Soil Extracellular Enzyme Research Articles

Effects of seasonal and decadal warming on soil enzymatic activity in a P-deficient Mediterranean shrubland.

Soil enzymes are central in the response of terrestrial ecosystems to climate change, and their study can be crucial for the models' implementation. We investigated for 1 year the effects of warming and seasonality on the potential activities of five soil extracellular enzymes and their relationships with soil moisture, phosphorus (P) concentration, and other soil parameters in a P-limited Mediterranean semiarid shrubland. The site was continuously subjected to warming since 1999, and we compared data from this study to analogous data from 2004. Warming uniformly increased all enzymes activities, but only when a sufficient amount of soil water was available. Seasonality unevenly altered enzyme activities, thus affecting enzymatic stoichiometry. P deficiency affected enzymatic stoichiometry, favoring the activities of the phosphatases. The effect of warming was stronger in 2014 than 2004, excluding the hypothesis of acclimation of rhizospheric responses to higher temperatures and suggesting that further increases in extracellular enzymatic activities are to be expected if sufficient water is available. Climatic warming will likely generally stimulate soil enzymatic activities and accelerate nutrient mineralization and similar ecological processes such as the production and degradation of biomass and changes in community composition, but which will be limited by water availability, especially in Mediterranean soils in summer. Winters in such ecosystems will benefit from a general increase in activity and production, but biological activity could even decrease in summer, potentially leading to a negative overall balance of nutrient mineralization. This study suggests that a general increase in activity due to warming could lead to faster mineralization of soil organic matter and water consumption in colder climates, until one of these factors in turn becomes limiting. Such trade-offs between water and temperature in relation with enzyme activity should be considered in biogeochemical models.

Extracellular Soil Enzyme Activities in High-Elevation Mixed Red Spruce Forests in Central Appalachia, U.S.A.

Anthropogenic emissions have impacted terrestrial forest ecosystem processes in North America since the industrial revolution. With the passage of the Clean Air Act in 1970 in the United States, atmospheric inputs of nitrogen (N) and sulfur (S) into forests in the Appalachian Mountains have declined, which have, potentially, mitigated their effects on processes such as decomposition and nutrient cycling. Activities of microbial extracellular soil enzymes (ESEs) mediate many rate-limiting nutrient transformations in forest soils and play important roles in the decomposition of complex organic compounds. Soils in high-elevation red spruce forests are characterized by low pH and high carbon (C):N ratios and, having historically received extremely high levels of N deposition, may exhibit legacy impacts of deposition on nutrient availability and decomposition. We utilized four sites along a modeled gradient of N deposition in central Appalachia to assess contemporary ESEs in bulk soil under Acer rubrum L., Betula alleghaniensis Britt., and Picea rubens Sarg. in May, June, and July 2016. Increasing N deposition led to increases in organic fraction C and N and decreases in phosphorus (P). Sites receiving higher N also exhibited greater mineral fraction C, N, and P. ESEs were highest in organic fractions with acid phosphatases (AP) exhibiting the highest activity. There was little influence of N deposition on organic fraction ESEs, but strong evidence for a positive relationship between N deposition and activities of AP, β-glucosidases (BG), and chitinase (NAG) in mineral fractions. Species effects on ESEs were present with high AP in organic fractions under spruce and high mineral fraction fungal laccase (LAC) under birch. The sampling season demonstrated little effect on ESEs. ESEs were more strongly influenced by plot-level factors, such as tree species diversity and abundance of ectomycorrhizal (ECM) tree species, than temporal or soil factors or nutrient status related to modeled cumulative N deposition across these sites. Decreases in AP, BG, and NAG activities with greater abundance of broadleaf deciduous species and increases in activities with ECM host abundance indicate that microbial communities driven by these plant functional groups are responsible for the differences in ESEs observed in these high-elevation mixed red spruce stands.

