Matthew Wallenstein

Colorado State University | CSU · Natural Resource Ecology Laboratory

The adoption of conservation agriculture has gained considerable attention due to growing interest in managing soil biological diversity and overall soil health. However, there is limited understanding of how practices such as conservation tillage and residue retention affect soil biota across different spatial scales and are associated with altera...

Semi-arid regions support the majority of global wheat production, but they are threatened by continued soil erosion and increased risk of drought and extreme temperatures from climate change. Enhancing soil organic matter (SOM) is a key adaptation strategy for sustaining agriculture in these regions because it can improve water retention and nutri...

Soil health is a promising lens through which to approach land management, having the potential to serve as a descriptor of biophysical processes and as an effective communication tool across stakeholders. However, this potential has been largely unrealized due to difficulty in quantitatively assessing soil health and linking those assessments to o...

The dissolved organic matter pool is fundamental to regulating soil properties, but there is currently a limited understanding of its molecular composition due to its complexity. Mass spectrometry-based environmental metabolomics is a promising tool for discerning which components of the dissolved organic matter pool may be relevant for and/or resp...

Plant roots add carbon (C) -rich rhizodeposits to the soil, which can alter microbial activity and nitrogen (N) cycling with implications for N availability and uptake by plants. We evaluated root architecture, rhizodeposit C, and microbial community structure and function across a breeding gradient of twelve winter wheat genotypes and examined how...

Soil organic matter (SOM) plays a central role in mediating soil productivity through its impacts on nutrient cycling and retention, aggregate stability and water retention. Thus, management techniques or technologies including novel soil amendments could benefit farmers through the accumulation of carbon (C) and other nutrients in SOM. However, th...

Soil microbes form complex interactive networks throughout the soil and plant rhizosphere. These interactions can result in emergent properties for consortia that are not predictable from the phenotypes of constituents in isolation. We used a four-species consortium to assess the capacity of individual microbial species versus different consortia p...

Atmospheric CO2 concentration is increasing, largely due to anthropogenic activities. Previous studies of individual free-air CO2 enrichment (FACE) experimental sites have shown significant impacts of elevated CO2 (eCO2) on soil microbial communities; however, no common microbial response patterns have yet emerged, challenging our ability to predic...

To meet the nutritional demands of a rapidly growing population in the face of increasing climate variability, innovative tools are needed to rapidly regenerate soil health in agricultural systems. Using food wastes to improve soil health presents a viable opportunity to improve soils and efficiently manage waste. In a previous laboratory study, we...

Agricultural systems are increasingly managed for improving soil carbon (C) accumulation. However, there are limits to C returns in agricultural systems that constrain soil C accumulation capacity. Increasing the efficiency of how soil microbes process C is gaining interest as an important management strategy for increasing soil C and is a key feat...

The timing and duration of the plant growing season and its period of peak activity have shifted globally in response to climate change. These changes alter the period of maximum and potential total carbon uptake, especially in highly seasonal environments such as the Arctic. Earlier plant growth has been observed, and if plant senescence remains t...

Soil organic matter (SOM) dynamics in ecosystem-scale biogeochemical models have traditionally been simulated as immeasurable fluxes between conceptually defined pools. This greatly limits how empirical data can be used to improve model performance and reduce the uncertainty associated with their predictions of carbon (C) cycling. Recent advances i...

Biogeochemical processing of dissolved organic matter (DOM) in headwater rivers regulates aquatic food web dynamics, water quality, and carbon storage. Although headwater rivers are critical sources of energy to downstream ecosystems, underlying mechanisms structuring DOM composition and reactivity are not well quantified. By pairing mass spectrome...

Permafrost thaw is projected to restructure the connectivity of surface and subsurface flow paths, influencing export dynamics of dissolved organic matter (DOM) through Arctic watersheds. Resulting shifts in flow path exchange between both soil horizons (organic-mineral) and landscape positions (hillslope-riparian) could alter DOM mobility and mole...

Soil microbial communities affect species demographic rates of plants. In turn, plants influence the composition and function of the soil microbiome, potentially resulting in beneficial feedbacks that alter their fitness and establishment. For example, differences in the ability to stimulate soil enzyme activity among plant lineages may affect plan...

Soil organic matter (SOM) dynamics in ecosystem-scale biogeochemical models have traditionally been simulated as immeasurable fluxes between conceptually-defined pools. This greatly limits how empirical data can be used to improve model performance and reduce the uncertainty associated with their predictions of carbon (C) cycling. Recent advances i...

Translating the ever-increasing wealth of information on microbiomes (environment, host or built environment) to advance our understanding of system-level processes is proving to be an exceptional research challenge. One reason for this challenge is that relationships between characteristics of microbiomes and the system-level processes that they i...

