Ratio Of Soil Organic Carbon Research Articles

Wheat Straw Incorporation Affecting Soil Carbon and Nitrogen Fractions in Chinese Paddy Soil

Soil organic carbon (SOC) and nitrogen (N) fractions greatly affect soil health and quality. This study explored the effects of wheat straw incorporation on Chinese rice paddy fields with four treatments: (1) a control (CK), (2) a mineral NPK fertilizer (NPK), (3) the moderate wheat straw (3 t ha−1) plus NPK (MSNPK), and (4) the high wheat straw (6 t ha−1) plus NPK (HSNPK). In total, 0–5, 5–10, 10–20, and 20–30 cm soil depths were sampled from paddy soil in China. Compared with the CK, the HSNPK treatment (p < 0.05) increased the C fraction content (from 13.91 to 53.78%), mainly including SOC, microbial biomass C (MBC), water-soluble organic C (WSOC), and labile organic C (LOC) in the soil profile (0–30 cm), and it also (p < 0.05) increased the soil N fraction content (from 10.70 to 55.31%) such as the soil total N (TN) at 0–10 cm depth, microbial biomass N (MBN) at 0–20 cm depth, total water-soluble N (WSTN) at 0–5 and 20–30 cm depths, and total labile N (LTN) at 0–30 cm depth. The primary components of soil LOC and LTN are MBC and MBN. Various soil C and N fractions positively correlated with each other (p < 0.05). The HSNPK treatment promoted the soil MBC, WSOC, and LOC to SOC ratios, and also promoted MBN, WSTN, and LTN to soil TN ratios at a depth of 0–20 cm. To summarize, the application of HSNPK could maintain and improve rice paddy soil quality, which leads to increased rice grain yields.

Effect of plateau zokor on soil carbon and nitrogen concentrations of alpine meadows

Small subterranean mammals cause extensive disturbance of grasslands by producing many mounds in the grasslands. This study aimed to evaluate the effect of a small subterranean mammal, plateau zokor (Myospalax fontanierii), on soil carbon and nitrogen concentrations in alpine meadows. In this study, the disturbance effect by plateau zokor on alpine meadow was classified into mound, edge vegetation zone and undisturbed vegetation areas, and a random stratified paired sampling design was used to collect soil samples at mound, edge vegetation zone and undisturbed vegetation area. The results of the present study found that the soil total carbon, organic carbon and total nitrogen concentrations in undisturbed soil were higher than those in mound soil and lower than those in edge soil; the nitrate nitrogen (NO3−-N) concentration in edge soil was higher than that in undisturbed soil and lower than that in mound soil. However, the soil inorganic carbon and ammonium nitrogen (NH4+-N) concentrations were site dependent. The results of the present study also found that ratios of soil organic carbon to soil total nitrogen (C: N) were lower in mound soil than in edge soil and undisturbed soil, and the ratios of NH4+-N to NO3−-N (ANR) were higher in mound soil than in edge soil and undisturbed soil across the three sites and at individual site, which imply that the lower C: N and higher ANR in mounds are a possible mechanism by which bare mound caused by small subterranean mammals can naturally recover. The findings of this study reveal the general patterns of soil total carbon, soil organic carbon, soil total nitrogen, NO3−-N, C: N, and ANR in relation to disturbance effects, and present a possible approach for estimating how the presence of a small subterranean mammals influences grassland soil carbon and soil nitrogen.

Effects of long-term (42 years) tillage sequence on soil chemical characteristics in a dryland farming system

