Soil Extracellular Enzyme Activities Research Articles

Effects of thinning and understorey removal on soil extracellular enzyme activity vary over time during forest recovery after treatment

Effects of thinning and understorey removal on soil extracellular enzyme activity vary over time during forest recovery after treatment

Impacts of Land Use Intensification Level on Fluvo-aquic Cropland Soil Microbial Community Abundance and Necromass Accumulation in North China

Despite the essential role of soil microorganisms in nutrient turnover in soil ecological systems and the recognized paramount significance of microbial necromass to soil organic carbon accumulation, how microbial community abundance and necromass respond to land use intensification level regulation remains poorly understood. To address this knowledge gap, based on the land use intensification level, three treatments were set up[annual wheat-maize rotation (CC), alternating temporary grassland with wheat planting (TG), and perennial grassland (PG)], and a long-term fixed filed experiment was established to investigate the influences of the regulation of land use intensification level on bacterial and fungal community abundances; the accumulation of bacterial, fungal, and total microbial necromass; and their contributions to SOC sequestration using droplet digital PCR and amino sugar detection technologies. We further sought to determine the key factors driving the bacterial, fungal, and total microbial necromass C accumulation. Our results demonstrated that fungal community abundance was strongly affected by land use intensification level regulation compared to that of the bacterial community, which increased with decreasing land use intensification level. The total microbial necromass C predominated the SOC accumulation across all three land use intensification levels, which contributed 52.78%, 58.36%, and 68.87% to SOC, respectively, exhibiting an increasing trend with the decline in land use intensification level. Fungal necromass C accounted for more than 80% of the total microbial necromass C, indicating its predominance in the accumulation of the total microbial necromass C and active variation via the reduction in land use intensification level. There was no significant difference in bacterial necromass C (MurA) content, with the trend of CC<PG<TG, whereas fungal necromass C (GluN) was observed to be significantly shifted by the modulation of land use intensification level, with contents in the TG and PG treatments being higher than that in the CC treatment, especially for the PG treatment (with an increase of 66.10%). The increase in bacterial necromass C accumulation was associated with microbial demand for N and was affected by the balance between soil C and N; however, the accumulation of fungal necromass C was jointly manipulated by a wide variety of biotic and abiotic factors. Altogether, our work provides evidence that agricultural land use intensification level regulation can enhance soil extracellular enzyme activity and accelerate nutrient transformation through changing edaphic properties, thus improving fungal amount and necromass C accumulation, with active contribution to total microbial necromass C and even SOC.

Changes in the activity of soil enzymes after fire

Fire can have widespread impacts on biogeochemical processes of carbon (C) and nutrient cycling. Soil extracellular enzyme activity (EEA) plays crucial roles in biogeochemical processes, while the general response pattern of EEAs to fire remains elusive. Here, we synthesized 1064 paired observations of fire effects on eight soil EEAs of β-D-Cellobiosidase (CB), β-1,4-Glucosidase (BG), β-1,4-Xylosidase (XYL), N-acetyl-glucosaminidase (NAG), urease (URE), phosphatase (PHO), peroxidase (PER), and phenol oxidase (POX) from 51 publications on a global scale. Results showed that fire significantly decreased hydrolases of C acquisition (sum of CB, BG, and XYL), N acquisition (sum of URE and NAG), and P acquisition (PHO) EEAs by 21.0%, 25.5%, and 29.9%, respectively. In contrast, fire significantly enhanced oxidative enzyme (sum of PER and POX) activities by 12.4%. Among all experimental, environmental, and soil variables, ecosystem type and soil C and N had greater effects on the various responses of EEAs to fire across studies. In addition, changes in soil C and N pools and microbial biomass were positively correlated with changes in hydrolytic EEAs but negatively correlated with changes in oxidative EEAs. These results suggest that the differential fire effects on soil hydrolytic and oxidative EEAs may be a crucial mechanism regulating soil C and nutrient cycling following fire events.

