Soil pathogens and spatial patterns of seedling mortality in a temperate tree

Packer, Alissa; Clay, Keith

doi:10.1038/35005072

Cited by 814 publications

(901 citation statements)

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“…Plant traits commonly show a phylogenetic signal, including the ones that are important in plant–enemy interactions, where close relatives are more likely to have similar traits (Agrawal, 2007), and are thereby susceptible to colonization by closely related pathogens. Due to their limited dispersal ability, initial colonization of fungi is most likely to occur on spatially associated hosts (e.g., Packer & Clay, 2000). Closely related tree species may also favor similar environmental conditions such as light and soil moisture (Emerson & Gillespie, 2008), which could facilitate the growth and reproduction of some closely related fungi that also prefer the same environments (Horn, Caruso, Verbruggen, Rillig, & Hempel, 2014).…”

Section: Discussionmentioning

confidence: 99%

“…For these mechanisms to help maintain species diversity, local host specificity or selectivity of the enemies for host species is required, and as such, knowledge of the host range of pathogens is fundamental to understanding their impacts. However, most studies of pathogens in such feedback systems have either focused on specific plant–pathogen interactions (e.g., Gilbert, Hubbell, & Foster, 1994; Packer & Clay, 2000) or have treated the whole pathogen community as a black box without identifying its composition and diversity (e.g., Bever, 1994; Klironomos, 2002; Liu et al., 2012; Mangan et al., 2010; Petermann, Fergus, Turnbull, & Schmid, 2008; Spear, Coley, & Kursar, 2015). Neither approach provides a clear picture of how diverse sets of interacting host and pathogen species shape community diversity.…”

Section: Introductionmentioning

confidence: 99%

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Phylogenetic congruence between subtropical trees and their associated fungi

Liu

Liang

Etienne

et al. 2016

Ecology and Evolution

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Recent studies have detected phylogenetic signals in pathogen–host networks for both soil‐borne and leaf‐infecting fungi, suggesting that pathogenic fungi may track or coevolve with their preferred hosts. However, a phylogenetically concordant relationship between multiple hosts and multiple fungi in has rarely been investigated. Using next‐generation high‐throughput DNA sequencing techniques, we analyzed fungal taxa associated with diseased leaves, rotten seeds, and infected seedlings of subtropical trees. We compared the topologies of the phylogenetic trees of the soil and foliar fungi based on the internal transcribed spacer (ITS) region with the phylogeny of host tree species based on matK, rbcL, atpB, and 5.8S genes. We identified 37 foliar and 103 soil pathogenic fungi belonging to the Ascomycota and Basidiomycota phyla and detected significantly nonrandom host–fungus combinations, which clustered on both the fungus phylogeny and the host phylogeny. The explicit evidence of congruent phylogenies between tree hosts and their potential fungal pathogens suggests either diffuse coevolution among the plant–fungal interaction networks or that the distribution of fungal species tracked spatially associated hosts with phylogenetically conserved traits and habitat preferences. Phylogenetic conservatism in plant–fungal interactions within a local community promotes host and parasite specificity, which is integral to the important role of fungi in promoting species coexistence and maintaining biodiversity of forest communities.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Phylogenetic congruence between subtropical trees and their associated fungi

Liu

Liang

Etienne

et al. 2016

Ecology and Evolution

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“…Since soil pathogens can reduce survival of tree seedlings (Augspurger 1984;Packer and Clay 2000) and reduce the abundance of trees relative to herbaceous vegetation (Weste 1986), it is possible that pathogenic infection rates differed between the non-indigenous and native grass subplots. At Cedar Creek, Johnson et al (1991) found that different grass species support different the communities of vesicular-arbuscular mycorrhizal (VAM) fungi, and, in particular, that VAM fungi communities differed between garden plots composed of Schizachyrium scoparium and Poa pratensis, respectively (Johnson et al 1992).…”

