Intra-and Inter-Specific Variations In Stem Respiration Of Major Temperate Tree Species In Northeast China

The stems are not only the largest storages of the biomass in forest ecosystems, but also represent a huge and long-term carbon sink. Respiration in the living cells of the stem tissue occurs all the year round, and results in substantial amounts of photosynthetically fixed CO2 being released back to the atmosphere. This process can influence the annual carbon balance of forest ecosystems. As a major component of autotrophic respiration in forest ecosystems, the stem surface CO2 flux (RW) reflects tree growth activities and metabolism, and affects the productivity of forest ecosystems. The forest in northeastern China is sensitive to climate change, and plays a crucial role in maintaining local and regional ecosystem carbon balance. There are, however, many uncertainties on the forest carbon budget, one of which is lacking of quantifying the magnitude of woody tissue respiration. Up to date, the RW variability has not been well quantified for the Chinese temperate forests.The RW was in situ measured throughout 2009 on 14 major tree species coexisting in the temperate forests in northeastern China. A subset of the tree species was remeasured during 2010. The species included diffuse-porous species ((Betula platyphylla), B. costata, Populus davidiana, Tilia amurensis, and Acer mono), ring- and semi-ring-porous species (Ulmus propinqua, Phellodendron amurense, (Juglans mandshurica), Ouercus mongolica, and Fraxinus mandshurica), and coniferous species (Larix gmelinii, Pinus koraiensis, Picea koraiensis, and P. sylvestris var. mongolica). The objectives of this study were to (1) quantify intra- and inter-specific variations in RW, total annual respiration (RT) and annual growth respiration (RG) at the chamber level for the tree species, and (2) examine changes in Rw, RT and RG with tree diameters and seasons. These results will provide solid data for developing and validating the carbon cycling model for the temperate forests, and be important for mechanistically understanding the forest carbon cycling.For each tree species,12-18 trees were randomly sampled to cover as wide DBH (diameter at breast height) ranges in the stands as possible. A polyvinyl chloride collar (inner diameter 10.4 cm, height 5.0-6.0 cm) was cut and polished to fit the stem surface shape of each sample tree, and installed on the north side at breast height (1.3 m). The collar was attached with waterproof silicon adhesive to the stem surface that was pretreated without causing any injury of the live tissues, and remained in place throughout the measuring period. An infrared gas exchange analyzer (LI-6400 IRGA) was used to measure the Rw once and twice every month from 08:00 to 17:00 within three to four consecutive non-rainy days during the period from June to October 2009 and May to November 2010, respectively. Stem temperature at 1 cm depth beneath the bark (TW) was simultaneously measured with a digital thermometer. Diameter increments and continuous air temperatures were also monitored.Tree species, measuring month and their interactions significantly influenced the Rw (P< 0.001). The mean RW of during the measuring period of 2009 varied from 1.32.μmol CO2·m-2·-1 for P. amurense to 3.12μmol CO2·m-2·-1 for L. gmelinii. The mean RW for the ring-and semi-ring-porous species was greater than that for the diffuse-porous species, while the mean RW for the coniferous species varied greatly. The mean Rw for all species showed a unimodal seasonal pattern, with the maximum and minimum occurring in July and October, respectively. The intra-specific mean absolute (standard errors) and relative variations (coefficients of variation) varied from 0.11-0.29μmol CO2·m-2·-1 and 61%-89%, respectively. The RW tended to increase with DBH increasing for all species, but the forms and determination coefficients of the regression models were species-dependent. There were significant relationships between mean RW and DBH (P<0.05) for all species except for U. propinqua and F. mandshurica (P>0.05), suggesting that DBH be a simple and practical proxy for predicting and extrapolating tree- or stand-level RW.The RT and RG differed significantly (α=0.05) among intra- and inter-specific of 12 tree species in 2010. The mean RT and RG varied from 144.13 gC·m-2·a-1 for P. koraiensis to 628.08 gC·m-2·a-1 for Q. mongolica and from 27.24 gC·m-2·a-1 for P. koraiensis to153.27 gC·m-2·a-1 for F. mandshurica, respectively. The mean RT and RG for the ring-porous species were greater than that for the diffuse-porous species and the coniferous species. The total monthly respiration (RM) for all species showed a unimodal seasonal pattern. with the maximum occurring in June or July. The intra-specific mean absolute variations (standard diviations) of the RT and RG varied from 67.07-320.20 gC·m-2·a-1 and 18.86-90.19 gC·m-2·a-1, respectively. The intra-specific relative variations (coefficients of variation) varied from 40%-68% and 38%-79%, respectively. The RT and RG tended to increase with DBH increasing for all species, but the forms and determination coefficients of the regression models dependented on species. There were significant relationships between mean RT and RG and DBH (P<0.05) for all species except for P. amurense (RT) and F. mandshurica (RG) (P> 0.05), suggesting that DBH be a simple and practical proxy for predicting tree- or stand-level RT and RG. The contributions of RG to Rτfor all tree species were less than 50% despite in the growing season or throughout the year, suggesting the maintenance cost have a larger proportion of the RT which may nearly offset the increased growth. This study highlights the importance of taking the intra- and inter-specific variations in RW measurements into account in cross-comparing RW and extrapolating chamber-based RW measurements to tree- or stand-level estimates.