Impacts of Different Long-Term Fertilizer Management Regimes on Soil Nitrogen Mineralization and Its Enzyme Activities under a Double-Cropping Rice System in Southern China

Soil extracellular enzyme activities play an important role in regulating the soil nitrogen (N) mineralization process in paddy fields. However, there is still a need to further study how N mineralization responds to different fertilizer management techniques and the soil extracellular enzyme activities for N mineralization in paddy fields. Therefore, the influence of different long-term (35 years) fertilizer regimes on soil N mineralization, hydrolysable N fractions—such as hydrolyzed unknown nitrogen (HUN), amino acid nitrogen (AAN), amino sugar nitrogen (ASN), ammonia nitrogen (AN), and total acid-hydrolyzed nitrogen (TAN)—and their extracellular enzyme activities (soil urease, L-glutaminase, β-glucosidase, arylamidase, and β-glucosaminidase) in a double-cropping rice field in southern China were investigated in this study. The field experiment included the following fertilizer regimes: rice straw and inorganic fertilizer (RF), 30% organic manure and 70% inorganic fertilizer (OM), inorganic fertilizer alone (MF), and no application of inorganic fertilizer as a control (CK). The results show that the soil ammonium N, amino sugar N, hydrolysable unidentified N, and amino acid N contents in the paddy field with RF treatment increased by 30.56%, 5.51%, and 62.74% compared with the CK treatment. The results show that the soil aerobic and anaerobic N mineralization rates in the paddy fields with OM and RF treatments increased by 22.92% and 18.27% compared with those with MF treatment. Moreover, soil extracellular enzyme activities under RF and OM treatments significantly increased, which indicated that the main substrate of microbial activity was effective. Correlation analysis indicated that the soil L-glutaminase activity, amino sugar N, amino acid N, and total acid-hydrolysable N contents were positively correlated with soil aerobic and anaerobic N mineralization rates in paddy fields. However, there was a negative correlation between the soil N mineralization rate and soil β-glucosaminidase activity in paddy fields. This finding shows that the yields of early rice and late rice under the RF and OM treatments were significantly higher than those under the MF and CK treatments. Compared with the MF treatment, the yields of double-cropping rice with RF and OM treatments increased by 9.84% and 11.37%, respectively. As a result, the application of straw or organic manure and inorganic fertilizer was effective for improving soil N mineralization, the soil acid-hydrolyzed N content, and extracellular enzyme activities in double-cropping rice fields.

Extracellular enzyme activities response to nitrogen addition in the rhizosphere and bulk soil: A global meta-analysis

Plant roots play a crucial role in acquiring available nutrients and regulating microbial decomposition, leading to faster nutrient cycling in the rhizosphere than in bulk soil. With increasing nitrogen (N) loading, rhizosphere processes may become more crucial than bulk soil processes for accurately predicting nutrient cycling process changes. However, it remains unclear how the rhizosphere and bulk soil extracellular enzyme activities (EEAs) respond to N addition on a global scale. Therefore, we used a global meta-analysis to examine the effects of N addition on EEAs involved in carbon (C), N, and phosphorus (P) acquisition in paired rhizosphere and bulk soils, based on 1992 observations from 40 studies. Overall, N addition significantly increased β-xylosidase (BXYL) activity by 17.0% in bulk soil, together with urease (URE) activity in both the rhizosphere (25.3%) and bulk soil (33.6%). In addition, N addition marginally significantly decreased phenol oxidase (PHEO) activity in the rhizosphere (−18.4%), as well as peroxidase (PERO) activity in both the rhizosphere (−12.6%) and bulk soil (−13.6%). The reductions may be caused by fungi: bacteria ratio and Gram+ bacteria: Gram− bacteria ratio (F: B and G+: G−, respectively) reductions. We also found that EEAs (e.g., acid/alkaline phosphatase (AP) and PHEO) did not always have a simple linear relationship with higher N addition rate and duration. Additionally, the responses of β-1,4-N-acetyl-glucosaminnidase (NAG) and PHEO significantly increased with increase in mean annual temperature (MAT), whereas those of microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) significantly decreased with increase in mean annual precipitation (MAP). Moreover, the responses of PHEO and PERO significantly decreased along altitudinal gradients. Furthermore, we found that the N sensitivity of rhizosphere C-acquisition (BG, PHEO, and PERO) and P-acquisition (AP) enzyme activities was significantly lower than that of bulk soil, but no significant difference was noted in N-acquisition enzyme activities except for the NAG which exhibited marginal significant differences between the rhizosphere and bulk soil. Our results suggest that EEAs in the rhizosphere and bulk soil have different response patterns, and these differences might mainly be caused by soil nutrient availability and microbial attributes. These results deepen our understanding of rhizosphere and bulk soil nutrient cycling processes under increasing N loading. They also provide extensive evidence and a basis for the parameterization of global nutrient cycling models that incorporate rhizosphere responses to climate change.

Variations in soil microbial community structure and extracellular enzymatic activities along a forest-wetland ecotone in high-latitude permafrost regions.

