Spartina alterniflora invasion controls organic carbon stocks in coastal marsh and mangrove soils across tropics and subtropics

Abstract

Coastal wetlands are among the most productive ecosystems and store large amounts of organic carbon (C)—the so termed “blue carbon.” However, wetlands in the tropics and subtropics have been invaded by smooth cordgrass (Spartina alterniflora) affecting storage of blue C. To understand how S. alterniflora affects soil organic carbon (SOC) stocks, sources, stability, and their spatial distribution, we sampled soils along a 2500 km coastal transect encompassing tropical to subtropical climate zones. This included 216 samplings within three coastal wetland types: a marsh (Phragmites australis) and two mangroves (Kandelia candel and Avicennia marina). Using δ13C, C:nitrogen (N) ratios, and lignin biomarker composition, we traced changes in the sources, stability, and storage of SOC in response to S. alterniflora invasion. The contribution of S. alterniflora‐derived C up to 40 cm accounts for 5.6%, 23%, and 12% in the P. australis, K. candel, and A. marina communities, respectively, with a corresponding change in SOC storage of +3.5, −14, and −3.9 t C ha−1. SOC storage did not follow the trend in aboveground biomass from the native to invasive species, or with vegetation types and invasion duration (7–15 years). SOC storage decreased with increasing mean annual precipitation (1000–1900 mm) and temperature (15.3–23.4℃). Edaphic variables in P. australis marshes remained stable after S. alterniflora invasion, and hence, their effects on SOC content were absent. In mangrove wetlands, however, electrical conductivity, total N and phosphorus, pH, and active silicon were the main factors controlling SOC stocks. Mangrove wetlands were most strongly impacted by S. alterniflora invasion and efforts are needed to focus on restoring native vegetation. By understanding the mechanisms and consequences of invasion by S. alterniflora, changes in blue C sequestration can be predicted to optimize storage can be developed.

Environmental Filtering by pH and Salinity Jointly Drives Prokaryotic Community Assembly in Coastal Wetland Sediments

“…Besides, sediment availability of nutrients such as organic carbon can regulate the composition, structure and diversity of microbial communities (Hu et al, 2014;Yang et al, 2016). Previous studies reported that coastal wetlands (e.g., mangroves and salt marshes) have high carbon sequestration rates, and usually maintain soil organic carbon stocks, which plays an important role in shaping microbial community structures (Sun et al, 2019;Xia et al, 2021). Neutral sediment pH showed a positive relationship with the organic carbon content, which contributes to utilization of the organic carbon by microorganisms (Sun et al, 2019).…”

Effects of Spartina invasion on the soil organic carbon content in salt marsh and mangrove ecosystems in China

“…Mature mangroves can resist S. alterniflora invasions through light competition, but this resistance is compromised due to canopy gaps within mangroves and because the mangrove seedlings at the forest edge do not create enough shade (Zhang et al, 2012). By invading the opened canopy in mangroves or competitively replacing mangrove seedlings at the forest edge, S. alterniflora can increase SOC content, but the increment was lower than that of mature mangroves (Su et al, 2020; Wang et al, 2019), which was probably because mature mangroves are more productive than S. alterniflora ‐dominated marshes (Kelleway et al, 2017; Xia et al, 2021). Our results support this finding, but significant negative effects were found only for S. alterniflora invasions in mangroves dominated by K .…”

“…biological invasion, blue carbon, carbon sink, coastal wetlands, mangrove, salt marsh, soil organic carbon, Spartina alterniflora Xia et al, 2021). Their results showed that S. alterniflora invasions decreased the SOC content in mangroves dominated by Kandelia obovata and Avicennia marina but had no significant effect on the SOC content in Phragmites australis-dominated saltmarshes.…”

“…The changes in primary productivity that occur following S. alterniflora invasions also vary with ecosystem type (e.g. salt marshes or mangroves) and among native ecosystems dominated by different native species, resulting in highly variable magnitudes and directions of SOC content responses to S. alterniflora invasions (Meng et al, 2020; Xia et al, 2021).…”

“…Jin et al, 2016; Liu, Han, et al, 2017; Meng et al, 2020), the findings of which are crucial for understanding the effects of invasions. By collecting soil samples to a depth of 40 cm from nine paired locations, two biogeographical surveys studied the effects of S. alterniflora invasions on SOC content across tropical and subtropical regions (21–31°N) in coastal China (Wang et al, 2019; Xia et al, 2021). Their results showed that S. alterniflora invasions decreased the SOC content in mangroves dominated by Kandelia obovata and Avicennia marina but had no significant effect on the SOC content in Phragmites australis ‐dominated saltmarshes.…”