Search

Reforestation or natural forest regeneration is an alternative measure for controlling soil erosion in degraded land on the Chinese Loess Plateau (CLP). However, our understanding of the temporal dynamics and the spatial patterns of forest regeneration remains inadequate. Two oak forests at different development stages were investigated to determine the spatial patterns of competitions (intraspecies and interspecies) during different successional stages. The intraspecies and interspecies spatial relationships among different tree diameters at breast height were analyzed at multiple scales by Kriging interpolation method and univariate and bivariate O-ring statistics. Our analytical results indicated that self-correlation and competition intensity were relatively high between oak and pine trees in the early development stage of oak forests due to their clumped distributions of heavy seeds. Birch trees had a lower competition in comparison to oak trees although birch was the dominant species. Therefore, asymmetric competition of oak trees was most likely to have led to their edge dispersal and their success in replacing the pioneer species. Asymmetric competition means that larger individuals obtained a disproportionately large share of the resources and suppressed the growth of smaller individuals. Kriging interpolation analysis showed a tendency towards homogenization caused by interspecies competition during the succession of oak forests. Our results demonstrated that the competition was the driving factor in the spatial distribution of oak forests on the CLP.

Microbial C/N/P stoichiometry ratios are of interest because of important ecosystem fluxes of C, N, and P, such as mineralization and immobilization, and they can help to characterize the cycling of soil elements, especially regarding soil C sequestration. However, it is not clear how soil microbial C/N/P stoichiometry influences C cycling. In this study, the concentrations of microbial biomass C, microbial biomass N, microbial biomass P, and soil C fractions were measured in 45-, 40-, and 25-yr-old black locust (Robinia pseudoacacia L.) forest soils and a sloped cropland. The results showed that soil organic C (SOC) concentrations or stocks and the percentage increment of the SOC stocks were highest under 45-yr-old black locust (RP45a). The concentrations of each C fraction in the black locust forest soils (45a, 40a, and 25a) were higher than that of sloped cropland in the 0- to 30-cm soil profile. The concentrations of microbial C, N, and P in RP45a were also higher by an average of 29.6 to 232.9, 9.2 to 17.9, and 0.6 to 1.1 mg kg⁻¹, respectively, compared with the same concentrations in sloped cropland at the 0- to 30-cm soil depth. Redundancy analysis indicated that soil C fractions, especially for particulate organic C (53–2000 and >2000 μm), were significantly correlated with the microbial C/P and N/P ratios, and the “best” model selection indicated that the microbial N/P and C/P ratios significantly changed with soil C fractions with regard to stand age and soil depth in the black locust forests. Therefore, the present study demonstrated that C fractions respond to microbial C, N, and P stoichiometry after farmland-to-forest conversion and hence have the potential to affect C storage in the loess hilly region.

Temporal variation in soil enzyme activities has important significance for soil quality after afforestation. This study investigated the temporal variation in soil enzyme activities and their response to changes in soil properties following afforestation. Soil samples were collected during different periods of vegetation growth at sites in the Loess Plateau with different land use types: 40 year-old Robinia pseudoacacia L. (RP40a), Caragana Korshinskii Kom (CK40a), and abandoned land (AL40a), as well as millet ( Setaria italica ) farmland (FL). Activities of four enzymes (catalase, saccharase, urease and alkaline phosphatase) that are involved in C, N, P cycling and soil water content (SWC), dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and available phosphorus (AP) were measured. The results revealed that temporal variation and land-use have significant effects on the patterns of SWC, DOC, and DON, although not on that of AP. In addition, the activities of soil enzymes were highest in June, indicating that there are differences in the temporal variation of soil enzyme activities within a given land-use type, especially for alkaline phosphatase. The consistent ranking of soil enzyme activities was also significantly increased by afforestation. Furthermore, nonmetric multidimensional scaling analysis showed that the influence degree of afforestation on activities of the four enzymes was higher than that of temporal variation. Significant correlations between soil enzyme activities and soil properties indicated that soil enzyme activities are closely related to soil nutrients dynamics, particularly with respect to DON. The present study accordingly demonstrates that soil enzyme activities respond to farmland-to-forest conversion and hence have the potential to affect soil qualities in the Loess Plateau.

Ecological stoichiometry (C:N:P ratios) in soil plays an important role in ecosystem dynamics and functioning; however, its relationship with below-ground microbial diversity following afforestation remains poorly understood. To illustrate the linkage of C, N, and P in soil and microbial biomass, and the effect on the soil bacterial community, soil samples were collected from farmland and from three afforested land, namely Robinia pseudoacacia L., Caragana korshinskii Kom, and abandoned land, which have been arable for the past 40 years. Quantitative PCR and Illumina sequencing of the 16S rRNA genes were used to analyze soil bacterial abundance, diversity, and composition. Additionally, soil properties and C, N, and P levels in soil and microbial biomass were estimated. The results revealed that C, N, and P levels in soil and microbial biomass increased following afforestation, with a significant correlation observed, especially for the N:P ratio. Additionally, a rise in 〈alpha〉- and 〈beta〉-diversity of soil bacteria was observed in response to afforestation, and was linked to soil C:P and N:P ratios. Soil bacterial phyla with high relative abundance (relative abundance > 1%) across all samples showed inconsistent directional trends in the composition response after afforestation. An increased abundance of Proteobacteria, Acidobacteria, and Nitrospirae were observed, while the abundance of Chloroflexi was opposite (P

In order to provide a clear guidance for biogas development in rural China, the progress and current status of rural biogas, critical factors influencing biogas development in rural areas, and probable biogas transformations are discussed in this paper. Rural biogas in China experiences rapid development in the past fifteen years and subsidies and policies from Chinese government are two main driving forces for promoting this development. For the recent days, the growth rate of household biogas decreased and that of Medium-to-large biogas projects (MLBPs) obviously increased. Several surveys showed that the utilization rate of household biogas greatly decreased and more and more digesters were discontinued. The underlying reasons for these changes come from the development of large-scale livestock farms, agricultural modernization and urbanization, which deeply affect the agricultural and social environment in rural China. The development of these agricultural and social factors all create positive conditions for MLBPs, but they negatively affect household biogas projects in terms of biomass supply and their participation in modern agricultural processes. Ongoing transformations and developments in local agriculture and rural society significantly influence the patterns of biogas projects. For future biogas development, MLBPs should be encouraged and the reduction of household biogas projects should be allowed to continue. However, recommendations on probable biogas development transformations suggest that the decision for expanding or abandoning the household projects in certain regions should be consistent with the developments and trends of local agriculture and society. For MLBPs, suitable developing models and reasonable operating mechanisms should be fully considered for assuring their benefits and continuous operation.

