The research was led by Erica J. Prentice of Te Aka Mātuatua School of Science at the University of Waikato, together with Vickery L. Arcus and Louis A. Schipper of the same institution, and Charlotte J. Alster of the Department of Soil and Physical Sciences at Lincoln University. Working at a field site on a golf course at Arikikapakapa, near the geothermal heartland of Rotorua, the team took advantage of a remarkable natural experiment: soils that have been sitting at different mean annual temperatures for more than twenty years, not because of a laboratory manipulation, but because of the steady, spatially variable heat rising from the Earth below. This kind of long-term geothermal gradient is highly prized by soil scientists precisely because it allows them to ask whether microbial communities adapt to sustained warming in ways that short-term laboratory experiments simply cannot capture.

The focus of the study was extracellular enzyme activity, a critical but often overlooked stage in the decomposition cascade. Soil microbes cannot directly swallow the large, complex molecules that make up dead plant and microbial material. Instead, they invest energy in secreting enzymes into the surrounding soil, where those proteins cleave polymers into small, soluble units that can be transported into microbial cells. Three enzyme classes were measured in the new work: β-glucosidases, which break down cellulose-derived sugars; β-N-acetylglucosaminidases, which target chitin-like nitrogen-containing compounds; and phosphatases, which liberate phosphate from organic molecules. Because these enzymes perform the substrate-acquisition step of decomposition, their temperature sensitivity effectively sets the pace at which nutrients and carbon become available to the rest of the soil food web.

To characterize the thermal responses, the researchers incubated soils collected from across the gradient and measured enzyme activities across a broad range of assay temperatures, extending up to 60 degrees Celsius. Rather than fitting the data to a simple bell curve, the team quantified key parameters of the thermal performance profile: the activation energy, which describes how steeply activity rises with temperature at low temperatures; the curvature of the response; and both the minimum and optimum temperatures of activity. These parameters matter because thermal adaptation theory makes specific predictions about them. If microbial communities adapt to warmer conditions, their enzymes should, in principle, shift their thermal optima upward, and their activity curves should adjust in ways that reflect a physiology tuned to the prevailing temperature regime.

What the team actually found was striking. Across the entire long-term gradient, enzyme thermal responses showed increasing rates of activity all the way up to the highest characterized temperature of 60 degrees Celsius, regardless of the mean annual soil temperature at which the communities had been living. The parameters that theory says should shift under adaptation—activation energy, curvature, the optimum and minimum temperatures of activity—showed minimal change across the gradient. In other words, enzymes collected from soils that have been warm for decades behaved, thermally, much like enzymes from cooler soils only meters away. There was no measurable upward shift in thermal optima, no flattening of the temperature response, no evidence that decades of sustained warmth had sculpted the catalytic machinery of decomposition into a heat-tuned form.

The surprise deepens when these results are set against earlier work at the same site. Previous measurements of soil respiration and microbial growth along the same geothermal gradient had told a very different story. Respiration and growth, the processes by which microbes convert acquired substrates into carbon dioxide, energy, and new biomass, showed optimum temperatures of activity around 30 to 45 degrees Celsius, well below the assay ceiling used for the enzymes. More importantly, those processes displayed clear, measurable rates of thermal adaptation across the gradient: microbial communities in warmer soils had shifted their respiratory and growth responses in ways consistent with long-term acclimatization. The new enzyme data therefore reveal a fundamental divergence within a single soil ecosystem between the thermal behavior of substrate acquisition and the thermal behavior of substrate utilization.

This divergence is not merely a technical curiosity. It strikes at the heart of how scientists model soil carbon feedbacks under climate change. Most Earth system models treat decomposition as a single temperature-sensitive process, implicitly assuming that the different steps—enzyme-catalyzed depolymerization, microbial uptake, respiration, and growth—respond to temperature in a coordinated way. If, instead, the acquisition step remains poised for ever-increasing rates up to 60 degrees Celsius while the utilization step peaks and adapts at much lower temperatures, then sustained soil warming could decouple the two. Enzymes might liberate carbon and nutrients from organic matter faster than microbes can process them, or faster than the microbial biomass can be maintained, with unpredictable consequences for nutrient bioavailability, carbon storage, and the balance of greenhouse gas fluxes from soils.

