Non-Growing Season Soil Respiration Of Five Temperate Forests

Most previous studies on soil respiration (Rs) are for growing seasons, while few for non-growing seasons. Winter CO2 efflux from soils is a significant component of annual carbon budges and can greatly determine carbon balance of ecosystems. Spring soil thawing period is critical in the intra—annual dynamics of Rs in mid—and high latitudes forest ecosystems, in which the frequently occurring alternate freezing and thawing events strongly influence the availability and dynamics of soil carbon and nutrients. However the temporal changes of Rs and involved mechanisms are poorly understood. Especially in situ measurements of Rs in spring soil thawing process are needed. In this study, a static closed chamber—gas chromatograph technique was used to measure the Rs and related biophysical factors in representative temperate forests of Northeast China during the non-growing season. The experimental design included five forest types, three random plots in each forest type, and three randomly installed static chambers in each plot. The forests were oak forest dominated by Quercus mongolica, poplar—birch forest dominated by Populus davidiana and Betula platyphylla, hardwood forest dominated by Fraxinus mandshurica, Juglans mandshurica and Phellodendron amurense, Korean pine (Pinus koraiensis) plantation, and Dahurian larch (Larix gmelinii) plantation. The results showed:During winter period, there were no obvious temporal trends for the Rs. We found the highest CO2 fluxes in late winter and patterns of Rs for different forest types were independent of soil temperature except for hardwood forest. Compared with growing seasons, soil temperature and water content did not significantly influence the Rs (R2=0.266—0.422) The annual fluxes for the hardwood, poplar—birch, and oak, pine and larch forests were 2114.90 g·m-2yr-1,1989.66 g·m-2yr-1,1860.88 g·m-2yr-1,1435.56g·m-2yr-1, and 1934.59 g·m-2yr-1,respectively; the ratio of winter fluxes for those were 9.63%,10.19%,13.08%,12.78%, and 10.13%, correspondingly. In winter, the temperature coefficients of Rs (Q10) for the hardwood, larch, poplar—birch, pine, and oak forests were 12.5,10.5,6.8,4.6, and 2.4, respectively. Q10 during winter time were much higher than those in the whole year except for pine and oak forests.During the soil thawing period, the forest types, thawing periods and their interaction significantly affected the Rs. The Rs for the pine, larch, hardwood, poplar—birch, and oak forests varied from 10.0—196.0 mg·m-2·h-1,5.8—217.1 mg·m-2·h-1,9.7—382.1 mg·m-2·h-1, 15.8—269.0 mg·m-2·h-1, and 35.9—262.5 mg·m-2·h-1, respectively. The mean Rs, T2 and W2 differed significantly among the five forest types(P<0.001). The Rs for broadleaved forests were generally higher than coniferous plantations. The mean values of RS increased as the soil thawing proceeded, and were largely consistent with the changes in soil temperature. Soil temperature significantly influenced the Rs, while the effect of soil water content on the Rs varied with forest types and soil depths. The Rs was significantly affected by W2 for all forests except for the oak forest. The statistical models of the Rs against T2 and W2 explained 60%—77% of the variability in the Rs measurements. The Q10 during the spring soil thawing period were much higher than those in the growing season, and changed with forest types. The Q10 for the larch, hardwood, pine, poplar—birch, and oak forests were 10.9,7.1,6.5,4.3, and 2.3, respectively. Further studies should focus on the mechanisms controlling Rs in the in situ soil, especially on temporal dynamics of soil microbial population in non-growing seasons and the relationship between soil respiration and soil microbial activity and composition.