Temperature sensitivities of extracellular enzyme Vmax and Km across thermal environments

Modelling optimal ligninolytic activity during plant litter decomposition

A large fraction of plant litter comprises recalcitrant aromatic compounds (lignin and other phenolics). Quantifying the fate of aromatic compounds is difficult, because oxidative degradation of aromatic carbon (C) is a costly but necessary endeavor for microorganisms, and we do not know when gains from the decomposition of aromatic C outweigh energetic costs. To evaluate these tradeoffs, we developed a litter decomposition model in which the aromatic C decomposition rate is optimized dynamically to maximize microbial growth for the given costs of maintaining ligninolytic activity. We tested model performance against > 200 litter decomposition datasets collected from published literature and assessed the effects of climate and litter chemistry on litter decomposition. The model predicted a time-varying ligninolytic oxidation rate, which was used to calculate the lag time before the decomposition of aromatic C is initiated. Warmer conditions increased decomposition rates, shortened the lag time of aromatic C oxidation, and improved microbial C-use efficiency by decreasing the costs of oxidation. Moreover, a higher initial content of aromatic C promoted an earlier start of aromatic C decomposition under any climate. With this contribution, we highlight the application of eco-evolutionary approaches based on optimized microbial life strategies as an alternative parametrization scheme for litter decomposition models.

Spatio-temporal microbial regulation of aggregate-associated priming effects under contrasting tillage practices

Tillage intensity significantly influences the heterogeneous distribution and dynamic changes of soil microorganisms, consequently shaping spatio-temporal patterns of SOC decomposition. However, little is known about the microbial mechanisms by which tillage intensity regulates the priming effect (PE) dynamics in heterogeneous spatial environments such as aggregates. Herein, a microcosm experiment was established by adding 13C-labeled straw residue to three distinct aggregate-size classes (i.e., mega-, macro-, and micro-aggregates) from two long-term contrasting tillage histories (no-till [NT] and conventional plow tillage [CT]) for 160 days to observe the spatio-temporal variations in PE. Metagenomic sequencing and Fourier transform mid-infrared techniques were used to assess the relative importance of C-degrading functional genes, microbial community succession, and SOC chemical composition in the aggregate-associated PE dynamics during straw decomposition. Spatially, straw addition induced a positive PE for all aggregates, with stronger PE occurring in larger aggregates, especially in CT soil compared to NT soil. Larger aggregates have more unique microbial communities enriched in genes for simple C degradation (e.g., E5.1.3.6, E2.4.1.7, pmm-pgm, and KduD in Nitrosospeera and Burkholderia), contributing to the higher short-term PE; however, CT soils harbored more genes for complex C degradation (e.g., TSTA3, fcl, pmm-pgm, and K06871 in Gammaproteobacteria and Phycicoccus), supporting a stronger long-term PE. Temporally, soil aggregates played a significant role in the early-stage PEs (i.e., < 59 days after residue addition) through co-metabolism and nitrogen (N) mining, as evidenced by the increased microbial biomass C and dissolved organic C (DOC) and reduced inorganic N with increasing aggregate-size class. At a later stage, however, the legacy effect of tillage histories controlled the PEs via microbial stoichiometry decomposition, as suggested by the higher DOC-to-inorganic N and DOC-to-available P stoichiometries in CT than NT. Our study underscores the importance of incorporating both spatial and temporal microbial dynamics for a comprehensive understanding of the mechanisms underlying SOC priming, especially in the context of long-term contrasting tillage practices.

Environmental drivers of increased ecosystem respiration in a warming tundra

Arctic and alpine tundra ecosystems are large reservoirs of organic carbon1,2. Climate warming may stimulate ecosystem respiration and release carbon into the atmosphere3,4. The magnitude and persistency of this stimulation and the environmental mechanisms that drive its variation remain uncertain5-7. This hampers the accuracy of global land carbon-climate feedback projections7,8. Here we synthesize 136 datasets from 56 open-top chamber in situ warming experiments located at 28 arctic and alpine tundra sites which have been running for less than 1 year up to 25 years. We show that a mean rise of 1.4 °C [confidence interval (CI) 0.9-2.0 °C] in air and 0.4 °C [CI 0.2-0.7 °C] in soil temperature results in an increase in growing season ecosystem respiration by 30% [CI 22-38%] (n = 136). Our findings indicate that the stimulation of ecosystem respiration was due to increases in both plant-related and microbial respiration (n = 9) and continued for at least 25 years (n = 136). The magnitude of the warming effects on respiration was driven by variation in warming-induced changes in local soil conditions, that is, changes in total nitrogen concentration and pH and by context-dependent spatial variation in these conditions, in particular total nitrogen concentration and the carbon:nitrogen ratio. Tundra sites with stronger nitrogen limitations and sites in which warming had stimulated plant and microbial nutrient turnover seemed particularly sensitive in their respiration response to warming. The results highlight the importance of local soil conditions and warming-induced changes therein for future climatic impacts on respiration.

Warming affects leaf light use efficiency and functional traits in alpine plants: evidence from a 4-year in-situ field experiment

Introduction

Light use efficiency (LUE) is a crucial determinant of plant productivity, while leaf functional traits directly affect ecosystem functions. However, it remains unclear how climate warming affects LUE and leaf functional traits of dominant species in alpine meadows.