The authors point out that understanding these processes has long been hampered by the sheer complexity and variability of soil systems, and by inconsistencies in the methodologies used to quantify microbial thermal adaptation. Different studies measure different endpoints—respiration, growth, enzyme activity, community composition—over different timescales, and short-term assays can be confounded by the immediate effects of changing temperature on existing enzymes rather than on the organisms that produce them. The geothermal gradient approach sidesteps one of the central difficulties: by sampling soils that have experienced different temperatures for over twenty years in situ, the researchers could look for adaptation that reflects genuine, long-term evolutionary and community-assembly processes rather than transient physiological adjustment.

The study also speaks to a long-running debate in thermal biology about the extent to which enzyme thermal properties constrain the organisms that depend on them. One influential framework holds that the temperature dependence of microbial growth is ultimately dictated by the thermodynamics of the enzymes themselves, so that adaptation of growth should be mirrored by adaptation of key enzymes. The new results challenge that expectation in soil systems: growth and respiration adapted, but the extracellular enzymes upstream of them apparently did not. Whether this reflects the fact that the enzymes were assayed outside their cellular context, that different microbial taxa with different enzyme variants dominate different temperature zones, or that enzyme production rather than enzyme catalysis is what adapts, remains an open question that the authors’ findings are likely to stimulate considerable follow-up work on.

The practical implications for future soil warming are significant. Soils worldwide hold vast reserves of organic carbon, and the rate at which microbes decompose that material is a key uncertainty in climate projections. If extracellular enzymes maintain rising activity with warming, up to surprisingly high temperatures, while the microbial processes that consume the released substrates slow or adapt downward, the resulting imbalance could alter both the timing and the form of carbon loss from soils. Nutrients such as nitrogen and phosphorus, whose availability depends on enzymatic release, might be liberated at rates that outstrip biological demand, potentially increasing leaching losses or shifting competition among soil organisms. Conversely, the apparent robustness of enzyme thermal profiles might, in some scenarios, buffer decomposition against temperature change in ways not captured by current models.

The study is also a reminder of the value of unusual natural settings for fundamental science. The Arikikapakapa site, better known to golfers than to most climate scientists, provided precisely the combination of long-term temperature differences, shared parent material, vegetation, and climate history that controlled experiments struggle to achieve. The authors acknowledge the groundskeeping team at the golf course for their continued support and access, and Seager Ray for sample collection. The work was supported by the Marsden Fund of New Zealand under grant number 19-UOW-035, with open access funding enabled and organized by CAUL and its member institutions.

As the authors note in their published abstract, the divergence between the thermal response of extracellular enzyme activity and that of respiration and growth “raises questions around future nutrient bioavailability and utilisation if these two processes are decoupled at elevated temperatures under future soil warming.” Those questions are now likely to move to the center of soil biogeochemistry research. If the enzymes that unlock soil organic matter are largely indifferent, in their thermal tuning, to two decades of warming, while the microbes that depend on them continue to adapt, then the assumption that soil carbon cycling responds to temperature as a unified process may need serious revision. For a planet whose soils are steadily warming, that revision could matter a great deal.

The research, published in Plant and Soil, examined plantations of Populus × euramericana cultivar ‘74/76’ using a framework called the random structural unit. Each unit consists of one reference tree and its four nearest neighbours. Researchers assessed the angles formed between those neighbouring trees around the reference tree. A unit is classified as random when two consecutive angles are smaller than 72 degrees and two are 72 degrees or larger. The geometry can produce two contrasting patterns. In a “dumbbell” configuration, the smaller and larger angles alternate around the reference tree; in a “torch” configuration, the two smaller angles and the two larger angles occur in adjacent pairs. These patterns turn an abstract description of forest structure into a measurable spatial signature.

The team studied 15 plots divided among five plantation arrangements, with three plots representing each treatment. The control, designated CK, had no random structural units and represented a regular planting pattern. The other treatments contained random units at proportions of 80 percent, 75 percent, 60 percent and 63 percent, labelled HR, MHR, MR1 and MR2, respectively. HR, MHR and MR1 were dominated by dumbbell-shaped units, while MR2 was dominated by torch-shaped units. This design allowed the researchers to examine two questions at once: whether the amount of spatial randomness affects soil functioning, and whether the specific geometry of that randomness matters.

