Summary
The plant–soil feedback (PSF) framework has become an important theory in plant ecology, yet many ecological and evolutionary factors that influence PSFs have yet to be fully considered. ...Here, we discuss the importance of local adaptation among plants and root‐associated fungi and bacteria. Furthermore, we show how inclusion of the optimal resource allocation (OA) model can help predict the direction and outcome of PSFs under environmental change.
Plants and associated soil microbes have co‐evolved for millennia, generating adaptations to each other and to their local environment. This local co‐adaptation is likely generated by a suite of multidirectional exchanges of goods and services among plants, fungi and bacteria, and the constant changes in above‐ground–below‐ground interactions.
Resource limitation may be a driver of local adaptation among organisms involved in nutritional symbioses. The OA model states that when an essential resource is limited, natural selection will favour taxa that forage optimally by adjusting their biomass and energy allocation such that productivity is equally limited by all resources. Co‐adaptation will therefore respond to the local limiting resource conditions through taxa‐specific resource transfer interactions.
The OA model can help predict the outcomes of PSFs across a range of resource gradients and environmental changes such as increasing drought or atmospheric nitrogen deposition. Positive feedback is predicted in systems where resource exchange among plants and associated soil microbes can ameliorate resource limitation, or in systems where microbes provide another important service such as pathogen defence. Feedback strength is expected to diminish as resources become less limiting. Negative feedback is predicted when resources are in luxury supply and populations of opportunistic plant pathogens increase relative to commensal or mutualist microbes.
Future, field‐based studies that integrate naturally co‐occurring systems of plants, microbes and their local soil are needed to further test the hypothesis that resource availability is an effective predictor of the direction and magnitude of PSFs. A more mechanistic understanding of PSFs will help land managers and farmers to manipulate plant–microbial soil interactions to respond to environmental change and to effectively harness beneficial symbioses for plant nutrition and pathogen control.
Lay Summary
Fungal load quantification is a critical component of fungal community analyses. Limitation of current approaches for quantifying the fungal component in the human microbiome suggests the need for ...new broad-coverage techniques.
We analyzed 2,085 18S rRNA gene sequences from the SILVA database for assay design. We generated and quantified plasmid standards using a qPCR-based approach. We evaluated assay coverage against 4,968 sequences and performed assay validation following the Minimum Information for Publication of Quantitative Real-Time PCR Experiments (MIQE) guidelines.
We designed FungiQuant, a TaqMan® qPCR assay targeting a 351 bp region in the fungal 18S rRNA gene. Our in silico analysis showed that FungiQuant is a perfect sequence match to 90.0% of the 2,617 fungal species analyzed. We showed that FungiQuant's is 100% sensitive and its amplification efficiencies ranged from 76.3% to 114.5%, with r(2)-values of >0.99 against the 69 fungal species tested. Additionally, FungiQuant inter- and intra-run coefficients of variance ranged from <10% and <20%, respectively. We further showed that FungiQuant has a limit of quantification 25 copies and a limit of detection at 5 copies. Lastly, by comparing results from human-only background DNA with low-level fungal DNA, we showed that amplification in two or three of a FungiQuant performed in triplicate is statistically significant for true positive fungal detection.
FungiQuant has comprehensive coverage against diverse fungi and is a robust quantification and detection tool for delineating between true fungal detection and non-target human DNA.
The disruption of mutualisms between plants and mycorrhizal fungi is a potentially powerful mechanism by which invasives can negatively impact native species, yet our understanding of this ...mechanism's role in exotic species invasion is still in its infancy. Here, we provide several lines of evidence indicating that invasive tamarisk (
Tamarix
sp.) negatively affects native cottonwoods (
Populus fremontii
) by disrupting their associations with arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) fungi. At a field site in the early stages of tamarisk invasion, cottonwoods with tamarisk neighbors had reduced EM colonization and altered EM fungal community composition relative to cottonwoods with native neighbors, leading to reductions in EM propagule abundance in the soil beneath tamarisk. Similarly, AM colonization of cottonwoods was reduced with a tamarisk neighbor, but there were no significant changes in AM fungal spore communities or propagule abundance. Root colonization by nonmycorrhizal fungi, including potential pathogens, was higher in cottonwoods with tamarisk neighbors. A greenhouse experiment in which AM and EM inoculation and plant neighbor were manipulated in a fully factorial design showed that cottonwoods benefited from mycorrhizas, especially EM, in terms of shoot biomass when grown with a conspecific, but shoot biomass was similar to that of nonmycorrhizal controls when cottonwoods were grown with a tamarisk neighbor. These results are partially explained by a reduction in EM but not AM colonization of cottonwoods by a tamarisk neighbor. Tamarisk neighbors negatively affected cottonwood specific leaf area, but not chlorophyll content, in the field. To pinpoint a mechanism for these changes, we measured soil chemistry in the field and the growth response of an EM fungus (
Hebeloma crustuliniforme
) to salt-amended media in the laboratory. Tamarisk increased both NO
3
−
concentrations and electrical conductivity 2.5-fold beneath neighboring cottonwoods in the field. Salt-amended media did not affect the growth of
H. crustuliniforme
. Our findings demonstrate that a nonnative species, even in the early stages of invasion, can negatively affect a native species by disrupting its mycorrhizal symbioses. Some of these changes in mycorrhizal fungal communities may remain as legacy effects of invasives, even after their removal, and should be considered in management and restoration efforts.