Soil water-stable aggregates (WSAs) are the basic unit of soil constitution and can contribute to remaining the stable soil constitution. The objective of this study was to clarify the distribution and stability of WSAs and the soil organic carbon (SOC), the total nitrogen (TN), and the total phosphorus (TP) concentrations in 0 - 20 cm and 20 - 40 cm soil layers under the different ages of Robinia pseudoacacia plantations. The 20, 25, 40, and 50 years-old Robinia pseudoacacia plantations were selected. Stepwise regression analysis showed that >5 mm and 1 - 2 mm WSAs, SOC concentration in 2 - 5 mm WSAs, and TN and TP concentrations in < 0.25 mm WSAs were dominant independent variables affecting aggregate stability and that SOC in 0.25 - 0.5 mm WSAs, TN in

Nitrogen fertilization significantly increases greenhouse gases (GHGs) emission, when applied from inorganic or organic sources. Minimizing GHGs from agroecosystems without compromising crop yield for stabilization of green production systems remains a challenge. Being an integral component of wheat production technology, the nitrogen (N) application deems to be indispensable. Thus, to reduce the application of N fertilizer and keep in view the minimization of GHGs emission, without compromising soil fertility and wheat production, field experiments were performed with treatments included maize straw mulch (S1: 0, S2: 4500, S3: 9000 kg ha−1) and nitrogen fertilizer (N1: 0, N2: 192 and N3: 240 kg ha−1) during 2015–17. Results showed that the cumulative CO2 and N2O emission from 9000 kg ha−1 of maize straw mulch with 192 kg N ha−1 (S3N2) significantly decreased by 0.67% and 33.7%, respectively, averaged over two years compared with that of 9000 kg ha−1 of maize straw mulch with 240 kg N ha−1 (S3N3). Likewise, the average soil moisture content significantly increased by 10% and 10.6% for S3N2 and S3N3 treatments at 0–10 cm soil depth, respectively, compared to S1N1. Similarly, the S3N2 and S3N3 treatments had lowered the soil temperature by 0.2 and 0.1 °C, respectively, over S1N1 in wheat grown fields. The grain yield of wheat was increased by 45% and 45% under S3N3 and S3N2 treatments than S1N1, respectively. The S3N2 treatment was more economical than S3N3 for wheat crop. Therefore, maize straw mulch (S3) combined with 20% less N fertilizer (N2) from commercial source were considered as a viable production technology to improve crop yield, and reduce soil CO2 and N2O emissions.

Afforestation has been proven to have enormous potential for carbon (C) sequestration; however, the dynamics of aggregate-associated organic carbon (OC) following afforestation and their contribution to changes in bulk soil OC are not well understood in regions with serious soil erosion. Therefore, we investigated the dynamics of OC associated with aggregates along a Robinia pseudoacacia (RP) afforestation chronosequence in the Loess Plateau. Soil aggregate size distribution and OC dynamics in bulk soil were analyzed 10, 18, 28, and 42 years after RP afforestation at depths of 0-20 cm and 20-40 cm. Results showed that total macroaggregates (0.25 mm), mean weight diameter, and geometric mean diameter increased significantly with stand age, after 42 years of afforestation, increased by 433.5%, 437.2%, 302.1% in the 0-20 cm depth, respectively, while microaggregate amounts decreased by 52.9%, and the proportions of silt + clay fraction showed no obvious changes. Long-term afforestation increased OC content and stock, both in bulk soil (245.6% and 222.9% in the 0-20 cm depth, respectively) and soil aggregates. The improvement of soil structure and enrichment of OC stocks were greater at the 0-20 cm depth than the 20-40 cm depth. In addition, small macroaggregates (2-0.25 mm) contained the highest OC content and microaggregates (0.025 mm) had the highest OC stocks regardless of soil depth and stand age. Across the afforestation chronosequence, OC content and stock in bulk soil positively correlated with large macroaggregate (2 mm) amounts and small macroaggregate (2-0.25 mm) associated OC dynamics (P 0.01). These results indicated that changes in bulk soil OC dynamics mainly depend on changes in the proportion of large macroaggregates and in the OC dynamics associated with small macroaggregates after RP afforestation.

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&ndash, soil&ndash, 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&ndash, 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&ndash, 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&ndash, 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&ndash, soil systems in afforested ecosystems and could help in improving the predictions of sustainably restoring C. korshinskii plantations.

Soil microorganisms play an important role in the functional connection of nutrient cycling between plants and soil ecosystems, but the exact responses of microbial communities to change in plant characteristics and soil properties remain uncertain. We analyzed the soil microbial communities of afforested tree stands of varying ages to assess the effects of vegetation and soil quality on soil microbial communities. We studied Robinia pseudoacacia plantations in the Loess Plateau for three age classes (RP13, RP29, and RP44), and compared results from these classes to one farmland (FL) control. The responses of soil microbial communities to changes in understory flora and soil physicochemical properties, including the Shannon index, richness, coverage, and biomass were analyzed. Compared with FL, afforestation significantly increased the Shannon index, species richness, coverage, and biomass of understory plants, which were highest in RP29. The concentrations of soil organic carbon (SOC), total nitrogen (TN), nitrate nitrogen (NO3−-N), and ammoniacal nitrogen (NH4+-N) were highest in RP44. The soil microbial community diversity index was significantly affected by afforestation. The relative abundances of bacterial populations were also affected, with Proteobacteria being dominant in RP29 and Actinobacteria being dominant in FL. Similarly, in fungi, the relative abundance of Basidiomycota was highest in FL, while the relative abundances of Zygomycota were highest in RP29. Pearson correlation analysis revealed that the Shannon and Chao indices of soil fungi were significantly positively correlated with SOC and NH4+-N. RDA showed that SOC, NH4+-N, and soil water content (SWC) were significantly associated with soil bacterial community composition. Soil fungal community composition were significantly affected by the Shannon and Richness indexes of understory flora. The results showed that characteristics of understory flora, soil properties, and soil microbial community composition were all affected by afforestation. The composition of the fungal community was correlated with changes in the diversity of understory flora. The changes in nutrients such as organic carbon and inorganic nitrogen was the key to the changes of soil microorganisms as plant colonization.