The structure and function of soil microbiomes often change in response to experimental climate manipulations, suggesting an important role in ecosystem feedbacks. However, it is difficult to know if microbes are responding directly to environmental changes or are more strongly impacted by plant responses. We investigated soil microbial responses t...

Greenhouse gas (GHG) emissions from thawed permafrost are difficult to predict because they result from complex interactions between abiotic drivers and multiple, often competing, microbial metabolic processes. Our objective was to characterize mechanisms controlling methane (CH4) and carbon dioxide (CO2) production from permafrost. We simulated pe...

Plants co-evolved with microbes, and plant genotypes that supported microbiomes that increased their own health likely had a fitness advantage under natural selection. Plant domestication and crop breeding under fertilization have largely decoupled the rhizosphere microbiome from plant selection. If important interactions have been lost as a result...

It is becoming increasingly clear that plant roots can impact the decomposition of existing soil C in the rhizosphere. Studies under controlled conditions suggest this impact may be plant-species dependent, but whether this is the case in natural conditions or what factors underlie this variation is mostly unknown. 2.With a novel field-based isotop...

Soil organic matter (SOM) is extremely complex. It is composed of hundreds of different organic substances and it has been difficult to quantify these diverse substances in a dynamic- ecosystem functioning standpoint.Analytical pyrolysis has been used to compare chemical differences between soils, but its ability to measure the absolute amount of a...

The activity of soil microbial extracellular enzymes is strongly controlled by temperature, yet the degree to which temperature sensitivity varies by microbe and enzyme type is unclear. Such information would allow soil microbial enzymes to be incorporated in a traits-based framework to improve prediction of ecosystem response to global change. If...

Phosphorus (P) is a critical nutrient used to maximize plant growth and yield. Current agriculture management practices commonly experience low plant P use efficiency due to natural chemical sorption and transformations when P fertilizer is applied to soils. A perplexing challenge facing agriculture production is finding sustainable solutions to de...

Raw data table Detailing the data collected from the different greenhouse experiments.

There is compelling evidence that microbial communities vary widely in their temperature sensitivity and may adapt to warming through time. To date, this sensitivity has been largely characterized using a range of models relying on versions of the Arrhenius equation, which predicts an exponential increase in reaction rate with temperature. However,...

Climate change over the past ∼50 years has resulted in earlier occurrence of plant life cycle events for many species. Across temperate, boreal and polar latitudes, earlier seasonal warming is considered the key mechanism leading to earlier leaf expansion and growth. Yet, in seasonally snow-covered ecosystems, the timing of spring plant growth may...

Soil organic matter is critical to sustainable agriculture because it provides nutrients to crops as it decomposes and increases nutrient- and water-holding capacity when built up. Fast- and slow-cycling fractions of soil organic matter can have different impacts on crop production because fast-cycling fractions rapidly release nutrients for short-...

Global agricultural productivity may be constrained by the finite and limited supply of phosphorus (P), adding to the challenges in meeting the projected needs of a growing human population in the coming decades. In addition, when P fertilizers are added to soils, they can become bound to soils resulting in low fertilizer efficiency. However, P-mob...

Global agricultural productivity may be constrained by the finite and limited supply of phosphorus (P), adding to the challenges in meeting the projected needs of a growing human population in the coming decades. In addition, when P fertilizers are added to soils, they can become bound to soils resulting in low fertilizer efficiency. However, P-mob...

Climate change is altering the timing and magnitude of biogeochemical fluxes in many highelevation ecosystems. The consequent changes in alpine nitrification rates have the potential to influence ecosystem scale responses. In order to better understand how changing temperature and moisture conditions may influence ammonia oxidizers and nitrificatio...

A major goal of microbial ecology is to identify links between microbial community structure and microbial processes. Although this objective seems straight forward, there are conceptual and methodological challenges to designing studies that explicitly evaluate this link. Here, we analyzed literature documenting structure and process responses to...

Legacy phosphorus (P) that has accumulated in soils from past inputs of fertilizers and manures is a large secondary global source of P that could substitute manufactured fertilizers, help preserve critical reserves of finite phosphate rock to ensure future food and bioenergy supply, and gradually improve water quality. We explore the issues and ma...

Although elevated CO2 (eCO2 ) significantly affects the α-diversity, composition, function, interaction and dynamics of soil microbial communities at the local scale, little is known about eCO2 impacts on the geographic distribution of microorganisms regionally or globally. Here we examined the β-diversity of 110 soil microbial communities across s...

Previously-frozen stores of organic carbon (C) are now subject to decomposition due to a warming Arctic climate and associated permafrost thaw; however, estimates of the amount of greenhouse gases (GHG) that may be released are not well constrained. Knowing more about the functions of the extant permafrost microbial community will inform this knowl...

