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Abstract Soil microbial growth, a vital biogeochemical process, governs both the accrual and loss of soil carbon. Here, we investigate the biogeography of soil microbiome potential growth rates and show that microbiomes in resource-rich (high organic matter and nutrients) and acid-neutral soils from cold and humid regions exhibit high potential growth. Conversely, in resource-poor, dry, hot, and hypersaline soils, soil microbiomes display lower potential growth rates, suggesting trade-offs between growth and resource acquisition or stress tolerance. In addition, the potential growth rates of soil microbiomes positively correlates with genome size and the number of ribosomal RNA operons but negatively correlates with optimum temperature, biomass carbon-to-phosphorus and nitrogen-to-phosphorus ratios. The spatial variation of microbial potential growth rates aligns with several macroecological theories. These findings not only enhance our understanding of microbial adaptation to diverse environments but also aid in realistically parameterizing microbial physiology in soil carbon cycling models.

Abstract Understanding the large-scale pattern of soil microbial carbon use efficiency (CUE) and its temperature sensitivity (CUET) is critical for understanding soil carbon–climate feedback. We used the 18O-H2O tracer method to quantify CUE and CUET along a north-south forest transect. Climate was the primary factor that affected CUE and CUET, predominantly through direct pathways, then by altering soil properties, carbon fractions, microbial structure and functions. Negative CUET (CUE decreases with measuring temperature) in cold forests (mean annual temperature lower than 10 °C) and positive CUET (CUE increases with measuring temperature) in warm forests (mean annual temperature greater than 10 °C) suggest that microbial CUE optimally operates at their adapted temperature. Overall, the plasticity of microbial CUE and its temperature sensitivity alter the feedback of soil carbon to climate warming; that is, a climate-adaptive microbial community has the capacity to reduce carbon loss from soil matrices under corresponding favorable climate conditions.

Abstract Soil organic carbon (SOC) persistence is predominantly governed by mineral protection, consequently, soil mineral-associated (MAOC) and particulate organic carbon (POC) turnovers have different impacts on the vulnerability of SOC to climate change. Here, we generate the global MAOC and POC maps using 8341 observations and then infer the turnover times of MAOC and POC by a data-model integration approach. Global MAOC and POC storages are $${975}_{964}^{987}$$ 975 964 987 Pg C (mean with 5% and 95% quantiles) and $${330}_{323}^{337}$$ 330 323 337 Pg C, while global mean MAOC and POC turnover times are $${129}_{45}^{383}$$ 129 45 383 yr and $${23}_{5}^{82}$$ 23 5 82 yr in the top meter, respectively. Climate warming-induced acceleration of MAOC and POC decomposition is greater in subsoil than that in topsoil. Overall, the global atlas of MAOC and POC turnover, together with the global distributions of MAOC and POC stocks, provide a benchmark for Earth system models to diagnose SOC-climate change feedback.

Vegetation restoration is an effective measure to cope with global climate change and promote soil carbon sequestration. However, during vegetation restoration, the turnover and properties of carbon within various aggregates change. The effects of plant source carbon input on surface soil and subsurface soil may be different. Thus, the characteristics of carbon components in aggregates are affected. Therefore, the research object of this study is the Robinia pseudoacacia forest located in 16–47a of the Loess Plateau, and compared with farmland. The change characteristics of organic carbon functional groups in 0–20 cm, 20–40 cm, and 40–60 cm soil layers were analyzed by Fourier near infrared spectroscopy, and the relationship between the chemical structure of organic carbon and the content of organic carbon components in soil aggregates was clarified, and the mechanism affecting the distribution of organic carbon components in soil aggregates was revealed in the process of vegetation restoration. The results show the following: (1) The stability of surface aggregates is sensitive, while that of deep aggregates is weak. Vegetation restoration increased the surface soil organic carbon content by 1.97~3.78 g·kg−1. (2) After vegetation restoration, the relative contents of polysaccharide functional groups in >0.25 mm aggregates were significantly reduced, while the relative contents of aromatic and aliphatic functional groups of organic carbon were significantly increased. The opposite is true for aggregates smaller than 0.25 mm. (3) With the increase in soil depth, the effect of litter on organic carbon gradually decreased, while the effect of root input on the accumulation of inert carbon in deep soil was more lasting.