Effect of repeated drying-rewetting cycles on soil extracellular enzyme activities and microbial community composition in arid and semi-arid ecosystems

Climate change is predicted to alter precipitation patterns, which may have profound consequences on soil microbial communities and functions in arid and semi-arid ecosystems. However, it is uncertain if the direction and magnitude of soil microbial function and community responses to repeated drying and rewetting (DRW) events differ in diverse arid and semi-arid ecosystems. We collected surface soils in forest, farmland, grassland, and desert ecosystems from the Chinese Ecosystem Research Network (CERN) with mean annual precipitation ranged from 164 to 600 mm. Soils were then exposed to 0, 2, 5, 7 and 14 DRW cycles with variable drought periods at 20 °C. Soil respiration was measured in the rewetting phases of each DRW cycle. We also measured microbial biomass carbon (C), dissolved organic C, inorganic nitrogen, activities of four C-acquisition extracellular enzymes (β-glucosidase, cellobiohydrolase, phenol oxidase, and peroxidase), and microbial community structure after the last DRW cycle. Results showed that repeated DRW cycles significantly affected most microbial parameters in our study. Specifically, repeated DRW cycles increased activities of β-glucosidase and cellobiohydrolase. Lower DRW frequencies with longer drought periods had higher soil respiration, microbial biomass C, and the relative abundance of fungi. The responses of soil enzyme activities to repeated DRW were similar in the four ecosystems. However, soil microbial biomass and community composition were generally more resistant to repeated DRW cycles in the forest soil, while they were more vulnerable to repeated DRW stress in the desert soil, suggesting that altered precipitation patterns may have a greater impact on soil microbial communities in more arid ecosystems.

Soil extracellular enzyme activity and stoichiometry in China's forests

Abstract Ecoenzymatic stoichiometry links microbial decomposition with nutrient mineralization and improves our understanding of nutrient cycling in terrestrial ecosystems. Microbial C:N:P acquisition in the topsoil converged at a ratio of 1:1:1 in global ecosystems. However, whether the ratio of microbial acquisition is stable in forest soils, and is applicable among different soil depths remain unknown. Based on large‐scale soil sampling in China's forests, we examined the patterns and environmental drivers of the eight most‐widely measured enzyme activities and the relevant stoichiometry. We found that the ratio of C:N:P acquisition significantly deviated from 1:1:1. The specific enzyme activities (normalized by SOC) did not change significantly with latitude except those for xylosidase and acid phosphatase. Similarly, only the C:P acquisition ratio increased with latitude. Vertically, the specific activities of C‐acquiring enzymes mainly increased, N‐acquiring enzymes decreased and P‐acquiring enzymes did not change with soil depth. Moreover, all ratios of microbial acquisition decreased, and the percentage of recalcitrant C increased significantly with increasing depth. Our study also showed that temperature and soil C:N ratio were the important factors in explaining the variations in specific enzyme activities and microbial nutrient acquisition, respectively. Our results indicated that no constant microbial C:N:P acquisition ratio can be widely recognized, and that SOC quality changed from labile to recalcitrant with depth. We highlight that depth‐dependent enzymatic processes should be considered in future SOC dynamic models. A free Plain Language Summary can be found within the Supporting Information of this article.

Microbial consortia inoculants stimulate early growth of maize depending on nitrogen and phosphorus supply

Adoption of microbial consortia as plant growth-promoting microorganisms (PGPMs) instead of single-strain inoculants is discussed as an approach to increase the efficiency and flexibility of PGPM-assisted production strategies. This study provides the functional characterisation of a commercial microbial consortia product (MCP) in a series of greenhouse experiments with maize on a silty-loam field soil (pH 5.9). A 60%-increased abundance of bacteria that could be cultivated after rhizosphere extraction was measured after MCP inoculation at the end of the 42-days culture period. MCP inoculation did not stimulate shoot biomass production of maize fertilised with nitrate, but growth improvement was recorded in combination with stabilised ammonium, especially with reduced phosphorus (P) supply. The MCP inoculant improved the acquisition of ammonium-N but also increased shoot-P. MCP inoculation stimulated root length development under reduced P supply with stabilised ammonium by 52%. This was accompanied by the increased auxin production capacity of rhizosphere bacteria. C-, N-, and P-turnover in the rhizosphere were little affected by the MCP inoculation, as deduced from the analysis of activities of extracellular soil enzymes. The findings suggest that the form of N supply is crucial for the efficiency of plant-MCP interactions.