Permafrost degradation by global warming is expected to alter the hydrological processes, which results in changes in vegetation species composition and gives rise to community succession. Ecotones are sensitive transition areas between ecosystem boundaries, attract particular interest due to their ecological importance and prompt responses to the environmental variables. However, the characteristics of soil microbial communities and extracellular enzymes along the forest-wetland ecotone in high-latitude permafrost region remain poorly understood. In this study, we evaluated the variations of soil bacterial and fungal community structures and soil extracellular enzymatic activities of 0-10 cm and 10-20 cm soil layers in five different wetland types along environmental gradients, including Larix gmelinii swamp (LY), Betula platyphylla swamp (BH), Alnus sibirica var. hirsute swamp (MCY), thicket swamp (GC), and tussock swamp (CC). The relative abundances of some dominant bacterial (Actinobacteria and Verrucomicrobia) and fungal (Ascomycota and Basidiomycota) phyla differed significantly among different wetlands, while bacterial and fungal alpha diversity was not strongly affected by soil depth. PCoA results showed that vegetation type, rather than soil depth explained more variation of soil microbial community structure. β-glucosidase and β-N-acetylglucosaminidase activities were significantly lower in GC and CC than in LY, BH, and MCY, while acid phosphatase activity was significantly higher in BH and GC than LY and CC. Altogether, the data suggest that soil moisture content (SMC) was the most important environmental factor contributing to the bacterial and fungal communities, while extracellular enzymatic activities were closely related to soil total organic carbon (TOC), nitrate nitrogen () and total phosphorus (TP).

Sampling for biological indicators of soil health: How does sampling methodology affect research results?

A wide variety of soil sampling methods have been adopted, yet limited research has addressed how sampling methods can impact research results particularly for spatially variable soil properties. To address these concerns, we intensively sampled two existing soil health trials in Texas for analysis of soil extracellular enzymatic activities (EEAs), permanganate oxidizable C (POXC), soil organic C (SOC), and pH. The data generated was used to quantify the effect of composite sampling, sampling position (in-row vs between-row), and number of samples on statistical results. We compared a Monte Carlo simulation approach with a traditional power analysis to quantify the impact of the number of samples on our results. Calculated composite sampling resulted in lower statistically significant results compared to discrete sampling, demonstrating lower sensitivity of composite sampling. Sampling in-row resulted in greater values specifically for EEAs, pH, POXC, and SOC. Simulation generated estimated number of samples were mainly driven by the effect size and spatial variation. EEAs were highly variable, resulting in a higher estimated number of samples as compared to other soil properties such as POXC and SOC. In our study with two sites, soil with greater clay content resulted in overall lower estimated number of samples compared to a relatively sandy soil, demonstrating a greater sampling requirement for sandy soil. The simulation approach had a weak correlation with traditional power analysis. The simulation predicted lower estimated number of samples when compared to power analysis, which can help save cost in the long run. Overall, factors like composite sampling, sampling in-row vs between-row, and number of samples taken did impact research results. The impact of these sampling strategies on soil parameters of interest needs to be investigated to achieve the most accurate research results in soil science.

Effects of 24 Years Different Straw Return on Soil Carbon, Nitrogen, Phosphorus, and Extracellular Enzymatic Stoichiometry in Dryland of the Loess Plateau, China

