Timothy Filley

Purdue University | Purdue · Department of Earth, Atmospheric Sciences, and Planetary Sciences

Intensive row crop agriculture on loess mantled hillslopes in the upper Midwest, USA, accelerates soil erosion and the loss of organic matter by increasing soil aggregate breakdown, changing surface roughness patterns, and leaving soil exposed to rainfall and wind for much of the year. There is a knowledge gap, however, in relating how the dynamics...

Analysis of historic and contemporary high-resolution imagery can help to fill knowledge gaps in land cover and management history in locations where documentation is non-existent or records are difficult to access. Historic imagery dating back to the 1960s can be used to structure quantitative investigation and mapping of land use and land cover c...

Management of crop production using plastic film mulching (PFM) has the potential to improve soil health by accelerating nutrient cycling and facilitating stable C pool production; however, a key aspect of this process—microbial immobilization of residue C—is poorly understood, especially under PFM when combined with different fertilization treatme...

In temperate deciduous forests of eastern USA, most earthworm communities are dominated by invasive species. Their structure and functional group composition have critical impacts on ecological properties and processes. However, the factors determining their community structure are still poorly understood, and little is known regarding their dynami...

Tree taxa and pyrolysis temperature are the major controllers of the physicochemical properties of the resultant pyrogenic organic matter (PyOM) produced in fire-prone forests. However, we know little about how these controls determine the residence time of PyOM once introduced to soil. In this study, we tracked the fate of 13C-enriched red maple (...

Few studies have quantitatively assessed the interacting controls of taxa-specific properties and PyOM production temperature on native soil C (NSC) stabilization/de-stabilization dynamics (i.e. priming effects - PE) because of difficulty in distinctly assessing NSC reactivity apart from added PyOM-C. To quantify PyOM-induced PE, we incubated ¹³C-e...

Expansion and intensification of managed landscapes for agriculture have resulted in severe unintended global impacts, including degradation of arable land and eutrophication of receiving water bodies. Modern agricultural practices rely on significant direct and indirect human energy inputs through farm machinery and chemical use, respectively, whi...

Highlights This work utilizes “multi-stage pulse labeling” ¹⁵N applications, primarily during reproductive growth stages, as a phenotyping strategy to identify maize hybrids with superior N use efficiency (NUE) under low N conditions. Research using labeled isotopic N (¹⁵N) can precisely quantify fertilizer nitrogen (N) uptake and organ-specific N...

The surface chemistry of pyrogenic organic matter (PyOM) is altered by a variety of abiotic and biotic oxidative and sorption/desorption processes in the environment. Exposure of PyOM to high energy light prior to addition to soil or sediment, or while entrained in the atmosphere, may induce significant surface photooxidation, i.e., photochemical w...

To test the impact of a range of long-term land use types on the partitioning of microbial residues among soil particles, samples from a Mollisol with plots under 100 years of continuous arable cropping, 30 years of simulated overgrazing to severely degraded bare soil, or 30 years of grassland restoration were investigated. The microbial residues,...

The environmental fate of functionalized carbon nanomaterials (CNM) remains poorly understood. Using 13C-labeled nanomaterial we present the results of a study investigating the mineralization and microbial uptake of surface-functionalized C60 (fullerols) in agricultural soils with contrasting properties. Soil microcosms rapidly mineralized fullero...

While soil organic carbon (SOC) accumulation and stabilization has been increasingly the focus of ecosystem properties, how it could be linked to soil biological activity enhancement has been poorly assessed. In this study, topsoil samples were collected from a series of rice soils shifted from salt marshes for 0, 50, 100, 300 and 700 years from a...

We know little about how shifts in tree species distribution and increases in forest fire intensity could affect the formation of pyrogenic organic matter (PyOM) or charcoal, one of the most important and persistent soil organic matter pools. This limitation arises partly because the role of the precursor wood in controlling PyOM formation is uncle...

Aims Woody encroachment and subsequent brush management aimed at reducing woody plant cover can alter soil organic carbon (SOC) pools. However, brush management influences on the sources and stability of SOC is unknown. Using a space-for-time approach in a site with closely co-located patches representing unencroached grassland, woody encroachment,...

East African climate change since the Late Miocene consisted of persistent shorter-term, orbital-scale wet-dry cycles superimposed upon a long-term trend towards more open, grassy landscapes. Either or both of these modes of palaeoclimate variability may have influenced East African mammalian evolution, yet the interrelationship between these secul...

