Meta-analysis shows the impacts of ecological restoration on greenhouse gas emissions.

International initiatives set ambitious targets for ecological restoration, which is considered a promising greenhouse gas mitigation strategy. Here, we conduct a meta-analysis to quantify the impacts of ecological restoration on greenhouse gas emissions using a dataset compiled from 253 articles. Our findings reveal that forest and grassland restoration increase CH4 uptake by 90.0% and 30.8%, respectively, mainly due to changes in soil properties. Conversely, wetland restoration increases CH4 emissions by 544.4%, primarily attributable to elevated water table depth. Forest and grassland restoration have no significant effect on N2O emissions, while wetland restoration reduces N2O emissions by 68.6%. Wetland restoration enhances net CO2 uptake, and the transition from net CO2 sources to net sinks takes approximately 4 years following restoration. The net ecosystem CO2 exchange of the restored forests decreases with restoration age, and the transition from net CO2 sources to net sinks takes about 3-5 years for afforestation and reforestation sites, and 6-13 years for clear-cutting and post-fire sites. Overall, forest, grassland and wetland restoration decrease the global warming potentials by 327.7%, 157.7% and 62.0% compared with their paired control ecosystems, respectively. Our findings suggest that afforestation, reforestation, rewetting drained wetlands, and restoring degraded grasslands through grazing exclusion, reducing grazing intensity, or converting croplands to grasslands can effectively mitigate greenhouse gas emissions.

Effects of drought and nutrient deficiencies on the allocation of recently fixed carbon in a plant-soil-microbe system.

Carbon (C) allocation plays an important role in plant adaptation to water and nutrient stresses. However, the effects of drought and nutrient deficiencies on the allocation of recently fixed C in the plant-soil-microbe system remain largely unknown. Herein, we studied the response of C allocation of Sophora moorcroftiana (an indigenous pioneer shrub in Tibet) to drought, nitrogen (N) deficiency and phosphorus (P) deficiency using a microcosm experiment. The 13CO2 continuous labeling was used to trace C allocation in the plant-soil-microbe system. We found that drought significantly reduced plant 13C, but it increased 13C accumulation in soil. The decreased plant 13C under drought was attributed to the decrease of 13C in stem and root rather than that in leaf. The excess 13C fraction in the microbial biomass (MB13C) was reduced by N deficiency, but it was not affected by the combination of drought and N deficiency, indicating that drought weakened the effects of N deficiency on MB13C. By contrast, MB13C increased under the combination of drought and P deficiency, suggesting that drought enhanced the effects of P deficiency on MB13C. Drought and nutrient deficiencies regulated the belowground 13C allocation. Specifically, drought and P deficiency increased the allocation of 13C to root and N deficiency regulated the allocation of 13C to microbial biomass C and dissolved organic C in soil. Notably, soil 13C decreased with increasing plant 13C, while MB13C first decreased and then increased with increasing plant 13C. Overall, our study demonstrated that drought and nutrient deficiencies interactively affected C allocation in a plant-soil-microbe system and provided insights into C allocation strategies in response to multiple resource (water and nutrient) stresses under environmental changes.

Organic amendments improved soil quality and reduced ecological risks of heavy metals in a long-term tea plantation field trial on an Alfisol.

