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Enzyme activity as a method for soil biochemistry and microbiology research has a long history of more than 100 years that is not widely acknowledged in terms of adherence to strict assay protocols and the interpretation of results. However, in the recent past, there is a growing lack of recognition of the historic advancements among researchers that use soil enzymology. Today, many papers are being published that use methods that either do not follow exact protocols as originally vetted in the research literature or individual labs use their own method that has not been optimized for pH, co-factors, substrate concentrations, or other conditions. This is of particular concern for fluorogenic substrates and microplate methods. Furthermore, there is a lack of understanding of the origin and location of a given enzyme being studied. Notably, regardless of the enzyme, it is too often assumed that enzyme activity equals microbial activity—which is not the case for most hydrolytic enzyme assays. Because as established by Douglas McLaren in the 1950s, a considerable amount of activity can come from catalytic enzymes stabilized in the soil matrix but that are no longer associated with viable cells (known as abiontic enzymes). In summary, today, many papers are using imperfect methods and/or misinterpret enzyme activity data that at a minimum confounds cross paper studies and meta-analysis. However, most importantly, lack of historical perspectives and ignoring strict protocols cause redundancy and fundamentally undermine the discipline and understanding of soil microbiology/biochemistry when enzymology methods are used.

It is still problematic to use enzyme activities as indicators of soil functions because: (1) enzyme assays determine potential and not real enzyme activities; (2) the meaning of measured enzyme activities is not known; (3) the assumption that a single enzyme activity is an indicator of nutrient dynamics in soil neglects that the many enzyme activities are involved in such dynamic processes; (4) spatio-temporal variations in natural environments are not always considered when measuring enzyme activities; and (5) many direct and indirect effects make difficult the interpretation of the response of the enzyme activity to perturbations, changes in the soil management, changes in the plant cover of soil, etc. This is the first review discussing the links between enzyme-encoding genes and the relative enzyme activity of soil. By combining measurements of enzyme activity in soil with expression (transcriptomics and proteomics) of genes, encoding the relative enzymes may contribute to understanding the mode and timing of microbial communities’ responses to substrate availability and persistence and stabilization of enzymes in the soil.

Plant invasion can significantly alter soil nutrient cycling of ecosystems. How these changes are linked to soil enzyme activities is still unknown, however, even though these are proximate agents of organic matter decomposition and nutrient release. We performed a meta-analysis of 60 case studies examining responses of 10 unique soil enzymes to plant invasion, and tested whether invaded soils differed in their enzyme activities from uninvaded soils. We also examined whether increases in soil nutrient-releasing enzyme activity were paralleled by enhanced soil nutrient availability after plant invasion. Overall, we found that plant invasion had significant impacts on the activities of seven types of soil enzymes. Plant invasion had inconsistent impacts on C-decomposing enzymes, but invaded sites had significantly higher activities of soil enzymes related to N- and P-release than noninvaded sites. Increases in nutrient- releasing enzyme activity after plant invasion ranged from +23% to +69%, which potentially results in a linear increase of soil nutrient availability in response to enhanced enzyme activities. Invaded soils also had higher nutrient stocks and soil microbial biomass than uninvaded soils. Our results suggest that enhanced activity of soil nutrient-releasing enzymes after plant invasion may accelerate nutrient cycling, potentially creating a nutrient-rich soil environment that benefits invaders and promotes their persistence, as invasive plants often appear to be more resource-demanding and competitive than native species.

