| Acid deposition has been a serious environmental issue in southern China. Subtropical forest ecosystemsDinghushan Nature Reserve was selected as a research object in this study, and long-term simulated acid rain (SAR) controlled plots were established. The elements’dynamics of three different forest soil types in different successional stages were analyzed based on a three-year studying, including soil acidity and base ions (K+、Na+、Ca2+、Mg2+), especially exchangeable Ca2+cation dynamic changes and their responses to acid deposition were discussed. The main conclusions are as followings:(1) It indicated that the pH value of Pinus massoniana forest was significantly higher than that of the other two forest types, the forest soil pH value increased with the soil acidity, which was consistent with previous studies. The soil pH values varied with seasons after three years’SAR, higher in dry season, lower in rainy season, and has showed no significantly reducing tendency during the3experiment years. The soil pH values of three different forest ecosystems decreased with the acidity of SAR, and the soil pH value in June,2012, has reduced1.2%,3.2%,2.9%, respectly compared with that in December,2009. They showed no obviously variation for Pinus massoniana forest and mixed forests (except for June2011), compared with the monsoon forest ecosystem which had reached statistical significance level (P<0.05) after18months’cummulative SAR treatment.(2) The three forest soil acidity (H+, Al3+) was not significantly exchanged during the three-years’SAR treatment, but the background exchangeable acid content is gennerally high in the studying area, especially for mixed forest, up to151.33±7.64mmol·kg-1. The input of H+has led to the activity of soil Al3+, which has reached to40.32±1.28mmol·kg-1,136.48±4.76mmol·kg-1, and102.91±3.28mmol·kg-1, individually.(3) Response of soil exchangeable base cations to SAR differed greatly for different forest types, acid treatment duration and pH levels. The leaching release order is as followings:K+>Na+>Ca2+> Mg2+. There existed significantly negative relationship between soil pH value and soil exchangeable cations except for K+and Na+in pine coniferous forest soil. The soil element contents of three different forest types had the similar order C22=> Mg2+> K+, Na+,and the surface soil layers had the highest element contents. There are very low content of base cations, especially that the average concentration of K+and Mg2+were0.64±0.09mmol·kg-1and0.81±0.08mmol·kg-1mmol·kg-1respectively. Three years’SAR increased soil acidification, this might cause soil nutrient loss (K+, Na+,Ca2+,Mg2+) of Pinus massoniana forest, andthus lead to possible nutrition lack of vegetation.(4) In the condition of hot and rainy weather in south China, the leaching of base cations is normal, especially calcium deficiency in lateritic red soil, exchangeable Ca2+cations is the instruction cations in south China. The results of this study indicated that:The exchangeable Ca2+content response to acid deposition of Dinghushan natural reserve were different due to forest successional stage, soil depth, acid deposition pH value and treatment time; the average content of exchangeable Ca2+of3forest types are as followings:monsoon forest (2.44mmol.kg-1)> mixed forest (2.10mmol.kg-1)> Pinus massoniana forest (1.87mmol.kg-1). For the whole soil profile, the upper layers were strongly response to soil acid deposition compared with the lower layers, and soil exchangeable Ca2+content was decreased with the soil depth; meanwhile, the three forest soil exchangeable Ca2+content decreased with pH value of the SAR treatment. Leaching of exchangeable Ca2+of3forest types under3year cumulative acid treatment are as followings:Pinus massoniana forest (0.67mmol.kg-1)> mixed forest (0.37mmol.kg-1)> monsoon forest (0.18mmol.kg-1). |
PDF Full Text Request