Nutrient resorption by senesced leaves is an important mechanism for the preservation of plant nutrients. However, our understanding of nutrient resorption patterns and drivers of plantations in Loess Plateau is limited. In this study, four main tree species (Robinia pseudoacacia [RP], Pinus tabuliformis [PT], Armeniaca sibirica [AS], and Caragana korshinskii [CK]) were compared in plantations on the Loess Plateau. We explored the relationships among nitrogen resorption efficiency (NRE), phosphorus resorption efficiency (PRE), plant nutrients (green leaf total nitrogen [TNgr] and total phosphorus [TPgr]), stand ages, growth rates (height growth rate [HGR] and diameter growth rate [DGR]), soil nutrients (soil total nitrogen [STN] and total phosphorus [STP]), available nutrients (soil inorganic nitrogen [SIN] and available phosphorus [SAP]), soil water content (SWC), and stoichiometries. We found that significant differences in nutrient resorption efficiencies among different afforested tree species. And the increase of N:P ratios of leaves and soil, and the decrease of SAP enhanced P-limited. Furthermore, the resorption efficiencies of different species differed in response to nutrients, stoichiometries, and plant growth. PRE was significantly negatively correlated with the DGR of deciduous species; however, NRE of N-fixing plant was positively correlated with plant growth rates. And the contributions of SWC and SAP were greater for nutrient resorption compared to other variables. The STN:STP and SIN:SAP were significantly correlated with leaf N:P, NRE, PRE, and PRE: NRE. Overall, plant growth rates may be regulated by absorption strategies due to leaf lifespan and N-fixing capacity of tree species. Resorption efficiencies were significantly correlated with SWC and SAP showed that soil moisture and available phosphorus were the primary drivers of nutrient resorption strategies. The association of PRE: NRE with N:P ratios indicated that nutrient resorption was driven by the coupling effect of N and P in plants and soil.

Non-point source pollution (NPSP) is a major challenge for current global water resources. The output characteristics of pollutants under different land use types are very important for controlling NPSP. In this study, long-term positioning monitoring and an analysis of rainfall runoff from different land use types were used to evaluate a typical watershed in the water source area of the middle route of the South-to-North Water Diversion Project (MR-SNWDP). The results show significant differences in nitrogen and phosphorus content in the runoff water bodies of various land use types. The nitrogen and phosphorus content in the MR-SNWDP was directly related to rainfall intensity and the fertilization period in the runoff following fertilization of farmland and vegetable plots. This nitrogen and phosphorus content was also observed to be significantly higher in the fertilization period than in other periods. The loss of nitrogen and phosphorus in forestland was greatly affected by rainfall intensity. Nitrogen in runoff comes primarily from farmland and vegetable fields, where its main form is nitrate nitrogen (NN). Vegetable fields are the main source of phosphorus, where its primary form is soluble phosphate (PO43&minus, P). Nitrogen and phosphorus have a defined incubation period during the dry season. Farmland and vegetable fields receive less rainfall during the dry season and it is difficult to form effective runoff, this allows nitrogen and phosphorus deposition. The runoff formed by the first rainfall at the beginning of the flood season (April or May) will carry a large amount of nitrogen and phosphorus from the soil into water bodies. Therefore, it is crucial to pay careful attention to the season when attempting to control NPSP.

Agricultural non-point source (NPS) pollution in water source protection areas poses serious challenges for governments in developing countries. It is important to consider the environmental behavior of farmers when exploring the causes of NPS pollution as well as when establishing scientific controls and management measures. However, the poor understanding of factors influencing the environmental behavior of farmers and the lack of a suitable environmental socio-psychological model limit the application of the environmental behavior of farmers in NPS pollution management. In this study, we therefore integrated the theory of planned behavior (TPB) and the protection motivation theory (PMT) to identify the main determinants of the NPS pollution-related environmental behavior and intention of farmers in the Water Source Area of the Middle Route of the South-to-North Water Diversion Project in China. Results indicated that the integrated model provided a better understanding of the environmental behavior and intention of farmers than that provided by each component when used individually, and revealed that farmers perceived that the susceptibility and severity of threats caused by water deterioration influenced environmental intention through the mediating effects of subjective norm and attitude toward adopting pro-environmental behavior. At the same time, the perceived vulnerability of farmers was relatively high and their perceived severity was relatively low. Furthermore, the subjective norm, attitude, self-efficacy (i.e., the perceived behavioral control), and response efficacy positively and significantly influenced intention. However, response cost had a significantly negative effect on intention. Among them, subjective norm had the largest effect on intention. Intention was the key determinant for the actual environmental behavior of farmers, while self-efficacy also had a significantly positive effect on behavior. Managing and controlling agricultural NPS pollution requires a multi-disciplinary and comprehensive approach. Therefore, an integrated theoretical framework was developed in this study by integrating TPB and PMT to gain insight into the environmental behaviors and intention of farmers. The results provided a theoretical basis for NPS pollution control.

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&ndash, 10 and 10&ndash, 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 microorganisms play an important role in the functional connection between above- and below-ground ecosystems during vegetation restoration. However, the influencing patterns of plants and soils on the microbial properties in the process remain unclear, especially in ecologically fragile zones. Here, we investigated soil bacterial and fungal communities at twelve Pinus tabulaeformis stands on Ziwuling Mountain in Loess Hilly Region, along an age gradient from 15- to 45-year-old stands, with respect to abundance and diversity using Illumina sequencing of the 16S rRNA gene and ITS gene, respectively. Soil microbial biomass, enzyme activity, vegetation characteristics (i.e., coverage, fine root biomass, and the composition and diversity) and soil properties (i.e., bulk density, organic C, total N, and available N) were also determined. The results showed that the microbial biomass increased significantly along the restoration chronosequence, being consistently the highest at the 45-y site. However, the saccharase, urease, catalase, and alkaline phosphatase that regulate soil organic matter and nutrient transformation were less impacted by the restoration time. Bacterial alpha diversity gradually increased with time whereas fungal alpha diversity was highest at the 30-y site, which was related to increasing levels of NO3−, coverage, and fine root biomass. The response of soil bacterial beta diversity to the age gradients was larger than that of fungal beta diversity, although both groups were significantly affected by vegetation restoration. Moreover, bacterial communities were dominated by oligotrophic Actinobacteria at 15-y and 25-y sites and transformed into copiotrophic Proteobacteria-dominant at 30-y and 45-y sites. However, no significant variation in the fungal dominant phyla (i.e., Ascomycota, Basidiomycota, and Zygomycota) were detected with restoration. Furthermore, the dominant species [Pinus tabulaeformis (tree) and Carex tristachya (herb)] affected the microbial biomass, diversity, and abundance of bacterial dominant phyla significantly, but affected the fungal community composition much less. Vegetation diversity has no significant effect on microbial diversities (alpha and beta diversity). Soil physicochemical factors could widely explain the variations in microbial diversity and community composition, enzyme activity, and microbial biomass in restoration processes, especially bulk density and NO3−. Overall, our results demonstrate that soil bacteria rather than fungi can reflect the changes in plant and soil properties with increasing stand age, and the shifts in the predominant bacterial and fungal characteristics along the age gradient were mainly the result of differences in soil physicochemical factors prevailing at each restoration stage.

