Effect of climatic factors on the temporal variation of stem respiration in Larix principis-rupprechtii Mayr

Stem respiration is a critical yet unavailable component of forest ecosystem carbon cycle dynamics. It is therefore necessary to study the variation in stem respiration at different time scales, especially regarding the response of the temporal variation in stem respiration to climatic factors. However, stem respiration is commonly measured only a few times a year during the daytime. In this study, we investigated the stem respiration of Larix principis-rupprechtii Mayr at different time scales, including hours, days, months, and seasons, and in forests of different ages as well as its connection with climatic factors using a soil carbon flux system (Li-8100) in North China during the growing season (May to September) and the non-growing season (October) from 2013 to 2015. The maximum daily stem respiration rate (abbreviated as RS) occurred between 14:00 and 18:00, and the minimum occurred between 4:00 and 8:00 (2.01-4.24, 1.71-4.25 and 1.02-1.72 vs. 10.83-2.93, 1.08-2.28 and 0.51-1.17 μmol m−2 s−1, respectively) for three forestry ages, which was in accordance with single-peak curves. The seasonal respiration was highest in late July and lowest in late October (3.84 vs. 0.27 μmol m−2 s−1, respectively). Calculation of RS indicated that the annual CO2 efflux per unit area was ranked by forest age as follows: 25 (11.53 ± 2.08 t ha−1) > 16 (7.45 ± 1.02) > 41 (4.87 ± 0.66) years of age. The average annual Q10 values were 3.85 (16 years of age), 3.41 (25), and 2.23 (41). The Q10 value of the 16-year-old forest peaked (9.89) during low temperature (0-5 °C) and subsequently decreased with increasing air temperature. These results not only clarify the response of RS to climatic factors at different time scales but also reveal the relationship between stem respiration in forests of different ages and their temperature sensitivity. These results suggest that the sensitivity of RS to temperature is negatively correlated with stand age and air temperature. Methodologically, incorporating stand age and air temperature into the conventional method would improve the accuracy of annual stem respiration estimates.