Tea plantation can cause strong soil degradation, e.g. acidification, basic nutrient decrease and microbial diversity loss, naturally by its root activity and secondary by practically tremendous synthetic N input. Organic amendments application is considered a practical way to mitigate the above adverse consequence. However, the trade-off between agronomic and environmental effects on the application of the organic amendments is still under debate. Herein, we conducted a long-term field experiment with four treatments, including control (without and fertiliser) (CK), chemical fertiliser treatment (CF), chicken manure treatment (CM) and chicken manure combined with biochar treatment (CMB) to investigate the effects of organic amendments application on soil quality, heavy metal contamination and tea production in a tea plantation. Totally 16 plots were arranged randomly with a completely randomised design. The results showed that CM and CMB treatments improved soil nutrient, mitigated soil acidification and ameliorated soil porosity compared to CF treatment. CMB treatment displayed a relatively high tea yield and quality in three consecutive years of monitoring. However, CM and CMB treatments elevated the heavy metal (HM) potential ecological risk (RI) and Nemerow's composite index (Ps). CM treatment significantly increased available As, Pb, Cu and Zn concentrations compared to CF treatment, while CMB treatment significantly decreased available Cr and Cu concentrations and slightly decreased available Cd, Pb and Ni concentrations compared to CM treatment. But the increase of available As and Zn in CMB treatment compared to CM treatment also indicated adverse effects of biochar addition. The PLS-PM model showed HM risk had direct negative effects on tea quality. Moreover, soil fungal community revealed positive effects on tea yield and negative effects on tea quality. Overall, our study proved that CMB treatment could improve soil quality, reduce available Cr and Ni concentrations, maintain tea yield and increase tea quality.

Long-Term Compost Amendment Spurs Cellulose Decomposition by Driving Shifts in Fungal Community Composition and Promoting Fungal Diversity and Phylogenetic Relatedness.

Cellulose is the most abundant polysaccharide in plant biomass and an important precursor of soil organic matter formation. Fungi play a key role in carbon cycling dynamics because they tend to decompose recalcitrant materials. Here, we applied [12C]cellulose and [13C]cellulose to distinguish the effects of application of compost, nitrogen-phosphorus-potassium (NPK) fertilizer, and no fertilizer (control) for 27 years upon cellulose decomposition via RNA-based stable isotope probing (RNA-SIP). The loss ratio of added cellulose C in compost soil was 67.6 to 106.7% higher than in NPK and control soils during their 20-day incubation. Dothideomycetes (mainly members of the genus Cryptococcus) dominated cellulose utilization in compost soil, whereas the copiotrophic Sordariomycetes were more abundant in NPK and unfertilized soils. Compared with NPK and control soils, compost application increased the diversity of 13C-assimilating fungi. The 13C-labeled fungal communities in compost soil were more phylogenetically clustered and exhibited greater species relatedness than those in NPK and control soils, perhaps because of stringent filtering of narrow-spectrum organic resources and biological invasion originating from added compost. These changes led to an augmented decomposition capacity of fungal species for cellulose-rich substrates and reduced cellulose C sequestration efficiency. The RNA-SIP technique is more sensitive to responses of fungi to altered soil resource availability than DNA-SIP. Overall, long-term compost application modified fungal community composition and promoted fungal diversity and phylogenetic relatedness, accelerating the decomposition of substrate cellulose in soil. This work also highlights the RNA-SIP technique's value for comprehensively assessing the contributions of active fungi to the substrate decomposition process. IMPORTANCE Cellulose is a very rich component in plant biomass and an important precursor of soil organic matter formation. Fungal communities are known to be important drivers of organic carbon accumulation in arable soils. However, current understanding of responses of fungal species to cellulose amendment and the contributions of active fungi to substrate decomposition process is still very superficial. Here, we established a [13C]cellulose microcosm experiment with soils subjected to long-term application of compost, nitrogen-phosphorus-potassium (NPK) fertilizer, and no fertilizer (control). The novel 13C-RNA-SIP technique with subsequent high-throughput sequencing was used to investigate the linkages between active fungal taxa and cellulose decomposition. Our study demonstrated that Dothideomycetes dominated cellulose utilization in compost soil, whereas the copiotrophic Sordariomycetes were more enriched in both NPK and unfertilized soils. We also found that the compost amendment promoted fungal diversity and phylogenetic relatedness and strengthened the decomposition capacity of fungi for cellulose-rich substrates by enhancing synergistic interactions, thereby reducing cellulose C sequestration efficiency. Overall, our research has implications for our understanding of the role of active fungi in cellulose C transformation in soils undergoing different types of long-term nutrient management.