Sustainable food system development is the cornerstone of global human survival and development. This research briefly analyzes the challenges facing the current food system, summarizes the directions of food system transformation, expounds the role of geography in the transformation of food system, and discusses the future paths to promote the sustainable development of food system. The main conclusions are as follows: 1) The interaction of factors such as regional conflicts, climate change, slowdown in development, raging epidemics, and resource and environmental constraints pose multiple challenges to the global food system. 2) The food system should be high-quality, efficient, nutritious and healthy, green and low-carbon, inclusive and inclusive transformation. 3) Geography can provide solutions for the transformation of food systems. 4) The transformation paths of the food system includes: establishing a global food system with benefit sharing, cleaner production, and fair participation, improving the innovation capability of the food system, and establishing an effective organizational guarantee system.

In the agroforestry system, the organic matter in the farmland and natural ecosystem enters the farmland soil in a mixed form to improve soil fertility and carbon pool quality. However, it is unclear how soil microbial carbon-degrading enzyme activity responds to carbon dynamics in this process. Therefore, we took farmland in the Loess Plateau as the research object, combining the application of corn straw and Robinia pseudoacacia leaves in a mass ratio of 4:0, 3:1, 2:2, 1:3, and 0:4 for returning to the field. We measured corn grain yield, carbon emission, organic carbon pool component content, and carbon-degrading enzyme activity of the farmland. The results showed that combining corn straw and Robinia pseudoacacia leaves had a significant impact on soil organic carbon components (readily oxidizable organic carbon and recalcitrant organic carbon), carbon-degrading enzymes (polyphenol oxidase, peroxidase, and cellobiohydrolase), and cumulative carbon emissions. The trend of different indicators in different treatments during the corn growth period was similar. We found that soil carbon emissions were closely related to ROC and soil oxidase activity, while soil carbon content was closely related to soil hydrolase activity. Compared to not returning straw to the field, the corn straw and Robinia pseudoacacia leaves returned to the field in a mass ratio of 1:3(Y1C3) can increase corn grain yield by 32.04%. The Y1C3 treatment has the highest soil carbon content and the lowest crop carbon emission efficiency. Soil water content plays a crucial role in the process of carbon pool transformation driven by soil carbon-degrading enzymes. In conclusion, soil carbon dynamics are closely related to the activity of soil carbon-degrading enzymes. Combining the application of corn straw and Robinia pseudoacacia leaves may be a more suitable farming measure for fragile habitats in the Loess Plateau than other solutions.

Soil warming is expected to accelerate microbial carbon (C) degradation, increasing carbon dioxide (CO2) emissions. This process greatly contributes to global warming. To validate this positive feedback loop in semiarid restored ecosystems, we examined the effects of 2 years of open-top chamber warming on soil CO2 efflux (soil respiration) and microbial metabolic characteristics in abandoned farmland on the Chinese Loess Plateau. Soil warming of 1.3 °C above ambient at 10 cm depth significantly stimulated CO2 emissions by 40.5 %. Despite short-term warming alleviating the C (energy) limitation on microbial activity, no substantial differences in microbial C use efficiency or biomass turnover rate were noted compared to those in the control. Importantly, we found little evidence that warming altered the expression levels of carbohydrate metabolism genes annotated using the eggNOG, KEGG, and CAZy databases. All expressed genes targeting the degradation of diverse carbonaceous components were assigned to bacterial taxa unaffected by warming. Therefore, short-term warming stimulated soil CO2 emissions from non-microbial sources but did not drive the abandoned farmland in the reverse direction to a C source. Our findings highlight the importance of conducting long-term comparisons of microbial metabolic profiles and soil respiration components to elucidate the mechanisms underlying changes in C-cycling in ecosystems that have undergone restoration and experienced warming.

Abstract To alleviate pollution and promote clean energy production, food waste can be used to produce methane through anaerobic digestion (AD). In this study, wheat straw was used to produce biochar (BC) and magnetic biochar (MB) as additives for AD of food waste. MB2.5% and BC2.5% led to the highest methane production. The main action mechanism of the additives in AD was the change in environmental factors upon stimulating microorganisms to rapidly metabolize volatile fatty acids. The stimulation of microbial function increased the abundance of the methanogenesis pathways. Methanosarcina was the most dominant archaea in the four methanogenesis modules, and the microbial community changed more clearly with time than with treatment. This study is innovative in finding the effectiveness of BC and MB treatments attributed to the abundance of methanogenesis modules, especially MB2.5% treatment retained its advantage until the later stage of digestion in AD process.

