Response of Linzhi Spruce' s Net Photosynthetic Rate to Environmental Factors in Tibet

The daily change of net photosynthetic rate(NPR) and its response to environment factors such as quantum radiation, relative humidity and CO2 concentration of Linzhi spruce(Picea likiangensis var.linzhiensis) was monitored with a portable photosynthesis system. It is showed that the maximal NPR happened at 11:00, then the rate decreased and down below zero at about 19:00 in which Linzhi spruce entered dark respiration. NPR of top and outlayer needles on tree' s crown is bigger than that of the lower part needles due to sunlight. On the lower part of tree crown, southern needle' s NPR is higher than the northern. However, no difference was presented of NPR of southern and northern needles on the top of the tree crown. Under the conditions of air temperature 20℃, relative humidity 70%±5% and CO2 concentration 305mg·kg-1, the light compensation point of Linzhi spruce is 107.5 μmol·m-2·s-1and its light saturation point is 770 μmol·m-2·s-1. As increasing the light density to 800 μmol·m-2·s-1, the CO2 compensation point is 157.2 mg·kg-1and the CO2 saturation point is 3 811.33 mg·kg-1.