Methods

We conducted a 4-year in-situ field warming experiment to investigate the eco-physiological characteristics for a dominant species (Elymus nutans) and a common species (Potentilla anserina) on the Tibetan Plateau. The leaf traits, photosynthesis and fluorescence characteristics were measured, along with the soil physical-chemical properties associated with the two species.

Results and discussions

Experimental warming increased the leaf LUE, maximum photochemical efficiency, non-photochemical quenching, relative water content and specific leaf area for both species. However, there was a decrease in leaf and soil element content. Different species exhibit varying adaptability to warming. Increasing temperature significantly increased the photosynthetic rate, stomatal conductance, transpiration rate, total water content, and specific leaf volume of E. nutans; however, all these traits exhibited an opposite trend in P. anserina. Warming has a direct negative impact on leaf LUE and an indirectly enhances LUE through its effects on leaf traits. The impact of warming on plant photosynthetic capacity is primarily mediated by soil nutrients and leaf traits. These results indicate that the two different species employ distinct adaptive strategies in response to climate change, which are related to their species-specific variations. Such changes can confer an adaptive advantage for plant to cope with environmental change and potentially lead to alterations to ecosystem structure and functioning.

Michaelis-Menten kinetics during dry etching processes

The chemical etching of germanium in Br2 environment at elevated temperatures is described by the Michaelis-Menten equation. The validity limit of Michaelis-Menten kinetics is subjected to the detailed analysis. The steady-state etching rate requires synergy of two different process parameters. High purity gas should be directed to the substrate on which intermediate reaction product does not accumulate. Theoretical calculations indicate that maximum etching rate is maintained when 99.89% of the germanium surface is covered by the reaction product, and 99.9999967% of the incident Br2 molecules are reflected from the substrate surface. Under these conditions, single GeBr2 molecule is formed after 30 million collisions of Br2 molecules with the germanium surface.

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.

Soil enzyme kinetics and thermodynamics in response to long-term vegetation succession

Our current knowledge regarding soil organic matter (SOM) turnover during vegetation succession is often limited to conventional C decomposition models. However, microbial enzyme-mediated SOM degradation and nutrient cycling are mainly reflected in the kinetic parameters of these enzymes. Changes in the composition and structure of plant communities are typically accompanied by alterations in soil ecological functions. Therefore, it is important to clarify the kinetic parameters of soil enzymes and their temperature sensitivity in response to vegetation succession, especially under the current trend of climate change-related global warming; however, these are still understudied. Here, we examined the kinetic parameters of soil enzymes, their temperature sensitivity, and their associations with environmental variables over long-term (approximately 160 years) vegetation succession on the Loess Plateau using a space-for-time substitution method. We found that the kinetic parameters of soil enzymes changed significantly during vegetation succession. Specific response characteristics varied depending on the enzyme. Overall, the temperature sensitivity (Q₁₀, 0.79-1.87) and activation energy (E_a, 8.69-41.49 kJ·mol^-1) remained stable during long-term succession. Compared with N-acetyl-glucosaminidase and alkaline phosphatase, β-glucosidase was more sensitive to extreme temperatures. In particular, two kinetic parameters (i.e., maximum reaction rate, V_max; half-saturation constant, K_m) of β-glucosidase were decoupled at low (5 °C) and high (35 °C) temperatures. Overall, V_max was the primary determinant of variations of enzyme catalytic efficiency (K_cat) during succession, and soil total nutrients had a greater impact on K_cat than available nutrients. Our results suggested that soil ecosystems played an increasingly important role as a C source during long-term vegetation succession, as indicated by the positive responses of the C cycling enzyme K_cat, while the factors related to soil N and P cycling remained relatively stable.

Substrate availability and not thermal acclimation controls microbial temperature sensitivity response to long-term warming

Microbes are responsible for cycling carbon (C) through soils, and predicted changes in soil C stocks under climate change are highly sensitive to shifts in the mechanisms assumed to control the microbial physiological response to warming. Two mechanisms have been suggested to explain the long-term warming impact on microbial physiology: microbial thermal acclimation and changes in the quantity and quality of substrates available for microbial metabolism. Yet studies disentangling these two mechanisms are lacking. To resolve the drivers of changes in microbial physiology in response to long-term warming, we sampled soils from 13- and 28-year-old soil warming experiments in different seasons. We performed short-term laboratory incubations across a range of temperatures to measure the relationships between temperature sensitivity of physiology (growth, respiration, carbon use efficiency, and extracellular enzyme activity) and the chemical composition of soil organic matter. We observed apparent thermal acclimation of microbial respiration, but only in summer, when warming had exacerbated the seasonally-induced, already small dissolved organic matter pools. Irrespective of warming, greater quantity and quality of soil carbon increased the extracellular enzymatic pool and its temperature sensitivity. We propose that fresh litter input into the system seasonally cancels apparent thermal acclimation of C-cycling processes to decadal warming. Our findings reveal that long-term warming has indirectly affected microbial physiology via reduced C availability in this system, implying that earth system models including these negative feedbacks may be best suited to describe long-term warming effects on these soils.

The carbon-quality temperature hypothesis: Fact or artefact?