Effects of plastic mulch and nitrogen fertilizer on the soil microbial community, enzymatic activity and yield performance in a dryland maize cropping system

AbstractFarming practices that integrate plastic film mulching and nitrogen (N) fertilization have been extensively used to enhance crop productivity. However, the interactive effects of mulching and N application on soil microbial properties and crop yields have received little attention. A 2‐year field experiment was carried out in the Loess Plateau to investigate the independent and combined effects of plastic mulch and N application rate on the soil microbial population, enzymatic activity and grain yield. From 2016 to 2017, two mulching patterns (i.e., plastic mulching and no mulching) were exposed to five different N application rates (0 (N0), 80 (N80), 160 (N160), 200 (N200) and 240 (N240) kg N ha−1). N application significantly affected the soil microbial community composition, as suggested by significant increases in soil total bacteria, cellulose‐decomposing bacteria and the bacterial‐to‐fungal ratio with N rates. In contrast, the mulching pattern significantly affected soil extracellular enzyme production. Furthermore, there were significant effects of mulching, N application and their interaction on grain yield. The highest grain yield (11,728 kg N ha−1 in 2016 and 12,350 kg N ha−1 in 2017) in both growing seasons was consistently obtained under plastic mulching with a N level of 200 kg N ha−1. Our study showed that plastic mulching significantly affected extracellular enzyme production, and N fertilizer application significantly affected the composition of the soil microbial community.Highlights Independent and coupled effects of mulching and N application on soil biological properties and grain performance were explored. N application significantly influenced soil microbial community composition. Mulching pattern rather than N application independently and significantly affected soil extracellular enzyme production The combined application of plastic mulching with 200 kg N ha−1 should be seem as an optimum crop production pattern in this area.

Short-Term Nitrogen Fertilization Affects Microbial Community Composition and Nitrogen Mineralization Functions in an Agricultural Soil.

Soil extracellular enzymes play a significant role in the N mineralization process. However, few studies have documented the linkage between enzyme activity and the microbial community that performs the function. This study examined the effects of inorganic and organic N fertilization on soil microbial communities and their N mineralization functions over 4 years. Soils were collected from silage corn field plots with four contrasting N treatments: control (no additional N), ammonium sulfate (AS; 100 and 200 kg of N ha-1), and compost (200 kg of N ha-1). Illumina amplicon sequencing was used to comprehensively assess the overall bacterial community (16S rRNA genes), bacterial ureolytic community (ureC), and bacterial chitinolytic community (chiA). Selected genes involved in N mineralization were also examined using quantitative real-time PCR and metagenomics. Enzymes (and marker genes) included protease (npr and sub), chitinase (chiA), urease (ureC), and arginase (rocF). Compost significantly increased diversity of overall bacterial communities even after one application, while ammonium fertilizers had no influence on the overall bacterial communities over four seasons. Bacterial ureolytic and chitinolytic communities were significantly changed by N fertilization. Compost treatment strongly elevated soil enzyme activities after 4 years of repeated application. Functional gene abundances were not significantly affected by N treatments, and they were not correlated with corresponding enzyme activities. N mineralization genes were recovered from soil metagenomes based on a gene-targeted assembly. Understanding how the structure and function of soil microbial communities involved with N mineralization change in response to fertilization practices may indicate suitable agricultural management practices that improve ecosystem services while reducing negative environmental consequences.IMPORTANCE Agricultural N management practices influence the enzymatic activities involved in N mineralization. However, specific enzyme activities do not identify the microbial species directly involved in the measured process, leaving the link between the composition of the microbial community and the production of key enzymes poorly understood. In this study, the application of high-throughput sequencing, real-time PCR, and metagenomics shed light on how the abundance and diversity of microorganisms involved in N mineralization respond to N management. We suggest that N fertilization has significantly changed bacterial ureolytic and chitinolytic communities.

High-severity wildfire leads to multi-decadal impacts on soil biogeochemistry in mixed-conifer forests.

