The development and decline dynamics of two ectomycorrhizal fungal mat soil microbial communities in response to a reciprocal soil transfer experiment in old-growth Douglas-fir forests

Ectomycorrhizal fungi (EmF) form symbioses with trees. These symbioses profoundly influence forest ecology. Certain EmF form specialized profusions of hyphae, known as ectomycorrhizal fungal mats (mats) which are visible to the naked eye, alter forest soil biogeochemistry, substantially contribute to soil microbial biomass/respiration and support unique microbial communities. Piloderma and Ramaria mats stratify in organic and upper mineral soil, respectively, and are the dominant mat-forming fungi of old-growth Douglas-fir forests of the Pacific Northwest, USA. The importance of Piloderma and Ramaria mats to forest ecosystem processes has driven the need to better understand their associated microbial communities, particularly development (birth) and decline (death) dynamics. To explore these dynamics, a reciprocal soil transplant experiment was established at seven old-growth Douglas-fir sites in the H.J. Andrews Experimental Forest. At each site Piloderma, Ramaria and non-mat soils underwent birth (non-mat into mat enclosed in 2-mm mesh), death (mat into non-mat enclosed in PVC pipe), disturbance control (core non-mat soil, replace in 2-mm mesh) and background (no manipulation) treatments. After 51 months, treatments were harvested and three microbial community components were assessed through molecular analyses: active EmF root-tips using Sanger sequencing and soil fungi and bacteria using 454-pyrosequencing. Results from this study revealed differential persistence of mats formed by Piloderma and Ramaria. In the mineral horizon, we found few microbial community differences. Originally unique Ramaria mat microbiota were no different from non-mat soils after 51 months, and the mat-forming genus, Ramaria, was notably missing from fungal sequences; these data support the ephemeral nature of Ramaria mats where their hydrophobic powdery structure may, at times, be a visual legacy of mat presence, a remnant of physical alteration of the soil environment. In the organic horizon, Piloderma mat fungal communities persisted for 51 months and remained distinct from non-mat soils; this permitted birth and death treatment analysis. Our data indicate strong development of Piloderma mat fungal communities in birth treatments, beyond colonization by Piloderma, making them indistinguishable from Piloderma mats; mat development can take many years. Death treatments were dissimilar to Piloderma mats and contained similar fungal communities to non-mat soils. Enclosure in PVC pipe, thereby removing roots and EmF from the system, significantly shifted the soil fungal community toward saprotrophic dominance. To compliment Piloderma, the EmF genus Russula was a robust indicator of non-mat organic soils; there was strong evidence for the competitive exclusion of Russula in Piloderma mats, though it may take many years for exclusion to occur. For organic horizon bacterial communities, only death treatments differed from others. Strong similarities were found between overall Piloderma mat and non-mat bacterial communities; however, Piloderma mat and non-mat soils impose selection pressure on a small subset of bacterial taxa masked when the community is considered as a whole. This work contributes to the body of knowledge regarding complex microbial community dynamics of EmF mats. The occurrence and distinct microbial taxa of Piloderma mats in these forests suggests large-scale spatial differences in ecological function. The extent of functional differences is currently unknown, but Piloderma mats present a unique microbial system, supported by over 30 years of research, to test difficult microbial ecology questions

A Method to Characterize Biological Degradation of Mass Timber Connections

Biological durability issues in cross-laminated timber (CLT) have been majorly ignored in North America because of the European origin of the material and careful construction practices in Europe.  However, the risks of fungal and insect attacks are increased by the North American climatic conditions and lack of job-site measures to keep the material dry. The methods to evaluate durability in solid timber are inadequate for use in mass timber (MT) for a number of reasons, such as moisture variation and size being critical issues. This study therefore proposes a method, which is suitable to evaluate the strength of MT assemblies that are exposed to fungal degradation. The objective of the study was to explore a controlled method for assessing the effects of wetting and subsequent fungal attack on the behavior of CLT connections. Two different methods were used to create fungal attack on CLT assemblies. Although they were both successful, one was cumbersome, left room for many errors, and was not as efficient as the other. In addition, a standardized method to evaluate and characterize key performance metric for the connections is presented.