Exploring the biogeochemical cycle characteristics of soil carbon, nitrogen, and phosphorus in farmland in the dryland of the loess plateau can provide scientific basis and technical support for efficient crop production and sustainable land use. Here, based on a long-term (24 year) straw return field experiment in Shouyang, Shanxi province, the effects of different straw return regimes, i.e., straw mulching (SM), direct straw return (DS), animal-digested straw return (AS), and non-straw return (CK), on the stoichiometric ratio of soil elements and extracellular enzyme activities were studied. The vector angle and length were calculated to indicate the resource constraints faced by microorganisms. The vector angle was greater than 45° and less than 45°, indicating that microorganisms were limited by phosphorus and nitrogen, respectively. The greater the deviation from 45°, the greater the degree of limitation, and the longer the vector length, the more severely limited by carbon. The results showed that ① the soil C/N and C/P of long-term straw returning ranged from 9.81 to 14.28 and from 14.58 to 21.92, with the mean values of 12.36 and 17.51, respectively, which were 6.0% and 4.2% lower than that at the initial stage of the experiment. The soil N/P was distributed between 1.27 and 1.57, with an average of 1.42, which was 2.2% higher than that in the initial stage. The soil C/N and C/P ratios showed a trend of first decreasing and then increasing, the soil N/P ratio basically showed a flat trend, and there was no significant difference in soil element metering ratios between different straw returning treatments. ② Compared with the 24-year long-term non-straw return treatment, the activities of β-1,4-glucosidase (BG) and β-1,4-N-acetylglucosaminidase (NAG) in the soil of the long-term straw mulching treatment increased by 134.4% and 107.5% (P<0.05), the activities of BG and alkaline phosphatase (AP) in the soil of the long-term straw mulching treatment decreased by 59.3% and 59.5% (P<0.05), respectively, and the activities of NAG in the soil of the long-term straw mulching treatment increased by 102.8% (P<0.05). Under the long-term straw returning treatment, soil microorganisms were faced with carbon and phosphorus limitation as a whole. Long-term straw mulching aggravated microbial carbon limitation, and animal-digested straw return could alleviate the degree of carbon limitation. Compared with that in the 24-year long-term non-straw return treatment, soil EEAC/N could be significantly reduced by the animal-digested straw return treatment, and soil EEAC/P could be increased by the direct straw return treatment. The three straw returning methods had no significant indigenous effect on soil EEAN/P. The overall vector angle was greater than 45°, and the vector length increased by 3.8%-20.1% compared with that in the initial stage. ③ Correlation analysis showed that C and N inputs were significantly negatively correlated with BG activity; available nitrogen was significantly correlated with NAG activity, AP activity, and EEAC/N; C/P was significantly positively correlated with EEAC/N; there were significant correlations between N/P and NAG activity, AP activity, EEAC/N, and EEAC/P; and there was no significant correlation between EEAN/P and any environmental factors. In conclusion, the availability of soil nitrogen and phosphorus elements and N/P ratio had significant effects on soil extracellular enzyme activity and stoichiometric characteristics under different long-term straw returning treatments. In the future, more attention should be paid to the improvement of organic carbon and the promotion of nitrogen and phosphorus availability in farmland soil in soil-efficient cultivation and agricultural production activities.

Self-Regulation of Soil Enzyme Activity and Stoichiometry under Nitrogen Addition and Plastic Film Mulching in the Loess Plateau Area, Northwest China

Soil extracellular enzyme activity (EA) and its eco-enzyme stoichiometric ratio (ES) are extremely sensitive to environmental change. This study aimed to clarify the change law of EA and ES in soil with different nitrogen addition levels under plastic film mulching, and to optimize the application amount of nitrogen fertilizer that was used. Based on the location experiment of plastic film mulching fertilization that has been ongoing since 2015, soil samples were collected from different depths (0–10 cm, 10–20 cm and 20–30 cm) during the harvest period of spring maize in October 2021. Four soil extracellular enzyme activities (β-1,4 glucosidase (βG), β-1, 4-N-acetylglucosidase (NAG), leucine aminopeptidase (LAP) and alkaline phosphatase (AP)) involved in soil carbon (C), nitrogen (N) and phosphorus (P) cycling at different nitrogen application levels (0, 90, 150, 225 and 300 kg·hm−2) were studied under two planting patterns of no plastic film mulching (LD) and plastic film mulching (PM). The latest discovery of this study is that the activities of soil EA involved in the cycling of soil carbon C, N and P are similar in different soil depths (0–10 cm, 10–20 cm and 20–30 cm). Both EC:P and EC:P in the soil in this area are less than 1:1, indicating that the soil is limited by N and P. Comprehensive analysis showed that a nitrogen application level of 225 kg·hm−2 was beneficial to the balance of soil nutrients and the improvement of soil EA at harvest. At the same time, PM can effectively improve the soil EA and is more conducive to the balance of soil nutrients. Redundancy analysis (RDA) showed that EA and ES were strongly correlated with pH, soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP). Most importantly, this study revealed that the activity of extracellular enzymes in arid and semi-arid areas was constantly self-regulated with the addition of nitrogen, which provided theoretical and technical support for the efficient use of nitrogen under the condition of plastic film mulching.

Impacts of microplastics and heavy metals on the earthworm Eisenia fetida and on soil organic carbon, nitrogen, and phosphorus