No-tillage can improve soil quality but can also increase the stratification of soil chemical parameters. Nutrient uptake by crops might be limited when nutrients are stratified, especially in semi-arid or Mediterranean regions. To reduce stratification, infrequent tillage could be considered. However, there is a paucity of information on the effects of long-term infrequent tillage on the stratification of soil chemical parameters. This study aimed to assess the effects of long-term infrequent tillage on the stratification of selected soil chemical parameters to a depth of 300 mm. The research was conducted on a long-term (42 years) research site at Langgewens Research Farm in South Africa. Seven tillage treatments were investigated: continuous mouldboard ploughing to a depth of 200 mm, tine-tillage to 150 mm, shallow tine-tillage to 75 mm, no-tillage, shallow tine-tillage every second year in rotation with no-tillage, shallow tine-tillage every third year in rotation with no-tillage and shallow tine-tillage every fourth year in rotation with no-tillage. Tillage treatments had differential effects on the distribution of soil chemical parameters. The mouldboard plough prevented stratification of most soil chemical parameters, such as soil acidity, soil organic carbon (SOC), extractable P, exchangeable Ca and Mg and cation exchange capacity (CEC). However, mouldboard ploughing also led to significantly lower SOC stocks and extractable P stocks. The SOC stocks and extractable P stocks of the no-tillage treatment were not significantly different from those of the infrequent tillage treatments. Overall, the infrequent tillage treatments were no better (P > 0.05) than the no-tillage treatment as infrequent tillage could not effectively ameliorate the stratification of most soil chemical parameters and did not increase the stocks and stratification ratios of SOC and extractable P.

Permafrost Thaw Increases Methylmercury Formation in Subarctic Fennoscandia.

Methylmercury (MeHg) forms in anoxic environments and can bioaccumulate and biomagnify in aquatic food webs to concentrations of concern for human and wildlife health. Mercury (Hg) pollution in the Arctic environment may worsen as these areas warm and Hg, currently locked in permafrost soils, is remobilized. One of the main concerns is the development of Hg methylation hotspots in the terrestrial environment due to thermokarst formation. The extent to which net methylation of Hg is enhanced upon thaw is, however, largely unknown. Here, we have studied the formation of Hg methylation hotspots using existing thaw gradients at five Fennoscandian permafrost peatland sites. Total Hg (HgT) and MeHg concentrations were analyzed in 178 soil samples from 14 peat cores. We observed 10 times higher concentrations of MeHg and 13 times higher %MeHg in the collapse fen (representing thawed conditions) as compared to the peat plateau (representing frozen conditions). This suggests significantly greater net methylation of Hg when thermokarst wetlands are formed. In addition, we report HgT to soil organic carbon ratios representative of Fennoscandian permafrost peatlands (median and interquartile range of 0.09 ± 0.07 μg HgT g–1 C) that are of value for future estimates of circumpolar HgT stocks.

Impacts of continuous biochar application on major carbon fractions in soil profile of North China Plain’s cropland: In comparison with straw incorporation

Although the increase of soil organic carbon (SOC) in biochar-amended soil has been well documented, there is a lack of understating on the responses of soil inorganic carbon (SIC) to biochar application in soil profile. Here, we conducted a field study to investigate the effects of 10-year application of biochar at 4.5 Mg ha−1 yr−1 (B4.5) and 9.0 Mg ha−1 yr−1 (B9.0), and straw return (SR) of 15 Mg ha−1 yr−1 on SOC and SIC and their dissolved fractions. Our results showed significant difference in SOC content over 0–20 cm, with an order of B9.0 (8.46 g kg−1) > B4.5 (7.58 g kg−1) > SR (6.81 g kg−1) > control (5.26 g kg−1). However, SIC content was significantly lower under biochar (1.0–2.0 g kg−1) and control (1.0–2.0 g kg−1) than straw incorporation (3.2–3.7 g kg−1) over 0–40 cm. On average, DOC:SOC ratio (an index of SOC desorption) was significantly lower under biochar (~2.0%) and SR (2.6%) treatments than under control (3.1%), implying that both biochar and straw amendments can enhance SOC stability. Over the ten years, 62–81% of biochar-C was converted to SOC in the 0–100 cm layer, which was significantly higher than that (21%) of straw-C. Our estimation suggested that total carbon loss rate was 51–53% under biochar amendment and 70% with straw incorporation. This study highlights that biochar application has great potential for carbon sequestration in cropland of north China.

