C-cycling Enzymes Research Articles

Biochar applications and enzyme activity, carbon dioxide emission, and carbon sequestration in a calcareous soil

Biochar is a carbon-rich product obtained by biomass pyrolysis and is considered as a means of carbon sequestration. However, there is limited knowledge regarding responses of soil respiration and C-cycle enzyme activities to BC in a calcareous soil. In this study, different biochar AS, TS, PP, CS were applied to the soil at different rates (0.5, 1.0, and 1.5%) The highest increase in soil organic C content was observed in the TS treatment, while the AS treatment caused a slight increase of soil organic C. The highest MBC content was recorded in AS treatment and the lowest was observed in TS. The highest CO2-C emission was recorded in the TS treatment. In contrast, the lowest CO2-C emission was observed in the PP treatment due to its high recalcitrant C content and was attributed to a positive priming effect, stabilizing BC mineralization to improve the soil. The highest β-galactosidase enzyme activity was observed in the CS treatment and the lowest activity was observed in AS. The highest change in β-glycosidase enzyme activity was observed of PP treatment and the lowest was in AS biochar application. Thus, TS treatment is recommended to increase the organic C content of soils, and the PP biochar can be used to reduce CO2-C emission. The TS, PP, and CS can be applied to increase enzyme activities. The study clearly shows that the addition of BC to arid soils may have a high potential to improve soil enzyme activities and subsequent carbon sequestration and biochemical cycles.

Animal manures increased maize yield by promoting microbial activities and inorganic phosphorus transformation in reclaimed soil aggregates

Animal manures positively affect soil microbial activity and inorganic phosphorus (Pi) accumulation. However, how different types of manures affect microbial-driven Pi transformation at the aggregate scale is largely unclear. Here, we conducted a field experiment focused on maize cultivation in a reclamation site. Five fertilization treatments included no fertilizer (CK), chemical fertilizer (CF), chicken manure (CHM), pig manure (PM), and cow manure (CM). We examined microbial biomass, soil extracellular enzyme activities associated with carbon and phosphorus cycling, and Pi fractions (Labile-P, Moderately labile-P, and Stable-P) in three aggregate sizes (> 2 mm large macro-aggregates, 0.25–2 mm small macro-aggregates, and < 0.25 mm micro-aggregates), as well as grain yield. The results showed that manures addition significantly increased the proportion of large macro-aggregates and aggregate stability compared to chemical fertilizer. Stable-P constituted the largest proportion among the Pi fractions, accounting for 63 %–72 %. However, manures reduced Stable-P (5.4 %–10.7 %) and increased Labile-P (111 %–190 %) in Pi, especially in micro-aggregates. Both chemical fertilizer and manures increased microbial biomass and enzyme activities in aggregates, with manures causing a greater enhancement of soil microbial biomass carbon (SMBC) and C-cycling enzymes, especially under pig manure, and improving soil microbial biomass phosphorus (SMBP) and P-cycling enzymes, especially under chicken manure. Phytase, phosphatase and SMBP accounted for 81.4 %, 81.2 % and 87 % of the differences in large macro-aggregates, small macro-aggregates, and micro-aggregates, respectively. The structural equation model (SEM) demonstrated that manures facilitated the transformation of Stable-P to Labile-P by regulating aggregates and microbial activity, which consequently increased yield. In summary, manures addition, particularly chicken manure, can enhance inorganic phosphate (Pi) accumulation and transformation, thereby mitigating phosphorus (P) limitation in calcareous reclamation soils.

Responses of SOC, labile SOC fractions, and amino sugars to different organic amendments in a coastal saline-alkali soil

Organic amendment combined with mineral fertilizer is known as an effective management practice to improve soil carbon (C) sequestration in cropland. We evaluated the effects of three organic amendments combined with mineral fertilizer on soil organic carbon (SOC), labile SOC fractions, amino sugars, C mineralization, and C-cycle enzyme activities in a coastal saline-alkali soil. The three amendments, including straw (C/N of 75.5:1), straw biochar (C/N of 43:1), and soybean cake (C/N of 7.4:1), were continuously added into the soil at an equal C amount of 2250 kg C ha−1 for four years. Compared to mineral fertilizer alone, the contents of SOC in plots receiving straw, straw biochar, and soybean cake were increased by 7.6%, 17.3%, and 12.7%, respectively. The amendment of straw biochar mainly increased easily oxidizable carbon (EOC), particulate organic carbon (POC), and fungal-derived glucosamine, whereas straw and soybean cake mainly increased dissolved organic carbon (DOC), microbial biomass carbon (MBC), and bacteria-derived muramic acid. Meanwhile, the activities of C-cycle enzymes and C mineralization were higher in straw and soybean cake treatments than in straw biochar treatment. EOC and POC, but not DOC and MBC, were strongly positively correlated with fungal-derived glucosamine and SOC, suggesting that EOC or POC could be used as appropriate indicators to predict SOC sequestration potential. In addition, the C/N ratio of organic material did not affect SOC and its components. In conclusion, straw biochar promotes the maximum accumulation of SOC through increasing EOC, POC, and fungal necromass.