During the past century, systematic wildfire suppression has decreased fire frequency and increased fire severity in the western United States of America. While this has resulted in large ecological changes aboveground such as altered tree species composition and increased forest density, little is known about the long-term, belowground implications of altered, ecologically novel, fire regimes, especially on soil biological processes. To better understand the long-term implications of ecologically novel, high-severity fire, we used a 44-yr high-severity fire chronosequence in the Sierra Nevada where forests were historically adapted to frequent, low-severity fire, but were fire suppressed for at least 70yr. High-severity fire in the Sierra Nevada resulted in a long-term (44+yr) decrease (>50%, P<0.05) in soil extracellular enzyme activities, basal microbial respiration (56-72%, P<0.05), and organic carbon (>50%, P<0.05) in the upper 5cm compared to sites that had not been burned for at least 115yr. However, nitrogen (N) processes were only affected in the most recent fire site (4yr post-fire). Net nitrification increased by over 600% in the most recent fire site (P<0.001), but returned to similar levels as the unburned control in the 13-yr site. Contrary to previous studies, we did not find a consistent effect of plant cover type on soil biogeochemical processes in mid-successional (10-50yr) forest soils. Rather, the 44-yr reduction in soil organic carbon (C) quantity correlated positively with dampened C cycling processes. Our results show the drastic and long-term implication of ecologically novel, high-severity fire on soil biogeochemistry and underscore the need for long-term fire ecological experiments.

Enzyme stoichiometry indicates the variation of microbial nutrient requirements at different soil depths in subtropical forests.

Soil extracellular enzyme activities and associated enzymatic stoichiometry are considered sensitive indicators of nutrient availability and microbial substrate limitation. However, many of previous studies have been focusing on uppermost soil layer with a single enzyme as representative of the whole nutrient acquisition, leading to critical uncertainties in understanding soil nutrient availability and its relationship with microbial activities in deeper soils. In the current study, we investigated C-, N- and P-acquiring enzyme activities across a range of soil layers (0–10, 10–20, 20–40 and 40–60 cm), and examined the microbial C, N and P limitation in natural secondary forests (NSF) and Chinese fir (Cunninghamia lanceolata) plantation forests (CPF) in subtropical China. The results showed that microbial C and P co-limitation was detected in the two typical subtropical forests at all soil depths, rather than microbial N limitation. Microbial C and P limitation fluctuated along soil depth, but higher N was demanded by microbes in soil under 20 cm in both forests. The present results highlight the asymmetrical patterns of microbial nutrient limitation along the whole soil profile, and provide essential information in understanding nutrient limitations in deeper soils. These vertical and asymmetrical nutrient limitation patterns should be incorporated into future research studies priority.

Elevation gradients affect the differences of arbuscular mycorrhizal fungi diversity between root and rhizosphere soil

Despite the evident importance of arbuscular mycorrhizal fungi (AM fungal) associated with the root and rhizosphere system of elevation gradients, limit is known about the difference in AM fungal diversity between root and rhizosphere and their influencing factors along elevation gradients. AM fungal Here, we designed an elevation gradient experiment, which covered six elevations and three vegetation types, and collected plant and soil samples. We used Illumina gene sequencing to analyze AM fungal diversity in roots and rhizosphere soils; other potential factors, such as plant diversity, leaf C, N, and P, litter, soil and microbial biomass, extracellular enzymes activity, and the bacterial and ITS broad-fungal diversity, were also determined. We found that AM fungal diversity differences between root and rhizosphere soil diminished as elevation increased, despite that AM fungal diversity had a well-known pattern with elevation (unimodal patterns). Compared with plant characteristics, soil properties (soil C, N, P, C:N, C:P, N:P) were stronger effect on AM fungal diversity between root and rhizosphere. Particularly, soil extracellular enzymes activity and bacterial and ITS broad-fungal diversity explained more variation in AM fungal diversity dynamics along the elevation gradients. Our findings indicate that the diminishment of AM fungal diversity in root and rhizosphere soil are a response to elevation gradients through changes of soil extracellular enzymes activity and the bacterial and fungi communities, which provided evidence that AM fungal community dynamics link to climate change.