To determine how the different layouts influenced the soil ecosystem, the researchers measured nutrients, microbial biomass, enzyme activity and microbial community characteristics. Soil microbial biomass carbon served as an indicator of the living microbial pool—the bacteria, fungi and other microscopic organisms responsible for decomposing organic matter and transforming nutrients. They also calculated the microbial quotient, which relates microbial biomass carbon to total soil organic carbon and can indicate how much of the soil’s carbon is held in living microbial tissue. Enzymes provided a functional readout: protease helps break down proteins and release nitrogen-containing compounds, while alkaline phosphatase helps liberate phosphorus from organic molecules. Together, these measurements capture not only what is present in the soil, but what the soil’s biological community is doing.

The most pronounced integrated biological responses occurred in the two intermediate treatments, MR1 and MR2. Relative to the regular-pattern control, MR1 had higher microbial biomass carbon, a higher microbial quotient, and greater activities of protease and alkaline phosphatase. The result indicates that the MR1 arrangement supported both a larger or more active microbial community and stronger nutrient-processing capacity. Yet the treatment with the highest proportion of random units did not deliver an additional biological advantage. Increasing randomness beyond the intermediate range therefore appeared to produce diminishing returns, at least under the conditions represented by these poplar plots.

The researchers also found evidence linking soil chemistry to the microbial response. Phosphorus and potassium were associated with microbial biomass, suggesting that the availability or distribution of these nutrients helped shape the size of the soil microbial community. Bacterial richness and the relative presence of Acidobacteria were associated with microbial biomass and protease activity. Acidobacteria is a broad bacterial group frequently detected in soils, with members adapted to diverse conditions and involved in carbon and nutrient transformations. The study does not establish that these bacteria directly caused the enzyme changes, but the relationships point to a coordinated system in which tree arrangement, soil nutrients and microbial communities interact.

To analyse those relationships, the authors used redundancy analysis and partial least-squares structural equation modelling. Redundancy analysis is an ordination method that estimates how much variation in a community or response dataset can be related to measured environmental variables. Partial least-squares structural equation modelling, or PLS-SEM, is used to test networks of direct and indirect associations among several groups of variables, particularly when the data do not fit the assumptions required by conventional covariance-based models. In this study, the modelling associated random structural units with microbial biomass and connected enzyme activity indirectly through soil nutrients. The proposed pathway is biologically plausible: spatial arrangement alters local conditions such as light penetration, litter distribution, root activity and moisture, which can influence nutrients; those nutrients then affect microbial growth and enzyme production.

The researchers combined these indicators into a soil quality index, or SQI, designed to summarize several dimensions of soil functioning in a single assessment. SQIs typically integrate variables that represent chemical fertility and biological activity, often after standardizing measurements and assigning weights. Here, MR1 received the highest overall soil quality score, and its ranking remained strongest across different weighting approaches. The dumbbell-dominated treatment also had a higher SQI than the torch-dominated treatment, even though the overall composition of structural units differed between them. That comparison suggests that randomness alone is not the key ecological property: how random units are configured may influence the distribution of resources and biological activity within the stand.

The implications extend beyond one plantation experiment. Poplar plantations are widely used for timber production, ecological restoration and land rehabilitation, but regular spacing can simplify the vertical and horizontal structure of a forest. A more varied arrangement may create a mosaic of root zones, litter layers, canopy gaps and microclimates, giving soil organisms a wider range of habitats and substrates. The study suggests that managers should aim to optimize spatial heterogeneity rather than maximize it. However, the evidence comes from 15 plots within a plantation system and identifies associations rather than proving a universal causal rule. Longer-term experiments across soil types, climates, plantation ages and tree species will be needed to determine whether the intermediate optimum persists. Even so, the central message is strikingly simple: when designing forests to function more like natural ecosystems, the best pattern may lie between rigid order and complete disorder.

At the heart of this investigation lies the complex interaction between peat smouldering and soil enzyme activity. Soil enzymes are vital for nutrient cycling, influencing both plant growth and soil structure. When peat burns, whether through natural occurrences or human intervention, it produces smoke that can alter the biochemical environment in which these enzymes function. The study aims to quantify these changes and model the effects of such smoke on soil enzymes globally, filling a critical gap in environmental science.

The researchers used advanced methodologies to evaluate the impact of peat fire smoke on soil microbial communities and enzymatic functions. By conducting controlled experiments that simulate the conditions of smouldering peat fires, they could effectively analyze how these environmental stressors alter soil chemistry. The results show a clear indication that the presence of peat smouldering smoke leads to a significant decline in key soil enzyme activities, particularly those associated with carbon and nitrogen cycling.