Polyethylene microplastics alter soil microbial community assembly and ecosystem multifunctionality

Although pervasive microplastics (MPs) pollution in terrestrial ecosystems invites increasing global concern, impact of MPs on soil microbial community assembly and ecosystem multifunctionality received relatively little attention. Here, we manipulated a mesocosm experiment to investigate how polyethylene MPs (PE MPs; 0, 1%, and 5%, w/w) influence ecosystem functions including plant production, soil quality, microbial community diversity and assembly, enzyme activities in carbon (C), nitrogen (N) and phosphorus (P) cycling, and multifunctionality in the maize–soil continuum. Results showed that PE MPs exerted negligible effect on plant biomass (dry weight). The treatment of 5% PE MPs caused declines in the availability of soil water, C and P, whereas enhanced soil pH and C storage. The activity of C-cycling enzymes (α/β-1, 4-glucosidase and β-D-cellobiohydrolase) was promoted by 1% PE MPs, while that of β-1, 4-glucosidase was inhibited by 5% PE MPs. The 5% PE MPs reduced the activity of N-cycling enzymes (protease and urease), whereas increased that of the P-cycling enzyme (alkaline phosphatase). The 5% PE MPs shifted soil microbial community composition, and increased the number of specialist species, microbial community stability and networks resistance. Moreover, PE MPs altered microbial community assembly, with 5% treatment decreasing dispersal limitation proportion (from 13.66% to 9.96%). Overall, ecosystem multifunctionality was improved by 1% concentration, while reduced by 5% concentration of PE MPs. The activity of α/β-1, 4-glucosidase, urease and protease, and ammonium-N content were the most important predictors of ecosystem multifunctionality. These results underscore that PE MPs can alter soil microbial community assembly and ecosystem multifunctionality, and thus development and implementation of practicable solutions to control soil MPs pollution become increasingly imperative in sustainable agricultural production.

Phosphorus addition accelerates soil organic carbon mineralization by desorbing organic carbon and increasing microbial activity in subtropical forest soils

The magnitude and direction of soil organic carbon (SOC) mineralization are closely regulated by exogenous nutrient addition – and, especially, by limited nutrients such as phosphorus (P) – in tropical and subtropical ecosystems. However, the response of SOC decomposition to P addition and the underlying mechanisms operating in subtropical P-limited forest soils remain unclear. In this study, four subtropical forest soils (sandstone and granite soils planted with the chinkapin Castanopsis carlesii and Cunninghamia lanceolata (Chinese fir)) in Sanming City, Fujian Province, China were selected, and an incubation experiment with three levels (0, 0.1, 0.6 mg P g−1 soil) of P addition was conducted to explore the impact of P addition on SOC mineralization in subtropical forest soils. SOC mineralization, phospholipid fatty acids (PLFAs), enzymatic activities, and soil properties were determined. Results showed that P addition significantly increased the cumulative mineralization of SOC (P < 0.001). Additionally, the microbial biomass (e.g., fungal, bacterial, and total PLFAs) and the activities of C-cycling enzymes significantly increased (by 11.95 %–570.25 %) after P addition (P < 0.001), which suggests that exogenous P input enhanced microbial activity and thus accelerating SOC mineralization. P addition also significantly increased the concentration of dissolved organic C (DOC) (P < 0.001), thereby making soil C more available to microorganisms and allowing it to become quickly decomposed. A variance partitioning analysis (VPA) showed that DOC and fungal biomass acted as the predominant abiotic and biotic factors accelerating SOC mineralization under P addition. Using the results of a partial least squares path analysis (PLM-PM), we conclude that P addition stimulated the decomposition of SOC in these subtropical P-limited forest soils. Two processes help explain these results: (i) the enhancement of microbial activity in response to the alleviation of microbial P limitation and (ii) the fact that P addition desorbed the microbial inaccessible organic C and converting it into DOC, which is easily accessible to microbes, thereby contributing to SOC mineralization. Our study reveals how P input influences organic C mineralization in subtropical forest soils where P is limited. It also provides novel insight into the uncertainty of the global soil C sink, which might be partially attributable to exogenous nutrient inputs, especially in the case of limiting nutrients.

