Background: Microbial indicators and forest soil health: Soil fertility is a prerequisite for sustainable forest ecosystems. One way to measure soil fertility is to simply measure the amount of available nutrients (N, P, K, etc.). This approach takes a kind of 'snapshot? of soil status, and it is a reasonable method for assessing general soil conditions at a point in time. Other indicators such as soil moisture, bulk density measurements, etc. can be helpful in determining the extent of disturbance impacts and some underlying mechanisms of disturbance. These approaches are relatively low cost, and they provide some immediate answers concerning soil conditions. However, they do not necessarily demonstrate sustainability, because they do not reveal underlying mechanisms controlling the dynamics of nutrient cycles vs. disturbance, nor do they necessarily predict soil status in the long term. For example, sites with low available soil nitrogen might or might not have a problem, depending on the long-term rate of N-fixation. Likewise, sites with good nutrient availability at early stages of succession might not remain that way; if the diversity of key microbe communities has been truncated, their function at later stages of succession may be impaired or degraded. Thus, questions can remain concerning the long-term impact of various types of forest disturbance, including forest management practices. One way to study the dynamics of soil nutrient cycles is to perform microcosm studies. For example, soil samples can be brought to the laboratory to monitor the extent of N mineralization over time. This provides some indication of the potential or capacity of the soil for maintaining fertility. However, these methods disrupt the complex in situ arrangement of microbial communities, which exist in localized consortia that include plant roots, mycorrhizal networks, and other microbes. Moreover, the incubation conditions may not truly reflect forest conditions, and the relatively long duration of a microcosm study rules out quick results or intensive sampling efforts. Even when significant changes are seen, there is still a question regarding the underlying driving mechanisms. The effort to catalog microbial indicators in forest soils generally has a two-fold purpose: to understand the 'black box? of nutrient cycle dynamics, and to quickly establish the health and condition of the soils in question. Put another way, there is a need to develop and validate microbial-based soil health measurements. While they may be cryptic as individual species, soil microbes (bacteria, fungi, and protista) are much more prevalent than other potential indicators, in some cases approaching 10,000 species/g (see e.g. Chatzinotas, 1998). Microbes are a very attractive measure of soil health because they are the drivers of key soil nutrient processes. Soil microorganisms are challenging to monitor; only about 10% of soil bacteria are culturable, and yet the bulk of N-fixation occurs in the so-called 'unculturable? fraction. However, advanced profiling methods are now enabling us to catalogue and understand the functional behavior of these communities. Indicator projects in B.C.: There are several research teams working in B.C. to understand the relationship between soil microbes and forest productivity and sustainability. At the Pacific Forestry Centre (PFC), one example is forest soil health indicator research being conducted in the LOGS (Levels of Growing Stock) plots (LTRI014) and in bioherbicide-treated plots. Another example is the green-tree retention study at UBC (FSP Project # Y073049), which is being conducted in the STEMS (Silviculture Treatments for Ecosystem Management) plots (LTRI026). These projects are using advanced molecular methods (e.g. PCR-DGGE), and biochemical methods (e.g. enzyme activity assays, CLPP) to understand how key functional microbial communities change vs. productivity, tree removal, herbicide or biocontrol applications, et ...
Dale, Phyllis L., Winder, Richard S.; Ka, K.H.. 2007. Development of a microbial indicator database for validating measures of sustainable forest soils. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report. FIA2007MR306
Topic: FLNRORD Research Program
Keywords: Forest, Investment, Account, (FIA), Soils, Nutrition, British, Columbia
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