固氮树种马占相思对巨尾桉人工林土壤团聚体粒径分布及稳定性的影响

Effects of nitrogen-fixing tree species Acacia mangium on particle size distribution and stability of soil aggregates in Eucalyptus grandis×urophylla plantations

土壤团聚体稳定性是评价土壤结构和土壤肥力的重要指标。为探究固氮树种马占相思对巨尾桉人工林土壤团聚体粒径分布及稳定性的影响,该文以17年生的巨尾桉纯林(PP)与巨尾桉/马占相思(固氮树种)混交林(MP)为研究对象,采用干筛法和湿筛法分别测定0~10 cm和10~20 cm土层团聚体粒径分布及平均重量直径(MWD)、几何平均直径(GMD)、分形维数(Dm)、水稳定性团聚体含量(WSA)、团聚体破坏率(PAD)和团聚体稳定性指数(ASI)等稳定性指标。结果表明:(1)与PP相比,MP的土壤理化性质有不同程度的提升,其中以土壤pH、有机碳(SOC)及全氮(TN)最为显著。(2)MP的土壤团聚体粒径分布优于PP,差异主要体现在>2.00 mm和<0.25 mm粒径中,均以大团聚体(>0.25 mm)为主;相较于PP,MP的土壤团聚体机械稳定性仅在0~10 cm土层显著提高,但其团聚体水稳定性在0~10 cm和10~20 cm土层均显著提高。(3)Mantel分析结果显示团聚体稳定性与TN相关性最强,通过RDA分析进一步说明TN是驱动其团聚体稳定性变异的最关键因子。综上认为,固氮树种马占相思对巨尾桉人工林土壤团聚体稳定性具有明显改善作用,该研究结果为南亚热带桉树人工林水土保持、养分管理及可持续经营等提供了科学的理论依据。

Soil aggregates are the basic unit of soil structure.The stability of soil aggregates is an important indicator for evaluating soil structure and soil fertility.In order to explore the effects of Acacia mangium on particle size distribution and stability of soil aggregates of Eucalyptus grandis&#215;urophylla plantations,we measured the distribution and stability of aggregates indicators such as mean weight diameter(MWD),geometric mean diameter(GMD),mass fractal dimension(Dm),water stable aggregates(WSA),percentage of aggregates destruction(PAD)and aggregates stability index(ASI)in the 0-10 cm and 10-20 cm soil layers by the dry sieving method and the wet sieving method,and a pure plantation of E.grandis&#215;urophylla(PP)and a mixed plantation containing E.grandis&#215;urophylla and Acacia mangium(nitrogen-fixing tree species)(MP)were selected as the research objects.The results were as follows:(1)Compared with PP,the soil physicochemical properties of MP were improved in varying degrees,especially soil pH,organic carbon(SOC)and total nitrogen(TN).(2)The particle size distribution of soil aggregates in MP was better than that of PP,and the differences mainly in the particle sizes of>2.00 mm and<0.25 mm,but both were dominated by large aggregates(>0.25 mm).Compared with PP,the mechanical stability of aggregates in MP only increased significantly at 0-10 cm soil layer,but the water stability of aggregates in MP increased significantly at 0-10 cm and 10-20 cm soil layer.The mechanical stability and water stability of soil aggregates tended to decrease with the deepening of soil layer.(3)Mantel analysis showed that the stability of aggregates was significantly correlated with pH,SOC,TN,TP,BD and SP,and the stability of aggregates had the strongest correlation with TN.RDA analysis indicated that TN was the most critical factor driving the variation of stability aggregates.Our findings suggest that nitrogen-fixing tree species A.mangium can significantly improve proportion of macroaggregates(>0.25 mm)and the stability of soil aggregates in Eucalyptus plantations.This study can provide a theoretical reference for soil and water conservation,soil nutrient management and sustainable management of Eucalyptus plantations in the South Asian tropics.