Climate warming can reduce global soil carbon stocks by enhancing microbial decomposition. However, the magnitude of this loss remains uncertain because the temperature sensitivity of the decomposition of the major fraction of soil carbon, namely resistant carbon, is not fully known. It is now believed that the resistance of soil carbon mostly depends on microbial accessibility of soil carbon with physical protection being the primary control of the decomposition of protected carbon, which is insensitive to temperature changes. However, it is still unclear whether the temperature sensitivity of the decomposition of unprotected carbon, for example, carbon that is not protected by the soil mineral matrix, may depend on the chemical recalcitrance of carbon compounds. In particular, the carbon-quality temperature (CQT) hypothesis asserts that recalcitrant low-quality carbon is more temperature-sensitive to decomposition than labile high-quality carbon. If the hypothesis is correct, climate warming could amplify the loss of unprotected, but chemically recalcitrant, carbon and the resultant CO₂ release from soils to the atmosphere. Previous research has supported this hypothesis based on reported negative relationships between temperature sensitivity and carbon quality, defined as the decomposition rate at a reference temperature. Here we show that negative relationships can arise simply from the arbitrary choice of reference temperature, inherently invalidating those tests. To avoid this artefact, we defined the carbon quality of different compounds as their uncatalysed reaction rates in the absence of enzymes. Taking the uncatalysed rate as the carbon quality index, we found that the CQT hypothesis is not supported for enzyme-catalysed reactions, which showed no relationship between carbon quality and temperature sensitivity. The lack of correlation in enzyme-catalysed reactions implies similar temperature sensitivity for microbial decomposition of soil carbon, regardless of its quality, thereby allaying concerns of acceleration of warming-induced decomposition of recalcitrant carbon.

Photosynthetic Traits of Páramo Plants Subjected to Short-Term Warming in OTC Chambers

Global warming and changes in land use are some of the main threats to high mountain species. Both can interact in ways not yet assessed. In this study, we evaluated the photosynthetic responses of six common páramo species within a warming experiment using open-top chambers (OTC) in conserved páramo areas with different land use histories. We did not find significant differences in the photochemical performance of the species as measured through Fv/Fm, ETR, and NPQ in response to passive warming, indicating that warmed plants are not stressed. However, NPQ values were higher in recovering areas, especially in the driest and warmest months. Leaf transpiration, stomatal conductance, and Ci were not affected by the OTC or the land use history. The photosynthetic capacity, maximum photosynthetic capacity, and carboxylation rate of RuBisCO increased in response to warming but only in the area with no anthropogenic intervention. These results suggest that species will respond differently to warming depending on the history of páramo use, and therefore not all páramo communities will respond equally to climate change. In disturbed sites with altered soil conditions, plants could have a lower breadth of physiological response to warming.

Short-term but not long-term perennial mugwort cropping increases soil organic carbon in Northern China Plain

Perennial cropping has been an alternative land use type due to its widely accepted role in increasing soil carbon sequestration. However, how soil organic carbon (SOC) changes and its underlying mechanisms under different cropping years are still elusive. A chronosequence (0-, 3-, 6-, 20-year) of perennial mugwort cropping was chosen to explore the SOC dynamics and the underlying mechanisms in agricultural soils of Northern China Plain. The results revealed that SOC first increased and then decreased along the 20-year chronosequence. The similar patterns were also found in soil properties (including soil ammonium nitrogen, total nitrogen and phosphorus) and two C-degrading hydrolytic enzyme activities (i.e., α-glucosidase and β-glucosidase). The path analysis demonstrated that soil ammonium nitrogen, total nitrogen, and plant biomass affected SOC primarily through the indirect impacts on soil pH, total phosphorus availability, and C-degrading hydrolytic enzyme activities. In addition, the contributions of soil properties are greater than those of biotic factors (plant biomass) to changes in SOC across the four mugwort cropping years. Nevertheless, the biotic factors may play more important roles in regulating SOC than abiotic factors in the long run. Moreover, SOC reached its maximum and was equaled to that under the conventional rotation when cropping mugwort for 7.44 and 14.88 years, respectively, which has critical implications for sustainable C sequestration of agricultural soils in Northern China Plain. Our observations suggest that short-term but not long-term perennial mugwort cropping is an alternative practice benefiting soil C sequestration and achieving the Carbon Neutrality goal in China.

Contrasting effects of maize litter and litter-derived biochar on the temperature sensitivity of paddy soil organic matter decomposition

Organic matter input regulates the rate and temperature sensitivity (expressed as Q10) of soil organic matter (SOM) decomposition by changing microbial composition and activities. It remains unclear how the incorporation of litter-made biochar instead of litter affects the Q10 of SOM decomposition. Using a unique combination of two-and three-source partitioning methods (isotopic discrimination between C3/C4 pathways and 14C labeling), we investigated: (1) how maize litter versus litter-made biochar (of C4 origin) addition influenced the Q10 of SOM (C3 origin) under 10°C warming, and (2) how the litter or biochar amendments affected the Q10 of 14C-labeled fresh organic matter (FOM) after long-term incubation. Compared with biochar addition, litter increased the rates and Q10 of mass-specific respiration, SOM and FOM decomposition, as well as the contents of SOM-derived dissolved organic C (DOC) and total phospholipid fatty acids (PLFA). Litter-amended soils have much higher activities (Vmax) of β-glucosidase, N-acetyl-β-glucosaminidase, and leucine aminopeptidase, suggesting larger enzyme pools than in soils with biochar. The Q10 of enzyme Vmax (1.6–2.0) and Km (1.2–1.4) were similar between litter-and biochar-amended soils, and remained stable with warming. However, warming reduced microbial biomass (PLFA) and enzyme activity (Vmax), suggesting decreased enzyme production associated with smaller microbial biomass or faster enzyme turnover at higher temperatures. Reductions in PLFA content and enzyme Vmax due to warming were larger in litter-amended soils (by 31%) than in the control and biochar-amended soils (by 4–11%), implying the active litter-feeding microorganisms have a smaller degree of heat tolerance than the inactive microorganisms under biochar amendments. The reduction in enzyme activity (Vmax) by warming was lower in soils with biochar than in the control soil. Our modeling suggested that the higher Q10 in litter-amended soils was mainly caused by faster C loss under warming, linked to reductions in microbial biomass and growth efficiency, rather than the slightly increased SOM-originated substrate availability (DOC). Overall, using straw-made biochar instead of straw per se as a soil amendment lowers the Q10 of SOM and FOM by making microbial communities and enzyme pools more temperature-tolerant, and consequently reduces SOM losses under warming.