Impacts of species mixture on soil nitrogen stocks in the Loess Plateau of China

Nitrogen (N) is one of the primary limiting elements in terrestrial ecosystems, and vegetation restoration has been regarded as an effective way to increase soil total nitrogen (STN) stocks. Despite compelling evidence indicating that mixed plantations can demonstrate higher vegetation productivity and carbon (C) sequestration capacity than monocultures, the effects of mixed plantations on STN stocks remain unclear. Therefore, we conducted a meta-analysis of 128 observations from 49 peer-reviewed articles across the Loess Plateau of China to evaluate the impact of different afforestation models (i.e., mixed plantations and monocultures) on the dynamics of STN stocks in mineral soil (0–30 cm). The results showed that, compared with monocultures, mixed plantations significantly increased STN stocks by 19.3%. For different mixed types, tree-shrub mixed plantations increased more STN stocks than tree-tree mixed plantations. However, the positive effect of mixed plantations on STN stocks was significant > 20 years after stand establishment. Moreover, for areas with steeper slope (>25°), lower elevation (<1200 m), and climate restricted (MAT < 8℃, MAP < 500 mm), mixed plantations had more advantages in increasing STN stocks than monocultures. Additionally, the response ratio of STN stocks was negatively correlated with the initial STN stocks, response ratios of soil pH, and bulk density (BD) but positively correlated with the response ratio of soil organic carbon (SOC) stocks. Our results demonstrate that increasing tree species richness is an important strategy to increase STN stocks.

Soil microbial biomass and enzyme kinetics for the assessment of temporal diversification in agroecosystems

In agroecosystems, temporal diversification creates a sequence of short-lived habitats through time. Crop species as well as the diversity of crops grown in sequence might affect soil biodiversity and nutrient cycling processes. In the present study, we focused on a long-term crop rotation established in 2006 in Lower Saxony, Germany on a Luvisol. Winter wheat (WW) and silage maize (SM) were grown in continuous cultivation as well as in rotations. WW rotations span up to six years (including silage maize, sugar beet, winter rape and/or grain pea). Over two years, microbial biomass carbon (MBC) as well as kinetics (Michaelis-Menten Vmax and Km) of extracellular hydrolytic enzymes (β-glucosidase (BG), N-acetyl-β-glucosaminidase (NAG) and acid phosphomonoesterase (AP)) were measured in topsoil (0–10 cm depth) three times during the growing season. Continuous wheat increased soil microbial parameters compared to continuous maize as indicated by the higher microbial biomass to soil organic carbon ratio and higher potential enzymes activities involved in the C- and N-cycles (Vmax of BG and NAG). The efficiency of these enzymes was lowest in continuous maize (highest Km of BG and NAG). Maize and sugar beet as preceding crop of WW significantly decreased MBC in the 1st year but not in the 2nd year WW. Sugar beet decreased BG activity as well as its substrate affinity (increased Km). The effect of sugar beet on MBC and enzyme kinetics depended on the preceding crop and lessened with grain pea as the preceding crop. Soil microorganisms in the wheat phase benefited from winter rape as the preceding crop, shown by an increased biomass and efficiency to turn over chitin and peptidoglycan (decreased Km of NAG). Differences between cultivated crops, cropping history and fluctuations within the year in soil microbial biomass and enzyme kinetics are shown.

Vegetation Restoration Alleviated the Soil Surface Organic Carbon Redistribution in the Hillslope Scale on the Loess Plateau, China

The redistribution of soil organic carbon (SOC) in response to soil erosion along the loess slope, China, plays an important role in understanding the mechanisms that underlie SOC’s spatial distribution and turnover. Consequently, SOC redistribution is key to understanding the global carbon cycle. Vegetation restoration has been identified as an effective method to alleviate soil erosion on the Loess Plateau; however, little research has addressed vegetation restoration’s effect on the SOC redistribution processes, particularly SOC’s spatial distribution and stability. This study quantified the SOC stock and pool distribution on slopes along geomorphic gradients in naturally regenerating forests (NF) and an artificial black locust plantation (BP) and used a corn field as a control (CK). The following results were obtained: 1) vegetation restoration, particularly NF, slowed the migration of SOC and reduced the heterogeneity of its distribution effectively. The topsoil SOC ratios of the sedimentary area to the stable area were 109%, 143%, and 210% for NF, BP, and CK, respectively; 2) during migration, vegetation restoration decreased the loss of labile organic carbon by alleviating the loss of dissolved organic carbon (DOC) and easily oxidized organic carbon (EOC). The DOC/SOC in the BP and NF increased significantly and was 13.14 and 17.57 times higher, respectively, than that in the CK (p &amp;lt; 0.05), while the EOC/SOC in the BP and NF was slightly higher than that in the CK. A relevant schematic diagram of SOC cycle patterns and redistribution along the loess slope was drawn under vegetation restoration. The results suggest that vegetation restoration in the loess slope, NF in particular, is an effective means to alleviate the redistribution and spatial heterogeneity of SOC and reduce soil erosion.

