洞庭湖西岸区防护林土壤和植物营养元素含量特征

Soil and plant nutrient status of protective forests in western bank of Dongting Lake

对洞庭湖西岸区4种防护林地土壤与植物中营养元素含量进行研究。结果表明:环湖低丘平原封山育林和补植封山育林的水土保持林、平原湖区防护林pH值为4.54—5.27,呈酸性反应;防浪护堤林pH值为8.18,呈碱性反应。有机质和全N含量以环湖低丘平原封山育林的水土保持林地高于其余3种防护林,N素和P素有效率均低,速效N仅占全N含量的1.46%—3.35%,速效P仅占全P的0.5%—1.6%,全K含量亦不高,除环湖低丘平原封山育林的水土保持林地含K量适量外,其余3种防护林地均为严重缺K型土壤,防浪护堤林地全Ca及Mg含量高于其余3种防护林地。各防护林群落中植物体内不同营养元素含量差异很大,同一元素在不同植物体内含量的变化范围亦很大,高低值达几倍到十几倍,甚至几十倍。植物对土壤中营养元素的积累能力分为最强、中等和最弱3个层次。研究结果可为防护林体系建设和土壤肥力评价提供科学依据。

Apart from providing wood materials and other forest side-products,forests provide a great deal of protective services,for example in soil and water conservation,in carbon sequestration,and in reducing the risks of impacts of floods,erosion and drought. The effect of forest structure on nutrient status and cycling is fundamental to our understanding of ecosystem function. To determine the influence of forest structure on concentration,distribution and accumulation of mineral elements,nutrient status in soil and plant of four protective forest types （ Preserved forests for soil and water conservation on hilly areas along the lake （ PF） ; Replanting preserved forests for soil and water conservation on hilly areas along the lake （ RPF） ; Protective forest bands on plain area （ PFB） ; and Wave-break Forest bands along the shores of the lake （ WFB） ） were investigated in western bank of Dongting Lake. Our specific objectives were to （ 1） quantify variation of pH value,bulk density,texture,organic matter content,and macronutrients （ N,P,K,Ca,and Mg） and available-nutrient elements （ available-N,available-P,and available-K） concentrations in soils in the four forest types; （ 2） determine distribution of macronutrient elements in different plant organs in the studied forest stands; （ 3） calculate biological absorption intensity of nutrients by plants from soil systems; and （ 4） examine effects of forest structure on nutrient status in these four forest communities. Results showed that average soil bulk density was higher in WFB （ 1. 52 g/cm3） than other forest types （ ranged 1. 21-1. 52g/cm3 ）. Soil pH value was acidic （ 4. 54 -5. 27） in PF,RPF and PFB,but alkaline （ 8. 18） in WFB. Soil organic matter and total N contents were significantly higher in PF due to more litter accumulated on the forest floor when compared with those in other three protective forest types. The concentrations of available N and P in soil were very low and accounted for 1. 46% -3. 35% of total N and 0. 5% -1. 6% of total P in PF,respectively. It was found that total K content was adequate in PF,but was considerable deficient in other three forest types. The average concentrations of total Ca and Mg in soils were statistically higher in WFB （ 16. 89 and 5. 03 g/kg,respectively） than in other three stand types. The contents of nutrients in plants changed greatly in different forest types and the concentration of same nutrient element in different plant organs varied widely within the same forest type as well. Based on the biological absorption coefficient （ A） （ calculated using the equation：A = （ Cp /Cn） ×100,where Cp and Cp are the concentrations of the same nutrient element in plant and soil,respectively） ,the total of 66 vegetation species （ including tree,shrub,and herbaceous species） in the study sites was classified into three groups：strong absorption species （ A 1000） ,medium absorption species （ A 100 -1000） and low absorption species （ A 100）. Our results demonstrated that nutrient status and distribution in forest stands were strongly influenced by forest community structure. The results provided scientific references for studying nutrient biogeochemistry cycling,constructing and managing the protective forest systems,and assessing and maintaining soil fertility in forest ecosystems.