Analysis of Basidiomycete Fungal Communities in Soil and Wood from Contrasting Zones of the AWPA Biodeterioration Hazard Map across the United States
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3.4. Community Analysis
The first step in analyzing the data set was to make broad comparisons based on species composition. NMDS in PC-ORD [36] was used to generate plots that offer a visual representation of basidiomycete fungal communities based on species composition across defined AWPA hazard zones. The first comparison was basidiomycete fungi present in wood versus those in soil (Figure 1). For all ordinations, stress values are indicated in parenthesis in figure captions, these values represent a measure of the difference between distance in the reduced dimension and the complete multidimensional space [36]. There was very little overlap between these communities which was expected given that wood represents a more specialized substrate with spatially restricted access.
Q1: Is basidiomycete soil fungal diversity similar to the observed fungal diversity in wood?
Soil represents a pool of potential inoculum for wood in soil contact, but the question remains what fungi persist in soil versus what fungi colonize and degrade the wood? NMDS ordinations indicated that soil and wood are dissimilar in their overall basidiomycete species composition although many species exhibited overlap occurring in both wood and soil. There was a total of 2025 basidiomycete OTUs present in all substrates, with 1964 OTUs present in soil and 739 present in wood. Of these totals, 1286 OTUs were unique to soil, while 61 were unique to wood. A total of 678 OTUs co-occurred in wood and soil. Based on MRPP analyses, basidiomycete communities were found to be significantly different with respect to community assemblage in wood vs. soil (p ≤ 0.00001).
Q2: Do zones of higher fungal decay hazard contain higher basidiomycete diversity?
The results are shown in Table 2. Lower diversity was noted in the wood samples, which is not surprising given the nutritional and spatial limitations of wood. In wood, no clear trend was noted between fungal diversity measures, but a general downward trend was noted and that was more distinct in soil than wood. These results would imply that fungal species richness is not simply higher in zones of more severe decay hazard. When comparing sites, stands, hazard and Scheffer zones, mean diversity measures were higher in zones of low hazard, followed by intermediate and severe (Table 2). Correlation coefficients were calculated using Pearson’s correlation coefficient in Microsoft Excel and Ave. Scheffer, Study-year Scheffer and AWPA Zone were all negatively correlated with species diversity −0.578, −0.567, −0.60, respectively.
These results are complimentary to previous studies looking at competitive interactions in wood decay fungi [42], that indicate more diverse assemblages are present in more moderate, temperate climates and more severe, tropical climates consist of well adapted species that outcompete and colonize the substrate more quickly and completely. Based on these results, the basidiomycete communities in more severe climates are not necessarily more diverse, but are comprised of different species, which may be more aggressive, combative, or temporally restricted in their habits. More work needs to be performed to further investigate these concepts, but the outcomes could change how we view wood protection in sub-tropical and tropical cl1imates.
Q3: Is basidiomycete fungal diversity in soil and wood different over AWPA hazard zones?
Ordinations by AWPA hazard zones are shown below (Figure 2). Referring to the 5-zone map, the trend follows a similar pattern as noted on the site comparisons. The less severe zones (low, moderate, and intermediate) tend to group together and high and severe zones, which represent a more severe decay hazard, had a more distinct fungal species composition. There is also a clear delineation from left to right along axis 2 indicating a gradual shift in species composition from zones of high to low hazard. In comparing the 3-zone map to the 5-zone map, the 3-zone map clustered in direct accordance with the high, medium, and low designations, whereas there was uncertainty in clustering of zones of intermediate decay hazards as delineated in the 5-zone map. Based on these observations, the 3-zone map seems better suited to describe regional decay hazards, except for areas with specific microclimatic variation [43,44,45].
Q4: Does forest overstory impact basidiomycete fungal diversity colonizing wood?
Ordinations of wood fungal community by site are shown below (Figure 3). More temperate sites clustered more closely indicating that they are more similar regarding fungal species composition and more subtropical sites (Ocala, Desoto, and San Juan) clustered more to the right of the ordination which indicates that the species composition is unique from the other sites. This observation is likely also influenced by soil characteristics and will be the subject of a more comprehensive study into this area to be published in the future. Overstory, listed as stand in the figure legend had a lesser influence on species composition than site, with locations clustering more closely than overstory types.
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