氮添加和凋落物增减对华西雨屏区常绿阔叶林土壤团聚体及其碳氮的影响

Effects of Nitrogen Addition and Litter Increase or Decrease on Soil Aggregates and Their C and N in Evergreen Broad-leaved Forest in Rain Screen Area of West China

大气氮沉降可通过改变土壤氮素可利用性(直接影响)和改变凋落物输入量(间接影响)对森林土壤碳氮动态产生影响。土壤团聚体是森林表层土壤最具代表性的基本结构单元,对于稳定贮存有机碳氮具有重要意义。通过氮添加和凋落物增减试验设计,探索氮添加和凋落物增减对土壤团聚体及其碳氮组分的影响。结果表明:(1)凋落物增加(+L)和减少(-L)都使A层土壤(0-10 cm)以及各粒径团聚体的TOC(有机碳)、TN(全氮)含量显著提高,使pH显著降低。氮添加使B层土壤(10-30 cm)pH显著降低,表现为高氮(HN)<低氮(LN)<对照(CK),其中HN还使A层土壤pH显著降低,使B层土壤以及各粒径团聚体的TOC含量显著提高。氮添加和凋落物增减并未显著影响土壤团聚体的稳定性。(2)A、B层土壤均以水稳性大团聚体(>0.25 mm)为优势粒径,粉黏粒组分(<0.053 mm)占比最低。TOC和TN的分布规律在A、B层土壤中相同,>2 mm团聚体的TOC和TN含量最高,0.25~2 mm团聚体的TOC和TN含量最低,A层高于B层,TOC和TN含量随着土壤团聚体粒径的减小呈“V”形分布。(3)土壤团聚体的稳定性与TOC、TN、AN、AP含量呈显著正相关,与pH显著负相关。研究结果可为森林可持续经营提供参考。

Atmospheric nitrogen deposition can affect soil carbon and nitrogen dynamics by changing soil nitrogen availability(direct effect)and litter input(indirect effect).Soil aggregate is the most representative basic structural unit of forest topsoil,which is of great significance for the stable storage of organic carbon and nitrogen.The results showed that:(1)The contents of TOC(total organic carbon)and TN(total nitrogen)in layer A soil and aggregates with different particle sizes were significantly increased,and soil pH was significantly decreased by increasing(+L)and decreasing(-L)litter.Nitrogen addition significantly reduced the soil pH in layer B,which showed high nitrogen(HN)<low nitrogen(LN)<control(CK),and HN also significantly reduced the soil pH in layer A,and significantly increased the TOC content in layer B and aggregates.The addition of nitrogen and litter increase or decrease did not significantly affect the stability of soil aggregates.(2)Water stable macro aggregates(>0.25 mm)was the dominant particle size in soil A and B,and the proportion of silt and clay(<0.053 mm)was the lowest.The distribution of TOC and TN was the same in layer A and B.the contents of TOC and TN in>2 mm aggregates were the highest,while those in 0.25~2 mm aggregates were the lowest.The contents of TOC and TN in layer A were higher than those in layer B.the contents of TOC and TN showed a V-shaped distribution with the decrease of soil aggregate size.(3)The stability of soil aggregates was positively correlated with the contents of TOC,TN,AN and AP,and negatively correlated with pH.The research results can provide reference for sustainable forest management.