Microbial denitrification is an important part of the soil nitrogen cycling process and is the main way that naturally-fixed nitrogen returns to the atmosphere. Research to date has mainly focused on the effects of temperature, pH and carbon sources on denitrification, with the effects of different vegetation types thought to be relatively small. This study investigated the soil denitrification process in the Loess hilly region of China. Four typical land-use types were selected: farmland (FL), abandoned land (AL), Caragana korshinskii (CK), and Robinia pseudoacacia (RP). The functional gene nosZ, which regulates nitrous oxide reductase (N2OR), was selected as the target primer. High-throughput sequencing was carried out and the composition of soil properties was determined. The physicochemical properties of soil, including nitrate nitrogen and organic carbon levels, were studied to explore soil microbial compositions and species diversities and their main influences. Compared with FL, the content of ammonium nitrogen (AN) in AL, CK, and RP soils was 28.5%, 29.7% and 28.8% higher, respectively, while nitrate nitrogen was 1.39-, 1.96-, and 1.55-fold higher, respectively. The Shannon index showed that the microbial diversity of the nosZ gene in RP was greater than that in FL. Nonmetric multidimensional scaling analysis showed that the FL distribution was much different from those of AL, CK, and RP; meanwhile, the AL, CK, and RP distributions tended to overlap, which indicates that there were only small differences in species compositions. Redundancy analysis showed that AN is a key environmental factor affecting the nosZ type microorganisms composition in different taxonomic levels, and the contribution rates can reach 74.3% (p = 0.006), 73.2% (p = 0.004), and 62.6% (p = 0.008), respectively (from phylum to order). This study revealed the α- and β -diversities of nosZ type microorganisms and the key environmental influences on the composition of microorganisms with the land-use change. It provides a reference for further study on the heterogeneity of nitrogen output processes in different land use types.

The use of crop residues as mulching materials or organic fertilizer, instead of burning, can help improve the soil organic carbon (SOC) and crop grain yield. An experiment was conducted for three consecutive seasons from 2013 to 2016, to study the effect of no straw (S0), S1/2 (700 kg/ha soybean straw, and 3000 kg/ha wheat straw), and S1 (1400 kg ha−1 soybean straw, and 6000 kg/ha wheat straw) treatments in wheat-soybean multi-crop system. The randomized complete block design was used with three repeats. Compared with the S0 regime, a significant increase of 0.5%–8.7% and 1.4%–27.7% in soil CO2 emission was observed in the S1 regime during all growth stages of summer soybean and winter wheat, respectively. Soil temperature of S1/2 and S1 was 0.1–1.1 °C and 0.3–1.4 °C higher than that of S0 during the seeding stage and greening stage for wheat, during 2013 to 2016. During wheat season, soil moisture was higher in the S1 than in the S0 treatment. Likewise, wheat, soybean crop resulted the same results. Soil CO2 emissions increase with the increasing in soil temperature, and 73.4–73.9% of the variation could be explained by seasonal variation in soil temperature in wheat season. Similarly, 69.5–74.7% of the variation in soil CO2 emissions is recorded by seasonal variation in soil temperature in summer soybean season. Meanwhile (S1) increased the SOC and grain yield of wheat and soybean when compared to S0. Straw input increasing soil CO2, grain yield and SOC content, considering the benefits of straw inputs to crops yield and SOC content, It is concluded that the addition of straw improve agriculture production. However, the types of straw inputs in order to promote the sequestration of soil organic carbon with the decrease in greenhouse gas emission is the future research direction for agriculture development in Guanzhong region of China.

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.

The environmental behavior of farmers plays an important role in exploring the causes of non-point source pollution and taking scientific control and management measures. Based on the theory of planned behavior (TPB), the present study investigated the environmental behavior of farmers in the Water Source Area of the Middle Route of the South-to-North Water Diversion Project in China. Results showed that TPB could explain farmers' environmental behavior (SMC=0.26) and intention (SMC=0.36) well. Furthermore, the farmers' attitude towards behavior (AB), subjective norm (SN), and perceived behavioral control (PBC) positively and significantly influenced their environmental intention; their environmental intention further impacted their behavior. SN was proved to be the main key factor indirectly influencing the farmers' environmental behavior, while PBC had no significant and direct effect. Moreover, environmental knowledge following as a moderator, gender and age was used as control variables to conduct the environmental knowledge on TPB construct moderated mediation analysis. It demonstrated that gender had a significant controlling effect on environmental behavior; that is, males engage in more environmentally friendly behaviors. However, age showed a significant negative controlling effect on pro-environmental intention and an opposite effect on pro-environmental behavior. In addition, environmental knowledge could negatively moderate the relationship between PBC and environmental intention. PBC had a greater impact on the environmental intention of farmers with poor environmental knowledge, compared to those with plenty environmental knowledge. Altogether, the present study could provide a theoretical basis for non-point source pollution control and management.

Farmers’ pro-ecological intentions (PEI) after ecological rehabilitation are crucial to the sustainability of ecological conservation achievements and attract attention from policy-makers and managers. However, studies regarding multiple factors and their mechanism of influence on farmer's PEI are limited in fragile environmental areas. We conducted a household survey that measures the perceptions and attitudes, and the individual, demographic, and economic properties of 2025 farmers in the Loess Plateau of China. Results showed that only 28.74% of the respondents intended to apply the pro-ecological behavior after ecological restoration. The structural equation model reported a high explanatory power of 77.6% for farmers’ PEI. Farmers’ intentions to apply pro-ecological behaviors are jointly affected by various factors, with their perceptions and attitudes found to be the most influential factor and a vital link to other factors. Farmers’ individual, demographic, and economic factors also showed significant effects. Younger male farmers with higher education degrees, and better self-assessment of their abilities and perception of environmental improvement tend to state a greater intention to apply pro-ecological behaviors after the ecological rehabilitation. Results suggest that policy-makers and managers wanting to encourage farmers taking pro-ecological actions after ecological programs should value both enhancing farmers’ abilities to conserve ecological achievements and their perceptions of ecological benefits.

