U.S. Geological Survey
345 Middlefield Rd., MS 962
Menlo Park, CA 94025
PHONE 650-329-5005
FAX 650-329-4920
mwaldrop@usgs.gov

Fungi are particularly important decomposers in boreal forests because they produce powerful ligninase enzymes that breakdown recalcitrant soil carbon.  My first objective was to determine the composition and abundance of soil fungi in burned and unburned Black Spruce stands present on permafrost or permafrost free soils.  The second objective is to determine whether change in composition or biomass affects the processing rate of soil carbon. To this end, I have extracted DNA from soils, amplified fungal DNA using PCR, analyzing microbial community composition using Denaturing Gradient Gel Electrophoresis (DGGE) and Denaturing High Performance Liquid Chromatography (DHPLC). I have quantified the abundance of different soil fungi and ligninase genes using quantitative PCR. Results have shown that wildfire and increasing soil moisture reduce the total microbial biomass and the biomass of soil fungi resulting in reductions in the oxidative enzyme production that also correlates to reduced turnover of soil carbon.  These data were presented at the Ecological Society of America meeting in Montreal, Canada

 

I am also testing productivity-diversity relationships in soil microbial communities across two continental transects in an effort to link ecological theory to soil processes. Over the course of human history, little has marked our impact on biotic resources more than the loss of biodiversity. Reductions in plant diversity are known to affect soil processes, ecosystem resilience, ecosystem services, and human society. Yet understand little about the extent of microbial diversity, its natural variation at large scales, the impact of anthropogenic activities on microbial diversity, or mechanistic linkages between microbial diversity and soil processes. Over the past 200 years and increasingly over the last few decades, a scientific revolution in microbial ecology has unveiled a strikingly diverse microbial community inhabiting soils. Nonetheless, we understand very little about what controls the diversity of microorganisms in soils, and how the level of soil microbial diversity might alter the manner in which terrestrial ecosystems function. A newly funded USDA project will allow us to uncover how soil carbon resources may control soil microbial diversity and determine whether reductions in the soil genetic stock will affect soil carbon cycling processes.

 

Black carbon,resulting from the oxidation of wood and forest floor carbon following wildfire, is thought to be largely biologically unavailable, but this has not been thoroughly examined.Utilizing ¹³C isotope techniques, I am determining whether black carbon can be decomposed by soil organisms, whether the extent of decomposition is affected by microbial species, and whether the mechanism of action is via extracellular oxidative enzymes

 

Carbon (C) stored within permafrost in northern boreal forest soils may become available for microbial metabolism if soil temperatures continue to increase over the coming decades, resulting in a positive feedback to climate warming. Understanding the potential of permafrost carbon to be degraded requires a detailed understanding of the microbiology and biochemistry of permafrost soils. Utilizing novel techniques in molecular biology, fluorometry, and mass spectrometry, we propose to analyze the biological and chemical constraints on C cycling at the molecular level. Testing the potential genetic and chemical limitations on decomposition are cutting-edge approaches that are only made possible through recent technological advances. Our detailed genetic and chemical analyses will provide data with which to make future predictions of C cycling processes, particularly when combined with larger scale biophysical and hydrologic models.

 

Moisture is one of the most important variables controlling carbon storage in northern ecosystems.In collaboration with Merritm Turetsky at Michigan State University and Dave McGuire (UAF and USGS) at the Bonanza Creek Long-Term Ecological Research (LTER) station, I am examining how natural gradients in soil moisture and manipulated soil moisture and temperature affect the size and activities of decomposers, methanogens, and methanotrophs

 

Microbial biomass is typically reduced following fire, although activity may increase, affecting nutrient cycling in unique ways. In Santa Cruz, CA, I will be collaborating with Jennifer Harden, Kristen Manies, Art White (USGS), GuntramVon-Kiparski (LLNL), and other researchers to determine the effects of fire and soil age on microbial turnover of soil C. Using an approach Intially developed at UC Irvine, we will use an accelerator mass spectrometer to examine the ¹⁴C content of microbial biomass and sporocarps that quantifies ages of substrate C metabolized by microorganisms.

 

Quantitative PCR of functional genes may work as a proxy for the abundance of functional groups within the environment. I am collaborating with several researchers at the USGS in order to utilize quantitative PCR techniques to determinewhether we use the quantity of nirS and nirK(nitrite reductase genes) in a soil profile to explain potential denitrification rates. I am also utilizing this technique to quantify soil methanogens and basidiomycetes

 

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