Linking between soil properties, bacterial communities, enzyme activities, and soil organic carbon mineralization under ecological restoration in an alpine degraded grassland.

Soil organic carbon (SOC) mineralization is affected by ecological restoration and plays an important role in the soil C cycle. However, the mechanism of ecological restoration on SOC mineralization remains unclear. Here, we collected soils from the degraded grassland that have undergone 14 years of ecological restoration by planting shrubs with Salix cupularis alone (SA) and, planting shrubs with Salix cupularis plus planting mixed grasses (SG), with the extremely degraded grassland underwent natural restoration as control (CK). We aimed to investigate the effect of ecological restoration on SOC mineralization at different soil depths, and to address the relative importance of biotic and abiotic drivers of SOC mineralization. Our results documented the statistically significant impacts of restoration mode and its interaction with soil depth on SOC mineralization. Compared with CK, the SA and SG increased the cumulative SOC mineralization but decreased C mineralization efficiency at the 0-20 and 20-40 cm soil depths. Random Forest analyses showed that soil depth, microbial biomass C (MBC), hot-water extractable organic C (HWEOC), and bacterial community composition were important indicators that predicted SOC mineralization. Structural equal modeling indicated that MBC, SOC, and C-cycling enzymes had positive effects on SOC mineralization. Bacterial community composition regulated SOC mineralization via controlling microbial biomass production and C-cycling enzyme activities. Overall, our study provides insights into soil biotic and abiotic factors in association with SOC mineralization, and contributes to understanding the effect and mechanism of ecological restoration on SOC mineralization in a degraded grassland in an alpine region.

Role of Agricultural Management in the Provision of Ecosystem Services in Warm Climate Vineyards: Functional Prediction of Genes Involved in Nutrient Cycling and Carbon Sequestration.

(1) Background: Maintaining soil fertility and crop productivity using natural microbial diversity could be a feasible approach for achieving sustainable development in agriculture. In this study, we compared soils from vineyards under organic and conventional management by predicting functional profiles through metagenomic analysis based on the 16S rRNA gene. (2) Methods: The structure, diversity and predictive functions of soil bacteria related to the biogeochemical cycle of the soil were analyzed, including oxidative and hydrolytic C-cycling enzymes, N-cycling enzymes and P-cycling enzymes. The inter-row spontaneous vegetation in the organic vineyards was also characterized. (3) Results: A clear effect of the farming system (organic vs. conventional) and cover management (herbicides plus tillage, mowing only and mowing plus tillage) on bacterial beta diversity and predicted functions was evidenced. While conventional viticulture increased the potential capacity of the soil to regulate the cycling of inorganic forms of N, organic viticulture in general enhanced those functions involving organic N, P and C substrates. Although the soil bacterial community responded differently to contrasting soil management strategies, nutrient cycling and carbon sequestration functions remained preserved, suggesting a high bacterial functional redundancy in the soil in any case. However, most of the predicted bacterial functions related to soil organic matter turnover were enhanced by organic management. (4) Conclusions: We posit the potential for organic viticulture to adequately address climate change adaptation in the context of sustainable agriculture.

Effect of planting and mowing cover crops as livestock feed on soil quality and pear production.

The increasing demand for animal-products has led to an increasing demand for livestock feed. Using cover crop as green manure in orchards is an effective measure to improve fruit yield and quality. However, the effect of mowing cover forage crops as livestock feed on soil quality and crop production is unclear. Therefore, a 4-year field experiment, which included two treatments, was conducted in pear orchards in Luniao County, China: natural grass (NG) and planting and mowing forage crop ryegrass as livestock feed (MF). Under MF treatment, most soil nutrient content, especially alkalihydrolysable N (AN), total phosphate (TP), available phosphate (AP), and microbial biomass phosphate (MBP), had decreased significantly (P<0.05), while β-D-glucosidase (BG, C-cycle enzyme) and soil C limitation at 10-20 cm depth and P limitation at subsoil (20-40 cm) was increased. In addition, the soil bacterial community component in topsoil (0-10 cm and 10-20 cm) and fungal community component in topsoil and subsoil were changed in the MF treatment. Network analysis showed that MF treatment had a lower edge number in topsoil but the community edge numbers increased from 12794 in NG to 13676 in MF in subsoil. The average weight degree of the three soil layers in MF treatment were reduced, but the modularity had increased than that in NG. For crop production, MF treatment was 1.39 times higher in pear yield and titratable acids (AC) reduced from 0.19% to 0.13% compared with NG. These changes were more associated with the indicators at the subsoil, especially for TP, AN, pH, and F-NMDS1 (non-metric multidimensional scaling (NMDS) axis 1 of fungi). These results provide data support for the feasibility of planting and mowing forage crops as livestock feed on orchards as well as a new idea for the integration of crop and livestock.

