模拟火干扰对森林土壤微生物活性及氮矿化的影响

Simulating the effects of fire disturbance on microbial activity and nitrogen mineralization in forest soil

火干扰产生热能从而诱导土壤有机质的化学氧化,改变碳和氮转换,对土壤的结构与功能产生严重影响,影响程度取决于火强度、火干扰持续时间和热渗透。在湖南省株洲市高枧林场选取马尾松次生林火烧迹地,按两种土壤、3个温度和3种土壤水势进行试验设计与方差分析,探讨火干扰对土壤微生物及氮矿化的影响。结果表明:无机氮的浓度与火强度和初始土壤有机质含量呈正相关关系;火干扰后短期内土壤碳和氮浓度较高,微生物生物量碳和潜在可矿化氮较低,温度和土壤水势对基础呼吸速率没有显著影响;当土壤温度达160℃时,未受火干扰土壤中潜在可矿化氮浓度迅速不稳定增加,温度达350℃时破坏90%的非微生物组织;土壤加热后水势对氮矿化过程有显著影响,水势越高,潜在可矿化氮损失越大,火干扰土壤的含水量与硝态氮之间呈正相关关系;培养14d期间,土壤火灾历史、热处理和土壤水势对微生物活性、碳和氮矿化有显著影响,-1.5 MPa水势下加热到380℃后两种土壤的微生物生物量碳含量最高,土壤水势和可溶性糖呈负相关关系;水势和火干扰之间的交互作用显著影响微生物活性和氮转换,低水势土壤中的微生物生物量碳、可溶性糖和潜在可矿化氮浓度较高。

Heat from fire disturbance induces chemical oxidation of soil organic matter that alters the conversion of carbon （C） and nitrogen （N）, which seriously influences soil structure and functions. However, the extent of oxidation depends on the fire intensity and duration, and heat penetration. In the present study, a burned area of Pinus massoniana secondary forest located in the Gaojian State Forest Farm, Zhuzhou, Hunan Province, was selected to conduct an experiment of the effects of fire disturbance on microbial activity and N mineralization of forest soil. The experiment was conducted in a completely randomized design based on two kinds of soil, three different temperatures, and three soil water potentials, with each treatment replicated three times. A variance analysis was performed on the data. The results showed the concentration of inorganic N and initial soil organic matter content were positively correlated with fire intensity. Shortly after fire disturbance, soil C and N concentration were high, but microbial biomass C and potentially mineralized nitrogen （PMN） were low, and temperature and soil water potential had no significant effect on the basic respiration. PMN loss was observed in the unheated control soils of fire disturbance compared with soils not exposed to fire. When soil temperature reached 160℃, it resulted in only a modest increase in PMN concentrations in the soil not previously exposed to fire. If soil temperature exceeded 160℃, the PMN content fluctuated, and then increased rapidly. A soil temperature of 350℃ resulted in the destruction of 90% non-microbial tissues. The soil water potential after heating had a significant effect on N mineralization：the higher the soil water potential, the more the PMN loss. There was a positive correlation between the water content of fire disturbed soil and nitrate N. During the 14 day incubation, microbial activity and C and N mineralization were significantly influenced by soil fire history, initial heat treatment, and soil water potential. The release of soil available C and N from fire disturbance supported the recovery of microbial activity in low water potentials. When soil was heated to 380℃ at -1.5 MPa water potential, soil microbial biomass C was the highest in both soils. A negative correlation between soil water potential and soluble sugar was observed for both soils. The concentration of soluble anthrone reactive carbon （ARC） dropped significantly（P〈0.05） in both soils over time, resulting from the microbial consumption of sugars released from the fire disturbance. The interaction between water potential and fire disturbance significantly affected the microbial activity and N conversion, and in low water potential soil, microbial biomass C, soluble sugar, and PMN were high. Newly formed labile N by fire disturbance was protected in soil with low water potential. Labile N remained lower in moist than in dry soils regardless of soil fire history.