Responses of soil extracellular enzyme activities to carbon input alteration and warming in a subtropical evergreen broad-leaved forest

Responses of soil extracellular enzyme activities to carbon input alteration and warming in a subtropical evergreen broad-leaved forest

冻融循环对川西亚高山森林土壤酶活性的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 冻融循环对川西亚高山森林土壤酶活性的影响 DOI: 10.5846/stxb201902250355 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金青年项目（31700542）；重点实验室开放基金（四川省科技厅）（ESP1704） Effects of the freeze-thaw cycle on soil enzyme activities in a sub-alpine forest in western Sichuan Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:土壤酶活性的研究有助于认识植物-微生物-土壤有机质之间的相互关系，土壤酶的生产遵循"经济法则"，冻融循环将会改变生产土壤酶的资源分配，最终影响土壤的有机质分解过程。亚高山森林土壤具有明显的季节性冻融循环，为深入研究亚高山森林冬季土壤生态过程，以川西亚高山针阔混交林、针叶林以及阔叶林土壤为研究对象，通过室内培养研究冻融循环对6种与碳（C）、氮（N）、磷（P）相关土壤酶活性的影响。结果表明，与N和P相关的土壤β-N-乙酰葡萄糖苷酶、磷酸酶活性受冻融循环影响显著，其中，β-N-乙酰葡萄糖苷酶活性在整个冻融处理过程中表现出先升高后降低并趋于平稳的趋势，磷酸酶活性在后期明显增加。与C相关的土壤纤维素酶、β-葡萄糖苷酶、过氧化物酶、多酚氧化酶在冻融循环过程中没有显著变化。林型对土壤酶活性产生了显著影响。其中，阔叶林的土壤纤维素酶活性显著低于针叶林；阔叶林的土壤过氧化物酶活性显著低于针阔混交林和针叶林；针叶林的土壤磷酸酶活性显著高于针阔混交林和阔叶林。冻融循环和林型的交互作用对土壤酶活性没有显著影响。结果表明，该地区土壤酶活性对冻融循环响应存在差异，气候变化引起的冻融循环将进一步影响川西亚高山森林土壤生态系统的有机质分解过程。 Abstract:Research on soil enzyme activities is beneficial to identify relationships between plants, microbes, and soil organic matter. Freeze-thaw cycles will change resource allocations for the production of soil extracellular enzymes, which affects organic matter decomposition processes in the soil. Based on the pre-recognition of sub-alpine seasonal freeze-thaw cycles and considering typical coniferous-broadleaf mixed forest, coniferous forest, and broadleaf forest soil in the sub-alpine region of western Sichuan, we controlled the freeze-thaw environment and analyzed the effects of freeze-thaw cycles on enzyme activities in the soil, including carbon, nitrogen, and phosphorus. According to the results, the freeze-thaw cycles had a significant impact on β-N-acetylglucosidase and phosphatase activities associated with soil N and P. The activity of β-N-acetylglucosidase was elevated at the beginning of freeze-thaw period and then decreased with an increase in freeze-thaw frequency. The phosphatase activity increased significantly in the later portion of the freeze-thaw cycle. However, the freeze-thaw cycle had no significant effect on C-related soil enzyme activities. The changes in C-related soil enzyme activities in this study were more determined by litter decomposition processes and forest types. Among them, cellulase and β-glucosidase activities were significantly correlated with the decomposition process of organic matter. The limiting factors of peroxidase and polyphenol oxidase and low temperature and low oxygen were still present in this test, so the activities of these two enzymes did not change significantly. On the other hand, the effect of forest types on cellulase, peroxidase and phosphatase activities was significant. The soil cellulase activity of broadleaf forest was significantly lower than that of coniferous forest. The peroxidase activity of broadleaf forest soil was significantly lower than that of coniferous-broadleaf mixed forest and coniferous forest. The soil phosphatase activity of coniferous forest soil was significantly higher than that of coniferous-broadleaf mixed forest and broadleaf forest. Our results indicate that the effects of the freeze-thaw cycles on extracellular enzyme activities in the soil vary in this area. Freeze-thaw cycles that result from climate change will further influence the organic matter decomposition processes of the soil ecology system in the sub-alpine forest in western Sichuan. 参考文献 相似文献 引证文献

Global meta-analysis on the responses of soil extracellular enzyme activities to warming