Plant genetic variation and soil microorganisms are individually known to influence plant responses to climate change, but the interactive effects of these two factors are largely unknown. Using ...long-term observational studies in the field and common garden and greenhouse experiments of a foundation tree species (Pinus edulis) and its mutualistic ectomycorrhizal fungal (EMF) associates, we show that EMF community composition is under strong plant genetic control. Seedlings acquire the EMF community of their seed source trees (drought tolerant vs. drought intolerant), even when exposed to inoculum from the alternate tree type. Drought-tolerant trees had 25% higher growth and a third the mortality of drought-intolerant trees over the course of 10 y of drought in the wild, traits that were also observed in their seedlings in a common garden. Inoculation experiments show that EMF communities are critical to drought tolerance. Drought-tolerant and drought-intolerant seedlings grew similarly when provided sterile EMF inoculum, but drought-tolerant seedlings grew 25% larger than drought-intolerant seedlings under dry conditions when each seedling type developed its distinct EMF community. This demonstration that particular combinations of plant genotype and mutualistic EMF communities improve the survival and growth of trees with drought is especially important, given the vulnerability of forests around the world to the warming and drying conditions predicted for the future.
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 altered EMF communities.
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 of EMF inocula, but led to altered EMF community composition including increased abundance of Geopora and reduced abundance of Tuber. Seedling biomass was strongly positively associated with Tuber abundance, 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 in EMF community composition with mortality could limit successful seedling establishment and growth in high-mortality sites.
Community-level genetic specificity results when individual genotypes or populations of the same species support different communities. Our review of the literature shows that genetic specificity ...exhibits both life and afterlife effects; it is a widespread phenomenon occurring in diverse taxonomic groups, aquatic to terrestrial ecosystems, and species-poor to species-rich systems. Such specificity affects species interactions, evolution, ecosystem processes and leads to community feedbacks on the performance of the individuals expressing the traits. Thus, genetic specificity by communities appears to be fundamentally important, suggesting that specificity is a major driver of the biodiversity and stability of the world's ecosystems.
1. Although drought frequency and severity are predicted to increase across numerous continental interiors, the consequences of these changes for dominant plants are largely unknown. Over the last ...decade, the south-western US has experienced six drought years, including the extreme droughts of 1996 and 2002, which led to widespread tree mortality across northern Arizona. 2. We examined the impact of these droughts on the co-dominant tree species of the pinyon-juniper woodland (Pinus edulis and Juniperus monosperma), a major vegetation type in the US. 3. Pinyon mortality following both droughts was 6.5-fold higher than juniper mortality. In addition, large pinyons suffered 2-6-fold greater mortality than small pinyons, a pattern associated with higher mortality of reproductively mature trees and survival of smaller pinyons resulting from facilitation by established vegetation. Differential mortality of large pinyons resulted in a vegetation shift such that the pinyon-juniper woodlands are becoming dominated by juniper, a species that is typical of lower elevations and more arid conditions. 4. Sites that experienced high pinyon mortality during the first drought suffered additional mortality during the second drought, so that reductions in tree densities and the resulting release from below-ground competition did not buffer surviving pinyons against additional mortality during the second drought. Such repeated mortality events also suggest that these stands may suffer chronic stress. 5. Reductions in biotic associations (e.g. avian seed dispersers, ectomycorrhizas and nurse plants) that will probably result from extreme mortality of large pinyons ensure that the observed vegetation shifts will be persistent. Because approximately 1000 species are associated with pinyon pine, the shift in the structure of these woodlands has large-scale community consequences.
Is there tree senescence? The fecundity evidence Qiu, Tong; Aravena, Marie-Claire; Andrus, Robert ...
Proceedings of the National Academy of Sciences - PNAS,
08/2021, Letnik:
118, Številka:
34
Journal Article
Recenzirano
Odprti dostop
Despite its importance for forest regeneration, food webs, and human economies, changes in tree fecundity with tree size and age remain largely unknown. The allometric increase with tree diameter ...assumed in ecological models would substantially overestimate seed contributions from large trees if fecundity eventually declines with size. Current estimates are dominated by overrepresentation of small trees in regression models. We combined global fecundity data, including a substantial representation of large trees. We compared size-fecundity relationships against traditional allometric scaling with diameter and two models based on crown architecture. All allometric models fail to describe the declining rate of increase in fecundity with diameter found for 80% of 597 species in our analysis. The strong evidence of declining fecundity, beyond what can be explained by crown architectural change, is consistent with physiological decline. A downward revision of projected fecundity of large trees can improve the next generation of forest dynamic models.