Biochar application can influence soil nitrogen (N) cycle through biological and abiotic processes. However, studies on comprehensive examination of the effects of biochar application on microbially mediated N‐cycling processes (N mineralization, nitrification, denitrification, and fixation) and soil N fate (i.e., plant N uptake, soil N2O emission, and N leaching) are warranted. Therefore, the aim of this study was to examine the effects of biochar application on soil N transformation, microbial functional gene abundance, enzyme activity, and plant N uptake. To achieve the objective of this study, a meta‐analysis involving 131 peer‐reviewed field experiments was conducted. Results showed that field application of biochar significantly enhanced soil NH4+ and NO3‐ content, N mineralization, nitrification, N2 fixation, and plant N uptake by 5.3%, 3.7%, 15.3%, 48.5%, 14.7%, and 18.3%, respectively, but reduced N2O emissions and N leaching by 14.9% and 10.9%, respectively. Biochar application also increased the abundance of soil denitrifying/nitrifying genes (amoA, narG, nirS/nirK+S, and nosZ), proportion of N2 fixation bacteria, and N‐acetyl‐glucosaminidase activity by 18.6%–87.6%. Soil NO3‐ content was positively correlated with AOA‐amoA abundance, and soil N2O emission was positively correlated with the relative abundance of genes (e.g., amoA, narG, and nirS/nirK) involved in N2O production. Furthermore, long‐term biochar application tended to increase AOB‐amoA and nirK+S abundance, especially soil N2O emission and N leaching. Overall, the findings of this study indicated that biochar application accelerated microbially mediated N‐cycling processes under field conditions, thereby enhancing soil N availability and plant productivity. However, long‐term biochar application may increase N losses. Therefore, future studies should be conducted to examine the effect of long‐term biochar application on the soil N cycle and the underlying microbial mechanisms. Based on a meta‐analysis, this study showed that biochar application accelerated microbially mediated N‐cycling processes (i.e., mineralization, nitrification, denitrification, and fixation), which improved soil N availability and plant N uptake. Especially, biochar application (load of 21–40 t ha−1) to soil was more favorable for enhancing N‐relevant microbial gene abundance and enzyme activity. However, long‐term biochar application may increase N losses. A decrease in biochar N adsorption with increase in treatment duration could pose potential ecological risk in the long run.

Soil microbes provide multiple ecosystem functions such as nutrient cycling, decomposition and climate regulation. However, we lack a quantitative understanding of the relative importance of microbial richness and composition in controlling multifunctionality. This knowledge gap limits our capacity to understand the influence of biotic attributes in the provision of services and functions on which humans depend. We used two independent approaches (i.e. experimental and observational), and applied statistical modelling to identify the role and relative importance of bacterial richness and composition in driving multifunctionality (here defined as seven measures of respiration and enzyme activities). In the observational study, we measured soil microbial communities and functions in both tree‐ and bare soil‐dominated microsites at 22 locations across a 1,200 km transect in southeastern Australia. In the experimental study we used soils from two of those locations and developed gradients of bacterial diversity and composition through inoculation of sterilized soils. Microbial richness and the relative abundance of Gammaproteobacteria, Actinobacteria, and Bacteroidetes were positively related to multifunctionality in both the observational and experimental approaches; however, only Bacteroidetes was consistently selected as a key predictor of multifunctionality across all experimental approaches and statistical models used here. Moreover, our results, from two different approaches, provide evidence that microbial richness and composition are both important, yet independent, drivers of multiple ecosystem functions. Overall, our findings advance our understanding of the mechanisms underpinning relationships between microbial diversity and ecosystem functionality in terrestrial ecosystems, and further suggest that information on microbial richness and composition needs to be considered when formulating sustainable management and conservation policies, and when predicting the effects of global change on ecosystem functions. A plain language summary is available for this article. Plain Language Summary

