Microbial Necromass, Lignin, and Glycoproteins for Determining and Optimizing Blue Carbon Formation.

Coastal wetlands contribute to the mitigation of climate change through the sequestration of "blue carbon". Microbial necromass, lignin, and glycoproteins (i.e., glomalin-related soil proteins (GRSP)), as important components of soil organic carbon (SOC), are sensitive to environmental change. However, their contributions to blue carbon formation and the underlying factors remain largely unresolved. To address this paucity of knowledge, we investigated their contributions to blue carbon formation along a salinity gradient in coastal marshes. Our results revealed decreasing contributions of microbial necromass and lignin to blue carbon as the salinity increased, while GRSP showed an opposite trend. Using random forest models, we showed that their contributions to SOC were dependent on microbial biomass and resource stoichiometry. In N-limited saline soils, contributions of microbial necromass to SOC decreased due to increased N-acquisition enzyme activity. Decreases in lignin contributions were linked to reduced mineral protection offered by short-range-ordered Fe (FeSRO). Partial least-squares path modeling (PLS-PM) further indicated that GRSP could increase microbial necromass and lignin formation by enhancing mineral protection. Our findings have implications for improving the accumulation of refractory and mineral-bound organic matter in coastal wetlands, considering the current scenario of heightened nutrient discharge and sea-level rise.

Storage, patterns and influencing factors for soil organic carbon in coastal wetlands of China.

Soil organic carbon (SOC) in coastal wetlands, also known as "blue C," is an essential component of the global C cycles. To gain a detailed insight into blue C storage and controlling factors, we studied 142 sites across ca. 5000 km of coastal wetlands, covering temperate, subtropical, and tropical climates in China. The wetlands represented six vegetation types (Phragmites australis, mixed of P. australis and Suaeda, single Suaeda, Spartina alterniflora, mangrove [Kandelia obovata and Avicennia marina], tidal flat) and three vegetation types invaded by S. alterniflora (P. australis, K. obovata, A. marina). Our results revealed large spatial heterogeneity in SOC density of the top 1-m ranging 40-200 Mg C ha-1 , with higher values in mid-latitude regions (25-30° N) compared with those in both low- (20°N) and high-latitude (38-40°N) regions. Vegetation type influenced SOC density, with P. australis and S. alterniflora having the largest SOC density, followed by mangrove, mixed P. australis and Suaeda, single Suaeda and tidal flat. SOC density increased by 6.25 Mg ha-1 following S. alterniflora invasion into P. australis community but decreased by 28.56 and 8.17 Mg ha-1 following invasion into K. obovata and A. marina communities. Based on field measurements and published literature, we calculated a total inventory of 57 × 106 Mg C in the top 1-m soil across China's coastal wetlands. Edaphic variables controlled SOC content, with soil chemical properties explaining the largest variance in SOC content. Climate did not control SOC content but had a strong interactive effect with edaphic variables. Plant biomass and quality traits were a minor contributor in regulating SOC content, highlighting the importance of quantity and quality of OC inputs and the balance between production and degradation within the coastal wetlands. These findings provide new insights into blue C stabilization mechanisms and sequestration capacity in coastal wetlands.

Distribution, sources, and decomposition of soil organic matter along a salinity gradient in estuarine wetlands characterized by C:N ratio, δ13 C-δ15 N, and lignin biomarker.

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 δ13 C increased with depth in aerobic soil layers (0-40 cm) but slightly decreased in anaerobic soil layers (40-100 cm). The δ15 N was significantly enriched in soil organic matter at all depths than in the living plant tissues, indicating a preferential decomposition of 14 N-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 (δ13 C and δ15 N), 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, δ13 C, δ15 N, and lignin biomarker provides a robust approach to decipher the decomposition and source of sedimentary organic matter along the river-estuary-ocean continuum.

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

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 (15.3-23.4℃). 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.

Characteristics and applications of biochar for remediating Cr(VI)-contaminated soils and wastewater.

