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

Biodiversity in mountain soils above the treeline

Biological diversity in mountain ecosystems has been increasingly studied over the last decade. This is also the case for mountain soils, but no study to date has provided an overall synthesis of the current state of knowledge. Here we fill this gap with a first global analysis of published research on cryptogams, microorganisms, and fauna in mountain soils above the treeline, and a structured synthesis of current knowledge. Based on a corpus of almost 1400 publications and the expertise of 37 mountain soil scientists worldwide, we summarise what is known about the diversity and distribution patterns of each of these organismal groups, specifically along elevation, and provide an overview of available knowledge on the drivers explaining these patterns and their changes. In particular, we document an elevation-dependent decrease in faunal diversity above the treeline, while for cryptogams there is an initial increase above the treeline, followed by a decrease towards the nival belt. Thus, our data confirm the key role that elevation plays in shaping the biodiversity and distribution of these organisms in mountain soils. The response of prokaryote diversity to elevation, in turn, was more diverse, whereas fungal diversity appeared to be substantially influenced by plants. As far as available, we describe key characteristics, adaptations, and functions of mountain soil species, and despite a lack of ecological information about the uncultivated majority of prokaryotes, fungi, and protists, we illustrate the remarkable and unique diversity of life forms and life histories encountered in alpine mountain soils. By applying rule- as well as pattern-based literature-mining approaches and semi-quantitative analyses, we identified hotspots of mountain soil research in the European Alps and Central Asia and revealed significant gaps in taxonomic coverage, particularly among biocrusts, soil protists, and soil fauna. We further report thematic priorities for research on mountain soil biodiversity above the treeline and identify unanswered research questions. Building upon the outcomes of this synthesis, we conclude with a set of research opportunities for mountain soil biodiversity research worldwide. Soils in mountain ecosystems above the treeline fulfil critical functions and make essential contributions to life on land. Accordingly, seizing these opportunities and closing knowledge gaps appears crucial to enable science-based decision making in mountain regions and formulating laws and guidelines in support of mountain soil biodiversity conservation targets.

One stone several birds-Sustainable valorization of pork processing wastes via versatile green solvent-prompted processes

The utilization of food waste as a valuable source for bioactive extraction is vital for sustainable development. This study developed an environmentally friendly solvent-involved enzymatic system, which served a novel and multifunctional platform for the preparation of pork processing waste-derived dressing films. The α-chymotrypsin (α-Chy) exhibited enhanced activity (121.11 %) and stability in the newly developed system. The hemin and enzymolysis products were obtained from pork waste using the green solvents and their mixture with α-Chy, respectively. The composite dressing film prepared by pork waste exhibited excellent multiple properties, particularly in terms of ultraviolet shielding and antibacterial activity. The green solvents play multifunctional roles (extractant, enzymolysis-enhanced medium, plasticizer, osmotic agent, and antibacterial agent) in whole process, acting as a means of "one stone several birds". This newly developed system was successfully applied to recover bioactive components from pork waste and convert them into value-added biomaterials.

Application of magnetic aldehyde-functionalized ionic liquids for immobilization of acetylcholinesterase

This study presents a simple and efficient approach for enzyme immobilization using magnetic aldehyde-functionalized ionic liquids, with acetylcholinesterase (AChE) as a model enzyme. We synthesized a new magnetic particle, Fe3O4@SiO2@[ImBa][Cl], by modifying silica-coated Fe3O4 with the ionic liquid 4-(imidazol-1-yl)benzaldehyde hydrochloride ([ImBa][Cl]), whose structure was characterized by SEM, TEM, FT-IR, EDS, TGA and VSM. Immobilization of AChE occurred through both physical adsorption and covalent bonding, driven by electrostatic interaction between cations of the ionic liquid and AChE, as well as Schiff base reaction between the aldehyde groups and protein amines. We identified the optimal immobilization conditions including solution pH (7), AChE concentration (0.8 mg/mL) and incubation time (90 min), under which the immobilization yield reached 16.38 μg/mg. Compared to free AChE, the immobilized AChE exhibited superior substrate affinity and catalytic activity based on kinetic study, also outperforming traditional covalent immobilization methods that utilized glutaraldehyde as cross-linker. Furthermore, the immobilized AChE demonstrated excellent reusability, as well as enhanced storage and thermal stability compared to free AChE. Additionally, it was employed for evaluation of drug inhibitory activity, which could be used for relevant drug discovery. This method indicates that magnetic aldehyde-functionalized ionic liquids are simple and efficient carriers for immobilization of enzymes.