Aims Increasing nitrogen (N) deposition has considerable effects on soil organic matter (SOM) decomposition mediated by soil enzyme activities. Few studies, however, have explored how N addition shapes soil enzyme activity patterns by changing plants, soils and microbes. Methods We conducted a five-year field fertilization experiment (0, 5, 10, and 15 g N m −2  yr. −1 ) to study how N addition affected soil enzyme activity patterns in the topsoil (0–20 cm) and subsoil (20–40 cm) in a Tibetan alpine meadow. Enzyme activity patterns were calculated by the percentage of the sum of all measured enzyme activities. The composition of the plant and microbial communities were evaluated through measuring the abundance of plant functional groups and quantifying microbial phospholipid fatty acids (PLFAs), respectively. Soil pH and available N were also measured. Results We found that soil N availability primarily controlled plant community composition, but pH controlled the composition of the microbial community, irrespective of soil depth. Soil enzyme activity patterns differed between two soil depths and among N addition rates. Importantly, N addition shaped soil enzyme activity patterns through the changes in soil pH rather than via the composition of the plant and microbial communities. Conclusions Our findings indicate that N addition can affect components of plant-soil system and, in particular, weaken the linkages between plant and microbial communities and enzyme activity patterns. The work suggests that N enrichment-induced soil acidification plays a key role in SOM decomposition and nutrient cycling in the Tibetan meadow ecosystem.

Aims Long-term nitrogen (N) fertilization has been shown to profoundly affect the soil microorganisms and strongly result in several imbalances in element concentrations. The objective of this study was to examine links among the soil microorganisms, enzyme activities, and soil carbon (C), N, and phosphorus (P) stoichiometry in a subtropical Chinese fir ( Cunninghamia lanceolata (Lamb.) Hook) plantation after continuous N fertilization for 13 years. Methods This study was performed in 25-year-old fir plantation along a fertilization gradient (0, 60, 120, and 240 kg N ha −1  yr. −1 ), designated as N0, N1, N2, and N3, respectively. Soil microbial properties, including the microbial community composition, as revealed by phospholipid fatty acids (PLFAs), and soil enzyme activities (i.e., sucrase, urease and catalase) were measured, and soil elemental stoichiometry was calculated based on soil C, N, and P concentrations. A redundancy analysis (RDA) was conducted to determine the relationship between soil C:N:P stoichiometry and soil microbial properties. Results Compared with the control (N0), N fertilization decreased the total PLFAs (−12.20%), bacteria (−14.33%), fungi (−12.97%), and actinomycetes (−17.11%) on average. Sucrase, urease and catalase activities were enhanced by low and middle levels of N (N1 and N2), but not with high level of N (N3). Long-term N fertilization decreased soil pH, C to N ratio (C/N), and C to P ratio (C/P), while increased soil C, N and N to P ratio (N/P). The RDA identified the first two axes of soil stoichiometry variation that explained 20.4% of the variation at the soil depth of 0–20 cm, 28.6% at 20–40 cm and 49.9% at 40–60 cm in PLFAs biomarkers and enzymes, respectively. Significant correlations between soil stoichiometry (soil N/P and C/P ratio) and soil microbial properties were found in this study. Conclusions These observations suggested that long-term N fertilization influenced soil microbial community composition and enzyme activities by changing the soil C/P and N/P ratios. Future studies are needed to consider the coupling relationships between soil microbial community composition, enzyme activities and elemental stoichiometry in different ecosystems under future climatic change.

Crop residue quality and quantity have contrasting effects on soil organic matter (SOM) decomposition, but the mechanisms explaining such priming effect (PE) are still elusive. To reveal the role of residue quality and quantity in SOM priming, we applied two rates (5.4–10.8 g kg −1 ) of 13 C-labeled wheat residues (separately: leaves, stems, roots) to soil and incubated for 120 days. To distinguish PE mechanisms, labeled C was traced in CO 2 efflux and in microbial biomass and enzyme activities (involved in C, N, and P cycles) were measured during the incubation period. Regardless of residue type, PE intensity declined with increasing C additions. Roots were least mineralized but caused up to 60% higher PE compared to leaves or stems. During intensive residue mineralization (first 2–3 weeks), the low or negative PE resulted from pool substitution. Thereafter (15–60 days), a large decline in microbial biomass along with increased enzyme activity suggested that microbial necromass served as SOM primer. Finally, incorporation of SOM-derived C into remaining microbial biomass corresponded to increased enzyme activity, which is indicative of SOM cometabolism. Both PE and enzyme activities were primarily correlated with residue-metabolizing soil microorganisms. A unifying model demonstrated that PE was a function of residue mineralization, with thresholds for strong PE increase of up to 20% root, 44% stem, and 51% leaf mineralization. Thus, root mineralization has the lowest threshold for a strong PE increase. Our study emphasizes the role of residue-feeding microorganisms as active players in the PE, which are mediated by quality and quantity of crop residue additions.

