Carbon Cycle Enzymes Research Articles

Leguminous green mulching alters the microbial community structure and increases microbial diversity by improving nitrogen availability in subtropical orchard systems in China

Microorganisms, the major decomposers of plant residues, are crucial for soil nutrient cycling. Living grass mulching effectively alters microbial community structure and promotes nutrient cycling. However, its consistency with mulching ages and growth periods remains unclear. Therefore, this study aims to clarify the dynamic characteristics of microbial communities and enzyme activities across different mulching ages. In this study, high-throughput sequencing technology was used to investigate bacterial and fungal community evolution in three mulching treatments with Vicia villosa for 8 years (VV_8), 4 years (VV_4), and clean tillage in a citrus orchard. This study covered three growth periods (citrus–grass: spring sprouting to budding period [SSBP], fruit swelling to withering period [FSWP], and fruit maturity to seeding period [FMSP]). The results showed that VV_4 and VV_8 treatments increased bacterial and fungal alpha diversity as well as the activities of nitrogen (N), carbon (C), and phosphorus cycling enzymes. C-cycling enzyme activity was the primary key factor driving changes in microbial diversity across growth periods. Under leguminous green mulching, bacteria alpha diversity increased the most during FSWP, while fungi increased the most during FMSP. Additionally, the relative abundance of Ascomycota and Basidiomycota significantly increased during the FSWP and FMSP, reaching 63.65–73.80 % and 79.73–84.51 %, respectively. With increasing mulching ages, the structural stability and synergistic effects of microorganisms were correspondingly enhanced. Furthermore, available nutrients determined microbial community evolution, with N availability being a key factor influencing microbial diversity, especially fungal diversity. In conclusion, as mulching ages increase, improved nutrient availability gradually enhances microbial diversity, synergistic interactions, and nutrient cycling functions, with copiotrophic taxa occupying a key position in the microbial network. FSWP is a critical turning point for enhancing microbial activity and C-cycling function. This study offers theoretical support for developing microbial regulation strategies to improve soil quality in orchard management practices.

IMPACT OF FOREST CONVERSION TO PASTURE ON SOIL ENZYMATIC ACTIVITY IN THE NORTHERN AMAZON

The conversion of forests to pastures in the Amazon results in deforestation and the loss of environmental services. This practice affects biogeochemical cycles and impairs soil enzyme activity, which is essential for maintaining soil quality. This study aimed to investigate the impact of converting part of the Amazon forest into pastures, focusing on soil enzyme activity. The study was conducted at Fazenda Canto Verde, Roraima, comparing native forest areas and pastures of Brachiaria brizantha and Brachiaria humidicola, established on Haplic acrisol, without fertilization or tillage, under a management regime of 30 days of grazing and 60 days of rest. Sampling involved 12 mini trenches per hectare at two depths, with analysis of enzyme activity post-incubation. Higher activity of carbon cycle enzymes (Cellulase, Invertase, β-Glucosidase) was observed in the forest compared to pastures, especially with B. humidicola. Nitrogen cycle enzymes (Urease, BAA-Protease) were more active in the forest, while B. humidicola showed the highest Casein-Protease activity. In the phosphorus and sulfur cycles, the forest led in Phosphomonoesterase and Phosphodiesterase, while B. humidicola excelled in Arylsulfatase. This study demonstrates that replacing forest with pastures significantly alters soil functionality, impacting biogeochemical cycles and their ecological functions.