Catchment scale spatial distribution of soil enzyme activities in a mountainous German coniferous forest

Topography features within catchments influence soil properties, nutrient status, microbial dynamics and ultimately enzyme activities. Extracellular soil enzymes are essential for the decomposition of organic substrates and play a central role in global biogeochemical cycles. How topography and soil properties drive the spatial expression of enzyme activities at the catchment scale is still underexplored, especially in coniferous forest ecosystems. This study investigated the activity of four extracellular soil enzymes: β-glucosidase (β-glu), β-cellobiosidase (β-cello), acid phosphatase (pho) and leucine-aminopeptidase (l-leu) in Oh and Ah horizons of a (27 ha) mountainous coniferous forest catchment (Wüstebach, Eifel National Park, Germany). Spatial patterns and "hot spots" of activities of these four enzymes (involved in C-,N-, and P- cycling) were examined in connection to catchment units differing in slope, exposure and soil type (Cambisol vs. Gleysol), and multiple soil parameters (i.e., moisture content, pH, C, N, P, K, Fe, Mn content, C:N, C:P and N:P ratio). Catchment enzyme activities were overall, except for β-cello, significantly higher in the Oh than Ah horizon. Lower β-glu, and l-leu activities were found where more anaerobic soil conditions did occur, e.g., the river valleys (RV). Neither enhanced Oh horizon erosion on steeper Eastern (ES) and Northeastern (NES) slopes nor larger spatial soil nutrients heterogeneity on Northern (NS) and Western (WS) slopes, did significantly affect enzyme activity. Landscape topography did lead to a spatial variation of the activity of the four enzymes examined. The site-specific variation in C-cycling enzymes (β-glu and β-cello) was most marked at drier East, Northeast and Northern slopes, for P-cycling (pho) within the central wetter river valley but was for N-cycling (l-leu) enzyme activity more homogeneously distributed over the whole catchment. Overall, enzyme activities were strongly correlated to soil properties (especially soil moisture and organic carbon), but locations NS (Wüstebach source area) and RV (Wüstebach river flow path) showed less site-specific correlations. Further refinement of site-specific soil and external factors driving spatial distribution of enzyme activities at catchment scales and beyond will help to further tool up this research at larger spatial scales.

Response of C-cycling enzymes in soil aggregate-size fractions to slurry application over a one year period in two contrasting soil types

The distribution of enzymatic activity in soil aggregates is a key determinant in the turnover of organic matter. This study aimed to address how the application of a carbon-rich slurry influences extracellular enzymatic activity within aggregate-size fractions over a one-year period. Twenty-four pots of either a loam or sand soil, sown with Lolium perenne, were kept slurry-free (control), or were treated with a high dry matter slurry. Pots were sampled after 31, 137 and 361 days (n = 4). Soils were physically fractionated to obtain four aggregate-size fractions: ≥2 mm, ≥250 μm, ≤250 μm and ≤53 μm with enzyme assays of seven C-cycling enzymes conducted on each, and the potential extracellular enzymatic activity (pEEA) calculated. The strongest response in individual pEEA was seen after 137 days, where the pEEA of at least one C-cycling enzyme was significantly higher in the slurry treatment in each of the four aggregate-size fractions in both soil types (all at least P ≤ 0.05). Additionally, nearly all seven C-cycling enzymes were significantly higher in the slurry treatment compared to the control in the ≤53 μm fraction (all at least P ≤ 0.05) in both. No significant increase in pEEA was seen in the slurry treatment in any aggregate-size fraction after 361 days in the loam soil (all P > 0.05), and this was also largely the case for the sand soil. The results of this study clearly indicate that pEEA within aggregate-size fractions was strongly influenced by slurry application in the initial months, though this was not sustained.

Microbial dynamics associated with the decomposition of coconut and maize residues in a microcosm experiment with tropical soils under two nitrogen fertilization levels.

