Effect of water and nitrogen on photosynthetic characteristics and growth of Rauvolfia vomitoria

A field experiment was conducted in Xishuangbanna during the dry season to study photosynthetic and growth characteristics of 2-year-old Rauvolfia vomitoria Afzel. under different water and nitrogen treatments. A well-watered condition and a water-stress condition for the water treatments, along with zero N, low N (1.25 g·plant^-1) and high N (3.75 g·plant^-1) treatments were used in the study. The results show that leaf relative water content (LRWC), maximum net photosynthetic rate (Pn), stomatal conductance (gs), specific leaf area (SLA), stem mass fraction (SMF) and relative growth rates of height (RGRH), basal diameter (RGRD) and biomass (RGRB) under water-stress condition are lower than those under the well-watered condition. Low N treatment significantly eases water stress induced depression in Pn, RGRH, RGRD and RGRB, and increases transpiration rate (E), root mass fraction (RMF). This significantly enhances root yield (Y_R) compared with zero N and water stress treatment. High N treatment increases drought sensitivity, aggravating photosynthetic and growth depressions of R. vomitoria. The interaction between N rate and drought significantly affects LRWC, Pn, instantaneous water use efficiency (WUEi), SLA, and RMF. This implies that different N rates have different effects under different water conditions. It is concluded that low nitrogen fertilization rate during dry season in Xishuangbanna maximizes root yield of R. vomitoria.