| Maintaining the flow and balance of nutrients in forest ecosystem is an importantecosystem service of forests, which involves the elements input, output and conversionprocesses, but also involves the storage and flow fluxes within the pools of vegetation and soil.The nutrient cycling is closely related to the hydrological cycle, thus it needs particularly asimultaneous observation and study on the cycling of both nutrients and water.In this study, the representative stand plots of Larix principis-rupprechtii plantation,secondary forest of Pinus armandii, secondary forest of Betula platyphylla, and the shrubcommunity of Prunus salicina were selected in the Liupan Mountains, located in the drylandregion of Ningxia in Northwest China. The simultaneous observation of hydrological processesand flows of main nutrients with rainwater were carried out in the growing season of2011(May24to October20). The varying fluxes of main nutrients with rainfall input, conversion ofrainfall within canopy layer, leaching from humus layer and soil layer of main root zone werecalculted. Thus, the main charateristics of the element cycling and balancing in the suduiedforest ecosystems were described. The main conclusions are:The rainfall in growing season of2011was amounted to724.3mm.. The canopyinterception depth (rate) in the4forests studied were in the order of: Betula platyphyllasecondary forest (145.6mm,20.11%)> Larix principis-rupprechtii plantation (124.9mm,17.25%)> Pinus armandii secondary forest (102.3mm,14.13%)> Prunus salicina shrub (86.2mm,11.91%). The depth (rate) of rainfall under canopy were in the order of: Prunus salicinashrub (631.8mm,88.09%)> Pinus armandii secondary forest (622.0mm,85.87%)> Larixprincipis-rupprechtii plantation (599.4mm,82.75%)> Betula platyphylla secondary forest(578.7mm,79.89%）. The humus leakage depth (rate) showed: Prunus salicina shrub (525.0mm,72.48%)> Pinus armandii secondary forest (424.3mm,58.59%)> Larixprincipis-rupprechtii plantation (407.2mm,56.22%)> Betula platyphylla secondary forest (368.3mm,50.85%). The0-30cm soil leakage depth (rate) showed: Pinus armandii secondaryforest (275.9mm,38.09%)> Larix principis-rupprechtii plantation (244.2mm,33.72%)。According to the measurement, the growing season evapotranspiration of Larixprincipis-rupprechtii plantation was482.5mm, with the the components depth (and ratio torainfall) of vegetation interception124.9mm (17.2%of), tree transpiration204.5mm (28.2%),floor evapotranspiration153.1mm (21.1%). The growing season evapotranspiration of Pinusarmandii secondary forest was477.1mm, with the component depth (and ratio to rainfall) ofvegetation interception102.3mm (14.1%), tree transpiration222.9mm (30.8%), floorevapotranspiration151.9mm (21.0%). For both stand plots, the contribution of components ofevapotranspiration is in the order of: tree transpiration> floor evapotranspiration> vegetationinterception.The change of soil water storage (mm) in0-100cm within the growing season of2011was: Larix principis-rupprechtii plantation (+63.39)> Betula platyphylla secondary forest(-4.85)> Pinus armandii secondary forest (-5.47)> Prunus salicina shrub (-10.50). This meansthat the soil water storage was dexreased for all forest plots except the Larixprincipis-rupprechtii plantation which showed an increase.The calculation of water balance in growing season of2011indicated that the rainfallamunt can fully meet the demand of evapotranspiration in the plots of Larixprincipis-rupprechtii plantation and Pinus armandii secondary forest. The water yield (i.e., thenet output from soil layer of0-30cm) performanced as Pinus armandii secondary forest (252.7mm)> Larix principis-rupprechtii plantation (178.3mm).The input flux with opeh field rainfall in the growing season2011for TOC、NH4+-N、NO3--N、PO43-、K+、Ca2+、Mg2+was53.17、3.04、4.27、0.00、8.91、47.51、6.01kg/hm2respectively. During the rainfall conversion to canopy rainfall (the sum of throughfall andstemflow), the elements/ions were leached from or absorbed by the canopy in different degree,resulting in various