Effects of Pneumatophore Density on Methane Emissions in Mangroves

Chiao-Wen Lin,Hsing-Juh Lin,Wei-Jen Lin,Chuan-Wen Ho,Yu-Chen Kao

doi:10.3390/f12030314

Abstract

Mangroves play an important role in carbon sequestration. However, mangroves can be sources of greenhouse gas (GHG) emissions. In this study, methane (CH4) emissions and related soil properties were determined in multiple mangroves in Taiwan, including Kandelia obovata and Avicennia marina mangroves. K. obovata possess prop roots, whereas pneumatophores are found in A. marina. Our results showed that mangrove soils were significant sources of CH4 emissions, which should be accounted for in mangrove carbon budgets. In particular, CH4 emissions in the A. marina mangroves were approximately 50- to 100-fold those of the K. obovata mangroves and the adjoining mudflats. Multiple regression analyses indicated that the soil salinity and pH in K. obovata mangroves and the soil redox potential and organic content in the mudflats were the key factors affecting CH4 emissions. However, the pneumatophore density alone explained approximately 48% of the variation in CH4 emissions in the A. marina mangroves. More pneumatophores resulted in higher CH4 emissions in the A. marina mangroves. Thus, compared with the assessed soil properties, the contribution of pneumatophores to the transportation of CH4 from soil was more significant. In addition to soil properties, our results demonstrated that the root structure may also affect GHG emissions from mangroves.

Highlights

Anthropogenic activities, such as deforestation and fossil fuel combustion, have generated a great amount of carbon dioxide (CO2) emissions, with accompanying greenhouse effects and global warming [1,2]
Serrano et al [10] reported that the soil carbon stock in 1-m-thick mangroves in Australia was approximately 251 Mg C ha−1, which was 1.5~2.5 times greater than the levels in seagrass meadows (112 Mg C ha−1) and salt marshes (168 Mg C ha−1)
The CH4 emissions were measured from the soils of the mangroves and mudflats with three to five replications during emersion periods

Summary

Introduction

Anthropogenic activities, such as deforestation and fossil fuel combustion, have generated a great amount of carbon dioxide (CO2) emissions, with accompanying greenhouse effects and global warming [1,2]. To establish carbon budgets accurately, CH4 emissions from mangrove ecosystems should be considered for evaluation Both biotic (e.g., mangrove tree species) and abiotic (e.g., soil properties) factors play important roles in affecting GHG emissions. Soil properties such as water content, organic matter content, pH, salinity, ORP, and temperature can influence CH4 emissions, as each parameter may regulate microbial processes [18,20,21,22,23]. He et al [24] reported that the root structure of mangrove trees contributed in various ways to CH4 emissions from soils. The objectives of this study were (1) to quantify CH4 emissions from the soils of K. obovata mangroves (prop roots), A. marina mangroves (pneumatophores), and adjoining mudflats; (2) to characterize the effects of soil properties on CH4 emissions in these three types of habitats; and (3) to determine the effects of pneumatophore density on CH4 emissions in A. marina mangroves

Site Description

Kandelia obovata

A B C D E1 E2 F G H

Findings

C D E2 F G