Mulching and nitrogen (N) fertilization are the main drivers for sustainable crop production. The sole use of nitrogen fertilizer threatened both the physiology and production of maize in rain-fed areas. Therefore, we proposed that wheat straw mulching with N fertilization would increase maize yield by improving soil fertility, physiology, and nitrogen use efficiency. A two-year field study evaluated the effects of CK (control), N (nitrogen application at 172 kg ha−1), HS (half wheat straw mulch, 2500 kg ha−1), HS+N (half wheat straw, 2500 kg ha−1 plus 172 kg N ha−1), FS (full wheat straw, 5000 kg ha−1), and FS+N (full wheat straw, 5000 kg ha−1 plus 172 kg N ha−1) on maize growth, physiology, and biochemistry. Compared with the control, the FS+N treatment resulted in the increase of 56% photosynthetic efficiency, 9.6% nitrogen use efficiency, 60% nitrogen uptake, 80% soluble sugar, 59% starches, 48% biomass, and 29% grain yield of maize. In addition, the FS+N regime increased 47%, 42%, and 106% of soil organic carbon and available P and N content in comparison with the control. Maize grain and biomass yields were positively correlated with N uptake, photosynthesis, soil organic carbon, and soil available N and P contents. Conclusively, the use of wheat straw at 5000 kg ha−1, along with 172 kg N ha−1, is a promising option for building a sustainable wheat–maize cropping system to achieve optimal crop yield and improved plant and soil health in a semi-arid region of China.

Straw retention and wheat-soybean rotation play critical role in maintaining soil quality. However, the correlation between bacterial diversity and community structure, and soil nutrients is unknown, and a systematic understanding of their responses to straw retention is lacking. In the field experiment, the straw retention treatments included no straw (NS), half straw (HS), and total straw (TS) retention during long-term wheat-soybean rotation. The mean contents of soil total nitrogen (TN), nitrate-N (NO3−-N), and microbial biomass nitrogen (MBN) increased by 15.06%, 21.10%, and 38.23%, respectively, with straw retention relative to NS, while that of ammonium-N (NH4+-N) reduced by 3.68%. The concentration of carbon components increased as straw retention increased. The levels of soil dissolved organic carbon (DOC), microbial biomass carbon (MBC), and soil organic carbon (SOC) increased by 4.34%, 7.63%, and 9.34%, respectively, with straw retention relative to NS. Soil bacterial alpha diversity was reduced with straw retention. Soil pH and nutrient content were identified as the main factors affecting the soil microbial diversity and structure at the phylum level. Accordingly, straw retention and soybean-wheat rotation enable sustainable agriculture in the dryland of northern China.

Field studies using wheat straw mulching effects on soil water storage and maize development were conducted in China. The studies contained four treatments during three years (2014-2016): CK (no straw and no nitrogen); N (no straw mulching with 172 kg N/ha); HS + N (half straw mulching at the rate of 2500 kg/ha with 172 kg N/ha), and FS + N (full straw mulching at the rate of 5000 kg/ha with 172 kg N/ha). The FS + N treatment significantly increased soil water storage in a drought period during crop growth stages and promoted plant growth along with increased evapotranspiration. The FS + N treatment increased the soil water storage (26.5, 19.9 and 11.1 mm), grain yield (28.7, 6.93 and 2.4%), and water use efficiency (26.6, 6.64 and 2.40%) compared to CK, N and HS + N, respectively. In conclusion, compared to N, HS + N or FS + N increased the biomass (11 and 19%) and water use efficiency (4 and 5%), respectively, and are considered beneficial in Guanzhong, China. Mulching levels were superior to N and compensated the wheat nitrogen requirements. Thus, further studies with minimum fertilizer nitrogen for an environmentally friendly and effective approach are recommended in semiarid regions of China.

Mulching can effectively maintain and improve soil health and functionality. The mechanisms, however, have not been fully elucidated. Therefore, the effects of temperature on the biogeochemical properties of soil were investigated in the present study in relation to nitrogen management and soil functionality. The results of the 3-year field experiments showed that integrated straw mulch (S) and nitrogen fertilizer (N) treatments enhanced the activities of soil urease, invertase, alkaline phosphatase, and catalase by >1.8, 2.1, 2.0 and 1.4 fold, respectively, compared with the control treatment. Furthermore, these treatments increased soil available N by 28%, phosphorus by 45%, and potassium by 55%. In general, the soil organic carbon, dissolved carbon and labile organic carbon content in the treated plot were approximately 1.2–2.9 folds greater than in the control plot. These improvements in soil fertility and carbon indices increased the biomass and grain yield of soybean (67 and 75%, respectively) during the three-year study period. During 2015–2017, the straw mulch and nitrogen fertilizer treatment increased the soil moisture (23%) and decreased the soil temperature (8%) in comparison to the control in the 0–0.2 m soil depth and, therefore, improved soil enzyme activities, nutrient availability, and carbon stocks, and ultimately, soil functionality and sustainability, in the semiarid region. Keywords: Soil hydrothermal properties, Nutrient availability, Enzyme activities, Soil carbon

