| Wetlands have been valuable as sources, sinks, and transformers of carbon and nitrogen. The value of wetlands for maintaining regional ecology balance, biodiversity protection and carbon, nitrogen storage was recognized for several years. Wetland impacts have included both wetland alteration and wetland destruction.In recent years, the most common alteration of wetlands have been draining, modification of the hydrology regime, cutting and so on. Forested wetlands interfered by cutting were at a higher level, especially in the Coniferous Forests of wetlands. In this research, three kinds of forested wetlands which are typical in Xing ’an Mountain (Larix-Carex schmidtii wetland,Larix-moss wetland, Larix-Sphagnum magellanicum wetland) were studied. Elementar vario MACRO Elemental analyzer was used to analyze the C and N of soil samples from different soil depth. The effects of thinning and clearing on soil carbon content and soil nitrogen content, soil carbon density and soil nitrogen density of different depth in0～50cm soil profile were compared. And the reasons for the effects were analyzed.The results are as follows:(1) The carbon content in0～50cm soil layers of samples controlled, thinning and clear cutting of Larix-Carex schmidtii, Lari-moss, Larix-Sphagnum magellanicum distributed between28.93～285.14,11.06～264.33,11.68～64.08;166.93～310.24,84.19297.18,202.68～313.35and271.06～304.85,246.88～332.63,216.09～317.49g.kg-1. The impacts on the soil carbon content distribution patterns of cutting were different in three swamps. The effects of cutting were strong in Lari-moss swamps, slight in Larix-Sphagnum magellanicum swamps, rare in Larix-Carex schmidtii swamps; the impacts on carbon content in different layers of cutting were different in three swamps, the carbon content in Larix-Carex schmidtii swamps was decreased significant (15.7%～85.2%), the carbon content in deeper layers of Lari-moss swamps was increased in clear cutting plot (81.5%), the carbon content in deeper layers of Larix-Sphagnum magellanicum swamps was increased in thinning plot (18.1%～18.7%).(2)The nitrogen content in0～50cm soil layersof controlled, thinning and clear cuttingof Larix-Carex schmidtii, Lari-moss,Larix-Sphagnum magellanicumsamplesdistributed between28.93～285.14,11.06～264.33,11.68～64.08;166.93～310.24,84.19297.18,202.68～313.35and271.06～304.85,246.88～332.63,216.09～317.49g-kg-1.The impacts on the soil nitrogencontent distribution patterns of cutting were different in three swamps.The nitrogen distribution patterns in Lari-mossandLarix-Sphagnum magellanicum swamps were changed in cutting plots.The nitrogen distribution pattern in Larix-Carex schmidtiiswamp was changed in clear cutting plot.The impactsofnitrogen content in different layersin cutting plots were different in three swamps.The nitrogen content in different layers of Larix-Carex schmidtiiswamp was decreased in clear cutting plot (51.0%～81.7%), the nitrogen content in different layers of Lari-moss and Larix-Sphagnum magellanicumswamps was little impacted in clear cutting plots.(3) In controlled, thinning and clear cutting plots of Larix gmelinii-Carex schmidtii sample,C/N ratio in0-50cm soil layer distributed between16.66～22.72,12.56～23.95,11.46～18.83.In controlled, thinning and clearing cutting plots of Larix gmelinii-moss sample,C/N ratio in0-50cm soil layers distributed between18.14～23.90,17.22～24.76,16.99～21.88.In controlled, thinning and clear cuttingplots Larix gmelinii-Sphagnum magellanicum sample,C/N ratio in in0～50cm soil layers distributed between16.34～22.53,16.23～18.87,16.34～29.24.The distribution pattern of soil C/N ratioof the three swamps had significant changes in thinning and clear cutting plots.The impacts of harvesting on C/N ratio of the three swamps soil layers were different:clearcutting significantly reduced C/N ratio of some soil layers of Larix gmelinii-Carex schmidtii and Larix gmelinii-moss samples (28.5%～40.5%), and significantly improved C/N ratioof upper soil layers of Larix gmelinii-Sphagnum magellanicum sample (18.8%to29.9%).(4) Incontrolled, thinning and clear cutting plots of Larix gmelinii-Carex schmidtii sample,carbon density in0～50cm soil layerswere as follows:25.89,25.39,15.39kg·m-2.In controlled, thinning and clear cutting plots of Larix gmeliniii-moss sample,carbon density in0-50cm soil layers were as follows:34.76,31.69,28.39kg·m-2.In controlled,thinning and clear cutting plots of Larix gmelinii-Sphagnum magellanicum sample, carbon density in0-50cm soil layers were as follows:28.88,36.75,21.46kg·m-2.There were some different impacts of cutting on soil carbon densityin the three swamps:clearcutting significantly reduced soil carbon densityof Larix gmelinii-Carex schmidtii sample (40.6%); and harvesting has little effect on soil carbon density of Larix gmelinii-moss sample; thinning significantly improved soil carbon density of Larix gmelinii-Sphagnum magellanicum sample (27.3%).(5)In controlled, thinning and clear cuttingplots of Larix gmelinii-Carex schmidtii sample, nitrogen density in0-50cm soil layers were as follows:0.42,0.89,2.77kg·m-2.In controlled thinning and clear cuttingplots of Larix gmelinii-mosssample, nitrogen density in050cm soil layers were as follows:1.25,1.85,1.53kg-m"2.In controlled, thinning and clear cutting plots of Larix gmelinii-Sphagnum magellanicumsample,nitrogen density in0-50cm soil layers were as follows:1.61,2.16,1.42kg·m-2.The impacts of harvesting on soil nitrogen density of the three swamps were different:clearcutting significantly improved soil nitrogen density of Larix gmelinii-Carex schmidtii sample (559.5%); clearcutting only significantly improved soil nitrogen density of30～40cmof Larix gmelinii-mosssamplt (262.5%); thinning significantly improved soil nitrogen density of Larix gmelinii-Sphagnum magellanicum sample (34.2%), and clearcutting reduced soil nitrogen density (11.8%), but only30-40cm were significantly reduced, and the impact on the total soil nitrogen density was not significant.Soil carbon density and nitrogen density had a balance depending on the input and output of the soil carbon pool and nitrogen pool. Harvesting led to changes in the input of soil carbon and nitrogen, and the output of the soil carbon and nitrogen pool due to the changes of soil water and temperature conditions, resulting in changes in soil carbon and nitrogen density.The impacts of harvesting on soil carbon and nitrogen density depended on the differences in cutting intensity, mode, forest type, location, time after cutting and other factors. |
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