Environmental Biogeochemistry

Laboratory

Studies of Regional and Global

Environmental Change

General soil C cycle studies

Grandy, A.S., and J.C. Neff. (2008). Molecular C Dynamics Downstream: The Biochemical Decomposition Sequence and its Impact on Soil Organic Matter Structure and Function. Science of the Total Environment. doi:10.1016.j.scitotenv.2007.11.013. This manuscript presents a conceptual model of soil organic matter changes across size fractions and suggests that these differences represent a common sequence of structural changes that occur during decomposition. The manuscript is intended to be provocative and to stimulate a discussion about whether there is a general pattern of structural change in organic matter during decomposition and soil formation. PDF

Prior,C.A., W.Troy Baisden, F. Bruhn, and J.C. Neff. (2007). Identifying the optimal soil fractions for modeling soil carbon dynamics in New Zealand.Radiocarbon 49 (2) 1093-1102. This manuscript uses a combination of modeling and analytical approaches to define the size and functional properties of SOM pools and to use these pools in modeling. The analysis is based on archived and contemporary samples taken from sites in New Zealand. PDF

Holland E.A., J.C. Neff, A.R. Townsend & R. McKeown. (2001). Variability in the temperature response of decomposition in sub-tropical and tropical soils. Global Biogeochemical Cycles.14(4): 1137-1153.This manuscript describes a laboratory study of the decomposition of soils from a variety of tropical and sub-tropical settings under a range of temperature. The study was designed ot examine the temperature sensitivity of decomposition.

Silver W., J.C. Neff,E. Veldkamp, M. McGroddy, & M. Keller (2000) Patterns in soil chemical properties and root biomass along a soil texture gradient in a lowland Amazonian tropical forest. Ecosystems, 003(02): 0193-0209. This study presents data from the Tapajos Forest near Santarem, Brazil. The forest contains two soil types that differ in textural composition although both are old, lowland tropical soils. These soil differences appear to translate into variation in rooting patterns and soil chemical properties.

SW US Carbon Cycle Studies

J.C. Neff, N.N. Barger, W.T. Baisden, D.P. Fernandez, and G.P. Asner. In Review. Soil carbon storage responses to expanding pinyon-juniper populations in Southern Utah. Ecological Applications. In this work, we present an examination of soil organic matter turnover in grazed and ungrazed sites located in Grand Staircase Escalante National Monument in S. Utah. The study uses SOM age and pool size measureemnts along with ttree age (as a surrogate for the timecourse of inputs to SOM) to estimate turnover times of carbon in this dryland ecosystem. The results suggest very rapid surface carbon turnover and much slower subsurface turnover. The study also shows that very little carbon in this setting is stabilized into inherantly slow turnover pools (e.g. mineral surfaces or aggregates) and is therefore subject to loss with disturbance.

Fernandez D. P., J.C. Neff, J. Belnap, and R. L. Reynolds. (2006) Soil respiration in a cold desert environment: abiotic regulators and thresholds. Biogeochemistry. 78(3): 247-265. This paper describes the controls over soil respiration in sites near Canyonlands National Park, Utah. Using a series of field flux measurements combined with repeated measurements of soil moisture, we examine the factors that control soil respiration and using regression tree modeling, partition those factors into a moisture and temeperature range for decomposition that occurs for a very limited portion of the year. PDF

Fernandez, D.P., J.C. Neff, R.L. Reynolds. (2007). Biogeochemical and ecological impacts of livestock grazing in semi-arid Southeastern Utah, USA, Journal of Arid Environments. doi:10.1016/j.jaridenv.2007.10.009. This paper was developed during a master's thesis using a set of grazed and ungrazed sites near Canyonlands National Park, Utah. The study pairs sites using soil, geologic and elevational criteria and then examines the potential long-term impacts of grazing on soil properties. The conclusions are similar to those in Neff et al., 2005 and suggest large declines in C and N with grazing in these settings but suggest some variability in other properties across these diverse environments. PDF

Neff J.C., R. Reynolds, J. Belnap, and P. Lamothe. 2005. Multi-decadal impacts of grazing on soil physical and biogeochemical properties in Southeast Utah. Ecological Applications, v15 (1), 87-95. We use the magnetic properites of soils as a proxy for the integrated dust deposition and wind erosion in this study. In parallel studies (see the Reynolds et al papers), we show that the presense of magnetite in these soils is a marker for the long term accumulation of dust. Here we examine a historically disturbed site and compare it to a carefully paired undisturbed site to show that land use destabilizes surface soils and leads to wind erosion of soils. The resulting erosion and/or decomposition leads to large declines in cations, C and N, even in a site that has not been grazed for 30 years. PDF

Alpine C cycling

D.R. Nemergut, A.R. Townsend, S.R. Sattin, K. Freeman, N. Fierer, J.C. Neff, W.D. Bowmand, C.W. Schadt, M.N. Weintraub, and S.K. Schmidt. In Press . The effects of chronic nitrogen fertilization on alpine tundra soil microbial communities: implications for carbon and nitrogen cycling. Environmental Microbiology. This study uses a range of measurements to examine the long term implications of N addition for microbial processes, composition and soil organic matter strucutre. The results provide a detailed examination and partial explanation for the patterns observed in the Neff et al, Nature publication.

S. Grandy, J.C. Neff and M.N. Weintraub. (2007). Carbon structure and enzyme activities in alpine and forest ecosystems. Soil Biology and Biochemistry. v39: 2701-2711. Using sites in the San Juan Mountains of Colorado and pyrolysis GC/MS techniques, this study examines how carbon structure and enzyme activities parallel one another in high elevation forest and alpine settings in Colorado. The study also separates soils into light and heavy (density separated) fractions to examine structural differences and shows that most plant lignins are present in the light fraction of the soil. PDF

Neff J.C.,A.R. Townsend,G. Gleixner, S. Lehman, J. Turnbull and W. Bowman (2002). Variable effects of nitrogen additions on the stability and turnover of soil carbon. Nature. 419: 915-917. This study used a combination py-GC/MS and 14C techniques to examine the long term implications of nitrogen addition on soil carbon dynamics. The paper's results were interesting in large part because bulk soils pools appeared unchanged by fertiliation even while N altered turnover and the molecular characteristics of SOM. These changes, when viewed in the context of the uncertain responses of soils to N deposition, were notable. Please email for PDF.