ДИНАМИКА АКТИВНОСТИ ФЕРМЕНТОВ УГЛЕРОДНОГО ЦИКЛА В УСЛОВИЯХ ПЕРЕХОДА НА МИНИМАЛЬНЫЕ ТЕХНОЛОГИИ ОБРАБОТКИ

The purpose of research is to study the dynamics of the activity of enzymes in the carbon cycle of agrochernozems and its effect on the transformation of easily mineralizable organic compounds when using waste and surface treatment methods. Field observations were carried out on the basis of the production experience of OOO OPH Dary Malinovki in the Sukhobuzimo District in the Krasnoyarsk forest-steppe (56°10′ N and 91°47′ E). The impact of dump and minimal processing technologies on the seaso¬nal dynamics of the activity of carbon cycle enzymes in the layers of agrochernozem is considered. The field experiment scheme is represented by the following options: moldboard plowing (standard), minimal tillage (surface disking), flat-cut tillage (cultivation). The level of polyphenol oxidase activity in the soil of the experimental variants was estimated to be weak. The intraseasonal dynamics of the studied enzymes was significant and correlated with the transformation of the humus accumulation coefficient. On non-dumping backgrounds, the variability of polyphenol oxidase was less variable. The minimum va¬lues of the humus accumulation coefficient were found at the initial stage of introducing the technologies under study during the fallow period of agrochernozems, as well as during the barley growing season. The maximum is in the soil under spring wheat crops. The use of flat-cut cultivators led to a strong relationship between the activity of polyphenol oxidase and the coefficient of humus accumulation. In the soil of all variants, an inverse relationship was observed between peroxidase activity and the coefficient of humus accumulation. The participation of peroxidase in the biochemical processes of mineralization was carried out mainly under the conditions of dump processing of agrochernozems. The activity of oxidoreductase enzymes indicated favorable conditions for the humification of organic compounds and the accumulation of newly formed humic substances in the soil when spring wheat was placed in fallow under conditions of using no-moldboard technologies.

Parent material influences soil properties to shape bacterial community assembly processes, diversity, and enzyme-related functions

Soil parent material is the second most influential factor in pedogenesis, influencing soil properties and microbial communities. Different assembly processes shape diverse functional microbial communities. The question remains unresolved regarding how these ecological assembly processes affect microbial communities and soil functionality within soils on different parent materials. We collected soil samples developed from typical parent materials, including basalt, granite, metamorphic rock, and marine sediments across soil profiles at depths of 0–20, 20–40, 40–80, and 80–100 cm, within rubber plantations on Hainan Island, China. We determined bacterial community characteristics, community assembly processes, and soil enzyme-related functions using 16S rRNA high-throughput sequencing and enzyme activity analyses. We found homogeneous selection, dispersal limitation, and drift processes were the dominant drivers of bacterial community assembly across soils on different parent materials. In soils on basalt, lower pH and higher moisture triggered a homogeneous selection-dominated assembly process, leading to a less diverse community but otherwise higher carbon and nitrogen cycling enzyme activities. As deterministic process decreased, bacterial community diversity increased with stochastic process. In soils on marine sediments, lower water, carbon, and nutrient content limited the dispersal of bacterial communities, resulting in higher community diversity and an increased capacity to utilize relative recalcitrant substrates by releasing more oxidases. The r-strategy Bacteroidetes and genera Sphingomonas, Bacillus, Vibrionimonas, Ochrobactrum positively correlated with enzyme-related function, whereas k-strategy Acidobacteria, Verrucomicrobia and genera Acidothermus, Burkholderia-Caballeronia-Paraburkholderia, HSB OF53-F07 showed negative correlations. Our study suggests that parent material could influence bacterial community assembly processes, diversity, and soil enzyme-related functions via soil properties.

Analyzing soil enzymes to assess soil quality parameters in long-term copper accumulation through a machine learning approach