Temperature sensitivity of soil enzyme kinetics under N and P fertilization in an alpine grassland, China

Soil nutrient cycling can be best studied by supplementing the soil with N and P fertilizers. Soil enzyme kinetic parameters (Vmax and Km) can be used to reflect the maximum reaction rates and affinities of soil enzymes. However, how N and P fertilizers affect the temperature sensitivity of soil enzyme kinetics is poorly understood. Therefore, our study investigated the response of soil enzyme kinetic temperature sensitivity relevant to C, N, and P cycles based on a 9-year fertilization (N and P) experiment performed in an alpine grassland on the Qinghai-Tibetan Plateau in China. Our results showed the following: N and P addition positively affected the Km of β-glucosidase (BG); P and NP interaction significantly increased the Km of phosphatase (AP), indicating that N and P addition significantly negatively affected the substrate affinity of soil enzymes. The temperature sensitivity of Michaelis-Menten kinetics was different for different enzymes. N and P fertilization decreased the temperature sensitivity of Km of BG but increased the temperature sensitivity of the Km of N-acetyl-glucosaminidase (NAG) and AP. In our study, P and NP fertilization increased the temperature sensitivity and activation energy of the Vmax of BG, indicating that P elements promoted the secretion of more extracellular enzymes by soil microbes to cope with temperature changes. The enzymes involved in the soil N and P cycle responded to the exogenous N and P through increases and decreases in the temperature sensitivity of the Km and Vmax, respectively. This study is crucial for investigating the impact of nutrient input on soil ecosystem functions under future climate warming conditions.

Enhancing the secretion of a feruloyl esterase in Bacillus subtilis by signal peptide screening and rational design

Feruloyl esterase is a subclass of α/β hydrolase, which could release ferulic acid from biomass residues for use as an efficient additive in food or pharmaceutical industries. In the present study, a feruloyl esterase with broad substrate specificity was characterised and secreted by Bacillus subtilis WB600. After codon usage optimisation and signal peptide library screening, the secretion amount of feruloyl esterase was enhanced by up to 10.2-fold in comparison with the base strain. The site-specific amino acid substitutions that facilitate protein folding further improved the secretion by about 1.5-fold. The purified rationally designed enzyme exhibited maximal activity against methyl ferulate at pH 6.5 and 65 °C. In the solid-state fermentation, the genetically engineered B. subtilis released about 37% of the total alkali-extractable ferulic acid in maize bran. This study provides a promising candidate for ferulic acid production and demonstrates that the secretion of a heterologous enzyme from B. subtilis can be cumulatively improved by changes in protein sequence features.

Enzyme kinetics inform about mechanistic changes in tea litter decomposition across gradients in land-use intensity in Central German grasslands

Grassland ecosystems provide important ecosystem services such as nutrient cycling and primary production that are affected by land-use intensity. To assess the effects of land-use intensity, operational and sensitive ecological indicators that integrate effects of grassland management on ecosystem processes such as organic matter turnover are needed. Here, we investigated the suitability of measuring the mass loss of standardized tea litter together with extracellular enzyme kinetics as a proxy of litter decomposition in the topsoil of grasslands along a well-defined land-use intensity gradient (fertilization, mowing, grazing) in Central Germany. Tea bags containing either green tea (high-quality litter) or rooibos tea (low-quality litter) were buried in 5 cm soil depth. Litter mass loss was measured after three (early-stage decomposition) and 12 months (mid-stage decomposition). Based on the fluorescence measurement of the reaction product 4-methylumbelliferone, Michaelis-Menten enzyme kinetics (V_max: potential maximum rate of activity; K_m: substrate affinity) of five hydrolases involved in the carbon (C)-, nitrogen (N)- and phosphorus (P)-cycle (β-glucosidase (BG), cellobiohydrolase (CBH), cellotriohydrolase (CTH), 1,4-β-N-acetylglucosaminidase (NAG), and phosphatase (PH)) were determined in tea litter bags and in the surrounding soil. The land-use intensity index (LUI), summarizing fertilization, mowing, grazing, and in particular the frequency of mowing were identified as important drivers of early-stage tea litter decomposition. Mid-stage decomposition was influenced by grazing intensity. The higher the potential activity of all measured C-, N- and P-targeting enzymes, the higher was the decomposition of both tea litters in the early-phase. During mid-stage decomposition, individual enzyme parameters (V_max of CTH and PH, K_m of CBH) became more important. The tea bag method proved to be a suitable indicator which allows an easy and cost-effective assessment of land-use intensity effects on decay processes in manged grasslands. In combination with enzyme kinetics it is an appealing approach to identify mechanisms driving litter break down.