To enhance biogas production and identify new additive materials for the co-digestion of wheat straw, sheep manure, and chicken manure, batch experiments were investigated in this study. Experiments were conducted on the influence of additive materials on a range of manure/straw ratios (3:7, 5:5, and 7:3) and biogas production under a mesophilic temperature (35 °C). Results showed that the maximum increments of methane production (L/kg · VSadd) with the addition of 3 g magnetite and 1 g natural zeolite were 52.01% and 51.01%, respectively. The addition of magnetite and zeolite in the anaerobic digestion process produced a good fermentation environment. By using the response optimizer when the manure proportion was 52%, the best methane yield was obtained with the addition of 2.7 g magnetite. For zeolite, the best addition dose was 1 g and the optimum manure proportion is 63%. Magnetite had a more extensive increase in methane yield than zeolite.

This study investigated the effects of different initial pH (6.0, 6.5, 7.0, 7.5 and 8.0) and uncontrolled initial pH (CK) on the lab-scale anaerobic co-digestion of kitchen waste (KW) with cow manure (CM). The variations of pH, alkalinity, volatile fatty acids (VFAs) and total ammonia nitrogen (NH4(+)-N) were analyzed. The modified Gompertz equation was used for selecting the optimal initial pH through comprehensive evaluation of methane production potential, degradation of volatile solids (VS), and lag-phase time. The results showed that CK and the fermentation with initial pH of 6.0 failed. The pH values of the rest treatments reached 7.7-7.9 with significantly increased methane production. The predicted lag-phase times of treatments with initial pH of 6.5 and 7.5 were 21 and 22 days, which were 10 days shorter than the treatments with initial pH of 7.0 and 8.0, respectively. The maximum methane production potential (8579 mL) and VS degradation rate (179.8 mL/g VS) were obtained when the initial pH was 7.5, which is recommended for co-digestion of KW and CM.

The contradictions between the increasing energy demand and decreasing fossil fuels are making the use of renewable energy the key to the sustainable development of energy in the future. Biogas, a renewable clean energy, can be obtained by the anaerobic fermentation of manure waste and agricultural straw. This study examined the initial pH value had obvious effect on methane production and the process in the thermophilic anaerobic co-digestion. Five different initial pH levels with three different manure ratios were tested. All digesters in different initial pH showed a diverse methane production after 35 days. The VFA/alkalinity ratio of the optimum reaction condition for methanogens activity was in the range of 0.1-0.3 and the optimal condition that at the 70% dung ratio and initial pH 6.81, was expected to achieve maximum total biogas production (146.32 mL/g VS).

The afforestation of abandoned land could offer opportunities to sequester soil organic carbon (SOC), promote nutriment elements cycling, improve plant diversity in the plantation understory and provide ecosystem services. The objectives of this study were to identify plant diversity in the plantation understory, quantify the changes in SOC and total nitrogen (TN) storage in deep soil, assess the SOC, TN, and total phosphorus (TP) stoichiometries, and investigate their relationships in the Loess Plateau Region (LPR) undergoing long-term afforestation. Soil samples were collected at a soil depth of 0–200 cm under 30-yr old Robinia pseudoacacia L. and adjacent abandoned sites, and SOC, TN and TP were determined in different soil depth. Additionally, plant composition and diversity in the plantation understory were evaluated. The results showed that land subjected to long-term afforestation had greater plant coverage, plant density, richness index ( R ) and Shannon–Wiener diversity ( H ) compared to abandoned land communities ( P P P P R CN , R CP , and R NP ratios.

Energy crisis is receiving attention with regard to the global economy and environmental sustainable development. Developing new energy resources to optimize the energy supply structure has become an important measure to prevent energy shortage as well as achieving energy conservation and emission reduction in China. This study proposed the concept of energy agriculture and constructed an energy agricultural technical support system based on the analysis of energy supply and demand and China’s foreign dependence on energy resources, combined with the function of agriculture in the energy field. Manufacturing technology equipment and agricultural and forestry energy, including crop or forestry plants and animal feces, were used in the system. The current status and future potential of China’s marginal land resources, energy crop germplasm resources, and agricultural and forestry waste energy-oriented resources were analyzed. Developing the function of traditional agriculture in food production may promote China’s social, economic, and environmental sustainable development and achieve energy saving and emission reduction.

Alt'itudinal gradients strongly affect plant biodiversity, but the effects on microbial patterns remain unclear, especially in the large scale. We therefore designed an altitudinal gradient experiment that covered three climate zones to monitor soil microbial community dynamics and to compare those with plant and soil characteristics. Illumina sequencing of the 16S rRNA gene and ITS gene was used to analyze soil microbial (bacterial and fungal) diversity and composition, and fumigation-extraction was used to determine microbial biomass; the plant community metrics (i.e., percent cover, Shannon-Wiener, grass biomass, and carbon/nitrogen in leaf and biomass) and soil properties (i.e., soil moisture, soil temperature, bulk density, organic carbon, total nitrogen, and available nitrogen) were determined. The results showed that carbon/nitrogen in microbial biomass was higher at medium altitude and was positively related to carbon and nitrogen in both soil and grass biomass along the altitudinal gradients. Soil bacterial alpha diversity was significantly higher at medium altitude but fungal alpha diversity did not affected by altitudinal gradients; the effect of altitudinal gradients on bacterial beta diversity was larger than that on fungal beta diversity, although both groups were significantly affected by altitudinal gradients. Moreover, Alpha-proteobacteria, Beta-proteobacteria, and Gemmatimonadetes were significantly more abundant in higher altitude than in lower altitude, both Acidobacteria and Actinobacteria significantly declined with increasing altitude; other bacterial taxa such as Chloroflexi, Nitrospirae, Gamma-proteobacteria, and Delta-proteobacteria were significantly higher at medium altitudes. For fungal taxa, Basidiomycota and Ascomycota were the dominant phyla and responded insignificantly to the altitudinal gradients. The responses of microbial alpha diversity were mostly associated with plant Shannon index, organic carbon, and total nitrogen, whereas microbial beta diversity and composition mainly depended on soil moisture and temperature. Overall, these results suggest that soil bacteria rather than fungi can reflect changes in plant and soil characteristics along altitudinal gradients.

Anaerobic digestion (AD) with livestock manure is a promising way for biogas production. This work presents the influence of photo-dark fermentation on biogas production of pig manure (PM) and dairy manure (DM). All sets were conducted with temperature 35 ± 2 °C and total solid concentrations 8%: PM1 and DM1 in transparent reactor under sunlight for photo-dark fermentation, and PM2 and DM2 in non-transparent reactor for dark fermentation. DM2 had the best cumulative biogas production (CBP) of 15,447.5 mL, followed by PM1 (15,020 mL) with stable pH and low total ammonium nitrogen (TAN) concentration (1384.99 mg/L), and DM1 and PM2. The CBP of DM2 was 5.77 times as much as PM2. The relationship between CBP and four factors including volatile fatty acid (VFA), TAN, total alkalinity and pH was analyzed. pH gained the maximum determination coefficient with the CBP among all sets and total alkalinity showed negative correlation with CBP of PM1 and DM1.

