Temporal Variations And Influencing Factors Of Stem Respiration For Major Temperate Tree Species In Northeastern China

Exploring spatiotemporal dynamics and influencing factors of stem respiration (RW) is important for estimating and modeling forest carbon budgets, and helpful to understand variability of forest productivity. In this study, we in situ measured the RW of four major tree species in the temperate forests of northeastern China. The species were Pinus koraiensis, Larix gmelinii, Betula platyphylla, and Fraxinus mandshurica. Our objective was to examine diurnal courses of RW across the growing season in order to understand spatiotemporal patterns and influencing factors of RW and its temperature coefficient (Q10) for the four species. Each month during May and September of 2008, the diurnal course of RW and stem temperature at 1 cm depth under bark (TW) was measured every two hours with a Li-6400 infrared gas analyzer and thermocouple. Besides, the species were Populus davidiana, Juglans mandshurica, Ulmus propinqua, Quercus mongolica, Tilia amurensis and Acer mono except for the four tree species above. Our objective was to examine seasonal and yearly courses of RW across the growing season in order to understand spatiotemporal patterns and influencing factors of RW and its temperature coefficient (Q10) for the ten species. Each month during May and Otc. of 2008 and 2009, the seasonal course of RW and stem temperature at 1 cm depth under bark (Tw) was measured once each month with a Li-6400 infrared gas analyzer and thermocouple. For each species, nine trees were randomly sampled to cover the distribution range of tree diameter. A PVC collar (inner diameter 10.2 cm, height 5 cm) was cut and polished to fit the stem shape of each sample tree, and installed on the northward side at breast height. The collar was attached with silicon adhesive to the stem surface that was pretreated without causing any injury of the live tissues, and was kept continuously throughout the measuring period. The measured RW was calibrated with the collar volume and stem surface area of each sample tree. The main results below:Tree species, diameter at breast height (DBH), month and their interactions significantly influenced the RW.The grand means of RW during the measuring period for the Larix gmelinii, Fraxinus mandshurica, Betula platyphylla and Pinus koraiensis were 3.69μmol·m-2·s-1,3.24μmol·m-2·s-1,1.64·μmol·m-2·s-1, and 1.62μmol·m-2·s-1, respectively. The diurnal courses of RW for all tree species during the growing season (except for July) overall showed a "unimodal" pattern, largely in accordance with those of TW. However, the occurring time of the peak RW varied with species and month, and delayed to that of the Tw by 2—6 hours. In July, however, the diurnal course of RW displayed a"sinusoidal"or non-peak pattern. The seasonal variation of daily mean RW showed a bell-shaped curve pattern, with its maximum occurring in July for all species, which was in consistent with the seasonality of temperature and canopy penology. There was a consistent seasonal pattern of Q10 for all tree species, with its minimum occurring in August and maximum in September. The Q10 was significantly different among tree species, varying from 1.09 for Pinus koraiensis and 2.95 for Larix gmelinii. The mean RW for each individual tree was significantly positively correlated with DBH for all species except for Betula platyphylla. However, the equation and variability of this correlation varied with tree species.Tree species, diameter at breast height (DBH), month, year and their interactions significantly influenced the RW The relationships between RW and TW for all tree species in the growing season have showed exponential functions, varing with tree species and year. The seasonal variation of RW showed a bell-shaped curve pattern, with its maximum occurring in June or July for most of tree species, which was in consistent with the seasonality of temperature and canopy penology. R10 of 2008 for all tree species was larger than that of 2009 (except for Pinus koraiensis and Quercus mongolica), while the grand mean Q10 of 2009 (3.08) for the ten tree species was 1.87 times than that of 2008 (1.65). The mean RW for each individual tree was significantly correlated with DBH for all species except for Betula platyphylla of 2008, Juglans mandshurica of 2008 and 2009. However, the equation and variability of this correlation varied with tree species and year. The total stem respiration in the growing season for all tree species was linear with DBH. However, the equation and variability of this correlation varied with not year but tree species.The carbon cost based on stem surface, the grand mean carbon cost for each collar in the growing season and all the year, and the carbon cost all the year around of nine samples for Larix gmelinii, Fraxinus mandshurica, Populus davidiana, Juglans mandshurica, Ulmus propinqua and Tilia amurensis in 2008 was more than that of 2009, so were the grand means of RW for these tree species in the growing season. While the others did not belong to this. The carbon cost for Pinus koraiensis, Larix gmelinii, Quercus mongolica, Tilia amurensis and Acer mono was linear with DBH. However, the equation and variability of this correlation varied with tree species and year.The study above showed that the temporal and inter-specific variations of stem respiration and its temperature sensitivity should be considered in developing mechanistic models of forest carbon cycles. Besides, the carbon cost for stem respiration varied with species and time.