Soil contamination by agrochemicals is a big concern for soil health and ecosystem functioning. This is especially true for non-degradable substances like heavy metals (HM) that, because of their long-term use, are reaching significant values today due to soil accumulation. Among agrochemicals, copper (Cu) has been important in fighting fungal diseases on perennial crops for centuries.Laboratory experiments can be useful to understand the highest potential toxic effect of Cu but need to reflect what happens with long-term application in a dynamic and living agroecosystem. This study uses multivariate data analysis and machine learning to investigate long-term Cu accumulation on soil quality parameters, especially soil extracellular enzymatic activities. We collected soil samples from 21 apple orchards in South Tyrol, Italy. The orchards had different concentrations of Cu. We took 315 samples in total and analyzed them for various soil properties. We also measured the concentrations of elements in apple leaves and the activities of soil extracellular enzymes. We depicted the effect of Cu on several enzymatic activities, shedding light on the effect of Cu on the soil microbial communities functionality. Our results show that Cu concentrations in the study area affect only phosphatase activity, showing effects above 60 mg kg−1 of available Cu. Protease activity was positively correlated with Cu, while soil organic matter and management mainly influenced the carbon (C) cycle enzymes. Phosphatase decrease could be of concern for the potential disruption of the Phosphorus (P) cycle in the soil and plays a role in plant nutrition, as seen by P concentration in apple trees' leaves.We demonstrated how machine learning can help interpret complex and multivariate environmental data and overcome some downsides of traditional statistical models.

Mechanisms of soil respiration and its temperature sensitivity in black soil farmland

Soil respiration is the process of decomposition of organic matter in soil and microbial metabolism to produce carbon dioxide. In the context of climate warming and degradation of agricultural soil fertility, it becomes crucial to explore the mechanisms of soil respiration to increase carbon sequestration. In this paper, five biochar applications (0, 3.79, 7.58, 11.36, 15.15 t/ha) and two tillage methods (shallow ploughing, deep ploughing) were set up to explore the mechanism of soil respiration and its temperature sensitivity by studying the effects of tillage methods and different amounts of biochar application on soil properties, soil enzyme activities, soil respiration and its temperature sensitivity during the growing season of soybeans in the black soil area. The results showed that soil respiration rate increased with biochar application in the low biochar application range; the opposite trend was observed for high biochar application beyond the threshold (11.36 t/ha). The application of 11.36 t/ha of biochar amount had the strongest promotion effect on soil respiration, reaching 2.42 μmol m−2·s−1 in the shallow ploughing treatment and increasing 0.32 μmol m−2·s−1 in the deep ploughing compared to the shallow ploughing. The application of biochar significantly increased the activity of nitrogen and phosphorus enzymes and had an inhibitory effect on carbon cycle enzymes; the increased activity of nitrogen and phosphorus cycle enzymes provided sufficient substrate for microbial respiration and thus increased soil respiration, and the decrease in the enzymatic reaction of carbon cycle enzymes led to a decrease in temperature sensitivity. The temperature sensitivity of deep ploughing (2.18–2.59) got a more substantial reduction than that of shallow ploughing (2.34–3.53), which indicates that deep ploughing treatments can better reduce the mineralization of organic carbon than shallow tillage. Meanwhile, the temperature sensitivity of soil respiration reached a minimum with the application of 7.58 t/ha of biochar, which was reduced by 16% under deep ploughing treatment compared to the control, 33% under shallow ploughing treatment compared to the control, and also reduced by 27.27% under deep ploughing compared to shallow ploughing, which suggests that the addition of biochar reduces the loss of carbon to a certain extent. This study is important for assessing the effects of tillage practices and biochar combinations on carbon sequestration in agricultural soils in black soil areas.

Back to the 'roots' of research: a hypothesis-driven approach provides predictive understanding of plant-herbivore-microbe interactions.

This article is a Commentary on Böttner et al. (2023), 239: 1475–1489.

Determining soil health parameters controlling crop productivity in a Citrus Greening disease affected orange grove