The microbial dynamics associated with the decomposition of maize (Zea mays) and coconut (Cocos nucifera) residues were investigated to assess the feasibility of using them as mulch in tropical soils. Phospholipid fatty-acid (PLFA) profiling, microbial biomass (MB-C), basal respiration, C-cycle enzyme activities and inorganic N dynamics were monitored in a microcosm experiment incubating soil samples with plant residues for 425days. Maize stover (MS) showed a higher decomposition, respiration rate, MB-C, enzymes activities and shift in microbial community structure than coconut husk (CH), which was barely changed. In MS, the lower N level increased C losses and decreased N mineralization compared to the higher N level. Maize stover is suitable for mulching and has a high potential of increasing soil quality if the proper N fertilization level is used, avoiding excessive C mineralization and N immobilization. Coconut husk decomposition was mostly impaired, indicating that a pre-processing is necessary to improve the benefits of this residue. Tropical soils are prone to degradation. Mulching can promote soil conservation, but depends on residue type and soil chemistry. Our study showed that MS managed under the recommended N fertilization level is suitable for mulching while CH is highly inaccessible for microbial degradation.

Impacts of simulated nitrogen deposition on soil enzyme activity in a northern temperate forest ecosystem depend on the form and level of added nitrogen

Extracellular enzymes in the soil are pivotal to nutrient cycling in the ecosystem. Simulated nitrogen (N) deposition has resulted in positive, negative, and neutral effects of added N on soil extracellular enzyme activity (EEA).A field experiment involving two levels (50 and 150 kg ha−1 yr−1) and three forms (NaNO3, NH4NO3, (NH4)2SO4) of added N was conducted in a northern temperate forest. Over 8 years beginning in 2011, we measured the extracellular enzyme activity of six soil-based enzymes involved in C- (β-glucosidase, BG; polyphenol oxidase, PPO; catalase, CAT), N- (urease, UR) and P- (acid phosphatase, ACP; alkaline phosphatase, AKP) cycling during the growing season (March to September).High-level N addition produced a more obvious effect in promoting the activity of C-cycling enzymes and ACP, while the activities of UR and AKP under high-level N addition decreased significantly at rates of 10.0 and 26.8%, respectively. NH4+-N had a stronger effect on soil EEAs than NO3−-N, except UR activity. Furthermore, N addition induced a time-lag effect on the activity of BG, PPO, and ACP. BG activity achieved a maximum value in 2016 after increasing at an average rate of 21.2%. Furthermore, additional N produced nonlinear effects in the inter-annual variation of BG and CAT activity, which emphasized the importance of long-term monitoring.The effects of N addition on soil EEAs depended on the forms and levels of N added. The stimulatory effects of N addition on the activity of C-cycling enzymes may lead to instability in the soil C pool.

Short-Term Effect of Biochar on Microbial Biomass, Respiration and Enzymatic Activities in Wastewater Irrigated Soils in Urban Agroecosystems of the West African Savannah

Irrigated urban agriculture (UA) supports the economy and health of urban inhabitants in low-income countries. This system is often characterized by high nutrient inputs and mostly utilizes wastewater for irrigation. Biochar has been proposed to increase crop yields and improve soil properties. In this study, we assessed the transient effect of rice husk biochar (20 t ha−1) and/or fertilizer (NPK: 15-15-15) on microbial respiration, microbial biomass carbon and enzyme activities of irrigated (wastewater and tap water) soil from an UA field experiment in the Guinea savannah zones of Ghana. Our results showed an increase by up to 123% in soil organic carbon (SOC) after a year of biochar application, while hot water extractable carbon (HWEC) was increased by only 11 to 26% and microbial biomass carbon (MBC) by 34%. Basal respiration was significantly increased in mineral fertilized soil by up to 46% but decreased by 12–45% under wastewater irrigation. Overall, the metabolic quotient (qCO2) indicated less stress for the microbial community and increased carbon use efficiency with biochar application and wastewater irrigation. Total enzymes activity was increased under wastewater irrigation and biochar treated soils exhibit a more diverse composition of C-cycling enzymes and a higher activity of aminopeptidases. Biochar and wastewater showed positive effects on biological soil properties and contributed to soil fertility. Our results suggest beneficial effects of biochar on non-biochar SOC stocks in the long term.

