Plant growth and water use efficiency of four Chinese conifer tree species under different air humidity

Zheng, Y Shimizu, H

PHYTON-ANNALES REI BOTANICAE 45:4 575-582

Air humidity is an important controlling factor for the establishment of tree seedlings. It is predicted that the annual amount of rainfall will decline in some parts of China due to the global climate change in the foreseeable future. There is limited information on the potential responses of this region’s forest to the global climate change. Our study investigated the responses of four major Chinese conifer tree species to air humidity variations. Seedlings of Pinus massoniana Lamb. var. massoniana, Pinus tabulaeformis Carr. var. tabulaeformis, Platycladus orientalis (Linn.) Franco cv. Sieboldii and Cunninghamia lanceolata (Lamb.) Hook were grown in controlled environment chambers under four different air humidity (RH: 40, 50, 60 and 70% or VPD: 2.4, 2.0, 1.6 and 1.2 kPa). Results showed that the growth of these four species responded to air humidity differently. P. massoniana was the most sensitive species, P. tabulaeformis and P. orientalis were less sensitive and C. lanceolata was the least sensitive species. However, the biomass increment (Delta biomass) and the relative growth rate (RGR) over the experimental period were higher under the RH 70% treatment than that under the 40% treatment for all the four species. Delta biomass and RGR were reduced by 54% and 47%, respectively, under the RH 40% treatment compared with those under the RH 70% treatment for P. massoniana, 24% and 12% for P. tabulaeformis, 22 % and 16 % for P. orientalis, 9% and 5% for C. lanceolata. The decreased growth under drier air conditions was partially due to the closure of leaf stomata and subsequently the depression of photosynthesis. Plants under higher humidity conditions had higher water use efficiency (WUE). There was a positive linear relationship between WUE and RH in all the four species. Our results may suggest that if air humidity becomes lower in some regions of China in the future, the area of distribution for the humidity sensitive species P. Massoniana may become smaller or this species may move to higher humidity region while the other three species will be less affected by this change.

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