Simple Summary Microorganisms and their enzymes are crucial to ensuring soil quality, health, and carbon sequestration. Their numerous reactions are essential for biogeochemical cycles. However, a comprehensive review is lacking to summarize the latest findings in agricultural and enzymatic research. Although the relationships between soil enzyme activities and different soil ecosystems, such as arctic and permafrost regions, tropics and subtropics, tundra, steppes, etc., have been intensively investigated, particularly in the context of climate changes, only a few reviews summarize the impact of climate change on soil enzyme activity. This review aims to highlight the main groups of microbial enzymes found in soil (such as alpha-glucosidases and beta-glucosidases, phosphatases, ureases, N-acetyl-glucosaminidases, peptidases, etc.), their role in the global nutrient cycles of carbon, nitrogen, phosphorus, sulfur, carbon sequestration, and the influence of intensive agriculture on microbial enzymatic activity, and the variations in enzyme activity across different climate zones and soil ecosystems. Furthermore, the review will emphasize the importance of microbial enzymes for soil fertility and present both current challenges and future perspectives.Abstract The extracellular enzymes secreted by soil microorganisms play a pivotal role in the decomposition of organic matter and the global cycles of carbon (C), phosphorus (P), and nitrogen (N), also serving as indicators of soil health and fertility. Current research is extensively analyzing these microbial populations and enzyme activities in diverse soil ecosystems and climatic regions, such as forests, grasslands, tropics, arctic regions and deserts. Climate change, global warming, and intensive agriculture are altering soil enzyme activities. Yet, few reviews have thoroughly explored the key enzymes required for soil fertility and the effects of abiotic factors on their functionality. A comprehensive review is thus essential to better understand the role of soil microbial enzymes in C, P, and N cycles, and their response to climate changes, soil ecosystems, organic farming, and fertilization. Studies indicate that the soil temperature, moisture, water content, pH, substrate availability, and average annual temperature and precipitation significantly impact enzyme activities. Additionally, climate change has shown ambiguous effects on these activities, causing both reductions and enhancements in enzyme catalytic functions.

The active layer of permafrost in Ny angstrom lesund, Svalbard (79 degrees N) around the Bayelva River in the Leirhaugen glacier moraine is measured as a small net carbon sink at the brink of becoming a carbon source. In many permafrost-dominating ecosystems, microbes in the active layers have been shown to drive organic matter degradation and greenhouse gas production, creating positive feedback on climate change. However, the microbial metabolisms linking the environmental geochemical processes and the populations that perform them have not been fully characterized. In this paper, we present geochemical, enzymatic, and isotopic data paired with 10 Pseudomonas sp. cultures and metagenomic libraries of two active layer soil cores (BPF1 and BPF2) from Ny angstrom lesund, Svalbard, (79 degrees N). Relative to BPF1, BPF2 had statistically higher C/N ratios (15 +/- 1 for BPF1 vs. 29 +/- 10 for BPF2; n = 30, p < 10(-5)), statistically lower organic carbon (2% +/- 0.6% for BPF1 vs. 1.6% +/- 0.4% for BPF2, p < 0.02), statistically lower nitrogen (0.1% +/- 0.03% for BPF1 vs. 0.07% +/- 0.02% for BPF2, p < 10(-6)). The d(13)C values for inorganic carbon did not correlate with those of organic carbon in BPF2, suggesting lower heterotrophic respiration. An increase in the delta C-13 of inorganic carbon with depth either reflects an autotrophic signal or mixing between a heterotrophic source at the surface and a lithotrophic source at depth. Potential enzyme activity of xylosidase and N-acetyl-beta-D-glucosaminidase increases twofold at 15 degrees C, relative to 25 degrees C, indicating cold adaptation in the cultures and bulk soil. Potential enzyme activity of leucine aminopeptidase across soils and cultures was two orders of magnitude higher than other tested enzymes, implying that organisms use leucine as a nitrogen and carbon source in this nutrient-limited environment. Besides demonstrating large variability in carbon compositions of permafrost active layer soils only similar to 84 m apart, results suggest that the Svalbard active layer microbes are often limited by organic carbon or nitrogen availability and have adaptations to the current environment, and metabolic flexibility to adapt to the warming climate.