Impacts of salinity on the stability of soil organic carbon in the croplands of the Yellow River Delta

AbstractThis study aims to improve our understanding of the mechanisms regulating the stability of soil organic carbon (SOC) in saline–alkaline soils. We hypothesized that desorption of SOC is greater in higher salinity/higher pH soils, and the higher level of soil inorganic carbon (SIC) leads to enhanced SOC stability (or weaker SOC desorption) in saline–alkaline soils like those of the Yellow River Delta (YRD). We collected soils from 23 cropland sites (from 0–100 cm) along three lines (upper, middle, and lower lines, with different salinity) across the Yellow River, which have high pH (7.97–9.02). We analyzed SOC, SIC, and water‐extractable organic carbon (WEOC) and salts. Our data showed a large range in SOC (2.3–11.7 kg C m−2) and SIC stocks (13.3–24.7 kg C m−2) over 0–100 cm. The lowest SOC and SIC stocks were found in the lower YRD where soil pH was highest (8.6–9.0). WEOC:SOC ratio (an indicator for SOC desorption) was greater in soils with higher pH, lower SIC, and/or water‐extractable Ca2+ plus Mg2+, indicating that SOC stability is weak in high salinity/high pH soils, but high levels of SIC or Ca2+/Mg2+ can increase SOC stability. Our study suggests that amelioration practice may lead to an increase in both SOC and SIC stocks in saline–alkaline soils.

No till soil organic carbon sequestration could be overestimated when slope effect is not considered

No tillage (NT) soil management has been considered a strategy for the implementation of environmental sustainability and a possible tool of soil organic carbon (SOC) sequestration. Considering the wide range of data on SOC change after NT application in relation to conventional tillage (CT) in different studies, further researches are needed over a diverse range of soil and climate before a proper estimation of the benefits can be provided by the NT. A data set composed of cereal cropping system studies, comparing the SOC content under CT and NT was compiled from the literature using the scientific repositories “Scopus” and “Science direct”. This aims to i) discriminate and quantify the variation of SOC in relation to morphology (Flat area (FA) and Slope Area (SA)) and climates (Aridity index (Ai)); ii) provide a reliable forecast of C sequestration by NT in a specific environment. The results from collected datasets showed that SOC ratio between NT and CT was higher in sloping than flat areas and was also in correlation with the Ai. The average annual increase of SOC in NT in comparison to CT was 0.32 Mg ha−1y−1 and 0.21 Mg ha−1y−1 for SA and FA, respectively. The regression of the relative ratio (RRNT/CT) against Ai both for FA and SA showed a high statistical significance for FA. For SA the lack of significance is due to no response of the dependent variables to Ai changes and to the prevalent effect that NT has on the soil C erosion processes. These results highlighted that in SA, the SOC sequestration by NT is overestimated. These results provide concrete examples of the importance to discriminate soil morphology and climate when recommending NT soil management for soil C sequestration in order to individuate areas where NT can maximize its potentiality as a mitigation tool.

Investigations of the effect of the amount of biochar on soil porosity and aggregation and crop yields on fertilized black soil in northern China.

