Morphological and physiological responses to aridity in narrowly- and widely-distributed plant species in drylands.

Leaf functional traits play a pivotal role in understanding the adaptive strategy of plants in extreme environments, as well as in assessing their potential distribution range sizes and extinction risks under global climate change. However, the response of leaf functional traits to aridity in drylands remains unclear for plants with different range sizes. To fill this gap, we measured 10 leaf functional traits of 152 plant species across 172 dryland sites in China, and classified these species as either narrow- (NRS) or wide-ranging species (WRS) based on worldwide occurrence data. Our results showed that the NRS generally occurred in more severe arid areas, and had higher leaf water content (LWC) than WRS at high aridity levels (aridity>0.8). The scaling exponents between leaf volume (LV) and leaf dry weight (LDW) at high aridity levels were 1 for WRS and 1.56 for NRS, indicating that LV increased at a faster rate than LDW and therefore enabled NRS to store more water than WRS. Using moving window analysis, the above scaling exponents increased in NRS and decreased in WRS with increasing aridity at high aridity levels. Moreover, NRS with higher LWC tended to be more abundant at high aridity levels. Our results highlighted that NRS had higher LWC than WRS under high aridity, conferring them with a key advantage in adapting to extreme arid environments. These findings suggest that NRS and WRS use distinct adaptive strategies to cope with aridity. In the conservation of NRS in drylands, enhancing leaf water storage capacity is of particular importance.