Physiological and photosynthetic response to different water conditions of Taxus cuspidate seedlings

A total of 30 individuals of potted 4yearold Taxus cuspidata cutting seedlings were selected as the experimental materials. We studied the response of leaf chlorophyll content, protective enzyme activities and photosynthetic characteristics to light intensity in different water conditions of T. cuspidata seedlings, and the results showed that there was no significant difference between middle soil moisture conditions (water content was 50%±5%) and relatively high moisture conditions (water content was 80%±5%) in chlorophyll content, photosynthetic characteristics and the protection of enzyme activity. When the soil moisture content was relative drought（water content was 20%±5%), in early 14 days of potting, leaf chlorophyll content, protective enzyme activities and MDA content did not change significantly; after 14 days, leaf chlorophyll content of seedlings reduced significantly, and the protective enzyme activities of SOD and POD decreased, but the MDA content increased. There was a significant difference between middle soil moisture conditions and relatively high moisture conditions. From light response curves, we can know that relatively high moisture conditions had little influence on T. cuspidata, but drought stress reduced apparent quantum yield（AQY）, maximum net photosynthetic rate（Pmax）and light saturation point（LSP）, and increased light compensation point（LCP）, which decreased light use efficiency of T. cuspidata, inhibited photosynthesis, reduced the ability of mesophyll cells making use of CO2, and then hindered photosynthetic carbon assimilation and accumulation of organic obstruction of T. cuspidata seedlings.