Although permafrost soils contain vast stores of organic C, relatively little is known about the chemical composition of their constituent soil organic matter (SOM). Mineral permafrost and organic (OAL) and mineral active layer (MAL) soils from Sagwon Hills, AK were analyzed for total C and N content and SOM chemical composition using Fourier trans...

Increased plant productivity and decreased microbial respiratory C loss can potentially mitigate increasing atmospheric CO2, but we currently lack effective means to achieve these goals. Soil microbes may play critical roles in mediating plant productivity and soil C/N dynamics under future climate scenarios of elevated CO2 (eCO2) through optimizin...

Molecular ecology is poised to tackle a host of interesting questions in the coming years. The Arctic provides a unique and rapidly changing environment with a suite of emerging research needs that can be addressed through genetics and genomics. Here we highlight recent research on boreal and tundra ecosystems, and put forth a series of questions r...

Declining rates of soil respiration are reliably observed during long-term laboratory incubations. However, the cause of this decline is uncertain. We explored different controls on soil respiration to elucidate the drivers of respiration rate declines during long-term soil incubations. Following a long-term (707 day) incubation (30 °C) of soils fr...

For any enzyme-catalyzed reaction to occur, the corresponding protein-encoding genes and transcripts are necessary prerequisites. Thus, a positive relationship between the abundance of gene or transcripts and corresponding process rates is often assumed. To test this assumption, we conducted a meta-analysis of the relationships between gene and/or...

The pool of soil organic carbon (SOC) in the Arctic is disproportionally large compared to those in other biomes. This large quantity of SOC accumulated over millennia due to slow rates of decomposition relative to net primary productivity. Decomposition is constrained by low temperatures and nutrient concentrations, which limit soil microbial acti...

Background/Question/Methods Plant rhizospheres are considered ‘hot zones’ where carbon released from roots is quickly assimilated by soil microbes, consequently influencing microbial community assemblages as well as microbial C, N and P enzyme acquisition activities. However, the specific mechanisms used by plants to induce shifts in rhizosphere...

Background/Question/Methods Warming temperatures at northern latitudes are extending the period of favorable conditions for plant growth. Earlier snowmelt and later snowfall are occurring, but to what extent will plant species take advantage of extension in the snow-free season? Across northern latitudes, the timing of leafing and flowering is oc...

Background/Question/Methods The primary drivers of belowground activity, like water availability and temperature, may also impose strong indirect influences on soil function through altered plant chemistry. Studies already investigate the direct impacts of forecasted climate change on soil function, but it is unclear to what extent future climate...

Background/Question/Methods While it is understood that plants and particularly roots can alter soil organic matter dynamics, with potential impacts on the ecosystem’s C balance, we have little understanding of how variation in plant traits drives this response. In the available literature, observed indications of soil organic matter enhancement...

Background/Question/Methods The use of functional traits to link species composition and community function is an increasingly popular approach in ecological research, but tends to focus on species means and ignore important variation around those means. Furthermore, most research has emphasized the impact of aboveground traits, despite burgeonin...

Both biogeographical and rainfall manipulation studies show that soil water content can be a strong driver of microbial community composition. However, we do not yet know if these patterns emerge because certain bacterial taxa are better able to survive at dry soil moisture regimes or if they are due to other drought-sensitive ecosystem properties...

Global climate change is already having significant impacts on arctic and alpine ecosystems, and ongoing increases in temperature and altered patterns of precipitation will affect the strong seasonal patterns that characterize these temperature-limited systems. The length of the potential growing season in these tundra environments is increasing du...

Soil carbon stabilization is known to depend in part on its distribution in structural aggregates, and upon soil microbial activity within the aggregates. However, the influence of climate change on continued soil C storage within aggregates of different size classes is unknown. In this study, we applied a modified drysieving technique to separate...

Climate change will affect the biogeochemical processes driven by the complex microbial communities that inhabit soils. Microbial responses to climate change can result in both negative and positive feedbacks through soil decomposition and the release of CO2 and CH4 to the atmosphere. While the relationships between temperature and moisture with th...

The timing and magnitude of rainfall events are expected to change in future decades, resulting in longer drought periods and larger rainfall events. Although microbial community composition and function are both sensitive to changes in rainfall, it is unclear whether this is because taxa adopt strategies that maximise fitness under new regimes. We...

Microbes in soils and other environments produce extracellular enzymes to depolymerize and hydrolyze organic macromolecules so that they can be assimilated for energy and nutrients. Measuring soil microbial enzyme activity is crucial in understanding soil ecosystem functional dynamics. The general concept of the fluorescence enzyme assay is that sy...