As a renewable energy source, biogas not only alleviates energy shortage in rural areas but also effectively reduces the environmental risk associated with agricultural waste management. This study presents a comprehensive overview of development of household bio-digesters and medium and large-scale biogas plants (MLBPs) in China, and discusses the advantages and disadvantages of both biogas systems in terms of environmental performance, role in agriculture, economic benefit, government support, energy efficiency, societal influence, and resident living mode. Both systems have their relative strengths and weaknesses. The operation and maintenance of household bio-digesters are easier, and their environmental and economic performances are superior compared to those of MLBPs. However, MLBPs have higher energy efficiency and better social effect. Thus, the choice of a biogas generation system depends on the local circumstances. Household bio-digesters are suitable for undeveloped regions where the rural residents live far apart from each other, whereas MLBPs are suitable for developed regions where people live close together. The government can play a positive role in preventing the negative impacts of rural social structural change, such as those of urban migration of adults, on household biogas development. Additionally, establishment of scientific and technological support and service systems is recommended for further development of biogas in rural China.

Because of the resource abundance and high total nitrogen content, chicken manure (CM) is very suitable for anaerobic digestion (AD). In this study, a set of comparative assays was performed on the AD of CM using three main cereal residues (CRs) as co-substrates under various mixing combinations, with a total solid concentration of 8%. Under mesophilic conditions at 35 ± 1 °C, all combinations of CM and CRs significantly improved biogas and methane yields. Co-digestion of CM and corn stalks (CS) showed higher cumulative biogas productions than that of CM/wheat straw (WS) and CM/rice straw (RS). After 60 days of fermentation, the highest methane contents were produced by CM/WS, CM/CS, and CM/RS at a total solid (TS) ratio of 50:50 of 345, 383, and 378 mL/g of removed volatile solids (VSremoved), respectively. The value between 15 and 25 has been suggested as the optimal range of the C/N ratio for the co-fermentation of CM with CRs. The results of the volatile fatty acid/alkalinity analysis clearly demonstr...

The depth of sampling is an important factor for evaluating soil stability. The objective of this study was to test soil aggregate particle-size fractions and soil organic carbon (SOC) in water-stable aggregate by vegetation restoration through 0-60 cm soil profile. We collected soil samples in 30 years old Robinia psendoacacia (Rr); Platycladus orientalis (Po); Pinus tabulaeformis (Pt); abandoned land (Ab), and slope cropland (Sc), which were separated into > 2, 2-1, 1-0.25, 0.25-0.053, and 0.25 mm water-stable aggregates (WSA) and mean weight diameter (MWD) were calculated in 0-60 cm soil depth. Results showed that soil aggregate fractions (> 0.25 mm) of four vegetation types were significantly ( P 0.25 mm) under Rr, Po, Pt, and Ab was higher more than 37.7, 92.4, 92.5, 79.1%, respectively in 40-60 cm compared with Sc additionally, > 0.25 mm WSA and MWD was significantly higher in Pt soil in 20-40 cm, 40-60 cm soil depth ( P < 0.05 ). The results demonstrated that soil stability was enhanced and SOC content was increased after converting slope cropland to forest, especially under Pt forest that greatly influenced the subsoil.

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

Forest development gradually changes the above-ground plant community, but the potential effects on the below-ground microbial community remain unclear, particularly at the various succession stages. Here, we investigated six vegetation types that covered two succession stages (early and late stages) during forest development. The early stage showed changes from two pioneer communities (Betula platyphylla and Populus davidiana) to two mixed communities (Populus davidiana with Pinus tabuliformis), while the late stage showed changes from the two mixed communities to two climax communities (Quercus wutaishanica and Pinus tabuliformis). Illumina sequencing of the 16S rRNA gene and ITS gene were carried out to analyze soil microbial (bacterial and fungal) diversity and composition. Soil properties (i.e., moisture, bulk density, texture, ammonium nitrogen, nitrate nitrogen, organic carbon, total nitrogen, and total phosphorus) were also determined. The results showed that forest development had positive effects on microbial diversity. Particularly, bacterial diversity successions proceed faster than that of fungi at the early stage. Proteobacteria and Bacteroidetes significantly increased, but Actinobacteria and Acidobacteria significantly decreased during forest development. In contrast, the effect sizes of Proteobacteria, Actinobacteria, and Acidobacteria at the early stage were larger than those at the late stage. The dominant fungi phyla (i.e., Ascomycota, Basidiomycota, and Zygomycota) across all soil samples responded insignificantly to forest development. Such differential responses of the microbial diversity and dominant phyla were significantly correlated with soil texture, soil organic carbon, and total nitrogen. In contrast, the effect size of soil properties on bacterial phyla was larger than that on fungal phyla. Collectively, these results emphasize that the responses of the microbial community to forest development depend on the succession stage, and also suggest that bacteria and fungi may not follow the same successional trajectories due to the differed responses of bacteria and fungi to changing soil texture and carbon/nitrogen contents during forest development.

Vegetation restoration can control soil erosion and improve soil quality; however, these positive effects on soil quality can be challenged with inceasing aridity. It is vital to understand the mechanisms affecting soil quality along aridity gradients and to determine the appropriate revegetation types for soil restoration. In this study, we selected three revegetation types (forest, shrub, and grass) along four precipitation gradients (365, 452, 507, and 600 mm mean annual precipitation [MAP]) to analyze the changes in soil properties from two soil layers (0–10 and 10–20 cm). To quantify the variations in soil quality, a soil quality index (SQI) combining the chemical, physical, and biological properties was developed. The results showed that the SQI was formed based on total nitrogen, clay, urease, and pH. In both soil layers, SQI values increased significantly (P

Land use change is widely considered as a major factor that affects soil organic carbon (SOC) sequestration. Conversion of sloped croplands to perennial vegetation could increase SOC accumulation. The Grain-to-Green Program (GTGP) implemented in 1999, which converts low-yield sloped croplands into forest, shrub, and grassland, is not only a nationwide ecological recovery project but also the largest payment-for-ecosystem-service program in China. Based on data concerning carbon change in GTGP-related zones collected from published literature, this report (i) provides an estimate of the SOC sequestration potential and the rate of SOC sequestration caused by the GTGP in China; (ii) illustrates the differences in SOC sequestration in zones with different land use types (i.e., forest, shrub, and grassland), different precipitation rates, and restoration ages. Soil organic carbon sequestration caused by the GTGP was estimated to be 14.46 TG C year (a rate of 0.54 Mg C ha year). The SOC sequestration significantly increased in forest lands (P < 0.05), which was greater than 18.7% and 42.9% in shrublands and grasslands, respectively. However, the average rate of SOC accretion was greater in grassland, followed by forest lands. Annual average precipitation and restoration age greatly affected the SOC sequestration. The average SOC sequestration increased with restoration age, whereas the average rates of SOC sequestration decreased. The GTGP resulted in increased SOC storage, making significant contribution to carbon sequestration in China.

