 Site Description |
Microbial Observatory at the H. J. Andrews LTERIn October, 1999 we established a Microbial Observatory at the H.J. Andrews Experimental Forest with the support of a grant from the National Science Foundation. This Microbial Observatory is dedicated to the study of bacteria and fungi central to biogeochemical processes in coniferous forest ecosystems in the Central Cascade Mountains of Oregon. Because nitrogen (N) is the most limiting nutrient to tree growth in this ecosystem, we focused on the functional diversity of microorganisms that perform N cycling processes. Studies were carried out primarily on the microorganisms that produce and consume NO3- because of their pivotal role in supplying N for plant growth, and controlling N losses to ground and surface waters as NO3- or to the atmosphere as N2O. Most of our research effort has been devoted to determining the influence of grassland meadow and coniferous vegetation on the functional diversity of key N cycling microorganisms and processes. We have also initiated studies on how ectomycorrhizal affect N cycling and associated microorganisms. New Direction for the H.J. Andrews Microbial ObservatoryIn August 2005, funding for the H.J. Andrews Microbial Observatory was renewed by the National Science Foundation. Our new focus is on the microbial communities associated with ectomycorrhizal (EcM) mats, which are dense assemblages of fungal hyphae in symbiotic association with forest trees. Mats can contribute up to 40% of the forest soil microbial biomass, and cover about 20% of the forest floor area. Our research will encompass two major objectives: (1) Survey the phylogenetic diversity of EcM mat fungi and their associated microbial communities; and (2) explore the determinants of microbial community composition associated with EcM mats. We will use a combination of traditional biogeochemical assays and modern molecular methods to gain insight into both the community composition of the mats, and the factors that influence the composition. We will examine the diversity of the fungal and eukaryote community associated with EcM using T-RFLP of the ITS rDNA region, in conjunction with cloning and sequencing of rDNA genes. We suspect that oxalic acid, which is excreted by mat fungi in large quantities, is a major driver of the mat community composition. We will use 13C-labeled oxalate to specifically label DNA of the oxalate degraders associated with the mats and identify them. A major role of EcM fungi is to procure N sources for their tree symbionts. We will focus attention on two key enzymes (proteinases and chitinases) associated with this task. Functional diversity of EcM proteinase and chitinase activities will be fingerprinted using a combination of incubations at different pHs and with select inhibitors and substrates. Using published primer sequences, we will examine the genetic diversity of chitinases and proteinases of fungal and bacterial origins in the mats and compare them with representatives of oxalate and chitin degraders isolated into culture from the mats. In addition, we will examine the genetic and functional diversity of key enzymes involved in the processing of mineral N (ammonia monooxygenase and assimilatory NO3- reductases) and gain insight into the composition and temporal/spatial determinants of mineral N processors associated with EcMs. Acknowledgement
|