Temperature responsiveness of soil carbon fractions, microbes, extracellular enzymes and CO2 emission: mitigating role of texture

The interaction of warming and soil texture on responsiveness of the key soil processes i.e. organic carbon (C) fractions, soil microbes, extracellular enzymes and CO₂ emissions remains largely unknown. Global warming raises the relevant question of how different soil processes will respond in near future, and what will be the likely regulatory role of texture? To bridge this gap, this work applied the laboratory incubation method to investigate the effects of temperature changes (10-50 °C) on dynamics of labile, recalcitrant and stable C fractions, soil microbes, microbial biomass, activities of extracellular enzymes and CO₂ emissions in sandy and clayey textured soils. The role of texture (sandy and clayey) in the mitigation of temperature effect was also investigated. The results revealed that the temperature sensitivity of C fractions and extracellular enzymes was in the order recalcitrant C fractions > stable C fractions > labile C fractions and oxidative enzymes > hydrolytic enzymes. While temperature sensitivity of soil microbes and biomass was in the order bacteria > actinomycetes > fungi ≈ microbial biomass C (MBC) > microbial biomass N (MBN) > microbial biomass N (MBP). Conversely, the temperature effect and sensitivity of all key soil processes including CO₂ emissions were significantly (P < 0.05) higher in sandy than clayey textured soil. Results confirmed that under the scenario of global warming and climate change, soils which are sandy in nature are more susceptible to temperature increase and prone to become the CO₂-C sources. It was revealed that clayey texture played an important role in mitigating and easing off the undue temperature influence, hence, the sensitivity of key soil processes.

Recent Developments in Industrial Mycozymes: A Current Appraisal

Fungi, being natural decomposers, are the most potent, ubiquitous and versatile sources of industrial enzymes. About 60% of market share of industrial enzymes is sourced from filamentous fungi and yeasts. Mycozymes (myco-fungus; zymes-enzymes) are playing a pivotal role in several industrial applications and a number of potential applications are in the offing. The field of mycozyme production, while maintaining the old traditional methods, has also witnessed a sea change due to advents in recombinant DNA technology, optimisation protocols, fermentation technology and systems biology. Consolidated bioprocessing of abundant lignocellulosic biomass and complex polysaccharides is being explored at an unprecedented pace and a number of mycozymes of diverse fungal origins are being explored using suitable platforms. The present review attempts to revisit the current status of various mycozymes, screening and production strategies and applications thereof.

Comparative analysis of compound NSC13728 as Omomyc homodimer stabilizer by molecular dynamics simulation and MM/GBSA free energy calculation

Myc is a master transcriptional regulator that controls almost all cellular processes, whose function is dependent on dimerization with its obligate partner Max. Stabilization of Max homodimer by small molecules (such as compound NSC13728) has proven an effective way to reduce the availability of Myc-Max dimer. Omomyc, a peptide inhibitor of Myc, is able to form Omomyc homodimer, which can competitively inhibit the binding of Myc-Max to the E-box of DNA. Considering the high amino acid sequence homology between Omomyc and Max, we put forward the hypothesis that Max-Max stabilizers could stabilize the Omomyc homodimer. Hence, through molecular dynamics (MD) simulation and molecular mechanics/generalized Born surface area (MM/GBSA) free energy calculation, we discovered that the stability of Omomyc-Omomyc is remarkably higher than that of Max-Max. Moreover, after adding the compound NSC13728 into the well-defined "Site 3," the binding affinity between two Omomyc monomers can be further increased. Compound NSC13728 has stronger binding interaction to Omomyc-Omomyc than to Max-Max. "Site 3" of Omomyc is more hydrophobic than that of Max, which enlightens us that the more potent Omomyc-Omomyc stabilizers may be hydrophobic in structure.

Kinetic Properties of Microbial Exoenzymes Vary With Soil Depth but Have Similar Temperature Sensitivities Through the Soil Profile

Current knowledge of the mechanisms driving soil organic matter (SOM) turnover and responses to warming is mainly limited to surface soils, although over 50% of global soil carbon is contained in subsoils. Deep soils have different physicochemical properties, nutrient inputs, and microbiomes, which may harbor distinct functional traits and lead to different SOM dynamics and temperature responses. We hypothesized that kinetic and thermal properties of soil exoenzymes, which mediate SOM depolymerization, vary with soil depth, reflecting microbial adaptation to distinct substrate and temperature regimes. We determined the Michaelis-Menten (MM) kinetics of three ubiquitous enzymes involved in carbon (C), nitrogen (N) and phosphorus (P) acquisition at six soil depths down to 90 cm at a temperate forest, and their temperature sensitivity based on Arrhenius/Q₁₀ and Macromolecular Rate Theory (MMRT) models over six temperatures between 4–50°C. Maximal enzyme velocity (V_max) decreased strongly with depth for all enzymes, both on a dry soil mass and a microbial biomass C basis, whereas their affinities increased, indicating adaptation to lower substrate availability. Surprisingly, microbial biomass-specific catalytic efficiencies also decreased with depth, except for the P-acquiring enzyme, indicating distinct nutrient demands at depth relative to microbial abundance. These results suggested that deep soil microbiomes encode enzymes with intrinsically lower turnover and/or produce less enzymes per cell, reflecting distinct life strategies. The relative kinetics between different enzymes also varied with depth, suggesting an increase in relative P demand with depth, or that phosphatases may be involved in C acquisition. V_max and catalytic efficiency increased consistently with temperature for all enzymes, leading to overall higher SOM-decomposition potential, but enzyme temperature sensitivity was similar at all depths and between enzymes, based on both Arrhenius/Q₁₀ and MMRT models. In a few cases, however, temperature affected differently the kinetic properties of distinct enzymes at discrete depths, suggesting that it may alter the relative depolymerization of different compounds. We show that soil exoenzyme kinetics may reflect intrinsic traits of microbiomes adapted to distinct soil depths, although their temperature sensitivity is remarkably uniform. These results improve our understanding of critical mechanisms underlying SOM dynamics and responses to changing temperatures through the soil profile.