Combined biochar and double inhibitor application offsets NH3 and N2O emissions and mitigates N leaching in paddy fields.

The effects of combined biochar and double inhibitor application on gaseous nitrogen (N; nitrous oxide [N2O] and ammonia [NH3]) emissions and N leaching in paddy soils remain unclear. We investigated the effects of biochar application at different rates and double inhibitor application (hydroquinone [HQ] and dicyandiamide [DCD]) on NH3 and N2O emissions, N leaching, as well as rice yield in a paddy field, with eight treatments, including conventional urea N application at 280 kg N ha-1 (CN); reduced N application at 240 kg N ha-1 (RN); RN + 7.5 t ha-1 biochar (RNB1); RN + 15 t ha-1 biochar (RNB2); RN + HQ + DCD (RNI); RNB1 + HQ + DCD (RNIB1); RNB2 + HQ + DCD (RNIB2); and a control without N fertilizer. When compared with N leaching under RN, biochar application reduced total N leaching by 26.9-34.8% but stimulated NH3 emissions by 13.2-27.1%, mainly because of enhanced floodwater and soil NH4+-N concentrations and pH, and increased N2O emission by 7.7-21.2%, potentially due to increased soil NO3--N concentrations. Urease and nitrification inhibitor addition decreased NH3 and N2O emissions, and total N leaching by 20.1%, 21.5%, and 22.1%, respectively. Compared with RN, combined biochar (7.5 t ha-1) and double inhibitor application decreased NH3 and N2O emissions, with reductions of 24.3% and 14.6%, respectively, and reduced total N leaching by up to 45.4%. Biochar application alone or combined with double inhibitors enhanced N use efficiency from 26.2% (RN) to 44.7% (RNIB2). Conversely, double inhibitor application alone or combined with biochar enhanced rice yield and reduced yield-scaled N2O emissions. Our results suggest that double inhibitor application alone or combined with 7.5 t ha-1 biochar is an effective practice to mitigate NH3 and N2O emission and N leaching in paddy fields.

Effect of field-aged biochar on fertilizer N retention and N2O emissions: A field microplot experiment with 15N-labeled urea.

Biochar application is thought to improve crop yield and reduce N leaching and gas emissions; however, little is known about how field-aged biochar affects fertilizer N retention and N2O emissions. Here, a field microplot experiment is established in the North China Plain at maize season by applying 15N-labeled urea to the sandy loam soil both with (Biochar) and without (Control) application of 3-year field-aged biochar at 12 t ha-1. Overall, 25.6-26.2% of the urea N was taken up by maize aboveground biomass, field-aged biochar did not affect yield or fertilizer N recovery efficiency. After maize harvest, the residual ratio of applied N in the soil profile (0-40 cm) was 21.6 and 20.3% under Control and Biochar treatment, respectively, with an increase of 10.2% in the topsoil (0-20 cm) and decrease of 37.2% in the subsoil (20-40 cm) following biochar amendment, probably due to reduced NO3- leaching. Cumulative N2O emissions and urea N-induced N2O emissions under Control treatment were 2.06 and 0.78 kg N ha-1, and significantly decreased to 1.89 and 0.74 kg N ha-1 after Biochar treatment, respectively. N2O emissions derived from the applied N accounted for 38.0 and 39.4% of the total emissions under Control and Biochar treatment, respectively. N2O emissions from decomposition of soil organic N induced by the priming effect of the applied N was 0.69 and 0.56 kg N ha-1 under Control and Biochar treatment, respectively, contributing 33.7 and 29.7% of the total emissions. Overall, our results suggest that field-aged biochar increased the retention of fertilizer N in the topsoil by reducing NO3- leaching, while effectively reduced N2O emissions from fertilizer N and mineralization of organic N in the sandy loam soil.

Methane and nitrous oxide have separated production zones and distinct emission pathways in freshwater aquaculture ponds.