Soil enzymes play critical roles in the decomposition of organic matter and determine the availability of soil nutrients, however, there are significant uncertainties in regard to how enzymatic responses to global warming. To reveal the general response patterns and controlling factors of various extracellular enzyme activities (EEA), we collected data from 78 peer-reviewed papers to investigate the responses of extracellular enzyme activities (EEA), including β-1,4-glucosidase (BG), β-d-cellobiosidase (CBH), β-1,4-xylosidase (XYL), leucine amino peptidase (LAP), N-acetyl-glucosaminidase (NAG), urease (URE), phosphatase (PHO), peroxidase (PER), phenol oxidase (POX), and polyphenol oxidase (PPO), to experimental warming. Our results showed that warming treatments increased soil temperature by 1.9 °C on average. The oxidative EEA, calculated as the sum of PER, POX and PPO, was on average stimulated by 9.4% under warming. However, the responses of C acquisition EEA (the sum of BG, CBH and XYL), N acquisition EEA (the sum of LAP, NAG and URE), and P acquisition EEA to warming had large variations across studies. The warming effects on C, N, P acquisition EEA and oxidative EEA tended to increase with soil warming magnitude and duration as well as the mean annual temperature. The response of C acquisition EEA to warming was positively correlated with fungal biomass, while that of P acquisition EEA had positive relationships with fungi: bacteria ratios. The response of oxidative EEA was negatively correlated with the abundance of gram-positive bacterial biomass. Our results suggested that warming consistently stimulated oxidative EEA, but had diverse effects on hydrolytic EEA, which were dependent on the warming magnitude or duration, or environmental factors. The observed relationships between changes in microbial traits and extracellular enzymes suggested that microbial compositions drive changes in enzyme decomposition under warming. Thus, incorporation of microbial modification in biogeochemistry models is essential to better predict ecosystem carbon and nutrient dynamics.

Responses of soil extracellular enzyme activities and microbial community properties to interaction between nitrogen addition and increased precipitation in a semi-arid grassland ecosystem

Both atmospheric nitrogen (N) deposition and precipitation can strongly impact below-ground biogeochemical processes. Soil extracellular enzymes activities (EEAs) and microorganisms are considered as the key agents in ecosystem nutrient cycling. However, how the interaction between increasing N deposition and precipitation may affect soil EEAs and microbes remain poorly understood. In a 5-year field experiment in a meadow steppe in northern China, we tested the effects of N addition (N0, 0; N1, 5; N2, 10 g N m−2 yr−1) and increased precipitation (W0, ambient precipitation; W1, increase of 15% ambient precipitation; W2, increase of 30% ambient precipitation) on soil EEAs, microbial and chemical properties. Results showed that their interaction significantly affected all hydrolase activities, except for β-1,4-xylosidase (βX). Furthermore, increased precipitation and N addition interactively affected bacterial gene copies (P ≤ 0.05), and increased precipitation comparatively had a stronger effects. The results on the combination of N addition and increased precipitation showed that increased precipitation alleviated the positive effects of N addition on soil EEAs. This implies that the effects of either treatment alone on grassland biogeochemical processes may be alleviated by their simultaneous occurrence. Our results suggested that soil EEAs were mainly controlled by the content of N and phosphorus (P), and the ratio of C: N and C: P. Therefore, soil element content and stoichiometry could better explain the responses of EEAs to global changes. Moreover, soil microbial communities were mainly controlled by soil P content. Overall, our study highlights that the interaction between N deposition and precipitation may play a vital role in predicting the responses of soil enzyme activities to global changes in grassland ecosystems.