Microplastics (MPs) are increasingly being studied because they have become ubiquitous in aquatic and terrestrial environments. However, little is known about the negative effects of co-contamination by polypropylene microplastic (PP MPs) and heavy metal mixtures on terrestrial environment and biota. This study assessed the adverse effects of co-exposure to PP MPs and heavy metal mixture (Cu2+, Cr6+, and Zn2+) on soil quality and the earthworm Eisenia fetida. Soil samples were collected in the Dong Cao catchment, near Hanoi, Vietnam, and analyzed for changes in extracellular enzyme activity and carbon, nitrogen, and phosphorus availability in the soil. We determined the survival rate of earthworms Eisenia fetida that had ingested MPs and two doses of heavy metals (the environmental level - 1 × - and its double - 2 ×). Earthworm ingestion rates were not significantly impacted by the exposure conditions, but the mortality rate for the 2 × exposure conditions was 100%. Metal-associated PP MPs stimulated the activities of β-glucosidase, β-N-acetyl glucosaminidase, and phosphatase enzymes in soil. Principle component analysis showed that these enzymes were positively correlated with Cu2+ and Cr6+ concentrations, but negatively correlated with microbial activity. Zn2+ showed no correlation with soil extracellular enzyme activity or soil microbial activity. Our results showed that co-exposure of earthworms to MPs and heavy metals had no impact on soil nitrogen and phosphorus but caused a decrease in total soil carbon content, with a possible associated risk of increased CO2 emissions.

Contributions of plant litter to soil microbial activity improvement and soil nutrient enhancement along with herb and shrub colonization expansions in an arid sandy land

Shrubs and herbs are two important types of vegetation that play a pivotal role in combating land desertification in arid sandy land. Yet, the effects of plant litter on sandy soil microbial activities and soil nutrients during the shrub and herb colonization process are still unclear. Here, contributions of plant litter to soil microbial activity improvement and soil nutrient enhancement along herb and shrub colonization expansion interfaces were studied in an arid sandy landscape. Plant litter mass, soil water content, pH, nutrient content, extracellular enzyme activities, and microbial community structure (taxon composition, α-diversity, β-diversity, and co-occurrence pattern) of soils at depths of 0–10 cm were examined relative to the colonization processes of shrubs and herbs (shrub and herb vegetation → sand-shrub and sand-herb interface → a sand dune) in an arid sandy land. We found that the processes of both herb and shrub colonization significantly increased litter cumulative mass at the soil surface to soil depths of 5 cm, and shrub colonization contributed several folds more litter than herb colonization. Plant litter input significantly decreased soil pH, accelerated soil extracellular enzyme activities, increased abundances of some microbial phyla (Actinobacteria, Chloroflexi, Acidobacteria, Gemmatimonadetes, Patescibacteria, Armatimonadetes, Ascomycota, Moritierellomycota, and Chytridiomycota), enhanced both prokaryotic and fungal α-diversities, altered both prokaryotic and fungal communities, and promoted complexity of microbial networks during both herb and shrub colonization. As a result, microorganisms actively participated in litter decomposition and soil nutrient enhancement. Nevertheless, shrub colonization process exhibited greater potential in nutrient input than herb colonization process due to its greater plant litter input, though both colonization played a comparable role in accelerating soil enzyme activity and improving soil microbial community diversity and co-occurrence. Therefore, xeromorphic shrubs are still more important plants than herbs should be used for vegetation construction and ecological restoration in arid sandy land.

Soil extracellular enzymes characteristics and their controlling factors along the elevation gradient in Qinghai-Tibet Plateau, China

Soil extracellular enzyme activities (EEAs) and ecoenzymatic stoichiometry (EES) play an essential role in soil nutrient cycling and organic matter decomposition. Understanding EEAs and EES variation patterns and their influencing factors could offer direct information about the soil structure, function, and soil response to anthropogenic disturbances and climate change. This issue is noteworthy, especially in high-altitude areas where climate change is imminent and vegetation is diversified. This study measured different soil EEAs and EES characteristics and explored their key controlling factors along nine altitudes ranging from 2500 m to over 5200 m in the Qinghai-Tibet Plateau of western China. We also analyzed the effects of plant microhabitats on soil EEAs and EES. The results showed that most soil EEAs and EES had significant variability in spatial characteristics, and enzymatic activity increased with altitude. Compared to the soil nutrient distribution which also increased with altitude, this same change trend of soil EEAs and soil nutrients was inconsistent with the resource allocation theory. Microorganisms might mediate the effects of environmental factors on soil EEAs by altering the enzyme production efficiency. Specific soil EEAs (EEAs/g SOC), like soil enzyme carbon: phosphorus ratios (ECP), and nitrogen: phosphorus ratios (ENP), showed an opposing trend in variation, which decreased with increasing altitude. Plant microhabitats significantly promoted soil EEAs due to the accumulation of soil nutrients (carbon, nitrogen and phosphorus). Soil EEAs and EES's spatial variability was mainly determined by edaphic factors, accounting for >70.24 % and 55.67 % of latitudinal variations, respectively. Generally, carbon and nitrogen limitations were substantial in this area and gradually alleviated with increasing altitude. This study provided a data support for ecological protection of the Qinghai-Tibet Plateau based on the spatial variation of soil EEAs and nutrient limitation.

