| Loess Plateau, the most serious water and soil loss region, was one of the key implementregions of ecological construction and conservation and territorial management in westernChina. A large area of forest in Loess Plateau from long term environment construction playsa key role in regional soil and water conservation, environmental management and ecosystemsystem service function. This study aimed at the forest soil of Loess Plateau and analyzed thedistribution characteristics of soil carbon and nitrogen in different soil texture, forestvegetation, and altitude and forest type. The relationship among vegetation types, soil andsoil aggregate combined state organic carbon and nitrogen. Under the studies of thedistribution of carbon and nitrogen in soil aggregate and soil stability in different vegetationtypes, the evolvement characteristic of carbon and nitrogen in forest soils and its relationshipwith forest types and environments factors would be explicated. This can provide theoreticalfoundation to forecast the carbon-nutrient balance and succession characteristics of forestsoils. The mainly conclusions are as follows.(1) Distribution of Carbon (C) and nitrogen (N) in bulk soil and aggregate in aspenwoodlands were affected by soil texture in the northwest of Loess Plateau. In sandy soil,organic carbon (OC) and N stocks in0.25-0.053mm and <0.053mm aggregates were higherthan those in>0.25mm aggregates. In loamy soil, the distribution of soil aggregateassociated organic C stock was related with soil depth. The relationship between organic Cand N in soil aggregate and those in bulk soil was related with soil texture. The distribution oforganic C and N in loamy soil depended on those in each aggregate. In sandy soil, soilorganic C and N concentrations were due to those in <0.053mm aggregates, while C and Nstocks due to0.25-0.053mm aggregates.(2) In the northwest of Loess Plateau, soil structures in Larix principis-rupprechtii andPinus armandii forest lands were relatively better, but soil structure in Black Locust forestlands was relatively worse. In Black Locust forest lands, organic C and N concentrations andstocks in bulk soil and those in soil aggregate were low. Yet other forest lands had highconcentrations and stocks, related to aggregate types, species, and soil depth. Soil OC andtotal nitrogen (TN) in Larix principis-rupprechtii and Pinus armandii forest lands mainly stored in>0.25mm aggregates. There were no significant difference in soil aggregateassociated OC and N stocks between Pinus tabulaeformis and Picea crassifolia forest lands.(3) Bulk soil and aggregate associated C and N concentrations were related to altitudeand forest type in Liupan mountain, with broad-leaved forest lands higher than coniferousforest lands. OC and N at altitude2000-2600m were high for coniferous forest lands but lowfor coniferous forest lands. However, soil aggregate associated OC and N stocks in differentforest lands were not affected by altitude. In research area, soil OC and N concentrationsin>0.25mm aggregates accounted for over80%of soil total OC and N and had a significantpositive correlation, suggesting that soil OC and N mostly stored in>0.25mm aggregates.These results showed that soil C and N distribution, aggregate associated C and N,relationship between OC and N in bulk soil and those in aggregate, and impact factors wererelated to construction mode of forest land in northwest of Loess Plateau. Soil C and Ndistribution and relationship between OC and N in bulk soil and those in aggregate in aspenforest lands were relative to soil texture, yet natural secondary forest influenced by species,forest types and altitude. |
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