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火干扰对缙云山土壤团聚体稳定性的影响

Influence of fire interference on the stability of soil aggregates in Jinyun Mountain

  • 摘要: 为探究土壤团聚体稳定性在火干扰下的变化特征,以近期发生森林火灾的重庆缙云山典型林种针阔混交林为研究对象,采用Le Bissonnais(LB)法中快速湿润(FW)、慢速湿润(SW)和湿润振荡(WS)3种不同的破碎机制,模拟不同强度降雨条件对土壤团聚体的破坏,分析其在轻度(S)、中度(M)和重度(L)3种火干扰下团聚体破碎机制。结果表明:1)在火干扰下土壤团聚体均表现出FW处理下破坏程度最大,WS次之,SW处理下破坏程度最小;在FW处理下,>0.50 mm水稳性团聚体比例均表现出S<M<L<CK;SW处理下,S、M、L相对于CK表层土壤分别降低了2.94%、1.51%、1.59%;WS处理下,S表层土壤降幅最大,为18.87%。2)火干扰下林地土壤整体上表现出MWDFW<MWDWS<MWDSW的特征,不同火烧程度下土壤团聚体MWD值除在FW处理下的下层土壤表现为MWDS<MWDM<MWDL外,其余均表现出MWDS<MWDL<MWDM的特征。3)火干扰下表层土壤的相对消散指数、相对机械破碎指数和团聚体特征参数均大于下层土壤,表明针阔混交林火烧迹地土壤团聚体稳定性受不同火强度干扰的响应均有所不同,且火干扰下表层土壤的团聚体稳定性均大于下层土壤,以期为火烧迹地水土流失防治提供参考。

     

    Abstract:
    Background The occurrence of forest fires leads to increased soil erosion, and the effect of fire disturbance on the stability of soil aggregates is not yet clear. The Jinyun Mountains in Chongqing suffered a fire in August 2022, in which coniferous and broad-leaved mixed forests are widely distributed and highly flammable, and are the most vulnerable forest type to fire damage, so it is important to study the stability of soil aggregates under this forest.
    Methods Three 20×20 m sample plots were set up in Jinyun Mountain coniferous and broad-leaved mixed forests with mild (S), moderate (M) and severe (L) fire disturbance and non-fire disturbed areas (CK). Soil samples of topsoil (0~10 cm) and subsoil (10~20 cm) were collected by S-type sampling method at the sample site. Used three different fragmentation mechanisms of fast wetting (FW), slow wetting (SW) and wet stirring (WS) in Le Bissonnais (LB) method to simulate the damage of soil aggregates. The stability of soil aggregates is evaluated by measuring the average mass diameter (MWD) of soil aggregates and the relative dispersion index (RSI), relative fragmentation index (RMI) and characteristic parameter (Ka) calculated using the MWD values. The average mass diameter values under different fire interference intensities are respectively expressed by MWDS, MWDM and MWDL, and the average mass diameter values under different treatment methods are respectively expressed by MWDFW, MWDSW and MWDWS.
    Results 1) Under fire disturbance, soil aggregates in coniferous and broad-leaved mixed forests were damaged most under FW treatment, followed by WS, and the damage was least under SW treatment. Under FW treatment, the proportion of water stable aggregates >0.50 mm in coniferous and broad-leaved mixed forests showed S<M<L<CK. Compared with CK topsoil, S, M and L decreased by 2.94%, 1.51% and 1.59% respectively under SW treatment. Under WS treatment, S surface soil decreased the most by 18.87%. 2) Under the fire disturbance, the soil of the forest land showed the characteristics of MWDFW < MWDWS < MWDSW as a whole. MWD values of soil agglomerates under different degrees of fire exhibit MWDS < MWDM < MWDL except for the lower soil under FW treatment, which exhibits MWDS < MWDL < MWDM. MWD values were significantly higher (P < 0.05) in all soil layers under light fire disturbance and in the surface layer under moderate fire disturbance under the SW treatment than under the other treatments. 3) The RSI value, RMI value and Ka value of the topsoil of the forest under fire disturbance were higher than those of the subsoil.
    Conclusions The stability of soil aggregates in coniferous and broad-leaved mixed forests fire sites varied in response to different fire intensity disturbances, with light fire disturbances reducing the stability of soil aggregates and moderate and heavy fires increasing the stability of soil surface aggregates. The stability of soil aggregates is lowest under heavy or stormy rainfall, followed by mechanical disturbance and highest under light rainfall, and the stability of soil aggregates is higher in all the surface layers than in the lower layers.

     

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