Section: Discussionmentioning

confidence: 99%

Non-indigenous grasses impede woody succession

et al. 2005

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With the proliferation of old fields and the decline of native grasslands in North America, non-indigenous grasses, which tend to colonize and dominate North American old fields, have become progressively more abundant. These new grasses can differ from native grasses in a number of ways, including root and shoot morphology (e.g., density of root mat, height of shoots), growth phenology (e.g., cool season vs. warm season growth), and plant-soil-water relations due to differences in photosynthetic physiology (C 3 vs. C 4 ). Woody plants have been slow to colonize some old fields in the prairie-forest border area of North America and it is hypothesized that non-indigenous grasses may be contributing to the poor establishment success of woody plants in this region, possibly through more intense competition for resources. To test this hypothesis, a multi-factorial field experiment was conducted in which water, nitrogen, and grass functional group (non-indigenous C 3 and native C 4 species) were manipulated in a study of survival of oak seedlings. The grass type variously affected some of the different growth measurements, however, the effects of grass type on seedling growth were small compared to the effects on seedling survival. The results showed that when grown under dry conditions, seedlings growing in non-indigenous grasses experienced up to a 50% reduction in survival compared to those growing in native grasses under the same conditions. Analyses of root and shoot competition showed that the cause for the reduced survival in the non-indigenous grasses was due primarily to underground processes. The findings confirmed our initial hypothesis that nonindigenous grasses are likely contributing to the poor establishment success of woody plants in these old fields. However, the explanation for the reduced oak seedling survival in non-indigenous grasses does not appear to be due to reduced resource availability since soil water levels did not differ between nonindigenous and native grass plots and other resource levels measured (light, NO 3 , and NH 4 ) were higher in non-indigenous grass plots under dry conditions. An alternative explanation is that the non-indigenous grasses modify the soil environment in ways that, under dry conditions, are deleterious to emerging oak seedlings. Since current climate projections for the upper Midwest are for hotter and drier summers, the results suggest that the resistance of these old fields to oak encroachment will likely increase in the future.

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“…These stages of growth are important because they are the most numerous, and during these stages mortality can be very high. It now seems probable that intense mortality at the seed-to-seedling transition is frequently caused by plant pathogens, particularly Oomycota, which cause damping-off diseases in young seedlings (Augspurger 1983a(Augspurger ,b, 1990Dobson & Crawley 1994;Gilbert et al 1994;Gilbert & Hubbell 1996;Packer & Clay 2000;Gilbert 2005). In the rest of this paper, we will concentrate on the effects of pathogens on coexistence through seedling mortality, although many of the points that we make are equally applicable to other natural enemies.…”

Section: Introductionmentioning

confidence: 99%

Pathogens, density dependence and the coexistence of tropical trees

2006

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There is increasing interest in the role played by density-dependent mortality from natural enemies, particularly plant pathogens, in promoting the coexistence and diversity of tropical trees. Here, we review four issues in the analysis of pathogen-induced density dependence that have been overlooked or inadequately addressed. First, the methodology for detecting density dependence must be robust to potential biases. Observational studies, in particular, require a careful analysis to avoid biases generated by measurement error, and existing studies could be criticized on these grounds. Experimental studies manipulating plant density and pathogen incidence will often be preferable, or should be run in parallel. Second, the form of density dependence is not well understood and, in particular, there are no data indicating whether pathogens cause compensating or overcompensating density responses. Owing to this, we argue that the potential for pathogen-induced density dependence to generate diversity-enhancing outcomes, such as the Janzen-Connell effect, remains uncertain, as coexistence is far more probable if density dependence is overcompensating. Third, there have been few studies examining the relative importance of intra-or interspecific density dependence resulting from pathogens (or, more widely, natural enemies). This is essentially equivalent to asking to what extent pathogens are host-specific. If pathogens are generalists, then mortality rates will respond to overall plant density, irrespective of plant species identity. This will weaken the intraspecific density dependence and reduce the diversity-promoting effects of pathogens. Finally, we highlight the need for studies that integrate observations and experiments on pathogens and density dependence into the whole life cycle of trees, because as yet it is not possible to be certain of the degree to which pathogens contribute to observed dynamics.

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Soil pathogens and spatial patterns of seedling mortality in a temperate tree

Cited by 814 publications

References 26 publications

Phylogenetic congruence between subtropical trees and their associated fungi

Phylogenetic congruence between subtropical trees and their associated fungi

Non-indigenous grasses impede woody succession

Pathogens, density dependence and the coexistence of tropical trees

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