Untreated wastewater carries substantial amount of heavy metals and causes potential ecological risks to the environment, food quality, and soil health. The pot study was established to evaluate the effectiveness of woodchip-derived biochar (BC) on rapeseed biomass, photosynthetic pigments, antioxidant enzyme activities, such as peroxidase (POD), ascorbate peroxidase (APX), polyphenol peroxidase (PPO), catalase enzyme (CAT), and heavy metal-induced phytotoxicity under untreated domestic (DWW) and industrial (IWW) wastewater irrigation. Biochar was applied at three levels (0, 1, and 2%) combined with DWW and IWW treatments. Wastewater analysis indicated higher heavy metal concentrations than the safer limits set by FAO. Results revealed that DWW and IWW treatments without biochar incorporation adversely affected the rapeseed growth performance, photosynthetic pigments, and antioxidative defense system. Compared with DWW and IWW treatments, BC at 2% rate significantly enhanced shoot fresh biomass (41% and 72%), root fresh biomass (34% and 62%), total chlorophyll (79% and 85%), total pigments (77% and 108%), carotenoids (74% and 94%), and lycopene concentration (43% and 61%), respectively. In addition, BC also improved the antioxidant enzymes activities by reducing the heavy metal-induced oxidative stress in rapeseed leaves. Similarly, AB-DTPA extractable Cd was decreased by (44% and 26%), Pb (51% and 54%), Ni (59% and 56%), and Cu (45% and 41%) in soil when BC was applied at 2% application rate along with DWW and IWW treatments and thereby reduced their uptake in shoots and roots of rapeseed. Therefore, BC can be considered an efficient strategy to ameliorate the hazardous effects of untreated DWW and IWW wastewater and to enhance rapeseed biomass, physiological attributes, and antioxidant enzyme activities.

Aims The conservation tillage i.e. reduced tillage (incl. no tillage and minimum tillage) and straw return, plays an important role in the promotion of sustainable agriculture. However, comprehensive cognition is still weak on how conservation tillage improves soil. Methods Here, we collected 7613 paired observations from 308 publications to reveal the improvement of soil by conservation tillage in perspective of coupled soil nutrients and soil functional enzyme activities. Results (1) Conservation tillage had positive effect on soil organic matter, total nitrogen, total phosphorus, total potassium, dissoluble organic carbon, available nitrogen, ammonium nitrogen, available phosphorus, available potassium, microbial carbon, and microbial nitrogen (7.44–30.56%) via promoting soil enzyme activity, while significantly reduced nitrate nitrogen (-11.55%), and this effect was more concentrated in soil surface. (2) The accumulation of soil nutrients under conservation tillage was closely related to the soil functional enzyme activities with slope ranges from -0.07 to 0.94. The complexity of coupling and cycling among soil elements caused single soil functional enzyme and the accumulation of multiple nutrients were intensively related. (3) Soil depth contributes to differentiation of soil nutrients accumulation and is influenced by the type of tillage and crop. Besides, geography, climate and initial soil properties had limited moderating effects on nutrient response to conservation tillage. Conclusions Overall, conservation tillage promotes nutrient accumulation by improving the soil biochemical environment to enhance soil enzyme activity. This could effectively improve soil fertility and biochemical environment for sustainable agricultural development. The research could provide valuable references for sustainable agricultural management.