Diverging Responses of Two Subtropical Tree Species (Schima superba and Cunninghamia lanceolata) to Heat Waves

Abstract

The frequency and intensity of heat waves (HWs) has increased in subtropical regions in recent years. The mechanism underlying the HW response of subtropical trees remains unclear. In this study, we conducted an experiment with broad-leaved Schima superba (S. superba) and coniferous Cunninghamia lanceolata (C. lanceolata) seedlings to examine HW (5-day long) effects on stem water transport, leaf water use efficiency (WUE), morphology and growth, and to elucidate differences in the responses of both species. Our results indicated that HWs can significantly reduce hydraulic conductivity in both species. C. lanceolata experienced significant xylem embolism, with the percentage loss of conductivity (PLC) increasing by 40%, while S. superba showed a non-significant increase in PLC (+25%). Furthermore, HW also caused a reduction in photosynthesis rates (An), but transpiration rates (Tr) increased on the 5th day of the HW, together leading to a significant decrease in leaf WUE. From diurnal dynamics, we observed that the HW caused significant decrease of S. superba An only in the morning, but nearly the all day for C. lanceolata. During the morning, with a high vapor pressure deficit (VPD) environment, the HW increased Tr, which contributed a lot to latently cooling the foliage. In comparing the two tree species, we found that HW effects on S. superba were mostly short-term, with leaf senescence but limited or no xylem embolism. The surviving S. superba recovered rapidly, forming new branches and leaves, aided by their extensive root systems. For C. lanceolata, continued seedling growth initially but with subsequent xylem embolism and withering of shoots, led to stunted recovery and regrowth. In conclusion, apart from the direct thermal impacts caused by HW, drought stress was the main cause of significant negative effects on plant water transport and the photosynthetic system. Furthermore, S. superba and C. lanceolata showed clearly different responses to HW, which implies that the response mechanisms of broad-leaved and coniferous tree species to climate change can differ.

Repeated extreme heatwaves result in higher leaf thermal tolerances and greater safety margins

“…There are different ways plants demonstrate adaptative differentiation of thermal tolerance , such as differences in structural tissues, proteins, and physiology (Aspinwall et al ., 2019; Maher et al ., 2019). While there are substantial gaps in knowledge in our understanding of plant thermal tolerance (Geange et al ., 2020), common garden experiments controlling for environment have confirmed that traits providing tolerance to heatwaves are genetically determined across species (Ruthrof et al ., 2018; Aspinwall et al ., 2019; Qu et al ., 2020). Among examples of inter‐specific genotypic differentiation is a global study measuring 218 species across seven biomes, which found that thermal tolerance (measured as the maximum temperature for PSII) was highly variable among co‐occurring species (O’Sullivan et al ., 2017).…”

Radial Growth–Climate Relationship Varies with Spatial Distribution of Schima superba Stands in Southeast China’s Subtropical Forests

“…The reason may be due to the dropping water potential and increasing embolization in branches under high temperatures and transpiration during the hottest months [40]. Consequently, this may result in insufficient water supply, decreased stomata conductance of leaves [52][53][54], and even loss of photosynthetic tissue [55]. Further, this may result in a reduction in photosynthetic production and carbon reserves in the late growing season, with negative effects on radial growth in the current and following years [56,57].…”