Straw retention is an effective method to conserve soil water content and improve soil carbon stocks. However, how soil carbon dynamics respond to different straw retention practices remains unclear. In this study, we investigated soil respiration and soil carbon sequestration at depths of 0-100 cm. We conducted a two-year field experiment with three crop rotation treatments and three straw retention treatments in northwest China. The straw retention treatments included no straw retention (NS), retention of half the straw (HS), and retention of the total amount of straw (TS). The crop rotations treatments included winter wheat plus summer soybean (WS), winter wheat plus summer maize (WM), and winter wheat plus summer fallow (WF). Mean soil respiration rates under WS, WM, and WF treatments were 5.14, 6.53, and 5.49 μmol·m-2·s-1; and 5.67, 5.47, and 6.03 μmol·m-2·s-1 under TS, HS, and NS treatments. The mean soil water content were 15.50%, 15.57%, and 15.74% under WS, WM, and WF rotations, and 15.81%, 15.41%, and 15.50% under TS, HS, and NS treatments. The soil organic carbon (SOC) concentration was higher with increased straw retention, and lower at deeper soil depths. Mean SOC concentrations under different rotations and straw treatments of TS, HS, and NS, respectively were as follows: WS: 6.91, 6.63, 6.39 g/kg; WM: 6.90, 6.72, 6.57 g/kg; and WF: 6.49, 6.52, 6.37 g/kg. Soil temperature was the main determinant of soil respiration rates. We conclude that WS rotation resulted in lower soil respiration, WM rotation resulted in a higher soil carbon sequestration potential, and WF rotation resulted in higher soil water content. However, continued, long-term monitoring is needed to confirm the effect of rotations and straw retention on soil respiration and carbon sequestration in dryland cropping systems in northern China.

Soil microorganisms play crucial roles between plants and soil following afforestation. However, the relationship between the microbial community and carbon:nitrogen:phosphorus (C:N:P) stoichiometry in the plant–soil–microbe continuum remains unclear. In this study, we investigated this relationship by collecting plant and soil samples from Caragana korshinskii Kom. plantations with different years of afforestation (17-, 32-, and 42-year-old plantations), and from farmland. Illumina sequencing of the 16S rRNA and internal transcribed spacer (ITS) ribosomal RNA was used to examine the soil microbial community and the C, N, and P concentrations in plants, soil, and microbial biomass. Other soil characteristics were also measured. The results showed that the C and N concentrations in plants (leaves, herbs, and litter), soil, and microbial biomass increased as the vegetation restoration stage increased, but the P concentration in leaves and herbs slightly decreased. The C:P and N:P ratios in the plant–soil–microbe continuum substantially increased over time, particularly that of the microbial biomass. These results suggest that the unbalanced increase of C, N, and P following vegetation restoration may result in a P limitation in plant–soil systems. Moreover, bacterial and fungal alpha diversity significantly increased following afforestation. Afforestation had a greater impact on bacterial diversity (both alpha and beta diversity) than did fungal diversity. Among the dominant bacterial taxa, Proteobacteria increased significantly with afforestation time, whereas Actinobacteria decreased and Acidobacteria peaked in 32-year-old C. korshinskii plantations. However, there were no significant changes in the dominant fungal taxa. Collectively, we found that microbial diversity and dominant phyla were closely associated with the C:P and N:P ratios in the plant–soil–microbe continuum, particularly the N:P ratio. These results suggest that microbial diversity and composition may be limited by the imbalances of C, N, and especially P in afforested ecosystems, which provides evidence of linkages between microbial diversity and plant–soil systems in afforested ecosystems and could help in improving the predictions of sustainably restoring C. korshinskii plantations.

Variability in soil enzyme activity may have important implications for the knowledge of underground ecosystem functions driven by soil extracellular enzymes. To illustrate the temporal variation in soil enzyme activity after afforestation, we collected soil samples during different vegetative growth periods in three Caragana korshinskii Kom. stands of different ages (20, 30, and 40 years) and in a slope cropland in the Loess Plateau. These samples were used to analyze the catalase, sucrase, urease and alkaline phosphatase activities, the soil water content and the available soil nutrients (i.e., dissolved organic carbon, dissolved organic nitrogen, and available phosphorus). The results illustrated that the soil enzyme activities significantly increased following afforestation and varied with temporal variation. Overall, soil enzyme activities were higher in June and August, particularly, and both alkaline phosphatase and sucrase were more sensitive to temporal variation than the other two enzymes. In addition, redundancy analysis showed that soil enzyme activities were greatly correlated with soil nutrients, especially for dissolved organic carbon and dissolved organic nitrogen. Therefore, the results highlighted the importance of soil enzyme activities to soil nutrients under temporal variation following afforestation in the Loess Plateau, which may have practical significance for forest managers’ fertilization management of plantation in different seasons and different stand ages.

