六盘山华北落叶松林降水转化中的阳离子通量变化特征

在六盘山香水河小流域的华北落叶松人工林样地,测定了2011年生长季降水转化过程中的大气降水、穿透水、干流、枯落物渗透水和主根系层(30 cm土层)土壤渗透水的pH值与多种阳离子的浓度及通量变化.结果表明:林外降水的pH值平均为7.13,转化为穿透雨和干流后降为6.73和6.00,转化为枯落物渗透水和土壤渗透水后回升为6.87和7.28.在降水转为由穿透雨和干流组成的林下降水后,绝大多数阳离子的浓度都不同程度地增大,但Zn2+浓度下降；虽然林冠截持使林下降水的数量减小,但由于雨水对林冠的离子交换及淋洗,林下降水的多数阳离子通量都比林外降水明显增大,K+、Mg2+、H+、Mn2+、Cu2+、Fe3+由林外的17.23、12.51、0.06、0.09、0.13、0.19 mmol·m-2分别上升到林下的141.87、32.93、0.10、0.68、0.24、0.56 mmol·m-2,但Na+、Ca2+、Zn2+的通量分别由林外的33.73、112.91、2.05 mmol·m-2减小为林内的30.70、75.75、1.10 mmol·m-2.在枯落物层渗透水中,绝大多数阳离子的浓度都不同程度地下降,仅Mg2+浓度微弱上升；受枯落物截持部分降水及雨水中阳离子与枯落物交换的影响,枯落物渗透水中所有阳离子的通量都比林下降水明显减小,K+、Na+、Mg2+、Ca2+、H+、Mn2+、Cu2+、Zn2+、Fe3+分别降至83.06、12.30、23.96、65.73、0.04、0.12、0.09、0.13、0.32 mmol·m-2.在主根系层土壤渗透水中,一些阳离子(K+、Mn2+、Cu2、Fe3+)的浓度下降,另一些阳离子(Na+、Mg2+、Ca2+、Zn2+)的浓度则上升,尤其Ca2+浓度显著上升；Na+、M2+、Ca2+、Mn2+、Zn2+的通量比枯落物渗透水增大,其值分别为37.49、62.83、202.41、0.22、1.05 mmol·m-2,但K+、Cu2+、Fe3+的通量比枯落物渗透水减小,其值分别为27.14、0.07、0.09 mmol·m-2.相对于林外降水的阳离子输入通量,林冠层对多数阳离子(除Na+、Ca2+、Zn2+)的通量为净淋出(增加)作用,枯落物层对多数阳离子(除K+、Mg2+、Mn2+、Fe3+)的通量为净固定(减少)作用,主根系层土壤对盐基离子(Na+、K+、Mg2+、Ca2+)和Mn2+的通量为净淋失(增大)作用,但对其他阳离子(H+、Cu2+、Zn2+、Fe3+)的通量为净固定(减少)作用.

Variation of Cation Flux with Rain Water in a Larix principis-rupprechtii Plantation on Liupan Mountains

At a selected stand of Larix principis-rupprechtii plantation growing in the small watershed of Xiangshuihe of Liupan Mountains, NW China, the variation of pH-value, cation concentration and cation flux were measured in the rain water from open field precipitation, throughfall, stem flow, leakage under humus layer and under the mineral soil layer (30 cm) in the growing season of 2011. The results showed that the mean pH-value of open field rain water was 7.13, while it was 6.73 in throughfall, 6.00 in stem flow, 6.87 in the leakage under humus layer and 7.28 in the leakage under the soil depth of 30 cm. In the rain water under canopy, which is composed of throughfall and stem flow, the concentration of nearly all cations increased more or less, but the concentration of Zn²⁺ decreased. Although the depth of rain water under canopy decreased as a result of canopy interception, the cation exchange or wash out from canopy led to an obvious increase of flux of most cations. The cation flux (mmol·m^-2) for K⁺, Mg²⁺, H⁺, Mn²⁺, Cu²⁺, and Fe³⁺ increased from 17.23, 12.51, 0.06, 0.09, 0.13, and 0.19 of open field precipitation to 141.87, 32.93, 0.10, 0.68, 0.24, and 0.56 of rain water under canopy. However, the fluxes of Na⁺, Ca²⁺, Zn²⁺ decreased by the canopy, from 33.73 to 30.70, 112.91 to 75.75, and 2.05 to 1.10 respectively. In the leakage under humus layer, the concentration of most cations decreased more or less, only the concentration of Mg²⁺ increased slightly. Affected by the humus layer interception and the cation exchange with humus layer materials, the flux of all cations in the leakage under humus layer obviously reduced compared with the flux carried by the rain water under canopy, with a flux (mmol·m^-2) of 83.06 for K⁺, 12.30 for Na⁺, 23.96 for Mg²⁺, 65.73 for Ca²⁺, 0.04 for H⁺, 0.12 for Mn²⁺, 0.09 for Cu²⁺, 0.13 for Zn²⁺, and 0.32 for Fe³⁺. In the leakage under the soil layer of main root system, the concentration of some cations (K⁺, Mn²⁺, Cu²⁺, Fe³⁺) reduced, while the other cations (Na⁺, Mg²⁺, Ca²⁺, Zn²⁺) increased, especially the remarkable increase of Ca²⁺ concentration. Affected by the volume decrease of soil leakage and the cation exchange with soil, the flux of Na⁺, Mg²⁺, Ca²⁺, Mn²⁺, and Zn²⁺ in soil leakage increased compared with that of humus layer leakage, with the flux (mmol·m^-2) of 37.49, 62.83, 202.41, 0.22, and 1.05 respectively; but the cations of K⁺, Cu²⁺, Fe³⁺ decreased, with the flux (mmol·m^-2) of 27.14, 0.07, and 0.09 respectively. Compared with the cation input flux carried by the open field precipitation, the canopy played a role of net leakage (increase) for most cations (except Na⁺, Ca²⁺, Zn²⁺), while the humus layer played a role of net adsorption (decrease) for most cations (except K⁺, Mg²⁺, Mn²⁺, Fe³⁺), and the soil of main root layer played a role of net leakage (increase) for the base cations (Na⁺, K⁺, Mg²⁺, Ca²⁺) and Mn²⁺, and a role of net adsorption (decrease) for other cations (H⁺, Cu²⁺, Zn²⁺, Fe³⁺).