Long-term phosphorus addition alters soil enzyme kinetics with limited impact on their temperature sensitivity in an alpine meadow

The soil enzymes excreted by soil microorganisms and plant roots are essential for decomposing organic matter and regulating ecosystem function. However, phosphorus (P) deposition effects on the kinetics and thermodynamics of soil enzymes remain poorly understood. Here, an 11-year, multi-level P addition experiment was conducted in the alpine meadows of the Qinghai-Tibet Plateau, a region known as one of the most sensitive to global changes. We measured Vmax, Km and their temperature sensitivities (Q10) for six hydrolytic enzymes, along with soil properties and microbial community composition. P addition significantly reduced total soil organic C (SOC) and soil available N (NH4+-N and NO3--N), but increased dissolved organic N (DON), soil total P (TP) and available P (AP). Furthermore, P addition markedly decreased the abundance of Ascomycota, while increased that of Basidiomycota. However, the abundance of bacterial phyla remained unaffected by P addition. We found that P addition significantly increased the Vmax of β-glucosidase (BG), β-xylosidase (BX), cellobiohydrolase (CBH) and N-acetyl-glucosaminidase (NAG), but decreased that of acid phosphatase (APA) and L-leucine-aminopeptidase (LAP). P addition had no effect on Km of BX and CBH, but significantly lowered it for other enzymes. Specifically, P addition significantly reduced the Vmax-Q10 of BG and BX, but did not affect that of other enzymes. Conversely, P addition significantly increased the Km-Q10 of BG, while decreased the Km-Q10 of NAG, with no change in other enzymes. Variation partitioning analysis confirmed that microbial biomass and fungal community composition are crucial in influencing Vmax, Km, as well as their temperature sensitivities. This study highlights the critical influence of P addition on soil enzyme kinetics and temperature sensitivity and their relationships with microbial community, enhancing predictions of how microbial community and substrate availability interact to regulate the soil nutrient cycle under global environmental changes.

Effect of Compound Fertilizer on Foxtail Millet Productivity and Soil Environment

The effects of balanced fertilization with nitrogen, phosphorus, and potassium (NPK) on foxtail millet productivity and the soil environment under the same conditions of total nutrients have received limited research attention. Therefore, in this study, three balanced fertilization patterns of 27-14-10 (T1), 27-17-7 (T2), and 30-10-11 (T3), and one no fertilization treatment (CK), a total of four treatments, were set up through a two-year field experiment to study the effects of balanced fertilization patterns on foxtail millet yield and soil environment. Mantel analysis was conducted to reveal the correlation between soil environmental factors and the community and their contribution to productivity. The results showed that: (1) all balanced fertilization treatments significantly increased foxtail millet yield, with the highest yield in the T1 treatment. (2) The contents of EC, available K, available P, and alkaline-hydrolyzable nitrogen in the soil of the two-year TI treatments were higher than those of the other treatments and increased by 7.20-9.36%, 24.87-52.35%, 55.83-56.38%, and 21.05-43.95%, respectively, compared with CK. (3) Soil urease activity in the T1 treatment increased significantly by 26.67% and 9.00% compared with the control over the two years. Sucrase activity increased by 36.27% and 23.88% in the T1 treatment compared to CK, and glutaminase activity increased by 33.33% and 19.23% in the T1 treatment compared to CK. (4) T1 treatment significantly increased the OUT number and diversity index of the soil bacterial community. (5) Mantel analysis and principal component analysis showed that available soil nutrients and soil enzymes were positively correlated, and soil enzymes and soil nutrients contributed more to foxtail millet productivity. In this study, the 27-14-10 balanced fertilization pattern was more effective, providing a theoretical basis for the research and development of special fertilizers for foxtail millet and offering technical guidance for realizing the light simplified cultivation of foxtail millet and sustainable development of cost-saving and increased efficiency.

Temperature-mediated microbial carbon utilization in China's lakes

Microbes play an important role in aquatic carbon cycling but we have a limited understanding of their functional responses to changes in temperature across large geographic areas. Here, we explored how microbial communities utilized different carbon substrates and the underlying ecological mechanisms along a space-for-time substitution temperature gradient of future climate change. The gradient included 47 lakes from five major lake regions in China spanning a difference of nearly 15°C in mean annual temperatures (MAT). Our results indicated that lakes from warmer regions generally had lower values of variables related to carbon concentrations and greater carbon utilization than those from colder regions. The greater utilization of carbon substrates under higher temperatures could be attributed to changes in bacterial community composition, with a greater abundance of Cyanobacteria and Actinobacteriota and less Proteobacteria in warmer lake regions. We also found that the core species in microbial networks changed with increasing temperature, from Hydrogenophaga and Rhodobacteraceae, which inhibited the utilization of amino acids and carbohydrates, to the CL500-29-marine-group, which promoted the utilization of all almost carbon substrates. Overall, our findings suggest that temperature can mediate aquatic carbon utilization by changing the interactions between bacteria and individual carbon substrates, and the discovery of core species that affect carbon utilization provides insight into potential carbon sequestration within inland water bodies under future climate warming.

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.