六盘山典型森林伴随降水的总有机碳(TOC)通量变化特征

在六盘山香水河小流域,选择6种典型森林样地,测定了2011年生长季的大气降水、穿透水、干流、枯落物渗漏水和主根系层(0—30 cm深)土壤渗漏水的总有机碳(TOC)浓度及其相应的通量变化。结果表明,在降水转化为由穿透雨和干流组成的林下降水中,所有样地的TOC浓度都不同程度地增大;虽然林冠截持使林下降水减小,但因雨水淋洗和与林冠发生碳交换,各样地林下降水携带的生长季TOC通量(kg/hm2)(华北落叶松人工林132.28、华山松次生林106.56、油松人工林94.10、灌木林79.49、桦木林66.52、辽东栎次生林63.01)都比林外降水(53.17)不同程度地明显增大,整体看来,林冠的TOC淋出作用在针叶林很大,在阔叶林较弱。在6种森林样地的枯落物层渗漏水中,其TOC浓度彼此相差不大,平均为24.51 mg/L,高于林冠穿透水的TOC浓度;受枯落物截持部分降水及与枯落物TOC交换的影响,4个样地枯落物渗漏水的TOC通量(kg/hm2)(桦木次生林84.35、野李子灌丛129.35、辽东栎次生林79.21、油松人工林114.93)都比其林下降水TOC通量增加了,但华北落叶松人工林和华山松次生林的TOC通量分别降至90.76和104.90 kg/hm2。在测定的华北落叶松人工林和华山松次生林的主根系层(0—30 cm)土壤渗漏水中,TOC浓度均低于枯落物渗漏水;由于水量减小和与土壤发生碳交换,土壤渗漏水的TOC通量均显著低于枯落物渗漏水,两个林分样地分别降至43.04和66.33 kg/hm2。整体来看,林外降水携带的TOC输入通量在林地TOC输入中占有重要地位,林冠的TOC淋洗使其程度不同地增加TOC通量,枯落物层具有增加或减少TOC通量的作用,但主根系层土壤会显著减少TOC输出通量,所以是固定TOC的重要场所。

The variation of total organic carbon (TOC) flux with rain water in regional forests of Liupan Mountains, China

Both flux and concentration of total organic carbon(TOC)from rain water were documented and analyzed from six regional forests growing in the small watershed of Xiangshuihe inside Liupan Mounatins in NW China during the 2011 growing season. The results indicated that TOC concentration of all six forests was increased in term of rain water under canopy. Although the rain water volume under canopy was decreased due to the canopy interception, the TOC flux carried by the rain water under canopy was increased for all six forests as compared them with that carrying by the open field rainfall (53.17 kg/hm²) because of carbon exchange or wash out from canopy. The corresponding TOC flux (kg/hm²) of rain water under canopy was 132.28 for Larix principis-rupprechtii plantation, 106.56 for the secondary forest of Pinus armandii, 94.10 for the plantation of Pinus tabulaeformis, 79.49 for the shrub of Prunus salicina, 66.52 for the secondary forest of Betula platyphylla, and 63.01 for the secondary forest of Quercus liaotungesis. The canopy leaching (or wash out) effect of TOC was high for the coniferous forests, but weak for the broad-leaved forests. The difference of TOC concentrations in the leakage under humus layer was low among the six forest types, with an average of 24.51 mg/L, which was still higher than the TOC concentration in throughfall. As an integrated result of the humus interception loss and the TOC exchange with humus layer, the TOC flux carried by the humus leakage was increased than that carried by throughfall for four forests and they were 84.35 (kg/hm²) for the stand of Betula platyphylla, 129.35 for the bush of Prunus salicina, 79.21 for the stand of Quercus liaotungesis, 114.93 for the stand of Pinus tabulaeformis, but the TOC flux carried by the humus leakage was decreased to 90.76 and 104.90 kg/hm² for the stand of Larix principis-rupprechtii and Pinus armandii respectively. In the leakage under the soil layer of main root zone (0-30 cm), the TOC concentrations were reduced compared with that in humus leakage for the stands of Larix principis-rupprechtii and Pinus armandii. Affected by the water volume decrease and the TOC exchange with mineral soil, the TOC flux carried by the soil leakage under main root zone was significantly reduced, compared with the TOC flux of humus leakage, to 43.04 kg/hm² for the stand of Larix principis-rupprechtii and to 66.33 kg/hm² for the stand of Pinus armandii. In conclusion, the TOC input flux through open field rainfall played an important role in the TOC flux input to forest soil. The canopy of all six forest types could increase the TOC flux due the TOC leaching from canopy surface. The TOC flux in humus layer leakage were usually increased or decreased. However, the mineral soil at the main root zone greatly reduced the TOC flux output, thus the soil layer should be the most important pool for fixing the TOC.