Analytical techniques to assess the degree of alteration of pyrogenic black carbon (C) in soils and sediments are needed to gauge the role of environment and time in the dynamics of this stable carbon form. The benzenecarboxylic acids (BnCA, with n = number of carboxylic groups) and naphthalene analogues (NnCA) released by thermally assisted hydrol...

Woodland encroachment into grasslands is a globally pervasive phenomenon attributed to land use change, fire suppression, and climate change. This vegetation shift impacts ecosystem services such as ground water allocation, carbon (C) and nutrient status of soils, aboveground and belowground biodiversity, and soil structure. We hypothesized that wo...

While carbon stabilization had been increasingly concerned as ecosystem properties, the link between carbon stabilization and soil biological activity had been yet poorly assessed in soil dynamics of carbon and aggregation. In this study, topsoil samples were collected from rice soils derived from salt marsh under different lengths of rice cultivat...

The addition of pyrogenic organic matter (PyOM), the aromatic carbon-rich product of the incomplete combustion of plant biomass or fossil fuels, to soil can influence the rate of microbial metabolism of native soil carbon. The interaction of soil heterotrophs with PyOM may be governed by the surficial chemical and physical properties of PyOM that e...

Most available biogeochemical models focus within a soil profile and cannot adequately resolve contributions of the lighter size fractions of organic rich soils for Enrichment Ratio (ER) estimates, thereby causing unintended errors in Soil Organic Carbon (SOC) storage predictions. These models set ER as constant, usually equal to unity. The goal of...

The factors regulating soil animal communities are poorly understood. Current theory favors niche complementarity and facilitation over competition as the primary forms of non- trophic interspecific interaction in soil fauna; however, competition has frequently been suggested as an important community- structuring factor in earthworms, ecosystem en...

The U.S.-China EcoPartnership for Environmental Sustainability (USCEES), one of 30 EcoPartnerships, was established within the U.S.-China Strategic Economic Dialogue framework in May 2011 by a joint agreement between the U.S. Department of State and China's National Development and Reform Commission. The USCEES has the goal of fostering bi-nat...

Elevated nitrogen (N) deposition has the potential to increase litter and soil carbon (C) storage by suppressing lignolylic activity, but reports of the response of forest floor and soil have shown inconsistent responses. We investigated organic carbon and nitrogen as well as lignin phenols and substituted fatty acids (SFA) in forest floor litter a...

Carbon isotope (δ13C) compositions of total organic carbon (TOC) as well as several extracted higher plant derived lignin biomarkers, along with the recovery of grass phytoliths, provide the first direct evidence of existence of extensive grass land (C4) vegetation over the Ganges deltaic plain during the Last Glacial Maximum (LGM). The earliest Ho...

Efforts have been made in numerous studies to better understand N dynamics to increase corn yields and N efficiency, but most often it is not possible to separate the uptake of indigenous soil- versus fertilizer-derived N over time. The approach of using a “pulse-labeled N” technique provides potentially more accurate information about the fate of...

Pyrolysis molecular-beam mass spectrometry (PyMBMS) was tested as a high-throughput method for relative abundances of guaiacyl and syringyl lignin in lignocellulosic cell-wall materials from stems of a population of maize intermated B73 x Mo17 (IBM) recombinant inbred lines. Variations of up to twofold across the population in phenylpropanoid abund...

Background/Question/Methods In temperate soils, earthworms are the most significant ecosystem engineers. Recent studies of North American earthworms focusing on invasive European species have demonstrated that by consuming leaf litter and soil organic matter, invasive European earthworms redistribute nutrients in different pools in the soil and a...

Although carbon nanomaterials such as single-walled carbon nanotubes (SWCNT) are becoming increasingly prevalent in manufacturing, there is little knowledge on the environmental fate of these materials. Environmental degradation of SWCNT is hindered by their highly condensed aromatic structure as well as the size and aspect ratio, which prevents in...

Current carbon cycle-climate models predict that future soil carbon storage will be determined by the balance between CO2 fertilization and warming. However, it is uncertain whether greater carbon inputs to soils with elevated CO2 will be sequestered, particularly since warming hastens soil carbon decomposition rates, and may alter the response of...

As human activities have intensified along tropical coastlines, the anthropic influence on adjacent coral reefs has become increasingly deleterious. Changes in land use generally degrade water quality, but controversy persists over the degree to which reduced water quality affects the ecology of reef communities. We cored reef frameworks at 4 sites...

Background and aims: Previous studies have demonstrated positive net primary production effects with increased nitrogen (N) and water availability in Inner Mongolian semi-arid grasslands. However, the responses of soil carbon (C) and N concentrations and soil enzyme activities as indicators of impacts of long-term N (urea) and water addition are st...

