农田-防护林体系细根生物量与土壤水碳的耦合关系

Coupling relationship between fine root biomass and soil water and carbon in a farmland shelterbelt system

农田防护林系统对改善环境、防风治沙、保护农田具有重要意义,其中农-林系统界面处的植被细根空间分布随距林带边缘距离有所差异,将影响农作物对土壤水分吸收和土壤有机碳积累.选取内蒙古河套灌区典型防护林-农田样地,分析样带上距主林带0.3H、0.5H、0.7H和农田中心的防护林与农田作物西葫芦(Cucurbita pepo L.)细根生物量(FRBD)、土壤水分含量(SMC)及土壤有机碳(SOC)的分布特征,评价各样点的土壤水分亏缺(SMD)以及土壤有机碳累积(SOCA).在此基础上探讨防护林细根对农田SMC和SOC的影响.结果显示:(1)林带边缘植被细根主要分布在0-100 cm,其中西葫芦细根密集区在0-20 cm土层,防护林细根密集区在20-60 cm土层,林农细根上下交错分布.(2)林缘附近SMC表现为亏缺状态,SMD主要发生在0-100 cm土层,随着林带距离的增加SMD减轻;在垂直方向上SMD大致呈“高—低—高”的变化趋势,防护林与农作物水分竞争区域主要在20-60 cm土层.(3)林缘附近SOC处于碳汇状态,随着与林带距离的增加SOCA逐渐减小;100-200 cm土层SOCA是0-100 cm土层2-7倍,在100-200 cm土层SOC具有较大的固碳潜力.(4)各样点在0-200 cm土层FRBD、SOCD和SMC三者均存在极显著相关关系(P<0.01),三者相互影响主要发生在0-100 cm土层.(5)整个土层土壤碳水耦合协调度均为不协调发展,在0-100 cm土层其基本处于失调衰退类.本研究表明防护林与农作物细根交错分布形成了农林复合系统水资源有效利用的格局,但土壤碳水耦合度的不协调发展,可能会影响农作物的生长和农田防护林体系可持续发展的生态环境.

The farmland shelterbelt system is of great significance for improving the environment,preventing wind,controlling sand,and protecting farmlands.The spatial distribution of fine vegetation roots at the interface of the agricultural–forest system varies with the distance from the edge of the forest belt,which affects the absorption of soil moisture and accumulation of soil organic carbon by crops.In this study,a typical shelterbeltfarmland sample plot in the Hetao Irrigation District of Inner Mongolia in China was selected to analyze the distribution characteristics of fine root biomass density(FRBD),soil moisture content(SMC),and soil organic carbon(SOC)of the shelterbelt and farm crop Cucurbita pepo L.at 0.3H,0.5H,and 0.7H from the main forest belt and the center of the farmland.The soil moisture deficit(SMD)and soil organic carbon accumulation(SOCA)were evaluated at each sample point.Based on this,the effects of fine roots on SMC and SOC in farmlands are discussed.The results showed that:(1)The fine roots of the vegetation on the edge of the forest belt were mainly distributed in the 0–100 cm layer,the fine roots of C.pepo L.were concentrated in the 0–20 cm soil layer,the fine roots of the shelter forest were concentrated in the 20–60 cm soil layer,and the fine roots of the shelter forest and crops were staggered up and down.(2)SMC near the forest edge was deficient;SMD mainly occurred in the 0–100 cm soil layer and decreased with increasing forest distance.In the vertical direction,SMD roughly showed a trend of"high-low-high"moisture,and the water competition area between the shelter forest and crops was mainly in the 20–60 cm soil layer.(3)The SOC near the forest edge was a carbon sink,and the SOCA gradually decreased with increasing distance from the forest belt.The SOCA of the 100–200 cm soil layer was 2–7 times that of the 0–100 cm soil layer,and SOC had great potential for carbon sequestration in the 100–200 cm soil layer.(4)There was a significant correlation between FRBD,SOCD,and SMC in the 0–200 cm soil layer(P<0.01),and the interaction among them mainly occurred in the 0-100 cm soil layer.(5)The SOC-SWC coupling coordination degree in the entire soil layer was not coordinated,and was in the imbalance decline class in the 0–100 cm soil layer.This study showed that the pattern of effective utilization of water resources in agroforestry systems was formed by the interlaced distribution of shelter forest and crop fine roots,but the uncoordinated development of the SOC-SMC coupling degree may affect the growth of crops and the ecological environment of sustainable development of the farmland shelterbelt system.