华西雨屏区柳杉人工林土壤持水能力及其对土壤有机碳的指示作用

The soil water holding capacity and its indicative effect on soil organic carbon of Cryptomeria japonica plantations in the Rainy Area of West China

土壤持水能力是评估森林涵养水源和影响土壤碳库的重要指标之一,但不同生长阶段的森林土壤持水能力变化特征及其与有机碳的生态关联还不清楚.为探究不同林龄柳杉人工林的土壤持水能力及其对土壤有机碳的指示作用,选取华西雨屏区柳杉(Cryptomeria japonica)幼龄林(6 a)、中龄林(12 a)、近熟林(23 a)、成熟林(27,32 a)和过熟林(46,52 a)为研究对象,测定表层土壤(0-20 cm)的水分-物理性质、易氧化碳、颗粒碳和总有机碳含量.结果显示:林龄对柳杉人工林土壤容重、土壤孔隙度及持水量均有显著影响(P<0.05),且柳杉人工林土壤容重、土壤孔隙度及持水量随林龄增长呈二次函数变化.近熟林(23 a)、成熟林(27,32 a)和早期过熟林(46 a)的土壤孔隙度和土壤持水能力相较其他生长阶段更优.土壤深度对土壤孔隙度和持水量指标均有显著影响(P<0.05),0-10 cm土壤孔隙度和持水能力整体高于10-20 cm.土壤总有机碳和颗粒碳含量均与土壤容重呈显著负相关(P<0.05),与土壤孔隙度和持水量指标呈显著正相关(P<0.05);但颗粒碳与土壤容重、孔隙度、持水量指标的线性拟合决定系数(R^(2))均大于总有机碳,表明土壤水分-物理性质可能更能指示土壤颗粒碳的变化.根据主成分分析特征值大于1提取了第一主成分土壤孔隙度PCA1和土壤持水能力PCA1,累计贡献率为70.7%和76.1%.结构方程模型表明,林龄通过改变土壤孔隙度PCA1(路径系数为0.19),从而影响持水能力PCA1(路径系数为0.99),进一步调控颗粒碳(路径系数为0.60),最终影响总有机碳(路径系数为0.61).综上,华西雨屏区柳杉人工林土壤持水能力在不同生长阶段具有明显的变化特征,并且与土壤有机碳具有较强的生态关联;本研究结果可为森林的可持续经营和森林土壤碳循环模型的参数优化提供理论依据.

Soil water-holding capacity is an important indicator of forest water conservation and soil carbon pools.However,the variation characteristics of soil water-holding capacity and its ecological correlation with the soil organic carbon(SOC)of forest soils at different growth stages are still unclear.In this study,the physical properties of water,readily oxidizable carbon,particulate organic carbon,and total organic carbon of topsoil(0–20 cm)were measured across a typical chronosequence of Cryptomeria japonica plantations(including young forest growth(6 a),middle forest(12 a),near-mature forest(23 a),mature forest(27,32 a),and over-mature forest(46,52 a))in the Rainy Area of West China.The results showed that soil bulk density,soil porosity,and water-holding indices of C.japonica plantations were significantly affected by stand age(P<0.05)and changed in a quadratic manner as stand age increased.The soil porosity and soil water-holding capacity of the near-mature forest(23 a),mature forest(27 and 32 a),and early over-mature forest(46 a)were higher than those of the other stand ages.Soil porosity and water-holding capacity were significantly affected by soil layer(P<0.05),with soil porosity(except soil bulk density)and water-holding capacity at a depth of 0–10 cm being higher than that at 10–20 cm.Both SOC and particulate organic carbon were negatively correlated with soil bulk density(P<0.05)and positively associated with soil porosity and water-holding capacity indices(P<0.05).However,the linear fitting determination coefficient(R^(2))between particulate carbon and soil bulk density,porosity,and water-holding capacity was greater than that of total organic carbon,suggesting that soil water physical properties can better indicate changes in soil particulate organic carbon.Additionally,we extracted the first principal components,soil porosity PCA1,and soil water holding capacity PCA1,with cumulative contribution rates of 70.7%and 76.1%,respectively,based on the characteristic value of principal component analysis being greater than 1.Structural equation modeling showed that stand age could influence soil porosity PCA1(path coefficient of 0.19)and thus affect water-holding capacity PCA1(path coefficient of 0.99),thereby regulate particulate organic carbon(path coefficient of 0.60),and ultimately affect total organic carbon(path coefficient of 0.61).In summary,the soil water-holding capacity of C.japonica plantations displays clear variation characteristics at different growth stages in the Rainy Areas of West China and has substantial ecological correlations with soil organic carbon.This study provides a theoretical basis for the sustainable management of forests and parameter optimization of forest soil carbon cycle models.