Photosynthetic physiological response of Jatropha carcas and Pterocarya stenoptera seedlings to five simulated karst adversities

The karst ecosystem is vulnerable and rocky desertification in karst regions develops rapidly. The situation of karst ecosystem becomes increasingly severe. In order to quickly build a stable forest ecosystem, it is better to select the appropriate plant species to carry out revegetation. Research on photosynthetic response traits can help to quickly identify plant adaptability to karst environment. In this study, 5 different karst adversities including high pH, high bicarbonate, drought, low phosphorus (P) and low nutrient were simulated, and Hoagland solution was taken as control. Jatropha carcas and Pterocarya stenoptera seedlings were cultivated with these treatment solutions synchronously. Photosynthetic response traits of these two plant species to 5 different simulated adversities were analyzed through determining the photosynthetic characteristics and variation of stable carbon isotopic compositions (δ13C). On the 15th day, the net photosynthetic rates (Pn) of J. carcass seedlings under alkalescent, drought, low P, high bicarbonate and low nutrient were 4.39, 0.27, 2.58, 3.08, 6.26 μmol?m-2?s-1, respectively. On the 25th day, the values became 4.09, 0.66, 4.57, 3.83, 4.04 μmol?m-2?s-1, respectively. Pn and water use efficiency (WUE) of P. stenoptera seedlings were all lower than J. carcas seedlings. Pn of P. stenoptera seedlings under alkalescent, low P, high bicarbonate and low nutrient excepted for drought condition all increased on the 25th day compared to the values on the 15thday. On 25 days from the onset of adversity treatment, WUE of J. carcass seedlings under drought stress increased significantly, and was higher than the value under other adversities. However, WUE of P. stenoptera seedlings under drought stress remained the lowest compared to the values of WUEunder other adversities. Initial fluorescence (Fo) and primary conversion of light energy of PSII (Fv/Fm) values in J. carcas seedlings were independent of adversities, there was no significant change. But the value of Fo of P. stenoptera seedlings under drought stress increased significantly and Fv/Fm value decreased significantly, photosynthetic apparatus of P. stenoptera seedlings suffered more serious damage under drought stress than J. carcass seedlings . On the 25th day, δ13C values of J. carcas seedlings under those adversities were more positive compared to that under control, the intracellular bicarbonate use capacity of J. carcas seedlings was higher than P. stenoptera seedlings. The utilization of two different inorganic carbon resources in J. carcass seedlings enhanced its photosynthetic carbon fixation efficiency and growth potential, improved the adaptability of J. carcass seedlings to adversities. Meanwhile, higher WUE under drought stress conditions helped improve the inorganic carbon capture efficiency of J. carcas seedlings . And the damage of drought stress on photosynthetic apparatus of these two plant species was irreversible, but J. carcas seedlings exhibited better photosynthetic capacity under drought stress conditions compared to P. stenoptera seedlings. Therefore, in the water deficit hillside environments, it is better to plant J. carcas, whereas along the river streams dank environments, it is better to plant P. stenoptera.