Margalef) and PD along longitude and latitude showed a unimodal model, with the highest value in the central region. The dispersion of phylogenetic structure decreases with increasing altitude, with divergent patterns at low altitudes and clustered patterns at high altitudes. In addition, we found that soil factors such as soil available phosphorus (SAP), soil total phosphorus (STP), and soil available nitrogen (SAN) dominated the variation of species diversity, and the PD was also mainly regulated by soil available phosphorus (SAP), while the main influencing factor of the phylogenetic structure was the average annual temperature (AMT), indicating that the community diversity pattern was driven by soil nutrients and climatic factors. The study reveals the relative roles of different environmental factors in shaping community diversity and provides a scientific basis for formulating effective desert ecosystem protection strategies.