Reshaped acclimation traits of dominant tree species under manipulated rainfall would alter their coexisting relation in a low-subtropical secondary evergreen forest

Abstract. This study explores the seasonal transpiration and physiological responses of two dominant coexisting tree species, Schima superba and Michelia macclurei, to manipulated precipitation patterns in a subtropical evergreen broadleaf forest of South China, in which an ambient control treatment (BC), a drier dry and wetter wet season treatment (DD), and an extended dry and wetter wet season treatment (ED) were applied. Tree water use and associated ecophysiological characters, such as the daily whole tree transpiration (E_L), intrinsic water use efficiency (WUE_i), Huber values (A_s : A_l), and utilization proportions from different water sources were determined during the period from October 2012 to September 2013. For both tree species, no significant difference in transpiration among the three treatments was observed in the wet season, but a relatively stronger decrease of transpiration occurred under DD and ED treatments during the later dry season. Moreover, the higher transpiration of M. macclurei and its advantage of utilizing the shallow water derived from light rainfall under dry condition suggested that M. macclurei was more competitive in this subtropical forest. M. macclurei was inclined to adopt a drought-avoidance strategy, whereas S. superba that could uptake deeper soil water was more likely to be drought tolerant. The different spatial and temporal patterns of water use, together with the contrasting water use strategies, could partly explain the current coexistence of the two tree species. Their varying performance under different water conditions implies possible shifts in species dominance within the forest community that were potentially stimulated under future precipitation change scenarios from a long-term perspective.