Alterations of soil labile organic carbon fractions and biological properties under different residue-management methods with equivalent carbon input

Abstract Crop residue return to soil can greatly affect soil carbon (C) cycling. However, the differences in soil organic C (SOC) pool among different residue-management methods, including residue-biochar, are still unclear. We investigated the changes in SOC content, SOC stock, labile organic C fractions, C pool management index (CPMI), microbial abundance (bacteria, actinomycetes, and fungi), and C-cycle enzyme activities (invertase, cellulose, and β-glucosidase) after four years of applying residue and residue-biochar in a barley-cotton cropping system in Yancheng, China. Five treatments were developed based on equivalent C input: residue-biochar (RB, 3.5 Mg ha−1), residue plus microbial inoculant (RI, 5.0 Mg ha−1), residue (R, 5.0 Mg ha−1), residue mulching (RM, 5.0 Mg ha−1), and no residue or residue-biochar (CK). The results showed that SOC content, SOC stock, and the CPMI in RB were the highest among all treatments with residue and residue-biochar, being 16.3%, 8.7%, and 66.2% higher than that in CK, respectively. Regarding the labile organic C fractions, RB primarily increased the contents of particulate organic C (POC), light fraction organic C (LFOC), and permanganate oxidizable C (KMnO4-C), RI and R primarily increased the water-extractable organic C (WEOC) and microbial biomass C (MBC), whereas RM had a relatively small effect on all fractions. Soil microbial abundance and C-cycle enzyme activities were greatly enhanced by RI and R, particularly by RI. The principal component analysis revealed that POC, LFOC, and KMnO4-C were the major factors causing the changes in SOC, SOC stock, and CPMI. Soil microbial abundance and C-cycle enzyme activities were significantly correlated with WEOC and MBC. In conclusion, applying residue-biochar could effectively increase soil C sequestration by enhancing the POC, LFOC, and KMnO4-C contents in comparison with residue return.

Typhoon-induced increases in porewater nutrient concentrations and CO2 and CH4 emissions associated with salinity and carbon intrusion in a subtropical tidal wetland in China: A mesocosm study

Typhoons can alter carbon cycling by increasing carbon inputs and by the oceanic water intrusion at low latitudes. Our understanding of how typhoons impacts C and N cycles by reflecting combine and separate effects of elevated salinity and carbon enrichment is poor. We conducted a mesocosm experiment simulating the effect of a salinity of 10‰ and dissolved organic carbon (DOC) enrichment of the surface water with acetate as DOC source on the dynamics of porewater nutrients and the emissions of carbonaceous greenhouse gases using plants and soil system from a Cyperus malaccensis freshwater wetland in the Min River estuary, southeastern China. The concentrations of NH4+-N and NO3−-N in porewater rose under elevated salinity but decreased with DOC enrichment, salinity and DOC in combination acted antagonistically such that there was no effect compared to the control. A 10‰ increase in salinity increased the cumulative CO2 emissions (+29%) and decreased the cumulative CH4 emissions (−61%) during the growing season. In response to DOC, The cumulative emissions of CO2 and CH4 increased by 79% and 84%, respectively. In response to the combined elevated salinity and DOC enrichment, the cumulative emissions of CO2 increased by 69% and cumulative methane emissions increased by 44%. Elevated salinity plus DOC enrichment decreased the activity of the N-cycling enzyme β-1,4-N-acetylglucosaminidase, but increased the activities of two C-cycling enzymes (β-1,4-glucosidase and 1,4-β-cellobiosidase) and the P-cycling enzyme acid phosphatase, indicating a higher demand for C and P relative to N. The combination of increased C as CO2 in all cases, increased CH4 only in the case of DOC addition, and rising inorganic N fluxes only in the case of salt suggeated that elevated salinity and DOC enrichment induced by typhoons may thus accelerate the release of C but have little influence on N release from tidal freshwater wetland ecosystems.

Influence of peach (Prunus persica Batsch) phenological stage on the short-term changes in oxidizable and labile pools of soil organic carbon and activities of carbon-cycle enzymes in the North-Western Himalayas