Soil health is an important aspect for maintaining adequate crop production, but the specifics of what entails a healthy soil can vary from region to region and crop to crop. In highly managed agricultural systems, unhealthy soil can be masked by intensive management practices, yet there must be detrimental cutoff points in various characteristics, such as soil organic matter (SOM) concentrations, where even highly managed systems start to lose productivity. This negative impact was observed in a Florida citrus grove containing Valencia orange trees with observable differences in tree size yet were otherwise managed identically. A soil health index demonstrated that the areas with smaller trees had a significantly lower index score and those soils contained significantly less SOM (average SOM ​= ​0.57%) compared to areas with larger trees (average SOM ​= ​0.94%). The areas of lower crop productivity also had less enzymatic activity of common carbon-cycling enzymes and different microbial populations, which all together negatively affected soil health and corresponding plant productivity. This agricultural region is also known to have a Citrus Greening disease (HLB) infection rate of close to 100%, hence we developed a hypothesis that could explain how progression of this infection could be impacted by SOM concentrations and differences in microbial diversity. We posit that areas of this grove with healthier soil could have more resistance to the onset of fatal HLB symptoms. Consequently, soil organic matter distribution and concentration should be considered when establishing new groves in order to optimize soil and crop productivity.

Organic amendment regulates soil microbial biomass and activity in wheat-maize and wheat-soybean rotation systems

Long-term heavy application of inorganic fertilizers is associated with a decrease in soil quality and biodiversity. Organic amendments have been reported to positively affect soil quality; however, relatively little is known regarding soil carbon (C) cycle enzyme kinetic parameters (Vmax and Km), community-level physiological profiles (CLPP), and the interactions between these factors and soil microbes and physicochemical properties under sustained organic amendment. Therefore, this study aimed to evaluate the effect of organic amendments on crop yield, soil chemical properties, microbial activity, enzyme kinetic parameters of five extracellular C cycle-related hydrolase enzymes, and soil microbial functional diversity in wheat-maize (WM) and wheat-soybean (WS) rotation crop systems. The results of the study showed that combined application of organic and inorganic fertilizers increased crop yield (6.81–17.47%), soil total organic C (TOC, 29.44–39.54%), total nitrogen (TN, 24.22–50.79%), available potassium (AK, 39.47–59.62%), total dissolved nitrogen (TDN, 19.68–33.75%), dissolved organic C (DOC, 14.54–55.10%), available phosphorus (AP, 34.81–243.90%), and microbial biomass C and nitrogen (MBC, 17.65–40.86% and MBN, 18.63–50.76%) concentration. The combined application also enhanced microbial growth when compared with an inorganic amendments regime. Additionally, the combined application of organic and inorganic fertilizers increased soil microbial activity and catabolic diversity and maintained a high substrate-induced respiration (SIR) value. Furthermore, the conversion from a WM rotation to a WS rotation increased both soil pH and microbial biomass, and the resultant soil exhibited lower potential activity and higher enzyme-substrate affinity. Overall, the findings of this study showed that an increase in soil microbial biomass is a key determinant of microbial catabolic activity and functional diversity.

Dynamics Variation of Soil Labile Organic Carbon Fractions in Different Wetland Types of Dongting Lake under Seasonal Water Level Fluctuation

Soil labile organic carbon (LOC) fractions are very sensitive to environmental change and closely related to soil quality. They play an important role in the study of terrestrial carbon cycles. This study aimed to explore the sensitivity of soil LOC fractions to environmental changes and analyze their main influencing factors during three seasonal water level periods for scientific management of Dongting Lake wetlands. Soil under three typical wetland types (Carextristachya wetland (CTW), Phragmites australis wetland (PAW) and Salix babylonica (SBW)) in East Dongting Lake in China were collected during the normal season (May), rainy season (August) and dry season (December). Seasonal dynamics of soil LOC fractions (i.e., dissolved organic carbon (DOC), microbial biomass carbon (MBC) and easily oxidized carbon (EOC)) within these wetlands and their relationship to soil nutrients and carbon-cycle enzyme activity were analyzed. The results showed that the soil DOC contents of the three wetlands first increased and then decreased, with the exception of CTW from the normal season to the dry season, while the seasonal changes of soil MBC and EOC for all wetlands followed an opposite pattern. CTW had the largest DOC concentration (228.29 mg·kg−1) during dry season, while the highest contents of soil DOC, MBC and EOC were found in PAW during the three observed seasons, which ranged from 82.05 to 203.60 mg·kg−1, 262.54 to 325.74 mg·kg−1 and 3.30 to 4.61 g·kg−1, respectively. However, the contents of soil DOC and their proportions to soil organic carbon (SOC) of all wetlands during the normal season were 56.58~82.05 mg·kg−1 and 0.41~0.47%, respectively, which were the lowest among the three seasons. Nevertheless, the contents of both MBC and EOC as well as their ratios to SOC in these wetlands showed similar seasonal dynamics, with the lowest values recorded in the rainy season. From the normal season to the dry season, invertase activity in all wetlands increased, while cellulase activity decreased by 12.5–31.3%. The seasonal variation of catalase activity for all wetlands was less distinctive, and the highest enzyme activity was during the rainy season. Correlation analysis revealed that soil LOC fractions for all wetlands were closely related to SOC, TN, TP and invertase for the three seasons, especially during the rainy season, but were negatively correlated with TK, cellulase and catalase activity. Generally, soil LOC fractions of the three wetlands were affected by the seasonal fluctuations of water levels and presented different distribution characteristics.

