Interactive effects of increased temperature and CO2 on the growth of Quercus myrsinaefolia saplings

The interactive effects of increased temperature and CO2 enrichment on the growth of 2-year-old saplings of Quercus myrsinaefolia, an evergreen broad-leaved oak, were studied throughout an entire year in the vicinity of their northernmost distribution. Saplings were grown under different conditions in two chambers: (1) a temperature gradient chamber at ambient temperature, 3 and 5 degreesC warmer condition's with an ambient CO2 concentration, and (2) in a CO2 temperature gradient chamber at 3 degreesC warmer conditions,with 1.5 times the normal CO2 concentration, and 5 degreesC warmer conditions with doubled CO2 concentration. The 3 and 5 degreesC warmer conditions enhanced the relative growth rate during almost the entire year, producing 53 and 47% increases in annual biomass production, 27 and 44% enhancement of root growth during shoot dormancy and 3 and 5 week prolongation of the shoot growing period, respectively. However, a daily mean air temperature exceeding 30 degreesC under the 5 degreesC warmer condition caused a marked reduction in net assimilation rate (NAR) from July to September. The CO2 enrichment further enhanced the positive effects of warming in spring and the resulting increases in NAR almost completely compensated for the negative effect of warming during summer. From autumn to winter, attenuation of the effects of CO2 was compensated by the increased sink strength produced by the warming. The annual biomass production was more than doubled by the combination of temperature elevation and CO2 enrichment.