Microbial processes, including extracellular enzyme (exoenzyme) production, are a major driver of decomposition and a current topic of interest in Arctic soils due to the effects of climate warming. While enzyme activity levels are often assessed, we lack information on the specific location of these exoenzymes within the soil matrix. Identifying the locations of different soil enzymes is needed to improve our understanding of microbial and overall ecosystem function. Using soil obtained from Utqiagvik, Alaska, our objectives in the study are (1) to measure the activity of enzymes in soil pore water, (2) to examine the distribution of activity among soil particle size fractions using filtration, and (3) to cross these particle size fraction analyses with disruption techniques (blending to shred and sonication to further separate clumped/ aggregated soil materials) to assess how tightly bound the enzymes are to the particles. The results of the soil pore water assays showed little to no enzyme activity (<0.05 nmol g soil(-1) h(-1)), suggesting that enzymes are not abundant in soil pore water. In the soil cores, we detected activity for most of the hydrolytic enzymes, and there were clear differences among the particle size and disruption treatments. Higher activities in unfiltered and 50-mu m filters relative to much finer 2-mu m filters suggested that the enzymes were preferentially associated with larger particles in the soil, likely the organic material that makes up the bulk of these Arctic soils. Furthermore, in the sonication + blending treatment with no filter, 5 of 6 hydrolytic enzymes showed higher activity compared to blending only (and much higher than sonication only), further indicating that enzyme-substrate complexes throughout the organic matter component of the soil matrix are the sites of hydrolytic enzyme activity. These results suggest that the enzymes are likely bound to either the producing microbes, which are bound to the substrates, or directly to the larger organic substrates they are decomposing. This close-proximity binding may potentially minimize the transport of decomposition products away from the microbes that produce them.

Plant species composition influences belowground ecosystem function. However, there are few data on the interactive effects of plant diversity and soil function. We surveyed plant species diversity, and determined soil carbon (C), nitrogen (N) fractions and enzyme activity in five peatlands with different vegetation-types. We also investigated the interactions between plant species diversity and richness, and soil biochemical properties. We found a close relationship between plant species diversity and total carbon (TC) in both surface (0-15 cm) and subsoil (15-30 cm) layers. Plant diversity and richness positively correlated with soil dissolved organic carbon (DOC), NH4+-N in both soil layers and subsoil moisture and total nitrogen (TN), as well as topsoil pH. Plant species diversity and richness were also positively correlated with subsoil moisture, pH, protease, acid phosphatase activity and topsoil urease activity. Soil beta-glucosidase, invertase, urease, protease, and acid phosphatase activity positively correlated with soil TC, TN, DOC, available N and soil moisture. Our findings demonstrate that plant community diversity is linked with soil C and N turnover through soil enzyme activity. These results will improve our ability to more fully understand the linkages between aboveground and belowground components in peatland ecosystems.