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.

Response of soil labile organic carbon fractions and carbon-cycle enzyme activities to vegetation degradation in a wet meadow on the Qinghai–Tibet Plateau

Vegetation degradation resulting from climate change and human activities in wet meadows is an important issue worldwide. This phenomenon is known to influence soil labile organic carbon (LOC) and enzyme activities due to changes in environmental conditions. However, little is known about the response of LOC and enzyme activities to vegetation degradation in high-altitude wet meadows. In this study, we examined the response of LOC and carbon-cycle enzyme activities to different intensities of vegetation degradation (i.e., non-degraded (ND), slightly degraded (SD) moderately degraded (MD), and heavily degraded (HD)) in a Tibetan wet meadow. The contents of soil organic carbon (SOC), dissolved organic carbon (DOC), microbial biomass carbon (MBC) and light fraction organic carbon (LFOC) and the carbon-cycle enzyme activities (i.e., cellulase, amylase and β-glucosidase) were investigated in two growing seasons (2016 and 2017). We found that the content of soil SOC and LOC fractions declined with increasing soil depth in each degraded level except for HD. Vegetation degradation significantly decreased the amount of SOC at depths of 0–10 cm and 10–20 cm, and this decrease was attributed to the relative reduction of carbon source input and higher carbon decomposition. Vegetation degradation also significantly reduced the contents of SWC, DOC, MBC, LFOC, amylase and β-glucosidase in the topsoil layers (0–10 and 10–20 cm). However, the corresponding contents in deeper soil layers had no significant differences. In addition, the SWC, DOC, LFOC and the carbon-cycle enzyme activities were higher in 2016 than in 2017. Significant correlations were obtained between SWC, SOC, LOC fractions and enzyme activities. Soil moisture was found to be the main abiotic driver for variation of soil carbon and enzyme activities. Our results indicate that vegetation degradation in the Tibetan wet meadows decreased the quantity of topsoil labile carbon fractions and enzyme activities and heavily degraded vegetation may lead to a change of profile distribution in soil carbon pool.

Soil organic matter stabilization and carbon-cycling enzyme activity are affected by land management.

Increasing carbon (C) storage in soil is a key aspect of climate change mitigation strategies and requires an understanding of the impacts of land management on soil C cycling. The primary aim of this study is to investigate how land management impacts key soil organic matter stabilization and cycling processes affecting soil C storage. Soil sampling was undertaken across seven transects crossing the boundary between agriculture and forestry. The transects covered 3 pasture (AP) and 4 arable (AA) fields combined with 3 young secondary woodlands (50-60 years old - WY) and 4 mature/ancient semi-natural woodlands (110 to >400 years old - WM). Physical fractionation of soil organic matter pools was performed, together with pH, carbon and nitrogen content, as well as activity of four enzymes associated with C transformation in the soil. Woodland soils were associated with significantly higher content of light fraction C and greater enzyme activity in comparison to agricultural soils. Enzyme activity and soil organic C decreased with soil depth regardless of land-use type. We did not, however, observe any effect of the distance from the land use boundary on either enzyme activity and soil C pools. Our results indicate that analysis of soil organic matter (SOM) fractions can act as an indicator of decomposition rates of SOM in forest and agricultural ecosystems.