Laboratory decay resistance of palmyra palm wood

The decay resistance of palmyra palm wood[1] (Borassus flabellifer), also referred to as sugar palm, was assessed in laboratory soil block tests against Oligoporus placenta, Gloeophyllum trabeum, Irpex lacteus, and Trametes versicolor as well as in a non-sterile soil burial test designed to encourage soft rot attack. Mass losses on pine control blocks were consistent with aggressive decay conditions for all but those exposed to Irpex lacteus, while mass losses for palm wood blocks exposed to the same fungi ranged from 0.46% to 10.6%. The magnitude of mass losses would categorize palm wood as resistant to highly decay resistant, suggesting that these materials might perform well in exterior above ground applications. Mass losses were weakly correlated with density suggesting that selection of denser wood will result in better performing materials in these applications. Field tests to confirm these results are encouraged

Decay capabilities of basidiomycetes colonizing air-seasoning red oak and blackgum railroad ties

Fungi cultured from air-seasoning blackgum and red oak timbers were assessed for their ability to cause wood decay using two hardwoods and one soft wood species in an AWPA E10 soil block test. Weight losses were greatest for bigleaf maple and tended to be much lower on southern pine. Almost a quarter of the 35 taxa tested caused less than 5 % weight loss, suggesting they posed a relatively low decay risk, even under ideal laboratory conditions; despite all fungi tested having the ability to depolymerize wood. Three of the four fungi causing the largest weight losses were brown-rot fungi, although brown-rot fungi represented only small proportion of the total isolates from the original hardwood timbers. These results illustrate wide array of decay capabilities of fungi colonizing air-seasoning red oak and blackgum timbers, and the potential of many isolates to negatively affect wood properties through biodeterioratio

Effect of Distance Above Ground during Air Seasoning on Flexural Properties of Blackgum and Red Oak Ties

Stacks of red oak (Quercus rubra) and black gum (Nyssa sylvatica) railroad ties were seasoned 150, 200, or 300 mm above the ground to investigate the effect of height on fungal colonization and timber properties. Decay fungi became increasingly abundant as seasoning time increased. Decay fungi were more abundant on black gum than red oak ties, but fungal isolation frequency did not differ with variation in seasoning sill height. Similarly, neither MOR nor MOE differed with seasoning height. The results indicate that decreasing the tie seasoning height by 150 mm had no significant effect on either fungal colonization or timber properties.

Effect of brown rot degradation on mass loss and compressive strength of chinese poplar ("Populus simonii")

The wood of poplar species are generally perceived as susceptible to decay, however, poplar is still widely used as columns in traditional Chinese buildings. Understanding how decay affects the compressive properties of this material will help engineers better assess wood condition during routine inspection and maintenance. The effects of decay on compressive properties of Chinese poplar were explored using a brown rot decay fungus (Gloeophyllum trabeum). Changes in compression strength were fairly linear and more closely correlated with mass loss (R2= 0.75). The results suggest that residual compressive strength could be roughly predicted using wood density as a surrogate measure

Laboratory decay resistance of palmyra palm wood

The decay resistance of palmyra palm wood[1] (Borassus flabellifer), also referred to as sugar palm, was assessed in laboratory soil block tests against Oligoporus placenta, Gloeophyllum trabeum, Irpex lacteus, and Trametes versicolor as well as in a non-sterile soil burial test designed to encourage soft rot attack. Mass losses on pine control blocks were consistent with aggressive decay conditions for all but those exposed to Irpex lacteus, while mass losses for palm wood blocks exposed to the same fungi ranged from 0.46% to 10.6%. The magnitude of mass losses would categorize palm wood as resistant to highly decay resistant, suggesting that these materials might perform well in exterior above ground applications. Mass losses were weakly correlated with density suggesting that selection of denser wood will result in better performing materials in these applications. Field tests to confirm these results are encouraged

Analysis of Basidiomycete Fungal Communities in Soil and Wood from Contrasting Zones of the AWPA Biodeterioration Hazard Map across the United States

Wood deterioration due to basidiomycetous decay fungi shortens the useful life span of wood and wood-based materials. Prescriptive preservative treatment is the most effective way to reduce the detrimental effects of these microorganisms, particularly in soil contact and areas of critical use (difficult to replace or vital to structure). Current American Wood Protection Association (AWPA) guidelines in the standardized use category system specify 3 zones of severity regarding wood decay fungal hazards but contain very little information on the diversity and abundance of these fungi colonizing soil and wood. In this study, amplicon based sequencing was utilized to compare fungal communities in wood and adjacent soil to provide baseline data on the fungi involved in the process. A thorough understanding of decay hazards is critical for the proper selection and use of wood in soil contact. The goal of this work is to provide baseline data on basidiomycete fungal diversity and species composition in different zones of the existing 3-zone AWPA hazard map as compared to the previous 5-zone hazard map and Scheffer decay indices and discuss the ecological implications for wood decay