Abstract:Thinning is one of the intensive forest management techniques commonly applied to increase the merchantable timber volume. However, how thinning affects soil-atmospheric fluxes of greenhouse gases (GHGs) is poorly understood. A field experiment with four treatments (CK: unthinned; MB: medium intensity thinning from below; HB: high intensity thinning from below; and HI: high intensity thinning by removing every alternative row of trees) was conducted to assess the impact of thinning regimes on soil-atmospheric fluxes of GHGs (CO 2 , CH 4 , and N 2 O) and soil nitrogen mineralization in a poplar plantation established on a lowland. Thinning significantly increased soil water content and water table in the high thinning treatments (HB and HI) and tended to increase soil temperature (p < 0.10). The result of the one-year study showed that estimated annual emissions of CO 2 and CH 4 were higher in HB and HI than in other treatments, while the highest emission of N 2 O was in the CK. The thinning treatments increased the annual emission of CO 2 by 23%-64% and that of CH 4 by 190%-1200%, but decreased that of N 2 O by 41%-62%. Thinning increased annual N mineralization by 50.3% in HI and 30.1%in HB. Changes in soil temperature and water table drove CO 2 , CH 4 , and N 2 O emissions, while soil water content was the most important factor driving CH 4 emission. We conclude that the moderate thinning (MB) regime is the best thinning option to minimize the impact on GHG emissions for lowland poplar plantations with similar conditions to those tested in this study.
To investigate how reclamation of wetlands in three different soil types impacts the vertical distribution of soil organic carbon (SOC) content in soil profiles, contents and density of soil organic carbon (SOC) in soil profiles of three types of wetland soils in wetland, soybean and paddy field in Sanjiang Plain were determined. Both soybean and paddy field were reclaimed from wetland. We observed that reclamation significantly reduced SOC content in 0-10,10-20 and 20-30 cm soil layers in meadow albic soil and meadow marsh soil, and 0-10,10-20,20-30 and 30-40 cm soil layers in peat bog soil, there were no significant difference in SOC contents in soil layers under 0-30 or 0-40 cm before and after reclamation. After reclamation, SOC density in three types of wetland soils decreased, and SOC density in soybean field were higher than that in paddy field. Either in wetlands or farm lands in the three types of wetland soils, most of the SOC storage in 0-100 cm soil layer was stored in 0-50 cm soil layer. Though wetland reclamation reduced the SOC content, it hasn’t changed the regularity of SOC vertical distribution. The relationships between SOC content and soil depth in wetlands and farm lands all could be described by exponential functions in three types of soils. The specific functions are useful to estimate and predict the regional SOC pool by models.
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