Abstract
Most desert plants form symbiotic relationships with arbuscular mycorrhizal fungi (AMF), yet fungal identity and impacts on host plants remain largely unknown. Despite widespread recognition of the importance of AMF relationships for plant functioning, we do not know how fungal community structure changes across a desert climate gradient, nor the impacts of different fungal communities on host plant species. Because climate change can shape the distribution of species through effects on species interactions, knowing how the ranges of symbiotic partners are geographically structured and the outcomes of those species interactions informs theory and improves management recommendations. Here we used high throughput sequencing to examine the AMF community of Joshua trees along a climate gradient in Joshua Tree National Park. We then used a range of performance measures and abiotic factors to evaluate how different AMF communities may affect Joshua tree fitness. We found that fungal communities change with elevation resulting in a spectrum of interaction outcomes from mutualism to parasitism that changed with the developmental stage of the plant. Nutrient accumulation and the mycorrhizal growth response of Joshua tree seedlings inoculated with fungi from the lowest (warmest) elevations was first negative, but after 9 months had surpassed that of plants with other fungal treatments. This indicates that low elevation fungi are costly for the plant to initiate symbiosis, yet confer benefits over time. The strong relationship between AMF community and plant growth suggests that variation in AMF community may have long term consequences for plant populations along an elevation gradient.
Highlights
Symbioses between plants and mycorrhizal fungi are ubiquitous and diverse
To better understand how the role of climate, soil conditions, and fungal species influence symbiotic outcomes on a culturally significant plant in a desert environment, we focused on the mycorrhizal community of the Joshua tree (Yucca brevifolia) along an elevation gradient in Joshua Tree National Park (JTNP)
We examined how the arbuscular mycorrhizal fungi (AMF) community that associates with Joshua trees varies across an elevation gradient in JTNP and how those different fungal partners may impact Joshua tree fitness
Summary
Symbioses between plants and mycorrhizal fungi are ubiquitous and diverse. This ancient interaction evolved over 450 million years ago and is credited with assisting the early colonization of land by plants [1,2,3,4]. Joshua trees inoculated with mycorrhizal fungi nutrients and help plants resist disease, salinity, and drought, thereby playing a key role in plant fitness, productivity, and community composition [5,6,7]. These fungal symbionts are not always beneficial to the plant host; the fungi can sometimes function as parasites, reducing performance of their plant partners [8,9,10], depending on the species involved [11], the environmental conditions where the interaction occurs [12, 13] and developmental and phenological factors [14, 15]. The outcomes of the interactions are mutualistic when net benefits are greater than net costs for both partners, commensal when one partner benefits but the other receives neither benefit nor harm, and parasitic for either partner when costs exceed the benefits received [8, 15, 16]
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