武夷山国家公园马尾松林改为茶园后影响表层土壤碳含量的林缘效应

Edge Effect of Pinus massoniana Forest Converted into Tea Plantation on Topsoil Carbon Content in Wuyishan National Park

【目的】探究马尾松林改为茶园的土地利用/覆盖变化对土壤碳含量的影响,明确林缘形成对森林土壤碳含量的作用,为准确估算森林土壤碳储量和固碳功能提供科学依据。【方法】在武夷山国家公园选择马尾松纯林转为茶园的典型地点,研究马尾松林内不同林距(距“林—茶”接壤边缘1、20和50 m)及接壤茶园内4处位置的表层土壤(0~20 cm)总有机碳(TOC)、可溶性有机碳(DOC)和微生物生物量碳(MBC)含量变化及影响因素。【结果】马尾松林改为茶园16~28年后,土壤TOC、DOC和MBC含量分别比原马尾松林下降了57.1%、48.8%和16.9%。在马尾松林内至林缘方向上,TOC和DOC含量呈下降趋势,而MBC含量无显著差异(P>0.1),为TOC含量均值在林距50 m、20 m、1 m和毗邻茶园处依次为31.08、30.67、22.26和13.25 g·kg^(-1),DOC含量均值依次为269.7、259.8、226.5和135.5 mg·kg^(-1)。TOC和DOC含量与解释变量(土壤理化性质、土地利用/覆被类型和林缘年龄)的逐步回归方程拟合优度好,自变量分别解释了各自变异的87.7%和76.6%;但MBC的拟合效果很差。其中,土地利用/覆被类型和土壤氮组分含量对TOC和DOC产生不同程度的作用;而林缘年龄仅对DOC含量产生影响。【结论】马尾松林改为茶园的土地利用/覆盖变化使土壤碳含量下降(TOC和DOC最为明显),且随离开林缘的距离增加而降低。因此,需要考虑土壤碳含量的林缘效应,以降低景观尺度的森林土壤碳库和碳汇估算中的不确定性。

【Objective】This study aims to explore the impact of land-use/land-cover(LULC)changes on soil carbon sink and its stability in the conversion of Pinus massoniana forests to tea gardens,clarify the role of forest edge formation on forest soil carbon content,and provide a scientific foundation for accurate estimation of forest soil carbon storage and carbon sequestration.【Method】The study was conducted in a P.massoniana forest with the area partially converted to tea plantations in Wuyishan National Park.The soil carbon components in the topsoil(0·20 cm)collected from the forest at the locations of 1,20 and 50 m distances from the edge shared by the two land use types,including the total organic carbon(TOC),dissolved organic carbon(DOC),and microbial biomass carbon(MBC)were analyzed.【Result】After 16 to 28 years of converting P.massoniana forest into tea plantation,the TOC,DOC and MBC contents reduced by 57.1%,48.8%and 16.9%,respectively,compared to the original P.massoniana forest.The TOC and DOC gradually decreased from the interior of P.massoniana forest to the forest-tea edge.However,no significant difference was found for the MBC at those locations(P>0.1).The TOC content was 31.08,30.67,22.26 and 13.25 g·kg^(−1)at the locations of 50,20 and 1 m distance from the forest-tea edge and adjacent tea plantation,respectively.The DOC content was 269.7,259.8,226.5 and 135.5 mg·kg^(−1)at the same location gradient above.The TOC and DOC were able to be well-fitted with explanatory variables(topsoil physical and chemical properties,LULC,and boundary age)by the stepwise regression equation,with independent variables explaining 87.5%and 76.6%of their respective variations,respectively.Nonetheless,MBC provided the poorest fitting.Specifically,TOC and DOC were affected by variables of soil nitrogen compositions and LULC.Boundary age only had effect on the DOC content.【Conclusion】The LULC conversion of P.massoniana forest to tea plantation leads to the decrease of topsoil carbon content(particularly TOC and DOC),while the carbon loss magnitude reduces with the increasing distance to forest edge.Thus,the forest edge effects of soil carbon content need to be considered to reduce uncertainty in the estimation of forest soil carbon sinks on a landscape scale.