Organic pulses and bacterial invasion alleviated by the resilience of soil microbial community.

Biogas slurry is a nutrient-rich secondary product of livestock feces digestion which is recycled as a crop plantation fertilizer and provides exogenous microbes to the soil. However, the effects of biogas slurry microbes on the soil resident community remain unknown. In this study, we examined the ecological consequences of long-term biogas slurry pulse on the soil resident community and found that it promoted crop yield and altered soil characteristics. The soil microbial ecosystem was altered as a result of organic amendments due to the exogenous input of microbes and nutrients. Nevertheless, the soil resident communities were highly resilient to long-term organic pulses, as evidenced by community diversity and composition. The two dominant bacterial species in biogas slurry were Sterolibacterium and Clostridium. Notably, the abundance of Clostridium in biogas slurry increased following long-term amendments, while other species such as GP1 and Subdivision3_genera_incertae_sedis decreased; which was consistent with the results of module-eigengene analysis. Long-term organic pulses shifted the balance of microbial community assembly from stochastic to deterministic processes. Overall, our findings indicated that organic pulses accompanied with bacterial invasion could be alleviated by the resilience of soil microbial communities, thereby emphasizing the importance of microbiota assemblage and network architecture.

Revealing horizontal and vertical variation of soil organic carbon, soil total nitrogen and C:N ratio in subtropical forests of southeastern China.

Soil organic carbon (SOC) and total nitrogen (STN) are crucial soil quality indicators in a forest ecosystem. Their cycling processes and interactions have a key impact on the plants productivity, potential carbon sequestration and stability of the terrestrial ecosystem. In this study, soil profile samples (0-100 cm) were collected from 906 plots of typical subtropical forest in Zhejiang Province, southeastern China. Moran's I, geostatistics and geographic information system (GIS) techniques were used to study the vertical and horizontal heterogeneity of SOC, STN and C:N ratio. The results indicated that the contents of SOC and STN clearly decreased with the soil depth increasing (from 0 to 10 cm layer to 60-100 cm layer). The spatial distributions of SOC and STN were consistent with the topography, showing a decreasing trend from southwest to northeast of Zhejiang Province. The results of ANOVA and correlation analyses indicated that the dominant tree species, elevation and Normalized Difference Vegetation Index (NDVI) were the key factors affecting SOC and STN contents. For the total 0-100 cm soil layer, the mean densities of SOC and STN were 108.53 Mg ha-1 and 0.08 Mg ha-1, respectively. The total stocks of SOC and STN were 877.19 Tg and 84.42 Tg. Approximately 65% SOC and 45% STN were belonged to the upper 30 cm soil layer, which was strongly related to the actual soil thickness. The results could provide critical information for forestry and environmental management related to C and N accumulations in subtropical forests of China.

Spatial distribution and variability of carbon storage in different sympodial bamboo species in China.

Selection of tree species is potentially an important management decision for increasing carbon storage in forest ecosystems. This study investigated and compared spatial distribution and variability of carbon storage in 8 sympodial bamboo species in China. The results of this study showed that average carbon densities (CDs) in the different organs decreased in the order: culms (0.4754 g g(-1)) > below-ground (0.4701 g g(-1)) > branches (0.4662 g g(-1)) > leaves (0.4420 g g(-1)). Spatial distribution of carbon storage (CS) on an area basis in the biomass of 8 sympodial bamboo species was in the order: culms (17.4-77.1%) > below-ground (10.6-71.7%) > branches (3.8-11.6%) > leaves (0.9-5.1%). Total CSs in the sympodial bamboo ecosystems ranged from 103.6 Mg C ha(-1) in Bambusa textilis McClure stand to 194.2 Mg C ha(-1) in Dendrocalamus giganteus Munro stand. Spatial distribution of CSs in 8 sympodial bamboo ecosystems decreased in the order: soil (68.0-83.5%) > vegetation (16.8-31.1%) > litter (0.3-1.7%). Total current CS and biomass carbon sequestration rate in the sympodial bamboo stands studied in China is 93.184 × 10(6) Mg C ha(-1) and 8.573 × 10(6) Mg C yr(-1), respectively. The sympodial bamboos had a greater CSs and higher carbon sequestration rates relative to other bamboo species. Sympodial bamboos can play an important role in improving climate and economy in the widely cultivated areas of the world.