change of their fluxes. The flux (kg/hm2) of TOC, PO43-, K+was increasedto132.28,11.16,55.53in the Larix principis-rupprechtii plantation; to106.56,14.64,44.83in the Pinus armandii secondary forest; to66.52,12.47,40.09in the Betula platyphylla secondaryforest; and to79.49,5.01,39.52in the Prunus salicina shrub. The flux (kg/hm2) of NH4+-N,NO3--N, Ca2+was decreased to2.40,2.15,32.38in the Larix principis-rupprechtii plantation;to2.36,1.92,27.95in the Pinus armandii secondary forest; to2.08,2.14,28.75in the Betulaplatyphylla secondary forest; and to2.29,2.09,34.97in the Prunus salicina shrub. The flux(kg/hm2) of Mg2+flux was increased to7.37and6.28in the Larix principis-rupprechtiiplantation and Pinus armandii secondary forest, but decreased to5.44in the Betula platyphyllasecondary forest and5.40in the Prunus salicina shrub.The humus layer of stand plots plays a role of "source" or "sink" for the flux of theelements/ions studied, so that their fluxes were changed variously. After the canopy rainfallwas converted to humus leakage, the flux (kg/hm2) of NH4+-N and NO3--N was decreased in allthe plots, i.e., decreased to1.22and1.55in the Larix principis-rupprechtii plantation，1.40and1.82in the Pinus armandii secondary forest,1.55and1.69in the Betula platyphylla secondaryforest,1.79and2.31in the Prunus salicina shrub. The flus (kg/hm2) of Ca2+and Mg2+wasincreased in all plots, i.e., increased to40.76and8.71in the Larix principis-rupprechtiiplantation,56.52and12.26in the Pinus armandii secondary forest,48.58and12.30in theBetula platyphylla secondary forest,75.55and12.60in the Prunus salicina shrub. The flux ofTOC (kg/hm2) was behaviored differently, i.e., decreased to90.76in the Larixprincipis-rupprechtii plantation and104.90in the Pinus armandii secondary forest; whileincreased to84.35in the Betula platyphylla secondary forest and129.35in the Prunus salicinashrub. The flux (kg/hm2) of PO43-was decreased to2.97in the Larix principis-rupprechtiiplantation, to4.62in the Pinus armandii secondary forest, and to6.56in the Betula platyphyllasecondary forest, but increased to14.23in the Prunus salicina shrub. The flux (kg/hm2) of K+was decreased to51.59in the Larix principis-rupprechtii plantation, but increased to54.31inthe Pinus armandii secondary forest,48.84in the Betula platyphylla secondary forest, and57.80in the Prunus salicina shrub. The soil layer of main root zone (0-30cm) plays a different regulating role to the flux ofelements/ions carried by humus leakage. This soil layer serves as a “sink” for the flux (kg/hm2)of TOC, PO43-and K+through the absorption or fixation, they were decreased to43.04,0.00,12.67in the Larix principis-rupprechtii plantation; to66.33,0.00,23.23in the Pinus armandiisecondary forest. However, this soil layer serves as a “source” for the flux (kg/hm2) of NH4+-N,NO3--N, Ca2+, Mg2+, they were increased to1.76,17.17,121.07,23.27in the Larixprincipis-rupprechtii plantation, and to1.66,14.68,114.94,28.80in the Pinus armandiisecondary forest.Compared to the elements/ions flux with rainfull, The flux with soil leakage from themain root zone (0-30cm) in both the Larix principis-rupprechtii plantation and the Pinusarmandii secondary forest were lowered for TOC and NH4+-N, showing a “sink” effect throughabsorption or fixiation; while increased for the flux of NO3—N, Ca2+and Mg2+, showing a“source” effect.When looking the mineral soil layer of0-30cm and the humus layer together as the forestfloor, the difference between the floor output and floor input was calculated, i.e the net elementbalance of forest floor. Within all the4plots studied, the performance of C is negative,meaning a C fixation which was better in natural forests than in plantation. The net elementbalance of the0-30cm soil layer in the growing season of2011showed to be negative for C,but positive for N, P, K, Ca, Mg in both the Larix principis-rupprechtii plantation and thePinus armandii secondary forest. This indicates a C fixiation and net loss of nutrient elementsappeared in the mineral soil layer. |
PDF Full Text Request