Control of Soil Extracellular Enzyme Activities by Clay Minerals—Perspectives on Microbial Responses

Knowledge of how interactions of clay minerals and extracellular enzymes (EEs) influence organic matter turnover in soils are still under discussion. We studied the effect of different montmorillonite contents on EE activities, using two experiments—(1) an adsorption experiment with a commercially available enzyme (α-glucosidase) and (2) an incubation experiment (10 days) where microorganisms were stimulated to produce enzymes through organic carbon (OC) addition (starch and cellulose). Soil mixtures with different montmorillonite contents were created in four levels to a sandy soil: +0% (control), +0.1%, +1%, and +10%. The potential enzyme activity (pEA) of four enzymes, α-glucosidase, β-glucosidase, cellobiohydrolase, and aminopeptidase, involved in the soil carbon and nitrogen cycle were analysed. The adsorption experiment revealed a reduction in the catalytic activity of α-glucosidase by up to 76% with increasing montmorillonite contents. However, the incubation experiment showed an inhibitory effect on pEA only directly after the stimulation of in-situ EE production by OC addition. At later incubation stages, higher pEA was found in soils with higher montmorillonite contents. This mismatch between both experiments, with a transient reduction in catalytic activity for the incubation experiments, points to the continuous production of enzymes by soil microorganisms. It is conceivable that microbial adaptation is characterized by higher investment in EEs production induced by increasing clay contents and a stabilisation of the EEs by clay minerals. Our results point to the need to better understand EE-clay mineral-OC interactions regarding potential microbial adaptations and EE stabilisation with potentially prolonged activities.

Long-term phosphorus addition downregulates microbial investments on enzyme productions in a mature tropical forest

Phosphorus (P) addition could largely alter soil microbial activity. However, effects of long-term P addition on soil extracellular enzyme activity are not well understood in tropical forests. To address this question, we measured absolute activities (activity per unit of dry soil) and specific activities (activity per unit of microbial biomass carbon) of enzymes involved in carbon (C), nitrogen (N), and P cycling in a 10-year P addition experimental site in a tropical forest. Phosphorus addition decreased acid phosphatase absolute and specific activity by 37% and 47%, respectively. As to N-acquisition enzymes, P addition increased leucine amino peptidase absolute activity but decreased β-1,4-N-acetylglucosaminidase absolute activity by 33%. Meanwhile, P addition had no effects on leucine amino peptidase specific activity but decreased β-1,4-N-acetylglucosaminidase specific activity by 43%. Among C-acquisition enzymes, cellobiohydrolase, α-glucosidase, and β-glycosidase absolute and specific activities showed no significant responses to P addition, while P addition decreased β-xylosidase absolute and specific activity by 15% and 27% respectively. Phosphorus addition also decreased phenol oxidase absolute activity by 30% and peroxidase absolute activity by 29%. These results suggest a strong P shortage for microorganisms and that P addition could decline microbial productions of enzymes in phosphorus-poor tropical forests. Results from this study emphasize again the important role of available P in tropical forests.

Soil Extracellular Enzyme Activities and Uptake of N by Oilseed Rape Depending on Fertilization and Seaweed Biostimulant Application

The present study has aimed at enhancing the insufficient knowledge of functional soil enzymes properties influenced by inorganic fertilization and biostimulant application to increase the uptake of nitrogen affecting the winter oilseed rape yield. Field experiments were conducted in Poland (53° N, 18° E) in Alfisol (USDA). In this experiment, the NPK rates applied were as follows: high 180 N, 70 P and 160 K 132 N (kg ha−1) or low 144 N, 35 P and 66 K (kg ha−1); fertilization with elemental S 36 or 0 (kg ha−1); and the seaweed biostimulant Kelpak was applied or there was no such treatment. Due to low NPK fertilization rates, the activity of dehydrogenases, peroxidases, and catalase increased in subsistent generative development stages from flowering to ripening. At the ripening stage, the activity of these enzymes, as well as nitroreductase activity, were inhibited by high NPK fertilizer rates. The seaweed biostimulant application and S fertilization increased N accumulation in plants of oilseed rape in generative development, by 16% and 13%, respectively, as compared with the lack of these treatments. The application of S increased the uptake of nitrogen in shoots and in whole oilseed rape plants only after application of higher rates of NPK.

