RESUMEN
Plant species diversity (PSD) benefits soil organic carbon (SOC) accumulation, but mechanisms underlying the stimulative effects of PSD on SOC pools have not been well explored, especially in terms of how PSD impacts plant-derived C accumulation. Here, 45 plots covering a natural gradient of PSD ranging from 0.15 to 3.57 (Shannon's diversity index) were selected in a subtropical forest with calcareous soil to determine the pattern of and controls on the variation of plant-derived C as indexed by lignin phenols along with PSD. The absolute contents of lignin phenols ranged from 1.18 to 6.62 mg g-1 soil with an average of 2.48 ± 1.13 mg g-1 soil across the 45 plots. PSD significantly enhanced soil lignin accumulation via three mechanisms. First, PSD benefited lignin accumulation by stimulating plant detritus inputs. Second, PSD directly and indirectly increased reactive minerals, so that enhanced mineral protection of lignin. Third, decrease in microbial C limitation due to increased soil C availability resulted in lowered peroxidase activity and subsequently lignin degradation, which in turn benefited lignin accumulation. Our study provides mechanisms underlying SOC accumulation in response to increased PSD, which may be integrated into Earth system models in order to better predict SOC dynamics under PSD alteration.
Asunto(s)
Carbono , Lignina , Carbono/análisis , Lignina/metabolismo , Suelo , Bosques , Minerales , Plantas/metabolismo , China , FenolesRESUMEN
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 δ13 C, 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 (15.3-23.4â). 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.