Plant nitrogen (N) and phosphorus (P) resorption is an important strategy to conserve N and P in the face of nutrient limitation. However, little is known about the variation of N and P resorption efficiency (NRE and PRE) and their correlation with leaves and soil C:N:P stoichiometry in black locust forests (Robinia pseudoacacia L.) of different ages. In this study, we measured C, N, and P concentrations in soil, green leaves, and senesced leaves from black locust forests of different ages (i.e, 10-, 20-, 30-, 36-, and 45-year-old), and calculated the NRE, PRE, and C:N:P stoichiometry ratios. The NRE and PRE tended to increase and then decrease with stand age, ranging from 46.8% to 57.4% and from 37.4% to 58.5%, with averages of 52.61 and 51.89, respectively. The PRE:NRE decreased with increased stand ages. The C:P and N:P of soil and green leaves increased with stand ages, indicating the increase of P limitation. In the senesced leaves, C:P and N:P were lower than in green leaves and first increased and then decreased with stand age. The PRE was significantly negatively correlated with the C:P and N:P of soil and green leaves. The NRE was significantly correlated with the C concentration of green leaves, P of the senesced leaves, and C:N. Results suggested that the NRE and PRE responded differently to soil and plant nutrients in black locust forests of different ages. In addition, the black locust plantations would alter the conservation and use strategy of nutrients in the ecosystem through a plant-mediated pathway. Future studies should elucidate the central nutrient utilization strategy of black locust in response to a nutrient-poor environment and determine how it is involved in regulating nutrient resorption.

In the Loess Hilly Region of China, the widespread conversion of cropland to forestland and grassland has resulted in great increased in organic carbon (C), nitrogen (N) and phosphorus (P) stocks in the shallow soil layers. However, knowledge regarding changes in C, N, and P in deep soil is still limited. To elucidate the responses of deep soil C, N, and P stocks and stoichiometry in response to changes in land use, the soil from a 0-200 cm soil profile was collected from the following three typical land use patterns in the heartland of the region: forestland, grassland, and cropland. Compared with cropland, forestland and grassland had improved soil organic carbon (SOC) and total nitrogen (TN) contents and stocks at most soil depths but decreased total phosphorus (TP) contents and stocks. At soil depths of 0-200 cm in the forestland and grassland, the cumulative SOC stocks were improved by 34.97% and 7.61%, respectively, and the TN stocks were improved by 54.54% and 12.47%, respectively. The forestland had higher SOC, TN and TP contents and stocks compared to the grassland in almost all soil layers. The soil depths of 100-200 cm contained the highest percentages of SOC, TN and TP stocks (47.80%-49.93%, 46.08%-50.05% and 49.09%-52.98%, respectively). Additionally, the forestland and grassland showed enhanced soil C:P, N:P and C:N:P ratios, and the forestland had higher C:P, N:P and C:N:P ratios compared to the grassland. Furthermore, the SOC and TN stocks had significant impacts on the soil C:N, C:P and N:P ratios. It was concluded that afforestation was the best choice for soil nutrient restoration of degraded land, and deep soil provided an extremely important resource for evaluating soil C, N and P pools and cycling.

Artificial vegetation restoration can induce variations in accumulation and distribution of soil carbon (C), nitrogen (N) and phosphorus (P). However, little is known about variations in soil C, N and P nutrient fraction stratification following artificial vegetation in Loess Plateau China. Based on the hypothesis that re-vegetated can improve soil quality and stratification ratios (SR) can be used as an indicator to evaluate soil quality. This study measured contents and storages of soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP) and their SRs in topsoil (0-20 cm) and subsoil (20-60 cm) in three 30-year re-vegetated lands that had been converted from arable land (Robinia pseudoacacia L., Caragana Korshinskii Kom. and abandoned cropland with low interferences and few management measures) and one slope cropland (SC) as a control for three soil profiles(0-20 cm, 20-40 cm and 40-60 cm) from June 2009 to June 2013. The results showed that the contents and storages of SOC, TN and TP in re-vegetated land were significantly higher than those in the SC in both topsoil and subsoil. The storages of SOC, TN and TP in the topsoil (0-20 cm) of the re-vegetated lands increased by 16.2%-26.4%, 12.7%-28.4% and 16.5%-20.9%, respectively, and increased by smaller but significant amounts in subsoil from 2009 to 2013. The SRs for SOC, TN and TP in the re-vegetated lands were mostly >2 (either for 0-20:20-40 cm or 0-20:40-60 cm) and greater than that in the SC. The SRs showed an increasing trend with increasing restoration age. The results also showed that the land use type and soil depth were the most influential factors for the SRs and storages, and the SRs of SOC and TN had significantly positive correlations with their storages. The SRs were concluded to be a good indicator for evaluating the soil quality, which can be significantly enhanced through vegetation restoration. Moreover, vegetation restoration can significantly enhance SOC, TN and TP accumulation in both topsoil and subsoil.

