Forest Investment Account (FIA) - Forest Science Program
FIA Project Y071322

    Can the important microbial diversity and nutrient cycling characteristics of old growth Douglas fir forests be maintained in managed second growth forests?
 
Project lead: Winder, Richard
Author: Winder, Richard S.
Imprint: Victoria, BC : Natural Resources Canada, 2007
Subject: Forest Investment Account (FIA), Pseudotsuga Menziesii, British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
Description:
Background: Biodiversity emerges as the result of the many interactive factors that create niches for speciation. In forest ecosystems, drivers of biodiversity can include climate (Gaston 2000), fire regimes (Nasi et al. 2002), predation (Heath and Alfaro 1990), opportunities for long-term (e.g., mycorrhizal) symbioses (van der Heijden et al. 1999), parasitism and disease (Castello et al. 1995; Reynolds et al. 2003), and the intensity of nutrient utilization and competition (Loreau 1998). In old growth forests, the last factor is especially related to the amount of woody debris in the forest ecosystem. Logs, stumps, and other woody debris provide spatial niches for various organisms, but they also have important implications as the organic substrate for decomposition processes. These processes sustain many species of edaphic microbes and contribute to plant nutrition. Decomposers and other nutrient-cycling bacteria contribute the majority of species comprising biodiversity in any given forest ecosystem; in some cases the number of bacterial species can approach 10,000 species per gram of soil (see e.g. Chatzinotas, 1998). These microbes influence the complexity of niches for the other biotic components of a forest ecosystem. Understory plants, trees, mycorrhizal networks, and the 'food web’ associated with them rely on the nutrient services provided by microbes in forest soils, and nutrient availability is, to a large extent, regulated by microbial activity (Schimel and Bennet, 2004). The diversity of soil microbes in turn is impacted by the complexity of the other biotic components. Can woody debris in younger forest stands be managed to sustain the key microbial communities in old growth soils? Does this in turn have a positive implication for protecting biodiversity? In the long term, this project aims to provide some answers for these questions. A major difference between old growth forests and managed second growth forests is that the managed forests have less woody debris and forest floor organic material. This structural disparity is especially a concern as timber rotation ages have been reduced from 100 to 50 years (Wells & Trofymow, 1997; Trofymow et al. 2003). In the context of emulating old growth, there are two aspects of nutrient services to consider: 1) Are the necessary microbial communities maintained, and 2) How are the complex niches of other important microbe communities affected? In the first case, an example of an essential microbial community is the group of bacterial species involved in nitrogen cycling. Sources of nitrogen necessary for timber growth are obtained through microbial decomposition of organic material or microbial fixation of atmospheric di-nitrogen. However, nitrogen availability is limited in most forest soil ecosystems (Dawson, 1992) as is our understanding of microbial community interactions resulting in nitrogen fluxes in these systems (Bornmann et al, 1993). Understanding the dynamics of N–fixing and nitrogen-cycling microbe communities in forest systems, and how forestry-related activities may influence them, is important in evaluating forestry management practices. In the second case, methane-oxidizing bacteria are an important microbial community that can be disrupted by nutrient imbalances and N availability, potentially limiting the function of the forest ecosystem as a methane sink (Steudler et al., 1989). One obvious value of biodiversity is in maintaining these types of essential ecosystem services, but biodiversity is often a spectrum of choices relating to habitat diversity and niche complexity. Deliverables and impacts from this study will provide a better understanding of practices needed to emulate N-cycling of old growth, maintain biodiversity, and sustain ecosystem services. The proposed project: We propose to profile the soil microbial nitrogen-cycling and methane oxidizing communities at Shawnigan Lake Research Forest (LTRI014), as well as in old-growth forest sites in the nearby Coastal Forest Chronosequence project (LTRI016; q.v Trofymow et al. 1997). Shawnigan Lake Research Forest is an even-aged 58-60 year-old Douglas fir (Pseudotsuga menziesii) forest planted in 1948, with various levels of calibration thinning (LOGS - Levels of Growing Stock experiment), plus combinations of thinning and fertilization treatments. Thinned logs remain where they fell within the site. The LOGS site is described online at http://www.pfc.cfs.nrcan.gc.ca/silviculture/logs/index_e.html and the Coastal Forest Chronosequence project is described online at http://www.pfc.cfs.nrcan.gc.ca/ecology/chrono/c-stocks_e.html . Microhabitats will be surveyed in all sample plots and used to stratify the samples. Analysis of microbial communities will be accomplished via the analysis of genes necessary for nitrogen cycling, such as nitrogenase (nifH), ammonia monooxygenase (amoA), and nitrite reductase (nirK and nirS), as well as genetic sequences indicative of methane-oxidizing bacteria, including particular16S rRNA sequences and the PmoA and mmoX genes. We will also conduct biochemical assays for nitrogen fixation and methane oxidation occurring at the field sites. The hypothesis we will test in the 2006/2007 fiscal period is that differences in the nitrogen–cycling and methane-cycling communities and activities exist at these sites. The longer term objective is to link the observed microbial community composition to biochemical processes occurring in the ecosystem. To this end, in the second and third years, we will confirm the impact of particular community compositions with soil process studies (microcosm analysis) as well as ascertaining the nitrogen-cycling gene activity within the relevant microbial community as evidenced by soil-extracted messenger RNA/cDNA real-time PCR analysis (RT-PCR). This aspect is important, given the persistence of microbial DNA within the soil as well as the possibility that microbes possessing nitrogen-processing capacity are inactive.
Related projects:  FSP_Y082322FSP_Y093322
Contact: Winder, Richard S., (250) 363-0773, rwinder@pfc.cfs.nrcan.gc.ca

    Deliverables:

Executive Summary (17Kb)

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Updated August 16, 2010 

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