Effect of Calcium on the Photosynthetic Characteristics and Chlorophyll Fluorescence Parameters of Native Plant Species of Fraxinus malacophylla

PurposeTo explore the calcium adaptation mechanism of plants in karst rocky desertification areas.

MethodThe annual Fraxinus malacophylla seedlings of the native tree species in southeastern Yunnan used as test materials, and four CaCl₂ solutions with calcium concentration gradients of 0, 25, 50 and 75 mmol/L were watered, which used to determine the growth indexes, leaf photosynthetic characteristics, chlorophyll fluorescence parameters and photosynthetic pigment content of F. malacophylla seedlings.

ResultsWith the increase of calcium concentration, the growth of each organ of the seedlings increased first and then decreased. The growth of seedling height, ground diameter, and plant width were all largest at 50 mmol/L, and the seedling height and plant width were significantly different with CK (P<0.05), indicating that the calcium concentration was beneficial to the growth of F. malacophylla seedlings. During the diurnal changes of photosynthesis, net photosynthetic rate (P_n) was negatively correlated with intercellular CO₂ concentration (C_i), and positively correlated with stomatal conductance (G_s) and transpiration rate (T_r). P_n, G_s, water use efficiency (WUE), initial fluorescence yield (F_o), maximum fluorescence yield (F_m), PSⅡ maximum quantum yield (F_v/F_m), PSⅡ potential activity (F_v/F_o), and chlorophyl content increased first and then decreased with the increase of calcium concentration, and reached the maximum value at 50 mmol/L, indicating that the appropriate calcium concentration could promote photosynthesis of F. malacophylla seedling leaves; T_r showed an overall downward trend with the increase of calcium concentration, and chlorophyll a/chlorophyll b showed an overall upward trend with the increase of calcium concentration, reaching the minimum and maximum value at 75 mmol/L, respectively, indicating that high calcium will inhibit the photosynthetic efficiency of plants.

ConclusionThe appropriate exogenous calcium concentration for the growth of F. malacophylla seedlings is 50 mmol/L. When the calcium concentration is too high, it will inhibit the growth and photosynthesis of the lanceolate seedlings.