The combination of chemical fertilizer and biochar is regarded as a useful soil supplement for improving the properties of soil and crop yields, and this study describes how the biochar of maize straw can be used to improve the quality of the degraded black soil. This has been achieved by examining the effects of combining different amounts of biochar with chemical fertilizer on the porosities and aggregate formation of soil and exploring how these changes positively impact on crop yields. A field trial design combining different amounts of maize straw biochar [0 (NPK), 15.75 (BC1), 31.5 (BC2), and 47.25 t ha−1 (BC3)] with a chemical fertilizer (NPK) has been used to investigate changes in the formation of soil aggregate, clay content, soil organic carbon (SOC), and crop yields in Chinese black soil over a three year period from 2013 to 2015. The results of this study show that the addition of fertilizer and biochar in 2013 to black soil results in an increased soybean and maize yields from 2013 to 2015 for all the treatments, with BC1/BC2 affording improved crop yields in 2015, while BC3 gave a lower soybean yield in 2015. Total porosities and pore volumes were increased for BC1 and BC2 treatments but relatively decreased for BC3, which could be attributed to increased soil capillary caused by the presence of higher numbers of fine soil particles. The addition of biochar had a positive influence on the numbers and mean weight diameters (MWD) of soil macroaggregates (>0.25 mm) that were present, with the ratio of SOC to TN in soil macroaggregates found to be greater than in the microaggregates. The most significant amount of carbon present in macroaggregates (>2 mm and 0.25–2 mm) was observed when BC2 was applied as a soil additive. Increasing the levels of maze straw biochar to 47.25 t ha−1 led to an increase in the total organic carbon of soil, however, the overall amount of macroaggregates and MWD were decreased, which is possibly due to localized changes in microbial habitat. The supplementation of biochar increased in the amount of aromatic C present (most significant effect observed for BC2), with the ratio of aliphatic C to aromatic C found to be enhanced due to a relative reduction in the aliphatic C content with >2 mm particle fraction. These changes in organic carbon content and soil stability were analyzed using univariate quadratic equations to explain the relationship between the type of functional groups (polysaccharide C, aliphatic C, aromatic C, aliphatic C/aromatic C) present in the soil aggregates and their MWDs, which were found to vary significantly. Overall, the results of this study indicate that the use of controlled amounts of maize-straw biochar in black soil is beneficial for improving crop yields and levels of soil aggregation, however, the use of excessive amounts of biochar results in unfavorable aggregate formation which negatively impacts the yields of crop growth. The data produced suggest that aromatic C content can be used as a single independent variable to characterize the stability of soil aggregate when biochar/fertilizer mixtures are used as soil additives to boost growth yields. Analysis of soil and crop performance in black soil revealed that the application of maize-straw biochar at a rate of 15.75 and 31.5 t ha−1 had positive effects on crop yields, soil aggregation and accumulation of aromatic C in the aggregate fractions when a soybean-maize rotation system was followed over three years.

Soil prokaryotic community structure and co-occurrence patterns on the fragmented Chinese Loess Plateau: Effects of topographic units of a soil eroding catena

Soil prokaryotes composition and diversity are the key to uncovering the mechanisms that drive variations in soil biogeochemical processes. Soil erosion is a primary factor that affects the spatial distribution of the soil prokaryotic community, but how soil prokaryotes in soil-eroding catena respond to environmental factors related to topography remains largely unclear. In this study, topsoils were sampled from three typical erosion geomorphic units (autonomous, transitional and depositional zones) in 2018 to identify the soil prokaryotic community and interactions among the species on the Chinese Loess Plateau. The alpha-diversity was greater but the beta-diversity was lower in the autonomous and transitional zones than in the depositional zone. Gammaproteobacteria and Bacteroidetes were 73% and 68% lower in the autonomous and transitional zones than in the depositional zone. In addition, Deltaproteobacteria, Acidobacteria, Firmicutes, Actinobacteria, Chloroflexi, Gemmatimonadetes and Nitrospirae were significantly higher in the autonomous and transitional zones. A less clustered network and fewer co-occurrences within the prokaryotic community and functional groups of processes were found in the depositional zone than in the autonomous and transitional zones. The alpha-diversity index was significantly negatively correlated with clay particles, soil water content, soil organic carbon (SOC), and ratio of SOC and nitrogen (C/N) but positively correlated with total nitrogen (TN). The higher relative abundances of copiotrophic groups (including Gammaproteobacteria, Bacteroidetes, etc.) in the depositional zone was mainly due to the increased SOC caused by the deposition of SOC-rich clay. Reassembly of the soil physico-chemistry characteristics among the topographic units significantly altered the soil prokaryotic community along the soil-eroding catena.

Negative impacts of plant diversity loss on carbon sequestration exacerbate over time in grasslands