Post-thinning Responses of Microbial Substrate Utilization in Temperate Japanese Larch Forests

ABSTRACT The present study examined microbial substrate utilization by community level physiological profiling and carbon-cycling enzyme assays (cellobiohydrolase, β-xylosidase, and oxidases) in three Japanese larch forests. The forests differed in their locations, topographies, and soil microclimates, and each covered three treatments, namely 20 (IT) and 35% basal area thinning (HT) without intensive residue harvests and an un-thinned control (UTC). Microbial substrate utilization and soil properties (temperature, moisture, total carbon and nitrogen, inorganic nitrogen, and pH) were analyzed at 0–10 cm depth, six years after thinning. Microbial utilization of carbohydrate group under IT was 27 and 62% higher than that under UTC and HT, respectively, in only one of the forests. This might occur because this forest featured a steeper slope, rockier soil texture, and cooler and drier soil surface than the other two forests, where no thinning effect was observed. However, neither microbial utilization of any other substrate groups nor enzyme activity changed by thinning across all forests. It could result from the exclusion of intensive residue harvests or the lack of changes in soil inorganic nitrogen and pH. These results indicate that the thinning effects on microbial substrate utilization might be inconsistent across multiple sites, and at least, not decline the associated forest ecosystem functions and sustainability.

Effect of compost and inorganic fertilizer on organic carbon and activities of carbon cycle enzymes in aggregates of an intensively cultivated Vertisol.

Background and aimsThis paper was primarily devoted to understand the interactions of soil aggregates, organic carbon (C) and carbon cycle enzymes in aggregates under different fertilization managements, aiming to identify the effects of organic and inorganic fertilizer amendments on soil organic C accumulation and the activities of carbon cycle enzymes within aggregates in Vertisol.MethodsA Vertisol soil following 4-year compost and inorganic fertilizer amendments, i.e. no fertilizer (CK), mineral fertilizer (FR) and 60% compost N plus 40% fertilizer N (FRM), was collected to identify the dynamics of organic C, enzymes activities and their associations with macroaggregation using aggregate fractionation techniques.ResultsThe organic C content in all FR and FRM treatments was 8.24–41.15% higher than that in CK. An increased amounts of carbon cycle enzymes in aggregates or 0–20 cm bulk soil were also observed in FRM plots. Compared to FR, FRM significantly strengthened the structural stability of macroaggregates and the intimate connection between enzyme activities and macroaggregates.ConclusionsAs a recommended measure, supplementation with organic manure such as compost strengthened the process of mutual promotion between carbon cycle enzymes and macroaggregates, and the synergistic effect would be highly beneficial to soil organic C sequestration.

Soil depth and grassland origin cooperatively shape microbial community co‐occurrence and function