The labile organic carbon (C) and C-related enzymes are sensitive indicators capturing alterations of soil organic matter (SOM), even in a short-time scale. Although the effects of crop husbandry and land use change on these attributes have been well studied, there is no consensus about how plant phenology may impact them. This study aimed to determine the short-term effect of six distinct phenological stages (PS-1: full bloom; PS-2: fruit set; PS-3: pit hardening; PS-4: physiological maturity; PS-5: 60 d after physiological maturity; and PS-6: fall) of peach on the changes in soil organic carbon (SOC) fractions of different oxidizability, labile C pools, and C-cycle enzyme activities in soils, for two consecutive years (2015 and 2016) in the North-Western Himalayas (NWH). Peach rhizosphere soils were sampled at the topsoil (0–15 cm) and subsoil (16–30 cm) layers, along with rhizosphere soils from adjacent perennial grasses, which served as a control. Values for most of the assessed parameters, including very labile C, labile C, microbial biomass C, permanganate oxidizable C, dissolved organic C, mineralizable C, amylase activity, and carboxymethyl-cellulase activity, were significantly (P ≤ 0.05) higher at PS-3 than at other phenological stages of peach. Conversely, a sudden decline in these soil variables was recorded at PS-5, followed by a slight buildup at PS-6, particularly in the topsoil of the peach orchard. Short-term changes in organic C fractions of different oxidizability, influenced by peach phenological stage, significantly (P ≤ 0.05) affected C management index, C pool index, and lability index. Both the C management index and lability index showed their highest values at PS-3 and their lowest values at PS-5, clearly indicating short-term accretion and depletion of SOC, in tandem with the peach phenological events. Principal component analysis suggested that a composite of soil indicators, including microbial biomass C, dissolved organic C, amylase, and invertase, could help detect short-term changes in SOC content. It is concluded that peach phenological events had a major impact on the short-term variations of the studied soil variables, which could be attributed to changes in the above- and belowground plant residues, as well as the extent of nutrients and water acquisition.

Responses of soil C, N, and P stoichiometric ratios to N and S additions in a subtropical evergreen broad-leaved forest

Acid deposition from the emission of nitrogen (N) and sulfur (S) has become an important factor affecting the soil nutrient balance and biogeochemical cycling in terrestrial ecosystems. The average levels of N and S deposition in the rainy area of southwestern China from 2008 to 2010 were 9.5 g N m−2 y−1 and 19.3 g S m−2 y−1, respectively. External additions of N and S fertilizers combined with high levels of acid deposition may affect the soil ecological stoichiometry in the region’s widely distributed subtropical evergreen broad-leaved forest. Therefore, we investigated the responses of the soil stoichiometric ratios and enzyme activities to added N (+N), added S (+S), added N and S (+NS), and a control (Ctr) in the 0–20 cm layer in an evergreen broad-leaved forest in the rainy area of southwestern China from April 2013 to April 2015. The results showed that the soil total N (TN) concentration and N/P ratio were higher and the soil organic C (SOC) concentration and C/N ratio were lower in the fertilization treatments than the Ctr, although N and S additions did not significantly alter the soil total P (TP) concentration. The +N, +S, and +NS treatments increased the soil acid phosphatase activity and reduced the soil invertase, cellulase, catalase, and polyphenol oxidase activities. The +N and +NS treatments increased the soil urease activity and reduced soil peroxidase activity. The +S treatment reduced the soil urease activity and did not alter soil peroxidase activity. N and S additions had synergistic decreasing effects on the SOC concentration, C/N ratio, and soil cellulose and catalase activities. Moreover, structural equation models identified that N and S additions regulated the SOC, TN, and TP concentrations via shifting the activities of soil enzymes and the pathways differed between N addition and S addition. In conclusion, N and S additions decreased the SOC concentration, C/N ratio, and most soil C-cycle enzyme activities and increased the TN concentration, N/P ratio, and soil acid phosphatase activity. All these results indicated that external N and S additions combined with acid deposition increased soil N concentrations and exacerbated soil C and P limitations in this forest.

The diversity of microbial community and function varied in response to different agricultural residues composting.

Microbial activities are the dynamic core in the soil nutrient cycle. To improve the knowledges about the responses of soil microbial community structure and potential function to long-term cover crops practice. The co-occurrence patterns of soil microbial community structure and functional genes were evaluated using 16SrRNA, ITS and metagenomic technique in 13years cover crops of orchard grass (OG, Dactylis glomerata L.) with high C/N and white clover (WC, Trifolium repens L.) with low C/N. Conventional tillage (CT) was control. The experiment was implemented in an apple orchard located on the Loess Plateau, China, from 2006 to 2018. We also measured soil physicochemical properties and enzyme activities related to carbon and nitrogen cycling. The conclusions showed that the dominant bacterial phyla were Actinobacteria 27.68% in OG treatment and Proteobacteria 25.89% in WC treatment. Organic matter inputs stimulated growth of the phyla of Actinobacteria, Firmicutes, Chloroflexi, Ascomycota and genera of Bacillus, Blastococcus, Streptomyces and Penicillium. Interestingly, the OG and WC treatments promoted the fungal and bacterial alpha-diversity compared to CT treatment, respectively. In addition, compared to CT treatment, OG treatment was beneficial to the increase of C-cycle enzyme activity, while WC treatment tended to increase the N-cycle enzyme activity. Notably, compared to CT treatment, they both enriched carbon fixation and cycle pathways genes, while WC treatment increased the nitrogen metabolism pathway genes. Moreover, OG treatment was more conducive to the enrichment of carbohydrate enzymes genes involved in the hydrolysis of cellulose and hemicellulose compared to WC treatment. Overall, different quality of plant residues stimulated the specific expressions of soil microbial community structure and function. Long-term planted white clover was effective strategy to improve soil quality.

