漓江流域不同林地类型的土壤-凋落物-叶片化学计量特征OA

Ecological stoichiometry is a science that studies the interaction relationships of chemical elements in ecological components.By studying the nutrient element content and ecological indicator ratios in the"soil-litter-leaf"system,this study aims to analyze the correlation between nutrient elements and reveal the nutrient status of ecosystems,as well as the coupling process,balance mechanisms,and their impact on plant community structure and function. The study area is located in the Lijiang River Basin in Guilin,Guangxi.The basin has a subtropical humid monsoon climate and consists of a non-karst area upstream and a karst/non-karst mixture plain landform downstream.Nine representative sample plots were selected along the Lijiang River Basin,categorized into limestone soil(dominated by limestone/dolomite)and acidic red soil(derived from granite),with subgroups of natural forests(e.g.,evergreen broad-leaved)and plantations(e.g.,eucalyptus,bamboo).Soil,litterfall,and leaf samples were collected in autumn,spring,and summer of 2017 and 2018,respectively.The samples were analyzed for Total Organic Carbon(TOC),total nitrogen(N),total phosphorus(P),potassium(K),calcium(Ca),sodium(Na),and magnesium(Mg)as well as soil ammonium(NH4+),nitrate(NO3-)and Available P(AP).The biological absorption coefficient was calculated to reflect the ability of plants absorbing and accumulating chemical elements from the environment. The results showed that soil pH varied between 3.77 and 7.57,with significantly higher pH values in limestone soils compared to acidic red soils.There were no significant differences in soil C and N content between limestone and acidic red soils,but they varied significantly among different altitudes,showing low-altitude soils had lower C and N content compared to high-altitude soils,and plantations had lower soil C and N content compared to natural forests.Soil P content ranged from 0.39 g·kg-1 to 2.50 g·kg-1,with higher P content in acidic red soils compared to limestone soils.The C:N ratio in soils was below 25,indicating nitrogen saturation and the risk for N leaching,especially for the limestone soil.High-altitude soils had higher C:P and N:P ratios compared to low-altitude soils.Litterfall element content and stoichiometric ratios showed smaller differences among different soils and forest types.Litterfall C and N content were slightly higher in natural forests compared to plantations.Litterfall P content ranged from 0.94 g·kg-1 to 2.62 g·kg-1.The average C/N of litterfall for limestone soil and acidic red soil were 20.0 and 17.8,respectively,consistently below the 25 threshold,indicating rapid decomposition.Leaves had the highest C,N,P and Ca content compared to soil and litterfall.The N:P＞16 in leaves(common in both forest types)suggested P limitation,particularly in forests under acidic red soil.Except for K,the biological absorption coefficient of leaves was above 1 and varied among different elements and forest types,with higher absorption coefficients observed in natural forests for K and Mg,lower for Na.The plants under acidic red soil had higher biological absorption coefficient for Ca compared to those under the limestone soil.Soil C,N,P,C:P,and N:P ratios,as well as litterfall K and Ca,played a central role in the element coupling relationship.Plantation and natural forests under limestone soil had similar soil element stoichiometric characteristics,mainly influenced by pH,Ca,and Na.Plantations under acidic red soil were mainly influenced by K and Mg,while natural forests were influenced by C,N,C:P,and N:P ratios.Soil elements had closer coupling relationships with litterfall elements compared to soil and leaf elements.In plantations under acidic red soil,P-related indicators(P,C/P,N/P and AP)and Ca played a key role in element coupling.Significant positive correlations were observed between litterfall K and soil pH,P,Ca,and between litterfall Mg and soil Ca.In natural forests under acidic red soil,litterfall Mg showed stronger coupling relationships with soil factors. This study revealed the soil-litter-leaf element stoichiometric characteristics and coupling relationships in different forest types in the Lijiang River Basin.The study identifies potential N loss and P limitation issues in the basin and suggests that integrating natural forest restoration could enhance ecosystem resilience by improving nutrient retention and reducing erosion risks.It provides scientific guidance for ecological conservation and restoration efforts.