[Spatial and Temporal Scale Effects of Landscape Pattern on Riverine Nitrogen and Phosphorus Nutrients in the Qingshan Lake Watershed].

The influences of landscape pattern on water quality are dependent on spatial-temporal scales. However, the effects of landscape composition, landscape configuration, and landscape slope metrics on seasonal water quality at different spatial scales remain unclear. Based on the total nitrogen, total phosphorus, nitrate-N, and ammonium-N data from 26 sampling sites in the Qingshan Lake watershed, this study coupled landscape pattern analysis, redundancy analysis, and partial redundancy analysis to quantify the spatiotemporal scale effects of landscape pattern on riverine nitrogen （N） and phosphorus （P） concentrations. The results showed that： ① The explanatory ability of landscape pattern at the sub-watershed scale on riverine N and P concentrations was 6.8%-8.4% higher than that at the buffer scale, and this effect was more obvious in the dry season. ② At the sub-watershed scale, the percentage of forestland and the interspersion and juxtaposition degree of residential land had a greater influence on riverine N and P concentrations. At the buffer scale, the slope of farmland and residential land and the aggregation degree of forestland patches were the key factors affecting riverine N and P concentrations. ③ The contribution rate of landscape configuration to riverine N and P concentration variations （20.1%-36.5%） was the highest. The sensitivity of the effect of landscape configuration on riverine N and P concentrations to seasonal changes was the highest, and the effect of landscape slope on riverine N and P concentrations had the highest sensitivity to spatial scale changes. Therefore, landscape pattern-regulated non-point source pollution should be considered from a multi-scale perspective. These results can provide scientific basis for the formulation of landscape pattern optimization measures aiming at non-point source pollution control.

Combination system of full-scale constructed wetlands and wetland paddy fields to remove nitrogen and phosphorus from rural unregulated non-point sources.

Constructed wetlands (CWs) have been used effectively to remove nitrogen (N) and phosphorus (P) from non-point sources. Effluents of some CWs were, however, still with high N and P concentrations and remained to be pollution sources. Widely distributed paddy fields can be exploited to alleviate this concern. We were the first to investigate a combination system of three-level CWs with wetland paddy fields in a full scale to remove N and P from rural unregulated non-point sources. The removal efficiencies (REs) of CWs reached 57.3 % (37.4-75.1 %) for N and 76.3 % (62.0-98.4 %) for P. The CWs retained about 1,278 kg N ha(-1) year(-1) and 121 kg P ha(-1) year(-1). There was a notable seasonal change in REs of N and P, and the REs were different in different processing components of CWs. The removal rates of wetland paddy fields adopt "zero-drainage" water management according to local rainfall forecast and physiological water demand of crop growth reached 93.2 kg N ha(-1) year(-1) and 5.4 kg P ha(-1) year(-1). The rice season had higher potential in removing N and P than that in the wheat season. The whole combined system (0.56 ha CWs and 5.5 ha wetland paddy fields) removed 1,790 kg N year(-1) and 151 kg P year(-1), which were higher than those from CWs functioned alone. However, another 4.7-ha paddy fields were needed to fully remove the N and P in the effluents of CWs. The combination of CWs and paddy fields proved to be a more efficient nutrient removal system.

[Classification and Identification of Non-point Source Nitrogen Pollution in Surface Flow of the Shangwu River Watershed in the Qiandao Lake Region].

Accurate quantification of non-point source pollution is an important step for non-point source pollution control and management at the watershed scale. Considering the non-point source pollution from baseflow, an improved export coefficient model (IECM) on a weekly scale was established based on the traditional export coefficient model (ECM), which was then used to estimate the surface flow non-point source total nitrogen (TN) loads contributed by different land use types of the Shangwu River watershed in the Qiandao Lake Region. The results showed that IECM performed well for the predictions of TN loads in the studied watershed, with the Nash-Sutcliffe efficiency coefficient (NSE) and R2values of 0.82 and 0.77 (P<0.01) for the calibration period and 0.87 and 0.84 (P<0.01) for the validation period, respectively. The IECM estimated TN exports through surface flow and baseflow were 5.74 kg·(hm2·a)-1and 9.85 kg·(hm2·a)-1 from the Shangwu River watershed in the period of Nov. 2020 to Oct. 2021, which accounted for 36.80% and 63.20% of the corresponding streamflow TN load, respectively. Without consideration of the baseflow non-point source TN pollution, the ECM-estimated surface flow TN loading was 54.21% higher than that estimated by IECM. Obviously, attributing baseflow non-point source pollution to surface flow directly would lead to a serious load overestimation of surface flow. According to IECM, the estimated TN export intensity through surface flow from paddy fields, grasslands, woodlands, rainfed croplands, and residential lands was 10.95, 5.42, 5.20, 12.34, and 2.77 kg·(hm2·a)-1, respectively, which accounted for 5.80%, 4.00%, 26.55%, 0.38%, and 0.03% of the corresponding total streamflow TN loads. Therefore, the future management of non-point source nitrogen pollution in the studied watershed should focus mainly on the prevention and management of groundwater non-point source pollution and control of load export from surface flow on cultivated land (paddy fields and rainfed croplands).