Aquaculture systems receive intensive carbon (C) and nitrogen (N) loadings, and are therefore recognized as major anthropogenic sources of methane (CH4) and nitrous oxide (N2O) emissions. However, the extensively managed aquaculture ponds were identified as a hotspot of CH4 emission but just a weak N2O source. Here, we investigate annual CH4 and N2O fluxes from three earthen ponds used for crab culture, of different sizes, in southeast China. Our purposes are to identify the spatiotemporal variations of CH4 and N2O emissions and their components among ponds and to evaluate the zone for CH4 and N2O production. Static chamber-measured CH4 flux ranged from 0.03 to 64.7 mg CH4 m‒2 h‒1 (average: 9.02‒14.3 mg CH4 m‒2 h‒1), and temperature, followed by dissolved organic C (DOC) concentration, and redox potential, were the primary drivers of seasonal CH4 flux patterns. Annual mean diffusive CH4 flux was 1.80‒2.34 mg CH4 m‒2 h‒1, and that by ebullition was up to 7.20‒12.0 mg CH4 m‒2 h‒1 (79.1‒83.5% of the total CH4 flux). Annual CH4 emission was positively correlated with sediment DOC concentration but negatively (P < 0.05) correlated with water depth across ponds, with the highest CH4 emission occurred in a pond with low water depth and high DOC concentration. The calculated diffusive N2O flux by the gas transfer velocity was 0.32‒0.60 times greater than the measured N2O emission, suggesting that N2O in water column can not only evade as water-air fluxes but diffuse downwards and to be consumed in anaerobic sediments. This also indicates that N2O was primarily produced in water column. The highly reduced condition and depletion of NO3‒-N in sediments, can limit N2O production from both nitrification and denitrification but favor N2O consumption, leading the ponds to become a weak source of N2O annually and even a sink of N2O in summer. Our results highlight that the current global CH4 budget for inland waters is probably underestimated due to a lack of data and underestimation of the contribution of ebullitive CH4 flux in small lentic waters. The downwards N2O diffusion from the water column into sediment also indicates that the extensively-used model approach based on gas transfer velocity potentially overestimates N2O fluxes, especially in small eutrophic aquatic ecosystems.

Combined application of biochar with urease and nitrification inhibitors have synergistic effects on mitigating CH4 emissions in rice field: A three-year study.

Biochar and inhibitors applications have been proposed for mitigating soil greenhouse gas emissions. However, how biochar, inhibitors and the combination of biochar and inhibitors affect CH4 emissions remains unclear in paddy soils. The objective of this study was to explore the effects of biochar application alone, and in combination with urease (hydroquinone) and nitrification inhibitors (dicyandiamide) on CH4 emissions and yield-scaled CH4 emissions during three rice growing seasons in the Taihu Lake region (Suzhou and Jurong), China. In Suzhou, N fertilization rates of 120-280 kg N ha-1 increased CH4 emissions compared to no N fertilization (Control) (P < 0.05), and the highest emission was observed at 240 kg N ha-1, possibly due to the increase in rice-derived organic carbon (C) substrates for methanogens. Biochar amendment combined with N fertilization reduced CH4 emissions by 13.2-27.1% compared with optimal N (ON, Suzhou) and conventional N application (CN-J, Jurong) (P < 0.05). This was related to the reduction in soil dissolved organic C and the increase in soil redox potential. Addition of urease and nitrification inhibitor (ONI) decreased CH4 emissions by 15.7% compared with ON treatment. Combined application of biochar plus urease, nitrification and double inhibitors further decreased CH4 emissions by 22.2-51.0% compared with ON and CN-J treatment. ON resulted in the highest yield-scaled CH4 emissions, while combined application of biochar alone and in combination with the inhibitors decreased yield-scaled CH4 emissions by 12.7-54.9% compared with ON and CN-J treatment (P < 0.05). The lowest yield-scaled CH4 emissions were observed under combined application of 7.5 t ha-1 biochar with both urease and nitrification inhibitors. These findings suggest that combined application of biochar and inhibitors could mitigate total CH4 and yield-scaled CH4 emissions in paddy fields in this region.

