Limited leaf thermal acclimation but higher tolerance in subtropical trees after 10-year translocation in Dinghushan biosphere reserve

While many studies have investigated plant thermal acclimation to short-term warming, the effects of long-term warming remain poorly understood. We conducted a 10-year field experiment in a subtropical forest in southern China by translocating the seedlings of two native tree species (Machilas breviflora and Schima superba) from a cooler higher elevation site (600 m) to a warmer lower elevation site (30 m). Translocated treatment significantly promoted the growth of S. superba but inhibited growth of M. breviflora. Over a two-week period in the summer growing season of the 10th year of the translocated treatment, it had no effects on the net photosynthetic rate (A_net), maximum rate of carboxylation of Rubisco (V_cmax), maximum electron transport rate for RuBP regeneration (J_max) and their optimum temperatures (T_optA, T_optV and T_optJ) for M. breviflora and S. superba. Translocated treatment significantly increased respiration at 25 °C (R₂₅) for M. breviflora but did not alter R₂₅ of S. superba. These results indicated that both species displayed limited photosynthetic and respiratory thermal acclimation. M. breviflora and S. superba under translocated treatment had higher photosynthetic thermal tolerances and wider thermal safety margins, suggesting an increased thermal threshold of photosystem II to translocated treatment. Although these tree species exhibited limited capacity for thermal acclimation of carbon metabolism, translocated treatment was found to be beneficial for the growth of S. superba but not for M. breviflora. This study advanced our knowledge of the adaptive capacity of subtropical trees to future climate change that may inform global vegetation models.