基于Le Bissonnais法揭示桉树人工林土壤团聚体的崩解机制

The Disintegration Mechanism of Soil Aggregates in Eucalyptus Plantations:Based on the Le Bissonnais Method

以广西国有大桂山林场为研究区域,选择连栽第1代(Ⅰ)、第2代(Ⅱ)、第3代(Ⅲ)桉树人工林为研究对象。采集0~20 cm和20~40 cm土层原状土样,通过传统湿筛法和Le Bissonnais(LB)法探究土壤团聚体稳定性的变化规律,其中LB法包括快速湿润(FW)、慢速湿润(SW)和预湿扰动(WS)处理。结果表明,桉树人工林土壤主要以>2mm团聚体为主。在不同湿润处理下,土壤团聚体稳定性指标MWD和GMD值均表现为Ⅲ>Ⅱ>Ⅰ,说明连栽第3代的桉树人工林土壤团聚体稳定性最高。在桉树人工林中,MWD和GMD值随着土层深度的增加而减少,表明表层土壤团聚体稳定性较高于底层。在LB法的3种湿润处理中,桉树人工林土壤团聚体MWD和GMD值均表现为WS>SW>FW,表明FW处理对本研究区域的土壤团聚体破坏最大。该处理是模拟大雨突然来临时的情形,其破坏机制是团聚体内闭蓄空气被快速压缩而产生的气爆作用。因此,适当增加林下植被覆盖度则有利于桉树人工林土壤结构的改善。

In this study,the first generation(Ⅰ),second generation(Ⅱ),and third generation(Ⅲ)Eucalyptus plantations were planted in Daguishan Forest Farm,Guangxi.Undisturbed soil samples of 0~20 cm and 20~40 cm soil layers were collected,and the change rule of soil aggregate stability was investigated by traditional wet sieve method and Le Bissonnais(LB)method,in which the LB method included fast wetting(FW),slow wetting(SW),and wet disturbance(WS)treatment.The results showed that the soil of Eucalyptus plantations was mainly composed of>2 mm aggregates.Under different wetting treatments,the values of soil aggregate stability indexes(MWD and GMD)were III>II>I,indicating that the soil aggregate stability of the third successive generation of Eucalyptus plantations was the highest.In Eucalyptus plantations,the MWD and GMD values decreased with the increase of soil depth,indicating that the stability of soil aggregates in the top layer was higher than that in the bottom layer.In the three kinds of wetting treatments with LB method,the values of MWD and GMD of soil aggregates in Eucalyptus plantations were WS>SW>FW,indicating that FW treatment had the greatest damage to soil aggregates in this study area.The treatment is to simulate the situation of sudden heavy rain,and its failure mechanism is the gas explosion caused by the rapid compression of the enclosed air in the agglomeration.Therefore,an appropriate increase in understory vegetation coverage is beneficial to the improvement of soil structure of Eucalyptus plantations.