AbstractMany soils are deep, yet soil below 20 cm remains largely unexplored. Exotic plants can have shallower roots than native species, so their impact on microorganisms is anticipated to change with depth. Using environmental DNA and extracellular enzymatic activities, we studied fungal and bacterial community composition, diversity, function, and co‐occurrence networks between native and exotic grasslands at soil depths up to 1 m. We hypothesized (1) the composition and network structure of both fungal and bacterial communities will change with increasing depth, and diversity and enzymatic function will decrease; (2) microbial enzymatic function and network connectedness will be lower in exotic grasslands; and (3) irrigation will alter microbial networks, increasing the overall connectedness. Microbial diversity decreased with depth, and community composition was distinctly different between shallow and deeper soil depths with higher numbers of unknown taxa in lower soil depths. Fungal communities differed between native and exotic plant communities. Microbial community networks were strongly shaped by biotic and abiotic factors concurrently and were the only microbial measurement affected by irrigation. In general, fungal communities were more connected in native plant communities than exotic, especially below 10 cm. Fungal networks were also more connected at lower soil depths albeit with fewer nodes. Bacterial communities demonstrated higher complexity, and greater connectedness and nodes, at lower soil depths for native plant communities. Exotic plant communities’ bacterial network connectedness altered at lower soil depths dependent on irrigation treatments. Microbial extracellular enzyme activity for carbon cycling enzymes significantly declined with soil depth, but enzymes associated with nitrogen and phosphorus cycling continued to have similar activities up to 1 m deep. Our results indicate that native and exotic grasslands have significantly different fungal communities in depths up to 1 m and that both fungal and bacterial networks are strongly shaped jointly by plant communities and abiotic factors. Soil depth is independently a major determinant of both fungal and bacterial community structures, functions, and co‐occurrence networks and demonstrates further the importance of including soil itself when investigating plant–microbe interactions.

Soil enzymes and microbial elemental stoichiometry as bio-indicators of soil quality in diverse cropping systems and nutrient management practices of Indian Vertisols

Organic agriculture is attaining increasing popularity as it sustains crop productivity and soil health without deteriorating climate. But comprehensive information on carbon (C), nitrogen (N), phosphorus (P) and sulphur (S) cycling enzymes, microbial elemental stoichiometry and soil functional diversity are scanty in organic vis-à-vis conventional systems across the globe. The most discriminant biological factor(s) and enzyme activity based quick, effective, sensitive index of soil quality are unavailable for organic agriculture. To address these issues, we considered four major cropping systems of India i.e. soybean-wheat, soybean-mustard, soybean-pea and soybean-linseed under six nutrient management practices, namely, M1 (mineral fertilizers as used by farmers), M2 (recommended dose of mineral fertilizers), M3 (50% Inorganic +50% Organic), M4 (25% Inorganic +75% Organic), M5 (75% Organic + Innovative) and M6 (Organic; 100% Organic) in a Vertisol. Activities of eleven enzymes, soil microbial biomass C, N and P and soil organic C were analysed and geometric mean enzyme activity (GMEA) and other parameters were computed for surface and subsurface soils. Enzyme activities were significantly (P < 0.05) increased by organic amendments (~50–75%). Exceptionally, phenol oxidase and peroxidase activities were ~51 and 50% higher in subsurface than surface soils. Specific enzyme activities were lower in M6; it ascertained the capability of organic system to sequester higher amounts of C than M3 and M1. However, soil functional diversity was nearly 10 and 20% lower for M6 than M3 and M1, respectively. Discriminant function analysis confirmed SOC, arylsulfatase activity and available P to be the most effective discriminant factors between the conventional and organic nutrient management practices in India. The GMEA was ~55% higher for M6 than M1. It was strongly and positively correlated with treated soil quality index. Further, GMEA was cross validated with an independently performed principal component analysis to find its suitability as soil quality index. The GMEA was correlated (P < 0.05) with scores of first component and proved to be consolidative enough for explaining functional distinction between conventional and organic management by reducing the several soil enzyme activities to a single numerical point. Thus, GMEA is proposed to indicate soil quality quickly and accurately in Vertisol. Microbial biomass C to N ratio was correlated with system productivity and GMEA. But, we recommend for its recertification after developing baseline values to use it as a robust indicator of soil productivity.

