红树植物地上根系对表层沉积物碳库的影响机制

项目名称： 红树植物地上根系对表层沉积物碳库的影响机制

项目编号： No.41476071

项目类型： 面上项目

立项/批准年度： 2015

项目学科： 天文学、地球科学

项目作者： 陈鹭真

作者单位： 厦门大学

项目金额： 98万元

中文摘要： 红树林是热带碳储量最丰富的森林和滨海湿地的高效碳汇。沉积物是红树林的重要碳库。地表生物学过程包括沉积物和凋落物的捕获和分解、温室气体排放，都影响着沉积物的碳收支。地上根系(气生根)是红树植物适应潮间带厌氧和潮汐动力机械作用的特殊结构。气生根作为氧气进入地下根的门户已被广泛认识，然而它们在促进沉积、释放沉积物和地下根产生的温室气体等与沉积物碳库密切相关的作用还鲜为人知。由于红树林气生根数量巨大、结构多变，忽视它们对沉积物碳库收支的贡献，将极大影响红树林生态系统碳库的准确评估。 本研究采用野外原位测定、地面高程监测系统、气体通量测定技术和稳定同位素示踪法，探讨气生根的类型、密度、高度等对红树林沉积物碳固定、垂直沉积和地下碳释放的调控机理，评价它们对红树林蓝碳碳汇的重要贡献。在揭示气生根对沉积物碳收支影响机制的同时，还将为准确评估红树林地下碳库提供理论依据。

中文关键词： 红树林；碳通量；沉积作用；气生根；温室气体

英文摘要： Mangroves are among the most carbon-rich forests in the tropics and are efficient carbon sinks in coastal areas. Mangrove soils store 50-90% of this total carbon. Accordingly, soil carbon sequestration and loss are greatly influenced by some biological processes associated with the forest floor. Aerial roots are typical structures in mangroves and assist trees in adapting to tidal inundation and fluctuation. As a conduit for the passage of oxygen, aerial roots may assist mangroves in ameliorating anaerobic soil conditions by alleviating oxygen deficiency in root tissues. However, the same conduits can also channel CO2 from soil respiration to the atmosphere, which has not been extensively studied as an important component of soil carbon loss from mangrove ecosystems.This process is also often excluded from global carbon budgets in mangroves. At the same time, aerial roots can potentially slow water velocities, trapping plant litter and detrital particles, and promote sedimentation, which would also promote the carbon gain to mangrove soil. Since there are large numbers of morphologically variable structures associated with mangrove aerial roots, soil carbon sink potential by these biological and physical processes would be underestimated by neglecting these functions. We will conduct a series of in situ studies in mangroves dominated by different types of aerial roots in Dongzhaigang Mangroves Nature Reserves, Hainan Province. Field investigations of forest structure, aerial root structure, root productivities, litterfall trapping, and decomposition will be conducted. We will install sets of Rod Surface Elevation Tables (RSETs), and deploy these with feldspar marker horizons (RSET-MH method), to discern the mechanisms of surface elevation change by aerial root type, density, and height that might affect soil surface carbon gain. RSET-MH approaches allow us to identify rates of vertical accretion, shallow subsidence, and/or root zone expansion and their relative influence on soil surface elevation change.We also plan to conduct comparative measurements of gas (CO2 and CH4) flux from both the soil surface and different types of aerial roots using static flux chamber techniques followed by gas chromatography. Furthermore, we will also determine carbon sources for trapped surface sediments by aerial root type, and from emitted greenhouse gases by tracing their carbon stable isotope signals. The aim of this research is to determine the influences of aerial roots on soil surface carbon gain through their effects on sedimentation, litterfall and root decomposition, and soil respiration. We will also quantify the contribution of aerial roots to total soil carbon gain in mangrove ecosystems. We hope that the results of these studies will provide useful information to improve our understanding of the mechanisms used in mangrove forests to store carbon so efficiently, and thus influence management decisions to affect greater carbon storage in the future.

英文关键词： Mangroves;Carbon Flux;Sedimentation;Aerial Roots;Greenhouse Gas