Effects Of Forest Operation On Soil Respiration In Conifer/Broad-leaved Mixed Forests In Xiao-xing'anling

Forest ecosystems in northeastern China play an important role in both local and national carbon budgets because of the large area and huge amount of carbon storage. The study of effects of forest operation on soil respiration in conifer/broad-leaved mixed forests in Xiaoxing'anling directly affects the local and national carbon budgets and forest management. The study has important theoretical and practical meaning. In this study, the infrared gas exchange analyzer (LI-8100) was used to measure C0₂ fluxes on soil surface. Trenching plots were aligned to determine the heterothophic (RH) and autotrphic respiration (R_A) of soil components and on skidding trails under varied cutting intensity, and examine the effects of soil thermal and moisture content on soil respiration and heterotrophic respiration for different treatment, such as selective cutting, tractor or animal skidding, etc. The following results were obtained from this study:(1) Effects of selective cutting on soil respirationUnder different cutting intensity, the soil respiration rates varied from 0.6-8.2μmol·m^-2·s^-1 Higher soil respiration rates were reported in rainy season than the ones in dry season. During growing season, soil carbon fluxes varied from 1.68-18.82mol·m^-2 with the highest in July and the lowest in November. The annual average carbon fluxes was 84.37mol·m^-2 for the year of 2006.Under different cutting intensity, soil temperature and air humidity had more significant effects on soil respiration in dry season while less effect was noticed during rainy season. The comprehensive statistical models of Rs with soil temperature, soil moisture and their interactions as independent variables explained 68.10%-98.9% variations in Rs. It indicated that selective cutting had little impacts on soil carbon effux. The highest correlation between C0₂ flux and soil temperature and moisture was showed in mineral soil, followed by root, then by litterfall. However, the correlation between R and cutting intensity was the strongest in litter, followed by root and mineral soil. Trends of Litterfull respiration and mineral respiration are the same, both of them have large increase. They are the important part to control total respiration after cutting. In order to reduce C efflux, we should choose small intensity or middle intensity.(2) Effects of skidding operation on soil respirationThe sequence of different compaction is main skidding road> small skidding trail>control field. Main skidding road have more influence than small skidding trail. Soil CO₂ concentration became bigger as increase of the soil compaction in comparison of theoretical model to field data. The curve has a high dot that stand by the diurnal and seasonal variations of soil respiration. Soil temperature at 5cm deep did significantly on soil respiration, but soil moisture not. The skidding road soil has bigger variance than the control field. The average CO₂ flux of skidding road and control field are 2.36 and 3.22μmol·m^-2·s^-1. The propoty of skidding road CO₂ flux is 73% by the control field. The temperature sensitivity coefficient of soil respiration (Q₁₀) for the skidding road and control fields are 2.77and 2.72.Soil temperature and soil moisture affect soil respiration effux. Soil temperature is more important than soil moisture. By the mode of R=ae^bTW^c, soil temperature ,soil moisture and their interactions as independent variables explained 49%-90% variations in R_L.and 65%-93% variations in R_M.The modle is better than the oneonly includding soil temperature or soil moisture. In the growing season, the average soil littefull respiration flux are CO₂l.36,1.13 and 0.94μmol·m^-2·s^-1, varied from CO₂ 0.22-2.6,0.35-2.76 and 0.24-2.45μmol·m^-2·s^-1ï¼›and the soil minaral respiration are CO₂ 1.16,1.02å’Œ0.93μmol·m^-2·s^-1, varied from CO₂ 0.42-2.22,0.28-1.92 and 0.27-2.31μmol·m^-2·s^-1 in the main skidding road, small skidding trail and control field.The heterothophic respiration of main skidding road is highest, 82.7%,and the control field is lowest, 58.4%.R_L and R_M are almost equal prpperty in the R_H.And skidding operation make soil litterfull respiration flux lowerand the control field.(3) Effects of slash disposal on soil respirationIn 2006 and 2007, soil respiration in cumulated cleaning higher 16%-179% than control field.Soil temperature has significantly exponent relationship with cumulated cleaning field and control field. Q₁₀ value add to 1.99 from 1.48. 0-10cm The soil physical propoty in cumulated cleaning field have more effect than forest fields. Because added cutting surplus, make forest -23.62mol·a^-1 to 43.13mol·a^-1C, this is better to forest C operation.CO₂ come from litterfall is 21% to all the soil respiration.It's higher in rainy season than in dry season,and they have big disparity. Soil respiration varies fast and big in rain season. Getting off the litterfall change the relationship of R-T, make R² to the 0.5621 from 0.7219.Q₁₀ are 2.72 and 2.96.And Getting off the litterfall did not change the relationship of R-W.Soil temperature conthol soil respiration diurnal change. And in rainy season, soil moisture takeover temperature.R change bigger than control fields and the extreme value are ahead 2-3 h. the average soil respiration flux are CO₂ 2.8 and 3.8/μmol·m^-2·s^-1, varied from 0.7-5.58μmol·m^-2·s^-1 in fired field and 1.0-8.7μmol·m^-2·s^-1 in the control field.Temperature can explain the variation 77% and 74% in fired field and control field.Soil respiration in fired field is 73% of control field, Q₁₀ values are 2.25 and 3.03.This study provided a great deal of measured data and reseach framework for the effect of forest operation to belowground carbon pool and flux in representative forest ecosystems in northeastern China, and illustrated that soil CO₂ efflux in these ecosystems was affected by wood production operation and the microenvironment. Therefore, the carbon sink/source capacity of those ecosytems may change under global climate change conditions, which emphasized the siginificance and necessity of further studies on this subject.