Effects of increasing CO_2 concentration and leaf temperature on the photosynthesis of tall fescue (Festuca arundinacea Schreb.)

摘要

Carbon dioxide (CO_2) is well known to he a "greenhouse gas" which is capable of causing significant climatic changes. The optimum ranges in the growing area of grass species will likely shift as a result of climatic changes, and there will be corresponding changes in the vegetation zones here in Japan. It is therefore necessary to determine the optimum range for each species that will grow in the new vegetation zones expected from the result by the climatic changes. We measured the effect of increasing CO_2 concentration and leaf temperature on the net photosynthetic rate (Pn) of tall fescue. Tall fescue (Festuca arundinacea Schreb. cv. Nanryo) was grown in 1/5000a Wagner pots in two phytotrons with inflow CO_2 concentrations of 350 ppm and 700 ppm. Pn was measured under different environmental conditions. Six different leaf temperatures (15 deg, 20 deg , 25 deg , 30 deg , 33 deg and 35 deg C) and 8 different CO_2 concentrations (0, 30, 100, 200. 350, 500, 700 and 1,000ppm) were set for each tiller (grown in CO_2 concentration of either 350 or 700 ppm). The results showed that Pn increased with CO_2 concentration below 500 ppm at each temperature, and decreased with CO_2 concentrations above 700 ppm at leaf temperatures of 15, 20 and 25 deg C.The rate of decrease in Pn of tillers grown in 350 ppm was higher than that of tillers grown in 700 ppm. In order to examine the effect of doubling CO_2 concentration, the Pn was regressed by the quadratic of leaf temperature. The effect of the increasein CO_2 concentration on the relative photosynthetic ratios was calculated for each temperature, and the relationship between the relative photosynthetic ratio and leaf temperature was examined. The relative ratio was found to increase with rising leaf temperature. According to this relation, both of the examined parameters expected to increase with global warming, i.e. temperature and CO_2 concentration, would have positive effects on the growth of tall fescue.