Stoichiometric Soil Microbial and Enzymatic Characteristics under Three Different Plantation Types in China’s Luya Mountain

It is important to maintain soil ecosystem function and ecological balance stability. This study uses ecological stoichiometry to ascertain relational constraints of soil nutrient (i.e., carbon (C), nitrogen (N), phosphorus (P), etc.) cycling mechanisms and associated ecological balance characteristics in China’s temperate Luya Mountain Nature Reserve. To clarify changes and driving factors associated with soil and extracellular enzyme stoichiometry under different plantation types in July 2021, we analyzed soil nutrient, soil extracellular enzyme, and soil microbial stoichiometry characteristics and their key influencing factors in a Picea asperata Mast. forest, a Caragana jubata (Pall.) Poir. shrubland, and a Carex lanceolata Boott meadow in this reserve. Results revealed significant differences in soil physical and chemical properties, microbial biomass, soil extracellular enzyme activity, and stoichiometry among these different plantation types. Compared to the shrubland and forest plantations, meadow plantation soil was more severely C restricted while that of all three plantations was more N restricted. The main influencing soil stoichiometric ratios were total carbon (TC), total nitrogen (TN), total phosphorus (TP), ammonium (NH4+-N), soil water content (SWC), β-glucosidase, and microbial C, N, and P biomass. Effects associated with soil N:P, enzymatic N:P, enzymatic C:P, microbial C:N, microbial N:P, and microbial C:P ratios were important for bacterial and fungal community soil structure. This study provides a scientific basis to explicate microbial and regulatory effects of soil extracellular enzyme stoichiometry under different plantation types in one of China’s best preserved and most concentrated natural secondary forests.

Rural mixed pond water irrigation affected microbial community and eco-enzymatic stoichiometry of soil profiles

The application of rural mixed pond water (RMW) for irrigation has become a relatively normal agricultural practice in China. However, it is not clear whether soil microbial activity and soil stored nutrients are influenced by RMW. In this study, soil samples were collected from a depth of 0–60 cm for determining their basic physicochemical properties, microbial biomass and soil enzyme activities, moreover, the eco-enzymatic stoichiometry ratio was determined to evaluate microbial nutrient requirements. Our results showed that, with the increase in the soil depth, dissolved organic carbon, available phosphorus, microbial contents, and extracellular enzyme activities declined. We observed an increment in the microbial biomass nitrogen (MBN; 1.44 fold) and microbial biomass carbon (MBC; 1.23 fold) from 0 to 10 cm after RMW irrigation. The latter was more stable below 40 cm of the soil layer independent of irrigation water. The increase in carrier length and angular carrier indicated that the microorganisms were limited by carbon (C) and phosphorus (P). The RMW irrigation significantly decreased the β-1,4-Nacetylglucosaminidase (NAG), the leucine aminopeptidase (LAP), and the phosphatase (AP). In addition, RMW irrigation increased the α-diversity of surface soil microorganisms but suppressed them in deeper soil profiles. The RDA analysis suggested that random NAG of exoenzymes had the greatest relative contribution to microbial diversity, with bacteria and fungi accounting for 27.1 % and 25.1 %, respectively. This study showed that RMW irrigation led to changes the soil extracellular enzyme activities, resulting in alterations the enzyme stoichiometry ratios and microbial nutrient acquisition strategies.

Soil extracellular enzyme stoichiometry reflects microbial metabolic limitations in different desert types of northwestern China

Soil extracellular enzyme activity (EEA) stoichiometry reflects the dynamic balance between microorganism metabolic demands for resources and nutrient availability. However, variations in metabolic limitations and their driving factors in arid desert areas with oligotrophic environments remain poorly understood. In this study, we investigated sites in different desert types in western China and measured the activities of two C-acquiring enzymes (β-1,4-glucosidase and β-D-cellobiohydrolase), two N-acquiring enzymes (β-1,4-N-acetylglucosaminidase and L-leucine aminopeptidase), and one organic-P-acquiring enzyme (alkaline phosphatase) to quantify and compare the metabolic limitations of soil microorganisms based on their EEA stoichiometry. The ratios of log-transformed C-, N-, and P-acquiring enzyme activities for all deserts combined were 1:1.1:0.9, which is close to the hypothetical global mean EEA stoichiometry (1:1:1). We quantified the microbial nutrient limitation by means of vector analysis using the proportional EEAs, and found that microbial metabolism was co-limited by soil C and N. For different desert types, the microbial N limitation increased in the following order: gravel desert < sand desert < mud desert < salt desert. Overall, the study area's climate explained the largest proportion of the variation in the microbial limitation (17.9 %), followed by soil abiotic factors (6.6 %) and biological factors (5.1 %). Our results confirmed that the EEA stoichiometry method can be used in microbial resource ecology research in a range of desert types, and that the soil microorganisms maintained community-level nutrient element homeostasis by adjusting enzyme production to increase uptake of scarce nutrients even in extremely oligotrophic environments such as deserts.

