深圳湾红树林土壤碳同位素研究

Sedimentary Organic Carbon Dynamics in Mangrove Soil in Shenzhen Bay Based on Carbon Isotopic Analysis

陆地生态系统土壤有机质(SOM)的碳动态研究已引起科学界的广泛关注,对海陆交错带的相关研究则较少。本研究选取位于广东深圳湾的三个红树林群落土壤剖面,测定了土壤有机碳(SOC)含量和SOM的稳定碳同位素比率(13C)等含量。结果表明,地表100 cm土壤碳库分别为:桐花树(Aegiceras corniculatum)群落碳库量较大,达673.2 Mg/ha,而木榄(Bruguiera gymnorrhiza)+秋茄(Kandelia obovata)群落为371.9 Mg/ha,白骨壤(Avicennia marina)群落为325.2 Mg/ha。这三个剖面SOM的13C介于-29.4‰至-24.1‰之间,指示其来源主要为C3植被。不同于传统的SOM的13C随深度增加而增加的趋势,桐花树和白骨壤剖面底层的SOM的13C随深度增加而呈现亏损,而木榄+秋茄SOM的13C在整个剖面则基本稳定。红树林SOM的13C的垂直格局可能反映了大气CO2的13C的历史变化、有机质分解过程中的同位素分馏作用、植物根系分泌物和凋落物13C的差异,和土壤对植物组织的选择性保存等因素的综合作用。此外,诸如潮汐作用、群落演替阶段以及生物干扰等,也会对红树林土壤的碳动态产生一定的影响。结果还表明,在红树林有机质沉积过程中,土壤含水量通过作用于土壤分解过程在某种程度上控制SOC含量,同时间接作用于土壤同位素分馏过程而影响SOM的13C。

Mangrove ecosystems are highly productive and play an important role in tropical and global coastal carbon （C） budgets. However, soil organic carbon （SOC） storage and turnover in mangrove forests are still poorly understood. Based on C isotopic measurements of soil cores of three mangrove stands in Shenzhen bay, Southern China. SOC density was 673.2 Mg/ha in Aegiceras corniculatumstand stand, 371.9 673.2 Mg/ha in Bruguiera gymnorrhiza ＋ Kandelia candel-dominated stand） and 325.2 Mg/ha in Avicennia marina stand. SOC 13C values at the three mangrove sites ranged from -29.4 to -24.1%, which mean that the carbon came from C3 plant. The vertical variation of SOC 13C indicated the comprehensive results of depletion of 13C of atmospheric CO2 by fossil fuel emissions, the difference between root and leaf 13C, preferential microbial decomposition, and tidal process.