Responses of soil labile organic carbon and water-stable aggregates to reforestation in southern subtropical China

中国南亚热带土壤易分解有机碳和水稳性团聚体对造林的响应

Aims Reforestation can enhance soil carbon(C)stability and promote soil C accumulation.Experimental results are,however,highly variable,and the efficacy of reforestation in enhancing soil C stability is still in debate.Consequently,it remains unclear how the different soil C pools respond to reforestation in forest ecosystems.Methods The response of different soil C fractions to reforestation was examined in five subtropical forests,including the plantations of Eucalyptus urophylla(EU),Acacia crassicarpa(AC),Castanopsis hystrix(CH)and 10 species mixed(MX),and a naturally recovered shrubland(NS).Soil labile C fractions(readily oxidized organic C by KMnO4:ROC;dissolved organic C:DOC),distribution of aggregate-size classes and aggregate-associated C from different soil layers(0–10,10–20,20–40 and 40–60 cm)were evaluated.Important Findings We found that reforestation and forest type did not affect ROC concentration,yet the highest DOC concentration was detected in NS at four soil layers.Aggregate C concentration was the highest in all aggregate-size classes of CH at 0–10 cm depth.In addition,forest type did not alter the proportion of soil water-stable aggregates at four soil layers.However,soil depths significantly affected the distribution of soil aggregates with>0.25 mm aggregates dominating in the topsoils(0–20 cm),but 0.053–2 mm aggregates being dominant in the deep soils(20–60 cm).These results indicate that reforestation and forest type affected soil DOC(0–60 cm)and aggregate C(0–10 cm).Furthermore,soil DOC and aggregate C were more susceptive to reforestation than ROC.The findings suggest that plantations reduce soil DOC concentration,highlighting that C leaching loss may decrease compared with natural recovery.Moreover,C.hystrix plantation may enhance soil C stability by physical protection in topsoil.This study provides valuable information on tree species selection for reforestation concerning soil C sequestration in southern subtropical China.

造林被认为可以提高土壤碳稳定性并促进土壤碳累积。然而,实验结果差异很大,造林在提高土壤碳稳定性方面的作用仍存在争议。因此,在森林生态系统中不同土壤碳库对造林如何响应目前尚不清楚。基于此,本文对亚热带地区的尾叶桉林(Eucalyptus urophylla)、厚荚相思林(Acacia crassicarpa)、红锥林(Castanopsis hystrix)、10树种混交林和自然恢复草坡等5种不同林型的土壤碳组分进行了研究,评估其不同土层(0–10、10–20、20–40和40–60 cm)中的土壤易分解有机碳(容易被高锰酸钾氧化的有机碳ROC和土壤可溶性有机碳DOC)及土壤团聚体相关的碳对造林的响应。实验结果表明,造林(与自然恢复草坡比较)和林型并没有显著影响土壤ROC浓度,而自然恢复草坡土壤的DOC浓度在4个土层中均最高。0–10 cm土层中各径级的土壤团聚体其碳(C)浓度均是红锥林最高。此外,在任一土层中,林型对不同径级土壤水稳性团聚体比例的影响均不显著。但是土壤深度显著改变土壤团聚体的分布,0–20 cm土层主要为>0.25 mm粒径的团聚体,20–60 cm土层则是0.053–2 mm粒径的团聚体占主导。这些结果显示造林和林型影响土壤DOC和团聚体C,而且它们相比于ROC对造林的响应更为敏感。研究发现,与自然恢复相比,人工林降低了土壤DOC浓度,暗示它可能会减少土壤C的淋溶损失。此外,红锥林能够通过物理保护提高表土层中土壤碳的稳定性。本研究为关注土壤碳汇功能时的中国南亚热带地区造林树种选择提供了有价值的信息。