Lignocellulosic biomass is considered the most abundant renewable resource that has the potential to contribute remarkably in the supply of biofuel. Previous studies have shown that chemical pretreatment prior to anaerobic digestion (AD) can increase the digestibility of lignocellulosic biomass and methane yield. In the present study, the effect of rice straw pretreatment using ammonium hydroxide (NH3•H2O) and hydrogen peroxide (H2O2) on the biogasification performance through AD was investigated. A self-designed, laboratory-scale, and continuous anaerobic biogas digester was used for the evaluation. Results showed that the contents of the rice straw, i.e. the lignin, cellulose, and hemicellulose were degraded significantly after the NH3•H2O and H2O2 treatments, and that biogas production from all pretreated rice straw increased. In addition, the optimal treatments for biogas production were the 4% and 3% H2O2 treatments (w/w), which yielded 327.5 and 319.7 mL/gVS, biogas, respectively, higher than the untreated sample. Biogas production from H2O2 pretreated rice straw was more favorable than rice straw pretreated with same concentration of ammonia, ranking in the order of 4% ≈ 3% > 2% > 1%. The optimal amount of H2O2 treatment for rice straw biogas digestion is 3% when economics and biogas yields are considered.

Understanding the association between soil organic carbon (SOC) and texture under different climatic conditions is important for assessing the effects of future climate changes on SOC stocks. In this study, we conducted a climatic gradient experiment covering three climate types (humid, sub-humid, and semi-arid) with a steep rainfall ranging from 345 to 910 mm, and specifically determined SOC dynamics, clay content, and vegetation and soil characteristics. The results showed that, from semi-arid to humid regions, SOC stocks, SOC, and clay content increased synchronously and were closely related in layers of depths of both 0–10 and 10–20 cm. In contrast, under similar climatic conditions, SOC dynamics were mainly affected by vegetation and soil characteristics, especially total nitrogen and total phosphorus dynamics, but not the soil clay content. Therefore, these results suggest that the relationship between SOC stocks and clay content depended on scale sizes. Specifically, on a larger scale with different climatic gradients, the climate may partly determine the changes in SOC and clay dynamics, whereas, at a smaller scale where climate type does not vary considerably, the changes in SOC stocks and clay content may be related to vegetation diversity and soil nutrient dynamics. These results may contribute to future model development and the projection of changes in soil carbon storage.

Soil respiration (SR) is an important process in the carbon cycle. However, the means by which changes in understory plant community traits affect this ecosystem process is still poorly understood. In this study, plant species surveys were conducted and soil samples were collected from forests dominated by black locust (Robinia pseudoacacia L.), with a chronosequence of 15, 25, and 40 years (RP15, RP25, and RP40, respectively), and farmland (FL). Understory plant coverage, evenness, diversity, and richness were determined. We investigated soil microbial biomass carbon (MBC), nitrogen (MBN), phosphorus (MBP), and stoichiometry (MBC:MBN, MBC:MBP, and MBN:MBP). Soil enzyme assays (catalase, saccharase, urease, and alkaline phosphatase), heterotrophic respiration (HR), and autotrophic respiration (AR) were measured. The results showed that plant coverage, plant richness index (R), evenness, and Shannon-Wiener diversity were higher in RP25 and RP40 than in RP15. SR, HR, and AR were significantly higher in the forested sites than in farmland, especially for SR, which was on average 360.7%, 249.6%, and 248.2% higher in RP40, RP25, and RP15, respectively. Meanwhile, catalase, saccharase, urease, and alkaline phosphatase activities and soil microbial C, N, P, and its stoichiometry were also higher after afforestation. Moreover, significant Pearson linear correlations between understory plants (coverage, evenness, diversity, and richness) and SR, HR, and AR were observed, with the strongest correlation observed between plant coverage and SR. This correlation largely depended on soil enzymes (i.e., catalase, saccharase, urease, and alkaline phosphatase), and soil microbial biomass C, N, and P contents and its stoichiometry, particularly urease activity and the MBC:MBP ratio. Therefore, we conclude that plant communities are drivers of soil respiration, and that changes in soil respiration are associated with shifts in soil enzyme activities and nutrient stoichiometry.

