Biology subjects

Leopold, D. R.

Publications and source records attributed to Leopold, D. R..

3 recordsLinked to original sources

bioRxiv2020

Ericoid mycorrhizal diversity increases with soil age and progressive phosphorus limitation across a 4.1 million-year chronosequence

Ericaceous plants rely on ericoid mycorrhizal fungi for nutrient acquisition. However, the factors that affect the composition and structure of these fungal communities remain largely unknown. Here, we use a 4.1-myr soil chronosequence in Hawaii to test the hypothesis that changes in nutrient availability with soil age determine the diversity and species composition of fungi associated with ericoid roots. We sampled roots of a native Hawaiian plant, Vaccinium calycinum, and used DNA metabarcoding to quantify changes in fungal diversity and species composition. We also used a fertilization experiment at the youngest and oldest sites to assess the importance of nutrient limitation. We found an increase in diversity and a clear pattern of species turnover across the chronosequence, driven largely by putative ericoid mycorrhizal fungi. Fertilization with nitrogen at the youngest site and phosphorus at the oldest site reduced total fungal diversity, suggesting a direct role of nutrient limitation. Our results also reveal the presence of novel fungal species associated with Hawaiian Ericaceae and suggest a greater importance of phosphorus availability for communities of ericoid mycorrhizal fungi than is generally assumed.

ecology↗

bioRxiv2020

Greater local diversity under older species pools may arise from enhanced competitive equivalence

Local ecological communities tend to contain more species when they are located within a geologically older region, a pattern that has traditionally been attributed to the accumulation of species in the regional species pool. In this explanation, local species interactions are assumed to play a minor role in the formation of the regional species pool, which is instead thought to be driven by speciation and dispersal occurring across larger areas. Here, we provide evidence suggesting a more important role of local species interactions than generally assumed. In an experiment in which we assembled 320 local communities of root-associated fungi under 80 species pools, we varied the species richness of the experimental species pools and the mean age of the sites from which we collected the fungal species across a 4-myr soil chronosequence in Hawaii. We found that realized local species diversity in the assembled communities increased more extensively with increasing species-pool richness when species were from older sites. We also found that older species pools had lower functional and phylogenetic diversity, indicating that the evolution of greater competitive equivalence among potential colonists enabled higher local diversity under older species pools. Our results suggest that the tendency of older regions to have higher local richness arises not simply because older species pools are more speciose, but also because the constituent species have evolved traits that allow them to co-occur more readily in local communities.

ecology↗

bioRxiv2020

Joint effects of host genotype and species arrival order govern plant microbiome composition and function

The composition of host-associated microbiomes can have important consequences for host health and fitness [1-3]. Yet, we still lack understanding of many fundamental processes that determine microbiome composition [4,5]. There is mounting evidence that historical contingency during microbiome assembly may overshadow more deterministic processes, such as the selective filters imposed by host traits [6-8]. More specifically, species arrival order has been frequently shown to affect microbiome composition [9-12], a phenomenon known as priority effects [13-15]. However, it is less clear whether priority effects during microbiome assembly are consequential for the host [16], or whether intraspecific variation in host traits can alter the trajectory of microbiome assembly under priority effects. In a greenhouse inoculation experiment using the black cottonwood (Populus trichocarpa) foliar microbiome, we manipulated host genotype and the colonization order of common foliar fungi. We quantified microbiome assembly outcomes using fungal marker-gene sequencing and measured susceptibility of the colonized host to a leaf rust pathogen, Melampsora x columbiana. We found that the effect of species arrival order on microbiome composition, and subsequent disease susceptibility, depended on the host genotype. Additionally, we found that microbiome assembly history can affect host disease susceptibility independent of microbiome composition at the time of pathogen exposure, suggesting that the interactive effects of species arrival order and host genotype can decouple community composition and function. Overall, these results highlight the importance of a key process underlying stochasticity in microbiome assembly while also revealing which hosts are most likely to experience these effects.

ecology↗