Chromium (Cr) is a common environmental contaminant due to industrial processes and anthropogenic activities such as mining of chrome ore, electroplating, timber treatment, leather tanning, fertilizer and pesticide, etc. Cr exists mainly in both hexavalent [Cr(VI)] and trivalent [Cr(III)] form, being Cr(VI) with non-degradability and potential to be hidden, thereby affecting surrounding environment and being toxic to human health. Therefore, researches on remediation of Cr pollution in the environment have received much attention. Biochar is a low-cost adsorbent, which has been identified as a suitable material for Cr(VI) immobilization and removal from soil and wastewater. This review incorporates existing literature to provide a detailed examination into the (1) Cr chemistry, the source and current status of Cr pollution, and Cr toxicity and health; (2) feedstock and characterization of biochar; (3) processes and mechanisms of immobilization and removal of Cr by biochar, including oxidation-reduction, electrostatic interactions, complexation, ion exchange, and precipitation; (4) applications of biochar for Cr(VI) remediation and the modification of biochar to improve its performance; (5) factors affecting removal efficiency of Cr(VI) with respect to its physico-chemical conditions, including pH, temperature, initial concentration, reaction time, biochar characteristics, and coexisting contaminants. Finally, we identify current issues, challenges, and put forward recommendations as well as proposed directions for future research. This review provides a thorough understanding of using biochar as an emerging biomaterial adsorbent in Cr(VI)-contaminated soils and wastewater.

Biochar boosted high oleic peanut production with enhanced root development and biological N fixation by diazotrophs in a sand-loamy Primisol.

Peanut yield and quality face significant threats due to climate change and soil degradation. The potential of biochar technology to address this challenge remains unanswered, though biochar is acknowledged for its capacity to enhance the soil microbial community and plant nitrogen (N) supply. A field study was conducted in 2021 on oil peanuts grown in a sand-loamy Primisol that received organic amendments at 20 Mg ha-1. The treatments consisted of biochar amendments derived from poultry manure (PB), rice husk (RB), and maize residue (MB), as well as manure compost (OM) amendment, compared to no organic amendment (CK). In 2022, during the second year after amendment, samples of bulk topsoil, rooted soil, and plants were collected at the peanut harvest. The analysis included the assessment of soil quality, peanut growth traits, microbial community, nifH gene abundance, and biological N fixation (BNF) rate. Compared to the CK, the OM treatment led to an 8 % increase in peanut kernel yield, but had no effect on kernel quality in terms of oil production. Conversely, both PB and MB treatments increased kernel yield by 10 %, whereas RB treatment showed no change in yield. Moreover, all biochar amendments significantly improved oilseed quality by 10-25 %, notably increasing the proportion of oleic acid by up to 70 %. Similarly, while OM amendment slightly decreased root development, all biochar treatments significantly enhanced root development by over 80 %. Furthermore, nodule number, fresh weight per plant, and the nifH gene abundance in rooted soil remained unchanged under OM and PB treatments but was significantly enhanced under RB and MB treatments compared to CK. Notably, all biochar amendments, excluding OM, increased the BNF rate and N-acetyl-glucosaminidase activity. These changes were attributed to alterations in soil aggregation, moisture retention, and phosphorus availability, which were influenced by the diverse physical and chemical properties of biochars. Overall, maize residue biochar contributed synergistically to enhancing soil fertility, peanut yield, and quality while also promoting increased root development, a shift in the diazotrophic community and BNF.

Organic matter composition and stability in estuarine wetlands depending on soil salinity.

