三峡库区典型消落带土壤微生物生物量碳、氮的变化特征及其影响因素探讨

本文以三峡库区王家沟一典型消落带为研究对象,选择180、175、165和155 m这4个高程以探讨水位变化对土壤微生物生物量碳(SMBC)和微生物生物量氮(SMBN)的影响.其中,175、165和155m高程坐落在消落带内,分别表现为短、中和长期淹水,180 m高程作为对照,为永不淹水的陆地.土壤样品的采集深度为0~20 cm,每周采集一次.结果表明,180 m高程处土壤有机碳(SOC)和全氮(TN)均无明显的季节变化,而175 m高程处SOC和TN季节变化明显,表现为春夏季高于秋冬季;各高程上的SMBC和SMBN及其分配比例呈现出秋高夏低的季节变化形态,表明消落带夏季高温低湿的土壤环境限制了微生物活性及土壤有机碳氮的周转速率.数据分析表明,与180 m高程相比,消落带上的175 m和165 m高程SOC、TN、SMBC及微生物商、SMBN及其分配比例均得到不同程度的升高,而155 m高程除了SMBN及其分配比例与对照无显著差异外,其他指标均显著低于对照,表明与未淹水对照点相比较,中短期淹水有利于提高消落带土壤碳氮含量及周转速率和微生物生物量,而长期受到江水淹没胁迫的土壤则会抑制土壤碳氮以及SMBC含量,并降低SOC的周转速率.相关分析表明,SMBC和SMBN均与地下5 cm处温度和p H呈极显著负相关,说明地下5cm处的温度以及p H对土壤微生物生物量有强烈的影响.

Characteristics and Influencing Factors of Soil Microbial Biomass Carbon and Nitrogen in Drawdown Area in the Three Gorges Reservoir

Taking a typical drawdown area located in Wangjiagou of the Three Gorges Reservoir as the study object, four elevations 180,175,165 and 155 m were selected to explore the effect of water level change on soil microbial biomass carbon (SMBC) and microbial biomass nitrogen (SMBN). Wherein, 175,165 and 155 m elevations located in the fluctuating zone, manifested as short, medium and long-term flooding, respectively; 180 m was used as the control, located on the land and never flooded. Sampling depth in soil samples was 0-20 cm, collected once a week. The results indicated that, soil organic carbon (SOC) and total nitrogen (TN) contents at 180 m had no obvious seasonal changes, while they showed remarkable seasonal trends at 175m, which in spring and summer were significantly higher than in autumn and winter; SMBC and SMBN contents and their allocation ratio at four elevations were similar and had significant seasonal fluctuation, which were highest in autumn and lowest in summer at each elevation, indicating that in drawdown area the microbial activity and turnover rate of soil organic carbon and nitrogen were limited by the high-temperature and low-humidity soil environment in summer. Data analysis showed that, compared with the 180 m elevation, contents of SOC, TN, SMBC and microbial quotient, SMBN and its allocation proportion showed varying degrees of increase, while contents of these indexes were significantly lower than control except SMBN and its allocation proportion, meaning that compared with 180 m short and medium-term flooding was conducive to improve soil carbon, nitrogen and their turnover rate and microbial biomass, however, contents of soil carbon and nitrogen and microbial biomass carbon were significantly restricted at 155 m as soil was subjected to flooding stress, meanwhile the turnover rate of SOC was reduced. Correlation analysis implied that SMBC and SMBN had very significant negative correlation with temperature at 5 cm soil depth and pH, meaning that the two environmental factors had a strong effect on soil microbial biomass.