The effect of soil depth on temperature sensitivity of extracellular enzyme activity decreased with elevation: Evidence from mountain grassland belts

Temperature sensitivity of soil extracellular enzyme activity (EEA), indicated by the temperature coefficient Q₁₀, is used to predict the effect of temperature on soil carbon (C), nitrogen (N), and phosphorus (P) cycling. At present, we lack understanding of elevation and soil depth variations in Q₁₀ of EEA. Here, we measured the Q₁₀ of three enzymes participating in C- (β-1,4-glucosidase, BG), N- (leucine aminopeptidase, LAP), and P- (acid phosphatase, AP) cycling along a vertical grassland belt of China. Soils from five depths (0-10, 10-20, 20-40, 40-60, and 60-100 cm) were sampled from three elevations (low, <1000 m; middle, 1000-2000 m; high, 2000-3000 m) and incubated at four temperatures (5, 15, 25, 35 °C). The average Q₁₀ of soil EEA ranged from 0.97 to 1.11 and the Q₁₀ of LAP was higher than that of BG and AP. Generally, the Q₁₀ of BG and LAP both increased from low to middle elevation and then decreased, while the Q₁₀ of AP was stable. Moreover, the effect of soil depth on Q₁₀ of EEA was weakened from low elevation to high elevation, and the factors driving Q₁₀ of soil EEA changed with elevation. This study improved the understanding of the vertical pattern of Q₁₀ of soil EEA in water-limited ecosystems, and highlighted that elevation could regulate the effect of soil depth on Q₁₀ of EEA.

Leaf and Community Photosynthetic Carbon Assimilation of Alpine Plants Under in-situ Warming

The Tibetan Plateau is highly sensitive to elevated temperatures and has experienced significant climate warming in the last decades. While climate warming is known to greatly impact alpine ecosystems, the gas exchange responses at the leaf and community levels to climate warming in alpine meadow ecosystems remain unclear. In this study, the alpine grass, Elymus nutans, and forb, Potentilla anserina, were grown in open-top chambers (OTCs) for 3 consecutive years to evaluate their response to warming. Gas exchange measurements were used to assess the effects of in-situ warming on leaf- and community-level photosynthetic carbon assimilation based on leaf photosynthetic physiological parameters. We introduced a means of up-scaling photosynthetic measurements from the leaf level to the community level based on six easily measurable parameters, including leaf net photosynthetic rate, fresh leaf mass per unit leaf area, fresh weight of all plant leaves in the community, the percentage of healthy leaves, the percentage of received effective light by leaves in the community, and community coverage. The community-level photosynthetic carbon assimilation and productivity all increased with warming, and the net photosynthetic rate at the leaf level was significantly higher than at the community level. Under elevated temperature, the net photosynthetic rate of E. nutans decreased, while that of P. anserina increased. These results indicated that climate warming may significantly influence plant carbon assimilation, which could alter alpine meadow community composition in the future.

Soil chemical properties rather than the abundance of active and potentially active microorganisms control soil enzyme kinetics

Soil enzymes secreted by microorganisms play a critical role in nutrient cycling, soil structure maintenance, and crop production. However, understanding of the linkage between soil enzyme kinetics and microbial metabolism and active microbial communities is remarkably limited. In this study, we measured the kinetics of three hydrolase enzymes, active microbial abundance and substrate-induced respiration (SIR) from 21 farmlands differing in their fertilities collected from the Loess Plateau, China. Results showed the high fertility soils had higher total organic carbon (TOC) and nutrient contents, potential microbial activity, the colony-forming units (CFU) of actinomycetes, and values of enzyme V_max and K_m than those of low fertility soils. We also observed that the CFU of fungi and other bacterial groups did not change with soil fertility status. Soil chemical properties explained 74.0% of the variance in V_max and 28.3% of the variance in K_m, respectively. Whereas, the abundance of main microbial groups and fungi/bacteria ratio only explained 10.2% and 7% of the variance of V_max and K_m, respectively. The interactive effect of soil properties and microbial community could explain 20.2% of the variance in K_m. Our results suggest that the substrate availability would mainly drive enzyme kinetics compared to the abundance of active/potentially active microbes in the farmland soils.

Embracing a new paradigm for temperature sensitivity of soil microbes

The temperature sensitivity of soil processes is of major interest, especially in light of climate change. Originally formulated to explain the temperature dependence of chemical reactions, the Arrhenius equation, and related Q₁₀ temperature coefficient, has a long history of application to soil biological processes. However, empirical data indicate that Q₁₀ and Arrhenius model are often poor metrics of temperature sensitivity in soils. In this opinion piece, we aim to (a) review alternative approaches for characterizing temperature sensitivity, focusing on macromolecular rate theory (MMRT); (b) provide strategies and tools for implementing a new temperature sensitivity framework; (c) develop thermal adaptation hypotheses for the MMRT framework; and (d) explore new questions and opportunities stemming from this paradigm shift. Microbial ecologists should consider developing and adopting MMRT as the basis for predicting biological rates as a function of temperature. Improved understanding of temperature sensitivity in soils is particularly pertinent as microbial response to temperature has a large impact on global climate feedbacks.