This study investigated the effect of sunlight-dark conditions on volatile fatty acids (VFAs), total ammonium nitrogen (TAN), total alkalinity (TA) and pH during pig manure (PM) digestion and then the subsequent influence on biogas yield of PM. PM1 and PM2 were performed in a transparent reactor and a non-transparent reactor, respectively. Two sets of experiments were conducted with a temperature of 35.0±2.0 °C and a total solid concentration of 8.0% to the digestion material. The dynamic change of the four parameters in response to sunlight-dark conditions resulted in variations of the physiological properties in the digester and affected the cumulative biogas production (CBP). PM1 obtained higher CBP (15020.0 mL) with a more stable pH and a lower TAN concentration (1414.5 mg/L) compared to PM2 (2675.0 mL and 1670.0 mg/L, respectively). The direct path coefficients and indirect path coefficients between the four parameters and CBP were also analyzed.

Anaerobic digestion is a promising alternative to disposal organic waste and co-digestion of mixed organic wastes has recently attracted more interest. This study investigated the effects of temperature and carbon-nitrogen (C/N) ratio on the performance of anaerobic co-digestion of dairy manure (DM), chicken manure (CM) and rice straw (RS). We found that increased temperature improved the methane potential, but the rate was reduced from mesophilic (30∼40°C) to thermophilic conditions (50∼60°C), due to the accumulation of ammonium nitrogen and free ammonia and the occurrence of ammonia inhibition. Significant ammonia inhibition was observed with a C/N ratio of 15 at 35°C and at a C/N ratio of 20 at 55°C. The increase of C/N ratios reduced the negative effects of ammonia and maximum methane potentials were achieved with C/N ratios of 25 and 30 at 35°C and 55°C, respectively. When temperature increased, an increase was required in the feed C/N ratio, in order to reduce the risk of ammonia inhibition. Our results revealed an interactive effect between temperature and C/N on digestion performance.

Conversion of slope cropland to perennial vegetation has a significant impact on soil organic carbon (SOC) stock in A horizon. However, the impact on SOC and its fraction stratification is still poorly understood in deep soil in Loess Hilly Region (LHR) of China. Samples were collected from three typical conversion lands, Robinia psendoacacia (RP), Caragana Korshinskii Kom (CK), and abandoned land (AB), which have been converted from slope croplands (SC) for 30 years in LHR. Contents of SOC, total nitrogen (TN), particulate organic carbon (POC), and labile organic carbon (LOC), and their stratification ratios (SR) and carbon management indexes (CMI) were determined on soil profiles from 0 to 200 cm. Results showed that the SOC, TN, POC and LOC stocks of RP were significantly higher than that of SC in soil layers of 0-10, 10-40, 40-100 and 100-200 cm (P2.0 in most cases of RP, CK and AB. Moreover, CMI values of RP, CK, and AB increased by 11.61-61.53% in soil layer of 100-200 cm compared with SC. Significant positive correlations between SOC stocks and CMI or SR values of both surface soil and deep soil layers indicated that they were suitable indicators for soil quality and carbon changes evaluation. The Grain-to-Green Program (GTGP) had strong influence on improving quantity and activity of SOC pool through all soil layers of converted lands, and deep soil organic carbon should be considered in C cycle induced by GTGP. It was concluded that converting slope croplands to RP forestlands was the most efficient way for sequestering C in LHR soils.

Food security is chronically guaranteed in Egypt because of the food subsidy policy of the country. However, the increasing Egyptian population is straining the food supply. To study changes in Egyptian food security and future food supply capacity, we analysed the historical grain production, yield per unit, grain-cultivated area, and per capita grain possession of Egypt. The GM (1,1) model of the grey system was used to predict the future population. Thereafter, the result was combined with scenario analysis to forecast the grain possession and population carrying capacity of Egypt under different scenarios. Results show that the increasing population and limitations in cultivated land will strain Egyptian food security. Only in high cultivated areas and high grain yield scenarios before 2020, or in high cultivated areas and mid grain yield scenarios before 2015, can food supply be basically satisfied (assurance rate ≥ 80%) under a standard of 400 kg per capita. Population carrying capacity in 2030 is between 51.45 and 89.35 million. Thus, we propose the use of advanced technologies in agriculture and the adjustment of plant structure and cropping systems to improve land utilization efficiency. Furthermore, urbanization and other uses of cultivated land should be strictly controlled to ensure the planting of grains.

