Effects of Seasonal Drought on Water Status, Leaf Spectral Traits and Fluorescence Parameters in Tarenna depauperata Hutchins, a Chinese Savanna Evergreen Species

Chinese savanna evergreen plants can tolerate prolonged drought stress for more than half a year, but the mechanisms underlying the eco-physiological responses of these evergreen plants to drought stress are poorly understood. We selected a dominant evergreen species, Tarenna depauperata Hutchins, in this study and measured predawn leaf water potential, pressure-volume curves, leaf gas exchange, leaf spectral traits, chlorophyll fluorescence and P700 in the rainy and dry seasons, respectively. Results showed that predawn leaf water potential (Ψ_pd) decreased to-4.5 MPa in the dry season. Compared with the values in the rainy season, leaf specific hydraulic conductivity (K_L) decreased by 49.5%, the chlorophyll reflectance index (NDVI) decreased by 40.6%, and the anthocyanin reflectance index (ARI) increased to 0.074 in the dry season, which was 12.3 times as much as the value of the rainy season. The seasonal differences in Ψ_pd, K_L, NDVI and ARI were significant (P< 0.05). The maximum quantum yield of PSⅡ (F_v/F_m) decreased from 0.8 in the rainy season to 0.72 in the dry season (P< 0.05), indicating photoinhibition in PSⅡ; however, the activity of PSⅠ (P_m) remained stable during peak drought. In addition, maximum non-photochemical quenching (NPQ) increased by 31% and the maximum cyclic electron flow (CEF) decreased by 66% in the dry season compared with those in the rainy season. These results suggested that CEF was significantly inhibited by prolonged seasonal drought. The downregulation of light harvesting efficiency and the enhancement of NPQ played important roles in the photoprotection of this Chinese savanna evergreen woody species.