Monoculture or Mixed Culture? Relevance of Fine Root Dynamics to Carbon Sequestration Oriented Mangrove Afforestation and Restoration

Abstract

Fine root dynamics have the potential to contribute to ecosystem biogeochemical cycling, especially for carbon. This is particularly true in mangroves which are the most productive and carbon-rich ecosystems of the world. However, few studies comprehensively evaluated the contribution of mangrove fine root dynamics to soil organic carbon accumulation. In southern China, while the introduced fast-growing Sonneratia apetala and native shrubby Kandelia obovata have been widely used in mangrove reforestation/afforestation programs since the mid-1980s, their implications and ecosystem services are still unclear. Here we show distinct differences in fine root dynamic among 12-year-old S. apetala, K. obovata monocultures, and their mixed stand using root coring, ingrowth core, and intact-core methods. Soil organic carbon storage was examined by soil coring method. One-year observation showed significant differences among the three mangrove plantations in fine root biomass, necromass, turnover rate, and decomposition decay rate constant. Soil organic carbon stock was 15.8 ± 0.8, 7.8 ± 0.5, and 11.9 ± 1.6 Mg C ha–1 for K. obovata, S. apetala monocultures and their mixed stand, respectively. Live fine root biomass, fine root necromass, annual fine root production and fine root mass decay rate constant are significantly correlated to soil organic carbon content across plantations. We suggest that mangrove fine root dynamics were mainly affected by soil nutrient conditions and species composition. Mixed stands may not have higher soil organic carbon storage than monocultures. The functional trait of different mangrove species is responsible to determine the carbon storage function of mixed stands. Fine roots play an important role in carbon storage, and fine root dynamics have a significant effect on carbon sequestration in mangrove ecosystems. The shrubby native K. obovata had a higher potential for belowground carbon sequestration and storage than the tall introduced S. apetala.

Environmental selection and evolutionary process jointly shape genomic and functional profiles of mangrove rhizosphere microbiomes

“…Several studies also reported that coastal ecosystems vegetated with different mangrove species showed substantial variations in sediment properties, including pH, salinity, TC, and TN 32,47 . In this study, we observed different nutrient statuses (TC, TN, ammonium, and sulfate) and environmental conditions (pH and salinity) between native and introduced mangrove rhizospheres, which might be influenced by plant characteristics between native and introduced mangroves 32,48 . For example, the introduced mangrove could accelerate nutrient cycling with higher fine root turnover and decomposition rates, leading to fast growth rates, low carbon storage capacity, and decreased nutrient content in the sediment 32,48 .…”

“…In this study, we observed different nutrient statuses (TC, TN, ammonium, and sulfate) and environmental conditions (pH and salinity) between native and introduced mangrove rhizospheres, which might be influenced by plant characteristics between native and introduced mangroves 32,48 . For example, the introduced mangrove could accelerate nutrient cycling with higher fine root turnover and decomposition rates, leading to fast growth rates, low carbon storage capacity, and decreased nutrient content in the sediment 32,48 . Root exudates also showed direct impacts on rhizosphere properties (e.g., N and P) and microbial communities 35,46,49 .…”

Chemoautotrophic sulphur oxidizers dominate microbial necromass carbon formation in coastal blue carbon ecosystems

“…However, microbial necromass C and C content are not the only reason for determining C sequestration. Although the individual biomass of exotic S. alterniflora and S. sonnertia was higher than that of native species, they showed lower soil C stock and C sequestration potential under similar environmental conditions, which may be due to the fine root turnover rates, fine root biomass and C accumulation rates (Feng et al, 2017; He et al, 2018, 2020, 2021; Yu, Feng, et al, 2020). For example, fine roots could play an important role in C sequestration in mangrove ecosystems, and the C stock was positively correlated with live fine root biomass and fine root necromass (He et al, 2018).…”

“…coastal ecosystem, functional potential, metagenome sequencing, metagenome-assembled genome, microbial necromass carbon alien plants with high adaptability and growth rates are considered as pioneer species to improve degraded coastal habitats, but they have also caused a series of ecological and environmental risks, such as reduction of local biodiversity, decrease of C sequestration and increase of CH 4 emissions (He et al, 2018;Ren et al, 2008;Yu, Yang, et al, 2020). Most previous studies of soil C sequestration were mainly focused on the contribution of plant tissues (He et al, 2018(He et al, , 2021Zhu et al, 2020). For example, the introduced mangrove S. apetala was found to have higher fine root turnover rates but lower C sequestration compared to their native counterparts (He et al, 2021).…”

“…Most previous studies of soil C sequestration were mainly focused on the contribution of plant tissues (He et al, 2018(He et al, , 2021Zhu et al, 2020). For example, the introduced mangrove S. apetala was found to have higher fine root turnover rates but lower C sequestration compared to their native counterparts (He et al, 2021). Although coastal sediments vegetated by native or alien species harboured distinct microbial communities (Yu et al, 2022;Yu, Yang, et al, 2020), few reports have explored how microorganisms influence the sediment C sequestration in these ecosystems.…”