| This study was made during the growth season of2011at the Liupan Mountains of northwest China. It quantified the hydrological processes and the corresponding element flux varing with rain water transformation in a Larix principis-rupprechtii plantation stand. The main purpose is to provide scientific basis for the management of Larix principis-rupprechtii plantation and for the further understand of element cycling in such forest ecosystems. The main results were obtained as follows.(1)The Larix principis-rupprechtii stand studied was a25-years-old middle-younth growth, with a canopy density of0.8, an average of tree height of13.9m, an average of DBH of15.5cm, and a stand density of1128trees/hm2, and a canopy average LAI of2.59. The shrubs under forest canopy was sparse, with the average coverage of24.6%, the mean height of2.50m, and the mean basal diameter of3.19cm. The average height of grasses was about20cm, and the coverage of grasses was71.6%. The indexes of Simpson and Shonnon-Wiener for the shrubs layer and herbs layer were blow1.5, indicating low diversity of both shrub and herb species.(2) The value of bulk density of soil increased with the increasing of the soil depth under all stands of Larix principis-rupprechtii,from0.92at the0-10cm soil to1.18at the80-100cm layer.The water-holding capacity,water holded in capillary pores, the capillary porosity and field capacity decreased with the increasing of the soil depth under all stands,the content at the0-10cm layer was63.53%,60.58%,38.20%,36.43%,while the content at the80-100cm layer was54.85%,44.08%,32.05%,30.06%.The pH-value of soil increased with increasing soil depth, from7.15at the0-10cm soil layer to7.57at the80-100cm layer. The content of organic carbon and total nitrogen of soil decreased with increasing soil depth. The content variation of total potassium and total phosphorus were unconspicuous in the soil depth of0-100cm, with their average of0.86and3.48g/kg. The content of Ca, Cu, Zn increased with increasing soil depth, and the content at the80-100cm soil layer was9.58,0.05and0.36g/kg; the content variation of other element (Fe、Na、 S、Mg、Mn) did’t show any obvious trend within the soil depth range of0-100cm. (3)The total precipitation during the growing season2011(from May to October) amounted to773.7mm, of which75.25%concentrated in the period from July to September. The precipitation in May, June, and October accounted for only6.42%,12.77%and5.56%, respectively.The thoughfall in the growing season amounted to547.24mm,with the maximum month value of170.5mm (78%of monthly precipitation) in September, and low month values in May (41.05mm and83%) and October (36.44mm and71%). The total stemflow depth in the growing season was only2.14mm, with the highest month value in September (1.03mm) and lowest month value in May (0.05mm). The forest canopy interception during the growing season was224.32mm, with the highest month value in July (82.61mm) and follwed by September (47.92mm), June (40.99mm), May (8.58mm) and October (6.34mm).(4)The pH-value of rainwater changed obviously when it flowed though canopy layer, humus layer and root-zone (soil) layer. The average pH-value of rainwater in the open field was7.13, but decreased to6.73in thoughfall and6.00in stemflow, meaning that there may be some acid entered into the rainwater. However, the pH-value increased to6.87in the leachage under humus layer and7.28under the root-zone layer (0-30cm), indicating that the humus layer and soil layer supplied some alcline matters to buffer the rainwater acidity. The electrical conductivity (μs/cm) of rainwater in open field was31.33, then it was continuouely increased with the hydrological processes in forest ecoystems, to110.33in thoughfall,131.73in steamflow,145.67in the leackage under humus layer, and347.6in the leakage under the main root-zone soil layer.(5)The mean concentration of K+, Na+, Mg2+, Ca2+, Mn2+, Cu2+, Zn2+, Fe3+NH4+-N, NO3--N, Cl-, PO4-, SO42-in the rainwater at open field during the growing season were0.02,0.04,0.02,0.15,0.12,0.17,2.64,0.25,0.02,0.01,0.08,0.09,0.00mmol·L-1respectively. The corresponding flux of these ions was17.23,33.73,12.51,112.91,0.09,0.13,2.05,0.19,1.63,6.53,59.34,68.56,0.00mmol·m-2.(6)The flux of most cations (K+, Mg2+, Mn2+, Cu2+, Fe3+) with the rainwater under canopy, wihich is composed of the thoughfall and stemflow, was hiher than that inputed by the open field rainfall, with a flux difference of124.65,20.42,0.05,0.59,0.11,0.37mmol·m-2repectively, indicating that the forest canopy playing a role of "source" for these cations. However, the canopy played a role of "sinks" to the flux of pther cations including Na+, Ca2+, Zn2+, with the flux difference of-3.04,-37.17,-0.95mmol·m-2. The flux of all cations of the leakage under humus layer was lower than that ocarried by the rainwater under canopy, indicating that the humus layer had a "sinks" impact on the cation flux. The negative flux difference between the leakage under root-zone soil layer and the leakage under humus layer for the cations of K+, H+, Cu2+, Fe3+(with the values of-55.92,-0.03,-0.03,-0.19mmol·m-2) indicated that the root-zone soil layer had a "sinks" impact on the flux of these cations; however, it had a "source" impact on the flux of most other cations (Na+, Mg2+, Ca2+, Mn2+, Zn2+), with a flux difference of25.19,38.87,136.68,0.10, and0.92mmol·m-2.(7) Compared to the flux through upper layer, the flux differences of NH4+-N in canopy layer and humus layer was negative, with the value of-3.81and-5.62mmol·m-2; while the flux difference of the soil layer was positive (5.31mmol·m-2), indicating the canopy layer and humus layer had a sinks" impact but the soil layer had a "source" impact on the NH4+-N flux. To the flux of NO3--N, the canopy layer had a "sink" impact, causing a balance of-4.14mmol·m-2; while the humus layer and root-zone soil layer had a "source" impact causing a flux difference of2.59and12.24mmol·m-2.(8)The canopy had a "sinks" impact on the flux of SO42-, causing a flux difference of-4.72mmol·m-2compared with the flux with rainwater in open field; while it had a "source" impact on the flux of Cl-and PO43-with a flux differene of15.19and26.72mmol·m-2. The negative flux differences between the leackage under humus layer and the upper layer input for Cl-, SO42-, PO43-were-32.76,-39.97,-20.54mmol·m-2, indicating that the humus layer had a "sinks" impact on these three anions. The main root-zone soil layer had a "source" impact on the flux of Cl-, SO42-, and PO43-.(9)Compared to the TOC flux of upper layer, the canopy layer had a "source" impact, with an increase of64.66kg·hm-2; while the humus layer and root-zone soil layer had a "sinks" impact, with a difference of-53.08and-34.15kg·hm-2. |
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