Natural abundance of C-13 in CO2 respired from forest soils reveals speedof link between tree photosynthesis and root respiration

摘要

Soil respiration from a boreal mixed coniferous forest showed large seasonal variation in natural abundance of C-13, ranging from -21.6 parts per thousand to -26.5 parts per thousand. We tested if weather conditions could explain this variation in delta C-13 of respired CO2, and found that the air relative humidity 1-4 days before the days of CO2 sampling best explained the variation. This suggested that high delta C-13 values were caused by effects of air humidity on isotope fractionation during photosynthesis and that it took 1-4 days for the C from canopy photosynthesis: of 20-25 m trees to become available for root/rhizosphere respiration. We calculated that these new photoassimilates could account for at least 65% of total soil respiration.