The Impact of Microhabitat and Microtopography on the Photosynthetic Characteristics of Typical Karst Forest Plants in Guizhou, China

Twenty-four plants were studied in Guizhou province, China. Based on various microhabitats (soil surface, stone gully, and stone surface) and microtopographies (slope aspect, slope position, and slope degree), the photosynthetic characteristics of the plants were measured, including the net photosynthetic rate (Pn), carboxylation efficiency (CE), stomatal conductance (Gs), water use efficiency (WUE), transpiration rate (Tr), intercellular CO2 concentration (Ci), and light use efficiency (LUE). The results demonstrated remarkable variations in the WUE of four types of plants in three microhabitats, showing that stone gully > soil surface > stone surface; there were no remarkable variations in the Pn, Tr, Ci, Gs, CE, and LUE in the three microhabitats. The Pn, Tr, Gs, and LUE of deciduous trees exhibited remarkably higher values compared to the other species studied in the three microhabitats. The evergreen trees’ WUE was much higher than that of the other plants when they were growing on stone surfaces or in a stone gully. There were remarkable variations in the plants’ photosynthetic characteristics dependent on the microtopography. In terms of slope steepness, the Pn, CE, and LUE were the highest in plants on slopes ≤ 5°. Meanwhile, in terms of slope position, the Pn, Tr, CE, and LUE were highest for plants growing in depressions. Concerning slope aspect, the Pn, Gs, CE, and LUE reached the largest values in plants growing on flat land. Principal component analysis (PCA) indicated that the Pn, LUE, and WUE were the key photosynthetic parameters reflecting the adaptation of plants to karst environments. Correlation analysis revealed that the Pn and LUE displayed a striking positive correlation with the Tr, Ci, Gs, CE, and WUE. The Tr displayed a striking positive correlation with the Ci, Gs, CE, and LUE, while a striking negative correlation was observed with WUE. This study indicated that evergreen trees exhibit conservative strategies, while deciduous trees use strategies associated with high growth rates. This study provides insights important for the restoration and reconstruction of vegetation in karst regions.