林龄对刺槐人工林土壤团聚体、有机碳和细菌群落的影响

Impacts of stand ages on soil aggregate,organic carbon,and bacterial communities in Robinia pseudoacacia plantation

探究刺槐人工林土壤团聚体、有机碳及细菌群落的变化特征,可为提升土壤质量与功能提供理论依据。以黄土高原沟壑区不同林龄刺槐人工林(8年生、18年生和30年生)和刚撂荒的农耕地(CK)为研究对象,利用最适湿度筛分法获得不同粒径团聚体,测定其有机碳含量和细菌群落结构特征。结果表明:(1)各林龄土壤团聚体均以>0.25 mm粒径为主,含量为92.74%—95.78%。土壤团聚体稳定性随着林龄的增加显著提高,以30年生林地最高,团聚体平均重量直径(MWD)、几何平均直径(GMD)分别较CK显著增加48.19%和91.38%(P<0.05)。(2)各林龄均以<0.25 mm粒径有机碳含量最高。土壤有机碳含量和>2 mm粒径团聚体有机碳含量均随着林龄的增长而显著增加。(3)团聚体细菌群落主要由变形菌门(Proteobacteria)、放线菌门(Actinobacteria)和酸杆菌门(Acidobacteria)组成。随着林龄的增加,各粒径团聚体中放线菌门相对丰度先降低后增加,18年生林地最低。酸杆菌门变化趋势与放线菌门相反。变形菌门无明显变化。土壤有机碳、pH、全氮和全磷是影响团聚体细菌群落的主要因素。(4)>2 mm和2—0.25 mm粒径团聚体中,己科河菌门(Rokubacteria)对团聚体稳定性影响最大,既对团聚体稳定性产生直接正效应,又通过增加有机碳的含量间接提高团聚体稳定性。在<0.25 mm粒径团聚体中,有机碳含量对其稳定性的影响最大,有机碳含量越高,团聚体稳定性越强。综上,营造刺槐人工林有利于提高土壤团聚体稳定性,促进土壤有机碳的积累,可作为该区域生态恢复的有效措施。在生长发育过程中,人工林可通过改变土壤团聚体细菌群落和有机碳含量从而影响团聚体的稳定性。

Exploring the change characteristics of soil aggregate,organic carbon,and bacterial communities in Robinia pseudoacacia plantation could provide a theoretical basis for soil quality and function improvement.Robinia pseudoacacia plantations with different ages(eight,eighteen,and thirty years old)and abandoned farmland(CK)in gully region of the Loess Plateau were selected as the study sites.Soil aggregates with different particle sizes were obtained through the optimal moisture sieving method and then detected aggregate associated organic carbon contents and bacterial communities.The results showed that:(1)regardless of the Robinia pseudoacacia plantation age,the soil aggregates were primarily macroaggregates(>0.25 mm).The proportions of macroaggregates were 92.74%—95.78%in the Robinia pseudoacacia plantations with different ages.The stability of the soil aggregates increased with plantation ages and the maximum was observed in the 30-year Robinia pseudoacacia plantations.Compared to CK,the mean weight diameter(MWD)and geometric mean diameter(GMD)in the 30-year Robinia pseudoacacia plantations significantly increased by 48.19%and 91.38%,respectively(P<0.05).(2)In the plantations of different ages,soil organic carbon contents were concentrated in the<0.25 mm fractions.Both of the organic carbon content in soil and>2 mm fractions significantly increased with plantation age.(3)The bacterial communities in different particle size aggregates were mainly composed of Proteobacteria,Actinobacteria,and Acidobacteria.During Robinia pseudoacacia growth,the relative abundances of Actinobacteria firstly elevated and afterwards reduced and the minimum was observed in the 18-year Robinia pseudoacacia plantations.The change trends of Acidobacteria were contrary to Actinobacteria.There was no obvious change of Proteobacteria.Soil organic carbon,pH,total nitrogen and phosphorus were the main factors affecting bacterial communities of aggregates.(4)In the>2 mm and 2—0.25 mm fractions,the relative abundance of Rokubacteria had the greatest impact on aggregate stability,which exerted both direct and indirect effects on aggregate stability by increasing organic carbon contents.In the<0.25 mm fractions,the organic carbon contents had the greatest impact on aggregate stability.The higher the organic carbon content,the stronger the stability of the aggregate.In conclusion,Robinia pseudoacacia plantation not only improves the stabilization of soil aggregates,but also promotes the accumulation of organic carbon,which may be used as an effective measure to restore ecology in this region.During the growing process,the plantation impacts soil aggregate stability by altering the aggregate associated bacterial community and organic carbon contents.