Responses of litter, organic and mineral soil enzyme kinetics to 6 years of canopy and understory nitrogen additions in a temperate forest

Increasing atmospheric nitrogen (N) deposition could profoundly impact soil carbon, N and phosphorus cycling that are often regulated by extracellular enzymes. The potential activities of enzymes in response to N deposition have been studied extensively, but the kinetic mechanisms in response to canopy and understory N additions in different soil layers are poorly understood. Here, we conducted a six-year-long field manipulation experiment in a temperate deciduous forest to reveal the kinetic characteristics of seven extracellular hydrolytic enzymes in the litter, organic and mineral soil layers in response to canopy and understory N additions. Canopy N addition and understory N addition exerted similar effects on the kinetics parameters (V_max and K_m) of most enzymes under study. The kinetics parameters of most enzymes generally increased in the litter layer but decreased in the organic layer and had little change in the mineral soil layer in response to N addition. In addition, the changed kinetic parameters were mainly correlated with moisture in the litter layer, with pH, substrate properties (TC, TN, DOC and DON) and microbial communities (G⁺, G^-, total bacterial and fungal biomass) in the organic and mineral soil layers. These findings indicate that enzyme kinetics responses to N deposition differ in soil layers with varying determinant factors, and therefore are driven by various physical, chemical and microbial mechanisms.

Effects of Warming and N Deposition on the Physiological Performances of Leymus secalinus in Alpine Meadow of Qinghai-Tibetan Plateau

Warming and Nitrogen (N) deposition are key global changes that may affect eco-physiological process of territorial plants. In this paper, we examined the effects of warming, N deposition, and their combination effect on the physiological performances of Leymus secalinus. Four treatments were established in an alpine meadow of Qinghai-Tibetan plateau: control (CK), warming (W), N deposition (N), and warming plus N deposition (NW). Warming significantly decreased the photosynthetic rate (A_net ), stomatal conductance (g_s ), intercellular CO₂ concentration (C_i ), and transpiration rate (T_r ), while N deposition and warming plus N deposition significantly increased those parameters of L. secalinus. Warming significantly increased the VPD and L_s , while N deposition and warming plus N deposition had a significant positive effect. Warming negatively reduced the leaf N content, Chla, Chlb, and total Chl content, while N deposition significantly promoted these traits. Warming, N deposition, and their combination significantly increased the activity of SOD, POD, and CAT. Besides, warming and warming plus N deposition significantly increased the MDA content, while N deposition significantly decreased the MDA content. N deposition and warming plus N deposition significantly increased the Rubisco activity, while warming showed no significant effect on Rubisco activity. N deposition and warming plus N deposition significantly increased the Fv/Fm, ΦPSII, qP, and decreased NPQ, while warming significantly decreased the Fv/Fm, ΦPSII, qP, and increased NPQ. N deposition strengthened the relations between g_s , Chl, Chla, Chlb, Rubisco activity, and A_net . Under warming, only g_s showed a significantly positive relation with A_net . Our findings suggested that warming could impair the photosynthetic potential of L. secalinus enhanced by N deposition. Additionally, the combination of warming and N deposition still tend to lead positive effects on L. secalinus.

Combination of warming and N inputs increases the temperature sensitivity of soil N2O emission in a Tibetan alpine meadow

Many high-elevation alpine ecosystems have been experiencing significant increases in air temperature and, to a lesser extent, nitrogen (N) deposition. These changes may affect N-cycling microbes and enhance emissions of nitrous oxide (N₂O, a potent greenhouse gas) from soil. However, few studies have investigated whether and how the resulting changes in N-cycling microbes may affect the temperature sensitivity (Q₁₀) of N₂O emission and in turn feed back to N₂O emissions. We conducted two incubation experiments to examine N₂O emissions and their temperature sensitivities in soils that had experienced 3-yr field treatments of warming, N inputs and their combination in a Tibetan alpine meadow. Our results showed that neither N inputs nor warming alone affected the rate or Q₁₀ of soil N₂O emission, but combining the two significantly increased both parameters. Also, combined N and warming significantly increased the abundance of ammonia-oxidizing bacteria (AOB), corresponding with high soil N₂O emission. In addition, N₂O emission from nitrification accounted for 60-80% of total emissions in all soils, indicating that nitrifying microbes dominated the N₂O production and its temperature sensitivity. Using random forest (RF) and structural equation model (SEM) analyses, we further evaluated the effects of various soil characteristics on soil N₂O emissions and Q₁₀. We identified soil moisture, pH, N mineralization and AOB abundance as the main predictors of the Q₁₀ of N₂O emissions. Together, these findings suggest that alterations in soil moisture, pH and ammonia-oxidizing bacteria induced by long-term N inputs and warming may increase temperature sensitivity of soil N₂O emissions, leading to a positive climate feedback in this high-altitude alpine ecosystem.