Minor responses of soil microbial biomass, community structure and enzyme activities to nitrogen and phosphorus addition in three grassland ecosystems

Human activities have significantly increased nitrogen (N) and phosphorous (P) inputs to terrestrial ecosystems. However, the impact of N and P enrichment on soil microbial community structure and functioning in temperate and alpine grassland ecosystems remains unclear. In this study, we investigated the responses of soil microbial communities to nutrient (N and P) additions in two temperate and one alpine grassland ecosystems in China. We measured soil chemical properties, microbial community composition (indicated by the phospholipid fatty acids, PLFA) and potential enzyme activities related to carbon (C), N, and P cycling in the peak growing season after 4 years of nutrient addition. We found that N addition reduced soil pH and increased soil total N content at two meadow sites, P addition increased soil total P content at all three sites, but both N and P additions had minimal effects on soil organic C content. Bacteria and total microbial abundances did not change after N and P additions, while fungi and arbuscular mycorrhizal fungi (AMF) abundances were suppressed by N addition. Moreover, the activity of soil extracellular enzymes involved in C, N and P cycling and their stoichiometric ratios were not responsive to N and P additions, except for inhibition of acid phosphatase by P addition at the temperate meadow site. Despite significant changes in soil chemistry (e.g., pH and available nutrients), soil microbial biomass (except fungi and AMF abundances), community structure, and enzyme activities (except phosphatase) were generally resistant to 4 years of N and P addition in the three temperate and alpine grassland ecosystems in China.

Temporal Variations in Soil Enzyme Activities and Responses to Land-Use Change in the Loess Plateau, China

Variability in soil enzyme activity may have important implications for the knowledge of underground ecosystem functions driven by soil extracellular enzymes. To illustrate the temporal variation in soil enzyme activity after afforestation, we collected soil samples during different vegetative growth periods in three Caragana korshinskii Kom. stands of different ages (20, 30, and 40 years) and in a slope cropland in the Loess Plateau. These samples were used to analyze the catalase, sucrase, urease and alkaline phosphatase activities, the soil water content and the available soil nutrients (i.e., dissolved organic carbon, dissolved organic nitrogen, and available phosphorus). The results illustrated that the soil enzyme activities significantly increased following afforestation and varied with temporal variation. Overall, soil enzyme activities were higher in June and August, particularly, and both alkaline phosphatase and sucrase were more sensitive to temporal variation than the other two enzymes. In addition, redundancy analysis showed that soil enzyme activities were greatly correlated with soil nutrients, especially for dissolved organic carbon and dissolved organic nitrogen. Therefore, the results highlighted the importance of soil enzyme activities to soil nutrients under temporal variation following afforestation in the Loess Plateau, which may have practical significance for forest managers’ fertilization management of plantation in different seasons and different stand ages.

Impact of long-term nitrogen deposition on the response of dune grassland ecosystems to elevated summer ozone

Nitrogen deposition and tropospheric ozone are important drivers of vegetation damage, but their interactive effects are poorly understood. This study assessed whether long-term nitrogen deposition altered sensitivity to ozone in a semi-natural vegetation community. Mesocosms were collected from sand dune grassland in the UK along a nitrogen gradient (5–25 kg N/ha/y, including two plots from a long-term experiment), and fumigated for 2.5 months to simulate medium and high ozone exposure. Ozone damage to leaves was quantified for 20 ozone-sensitive species. Soil solution dissolved organic carbon (DOC) and soil extracellular enzymes were measured to investigate secondary effects on soil processes.Mesocosms from sites receiving the highest N deposition showed the least ozone-related leaf damage, while those from the least N-polluted sites were the most damaged by ozone. This was due to differences in community-level sensitivity, rather than species-level impacts. The N-polluted sites contained fewer ozone-sensitive forbs and sedges, and a higher proportion of comparatively ozone-resistant grasses. This difference in the vegetation composition of mesocosms in relation to N deposition conveyed differential resilience to ozone.Mesocosms in the highest ozone treatment showed elevated soil solution DOC with increasing site N deposition. This suggests that, despite showing relatively little leaf damage, the ‘ozone resilient’ vegetation community may still sustain physiological damage through reduced capacity to assimilate photosynthate, with its subsequent loss as DOC through the roots into the soil.We conclude that for dune grassland habitats, the regions of highest risk to ozone exposure are those that have received the lowest level of long-term nitrogen deposition. This highlights the importance of considering community- and ecosystem-scale impacts of pollutants in addition to impacts on individual species. It also underscores the need for protection of ‘clean’ habitats from air pollution and other environmental stressors.