Physiological responses of Robinia pseudoacacia L. of different origins to soil nitrogen supply.

Robinia pseudoacacia L. is a widely distributed tree species capable of adapting to different nitrogen (N) supplies in the soil. However, provenance-specific responses of Robinia to different soil N supplies are largely unexplored. To investigate the importance of soil N availability alone for the performance of Robinia, this study examined the physiological responses of five Robinia provenances to different N levels under conditions without exogenous inoculation. The provenances selected for this study originated from four provinces in China with different climates, i.e., Liaoning (LN), Ningxia (NX), Jiangxi (JX), and Shandong (L155 and L5001), and were cultivated under normal (1.4 mM), high (14.3 mM), and low (0 mM) N supplies. After 8 months (N treatments were conducted over the following three and a half months) of cultivation, CO2 and H2O gas exchange, the activities of enzymes involved in N metabolism, N contents and partitioning, and the accumulation and scavenging of reactive oxygen species were analyzed. The results revealed significant differences in biomass, photosynthesis, and N partitioning across provenances. JX and L155 exhibited improved N metabolism at high N supply, whereas L5001 and LN showed enhanced N metabolism under both high and low N supplies. Additionally, at low N, L155, L5001, and NX showed greater oxidative stress resistance and membrane stability compared to JX and LN. These physiological differences between provenances were found to be driven by local climate parameters, such as mean annual temperature and precipitation. Long-term adaptation to the climate at the site of origin plays a crucial role in shaping the performance of Robinia at different N supplies.