An important aspect of the study is its implications for carbon emissions. Peatlands are known to be carbon sinks, storing vast amounts of carbon in their organic matter. However, when they burn, they can release this carbon back into the atmosphere, contributing to climate change. The research illustrates a direct correlation between decreased enzymatic activity due to smouldering smoke and the potential for increased carbon release, raising concerns about the long-term sustainability of peatlands.

Furthermore, the effects of this enzymatic decline extend beyond carbon cycling. The researchers noted that essential functions such as phosphorus availability and organic matter decomposition were also impeded by the smoke. This could lead to a decreased nutrient supply for plants, negatively affecting plant health and biodiversity in ecosystems dependent on these soils. As peatlands cover extensive areas in many regions, the cascading effects on local flora and fauna could be far-reaching.

The involvement of human activities in increasing the frequency and intensity of peat fires cannot be overlooked. Urban expansion, agriculture, and changes in land management practices have significantly exacerbated the prevalence of these fires. Consequently, it becomes imperative that policymakers and land managers consider the findings of this research when developing strategies to mitigate the impacts of peat fires on ecosystem integrity.

Adaptive management practices aimed at preserving peatlands and reducing fire risk are essential. The study emphasizes the necessity of implementing preventative measures to protect these sensitive environments. This includes enhancing the hydrology of peatlands to keep them moist, thereby reducing their flammability. Additionally, the findings reinforce the need for controlled burn practices as a means to manage fuel loads safely and sustainably, rather than allowing uncontrolled smouldering events to occur.

Public awareness and education about the effects of peat fires also play a crucial role in conservation efforts. Engaging local communities in understanding the importance of peatlands can drive grassroots movements aimed at advocating for their protection. Highlighting the interconnectedness of peatland health, climate change, and its impact on local biodiversity can motivate individuals to take action in their spheres of influence.

As climate change continues to amplify the risks associated with peatland fires, ongoing research like that of Nizhelskiy and his colleagues is vital. Their findings set the stage for a more integrated understanding of land management, climate action, and biodiversity conservation. Future research should expand upon these insights, exploring the long-term implications of peatland fire smoke on not only soil enzymatic activity but also the broader ecological processes.

Moreover, while this study lays a solid foundation for understanding the immediate impacts of peat smouldering smoke, there’s a pressing need to investigate the cumulative effects over time. Longitudinal studies could provide clarity on how repeated exposure to fire smoke might permanently alter soil profiles, microbial diversity, and ecosystem resilience. As such, continuous monitoring and research funding should be prioritized for areas at high risk of peat fires.

In conclusion, the study by Nizhelskiy and colleagues represents a significant advance in our understanding of the interplay between peat smouldering smoke and soil health. Given the essential role that soil enzymes play in maintaining ecosystem balance, the insights from this research are crucial. They not only call attention to the immediate consequences of peat fires but also highlight an urgent need for preventative policies and enhanced public awareness to protect these vital ecological resources.

As peatlands play an integral role in carbon sequestration and supporting biodiversity, the findings serve as a clarion call to environmentalists, policymakers, and local communities alike. By fostering an understanding of the implications of peat fires, we can better equip ourselves to combat the multifaceted challenges posed by climate change. The path forward relies on collaborative efforts across disciplines, fostering innovation in land management, and promoting sustainable practices to navigate the complex interplay of fire, smoke, and soil.

In a world where climate dynamics are shifting rapidly, studies like the one conducted by Nizhelskiy et al. are instrumental in guiding our responses to environmental crises. Increased research funding and interdisciplinary collaboration will be indispensable in solving these pressing issues effectively. The conversation about peatlands and their conservation is far from over, and continued research will keep this critical environmental issue at the forefront of climate change discussions.

Subject of Research: Effects of peat smouldering smoke on soil enzymatic activity.

Article Title: Research on the effects of peat smouldering smoke on soil enzymatic activity (modelling of peat fires).

Article References:

Nizhelskiy, M., Kazeev, K., Vilkova, V. et al. Research on the effects of peat smouldering smoke on soil enzymatic activity (modelling of peat fires).
Environ Monit Assess 198, 146 (2026). https://doi.org/10.1007/s10661-026-15019-4

Image Credits: AI Generated

DOI: https://doi.org/10.1007/s10661-026-15019-4

Keywords: peat fires, smouldering smoke, soil enzymatic activity, carbon emissions, climate change, nutrient cycling, environmental science.