Elevated in-soil CO2 affects physiology and growth of Pinus densiflora and Quercus variabilis seedlings under an artificial CO2 release experiment

Abstract

It is important to understand how woody species are affected by elevated in-soil CO2 for carbon capture and storage (CCS). A study was conducted to analyze the effects of artificially released in-soil CO2 on the physiology and growth of 4-year-old Pinus densiflora and 3-year-old Quercus variabilis seedlings. Approximately 7.9 kg CO2 plot(-1)d(-1) was released at a depth of 0.5 m over the period from 20 June to 20 July 2017. For both species, chlorophyll fluorescence and content, photosynthetic rate, and leaf size significantly decreased after the CO2 release. However, stomatal behavior varied between these species under the elevated in-soil CO2 conditions. Elevated in-soil CO2 inhibited plant physiological functions by limiting available in-soil O-2. The leaf size of treatment plots showed significantly lower values of 0.60 +/- 0.05 cm(2) for P. densiflora and 12.05 +/- 1.47 cm(2) for Q. variabilis compared to those of control plots of 0.90 +/- 0.09 cm(2) for P. densiflora and 21.84 +/- 3.62 cm(2) for Q. variabilis, whereas the number of leaves increased from 2697 +/- 153 leaves to 3121 +/- 255 leaves for P. densiflora and from 95 +/- 4 leaves to 288 +/- 52 leaves for Q. variabilis. It was found that the decrease in leaf size resulted in a second flush, which increased the total leaf area per seedling. The biomass of P densiflora significantly decreased in the treatment plots (P < 0.05). Q. variabilis showed an increase in mortality, with a low percentage of fine root (<2 mm in diameter) with respect to the total root biomass (P < 0.05). These results indicated that the physiological responses to elevated in-soil CO2 are more sensitive than the growth responses for both species.