Research Article: Plant biomass and soil organic carbon are main factors influencing dry-season ecosystem carbon rates in the coastal zone of the Yellow River Delta

Date Published: January 14, 2019

Publisher: Public Library of Science

Author(s): Yong Li, Haidong Wu, Jinzhi Wang, Lijuan Cui, Dashuan Tian, Jinsong Wang, Xiaodong Zhang, Liang Yan, Zhongqing Yan, Kerou Zhang, Xiaoming Kang, Bing Song, Dafeng Hui.

http://doi.org/10.1371/journal.pone.0210768

Abstract

Coastal wetlands are considered as a significant sink of global carbon due to their tremendous organic carbon storage. Coastal CO2 and CH4 flux rates play an important role in regulating atmospheric CO2 and CH4 concentrations. However, the relative contributions of vegetation, soil properties, and spatial structure on dry-season ecosystem carbon (C) rates (net ecosystem CO2 exchange, NEE; ecosystem respiration, ER; gross ecosystem productivity, GEP; and CH4) remain unclear at a regional scale. Here, we compared dry-season ecosystem C rates, plant, and soil properties across three vegetation types from 13 locations at a regional scale in the Yellow River Delta (YRD). The results showed that the Phragmites australis stand had the greatest NEE (-1365.4 μmol m-2 s-1), ER (660.2 μmol m-2 s-1), GEP (-2025.5 μmol m-2 s-1) and acted as a CH4 source (0.27 μmol m-2 s-1), whereas the Suaeda heteroptera and Tamarix chinensis stands uptook CH4 (-0.02 to -0.12 μmol m-2 s-1). Stepwise multiple regression analysis demonstrated that plant biomass was the main factor explaining all of the investigated carbon rates (GEP, ER, NEE, and CH4); while soil organic carbon was shown to be the most important for explaining the variability in the processes of carbon release to the atmosphere, i.e., ER and CH4. Variation partitioning results showed that vegetation and soil properties played equally important roles in shaping the pattern of C rates in the YRD. These results provide a better understanding of the link between ecosystem C rates and environmental drivers, and provide a framework to predict regional-scale ecosystem C fluxes under future climate change.

Partial Text

Carbon dioxide (CO2) and methane (CH4) are key greenhouse gases (GHGs) that make substantial contributions to global warming [1]. Numerous studies have estimated global wetland CO2 and CH4 fluxes, but with great uncertainties, mainly due to complicated environmental drivers [2–4]. Coastal wetlands have been recognized as the most vulnerable and sensitive ecosystems, because they act as the ecotone between terrestrial and aquatic ecosystems [5]. Coastal estuary wetlands store at least 430 Tg of carbon (C) with a C sequestration rate of 45 g C m-2 yr-1, playing an important role in the global carbon cycle as natural carbon pools [6]. The coastal wetland is one of the most important wetland types for understanding C flux dynamics due to the high variations involved with water conditions, sedimentation characteristics, and vegetation types [7]. Coastal wetlands can act as greenhouse gas sinks via C burial, sediment deposition, and plant biomass accumulation, and as greenhouse gas sources through the release of CO2 and CH4 produced by the decomposition of organic matter [8], so they are of vital importance in governing the atmospheric concentrations of CO2 and CH4 [9]. However, due to the complicated interaction of environmental factors including vegetation and soil properties, how to disentangle the contributions of multiple drivers to CO2 and CH4 fluxes in estuary wetland remains unclear.

In conclusion, this study comprehensively investigated the regulation of ecosystem C flux rates under vegetation and soil property gradients in the coastal zone of the Yellow River Delta. This study showed that a combination of biotic and abiotic predictors, e.g., vegetation and soil, explained the majority of the variation in the investigated dry-season ecosystem C rates in the coastal zone of the Yellow River Delta. Plant biomass was found to be the main factor explaining all of the investigated carbon rates (GEP, ER, NEE, and CH4), while soil organic carbon was shown to be the most important for explaining the variability in the processes of carbon release to the atmosphere, i.e., ER and CH4. Vegetation and soil properties played equally important roles in shaping the pattern of C rates through variation partition analysis. The results of this research provide a better understanding of the link between ecosystem C rates and environmental drivers, and provide a good basis to predict regional‐scale ecosystem C fluxes under future climate change.

 

Source:

http://doi.org/10.1371/journal.pone.0210768

 

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