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Coastal salt marshes are sensitive to global climate change and may play an important role in mitigating global warming. To evaluate the impacts of Spartina alterniflora invasion on global warming potential (GWP) in Chinese coastal areas, we measured CH4 and N2O fluxes and soil organic carbon sequestration rates along a transect of coastal wetlands in Jiangsu province, China, including open water; bare tidal flat; and invasive S. alterniflora, native Suaeda salsa, and Phragmites australis marshes. Annual CH4 emissions were estimated as 2.81, 4.16, 4.88, 10.79, and 16.98 kg CH4 ha(-1) for open water, bare tidal flat, and P. australis, S. salsa, and S. alterniflora marshes, respectively, indicating that S. alterniflora invasion increased CH4 emissions by 57-505%. In contrast, negative N2O fluxes were found to be significantly and negatively correlated (P < 0.001) with net ecosystem CO2 exchange during the growing season in S. alterniflora and P. australis marshes. Annual N2O emissions were 0.24, 0.38, and 0.56 kg N2O ha(-1) in open water, bare tidal flat and S. salsa marsh, respectively, compared with -0.51 kg N2O ha(-1) for S. alterniflora marsh and -0.25 kg N2O ha(-1) for P. australis marsh. The carbon sequestration rate of S. alterniflora marsh amounted to 3.16 Mg C ha(-1) yr(-1) in the top 100 cm soil profile, a value that was 2.63- to 8.78-fold higher than in native plant marshes. The estimated GWP was 1.78, -0.60, -4.09, and -1.14 Mg CO2 eq ha(-1) yr(-1) in open water, bare tidal flat, P. australis marsh and S. salsa marsh, respectively, but dropped to -11.30 Mg CO2 eq ha(-1) yr(-1) in S. alterniflora marsh. Our results indicate that although S. alterniflora invasion stimulates CH4 emissions, it can efficiently mitigate increases in atmospheric CO2 and N2O along the coast of China., (© 2014 John Wiley & Sons Ltd.)

China is the world’s largest emitter of gaseous ammonia (NH 3 ), a compound that poses severe risks to human and ecosystem health. Adding biochar and inhibitors to soils has been suggested as a method to increase carbon sequestration and reduce nitrous oxide emissions, however, the effects of the amendments on NH 3 emissions are poorly understood. We conducted a field experiment to evaluate the effect of applying biochar combined with a urease inhibitor (hydroquinone, HQ) and a nitrification inhibitor (dicyandiamide, DCD) on NH 3 emissions, rice yields, and N use efficiency (NUE) during two growth seasons. Four replicates of seven treatments comprising no urea fertilizer (control), urea (N), biochar (B), urea + biochar (NB), NB + urease inhibitor (NBUI), NB + nitrification inhibitor (NBNI), and NB + urease and nitrification inhibitors (double inhibitor) (NBDI), were arranged in a randomized complete block design. Wheat straw biochar was applied once, in June 2014. Biochar in the NB treatment increased NH 3 losses by 14.1% in the first rice season ( P <  0.05), primarily due to increased pH and concentrations of NH 4 + -N in the floodwater, and decreased NH 3 losses in the second rice growth season by 6.8%, probably due to its high adsorption capacity for NH 4 + and increased nitrification. The combined application of biochar and DCD increased NH 3 losses by 47.0% and 17.2% in 2014 and 2015, respectively. The application of biochar + double inhibitors was shown to have no effect on NH 3 losses in the first rice growth season, but in the second year, NH 3 losses were reduced by 19.8% ( P <  0.05). The combination of biochar and HQ decreased NH 3 losses by 10.5–23.4% during the two growth seasons ( P <  0.05) and the addition of biochar either alone (NB), or in combination with HQ (NBUI) or double inhibitors (NBDI), increased rice yield by 7.4–16.5% and NUE from 29.4% in the N treatment (N) to 42.5%. The combined application of biochar and DCD did not have an effect on rice yield and NUE in the first year, but increased yield and NUE in the second year ( P <  0.05). Overall, our results suggest that the combination of biochar and HQ or the combined application of urease and nitrification inhibitors to soil enriched with biochar at least one year previously could be an effective practice for reducing NH 3 emissions and increasing rice yields. [ABSTRACT FROM AUTHOR]

