Abstract: Stem respiration plays an important role in global carbon cycle, the temporal and spatial variations of which drive the responses and feedback of global carbon pool to climate change. There is still large uncertainty, however, about the temporal variation of stem respiration, especially its stable carbon isotope composition (δ¹³C). To understand the temporal variation of stem respiration and its stable carbon isotope composition, we monitored stem respiration from six individuals of Pinus massoniana by the chamber method and the Picarro observation system based on cavity ringdown spectroscopy (CRDS) during August 2018 to October 2019. The sap flow rate and stem temperature were also measured. The results showed that: (1) there was no obvious diurnal variation of stem respiration rate and δ¹³C value, which were not significantly correlatedwith sap flow and stem temperature. (2) There was an obvious seasonal variation of stem respiration rate, ranging from 0.08 to 1.61 μmol·m^-2·s^-1. Stem temperature explained 82% of the seasonal variation of stem respiration rate. (3) δ¹³C of stem respiration increased first and then decreased. The average δ¹³C value (-23.25‰±0.91‰) of stem respiration in the non-growing season was significantly higher than that (-27.93‰±0.25‰) in the growing season. Our results suggest that stem respiration and its carbon isotope composition were different in different time scales, and that the seasonal dynamics of stable carbon isotope composition of stem respiration provides a new perspective for understanding stem respiration and possible intrinsic mechanisms.

Key words: correlation length-percentage of importance of omitted patches, Qingdao City., ecological network, betweenness centrality index, dynamic ecological security pattern