Enhancement of phytolith-occluded carbon accumulation of Moso bamboo response to temperatures elevation and different fertilization.

The accumulation of phytolith-occluded carbon (PhytOC) in Moso bamboo could be a novel long-term carbon sequestration strategy. The objective of this study was to investigate the effects of temperature change and different fertilization on PhytOC accumulation. The pot experiment was established with different fertilization (including control (CK), nitrogen fertilizers (N), silicon fertilizers (Si), and a combination of nitrogen and silicon (NSi)) under high- and low-temperature. Despite the different fertilization, the PhytOC accumulation of the high-temperature group increases by 45.3% on average compared with the low-temperature group, suggesting higher temperature is greatly beneficial to the PhytOC accumulation. Fertilization significantly increases the accumulation of PhytOC (increased by 80.7% and 48.4% on average for the low- and high-temperature group, respectively) compared with CK. However, the N treatment increased both Moso bamboo biomass and PhytOC accumulation. The difference in the accumulation of PhytOC in Si and NSi was insignificant, indicating the combination of N and Si didn't bring extra benefit to PhytOC accumulation compared to Si fertilizer alone. These results indicated the application of nitrogen fertilizer is a practical and effective method for enhancing long-term carbon sequestration for Moso bamboo. Based on our study, we conclude that global warming poses a positive effect on promoting the long-term carbon sequestration of Moso bamboo.

Mechanistic insights into the selective adsorption of phosphorus from wastewater by MgO(100)-functionalized cellulose sponge.

Metal oxides have remained state-of-the-art adsorbents for recovering phosphorus from aqueous solutions, but their practical application is still limited by their unsatisfactory adsorption capacities and selectivities in wastewater. Here, using MgO as a model metal oxide, the strategy of employing porous cellulose sponge to support metal oxides featuring exposed specific crystal facets was proposed to develop promising phosphate adsorbents. The phosphate adsorption isotherms and kinetics were measured and the phosphate adsorption mechanism was explored. The results show that cellulose sponge-supported MgO(100) (C-MgO(100)) has a saturation capacity of 28.3 mg P/g, over ten times higher than MgO(100) particles. Importantly, the phosphate adsorption properties of C-MgO(100) are almost not affected in wastewater, demonstrating its exceptional selectivity for phosphate adsorption. In contrast, the saturation capacity of MgO(111)-functionalized cellulose sponge is obviously declined in wastewater. Experimental together with theoretical analyses indicate that phosphate is chemically adsorbed on C-MgO(100) with obvious electrons transfer from the p-orbital of phosphate, and the adsorption energy of C-MgO(100) towards phosphate is maintained in the presence of coexisting anions. Ultimately, regeneration experiments reveal that a regenerant formulation composed of KOH (wt.1 %) and tap water is suitable for the regeneration of C-MgO(100) with >82.6 % phosphate desorption efficiencies after 5 cycles, further confirming its potential in practical application for the treatment of real water.

Controls for phytolith accumulation in Moso bamboo leaves across China.

Phytoliths are amorphous silica formed gradually in plant tissue, which have great potential to mitigate climate change due to their resistance to decomposition and their ability to occlude organic carbon. The accumulation of phytoliths is regulated by multiple factors. However, the factors controlling its accumulation remain unclear. Here, we investigated phytolith content in Moso bamboo leaves of different ages collected from 110 sampling sites of their main distribution regions across China. The controls for phytolith accumulation were studied by correlation and random forest analyses. Our results showed that phytolith content is leaf age-dependent (16-month-old leaf >4-month-old leaf >3-month-old leaf). Phytolith accumulation rate in Moso bamboo leaves is significantly correlated with mean monthly temperature (MMT) and mean monthly precipitation (MMP). About 67.1 % of the variance of the phytolith accumulation rate could be explained by multiple environmental factors, mainly MMT and MMP. Therefore, we conclude that the weather is the major driver that regulates the phytolith accumulation rate. Our study provides a unique dataset for estimating phytolith production rate and the potential carbon sequestration of phytolith through climatic factors.