Short-Term Response of the Soil Microbial Abundances and Enzyme Activities to Experimental Warming in a Boreal Peatland in Northeast China

Global warming is likely to influence the soil microorganisms and enzyme activity and alter the carbon and nitrogen balance of peatland ecosystems. To investigate the difference in sensitivities of carbon and nitrogen cycling microorganisms and enzyme activity to warming, we conducted three-year warming experiments in a boreal peatland. Our findings demonstrated that both mcrA and nirS gene abundance in shallow soil and deep soil exhibited insensitivity to warming, while shallow soil archaea 16S rRNA gene and amoA gene abundance in both shallow soil and deep soil increased under warming. Soil pmoA gene abundance of both layers, bacterial 16S rRNA gene abundance in shallow soil, and nirK gene abundance in deep soil decreased due to warming. The decreases of these gene abundances would be a result of losing labile substrates because of the competitive interactions between aboveground plants and underground soil microorganisms. Experimental warming inhibited β-glucosidase activity in two soil layers and invertase activity in deep soil, while it stimulated acid phosphatase activity in shallow soil. Both temperature and labile substrates regulate the responses of soil microbial abundances and enzyme activities to warming and affect the coupling relationships of carbon and nitrogen. This study provides a potential microbial mechanism controlling carbon and nitrogen cycling in peatland under climate warming.

Soil C/N and pH together as a comprehensive indicator for evaluating the effects of organic substitution management in subtropical paddy fields after application of high-quality amendments

Organic substitution management (OSM) is a key technology employed to reduce the amount of chemical fertilizer used in agricultural operations with the goal of reducing environmental pollution and ensuring green and sustainable agricultural development in China. However, there is still limited information regarding the underlying interactions between soil nutrients, enzyme activities and microbial community structures after long-term partial substitution of inorganic N with organic amendments, and no suitable evaluation indicators of organic substitution effects have been identified. Here, distance-based redundancy analysis (dbRDA), principal component analysis (PCA), the partial least squares method (PLS) and the partial least squares path model (PLS-PM) were used to better understand the impact of substitution effects on soil biochemical indexes in a 34-year field experiment. We found that soil C/N significantly directly affected rice yield, and that a soil C/N ranging from 10.12 to 10.19 could sustain a rice yield between 7000 and 6800 kg ha−1. Moreover, the soil hydrolase activities of the carbon and fungi communities were significantly influenced by both C/N and pH, and the carbon-cycling enzyme activities were found to be more susceptible to C/N than nitrogen-cycling enzyme activities. The low soil C/N and high pH after OSM decreased the ratio of G+ to G− and fungi to bacteria, indicating OSM increased the nutrient availability and benefited growth of the bacterial community. Hence, we believe that soil C/N and pH together can be used as a comprehensive index for suitable evaluation of the effects of OSM.

Microbial community structure and function respond more strongly to temporal progression than to the application of slurry in an Irish grassland

The application of slurry to grassland for fertilization purposes is common practice, but its effect on the soil microbiota is mostly overlooked. This study investigated the short term response of the functionality and composition of the soil microbiome to slurry application. A 180m2 field was divided into 36 plots. Slurry was splash-plate applied at a rate of 30tha−1. Sampling was conducted 5, 30 and 65 days after application. The functionality of the soil microbial community was examined using assays on 8 carbon cycling enzymes as well as basal respiration analysis. Microbial community structure was analysed via bacterial 16S rRNA gene and fungal internal transcribed spacer region terminal restriction fragment length polymorphism. Bacterial and fungal abundance was determined via quantitative PCR aiming at the same genetic targets. Furthermore, microbial biomass carbon and nitrogen were quantified. A significant increase in enzymatic activity with slurry treatment was reported on days 5 and 65, indicating a sequential response of the microbiota to slurry-derived carbon with the utilization of labile carbon on day 5 and the more stable carbon on day 65. This activity seemingly resulted from the microbial demand for N. In contrast, T-RFLP revealed that only bacterial community structures on day 5 were significantly affected by slurry application, all other bacterial and all fungal communities were not significantly altered by slurry. However, bacterial and fungal community structures, microbial biomass carbon and basal respiration significantly responded to temporal progression (day 5, 30 and 65). These findings suggest that soil microbial communities are responding to slurry applications via enhanced microbial activity but their structure remains largely unchanged with temporal progression having a greater impact.