Neonectria bordenii sp. nov., a potential symbiote of the alder bark beetle, and its detection by quantitative PCR.

A taxonomically comprehensive perspective on the fungal associates of bark beetles (Coleoptera: Curculionidae: Scolytinae), and powerful molecular tools for detection of these fungi, are imperative to understanding bark beetle impacts on forest ecosystems. The most common filamentous fungi living alongside bark beetles in infested trees are ophiostomatoids (Ascomycota: Ophiostomatales and Microascales), yet an undescribed species of Neonectria (Neonectria sp. nov.; Ascomycota: Hypocreales) was recently identified cohabitating with the alder bark beetle, Alniphagus aspericollis, in red alder, Alnus rubra. The hardwood-infesting alder bark beetle is found throughout the range of its red alder host in the Pacific Coast region of North America and is associated with Neonectria sp. nov. in southwestern British Columbia, Canada. The aim of this study was to describe and name Neonectria sp. nov. and to develop a quantitative PCR (qPCR) assay to enable rapid detection of Neonectria sp. nov. from individual adult alder bark beetles and to define the distribution of the fungus. Neonectria sp. nov. was phylogenetically and morphologically determined to represent a distinct species closely related to N. ditissima and is described herein as Neonectria bordenii sp. nov. Neonectria bordenii was reliably detected from individual whole-beetle DNA extractions using a probe-based qPCR assay targeting multi-copy internal transcribed spacers (ITS) of nuclear ribosomal DNA. The qPCR assay amplified the fungus from 87.8 % (36/41) of individual alder bark beetle samples and was highly sensitive to N. bordenii, with a lower limit of detection of 1 × 10-6 ng/µL of culture DNA (or ~262 genome copies). Application of the qPCR assay developed in this study will expedite future research evaluating N. bordenii as a potential symbiote of the alder bark beetle. Citation: Wertman DL, Tanney JB, Hamelin RC, Carroll AL (2024). Neonectria bordenii sp. nov., a potential symbiote of the alder bark beetle, and its detection by quantitative PCR. Fungal Systematics and Evolution 13: 15-28. doi: 10.3114/fuse.2024.13.02.

Annotated genome sequence of a fast-growing diploid clone of red alder (Alnus rubra Bong.).

Red alder (Alnus rubra Bong.) is an ecologically significant and important fast-growing commercial tree species native to western coastal and riparian regions of North America, having highly desirable wood, pigment, and medicinal properties. We have sequenced the genome of a rapidly growing clone. The assembly is nearly complete, containing the full complement of expected genes. This supports our objectives of identifying and studying genes and pathways involved in nitrogen-fixing symbiosis and those related to secondary metabolites that underlie red alder's many interesting defense, pigmentation, and wood quality traits. We established that this clone is most likely diploid and identified a set of SNPs that will have utility in future breeding and selection endeavors, as well as in ongoing population studies. We have added a well-characterized genome to others from the order Fagales. In particular, it improves significantly upon the only other published alder genome sequence, that of Alnus glutinosa. Our work initiated a detailed comparative analysis of members of the order Fagales and established some similarities with previous reports in this clade, suggesting a biased retention of certain gene functions in the vestiges of an ancient genome duplication when compared with more recent tandem duplications.

Tree-ring δ15N as an indicator of nitrogen dynamics in stands with N2-fixing Alnus rubra.

