氮沉降影响下酸性森林土壤中水溶性有机氮的分布特征

DISTRIBUTION PATTERN OF WATER SOLUBLE ORGANIC NITROGEN IN ACIDIC FOREST SOILS RECEIVING NITROGEN DEPOSITION

选取贵州雷公山(LGS)和重庆铁山坪(TSP)两个氮沉降量具有明显差异的森林小流域,对土壤中水溶性有机氮(WSON)的分布特征进行了对比研究.在氮沉降较低的LGS流域土壤水中WSON占总氮的比例可达30%—60%,显著高于氮沉降高的TSP流域.TSP流域土壤浸提液中WSON的比例相较于土壤水有显著增加,说明该流域中WSON多附着于土壤表面,流动性较弱.在0—90 cm典型剖面内,TSP流域WSON的比例显著高于LGS流域.两剖面中WSON的比例均在中部(30—60 cm)达到最高值,分别为35.37%和55.82%.两剖面中WSON和WSOC的纵向变化不完全同步,WSOM的C/N比值在剖面中部有低谷.在剖面中、下部(30—90 cm)TSP流域WSOM的C/N比值低于LGS流域,说明该流域WSOM中氮的富集程度更高.

Distribution pattern of water soluble organic nitrogen（WSON） in acidic forest soils was investigated in two selected catchments.In Leigongshan（LGS） catchment receiving lower nitrogen deposition,WSON was the important fraction of total dissolved nitrogen（TDN） in soil water,with the percentage ranging from 30% to 60%.However,the percentage was less than 10% in Teishanping（TSP） catchment receiving higher nitrogen deposition.In soil extracts of TSP catchment WSON percentage increased substantially,which indicates that WSON in this catchment mostly adsorbed on soil solid phase with low mobility.In the typical soil profiles（0—90 cm）,WSON percentage in TSP catchment was significantly higher than that in LGS catchment.In LGS and TSP catchment,WSON percentage reached its maximum in the middle depth（30—60 cm） with the values of 35.37% and 55.82%,respectively.Vertical change of WSON was not synchronous with water soluble organic carbon（WSOC） in the investigated soil depth range.In the middle depth,C/N ratio of water soluble organic matter（WSOM） reached minimum.In the middle and bottom depth（30—90 cm）,C/N ratio in TSP profile was significantly lower than in LGS profile,indicating higher nitrogen enrichment of WSOM in TSP catchment.