Increasing microbial carbon use efficiency with warming predicts soil heterotrophic respiration globally

The degree to which climate warming will stimulate soil organic carbon (SOC) losses via heterotrophic respiration remains uncertain, in part because different or even opposite microbial physiology and temperature relationships have been proposed in SOC models. We incorporated competing microbial carbon use efficiency (CUE)-mean annual temperature (MAT) and enzyme kinetic-MAT relationships into SOC models, and compared the simulated mass-specific soil heterotrophic respiration rates with multiple published datasets of measured respiration. The measured data included 110 dryland soils globally distributed and two continental to global-scale cross-biome datasets. Model-data comparisons suggested that a positive CUE-MAT relationship best predicts the measured mass-specific soil heterotrophic respiration rates in soils distributed globally. These results are robust when considering models of increasing complexity and competing mechanisms driving soil heterotrophic respiration-MAT relationships (e.g., carbon substrate availability). Our findings suggest that a warmer climate selects for microbial communities with higher CUE, as opposed to the often hypothesized reductions in CUE by warming based on soil laboratory assays. Our results help to build the impetus for, and confidence in, including microbial mechanisms in soil biogeochemical models used to forecast changes in global soil carbon stocks in response to warming.

The global soil community and its influence on biogeochemistry

Soil organisms represent the most biologically diverse community on land and govern the turnover of the largest organic matter pool in the terrestrial biosphere. The highly complex nature of these communities at local scales has traditionally obscured efforts to identify unifying patterns in global soil biodiversity and biogeochemistry. As a result, environmental covariates have generally been used as a proxy to represent the variation in soil community activity in global biogeochemical models. Yet over the past decade, broad-scale studies have begun to see past this local heterogeneity to identify unifying patterns in the biomass, diversity, and composition of certain soil groups across the globe. These unifying patterns provide new insights into the fundamental distribution and dynamics of organic matter on land.

Soil Metatranscriptomes Under Long-Term Experimental Warming and Drying: Fungi Allocate Resources to Cell Metabolic Maintenance Rather Than Decay

Earth’s temperature is rising, and with this increase, fungal communities are responding and affecting soil carbon processes. At a long-term soil-warming experiment in a boreal forest in interior Alaska, warming and warming-associated drying alters the function of microbes, and thus, decomposition of carbon. But what genetic mechanisms and resource allocation strategies are behind these community shifts and soil carbon changes? Here, we evaluate fungal resource allocation efforts under long-term experimental warming (including associated drying) using soil metatranscriptomics. We profiled resource allocation efforts toward decomposition and cell metabolic maintenance, and we characterized community composition. We found that under the warming treatment, fungi allocate resources to cell metabolic maintenance at the expense of allocating resources to decomposition. In addition, we found that fungal orders that house taxa with stress-tolerant traits were more abundant under the warmed treatment compared to control conditions. Our results suggest that the warming treatment elicits an ecological tradeoff in resource allocation in the fungal communities, with potential to change ecosystem-scale carbon dynamics. Fungi preferentially invest in mechanisms that will ensure survival under warming and drying, such as cell metabolic maintenance, rather than in decomposition. Through metatranscriptomes, we provide mechanistic insight behind the response of fungi to climate change and consequences to soil carbon processes.

Long-term As contamination alters soil enzyme functional stability in response to additional heat disturbance

The functional stability of soil enzymes is fundamental to the sustainability of soil biochemical processes and is affected by many environmental stressors. This study focused on the influences of long-term arsenic (As) contamination on soil enzyme functional stability: the resistance (ratio of the disturbed to control) and resilience (integrated recovery rate) of soil enzyme activities (β-glucosidase, urease, acid phosphatase, fluorescein diacetate (FDA) hydrolase) over 30 days incubation after an experimental heat disturbance (50 ^oC for 18 h). Results showed that the resistance of soil enzymes to heat disturbance differed among the enzyme types and followed the order: urease > β-glucosidase > acid phosphatase > FDA hydrolase. Urease activity was generally not affected and showed high stability against heat disturbance. The β-glucosidase activity recovered to the control level by 30 days, while 80% and 90% recovery on average occurred for acid phosphatase and FDA hydrolase, respectively. Long-term As contamination altered soil enzyme functional resistance and resilience to heat disturbance and resulted in three kinds of responses: (i) no apparent alteration (urease); (ii) moderate As contamination increased enzyme heat resistance (β-glucosidase); (iii) the resistance and resilience decreased with increasing As concentration (acid phosphatase and FDA hydrolase). The results demonstrated that different enzyme-catalytic biochemical processes have different functional stabilities under combined As and heat disturbance, and the negative changes in the soil enzyme activity led to losses in soil functions. Our study provides further evidence on the impacts of heavy metal/metalloid on soil enzyme functional stability in response to additional disturbance.

The Fate of Chemical Pollutants with Soil Properties and Processes in the Climate Change Paradigm—A Review

Heavy metal(loid)s and organic contaminants are two major groups of pollutants in soils. The fate and exposure of such pollutants in soil depends on their chemical properties, speciation, and soil properties. Soil properties and processes that control the toxicological aspects of pollutants include temperature, moisture, organic matter, mineral fractions, and microbial activities. These processes are vulnerable to climate change associated with global warming, including increased incidences of extreme rainfall, extended dry periods, soil erosion, and a rise in sea level. Here we explain evidence that relates to the effects of climate change-driven soil processes on the mobility, transport, and storage of pollutants in soil. The review found that changes in climate could increase human exposure to soil contaminants mainly due to processes involving soil organic carbon (SOC), surface runoff, redox state, and microbial community. However, uncertainties remain in relation to the extent of contaminant toxicity to human health, which is linked to global change drivers.