Elevated atmospheric CO 2 concentrations can change chemistry and input rate of plant tissue to soil, potentially influencing above‐ and below‐ground biogeochemical cycles. Given the important role played by leaf and root litter chemistry in controlling ecosystem function and vulnerability to environmental stresses, we investigated the hydrolyzable...

Soil organic carbon (SOC) in permafrost terrain is vulnerable to climate change. Perennially frozen peat deposits store large amounts of SOC, but we know little about its chemical composition and lability. We used plant macrofossil and biomarker analyses to reconstruct the Holocene paleovegetation and paleoenvironmental changes in two peat plateau...

In this study, we examined the response of surface soils to increased leaf and wood litter input within adjacent successional forests recovering from agricultural disturbance at the Smithsonian Environmental Research Center (SERC), Maryland, USA. Previous studies at this site demonstrated an arrested development of O-horizon, even after 130 years o...

Dissolved organic matter (DOM) plays a fundamental role for many soil processes. For instance, production, transport, and retention of DOM control properties and long-term storage of organic matter in mineral soils. Production of water-soluble compounds during the decomposition of plant litter is a major process providing DOM in soils. Herein, we e...

Pyrogenic organic matter (PyOM or biochar) is the product of the incomplete combustion of biomass. A better understanding of the microbial-mediated degradation of PyOM is critical to assess its role in soil C sequestration and to serve as an agricultural amendment. Recent studies have shown that PyOM additions can prime native soil C but results ha...

Fire is a major controller of forest C cycling by releasing CO 2 to the atmosphere and by contributing pyrogenic organic matter (PyOM or biochar) to soils. Recent studies have shown that much of fire-derived PyOM may turn over in soils at century time scales. Two likely controllers of the chemical structure of PyOM and its resulting decay rate are...

Pyrogenic organic carbon (PyOM) is the carbon-rich product of incomplete combustion of fossil fuel, or biomass, such as wood, manure, or leaves. The PyOM particles suspend in the atmosphere and stay airborne for days to weeks when they could possibly be photolyzed by ultraviolet (UV) in sunlight. Accessibility of photolyzed PyOM to microorganisms i...

Brown rot fungi are theorized to use both free radicals and enzymes to degrade wood. If these incompatible agents are employed in sequence (enzymatic after oxidative) in order to avoid interaction, this should be resolvable spatially in rotting wood. To assess this, we used thin spruce wafers as substrates, with the largest face the transverse plan...

Background/Question/Methods Elevated nitrogen (N) deposition has the potential to increase soil carbon (C) storage. Nonetheless, how N fertilization would influence biochemical composition of organic matter is still not well understood. It has been reported variable responses, indicating that N addition might suppress, increase, or have no signif...

The chemistry and physical association of soil organic matter in the patchwork of successional forest stands in the eastern US is strongly controlled by past land use. Invasive earthworm activity in these same systems, however, may impart a chemical and physical disturbance exceeding that of land use legacy. We established eight plots within forest...

Dissolved organic matter (DOM) is one of the most dynamic carbon pools linking the terrestrial with the aquatic carbon cycle. Besides the insecure contribution of terrestrial DOM to the greenhouse effect, DOM also plays an important role for the mobility and availability of heavy metals and organic pollutants in soils. These processes depend very m...

Up to 50% of organic C and 80% of organic N within soil can exist as amino acids, amino sugars and carbohydrates. To determine how potential microbial accessibility and turnover of these compounds is impacted by encroachment of woody plants into grasslands, we investigated changes in evolved CO2 during thermal analysis and in carbohydrate and amino...

Future rates of atmospheric N deposition have the potential to slow litter decay and increase the accumulation of soil organic matter by repressing the activity of lignolytic soil microorganisms. We investigated the relationship between soil biochemical characteristics and enzymatic responses in a series of sugar maple (Acer saccharum)-dominated fo...

Tillage practices affect soil microorganisms, which in turn influence many processes essential to the function and sustainability of soil. In this study, the changes in soil microbial biomass and community composition in response to conventional tillage (CT, moldboard plowing and post-harvest residue removal) and no-tillage (NT) practices were exam...

Encroachment of nitrogen-fixing trees and shrubs into grasslands and savannas is a well-documented land cover change that occurs worldwide. In the Rio Grande Plains region of southern Texas, previous studies have shown woody encroachment by leguminous Prosopis glandulosa (mesquite) trees increases soil C and N, decreases microbial biomass N relativ...

