Effects of acid deposition intensity on active aluminum in Pinus massoniana soil
To investigate the effects of varying acid deposition intensities on active aluminum in the understory soil of Pinus massoniana forest in a long-term natural environment,we selected Simian Mountain,Jinyun Mountain,and Tieshanping in Chongqing as our study areas. This study focused on the soil of P. massoniana forests with the same parent material and analyzed the interactive relationships between soil pH,nutrient elements,exchangeable cations,enzyme activities,and active aluminum under varying acid deposition levels. An increase in acid deposition intensity significantly decreased soil pH,total carbon(TC),total nitrogen(TN),exchangeable aluminum (Ex-Al),monomeric hydroxyl aluminum(Hy-Al),and acid-soluble inorganic aluminum(Ac-Al) content (P<0.05),whereas the exchangeable Mn2+content increased. Active aluminum primarily comprised Ac-Al and aluminum humate (Hu-Al),accounting for approximately 77.1％ to 84.9％ of the total active aluminum. Under acidic deposition,active aluminum soil content was significantly correlated with TC,TN,total sulfur (TS),ammonium nitrogen (NH+4-N),and urease activity (UE,P<0.05),of which NH+4-N was the main factor affecting the total active aluminum amount. Acid deposition dominantly influencedactive aluminum content. Specifically,a significant positive correlation between TC,TN,and TS,and the content of each form of active aluminum(P<0.05) was observed at Simian Mountain. Under the conditions of the Jinyun Mountain,the Mg2+content was significantly positively correlated with the Ac-Al content(P<0.05),and significantly negatively correlated with Ex-Al,Hy-Al,and Hu-Al contents (P<0.05). At Tieshanping,the nitrate nitrogen(NO-3-N) content was significantly negatively correlated with the Ex-Al content(P<0.01) and significantly positively correlated with the Hy-Al,Ac-Al,and Hu-Al contents (P<0. 01) . As the intensity of acid deposition increased,a loss of carbon and nitrogen,leaching of active aluminum,and an increase in exchangeable Mn2+content were observed in P. massoniana soil. The redundancy analysis showed that with increasing intensity of acid deposition,the main factors affecting the active aluminum content of soil in various forms changed from TC,TN,TS content to exchangeable Mg2+content and then NO-3-N content.
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