Core-shell P-laden biochar/ZnO/g-C3N4 composite for enhanced photocatalytic degradation of atrazine and improved P slow-release performance.

Technologies that can effectively address the environmental issues arisen from the use of agrochemicals and P fertilizers are needed for the development of green agriculture. Here, we reporta new core-shell P-laden biochar/ZnO/g-C3N4 composite (Pbi-ZnO-g-C3N4) used both as an efficient photocatalyst for degrading atrazine and a promising slow-release fertilizer for improving the P utilization efficiency. In comparison with P-laden biochar/ZnO (Pbi-ZnO), Pbi-ZnO-g-C3N4 exhibits enhanced photocatalytic activity with the maximum atrazine degradation efficiency of 85.3% after 260 min. Pbi-ZnO-g-C3N4 also shows superior P slow-release performance with the cumulative P release concentration of 216.40 g/L in 260 min. Besides, it is found that the coating of g-C3N4 on the surface of Pbi-ZnO improves the utilization of visible light and separation of photoinduced electron-hole pairs, producing more radicals (•OH and •O2-) under visible light irradiation. The mechanistic study reveals that Z-shaped heterojunction is formed between ZnO and g-C3N4 in Pbi-ZnO-g-C3N4, and biochar serves as an electron-transfer bridge that promotes the separation of electron-hole pairs. Finally, pot experiments reveal that the P utilization efficiency for pepper seedlings fertilized by Pbi-ZnO-g-C3N4 is higher than that by Pbi-ZnO. The application of Pbi-ZnO-g-C3N4 is beneficial for the growth of native soil microorganism.

Resilience of soil microbial metabolic functions to temporary E. coli invasion.

Due to the globalization and increasing human activities, there is a significant increase in bacterial invasions to the soil ecosystems. Soil resident communities are vulnerable to bacterial invasion and suffered legacy effects after unsuccessful invasion. However, whether such changes in the soil ecosystems are permanent or temporary remains unclear. Here, we investigated the functional resilience of soil ecosystems to bacterial invasion and intensive managements. We used Escherichia coli O157:H7 (E. coli) as model strain examined the soil microbial metabolic functions, including enzyme activities, nitrogen and carbon use efficiency, community niche, and carbon metabolic potential, as well as soil physicochemical properties and microbial invader survival in 8 soil samples, 4 from natural hardwood forests and 4 from intensively managed Moso bamboo forests. The results showed that soil ecosystems were not resistant to E. coli invasion regardless of the intensity of management, which the finding was significantly reflected in the nutrient-acquiring activities or carbon utilization, or both. Besides, the invasion legacy effect (the effect after invader apoptosis) was positively related to E. coli survival time. However, most of the metabolic functions could recover almost to the initial state after 135 days of incubation, suggesting a strong recovery capacity of the soil ecosystems. These data indicate that E. coli invasion has a legacy effect on the functions of soil resident communities. However, soil ecosystems are highly resilient even under intensive human management.

[Effects of Nitrogen Fertilizer Management on CH4 and N2O Emissions in Paddy Field].