Tree-ring δ15N may depict site-specific, long-term patterns in nitrogen (N) dynamics under N2-fixing species, but field trials with N2-fixing tree species are lacking and the relationship of temporal patterns in tree-ring δ15N to soil N dynamics is controversial. We examined whether the tree-ring δ15N of N2-fixing red alder (Alnus rubra Bong.) would mirror N accretion rates and δ15N of soils and whether the influence of alder-fixed N could be observed in the wood of a neighboring conifer. We sampled a 27-year-old replacement series trial on south-eastern Vancouver Island, with red alder and coastal Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) planted in five proportions (0/100, 11/89, 25/75, 50/50 and 100/0) at a uniform stem density. An escalation in forest floor N content was evident with an increasing proportion of red alder, equivalent to a difference of ~750 kg N ha-1 between 100% Douglas-fir versus 100% alder. The forest floor horizon also had high δ15N values in treatments with more red alder. Red alder had a consistent quadratic fit in tree-ring δ15N over time, with a net increase of $\sim$1.5‰, on average, from initial values, followed by a plateau or slight decline. Douglas-fir tree-ring δ15N, in contrast, was largely unchanged over time (in three of four plots) but was significantly higher in the 50/50 mix. The minor differences in current leaf litter N content and δ15N between alder and Douglas-fir, coupled with declining growth in red alder, suggests the plateau or declining trend in alder tree-ring δ15N could coincide with lower N2-fixation rates, potentially by loss in alder vigor at canopy closure, or down-regulation via nitrate availability.

Seasonal disconnect between streamflow and retention shapes riverine nitrogen export in the Willamette River Basin, Oregon.

Watershed nutrient balance studies traditionally focus on annual fluxes. In areas with strongly seasonal, Mediterranean-type climate regimes, riverine nutrient export may be greater during wet seasons when hydrologic forcing overwhelms or bypasses retention mechanisms. By combining data on riverine export with spatially detailed nutrient inputs, we examine how nitrogen (N) supply, retention, and streamflow shape annual and seasonal riverine N export in Oregon's Willamette River Basin (WRB). The WRB has pronounced dry summers and wet winters, and the distribution of farmland, cities and forests create significant spatial variations in N inputs. Local data on N inputs were coupled with streamflow and chemistry to calculate fractional N export for 22 WRB sub-watersheds in the mid-2000s. For the entire WRB, 78% of the N inputs came from agricultural activities, mainly as synthetic fertilizer (69%); the next largest inputs were deposition (10%), alder fixation (5%) and point sources (5%). Crop-specific estimates of fertilizer agreed with county fertilizer sales rates at the high end of extension recommendations. Fractional riverine N export (annual riverine N export / net watershed N input) averaged 38% of net inputs in WRB tributaries, greater than other regions of North America. Fall and winter together accounted for 60-90% of the riverine N export across all watersheds. Summer export was small but was greatest in the watersheds that receive seasonal snowmelt. Large wet season losses, when biotic sinks are less active, result in a relatively high proportion of N inputs exported in this region with a Mediterranean climate and high runoff.

Culture-based identification to examine spatiotemporal patterns of fungal communities colonizing wood in ground contact.

Timber durability is often assessed using small wood stakes exposed in direct soil contact, and the assessment generally emphasizes effects on wood rather than organisms involved. Understanding fungal colonization patterns can help identify key decay agents under varying conditions and use these patterns to improve wood protection strategies. Fungal colonization of red alder (Alnus rubra), Douglas-fir (Pseudotsuga menziesii) heartwood/sapwood, and western redcedar (Thuja plicata) field stakes was assessed over 2 y in western Oregon. Spatiotemporal fungal community variations were identified via culturing and DNA sequencing, where 814 isolates were identified from 84 stakes. Forty-six ascomycete genera were identified, with Phialophora, Trichoderma, and Epicoccum species occurring most frequently. Twenty-three basidiomycete genera were identified, with Trametes and Phanerochaete being the most common. Douglas-fir and western redcedar stakes contained the highest and lowest diversity levels, respectively, reflecting natural durability differences of these species. Fungal species abundance was higher below ground than in the above ground and groundline zones, likely reflecting more stable moisture regimes, proximity to soil-based fungi, and potential nutrient migration into wood beneath the soil surface. Ascomycetes were proportionally more abundant early in the exposure period, but basidiomycetes were also observed early in the process, and there appeared to be no consistent colonization pattern.