Brown rot fungi Gloeophyllum trabeum and Postia placenta were used to degrade aspen, spruce, or corn stover over 16 weeks. Decayed residues were saccharified using commercial cellulases or brown rot fungal extracts, loaded at equal but low endoglucanase titers. Saccharification was then repeated for high-yield samples using full strength commercial...

On-line thermally assisted hydrolysis and methylation (THM) in the presence of both unlabelled and 13C-labelled tetramethylammonium hydroxide (TMAH) was used to assess the relative contributions of phenolics (lignin, demethylated lignin and non-lignin phenolics) in a peaty gley soil profile beneath an unimproved grassland (LL), from a study site lo...

Forests growing under elevated concentrations of atmospheric CO2 and ozone exhibit changes to root and foliar chemistry and quality that are related to changes in physiology, N limitation, and leaf damage. Additionally, there are documented changes to the activity of some understory invertebrate populations, and a variety of responses to soil organ...

A combination of long-term fire suppression and livestock overgrazing has resulted in the progressive encroachment of C3 woodlands into native C4-dominanted grasslands in the Rio Grande Plains region of southern Texas. This common land-cover change alters the biogeochemical cycling of nutrients in the sandy loam soils of southern Texas so that C an...

We studied the degradation of lignin in leaf and needle litter of ash, beech, maple, pine and spruce using 13C-labelled tetramethylammonium hydroxide (13C TMAH) thermochemolysis. Samples were allowed to decompose for 27months in litter bags at a German spruce forest site, resulting in a range of mass loss from 26% (beech) to 58% (ash). In contrast...

Background/Question/Methods Many grass-dominated ecosystems around the world have experienced woody plant encroachment over the last century due to livestock grazing, fire suppression, and/or changes in climate and atmospheric chemistry. In the Rio Grande Plains of Texas, subtropical thorn woodlands dominated by N-fixing tree legumes have largely...

Woody plant encroachment into grasslands and savannas is a globally extensive land-cover change that alters biogeochemical processes and frequently results in soil organic carbon (SOC) accrual. We used soil physical fractionation, soil respiration kinetics, and the isotopic composition of soil respiration to investigate microbial degradation of acc...

The brown rot fungus Wolfiporia cocos and the selective white rot fungus Perenniporia medulla-panis produce peptides and phenolate-derivative compounds as low molecular weight Fe³+-reductants. Phenolates were the major compounds with Fe³+-reducing activity in both fungi and displayed Fe³+-reducing activity at pH 2.0 and 4.5 in the absence and prese...

Soil carbon turnover models generally divide soil carbon into pools with varying intrinsic decomposition rates. Although these decomposition rates are modified by factors such as temperature, texture, and moisture, they are rationalized by assuming chemical structure is a primary controller of decomposition. In the current work, we use near edge X-...

Exotic earthworm invasion in northern North American forests has the potential to significantly alter nitrogen and carbon cycling in forest soils, through litter layer losses, loss of organic horizon, and changes in fine root density. Earthworm influence on nitrogen cycling is currently being investigated in the free-air CO2 enrichment (FACE) sites...

Our work seeks to identify how earthworm (EW) activity and past land interact to control the relative importance of physical, chemical, and biochemical protection mechanisms governing SOM stabilization in deciduous forests. Within forests of the Smithsonian Environmental Research Center (SERC) in coastal Maryland, USA, wood and litter amendment plo...

Recent studies have demonstrated how invasive European earthworm species have caused large and long lasting perturbations to forest floor dynamics and soil composition in many northern hardwood forests. The type of perturbation is driven primarily by the composition and activity of the invasive species and the original state of the forest system. O...

Throughout many northern North American forests invasive earthworms have caused significant ecological alteration to soil structure and chemistry, fine root distributions, duff and litter layer thickness, and soil moisture. Additionally, this phenomenon has been implicated in shifts in herbaceous-layer vegetation. Over the past 4 years, we have est...

The influence of CO2-driven increase in net primary productivity on soil organic carbon accrual has received considerable emphasis in ecological literature with conclusions varying from positive, to neutral, to negative. What has been understudied is the coupled role of soil fauna, such as earthworms, in controlling the ultimate fate of new above a...

Soil fractionation schemes aim to isolate conceptually-defined soil organic carbon (SOC) pools with varying turnover times and stabilization potentials that can be represented in SOC models. Among these different fractions, mechanisms for SOC stabilization may vary in their importance. In order to examine the microbial response to SOC of varying ch...

