skip to main content

Attention:

The NSF Public Access Repository (NSF-PAR) system and access will be unavailable from 11:00 PM ET on Friday, May 17 until 8:00 AM ET on Saturday, May 18 due to maintenance. We apologize for the inconvenience.


Title: Ectomycorrhizal fungal community assembly on seedlings of a Neotropical monodominant tree
Abstract

Ectomycorrhizal tree species may benefit from positive plant–soil feedbacks, where soil environments near adult trees enhance conspecific seedling growth and survival. In tropical monodominant forests, seedling survival is particularly important, as seedling banks help maintain stand‐level dominance over generations. Positive plant–soil feedbacks may be mediated by diverse ectomycorrhizal fungal communities, which improve nutrient acquisition of heavily shaded seedlings. Despite the potential importance of these fungi, little is known about ectomycorrhizal fungal community development on seedlings of tropical monodominant trees. In Guyana, we sequentially monitored percent colonization and species composition of ectomycorrhizal fungi on an even‐age cohort of seedlings of the tropical monodominant treeDicymbe corymbosa(Fabaceae subfamily Detarioideae). Ectomycorrhizal fungi found onDcorymbosaseedlings over a 12‐month period of early development were compared to those of conspecific adults and four other ectomycorrhizal tree species in the region. Species turnover was high (80%) between 6‐ and 12‐month‐old seedlings, though the /russula‐lactarius, /clavulina, and /tomentella‐thelephora lineages were species‐rich on seedlings at all ages. The number of ectomycorrhizal morphotypes per seedling increased with age, but extent of fungal colonization did not. Seedling ectomycorrhizal fungi were shared with sympatric conspecific adults (55%) and, to a lesser extent, regional heterospecific adults (27%), but numerous species were previously unrecorded for Guyana. Over their developmentD. corymbosaseedlings did not rely strictly on adult trees for their mycobionts but appeared to foster unique assemblages of ectomycorrhizal fungi.

 
more » « less
NSF-PAR ID:
10367125
Author(s) / Creator(s):
 ;  ;  ;  
Publisher / Repository:
Wiley-Blackwell
Date Published:
Journal Name:
Biotropica
Volume:
53
Issue:
6
ISSN:
0006-3606
Page Range / eLocation ID:
p. 1486-1497
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Seedling recruitment can be strongly affected by the composition of nearby plant species. At the neighborhood scale (on the order of tens of meters), adult conspecifics can modify soil chemistry and the presence of host microbes (pathogens and mutualists) across their combined canopy area or rooting zones. At local or small spatial scales (on the order of one to few meters), conspecific seed or seedling density can influence the strength of intraspecific light and resource competition and also modify the density‐dependent spread of natural enemies such as pathogens or invertebrate predators. Intrinsic correlation between proximity to adult conspecifics (i.e., recruitment neighborhood) and local seedling density, arising from dispersal, makes it difficult to separate the independent and interactive factors that contribute to recruitment success. Here, we present a field experiment in which we manipulated both the recruitment neighborhood and seedling density to explore how they interact to influence the growth and survival ofDryobalanops aromatica, a dominant ectomycorrhizal tree species in a Bornean tropical rainforest. First, we found that both local seedling density and recruitment neighborhood had effects on performance ofDaromaticaseedlings, though the nature of these impacts varied between growth and survival. Second, we did not find strong evidence that the effect of density on seedling survival is dependent on the presence of conspecific adult trees. However, accumulation of mutualistic fungi beneath conspecifics adults does facilitate establishment ofDaromaticaseedlings. In total, our results suggest that recruitment near adult conspecifics was not associated with a performance cost and may have weakly benefitted recruiting seedlings. Positive effects of conspecifics may be a factor facilitating the regional hyperabundance of this species. Synthesis: Our results provide support for the idea that dominant species in diverse forests may escape the localized recruitment suppression that limits abundance in rarer species.

     
    more » « less
  2. Abstract

    Feedbacks between plants and their soil microbial communities often drive negative density dependence in rare, tropical tree species, but their importance to common, temperate trees remains unclear. Additionally, whether negative density dependence is driven by natural enemies (e.g., soil pathogens) or by high densities of seedlings has rarely been assessed. Density dependence may also depend on seedling size, as smaller and/or younger seedlings may be more susceptible to mortality agents. We monitored seedlings ofQuercus rubra, a common, canopy‐dominant temperate tree, to investigate how the density of neighboring adults and seedlings influenced their survival over two years. We assessed how the soil microbial community influenced seedling survival by growing seedlings in a glasshouse inoculated with soil collected from beneath conspecific and heterospecific mature trees. In the field, seedling survival was lower in areas with high densities of mature conspecifics but was unrelated to either conspecific or heterospecific seedling density. Smaller seedlings were also more sensitive than larger seedlings to neighboring adult conspecifics. In the glasshouse, seedlings grown with soil from beneath a conspecific adult had a higher mortality rate than seedlings grown with soil from beneath heterospecific adults or sterilized soil, suggesting that soil microbial communities drive the patterns of mortality in the field. These results illustrate the importance of negative density‐dependent feedbacks resulting from the soil microbial community in a common and ecologically important temperate tree species.