The type of mycorrhizal associations (i.e. ectomycorrhizal EM or arbuscular mycorrhizal AM) formed by trees is of fundamental importance for a range of soil properties and processes in forests, yet ...their importance for the distribution of other important soil biota such as bacteria is largely unknown.
We used an experimental common garden and amplicon sequencing to assess how abiotic and biotic variation differentially influenced bacterial communities associated with 13 climax tree species (8 EM members of the Dipterocarpaceae and 5 AM species from different families) planted into a secondary tropical forest in Borneo.
Rhizosphere bacterial (RB) communities differed significantly between EM and AM trees but not among EM species and only marginally among AM species.
RB communities were related to the density and size of neighbouring EM but not AM trees. Diversity of RB on AM trees responded positively to AM neighbours and negatively to EM neighbours but RB diversity associated with EM trees was unaffected by neighbourhood. Plant‐growth‐promoting taxa of RB assorted similarly to total RB but more strongly.
Synthesis. Our results suggest that the distribution of RB communities is associated with plant mycorrhizal type and plant neighbourhood. Because rhizosphere bacteria alter nutrient cycling and influence plant species composition, their distributions are likely important for understanding ecosystem processes and plant demographics in forest ecosystems.
Abstrak
Hubungan antara jenis mikoriza (iaitu mikoriza ekto‐ atau arbuskular) yang dibentuk oleh pepohon adalah asas yang penting bagi pelbagai jenis sifat dan proses‐proses tanah dalam sesebuah ekosistem hutan, namun kepentingannya dalam distribusi biota tanah yang lain seperti bakteria masih belum diketahui. Ia jelas sekali terutamanya dalam kepelbagaian jenis hutan tropika di mana pepohon dengan jenis mikoriza yang berbeza saling bercampuran dalam sesuatu persekitaran biotik dan abiotik yang amat heterogenus.
Di sini, kami menggunakan satu taman biasa eksperimental yang membantu kami menilai bagaimana variasi abiotik dan biotik mempengaruhi secara berbeza komuniti bakteria yang dikaitkan dengan pepohon yang ditanam di dalam hutan tropika sekunder Borneo.
Kami telah menggunakan penjujukan amplikon penjanaan tinggi untuk mencirikan komuniti bakteria rizosfera daripada 13 spesies pokok klimaks (8 ektomikoriza dan 5 mikoriza arbuskular) melalui hubungkait dengan ciri tumbuhan, kejiranan tumbuhan dan persekitaran abiotik.
Komuniti bakteria Rhizosphere (RB) berbeza dengan ketara antara pepohon EM dan AM tetapi tidak di kalangan spesies EM dan hanya sedikit di kalangan spesies AM.
Nutrien dedaun, terutamanya kalium, menunjukkan hubungan dengan komposisi komuniti RB.
Our results suggest that the distribution of rhizosphere bacterial communities is associated with plant mycorrhizal type and plant neighbourhood. Because rhizosphere bacteria alter nutrient cycling and influence plant species composition, their distributions are likely important for understanding ecosystem processes and plant demographics in forest ecosystems
Background and aims
Subtle morphological traits, such as leaf litter curling, may have unexpected legacy effects on ecosystems. We tested the hypotheses that litter curling is influenced by plant ...species, hybridization and genotype, and has extended consequences for associated organisms and soil processes.
Methods
A novel litter curling index (LCI) was used to characterize the curling of leaf litter from 11 plant species (including shrubs, trees and a forb) in natural field sites and of two
Populus
species (
P. fremontii
James,
P. angustifolia
S. Watson), their F
1
hybrids and replicated
P. angustifolia
genotypes from a common garden. Surveys of dominant, litter-dwelling spiders (Agelenidae), and a soil drying experiment, were used to test the potential extended ecological consequences of litter curling.
Results
Five results emerged. (1) LCI ranged 15-fold among plant species in natural sites. (2) LCI nearly doubled from
P. fremontii
to
P. angustifolia
, while average LCI for F
1
hybrids was intermediate (although not statistically different from
P. fremontii
). (3) LCI exhibited broad-sense heritability (
H
2
= 0.42) among
P. angustifolia
genotypes. (4) Abundance of spider webs was positively associated with increasing litter curl across the
Populus
hybrid system (
R
2
= 0.35). (5) After 57 days of drying, flat litter contained 1.4 times higher moisture than curled litter, which translated to wetter soil beneath flat litter.
Conclusion
Litter curling has a genetic basis, which has legacy effects on other trophic levels and soil moisture dynamics that may shape the ecology and evolution of complex communities.
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