Positive relationships between plant species diversity and carbon attributes have been observed in grasslands, but synthesis studies of how plant diversity affects the carbon balance of grasslands and how the response ratio changes over time both remain limited. By conducting a global meta-analysis with 811 paired observations of plant mixtures and monocultures from 83 studies in natural and manipulated grasslands, we investigated the impacts of plant diversity on six carbon attributes, its interaction with experimental duration, and the changes in carbon balance under different plant diversity loss scenarios in the future. We found that the aboveground biomass (AGB), belowground biomass (BGB), total biomass (TB), soil organic carbon (SOC), soil respiration (Rs), and heterotrophic respiration (Rh) significantly increased in the plant mixtures, and the response ratio for all carbon attributes increased logarithmically with species richness. We also found that the response ratio for all carbon attributes except Rs increased linearly with experimental duration. The increase in response ratio of AGB, BGB, TB, and SOC with species richness was more pronounced with the long-term experimental duration. Importantly, our results showed that the declines in carbon sequestration will be exacerbated by different plant diversity loss scenarios in the future. Our meta-analysis revealed that plant diversity loss has ubiquitous negative impacts on multiple carbon attributes in grasslands, underlined the interactive effects of plant diversity loss and experimental duration on carbon attributes, and suggested that the reduction of carbon storage in grasslands following biodiversity loss will be greater in the future.

Response of soil microbial communities to natural and managed vegetation restoration in a subtropical karst region

The soil microbial community is a key indicator to evaluate the effectiveness of vegetation restoration in degraded ecosystems. However, few studies have simultaneously compared the effects of managed and natural vegetation restoration strategies on the soil microbial community in the ecologically fragile karst region using signature lipid biomarker analysis to provide information on a variety of microbial properties. Here, phospholipid fatty acids (PLFAs) in the soil microbial community were measured following different restoration strategies in a karst region of southwest China. Managed vegetation restoration (including restoration with plantation forest, forage grass, and a combination of plantation forest and forage grass) and natural vegetation restoration (spontaneous regeneration to natural grassland) were compared, using cropland as a reference. The abundance of total PLFAs and the PLFAs of four microbial functional groups (bacteria, fungi, actinomycetes, and arbuscular mycorrhizal fungi [AMF]) significantly increased in the topsoil (0–5 cm soil depth) following vegetation restoration. In the sub-topsoil layer (5–10 cm soil depth), the abundance of PLFAs was not significantly higher than that in the cropland, except in AMF in natural vegetation restoration. Principal component analysis indicated that the microbial PLFA composition differed between the restoration strategies, and the abundance of AMF PLFAs was significantly higher in natural than in managed vegetation restoration for both soil depths. The ratio of soil organic carbon to total nitrogen and dissolved organic carbon content were the primary factors affecting the abundance of soil microbial communities in the topsoil and sub-topsoil, respectively. In addition, soil pH served as another explanatory variable for the topsoil. Our findings suggest that vegetation restoration over a relatively short period (15 years) mainly improved topsoil fertility. Moreover, natural vegetation restoration may be superior to managed vegetation restoration for the maintenance of multiple ecosystem functions in the short term in the karst regions, owing to the potentially significant role of AMF.

Depth of straw incorporation significantly alters crop yield, soil organic carbon and total nitrogen in the North China Plain

Appropriate straw incorporation has ample agronomic and environmental benefits in the North China Plain, but most studies are limited to straw mulching or incorporation on the soil surface. To determine the effect of depth of straw incorporation on crop yield, soil organic carbon (SOC) and total nitrogen (TN), a 3-year field experiment was established with the following four treatments: (i) no straw incorporation (CK); (ii) straw incorporation at 15 cm (S15); (iii) straw incorporation at 25 cm (S25) and (iv) straw incorporation at 40 cm (S40). The results showed that straw incorporation significantly increased SOC, TN and C:N ratio (P < 0.05). Compared with CK, substantial increases (P < 0.05) in SOC and TN were observed at the 0-20 cm layer under S15, at all depths under S25 and at the 40-60 cm depth under S40. Under S25 (20-40 cm) in particular, the SOC and TN levels considerably (P < 0.05) exceeded those under CK (8.83˜17.26% of SOC and 6.28˜10.25% of TN), S15 (3.66˜9.25% of SOC and 2.13˜4.70% of TN) and S40 (4.74˜8.23% of SOC and 3.21%˜4.27% of TN). The average SOC and TN at 0-60 cm under S25 was also significantly higher (P < 0.05) than those under S15 and S40. Straw incorporation also increased the C:N ratio and the response of C:N ratio to straw incorporation differed by the depth of straw incorporation and the soil layer. Compared with S15 and S40, S25 had a significant effect on the C:N ratio at each soil layer. Both S25 and S40 decreased the stratification ratio (SR) of SOC, TN and C:N ratio and promoted a uniform distribution of SOC and TN within the 0-60 cm depth. Compared with CK, straw incorporation also significantly increased (P < 0.05) crop yields, especially under S25, by 10.83% in 2014, 13.25% in 2015 and 7.68% in 2016. The grain yields of wheat and maize were positively correlated with SOC and TN (0-20 cm and 20-40 cm). Thus, in the North China Plain, straw incorporation at the 25 cm depth would boost soil fertility and crop yield.

