岷江上游不同退耕还林类型对土壤团聚体及有机碳动态的影响

Effects of Types of Farmland Returning to Forest on the Dynamics of Soil Aggregate and Organic Carbon in Upper Reaches of Minjiang River

【目的】在退耕还林政策实施20年之际,定量研究岷江上游退耕还林后土壤团聚体和有机碳动态变化,为干旱河谷区生态治理与生态农业发展提供数据支撑。【方法】以原生林为对照,退耕地生态林和果园(樱桃、脆李、苹果)为研究对象,分析各用地类型土壤水稳性团聚体粒径组成、稳定性和土壤有机碳的分布,应用混合效应确定林地类型、土层深度、海拔梯度、砾石含量等因素对土壤团聚体稳定性和有机碳动态的贡献度。【结果】果园土壤大团聚体(>0.25 mm)含量显著低于生态林,二者土壤大团聚体含量显著低于原生林。原生林和生态林土壤团聚体各粒级含量从高到低依次为5~10 mm>2~5 mm>0.25~2 mm>0.053~0.25 mm>0~0.053 mm,果园土壤团聚体各粒级含量从高到低依次为0.25~2 mm>2~5 mm>5~10 mm>0.053~0.25 mm>0~0.053 mm;在5~15 cm土层,樱桃园5~10、2~5 mm粒级团聚体含量显著高于脆李园和苹果园。土壤团聚体稳定性指标(MWD、GMD)均表现为原生林>生态林>果园;不同类型果园土壤团聚体稳定性表现为樱桃园>脆李园和苹果园,且脆李园、苹果园之间差异不显著。在0~5 cm土层,土壤有机碳含量表现为原生林>生态林>樱桃园>脆李园和苹果园,其差异随深度增加表现出减小趋势。对于0~30 cm深度的土壤有机碳储量,生态林最高(63.1 t/hm^(2)),樱桃园(56.1 t/hm^(2))、苹果园(52.5 t/hm^(2))、脆李园(51.3 t/hm^(2))次之,原生林最低(47.3 t/hm^(2));对于30~60 cm深度的土壤有机碳储量,樱桃园最高(40.3 t/hm^(2)),脆李园(32.9 t/hm^(2))和苹果园(29.3 t/hm^(2))次之,生态林最低(24.7 t/hm^(2))。原生林土壤有机碳的总体分布特征为高含量低储量,生态林为高含量高储量,果园为低含量高储量。土壤团聚体稳定性及有机碳含量的主控因素为林地类型,土壤有机碳储量的主控因素为土层深度。【结论】“谷上林地谷下园、缓坡梯田果牛羊”的立体式山地农业是干旱河谷农业发展的理想模式,提升表层土壤有机碳含量和稳定性应作为今后果园管理的重点。

【Objective】On the occasion of the implementation of the policy of returning farmland to forest for 20 years,the dynamic changes of soil aggregates and soil organic carbon(SOC)after returning farmland to forest in upper reaches of the Minjiang River were quantitatively studied,which provided scientific data support for ecological governance and ecological agriculture development in arid valleys.【Method】Taking the native forest as the control and the ecological forests(eco-forests)and orchards(cherry,crisp plum,apple)as research objects,the particle size composition,stability and SOC distribution of soil water-stable aggregates of various land types were analyzed,and the mixed effect was applied to determine the contribution of forest land type,soil depth,altitude gradient,gravel content(GC)and other factors to soil aggregate stability and organic carbon dynamics.【Result】The content of macro-aggregates(>0.25 mm)in orchards was significantly lower than that in eco-forests,and that in both was significantly lower than that in native forests.The contents of soil agglomerates of various sizes in the native and eco-forests showed as:5-10 mm>2-5 mm>0.25-2 mm>0.053-0.25 mm>0-0.053 mm,those in the orchards ranked as:0.25-2 mm>2-5 mm>5-10 mm>0.053-0.25 mm>0-0.053 mm.In the 5-15 cm soil layer,the contents of 5-10 mm and 2-5 mm agglomerates in cherry orchards were significantly greater than those in crisp plum orchards and apple orchards.Soil aggregate stability indexes(MWD and GMD)showed as:native forests>eco-forests>cherry orchards>crisp plum orchards and apple orchards,and there were no significant differences between crisp plum orchards and apple orchards.The SOC content(SOCC)in the 0-5 cm soil layer showed as native forests>eco-forests>cherry orchards>crisp plum orchards and apple orchards,and the difference showed a decreasing trend with the increase of soil depth.SOC(SOCS)stocks at a depth of 0-30 cm were highest in eco-forests(63.1 t/hm^(2)),followed by cherry orchards(56.1 t/hm^(2)),apple orchards(52.5 t/hm^(2)),and crisp plum orchards(51.3 t/hm^(2)),while the SOCS in native forests were the lowest(47.3 t/hm^(2)).At a depth of 30-60 cm,cherry orchards had the highest SOCS(40.3 t/hm^(2)),followed by crisp plum orchards(32.9 t/hm^(2)),and apple orchards(29.3 t/hm^(2)),and eco-forests had the lowest SOCS(24.7 t/hm^(2)).SOC distribution was characterized as‘high content and low stock’in native forests,‘high content and high stock’in eco-forests,and‘low content and high stock’in orchards.The dominant factor of soil aggregates stability and organic carbon content was forest type,and the dominant factor of SOCS was soil depth.【Conclusion】The mountain agriculture of‘eco-forests on the higher valley and orchards on the lower valley,fruit trees and cattle on the gentle slopes and terraced fields’is an ideal model for the agriculture development in arid valleys,and the improvement of SOC accumulation in the topsoil should be the priority for the management of orchards in the future.