Species and Elevation Differences in Climate Responses of Two Conifers at the Southern Edge of the Tengger Desert: Insights from Tree-ring Width and δ18O Analyses

Abstract The physiological response mechanisms of trees to climate change are complex, particularly across varying elevations and among different tree species. In this study, we collected tree ring samples from two dominant conifer species (Picea crassifolia and Pinus tabuliformis) at three elevations at the edge of the Tengger Desert. We used tree-ring width (TRW) and tree ring oxygen isotopes (δ18OTR) to investigate how species and elevations affect their responses to climate change. Pearson's correlation analysis and relative importance analysis were used to study the specific response processes of the two conifers to climate. The results showed that the TRW was mainly controlled by SPEI during the growing season, which means that drought stress had the greatest effect on it. And δ18OTR mainly responded to summer relative humidity (RH). Both TRW and δ18OTR of Picea crassifolia showed higher sensitivity to climate change. This sensitivity is largely attributed to the rapid uptake of precipitation by its developed shallow-rooted root system, which allows it to retain the precipitation signal in both TRW and δ18OTR. However, Picea crassifolia may be more susceptible to drought stress and growth decline or even death in the context of a warming region. Our results are important for understanding the impacts of climate change on forest ecosystems using multiple indicators and developing corresponding ecological conservation measures.