To investigate the feasibility of statistical methods in optimizing the feeding composition in anaerobic co-digestion, a simplex-centroid mixture design (SCMD) and central composite design (CCD) were evaluated with methane potential as the response variable. Dairy manure, chicken manure, swine manure and rice straw (RS) were selected as raw materials and two kinds of manures and RS were mixed in each blend. Each component served as an independent variable in the SCMD and CCD and involved two factors, the manure and C/N ratios. Co-digestion of three-component substrates resulted in higher methane potentials than single and two-component substrates. In response surface plots, SCMD showed the interactions among each component in the co-substrates and CCD presented the interaction between the ratio of manures and the C/N ratio. SCMD and CCD are both suitable methods for optimizing the feeding composition during anaerobic co-digestion.

In the present paper, we investigated the effects of afforestation on nitrogen fractions and microbial communities. A total of 24 soil samples were collected from farmland (FL) and three afforested lands, namely Robinia pseudoacacia L (RP), Caragana korshinskii Kom (CK), and abandoned land (AL), which have been arable for the past 40 years. Quantitative PCR and Illumina sequencing of 16S rRNA genes were used to analyze soil bacterial abundance, diversity, and composition. Additionally, soil nitrogen (N) stocks and fractions were estimated. The results showed that soil N stock, N fractions, and bacterial abundance and diversity increased following afforestation. Proteobacteria, Acidobacteria, and Actinobacteria were the dominant phyla of soil bacterial compositions. Overall, soil bacterial compositions generally changed from Actinobacteria (Acidobacteria)-dominant to Proteobacteria-dominant following afforestation. Soil N fractions, especially for dissolved organic nitrogen (DON), were significantly correlated with most bacterial groups and bacterial diversity, while potential competitive interactions between Proteobacteria (order Rhizobiales) and Cyanobacteria were suggested. In contrast, nitrate nitrogen (NO3−-N) influenced soil bacterial compositions less than other N fractions. Therefore, the present study demonstrated that bacterial diversity and specific species respond to farmland-to-forest conversion and hence have the potential to affect N dynamic processes in the Loess Plateau.

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.

Dairy manure (DM), chicken manure (CM) and wheat straw were used to investigate the possibility of optimizing the methane (CH4) potentials in anaerobic co-digestion of multiple substrates. Response surface methodology (RSM) was used to evaluate the individual and interactive effects of four variables [carbon/nitrogen (C/N) ratio, the feeding composition (DM/CM), initial substrate loading and inoculum-to-substrate ratio (ISR)] in the digestion process. All four variables had significant effects on CH4 potentials. Interactive effects of C/N and DM/CM ratios, C/N ratio and ISR, initial substrate loading and ISR were significant The optimum conditions were a C/N ratio of 26.31, a DM/CM ratio of 42.96:57.04, an initial loading of 15.90 g volatile solids (VS)/l and an ISR ratio of 2.34, with the maximum CH4 potential being 394 ml/g VS. The RSM model was appropriate for optimizing CH4 production in the process of anaerobic co-digestion of multiple substrates.

As a fuel, rural biogas is a promising renewable energy source. Policy support is a key initial impetus for industry development. This study explores household biogas development in rural China based on policy support found in literature. Relevant policies, which mainly include directive and guiding policies, economic inspiring policies, research policies, market policies, and other constructive policies, are gradually issued. Moreover, the National People's Congress has enacted five relevant laws, including the Agricultural Law, Renewable Energy Law, Animal Husbandry Law, Energy Conservation Law, and the Act on the Development of Circular Economy. The Energy Law is currently under revision. Relational rules and regulations have also been formed in response to the national policies and laws, which have already produced significant effects. The development of rural household biogas in China is growing steadily, and the technology standard projects have been established. The number of household biogas digesters and biogas annual output in 2010 was double of that in 2005. The offered financial incentive increased from 47 million dollars in 2002 to 760 million dollars in 2011. Policy supports play an important role in rural biogas development. And thus, additional national policy supports are necessary in the fields of scientific research, technological development, and biogas use model.

To clarify the differential responses of lianas and vines to rainfall, we investigated the distribution and abundance of climbers along the rainfall gradient in the Qinling Mountains of China. In our study, 28 climbing species were investigated across a rainfall gradient of 500–1,200 mm. Results indicated that most lianas and vines show restricted distribution along the rainfall gradient, which imply their adaptation to different water availabilities. A significant increase in the percentage of the total climbing species with rainfall was observed. The abundance and richness of lianas increased significantly with rainfall, whereas the vines remained constant. This difference implies that lianas have a higher sensitivity to water availability than vines. During drought, lianas may be vulnerable because of the drought-induced embolism, whereas vines are drought-resistant because of their shorter life spans and safer nutrient storage. Further research on the ecophysiological differences between lianas and vines is needed to provide a mechanistic explanation for the patterns described here.

It is not known if the species composition of herbaceous plant assemblies within tree-fall gaps is determined stochastically or whether it follows species-specific and environmentally-determined patterns. We applied three methods, fitting species abundance distribution models, comparing community similarities, and testing species–environmental variable association, to evaluate the relative importance of chance and deterministic rules in controlling herbaceous composition within canopy gaps in the Abies–Betula forests of Mt. Taibai, Central China. Herbaceous species abundance within canopy gaps was well fit by a neutral model, showing that relative abundance was qualitatively consistent with stochastic processes. Although species composition in gaps significantly differed from closed canopy sites (ANOSIM, R = 0.509, p = 0.001), there were no significant differences among gaps of different age groups (ANOSIM, R = 0.035, p = 0.191) or gaps of different size groups (ANOSIM, R = 0.089, p = 0.057). Similarly, gaps of similar age and size did not show significantly higher similarity (χ2 = 2.30, df = 3, p = 0.513) in species composition than gaps of distinct age or size. Moreover, there were only eight species, including two light-demanding species, confined to larger gaps among the 69 species, and only an additional seven species found more commonly in larger gaps, whereas most herbaceous species were gap size generalists. Canonical correspondence analysis and random permutation tests suggested that only 27% of species with abundance ⩾5 were associated with environmental variables in gaps. In summary, the species composition in gaps was not constrained significantly by gap traits; rather species were distributed stochastically, likely through by random dispersal and recruitment limitation of species from the surrounding available species pool. Measures that introduce gap disturbance, such as selective harvesting, are still recommended when the maintenance of total biodiversity in forests is a concern.