Methane (CH4) and nitrous oxide (N2O) are two extremely important greenhouse gases in the atmosphere. Nitrogen fertilizer is an important factor affecting CH4 and N2O emissions in rice fields. Rational application of nitrogen fertilizer can not only promote high yields of rice but also reduce greenhouse gas emissions. Existing studies have shown that nitrogen reduction and optimal application can effectively improve the nitrogen use efficiency of rice on the basis of ensuring the yield and reduce the loss of N2O caused by nitrification and denitrification of excessive nitrogen in soil. Fertilization times and fertilizer types have significant effects on CH4 and N2O emissions in paddy fields. In this study, a field experiment was conducted for two consecutive years (2019-2020) to study the effects of fertilizer application on CH4 and N2O emissions from rice fields by setting up four treatments consisting of no fertilizer (CK), customary fertilizer application by farmers (CF), twice fertilizer (TT), and 20% replacement of chemical fertilizer by organic fertilizer (OF) using static chamber-gas chromatography. Additionally, the effect of integrating rice yield and integrated global warming potential (GWP) on the greenhouse gas emission intensity (GHGI) per unit of rice yield was analyzed to explore fertilizer application for yield increase and emission reduction in a typical rice growing area in the middle and lower reaches of Yangtze River. The results showed that:① compared with those of CK, the fertilizer treatments reduced CH4 emissions by 14.6%-25.1% and increased N2O emissions by 610%-1836% in both years; ② compared with those of CF, both the TT and OF treatments showed a trend of increasing CH4 emissions and reducing N2O emissions. CH4 emissions increased by 1.8% (P>0.05) and 14.0% (P<0.05), respectively. The annual average of N2O emissions decreased by 63.3% (P<0.05) and 49.2% (P<0.05) in both the TT and OF treatments, respectively. ③ Compared with that of CK, both fertilizer applications increased rice yield and reduced GHGI; compared with that of CF, the OF and TT treatments increased the average annual rice yield by 17.0% and 10.7%, respectively, and reduced GHGI by 6.8% and 13.7%, respectively. The OF treatment had a better yield increase than that of the TT treatment, and the TT treatment had a slightly better emission reduction than that of the OF treatment. In terms of combined yield and GHG emission reduction, both twice fertilizer (TT) and 20% replacement of chemical fertilizer by organic fertilizer (OF) could reduce the intensity of GHG emission per unit of rice yield and achieve yield increase and emission reduction while ensuring rice yield.

Effects of biochar-based fertilizer on nitrogen use efficiency and nitrogen losses via leaching and ammonia volatilization from an open vegetable field.

It is essential for the sustainable development of agriculture to enhance nitrogen use efficiency (NUE) of crop plants by increasing yield and reducing nitrogen (N) losses. Biochar-based fertilizer (BF) has received increasing attention because of its full play to the advantages of chemical compounds with sufficient N and less N loss risk with good adsorption characteristics, but this potential was seldom reported for open-field vegetable crops, NUE of which were significantly lower than cereal crops. A field trial was conducted to investigate the efficacy of BF on NUE in vegetable cropping system by comparison with chemical fertilizer (CF) and partial substitution of organic fertilizers to chemical fertilizers (COF). The yield, plant N uptake, residual soil mineral N, and N losses via leaching and ammonia volatilization from an open vegetable (water spinach, Ipomoea aquatica L.) field were analyzed. The results indicated that BF treatment had significantly higher yield, plant N uptake, and NUE (agronomic efficiency and recovery efficiency as the NUE indicators), compared with those of CF and COF treatments. N losses via leaching were respectively accounted for 53.30%, 37.74%, and 33.39%; and N losses via ammonia volatilization were respectively accounting to 1.13%, 0.78%, and 1.54% of N fertilizer applied (at a rate of 200 kg N/ha) in CF, COF, and BF treatments. Despite the increasing ammonia volatilization due to the alkalinity of biochar, BF treatment significantly enhance NUE by increasing N uptake by water spinach and minimizing N losses via leaching. This study suggested that BF could serve as a promising slow-release N fertilizer for sustainable N management in field vegetable production and provided critical information for the development and dissemination of BF management guidelines.

Mitigation of methane emission in a rice paddy field amended with biochar-based slow-release fertilizer.

Despite improving soil quality and reducing nitrogen (N) loss in paddy soil, replacing chemical fertilizer with organic fertilizer would significantly accelerate greenhouse gas emission in terms of methane (CH4). The application of slow-release fertilizer has been proposed an effective approach to control CH4 emissions, in addition to reducing N loss. Yet, the understanding of CH4 emissions from paddy fields with the additions of different fertilizers is still less known. Therefore, the effects of different fertilizer treatments, including chemical fertilizer treatment (CF), mixed chemical and organic fertilizer treatment (OF), biochar-based slow-release fertilizer treatment (SF), and no fertilizer control treatment (CK) on CH4 emissions and methanogenic community structure in paddy soils were investigated through a field experiment. Results showed that slow-release fertilizer addition significantly decreased CH4 emissions by 33.4%, during the whole rice growing season compared to those in OF. The cumulative CH4 emissions were in a significantly positive relation to soil NH4+-N. Slow-release fertilizer amendment decreased the relative abundances of Methanosarcina and Methanoregula and increased the relative abundances of hydrogenotrophic Methanocella and Rice Cluster I. Reduced CH4 emissions with slow-release fertilizer amendment might be mainly attributed to the different forms of N in the fertilizer and available potassium (K) in the paddy soil. Our findings produce novel insights into the application of slow-release fertilizer in controlling CH4 emissions from rice fields.