Coastal wetlands are key players in mitigating global climate change by sequestering soil organic matter. Soil organic matter consists of less stable particulate organic matter (POM) and more stable mineral-associated organic matter (MAOM). The distribution and drivers of MAOM and POM in coastal wetlands have received little attention, despite the processes and mechanisms differ from that in the upland soils. We explored the distribution of POM and MAOM, their contributions to SOM, and the controlling factors along a salinity gradient in an estuarine wetland. In the estuarine wetland, POM C and N were influenced by soil depth and vegetation type, whereas MAOM C and N were influenced only by vegetation type. In the estuarine wetland, SOM was predominantly in the form of MAOM (> 70 %) and increased with salinity (70 %-76 %), leading to long-term C sequestration. Both POM and MAOM increased with SOM, and the increase rate of POM was higher than that of MAOM. Aboveground plant biomass decreased with increasing salinity, resulted in a decrease in POM C (46 %-81 %) and N (52 %-82 %) pools. As the mineral amount and activity, and microbial biomass decreased, the MAOM C (2.5 %-64 %) and N pool (8.6 %-59 %) decreased with salinity. When evaluating POM, the most influential factors were microbial biomass carbon (MBC) and dissolved organic carbon (DOC). Key parameters, including MBC, DOC, soil salinity, soil water content, aboveground plant biomass, mineral content and activity, and bulk density, were identified as influencing factors for both MAOM abundance. Soil water content not only directly controlled MAOM, but together with salinity also indirectly regulated POM and MAOM by controlling microbial biomass and aboveground plant biomass. Our findings have important implications for improving the accumulation and increased stability of soil organic matter in coastal wetlands, considering the global sea level rise and increased frequency of inundation.

Impact of grassland degradation on the distribution and bioavailability of soil silicon: Implications for the Si cycle in grasslands.

Grassland ecosystems play an important role in the global terrestrial silicon (Si) cycle, and Si is a beneficial element and structural constituent for the growth of grasses. In previous decades, grasslands have been degraded to different degrees because of the drying climate and intense human disturbance. However, the impact of grassland degradation on the distribution and bioavailability of soil Si is largely unknown. Here, we investigated vegetation and soil conditions of 30 sites to characterize different degrees of degradation for grasslands in the agro-pastoral ecotone of northern China. We then explored the impact of grassland degradation on the distribution and bioavailability of soil Si, including total Si and four forms of noncrystalline Si in three horizons (0-10, 10-20 and 20-40 cm) of different soil profiles. The concentrations of noncrystalline Si in soil profiles significantly decreased with increasing degrees of degradation, being 7.35 ±â€¯0.88 mg g-1, 5.36 ±â€¯0.39 mg g-1, 3.81 ±â€¯0.37 mg g-1 and 3.60 ±â€¯0.26 mg g-1 in non-degraded, lightly degraded, moderately degraded and seriously degraded grasslands, respectively. Moreover, the storage of noncrystalline Si decreased from higher than 40 t ha-1 to lower than 23 t ha-1. The corresponding bioavailability of soil Si also generally decreased with grassland degradation. These processes may not only affect the Si pools and fluxes in soils but also influence the Si uptake in plants. We suggest that grassland degradation can significantly affect the global grassland Si cycle. Grassland management methods such as fertilizing and avoiding overgrazing can potentially double the content and storage of noncrystalline Si in soils, thereby enhancing the soil Si bioavailability by >17%.

Crude oil removal from aqueous solution using raw and carbonized Xanthoceras sorbifolia shells.

Fruit shell residue from Xanthoceras sorbifolia was investigated as a potential biosorbent to remove crude oil from aqueous solution. The shell powder and its carbonized material were compared while assessing various factors that influenced oil removal capacity. The structure and sorption mechanism were characterized using scanning electron microscopy and Fourier-transform infrared spectroscopy. The oil removal capacity of the raw material (75.1 mg g-1) was better than the carbonized material (49.5 mg g-1). The oil removal capacity increased with greater saponin content, indicating that hydrophobic and lipophilic surface characteristics of the saponins improved adsorption by the raw X. sorbifolia shell. An orthogonal experimental design was used to optimize the adsorption. Using 4 g L-1 of raw X. sorbifolia shell (particle size of < 0.15 mm), the highest crude oil removal efficiency was obtained using an initial oil concentration of 400 mg L-1, adsorption temperature of 30 °C, adsorption time of 10 min at a shaking speed of 150 rpm. The adsorption of crude oil onto X. sorbifolia shell was best described using a pseudo-second-order kinetic model. Raw X. sorbifolia shell material was more efficient than the carbonized material at crude oil removal from aqueous solution. This was attributable to the functional groups of saponins in raw X. sorbifolia shell. This study highlights that some agricultural and forest residues could be a promising source of low-cost biosorbents for oil contaminants from water-without requiring additional processing such as carbonization.