Soil aggregate-related organic carbon and relevant enzyme activities as affected by tea (Camellia sinensis L.) planting age in hilly region of southern Guangxi, China

It is essential to reveal the variations in the activities of carbon (C)-cycling enzymes in soil aggregates of different sizes, so as to shed more light on the soil organic C (Corg) dynamics in the tea plantation ecosystems. In this study, the activities of cellobiohydrolase, xylanase, β-glucosidase, and invertase were detected in soil aggregates obtained at the depth of 0–20 cm from tea plantations of various ages (8, 17, 25, and 43-yr.) in hilly region of southern Guangxi, China. Soil aggregates were divided into >2, 2–1, 1–0.25, and <0.25 mm fractions through a dry sieving procedure. This study hypothesized that the potential of soil Corg decomposition would be higher at early stage (in the initial 17-yr.) than that at late stage (after 17-yr.). Our results suggested that, irrespective of the tea planting age, soil aggregate-related Corg contents were mainly distributed in the >2 and 2–1 mm fractions, and soil aggregates at the >2 mm sizes had the highest activities of C-cycling enzymes. Notably, the C-cycling enzyme activities in soil aggregates were closely correlated with Corg availability, and Corg contents might not exert a vital part. On the other hand, tea planting for a long time could promote soil Corg to be accumulated. At early stage, the accumulated soil Corg was primarily derived from the >2 mm fractions; meanwhile, the C-cycling enzyme activities in the >2 mm fractions were also markedly elevated, indicating that the accumulated Corg in soils at early stage was more easily decomposed and showed a higher potential of decomposition than that at late stage, thus supporting our hypothesis. Overall, the youthful tea plantations in the initial 17-yr. showed an increasing trend with respect to the potential of soil Corg decomposition; however, when tea plantations became mature, the potential of soil Corg decomposition was reduced in hilly region of southern Guangxi, China.

The responses of extracellular enzyme activities and microbial community composition under nitrogen addition in an upland soil.

Tremendous amounts of nitrogen (N) fertilizer have been added to arable lands, often resulting in substantial effects on terrestrial ecosystems, including soil acidification, altered enzyme activities and changes in microbial community composition. Soil microbes are the major drivers of soil carbon (C) and N cycling; therefore, understanding the response of microbial communities to elevated N inputs is of significant importance. This study was carried out to investigate the influences of different N fertilization rates (0, 182, and 225 kg ha-1 representing control, low, and high N supply for each crop season for summer maize and winter wheat) on soil biochemical attributes, extracellular enzyme activities, and the microbial community composition in a winter wheat-summer maize rotation cropping system in north-central China. The results showed that N addition significantly decreased the soil pH in both the wheat and maize seasons. Microbial biomass N (MBN) decreased following N fertilization in the wheat season, while the opposite trend in MBN was observed in the maize season. Response ratio analysis showed that the activities of enzymes involved in C, N, and phosphorus cycling were significantly enhanced under N enrichment in both the wheat and maize seasons, and higher enzyme activities were noted in the high N addition treatment than in the low N addition treatment. A linear increase in fungal abundance with the N addition gradient was observed in the wheat season, whereas the fungal abundance increased and then decreased in the maize season. The bacterial abundance showed an increased and then decreased trend in response to the N addition gradient in both the wheat and maize crop seasons. Moreover, the partial least squares path model (PLS-PM) analysis showed that soil pH and soil organic carbon (SOC) were the most important soil variables, causing shifts in the soil bacteria. Furthermore, compared with the N-cycling enzymes, the C-cycling enzymes were significantly affected by the soil pH and SOC. Taken together, these results suggest that the effect of N addition on enzyme activities was consistent in both crop seasons, while the effects on MBN and microbial community composition to N addition were highly variable in the two crop seasons. Moreover, N fertilization-induced changes in the soil chemical properties such as soil acidity and SOC played a substantial role in shaping the microbial community.