Flooding duration affects the temperature sensitivity of soil extracellular enzyme activities in a lakeshore wetland in Poyang Lake, China

Extracellular enzymes play central roles in the biogeochemical cycles in wetland ecosystems. Their activities are strongly impacted by hydrothermal conditions. Under the ongoing global change, many studies reported the individual effects of flooding and warming on extracellular enzyme activities, however, few researches investigated their interactive effects. Therefore, the current study aims to determine the responses of extracellular enzyme activities to warming in wetland soils under divergent flooding regimes. We investigated the temperature sensitivity of seven extracellular enzymes related to carbon (α-glucosidase, AG; β-glucosidase, BG; cellobiohydrolase, CBH; β-xylosidase, XYL), nitrogen (β-N-acetyl -glucosaminidase, NAG; leucine aminopeptidase, LAP), and phosphorus (Phosphatase, PHOS) cycling along the flooding duration gradient in a lakeshore wetland of Poyang Lake, China. The Q10 value, calculated using a temperature gradient (10, 15, 20, 25, and 30 °C), was adopted to represent the temperature sensitivity. The average Q10 values of AG, BG, CBH, XYL, NAG, LAP, and PHOS in the lakeshore wetland were 2.75 ± 0.76, 2.91 ± 0.69, 3.34 ± 0.75, 3.01 ± 0.69, 3.02 ± 1.11, 2.21 ± 0.39, and 3.33 ± 0.72, respectively. The Q10 values of all the seven soil extracellular enzymes significantly and positively correlated with flooding duration. The Q10 values of NAG, AG and BG were more sensitive to the changes in flooding duration than other enzymes. The Q10 values of the carbon, nitrogen, and phosphorus-related enzymes were mainly determined by flooding duration, pH, clay, and substrate quality. Flooding duration was the most dominant driver for the Q10 of BG, XYL, NAG, LAP, and PHOS. In contrast, the Q10 values of AG and CBH were primarily affected by pH and clay content, respectively. This study indicated that flooding regime was a key factor regulating soil biogeochemical processes of wetland ecosystems under global warming.

Inhibition of Extracellular Enzyme Activity by Reactive Oxygen Species upon Oxygenation of Reduced Iron-Bearing Minerals.

The dual roles of minerals in inhibiting and prolonging extracellular enzyme activity in soils and sediments are governed by enzyme adsorption to mineral surfaces. Oxygenation of mineral-bound Fe(II) generates reactive oxygen species (ROS), yet it is unknown whether and how this process alters the activity and functional lifespan of extracellular enzymes. Here, the effect of mineral-bound Fe(II) oxidation on the hydrolytic activity of a cellulose-degrading enzyme β-glucosidase (BG) was studied using two pre-reduced Fe-bearing clay minerals (nontronite and montmorillonite) and one pre-reduced iron oxide (magnetite) at pH 5 and 7. Under anoxic conditions, BG adsorption to mineral surfaces decreased its activity but prolonged its lifespan. Under oxic conditions, ROS was produced, with the amount of •OH, the most abundant ROS, being positively correlated with the extent of structural Fe(II) oxidation in reduced minerals. •OH decreased BG activity and shortened its lifespan via conformational change and structural decomposition of BG. These results suggest that under oxic conditions, the ROS-induced inhibitory role of Fe(II)-bearing minerals outweighed their adsorption-induced protective role in controlling enzyme activity. These results disclose a previously unknown mechanism of extracellular enzyme inactivation, which have pivotal implications for predicting the active enzyme pool in redox-oscillating environments.

