北京森林表土碳组分城郊梯度变化及其影响因素

Changes of forest topsoil carbon fractions across urban-rural transects in Beijing

快速的城市化进程深刻影响了城市森林土壤碳循环,重塑了城郊梯度上森林土壤碳空间分布特征。本文在北京市设置了4条城郊样带,测定了20个城市森林公园表土(表层0~10cm和亚表层10~20 cm)总碳及其不同碳组分含量,分析了各碳组分空间变化及其影响因素。结果表明,城郊样带森林表土总碳(表层21.0±1.6 g/kg;亚表层18.0±1.3 g/kg)以有机碳为主(表层占比64.6%±4.5%;亚表层占比54.9%±4.5%),有机碳含量从市中心到郊区表现出先下降后增加的非线性变化,无机碳含量在此梯度上呈显著线性下降趋势。城市森林表土有机碳(表层13.8±1.5 g/kg;亚表层10.0±1.2 g/kg)以颗粒态有机碳为主(表层占比71.3%±2.4%;亚表层占比70.5%±2.8%),颗粒态有机碳和矿物结合态有机碳含量在城郊梯度上均表现出先下降后增加的非线性变化;颗粒态有机碳的占比在城区相对更小,而矿物结合态有机碳占比在城区相对更大。土壤质地、土壤p H和公园年龄是解释表土碳组分在城郊梯度上空间变异的重要因素,城郊气候梯度以及树木多样性对城市森林土壤碳组分空间变化的影响并不明显。上述研究结果有助于认识气候变化及人类活动双重干扰下的城市森林土壤碳库特征,也对城市森林土壤管理具有重要的指导意义。

Rapid urbanization has profoundly altered soil carbon cycling and thereby reshaped the spatial pattern of soil carbon content and fractions across the urban-rural gradients.In this study,we measured the contents of total carbon and its different fractions in the topsoil(surface layer 0-10 cm and subsurface layer 10-20 cm)of twenty parks across four urban-rural transects in Beijing,China.We analyzed the spatial variations of different soil carbon fractions and their potential driving factors across the urban-rural gradients.The results showed that topsoil total carbon(topsoil:21.0±1.6 g/kg;subsurface soil:18.0±1.3 g/kg)was dominated by organic carbon(topsoil:64.6%±4.5%;subsurface soil:54.9%±4.5%).Topsoil contents of organic carbon showed a nonlinear trend from the urban core to the rural area,while the topsoil inorganic carbon content decreased significantly.Topsoil organic carbon(topsoil:13.8±1.5 g/kg;subsurface soil:10.0±1.2 g/kg)was dominated by particulate organic carbon(topsoil:71.3%±2.4%;subsurface soil:70.5%±2.9%).The contents of both particulate organic carbon and mineral associated organic carbon showed nonlinear changes across the urban-rural forest transects.The proportion of particulate organic carbon was relatively low in urban areas,while that of mineral associated organic carbon showed an opposite trend.Soil texture,soil pH,and park age were important drivers to shape the spatial variation of topsoil carbon components across the urban-rural transects,while the urban-rural climate gradient and species diversity were found to have an unimportant role.Our findings improve the understanding of how urbanization reshapes soil carbon fractions and have useful implications for soil management in urban forests.