In addition to warming temperatures, Arctic ecosystems are responding to climate change with earlier snowmelt and soil thaw. Earlier snowmelt has been examined infrequently in field experiments, and we lack a comprehensive look at belowground responses of the soil biogeochemical system that includes plant roots, decomposers, and soil nutrients. We experimentally advanced the timing of snowmelt in factorial combination with an open-top chamber warming treatment over a 3-year period and evaluated the responses of decomposers and nutrient cycling processes. We tested two alternative hypotheses: (a) Early snowmelt and warming advance the timing of root growth and nutrient uptake, altering the timing of microbial and invertebrate activity and key nutrient cycling events; and (b) loss of insulating snow cover damages plants, leading to reductions in root growth and altered biological activity. During the 3years of our study (2010-2012), we advanced snowmelt by 4, 15, and 10days, respectively. Despite advancing aboveground plant phenology, particularly in the year with the warmest early-season temperatures (2012), belowground effects were primarily seen only on the first sampling date of the season or restricted to particular years or soil type. Overall, consistent and substantial responses to early snowmelt were not observed, counter to both of our hypotheses. The data on soil physical conditions, as well interannual comparisons of our results, suggest that this limited response was because of the earlier date of snowmelt that did not coincide with substantially warmer air and soil temperatures as they might in response to a natural climate event. We conclude that the interaction of snowmelt timing with soil temperatures is important to how the ecosystem will respond, but that 1- to 2-week changes in timing of snowmelt alone are not enough to drive season-long changes in soil microbial and nutrient cycling processes.

Air temperatures are rising and the winter snowpack is getting thinner in many high-latitude and high-elevation ecosystems around the globe. Past studies show that soil warming accelerates microbial metabolism and stimulates soil carbon (C) and nitrogen (N) cycling. Conversely, winter snow removal to simulate loss of snow cover leads to increased soil freezing and reductions in soil microbial biomass, exoenzyme activity, and N cycling. The Climate Change Across Seasons Experiment (CCASE), located at Hubbard Brook Experimental Forest, NH (USA) is designed to evaluate the combined effects of growing season soil warming and an increased frequency of winter soil freeze-thaw cycles on a northern forest ecosystem. Soils were collected from CCASE over two years (2014 and 2015) and extractable C and N pool sizes, as well as microbial biomass, exoenzymes, and potential net N mineralization and microbial respiration were measured. Soil warming alone did not stimulate microbial activity at any sampling time. Extractable amino acid N and organic C, proteolytic and acid phosphatase activity, and microbial respiration were reduced by the combination of warming in the growing season and winter soil freeze-thaw cycles during the period following snowmelt through tree leaf out in spring. The declines in microbial activity also coincided with an 85% decline in microbial biomass N at that time. Growing season warming and winter soil freeze-thaw cycles also resulted in a two-fold reduction in phenol oxidase activity and a 20% reduction in peroxidase activity and these declines persisted throughout the snow-free time of the year. The results from this study suggest that positive feedbacks between warming and rates of soil C and N cycling over the next 100 years will be partially mitigated by an increased frequency of winter soil freeze-thaw cycles, which decrease microbial biomass and rates of soil microbial activity.

Climate change is expected to alter the mechanisms controlling soil organic matter (SOM) stabilization. Under climate change, soil warming and drying could affect the enzymatic mechanisms that control SOM turnover and dependence on substrate concentration. Here, we used a greenhouse climate manipulation in a mature boreal forest soil to test two specific hypotheses: (1) Rates of decomposition decline at lower substrate concentrations, and (2) reductions in soil moisture disproportionately constrain the degradation of low-concentration substrates. Using constructed soil cores, we measured decomposition rates of two polymeric substrates, starch and cellulose, as well as enzyme activities associated with degradation of these substrates. The greenhouse manipulation increased temperature by 0.8 A degrees C and reduced moisture in the constructed cores by up to 90 %. We rejected our first hypothesis, as the rate of starch decomposition did not decrease with declining starch concentration under control conditions, but we did find support for hypothesis two: Drying led to lower decomposition rates for low-concentration starch. We observed a threefold reduction in soil respiration rates in bulk soils in the greenhouses over a 4-month period, but the C losses from the constructed cores did not vary among our treatments. Activities of enzymes that degrade cellulose and starch were elevated in the greenhouse treatments, which may have compensated for moisture constraints on the degradation of the common substrate (i.e., cellulose) in our constructed cores. This study confirms that substrate decomposition can be concentration-dependent and suggests that climate change effects on soil moisture could reduce rates of decomposition in well-drained boreal forest soils lacking permafrost.