Biochar has been widely proposed for carbon (C) sequestration, but its residual effects on soil organic C (SOC) accumulation and microbial characteristics are unknown. Herein, we investigated the content and components of organic C, and the abundance and community characteristics of microbes in a fluvo-aquic soil, after 4 years of biochar application at rates of 3, 6 and 12 t ha−1. Biochar application increased the contents of SOC and recalcitrant organic C fraction by 11.02–22.13 % and 18.41–32.31 % at 6 and 12 t ha−1, respectively, and the increased proportion for recalcitrant organic C fraction was greater than that for SOC. Among C functional groups, aryl C content was increased by 26.50–95.41 % at all rates, compared with 23.83–56.73 % for phenolic C at 6 and 12 t ha−1, and both increases were higher than that for SOC. Biochar application decreased bacterial abundance by 9.25–35.77 %, and altered bacterial community structure by increasing the relative abundance of Chloroflexi phylum, members of which have a low C mineralisation rate and strong C fixation ability. Dissolved organic C was the most critical factor of bacterial abundance and community structure. By contrast, 12 t ha−1 biochar application decreased fungal diversity by 12.45 %, and altered fungal community structure by increasing the relative abundances of Sordariomycetes and Tremellomycetes classes, both of which favoured SOC formation. The C/N ratio was the most important variable affecting fungal diversity and community structure. Overall, our results suggest that field-aged biochar, especially at a high-dose rate, accelerates organic C accumulation by increasing aryl and phenolic C functional groups of recalcitrant organic C fractions and shifting microbial communities more conducive to C sequestration in the fluvo-aquic soil. • Biochar promoted SOC accumulation by increasing aryl and phenolic C functional groups of recalcitrant organic C fractions. • Biochar decreased bacterial abundance but increased Chloroflexi phylum. • Twelve t ha−1 biochar decreased fungal diversity but increased Sordariomycetes and Tremellomycetes classes. • Dissolved organic C altered bacterial abundance and communities while C/N ratio affected fungal diversity and communities. [ABSTRACT FROM AUTHOR]

Spartina alterniflora was intentionally introduced to China in 1979 for the purpose of sediment stabilization and dike protection, and has continuously replaced native plants or invaded bare mudflats in the coastal marsh. To evaluate the spatial variation of CH 4 emission and soil organic carbon (SOC) storage along the invasion chronosequence, we selected four sites including bare mudflat (Control, as first year invasion), and marshes invaded by S. alterniflora in 2002 (SA-1), 1999 (SA-2) and 1995 (SA-3), respectively, in Sheyang county, Jiangsu, China and set up the marsh mesocosm system for flux measurement. The mean accumulation rate of SOC in the 0–30 cm layer exponentially increased with the invasion time, ranging from 1.08 (over the first 9 years) to 2.35 Mg C ha −1 yr −1 (over the period of 12–16 years). The cumulative CH 4 emission during the growth season was 20.5, 75.4, 81.0 and 92.2 kg CH 4 ha −1 in Control, SA-1, SA-2 and SA-3, respectively, and there was a binomial relationship between CH 4 emission and invasion time. Cumulative CH 4 emission was logarithmically increased with SOC concentration; however the ratio of CH 4 emission to SOC concentration was inversely correlated with the invasion time in the S. alterniflora marsh, suggesting that the less increased SOC in the S. alterniflora marsh was converted into CH 4 . The net global warming potential (GWP) was estimated at 733 kg CO 2 -eq ha −1 yr −1 in the tidal mudflat and reduced to −1273 (SA-1) to −2233 kg CO 2 -eq ha −1 yr −1 (SA-3) in the S. alterniflora marsh. Our results indicated that S. alterniflora invasion effectively sequestrated atmospheric CO 2 and mitigated GWP in the coastal marsh of China. [ABSTRACT FROM AUTHOR]