Nitrous oxide emissions from China's croplands based on regional and crop-specific emission factors deviate from IPCC 2006 estimates.

Calculated N2O emission factors (EFs) of applied nitrogen (N) fertilizer are currently based upon a single, universal value advocated by the IPCC (Inter-governmental Panel on Climate Change) even though EFs are thought to vary with climate and soil types. Here, we compiled and analyzed 151 N2O EF values from agricultural fields across China. The EF of synthetic N applied to these croplands was 0.60%, on average, but differed significantly among six climatic zones across the country, with the highest EF found in the north subtropical zone for upland fields (0.93%) and the lowest in the middle subtropical zone for paddy fields (0.20%). Precipitation and soil pH, which showed non-linear relationships with EF, are among the factors governing it, explaining 7.0% and 8.0% of the regional variation in EFs, respectively. Annual precipitation was the key factor regulating N2O emissions from synthetic N fertilizers. Among crop types, legume crops had the highest EFs, which were significantly (P < 0.05) higher than those of cereals. Total soil N2O emissions from fertilized croplands with maize, rice, wheat, and vegetables in China, calculated using the climatic zone (regional) EFs, were estimated to be 239 Gg N yr-1 with an uncertainty of 21%. Importantly, this value was substantially (33%) lower than that (357 Gg N yr-1) derived from the IPCC default EF but close to the 253 Gg N yr-1 estimated using crop-specific EFs. N2O emissions from applied synthetic N fertilizer accounted for 66.5% of the total annual N2O emissions from China's maize, rice, wheat and vegetable fields. Taken together, our study's results strongly suggest that regional EFs should be included for accurate N2O inventories from croplands across China.

Effects of application of inhibitors and biochar to fertilizer on gaseous nitrogen emissions from an intensively managed wheat field.

The effects of biochar combined with the urease inhibitor, hydroquinone, and nitrification inhibitor, dicyandiamide, on gaseous nitrogen (N2O, NO and NH3) emissions and wheat yield were examined in a wheat crop cultivated in a rice-wheat rotation system in the Taihu Lake region of China. Eight treatments comprised N fertilizer at a conventional application rate of 150kgNha-1 (CN); N fertilizer at an optimal application rate of 125kgNha-1 (ON); ON+wheat-derived biochar at rates of 7.5 (ONB1) and 15tha-1 (ONB2); ON+nitrification and urease inhibitors (ONI); ONI+wheat-derived biochar at rates of 7.5 (ONIB1) and 15tha-1 (ONIB2); and, a control. The reduced N fertilizer application rate in the ON treatment decreased N2O, NO, and NH3 emissions by 45.7%, 17.1%, and 12.3%, respectively, compared with the CN treatment. Biochar application increased soil organic carbon, total N, and pH, and also increased NH3 and N2O emissions by 32.4-68.2% and 9.4-35.2%, respectively, compared with the ON treatment. In contrast, addition of urease and nitrification inhibitors decreased N2O, NO, and NH3 emissions by 11.3%, 37.9%, and 38.5%, respectively. The combined application of biochar and inhibitors more effectively reduced N2O and NO emissions by 49.1-49.7% and 51.7-55.2%, respectively, compared with ON and decreased NH3 emission by 33.4-35.2% compared with the ONB1 and ONB2 treatments. Compared with the ON treatment, biochar amendment, either alone or in combination with inhibitors, increased wheat yield and N use efficiency (NUE), while addition of inhibitors alone increased NUE but not wheat yield. We suggest that an optimal N fertilizer rate and combined application of inhibitors+biochar at a low application rate, instead of biochar application alone, could increase soil fertility and wheat yields, and mitigate gaseous N emissions.