As a renewable energy, biogas is not only an important part of the development of rural new energy, but also an important aspect of sustainable development in China. The development process and present status of household biogas, specifically the opportunities and constraints of household biogas in rural China, are discussed in this paper. Only about 19% of the biogas potential has been utilized in rural China. There are several opportunities for household biogas development in rural China, including the problem of rural household energy consumption, the availability of biogas fermentation materials, national financial subsidies, legal and international clean development mechanisms. Also, more research needs to be done in straw fermentation and cold fermentation technology. Training should be conducted to raise the level of biogas customers in comprehensive biogas utilization. Measures should be taken to improve the follow-up services and management of biogas plants. The information presented in this paper will be helpful not only to the sustainable development of household biogas in rural China, but also to the development of biogas in similar countries around the world.

Five different N sources were compared with null N treatment to evaluate their performance for N-rich reference plot establishment in corn (Zea mays L.). The sources, including calcium ammonium nitrate (CAN), urea ammonium nitrate (UAN), polymer-coated urea (PCU) and environmentally smart nitrogen (ESN) in 2007 and 2008, and urea (URE), were broadcast or in-soil banded at the rate of 225 kg N ha -1 . A greenhouse trial was also conducted with N applied as CAN, URE, and ESN. Net photosynthesis rate (P N ) and chlorophyll fluorescence parameters (Fv/Fm or Fv'/Fm') were measured to assess N sources effects on corn photosynthesis. Relative photosynthetic capacity (RPC) and relative chlorophyll fluorescence capacity (RCFC) were calculated to evaluate the performance ofN sources in N-rich reference plot establishment. There were no differences in the release pattern ofN from different sources that could lead to differences in RPC and RCFC during the period when N status diagnosis is normally performed. Hence, all sources were equally effective to establish N-rich reference plots in our experimental conditions. It was also found that growers have the flexibility to either broadcast N at sowing or to band N along the rows at a later time after corn emergence.

Studies on the ecological conservation behavior of farmers usually focus on individual and socio-economic characteristics without consideration of the underlying psychological constructs, such as farmers' intention and perceptions. This study uses the theory of planned behavior (TPB), a typical social psychology construct, to analyze the factors affecting the intention and behavior of farmers for conserving the ecological achievements from payment for ecosystem service (PES) programs in eco-environmentally fragile areas. Questionnaires based on TPB were administered to 1004 farmers from the Grain to Green Program area in the Loess Plateau, China, with the resulting dataset used to identify the underlying factors determining farmers' intention and behavior based on the structural equation model. The results show that the farmers' intention and behavior toward conserving ecological achievements were explained well by TPB. The farmers'behavior was significantly positively affected by their intention toward conserving ecological achievements, and their intention was significantly influenced by their attitude (positive or negative value of performance), the subjective norm (social pressure in engaging behavior), and perceived behavioral control (perceptions of their ability). The farmers' degree of support for PES programs and their recognition of environmental effects were the factors that most influenced the farmers' attitude. Pressure from neighbors was the most potent driver of the subjective norm. Meanwhile, perceptions of their ability to perform the behavior were the most potent factors affecting intention and it was mostly driven by the farmers' feelings toward environmental improvement and perceived ability (time and labor) to participate in ecological conservation. The drivers of attitude, subjective norm, and perceived behavioral control can be used by policy makers to direct farmers' intention and behavior toward conserving ecological achievements in fragile eco-environmentally areas through PES programs. Thus, this strategy can improve the sustainability of ecological and environmental restoration programs.

This study investigated a typical secondary Betula platyphylla forest in the Ziwuling Mountains, Loess Plateau, China. In the sample plot, the DBH (diameter at breast height) class structure of B. platyphylla was bimodal. Individuals with small and large DBH values were abundant. The DBH structures of Quercus wutaishanica and Pinus tabulaeformis were close to that of the logistic model, thus suggesting the increasing population of these species. B. platyphylla and Populus davidiana showed random spatial distributions at almost all scales. However, Q. wutaishanica and P. tabulaeformis were significantly clumped at small scales. B. platyphylla had a negative spatial relation with Q. wutaishanica at small spatial scales. P. tabulaeformis and Q. wutaishanica showed negative spatial correlations at small scales, but they had positive correlations at large scales. These results suggest that P. tabulaeformis and Q. wutaishanica shared habitat preferences at these scales. In the future, the secondary B. platyphylla forest in the Ziwuling Mountains in the Loess Plateau will probably change into a multi-species mixed forest (Quercus-Pinus mixed forest). Assisted restoration strategies must be employed to improve the regeneration dynamics of the forest in the long term.

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.

The lime pretreatment process for rice straw was optimized to enhance the biodegradation performance and increase biogas yield. The optimization was implemented using response surface methodology (RSM) and Box-Behnken experimental design. The effects of biodegradation, as well as the interactive effects of Ca(OH)2concentration, pretreatment time, and inoculum amount on biogas improvement, were investigated. Rice straw compounds, such as lignin, cellulose, and hemicellulose, were significantly degraded with increasing Ca(OH)2concentration. The optimal conditions for the use of pretreated rice straw in anaerobic digestion were 9.81% Ca(OH)2(w/w TS), 5.89 d treatment time, and 45.12% inoculum content, which resulted in a methane yield of 225.3 mL/g VS. A determination coefficient (R2) of 96% was obtained, indicating that the model used to predict the anabolic digestion process shows a favorable fit with the experimental parameters.

This study applies the environmental Kuznets curve to test the relationship between the regional economic growth and the different types of agricultural nonpoint source pollution loads in the Ningxia Yellow River irrigation area by using the Johnes export coefficient method. Results show that the pollution load generated by crop cultivation and livestock-breeding industries in the Ningxia Yellow River irrigation area shows an inverted U-shaped feature; however, this feature is absent in living-sewage pollution load. Crop pollution has shown a decreasing trend since 1997 because of the increased per capita income of farmers. Livestock-breeding pollution load reached its turning point when the per capita income of farmers reached 8386.74 RMB. Therefore, an increase in the per capita income of farmers corresponds to an increase in the livestock-breeding pollution load in the Ningxia Yellow River irrigation area.

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.