Post‐fire soil extracellular enzyme activities in subtropical–warm temperate climate transitional forests

AbstractWildfire impacts on soil microbial community structure and functional activity have attracted a growing attention because of the higher sensitivity of soil microbes to wildfire. Soil extracellular enzymes play pivotal roles in biogeochemical processes, such as mediating carbon (C) and nutrient cycling. However, little is known about how post‐fire changes in soil biogeochemical properties and microbial community composition affect soil extracellular enzyme activities. This study explored the responses and regulating factors of C‐, nitrogen‐(N), and phosphorus‐(P) acquiring extracellular enzyme activities across a wildfire chronosequence (i.e., 1, 6, 13, and 50 years after fire) in subtropical–temperate ecotonal forests in Central China. The activities of C‐(β‐glucosidase), N‐(N‐acetylglucosaminidase), and P‐(acid phosphatase) acquiring enzymes declined with time post‐fire, with the highest values one‐year post‐fire. The response of C‐acquiring enzyme activity to fire was positively correlated with bacterial biomass, suggesting that microbial compositions were related to post‐fire changes in extracellular enzyme decomposition. The response of N‐acquiring enzyme activity to fire was positively correlated with soil P availability, while P‐acquiring enzyme activity was positively correlated with soil N availability. Overall, soil extracellular enzyme activity declined with time post‐fire, suggesting wildfire may reduce microbial demand for nutrients over time. Future research is needed to elucidate fire impacts on microbial processes for nutrient‐microbial‐enzyme linkages.

Effects of multispecies restoration on soil extracellular enzyme activity stoichiometry in Pinus massoniana plantations of subtropical China

Multispecies restoration is considered a feasible practice to tackle the decline in ecosystem services provided by monocultures. However, our understanding of how multispecies restoration influences microbial catabolic and anabolic pathways in coniferous monocultures based on enzymatic stoichiometry remains limited. Here, to assess the microbial resource limitation and carbon (C) use efficiencies in topsoil and subsoil after multispecies restoration, we compared the soil enzyme activities and stoichiometry of two multispecies plantations (broadleaf-oriented transformation and replenishment with local broadleaved trees), two stand ages of Pinus massoniana monocultures, and secondary forests in subtropical China. According to the specific enzyme activities, the labile C decomposition was suppressed but the recalcitrant C decomposition was stimulated in the subsoil in multispecies restorations. Additionally, the vector analysis and microbial acquisition ratios consistently indicated that multispecies plantations aggravated the co-limitation of C and phosphorus (P) in the subsoil and that the limitation was equal to the level of secondary forests. We also found significant decreases in C use efficiencies in multispecies plantations compared with pine monocultures. These findings suggested a trade-off between obtaining multiple nutrients and increasing C use efficiency in the subsoil of forests with different restoration approaches. Furthermore, the microbial acquisition ratios and C use efficiencies were mainly influenced by soil pH and microbial biomass stoichiometry. Overall, our study integrated the microbial resource limitation and C use efficiency to provide an enzymatic perspective for underground C-cycling and nutrient mineralization after forest restoration, highlighting the critical role of multispecies plantations in inducing strong shifts in microbial metabolism, especially in the subsoil.

Determining changes in microbial nutrient limitations in bamboo soils under different management practices via enzyme stoichiometry

Moso bamboo (Phyllostachys edulis) is a plant species recognized for its extremely high carbon sequestration potential, and, along with soil microbes, play a key role in the carbon (C) cycle. Nevertheless, the metabolic constraints of soil microorganisms in the ecosystem have rarely been studied. We investigated changes in soil extracellular enzyme activities and microbial nutrients limitation in three different managed Moso bamboo plantations. The results showed that compared to nonmanagement (M0), extensive (M1) and intensive (M2) management significantly (p ≤ 0.05) decreased the activities of C- (β-1,4-glucosidase, BG) and N-acquiring (β-1,4-N-acetylglucosaminidase (NAG) and l-leucine aminopeptidase (LAP)) enzymes and significantly (p ≤ 0.05) increased the activity of soil P-acquiring enzymes (acid phosphatase, ACP). M1 and M2 exhibited significantly (p ≤ 0.05) decreased ratios of ln(BG):ln(ACP) and ln(NAG + LAP):ln(ACP) compared to M0. The ln(BG):ln(NAG + LAP) ratio in M2 was significantly (p ≤ 0.05) lower than in M0 bamboo plantations. M1 and M2 had a lower vector length and higher vector angle than M0, suggesting that management practices can reduce the microbial C and N limitations in bamboo plantations. In contrast, boosted activity of the C-acquiring enzyme, high levels of total organic C concentration, and increased microbial C constraint in M0 and M1 indicated that reducing disturbance benefits soil C stability and renders C hard to use by microorganisms. Random forest analyses indicated that total N and pH were the most important predictors of microbial C and N limitations in bamboo soils, respectively. This study revealed that the intensity of management practices markedly affected the balance between soil microbial nutrient requirements and C sequestration in Moso bamboo plantations.