Biochar production and applications in agro and forestry systems: A review.

Biochar is a product of biomass thermochemical conversion. Its yield and quality vary significantly with the production technology and process parameters, which also affect its performance in agro and forestry systems. In this review, biochar production technologies including slow pyrolysis, fast pyrolysis, gasification, and torrefaction were compared. The yield of biochar was found to decrease with faster heating rate or more oxygen available. The benefits of biochar application to agro and forestry systems were discussed. Improvements in soil health, plant growth, carbon sequestration, and greenhouse gas mitigation are apparent in many cases, but opposite results do exist, indicating that the beneficial aspect of biochar are limited to particular conditions such as the type of biochar used, the rate of application, soil type, climate, and crop species. Limitations of current studies and future research needed on biochar are also discussed. Specifically, the relationships among biochar production technologies, biochar properties, and biochar performance in agro and forestry systems must be better understood.

Silicon fertilizer and biochar effects on plant and soil PhytOC concentration and soil PhytOC stability and fractionation in subtropical bamboo plantations.

The use of exogenous silicon (Si) amendments, such as Si fertilizers and biochar, can effectively increase crop Si uptake and the formation of phytoliths, which are siliceous substances that are abundant in numerous plant species. Phytolith-occluded carbon (C) (PhytOC) accumulation in soil plays an important role in long-term soil organic C (SOC) storage. Nevertheless, the effects of both Si fertilizer and biochar application on PhytOC sequestration in forest plant-soil systems have not been studied. We investigated the impact of Si fertilizer and biochar applications on 1) the PhytOC pool size, the solubility of plant and soil phytoliths, and soil PhytOC in soil physical fractions (light (LFOM) and heavy fractions of organic matter (HFOM)) in Moso bamboo (Phyllostachys pubescens) forests; and 2) the relationships among plant and soil PhytOC concentrations and soil properties. We used a factorial design with three Si fertilizer application rates: 0 (S0), 225 (S1) and 450 (S2) kg Si ha-1, and two biochar application rates: 0 (B0) and 10 (B1) t ha-1. The concentrations of PhytOC in the bamboo plants and topsoil (0-10 cm) increased with increasing Si fertilizer addition, regardless of biochar application. Biochar addition increased the soil PhytOC pool size, as well as the LFOM- and HFOM-PhytOC fractions, regardless of Si fertilizer application. The Si fertilizer application increased or had no effect on soil phytolith solubility with or without biochar application, respectively. Soil PhytOC was correlated with the concentration of soil organic nitrogen (R2 = 0.32), SOC (R2 = 0.51), pH (R2 = 0.28), and available Si (R2 = 0.23). Furthermore, Si fertilizer application increased plant and soil PhytOC by increasing soil available Si. Moreover, biochar application increased soil PhytOC concentration in LFOM-PhytOC and the unstable fraction of PhytOC. We conclude that Si fertilizer and biochar application promoted PhytOC sequestration in the plant-soil system and changed its distribution in physical fractions in the Moso bamboo plantation in subtropical China.

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Elevated atmospheric CO2 concentration, altered precipitation regime, increased nitrogen deposition, and land cover change have not only changed the physical and chemical properties of forest soils, but also affected plant growth and microbial activity, with concequences on soil carbon and nitrogen cycles, including soil CH4 uptake. In this study, we summarized the important role of soil CH4 uptake in forests under global change scenarios. The differences of responses as well as the underlying mechanisms of soil CH4 uptake in forests to global change were reviewed. Elevated atmospheric CO2 concentration inhibits soil CH4 uptake. Reduced precipitation tends to promote soil CH4 uptake. Increased nitrogen input inhibits soil CH4 uptake in nitrogen-rich forests, but promotes or has no effects on soil CH4 uptake in nitrogen-poor forests. Conversion of forests to grassland, farmland, or plantations would reduce soil CH4 uptake, while afforestation increases soil CH4 uptake. The future research should explore the long-term and multiple effects of global changes on forest soil CH4 uptake. In addition, molecular biology methods should be developed to explore the microbial mechanism of soil CH4 uptake.

