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Abiotic and biotic stresses are the major factors limiting plant growth worldwide. Plants exposed to abiotic and biotic stresses often cause reduction in plant biomass as well as crop yield, resulting in plant biomass carbon loss. As a beneficial and quasiessential element, silicon accumulation in rhizosphere and plants can alleviate the unfavorable effects of the major forms of abiotic and biotic stress through several resistance mechanisms and thus increases plant biomass accumulation and crop yield. The beneficial effects of silicon on plant growth and crop yield have been widely reviewed over the last years. However, carbon accumulation of silicon-associated plant biomass under abiotic and biotic stresses has not yet been systematically addressed. This review article focuses on both the main mechanisms of silicon-mediated alleviation of abiotic and biotic stresses and their effects on plant biomass carbon accumulation in terrestrial ecosystems. The major points are the following: (1) the recovery of plant biomass via silicon mediation usually exhibits a bell-shaped response curve to abiotic stress severity and an S-shaped response curve to biotic stress severity; (2) although carbon concentration of plant biomass decreases with silicon accumulation, more than 96% of the recovered plant biomass contributes to plant biomass carbon accumulation; (3) silicon-mediated recovery generally increases plant biomass carbon by 35% and crop yield by 24%. In conclusion, silicon can improve plant growth and enhance plant biomass carbon accumulation under abiotic and biotic stresses in terrestrial ecosystems.

Despite increasing recognition of the critical role of coastal wetlands in mitigating climate change, sea‐level rise, and salinity increase, soil organic carbon (SOC) sequestration mechanisms in estuarine wetlands remain poorly understood. Here, we present new results on the source, decomposition, and storage of SOC in estuarine wetlands with four vegetation types, including single Phragmites australis (P, habitat I), a mixture of P. australis and Suaeda salsa (P + S, habitat II), single S. salsa (S, habitat III), and tidal flat (TF, habitat IV) across a salinity gradient. Values of δ13C increased with depth in aerobic soil layers (0–40 cm) but slightly decreased in anaerobic soil layers (40–100 cm). The δ15N was significantly enriched in soil organic matter at all depths than in the living plant tissues, indicating a preferential decomposition of 14N‐enriched organic components. Thus, the kinetic isotope fractionation during microbial degradation and the preferential substrate utilization are the dominant mechanisms in regulating isotopic compositions in aerobic and anaerobic conditions, respectively. Stable isotopic (δ13C and δ15N), elemental (C and N), and lignin composition (inherited (Ad/Al)s and C/V) were not completely consistent in reflecting the differences in SOC decomposition or accumulation among four vegetation types, possibly due to differences in litter inputs, root distributions, substrate quality, water‐table level, salinity, and microbial community composition/activity. Organic C contents and storage decreased from upstream to downstream, likely due to primarily changes in autochthonous sources (e.g., decreased onsite plant biomass input) and allochthonous materials (e.g., decreased fluvially transported upland river inputs, and increased tidally induced marine algae and phytoplankton). Our results revealed that multiple indicators are essential to unravel the degree of SOC decomposition and accumulation, and a combination of C:N ratios, δ13C, δ15N, and lignin biomarker provides a robust approach to decipher the decomposition and source of sedimentary organic matter along the river‐estuary‐ocean continuum.

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