Climate and soil properties regulate soil fungal communities on the Loess Plateau

This study investigated the effects of environmental variables on soil fungal communities under different vegetation types in order to advance our understanding of soil fungal community assembly associated with restored vegetation and under different climate conditions. Three vegetation types (no grazing and logging in grasslands and forests, and planted herbs and small shrubs in bare land in the desert) on the Loess Plateau in China were chosen as subjects, and pyrosequencing of the 18S rRNA gene region was used to analyze the changes in the diversity and community composition of soil fungi. Vegetation type had significant effects on soil fungal diversity. The forest and grassland soils had similar fungal diversity levels, which were significantly higher than that of the desert ecosystem. Multiple regression models indicated that total phosphorus in soil and the ratio of soil organic carbon to total nitrogen in soil (C:N) were the best predictors of soil fungal diversity. Ascomycota and Basidiomycota were the most dominant phyla in all soils, accounting for 83.6 % of fungal sequences. Dothideomycetes (26.6 %), Sordariomycetes (18.3 %), Eurotiomycetes (8.5 %), Pezizomycetes (12.1 %) and Dothideomycetes (10.7 %) were the dominant classes across the three vegetation types. Agaricomycetes and Sordariomycetes were more dominant in forest soils than grasslands and desert soils, while Pezizomycetes were more frequently observed in desert soils. Along an increasing mean annual precipitation (MAP) gradient, relative abundance of the Ascomycota phylum decreased and that of the Basidiomycota increased. Among local environmental factors, MAP, soil pH and soil organic matter were the main factors influencing the soil fungal community composition, explaining 20.9 %, 15.9 % and 10.4 % of the variation in the fungal community, respectively. Considering geographic distance, variation partitioning revealed that geographic distance explained more of the fungal community variation than measured environmental factors. This finding may help to predict the consequences in fungal communities in response to climate change and vegetation restoration in arid areas.

Forage yield, water use efficiency, and soil fertility response to alfalfa growing age in the semiarid Loess Plateau of China

Water availability is a major constraint for crop production in the Loess Plateau of China; thus, improving water use efficiency (WUE) is a main research target. The impact of alfalfa (Medicago sativa L.) growing age on forage yield, WUE, soil water storage, and soil fertility were examined in a 15-yr study in the western Loess Plateau of China. The results of this study indicate that long-term continuous production of alfalfa aggravated the soil water deficit and reduced soil available phosphorus (AP) and the ratio of soil organic carbon to soil total nitrogen, but increased soil organic carbon, soil total nitrogen, and the ratios of soil organic carbon to soil available phosphorus and soil total nitrogen to soil total phosphorus. After the ninth year of alfalfa production, the greatest soil water storage deficit degree was found in the 0–80 cm soil layer (63 %), followed by the 200–300 (57 %) and 80–200 cm (55 %) soil layers. Forage yield and WUE of alfalfa reached their greatest values following six- to nine-yr-old stands, and then decreased gradually. These results suggest that the yield decline with long-term stands of alfalfa may be related to reductions in soil water storage and AP, and their interaction, and the optimal alfalfa growing age should not extend beyond nine years in semiarid conditions.

Soil enzyme activities and their stoichiometry of typical plantations in mid-subtropical China