Carbon nanotube-grafted chitosan and its adsorption capacity for phenol in aqueous solution.

Chitosan was covalently grafted onto the surface of multi-walled carbon nanotubes to create a novel chitosan/multi-walled carbon nanotube. The structure of the new material was characterized using Fourier transform-infrared spectroscopy, cross polarization magic angle spinning 13C nuclear magnetic resonance, thermogravimetric analysis, XRD ray diffraction analysis, differential scanning calorimetry and scanning electron microscopy. The phenol adsorption capacity was determined and the Langmuir and Freundlich models were used to describe the adsorption isotherms. The adsorption capacity of the novel chitosan/multi-walled carbon nanotube material for phenol (86.96 mg/g) was improved compared to the original chitosan (61.69 mg/g). The kinetic studies showed rapid adsorption, exhibiting Lagergren second-order kinetics. Therefore, this study provides a reference for preparing functional materials from biological substrates that are able to remove toxic pollutants from an aqueous environment.

Belowground Phytolith-Occluded Carbon of Monopodial Bamboo in China: An Overlooked Carbon Stock.

Phytolith-occluded carbon (PhytOC), a highly stable carbon (C) fraction resistant to decomposition, plays an important role in long-term global C sequestration. Previous studies have demonstrated that bamboo plants contribute greatly to PhytOC sink in forests based on their aboveground biomass. However, little is known about the contribution of belowground parts of bamboo to the PhytOC stock. Here, we reported the phytolith and PhytOC accumulation in belowground trunk and rhizome of eight monopodial bamboo species that widely distributed across China. The results showed that the belowground parts made up an average of 39.41% of the total plant biomass of the eight bamboo species. There were significant (p < 0.05) variations in the phytolith and PhytOC concentrations in the belowground trunk and rhizome between the bamboo species. The mean concentrations of PhytOC in dry biomass ranged from 0.34 to 0.83 g kg-1 in the belowground rhizome and from 0.10 to 0.94 g kg-1 in the belowground trunk across the eight bamboo species, respectively. The mean PhytOC stocks in belowground biomass ranged from 2.57 to 23.71 kg ha-1, occupying an average of 23.36% of the total plant PhytOC stocks. This implies that 1.01 × 105 t PhytOC was overlooked based on the distribution of monopodial bamboos across China. Therefore, our results suggest that the belowground biomass of bamboo represents an important PhytOC stock, and should be taken into account in future studies in order to better quantifying PhytOC sequestration capacity.

Phytolith-occluded organic carbon as a mechanism for long-term carbon sequestration in a typical steppe: The predominant role of belowground productivity.

Phytolith-occluded organic carbon (phytOC) has recently been demonstrated to be an important terrestrial carbon (C) fraction resistant to decomposition and thus has potential for long-term C sequestration. Existing studies show that plant leaves and sheath normally have high phytOC concentration, thus most of phytOC studies are limited to the aboveground plant parts. Grassland communities comprise herbaceous species, especially grasses and sedges which have relatively high concentrations of phytoliths, but the phytOC production from grassland, especially from its belowground part, is unknown. Here we determined the phytOC concentration in different parts of major plant species in a typical steppe grassland on the Mongolian Plateau, and estimated the phytolith C sequestration potential. We found that the phytOC concentration of major steppe species was significantly (p<0.05) higher in belowground (0.67gkg-1) than aboveground biomass (0.20gkg-1) and that the belowground net primary productivity (BNPP) was 8-15 times the aboveground net primary productivity (ANPP). Consequently, the phytOC stock in belowground biomass (12.50kgha-1) was about 40 times of that in aboveground biomass (0.31kgha-1), and phytOC production flux from BNPP (8.1-15.8kgha-1yr-1) was 25-51 times of that from ANPP. Our results indicate that BNPP plays a dominant role in the biogeochemical silica cycle and associated phytOC production in grassland ecosystems, and suggests that potential phytolith C sequestration of grasslands may be at least one order of magnitude greater than the previous estimation based on ANPP only. Our results emphasize the need for more research on phytolith and phytOC distribution and flux in both above and below ground plant parts for quantifying the phytolith C sequestration.