Two new endophytic species enrich the Coniochaeta endophytica / C. prunicola clade: Coniochaeta lutea sp. nov. and C. palaoa sp. nov.

Coniochaeta (Coniochaetaceae, Ascomycota) is a diverse genus that includes a striking richness of undescribed species with endophytic lifestyles, especially in temperate and boreal plants and lichens. These endophytes frequently represent undescribed species that can clarify evolutionary relationships and trait evolution within clades of previously classified fungi. Here we extend the geographic, taxonomic, and host sampling presented in a previous analysis of the clade containing Coniochaeta endophytica, a recently described species occurring as an endophyte from North America; and C. prunicola, associated with necroses of stonefruit trees in South Africa. Our multi-locus analysis and examination of metadata for endophyte strains housed in the Robert L. Gilbertson Mycological Herbarium at the University of Arizona (ARIZ) (1) expands the geographic range of C. endophytica across a wider range of the USA than recognized previously; (2) shows that the ex-type of C. prunicola (CBS 120875) forms a well-supported clade with endophytes of native hosts in North Carolina and Michigan, USA; (3) reveals that the ex-paratype for C. prunicola (CBS 121445) forms a distinct clade with endophytes from North Carolina and Russia, is distinct morphologically from the other taxa considered here, and is described herein as Coniochaeta lutea; and (4) describes a new species, Coniochaeta palaoa, here identified as an endophyte of multiple plant lineages in the highlands and piedmont of North Carolina. Separation of CBS 120875 and CBS 121445 into C. prunicola sensu stricto and C. lutea is consistent with previously described genomic differences between these isolates, and morphological and functional differences among the four species (C. endophytica, C. prunicola, C. palaoa, and C. lutea) underscore the phylogenetic relationships described here. The resolving power of particular loci and the emerging perspective on the host- and geographic range of Coniochaeta and the C. endophytica / C. prunicola clade are discussed.

Persistence of remnant boreal plants in the Chiricahua Mountains, southern Arizona

Boreal plants growing along southern edge of their range on isolated mountains in a hot desert matrix live near the extreme of their physiological tolerance. Such plants are considered to be sensitive to small changes in climate. We coupled field observations (1974, 1993, 2019) about the abundance and vigor of small populations of ten remnant boreal plant species persisting in uppermost elevation spruce-fir forests of the Chiricahua Mountains, together with a theoretical modeling of the species' tolerances to three climate change cues: warming, drought, and forest fire, in order to explore the persistence of frontier boreal plant species in the frame of climate changes. We hypothesized that populations of these cryophilic plants have declined or become locally extinct during an adverse warming period since 1993, enforced by two large forest fires (1994, 2011). We used plant functional traits and principal component analysis to model tolerances of the plants to combined actions of warming, drought, and forest fire. Our model predicted selective sensitivity to warming for two species: Vaccinium myrtillus and Rubus parviflorus, while possible decline of the other species could be explained by drought and/or fire. We surveyed the study area in 2019 and found eight of the ten species still occur in the area. Five species occurred in wet canyons at lower elevations, but three species persisted in low vigor at the uppermost elevation highly affected by fires. Both warming-sensitive species did not show signs of decline: population of R. parviflorus increased in abundance and vigor, while V. myrtillus persists without significant changes since 1993. Despite the recorded increase in temperature in the study area over one degree Celsius between years 1975-1993 and 1994-2019, our study did not find evidence of the direct warming effect on the observed species. We conclude that severe wildfires and multi-decadal decrease in precipitation rather than warming are the main limiting factors of the remnant boreal species remarkable but limited persistence in the Chiricahua Mountains. Our study demonstrates how field observations can be combined with modeling to evaluate species selective responses to different environmental stresses for better environmental management decisions, particularly in light of climate change.

Short-interval wildfire and drought overwhelm boreal forest resilience

The size and frequency of large wildfires in western North America have increased in recent years, a trend climate change is likely to exacerbate. Due to fuel limitations, recently burned forests resist burning for upwards of 30 years; however, extreme fire-conducive weather enables reburning at shorter fire-free intervals than expected. This research quantifies the outcomes of short-interval reburns in upland and wetland environments of northwestern Canadian boreal forests and identifies an interactive effect of post-fire drought. Despite adaptations to wildfire amongst boreal plants, post-fire forests at paired short- and long-interval sites were significantly different, with short-interval sites having lower stem densities of trees due to reduced conifer recruitment, a higher proportion of broadleaf trees, less residual organic material, and reduced herbaceous vegetation cover. Drought reinforced changes in proportions of tree species and decreases in tree recruitment, reinforcing non-resilient responses to short-interval reburning. Drier and warmer weather will increase the incidence of short-interval reburning and amplify the ecological changes such events cause, as wildfire activity and post-fire drought increase synergistically. These interacting disturbances will accelerate climate-driven changes in boreal forest structure and composition. Our findings identify processes of ongoing and future change in a climate-sensitive biome.

Effects of invasive plant patch size and distance on the pollination and reproduction of native boreal plants

In pollinator-limited ecosystems in the earliest stages of the invasion process, the effects of invasive plants on the pollination and reproduction of co-flowering native plants may be particularly sensitive to the distance between native and non-native plants. Our study tests how the distance from invasive plant patches affects the pollination and reproduction of two native boreal shrubs. We established circular sites with plots of flowering Vaccinium vitis-idaea L. and Rhododendron groenlandicum (Oeder) Kron and Judd spanning from 1 to 40 m from the site center. In 2011 and 2012, we added flowering non-native Melilotus albus Medik. to the center of sites in small patches (40 individuals) or large patches (120 individuals) and left other sites as controls. In some cases, the effects of M. albus were uniform across the 40 m distance, such as the change in V. vitis-idaea seed production when large patches of M. albus were added. In other cases, relationships with distance were found, and changes in percent pollination or seed production occurred most rapidly over the first 10 m from the patch. Our data supports the hypothesis that the detectable impact an invasive species has on the pollination of native species is affected by the spatial scale over which it is evaluated.