We measured the activities of six kinds of enzyme, including β-glucosidase (BG), β-N-acetyl-glucosaminidase (NAG), leucine aminopeptidase (LAP), acid phosphatase (AP), polyphenol oxidase (POX), peroxidase (POD), as well as enzyme stoichiometric ratios and soil physical and chemical properties at 0-10 and 10-20 cm layers across typical Pinus massoniana plantation, Pinus elliottii plantation and mixed plantation of P. massoniana and Schima superba (broadleaved-conifer mixed plantation) in mid-subtropical China. Key factors driving the variation in soil enzyme activity and stoichiometry among different stand types were investigated. The results showed that the activities of soil BG and LAP were significantly affected by stand type. Soil BG activity at 10-20 cm soil layer was significantly higher in P. elliottii plantation than in P. massoniana plantation, while the activity of LAP was highest in the P. massoniana plantation. Soil BG/(NAG+LAP) and BG/AP at 10-20 cm layer of P. elliottii plantation were significantly higher than those of P. massoniana plantation, while (NAG+LAP)/AP of P. massoniana plantation was significantly higher than those of P. elliottii plantation and mixed plantation. The vector length of enzyme stoichiometry at 10-20 cm soil layer was significantly different among stand type, with an order of P. elliottii plantation > broadleaved-conifer mixed plantation > P. massoniana. The vector angles of enzyme stoichiometry in the three plantations were greater than 45°, with the vector angle in the P. elliottii plantation at 10-20 cm soil layer being significantly greater than that of the P. massoniana plantation. Results from redundancy analysis showed that soil carbon quality index and the ratio of soil organic carbon to total phosphorus (C/P), soil water content and C/P were the key factors affecting soil enzyme activity and stoichiometry at 0-10 and 10-20 cm soil layers, respectively. The quantity and quality of soil carbon and phosphorus, and soil water content played a key role in regulating nutrient cycling in mid-subtropical plantation ecosystem.

Soil Microbial Community and Its Interaction with Soil Carbon Dynamics Following a Wetland Drying Process in Mu Us Sandy Land.

Increasing drought globally is a severe threat to fragile desert wetland ecosystem. It is of significance to study the effects of wetland drying on microbial regulation of soil carbon (C) in the desert. In this study, we examined the impacts of wetland drying on microbial biomass, microbial community (bacteria, fungi) and microbial activity [basal microbial respiration, microbial metabolic quotient (qCO2)]. Relationships of microbial properties with biotic factors [litter, soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP)], abiotic factors (soil moisture, pH and clay content) and biological processes (basal microbial respiration, qCO2) were also developed. Results showed that the drying of wetland led to a decrease of soil microbial biomass carbon (MBC) content, microbial biomass nitrogen (MBN) content and fungi and bacterial abundance, and an increase of the fungi:bacteria ratio. Wetland drying also led to increased soil basal respiration and increased qCO2, which was attributed to lower soil clay content and litter N concentration. The MBC:SOC ratios were higher under drier soil conditions than under virgin wetland, which was attributed to stronger C conserve ability of fungi than bacteria. The wetland drying process exacerbated soil C loss by strengthening heterotrophic respiration; however, the exact effects of soil microbial community structure on microbial C mineralization were not clear in this study and need further research.

Soil and plant characteristics during two hydrologically contrasting years at the lakeshore wetland of Poyang Lake, China

The main objective of this research was to examine the effects of inter-annual water regime variation on soil and plant characteristics, and soil–vegetation relationship at the lakeshore wetland of Poyang Lake, China. Six transects which paralleled the lakeshore were established at a typical Carex lakeshore wetland of Poyang Lake. We performed the field investigation and sampling in the autumn growing seasons in a flooding year (2017) and a drought year (2018). Paired t test was carried out to determine the effects of inter-annual water regime variation on various soil and plant parameters. Redundancy analysis was used to examine the relationships of plant species composition with flooding and soil variables in both years. Soil water content (SW), soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), the ratio of SOC to TP (C/P ratio), the ratio of TN to TP (N/P ratio), ammonia nitrogen concentration (NH4-N), and nitrate nitrogen concentration (NO3-N) were 21 ~ 71% higher in the flooding year than in the drought year. Plant Shannon–Wiener indices were significantly lower in the drought year than in the flooding year, whereas aboveground and belowground plant biomass showed opposite patterns. Flooding and soil variables could strongly determine plant communities in both years. Flooding duration was the most important variable among all flooding and soil variables. After eliminating the effects of flooding duration, pH and SW still significantly affected plant community composition in the flooding year, while only NH4-N significantly impacted on plant species distribution in the drought year. The results provided direct evidences that the inter-annual water regime variation not only could dramatically modify soil and plant variables but also could change the soil–vegetation relationship in the wetlands. Our studies have great implications for the conservation and restoration of the wetlands, especially for the lake wetlands in the middle and lower reaches of Yangtze River.