     
    more » « less
  3. Yavitt, Joseph B. (Ed.)
    Conspecific negative density dependence (CNDD) promotes tree species diversity by reducing recruitment near conspecific adults due to biotic feedbacks from herbivores, pathogens, or competitors. While this process is well-described in tropical forests, tests of temperate tree species range from strong positive to strong negative density dependence. To explain this, several studies have suggested that tree species traits may help predict the strength and direction of density dependence: for example, ectomycorrhizal-associated tree species typically exhibit either positive or weaker negative conspecific density dependence. More generally, the strength of density dependence may be predictably related to other species-specific ecological attributes such as shade tolerance, or the relative local abundance of a species. To test the strength of density dependence and whether it affects seedling community diversity in a temperate forest, we tracked the survival of seedlings of three ectomycorrhizal-associated species experimentally planted beneath conspecific and heterospecific adults on the Prospect Hill tract of the Harvard Forest, in Massachusetts, USA. Experimental seedling survival was always lower under conspecific adults, which increased seedling community diversity in one of six treatments. We compared these results to evidence of CNDD from observed sapling survival patterns of 28 species over approximately 8 years in an adjacent 35-ha forest plot. We tested whether species-specific estimates of CNDD were associated with mycorrhizal association, shade tolerance, and local abundance. We found evidence of significant, negative conspecific density dependence (CNDD) in 23 of 28 species, and positive conspecific density dependence in two species. Contrary to our expectations, ectomycorrhizal-associated species generally exhibited stronger (e.g., more negative) CNDD than arbuscular mycorrhizal-associated species. CNDD was also stronger in more shade-tolerant species but was not associated with local abundance. Conspecific adult trees often have a negative influence on seedling survival in temperate forests, particularly for tree species with certain traits. Here we found strong experimental and observational evidence that ectomycorrhizal-associating species consistently exhibit CNDD. Moreover, similarities in the relative strength of density dependence from experiments and observations of sapling mortality suggest a mechanistic link between negative effects of conspecific adults on seedling and sapling survival and local tree species distributions. 
    more » « less
  4. Abstract

    Self‐reinforcing differences in fire frequency help closed‐canopy forests, which resist fire, and open woodlands, which naturally burn often, to co‐occur stably at landscape scales. Forest tree seedlings, which could otherwise encroach and overgrow woodlands, are killed by regular fire, yet fire has other effects that may also influence these feedbacks. In particular, many forest trees require symbiotic ectomycorrhizal fungi in order to establish. By restructuring soil fungal communities, fire might affect the availability of symbionts or the potential for symbiont sharing between encroaching trees and woodland vegetation.

    To investigate this possibility, we performed a soil bioassay experiment using inoculum from burned and unburned oak woodlands and Douglas‐fir forests. We examined how fire, ecosystem type, and neighboring heterospecific seedlings affect fungal root community assembly of Douglas‐firs and oaks. We asked whether heterospecific seedlings facilitated fungal colonization of seedling roots in non‐native soil, and if so, whether fire influenced this interaction.

    External fungal colonization of oak roots was more influenced by fire and ecosystem type than by the presence of a Douglas‐fir, and oaks increased the likelihood that Douglas‐fir roots would be colonized by fungi in oak woodland soil. Yet, fire increased colonization of Douglas‐fir in oak soil, diminishing the otherwise crucial role played by oak facilitation. Fire also strengthened the positive effect of Douglas‐firs on oak root‐associated fungal diversity in Douglas‐fir forest soil.

    Prior work shows that fire supports woodland ecosystems by stemming recruitment of encroaching seedlings. Here, we find evidence that it may contrastingly reduce fungal limitation of invasive seedling growth and establishment, otherwise relieved only by facilitation. Future work can investigate how these opposing effects might contribute to the net impact of changes in fire regime on landcover stability.

    Read the freePlain Language Summaryfor this article on the Journal blog.

     
    more » « less
  5. Summary

    Successive droughts have resulted in extensive tree mortality in the southwestern United States. Recovery of these areas is dependent on the survival and recruitment of young trees. For trees that rely on ectomycorrhizal fungi (EMF) for survival and growth, changes in soil fungal communities following tree mortality could negatively affect seedling establishment.

    We used tree‐focused and stand‐scale measurements to examine the impact of pinyon pine mortality on the performance of surviving juvenile trees and the potential for mutualism limitation of seedling establishment via alteredEMFcommunities.

    Mature pinyon mortality did not affect the survival of juvenile pinyons, but increased their growth. At both tree and stand scales, high pinyon mortality had no effect on the abundance ofEMFinocula, but led to alteredEMFcommunity composition including increased abundance ofGeoporaand reduced abundance ofTuber. Seedling biomass was strongly positively associated withTuberabundance, suggesting that reductions in this genus with pinyon mortality could have negative consequences for establishing seedlings.

    These findings suggest that whereas mature pinyon mortality led to competitive release for established juvenile pinyons, changes inEMFcommunity composition with mortality could limit successful seedling establishment and growth in high‐mortality sites.

     
    more » « less