To contribute to a better understanding of the regeneration strategy of Betula albosinensis forests and the likely reasons behind either the successful recovery or failure after strip clearcutting, we compared the population structures and spatial patterns of B. albosinensis in eight B. albosinensis stands in Qinling Mountains, China. Four cut and four uncut stands were selected, and each sampled using a single large plot (0.25 ha). Results indicated that, on the one hand, B. albosinensis recruitment was scarce (average of 48 stems ha(-1)) in the uncut stands, relative to the mature population (average of 259 stems ha(-1)), suggesting a failure of recruitment. On the other hand, the subsequent regeneration approximately 50 years after the strip clearcutting showed that the density of the target species seedlings and saplings has increased significantly, and the current average density of seedlings and saplings was 156 stems ha(-1). The clumped spatial pattern of B. albosinensis suggested that their regeneration was highly dependent on canopy disturbance. However, recruitment remained poor in the uncut stands because most gaps were small in scale. The successful regeneration of sunlight-loving B. albosinensis after strip clearcutting was attributed to the exposed land and availability of more sunlight. Bamboo density did not influence B. albosinensis recruitment in the uncut stands. However, stand regeneration was impeded after strip clearcutting; thus, removing bamboo is essential in improving the competitive status of B. albosinensis at the later stage of forest regeneration after clearcutting. The moderate severity of disturbance resulting from strip clearcutting reversed the degeneration trend of primary B. albosinensis stands. This outcome can help strike a balance between forest conservation and the demand for wood products by releasing space and exposing the forested land for recruitment. Life history traits and spatiotemporal disturbance magnitude are important factors to consider in implementing effective B. albosinensis regeneration strategies.

Goat manure (GM) is an excellent raw material for anaerobic digestion because of its high total nitrogen content and fermentation stability. Several comparative assays were conducted on the anaerobic co-digestion of GM with three crop residues (CRs), namely, wheat straw (WS), corn stalks (CS) and rice straw (RS), under different mixing ratios. All digesters were implemented simultaneously under mesophilic temperature at 35±1 °C with a total solid concentration of 8%. Result showed that the combination of GM with CS or RS significantly improved biogas production at all carbon-to-nitrogen (C/N) ratios. GM/CS (30:70), GM/CS (70:30), GM/RS (30:70) and GM/RS (50:50) produced the highest biogas yields from different co-substrates (14840, 16023, 15608 and 15698 mL, respectively) after 55 d of fermentation. Biogas yields of GM/WS 30:70 (C/N 35.61), GM/CS 70:30 (C/N 21.19) and GM/RS 50:50 (C/N 26.23) were 1.62, 2.11 and 1.83 times higher than that of CRs, respectively. These values were determined to be the optimal C/N ratios for co-digestion. However, compared with treatments of GM/CS and GM/RS treatments, biogas generated from GM/WS was only slightly higher than the single digestion of GM or WS. This result was caused by the high total carbon content (35.83%) and lignin content (24.34%) in WS, which inhibited biodegradation.

Soil dissolved carbon (C) and nitrogen (N) are early sensitive indexes to evaluate the changes in C and N pools in terrestrial ecosystems. However, there are few studies on the changes in soil dissolved C and N with revegetation age and their stratification ratios (SRs), especially for deep soil. The changes in soil dissolved C and N and their SRs in one farmland and five Robinia pseudoacacia plantations (RP: 15a, 20a, 25a, 30a and 40a) were studied. The results showed that RP plantations significantly increased the soil organic C (SOC) and total N (TN) stocks with increasing restoration age for 30 years in the shallow and middle soil layers and improved the stocks of dissolved total C (DTC), dissolved organic C (DOC), dissolved total N (DTN), dissolved organic N (DON) and dissolved inorganic N (DIN) in most soil layers, especially in the 20a, 25a and 30a plots. In the 0-200 cm soil layer, the middle and deep soil accounted for 50%-82% of the SOC and soil dissolved C stocks and 63%-84% of the soil TN and dissolved N stocks, respectively. At all soil depths, the SRs of SOC, TN, DTC, DOC and DIN in RP plots were greater than those in farmland plots, and the SRs of SOC and TN in almost all RP plots were >2. These results demonstrated that restoration age and soil depth had significant influences on SOC, TN and soil dissolved C and N, and RP forestation increased the SOC and TN stocks in the shallow and middle soil layers, and the soil dissolved C and N stocks in 20a, 25a and 30a plots were the largest; additionally, the middle and deep soil layers played important roles in estimating the soil C and N pools. In summary, RP afforestation significantly improved soil C and N and their dissolved fractions and the SRs, thus soil quality and nutrient availability consistently improved. [ABSTRACT FROM AUTHOR]