三峡库区消落带不同淹水期土壤可溶性碳氮的研究

以位于涪陵区珍溪镇王家沟的三峡库区消落带不同淹水期土壤为研究对象,设置180 m高程为永不淹水对照点,175m(短期淹水,90d),165m(中期淹水,175d)和155m(长期淹水,260d)高程消落区内不同淹水期取样点,研究消落带不同淹水期土壤可溶性有机碳(DOC)和可溶性有机氮(DON)的变化特征.结果表明,对照点土壤有机碳(SOC)及全氮(TN)均无明显的季节变化,而短期淹水则表现为春夏季显著高于秋冬季(p0.05);对照点和短期淹水的DOC及DON季节变化明显,DOC表现为春夏季显著高于秋冬季(p0.05),而DON则表现为冬夏季高于春秋季(p0.05).在相同时间段内(2011年5月22日至2011年9月3日),与对照点相比,中短期淹水的SOC质量分数显著增加(p0.05),而长期淹水处的SOC,TN,DOC及DON均显著降低(p0.05),表明消落带高程越低,淹水时间越长,越容易造成土壤碳氮及可溶性碳氮的损失.消落带3个淹水期的DOC分配比及SOC/TN与对照点相比差异不明显,中长期淹水的DON分配比显著低于对照点(p0.05),而DOC/DON则显著高于对照点(p0.05),表明淹水对土壤有机碳氮矿化作用和土壤有机碳的周转速率不明显,但中长期淹水抑制土壤氮周转速率和可溶性氮的矿化作用.相关分析表明,土壤可溶性碳氮主要受SOC、TN、土壤湿度、地下5cm温度以及pH的影响和调控.

Soil Dissolved Organic Carbon and Nitrogen in the Water-Level-Fluctuating Zone with Different Flooding Durations in the Three Gorges Reservoir Region

Sampling points were set in a typical drawdown area located in Wangjiagou of Fuling in the Three Gorges Reservoir region of Chongqing at an elevation of 180 m (control, never flooded), 175 m (short-term flooding, 90 days), 165 m (medium-term flooding, 175 days) or 155 m (long-term flooding, 260 days) to study the effect of different flooding durations on soil dissolved organic carbon (DOC) and soil dissolved organic nitrogen (DON). Soil organic carbon (SOC) and total nitrogen (TN) showed no obvious seasonal variations at the sampling point of 180 m (control). However, they were significantly higher in spring and summer than in autumn and winter at the sampling point of 175 m (short-term flooding, p < 0.05). As for DOC and DON, there were remarkable seasonal variations in the control and the short-term flooding treatment, the DOC in spring and summer being significantly higher than in autumn and winter (p < 0.05), while DON in winter and summer was higher than in spring and autumn (p < 0.05). In the same observing period (May 22nd 2010 to Sept. 3rd 2011), compared with that of the control, SOC significantly increased with medium-and short-term flooding (p < 0.05), but SOC, TN, DOC and DON significantly decreased with long-term flooding (p < 0.05), indicating that lower elevation and longer flooding time were likely to result in the loss of soil dissolved organic carbon and nitrogen in the drawdown area. Compared with the control, there were no obvious differences in DOC/SOC ratio and SOC/TN ratio in the three different flooding durations in the fluctuating zone, but the DON/TN ratios of medium and long-term flooding were significantly lower and the DOC/DON ratios were higher than the control (p < 0.05), which suggested that mineralization of soil organic carbon and nitrogen and turnover rate of SOC were not obvious in the drawdown area, meanwhile medium-and long-term flooding diminished turnover rate of nitrogen and mineralization of DON. Correlations analyses showed that the soil dissolved organic carbon and nitrogen were influenced and regulated mainly by TN, soil moisture, pH and soil temperature at 5 cm soil depth.