Coastal salt marshes are sensitive to global climate change and may play an important role in mitigating global warming. To evaluate the impacts of Spartina alterniflora invasion on global warming potential ( GWP) in Chinese coastal areas, we measured CH4 and N2O fluxes and soil organic carbon sequestration rates along a transect of coastal wetlands in Jiangsu province, China, including open water; bare tidal flat; and invasive S. alterniflora, native Suaeda salsa, and Phragmites australis marshes. Annual CH4 emissions were estimated as 2.81, 4.16, 4.88, 10.79, and 16.98 kg CH4 ha−1 for open water, bare tidal flat, and P. australis, S. salsa, and S. alterniflora marshes, respectively, indicating that S. alterniflora invasion increased CH4 emissions by 57-505%. In contrast, negative N2O fluxes were found to be significantly and negatively correlated ( P < 0.001) with net ecosystem CO2 exchange during the growing season in S. alterniflora and P. australis marshes. Annual N2O emissions were 0.24, 0.38, and 0.56 kg N2O ha−1 in open water, bare tidal flat and S. salsa marsh, respectively, compared with -0.51 kg N2O ha−1 for S. alterniflora marsh and −0.25 kg N2O ha−1 for P. australis marsh. The carbon sequestration rate of S. alterniflora marsh amounted to 3.16 Mg C ha−1 yr−1 in the top 100 cm soil profile, a value that was 2.63- to 8.78-fold higher than in native plant marshes. The estimated GWP was 1.78, −0.60, −4.09, and −1.14 Mg CO2eq ha−1 yr−1 in open water, bare tidal flat, P. australis marsh and S. salsa marsh, respectively, but dropped to −11.30 Mg CO2eq ha−1 yr−1 in S. alterniflora marsh. Our results indicate that although S. alterniflora invasion stimulates CH4 emissions, it can efficiently mitigate increases in atmospheric CO2 and N2O along the coast of China. [ABSTRACT FROM AUTHOR]

Nitrogen (N) and phosphorus (P) availability strongly affects carbon (C) cycling and storage in terrestrial ecosystems. Nutrient addition can increase C inputs into soil via increased above- and belowground plant productivity, but at the same time can accelerate organic matter decomposition in the soil. The mechanisms underlying these effects on soil organic C (SOC) dynamics remain unclear, especially in nutrient-limited alpine ecosystems that have been subjected to increasing N and P availability in recent decades. The aim of this study was to clarify the mechanisms underlying SOC decomposition and stabilization in an alpine grassland soil after four years of N and P additions. The soil aggregate size distribution, microbial community structure (lipid biomarkers), microbial C use efficiency (CUE) and microbial necromass composition (amino sugar biomarkers) were analyzed. Nutrient addition increased dominance of fast-growing bacteria (copiotrophs), while P addition alone intensified the competitive interactions between arbuscular mycorrhizal and saprotrophic fungi. These changes led to decreases in the microbial CUE of glucose by 1.6–3.5% and of vanillin by 8.5%, and therefore, reduced SOC content in the topsoil. The total microbial necromass remained unaffected by nutrient addition, but the contribution of fungal necromass to SOC increased. The increased abundance of arbuscular mycorrhizal fungi and fungal necromass under elevated N availability raised the mass proportion of soil macroaggregates (>250 μm) by 16.5–20.3%. Therefore, fungi were highly involved in macroaggregation following N addition, and so, moderated the SOC losses through enhanced physical protection. Overall, the complex interactions between microbial physiology (CUE), necromass composition (amino sugars) and physical protection (macroaggregation) in mediating SOC dynamics in response to nutrient enrichment were disentangled to better predict the capability of alpine grassland soils to act as a C sink or source under global change. • Four-year nutrient addition reduced C sequestration in topsoil of alpine grassland. • Nutrient addition lowered microbial glucose CUE, P alone lowered vanillin CUE. • Nutrient addition increased contribution of fungal necromass to SOC. • N addition increased macroaggregation but P addition alone did not. • Macroaggregate proportion was correlated with AMF abundance and fungal necromass. [ABSTRACT FROM AUTHOR]