Many grass-dominated ecosystems around the world have experienced woody plant encroachment over the last century due to livestock grazing, fire suppression, and/or changes in climate and atmospheric chemistry. In the Rio Grande Plains of Texas, subtropical thorn woodlands dominated by N-fixing tree legumes have largely replaced grasslands and alter...

High sedimentation rates along river-dominated margins make these systems important repositories for organic carbon derived from both allochthonous and autochthonous sources. Using elemental carbon/nitrogen ratios, molecular biomarker (lignin phenol), and stable carbon isotopic (bulk and compound-specific) analyses, this study examined the sources...

Background/Question/Methods Over 90 % of the forests in the Mid-Atlantic region are secondary forests at different successional stages. Soil macrofauna in these forests is often dominated by non native European and Asian earthworms, but native species can also be present. In 1999 we conducted a survey on the earthworm fauna at the Smithsonian Env...

Lignin is a major component of plant litter. However, its fate during litter decay is still poorly understood. One reason is the difficult analysis. Commonly used methods utilize different methodological approaches and focus on different aspects, e.g., content of lignin and/or of lignin-derived phenols and the degree of oxidation. The comparability...

Many forests within northern North America are experiencing the introduction of earthworms for the first time, presumably since before the last major glaciation. Forest dynamics are undergoing substantial changes because of the activity of the mainly European lumbricid species. Documented losses in litter layers, expansion of A-horizons, loss of th...

Many soils from forests in northern North America are undergoing a recent invasion of European Lumbricid earthworms with important implications for soil organic carbon (SOC) dynamics. Our work seeks to identify how native and invasive earthworm (EW) activity alters the relative importance of physical, chemical, and biochemical protection mechanisms...

The encroachment of woody plants into grasslands is a worldwide phenomenon. In the Rio Grande Plains of southern Texas, subtropical thorn woodlands dominated by the N-fixing tree Prosopis glandulosa have largely replaced native grasslands as a result of fire suppression and extensive cattle grazing. This land cover change has resulted in the increa...

Many northern North American forests are experiencing the introduction of exotic European lumbricid species earthworms with documented losses in litter layers, expansion of A-horizons, loss of the organic horizon, changes in fine root density, and shifts in microbial populations as a result. Some of these forests were previously devoid of these eco...

Woody plant encroachment (WPE) into savannas and grasslands is a global phenomenon that alters soil organic carbon (SOC) dynamics through changes in litter quality and quantity, soil structure, microbial ecology, and hydrology. To elucidate the controls on microbial accessibility to SOC, bulk soils from a chronosequence of progressive WPE into nati...

In many mid-Atlantic forests where both native and non-native earthworms exist, it is the non-native species that are the dominant component of the soil macrofauna. Few earthworm ecology studies, however, focus attention on these forest systems in order to determine the relative ecological roles and potential interactions of the native and non-nati...

Grass-dominated ecosystems around the world are experiencing woody plant invasion due to human land uses. Vast regions in southern Texas have been transformed from open grasslands to subtropical thorn woodlands during the past 150 yrs. These woodlands are dominated by N-fixing tree legumes which are more productive above- and belowground, and store...

Sequential density fractionation separated soil particles into “light” predominantly mineral-free organic matter vs. increasingly “heavy” organo-mineral particles in four soils of widely differing mineralogy. With increasing particle density C concentration decreased, implying that the soil organic matter (OM) accumulations were thinner. With thinn...

The GEMscholar (Geology, Environmental Science and Meteorology scholars) program seeks to increase the number of Native American students pursuing graduate degrees in the geosciences. Drawing on research from Native American student education models to address three key themes of mentoring, culturally relevant valuations of geosciences and possible...

Earthworms are frequently referred to as soil ecosystem engineers, reflecting their role as a potential major factor in controlling the dynamics of litter and soil organic matter transformations. Their significance is magnified when considering they are exotic in northern North American forests, humans acting as the main vector with transport of so...

In the Rio Grande Plains of southern Texas, subtropical thorn woodlands dominated by the N-fixing tree Prosopis glandulosa have largely replaced native grasslands over the last 150 years as a result of fire suppression and over grazing. This land cover change has resulted in the increase of belowground stocks of C, N, and P, changes to the amount a...

Climate change is expected to change precipitation patterns, which would alter the runoff of excess carbon and nitrogen into the surrounding waterways. If agricultural areas experience an increase in precipitation, then coastal areas downstream from these areas could expect to develop hypoxic conditions that are more widespread, continual, and seve...