Abstract
As communities assemble, species establishment can be driven by multiple factors. Two such factors, nutrients and consumers, are predicted to interact, but few studies have explored whether ...this interaction results from synergistically altering the same biotic and abiotic mediators or complementarily altering different mediators.
To test this, I added seeds of multiple native species to old field communities in which I experimentally manipulated soil nutrients, leaf litter and consumers (insect herbivores and fungal pathogens). Using Bayesian hierarchical modelling, I evaluated the degree to which changes in light and water availability, fungal disease and insect herbivory, and community functional composition influenced seedling establishment and the richness of colonizing species and were driven by experimental treatments. I then examined whether nutrients, litter and consumers interactively determined the success of colonizing species with different resource allocation strategies.
Contrary to expectation, nutrient addition and consumer exclusion reduced, and litter removal increased, seedling establishment and colonizer richness independently and via different pathways. Also contrary to expectation, seedling resource allocation strategy did not interact with nutrient addition and consumer exclusion to alter establishment success. Rather, as community damage (foliar fungal disease + insect herbivory) increased, seedlings with high % leaf nitrogen (a proxy for an acquisitive resource allocation strategy) become increasingly disadvantaged relative to seedlings with low % leaf nitrogen (a proxy for a conservative resource allocation strategy).
Synthesis
: These results indicate that seedling establishment is unlikely to be interactively impacted by nutrients and consumers (fungal pathogens + insect herbivores) because these two drivers act on different environmental pathways to influence community assembly.
We present unresolved questions in plant abiotic stress biology as posed by 15 research groups with expertise spanning eco-physiology to cell and molecular biology. Common themes of these questions ...include the need to better understand how plants detect water availability, temperature, salinity, and rising carbon dioxide (CO2) levels; how environmental signals interface with endogenous signaling and development (e.g. circadian clock and flowering time); and how this integrated signaling controls downstream responses (e.g. stomatal regulation, proline metabolism, and growth versus defense balance). The plasma membrane comes up frequently as a site of key signaling and transport events (e.g. mechanosensing and lipid-derived signaling, aquaporins). Adaptation to water extremes and rising CO2 affects hydraulic architecture and transpiration, as well as root and shoot growth and morphology, in ways not fully understood. Environmental adaptation involves tradeoffs that limit ecological distribution and crop resilience in the face of changing and increasingly unpredictable environments. Exploration of plant diversity within and among species can help us know which of these tradeoffs represent fundamental limits and which ones can be circumvented by bringing new trait combinations together. Better defining what constitutes beneficial stress resistance in different contexts and making connections between genes and phenotypes, and between laboratory and field observations, are overarching challenges.
Plants demonstrate a broad range of responses to environmental shifts. One of the most remarkable responses is plasticity, which is the ability of a single plant genotype to produce different ...phenotypes in response to environmental stimuli. As with all traits, the ability of plasticity to evolve depends on the presence of underlying genetic diversity within a population. A common approach for evaluating the role of genetic variation in driving differences in plasticity has been to study genotype-by-environment interactions (G × E). G × E occurs when genotypes produce different phenotypic trait values in response to different environments. In this review, we highlight progress and promising methods for identifying the key environmental and genetic drivers of G × E. Specifically, methodological advances in using algorithmic and multivariate approaches to understand key environmental drivers combined with new genomic innovations can greatly increase our understanding about molecular responses to environmental stimuli. These developing approaches can be applied to proliferating common garden networks that capture broad natural environmental gradients to unravel the underlying mechanisms of G × E. An increased understanding of G × E can be used to enhance the resilience and productivity of agronomic systems.
Seed mass is an ecologically important trait that often differs considerably among ecotypes. Yet, because few studies examine the impacts of seed mass on adult life-history traits, its role in local ...adaptation is unclear. In this study, using accessions of
that spanned the two major ecotypes, we examined whether covariation between seed mass, seedling and reproductive traits impacts ecotypic divergence and local adaptation. The perennial grass
has two distinct ecotypes-a large-seeded upland ecotype adapted to xeric environments and a small-seeded lowland ecotype adapted to mesic environments. In the greenhouse, seed mass varied greatly across
genotypes in a manner consistent with ecotypic divergence. Seed mass covaried significantly with several seedling and reproductive traits. At field sites representing the habitats of the two ecotypes, seed mass had different impacts on seedling and adult recruitment: selection favoured large seeds in upland habitat and small seeds in lowland habitat, which was consistent with local adaptation. By demonstrating the central role of seed mass in ecotypic differences in
and its importance to seedling and adult recruitment under field conditions, these studies show that early life-history traits can promote local adaptation and potentially explain ecotype formation.
High-resource environments typically favor quick-growing, poorly defended plants, while resource-poor environments typically favor slow-growing, well-defended plants. The prevailing hypothesis ...explaining this pattern states that, as resource availability increases, well-defended, slow-growing species are replaced by poorly defended, fast-growing species. A second hypothesis states that greater resource availability increases allocation to growth at the expense of defense, within species. Regardless of mechanism, if exotic species are released from enemies relative to natives, shifts in allocation to growth and defense both within and among species could differ by geographic provenance. To test whether resource availability alters growth or defense, within and among species, and whether any such effects differ between natives and exotics, we manipulated soil nutrient supply and access of aboveground insect herbivores and fungal pathogens under field conditions to individuals of six native and six exotic grass species that co-occurred in a North Carolina old field. The prevailing hypothesis’ prediction—that species-level enemy impact increases with species’ nutrient responsiveness—was confirmed. Moreover, this relationship did not differ between native and exotic species. The second hypothesis’ prediction—that individual-level enemy impact increases with nutrient supply, after accounting for species-level variation in performance—was not supported. Together, these results support the idea, across native and exotic species, that plant species turnover is the primary mechanism underlying effects of nutrient enrichment on allocation to growth and defense in plant communities.
Disease may drive variation in host community structure by modifying the interplay of deterministic and stochastic processes that shape communities. For instance, deterministic processes like ...ecological selection can benefit species less impacted by disease. When communities have higher levels of disease and disease consistently selects for certain host species, this can reduce variation in host community composition. On the other hand, when host communities are less impacted by disease and selection is weaker, stochastic processes (e.g., drift, dispersal) may play a bigger role in host community structure, which can increase variation among communities. While effects of disease on host community structure have been quantified in field experiments, few have addressed the role of disease in modulating variation in structure among host communities. To address this, we conducted a field experiment spanning three years, using a tractable system: foliar fungal pathogens in an old-field grassland community dominated by the grass Lolium arundinaceum, tall fescue. We reduced foliar fungal disease burden in replicate host communities (experimental plots in intact vegetation) in three fungicide regimens that varied in the seasonal duration of fungicide treatment and included a fungicide-free control. We measured host diversity, biomass, and variation in community structure among replicate communities. Disease reduction generally decreased plant richness and increased aboveground biomass relative to communities experiencing ambient levels of disease. These changes in richness and aboveground biomass were consistent across years despite changes in structure of the plant communities over the experiment's three years. Importantly, disease reduction amplified host community variation, suggesting that disease diminished the degree to which host communities were structured by stochastic processes. These results of experimental disease reduction both highlight the potential importance of stochastic processes in plant communities and reveal the potential for disease to regulate variation in host community structure.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Premise
Leaf tensile resistance, a leaf's ability to withstand pulling forces, is an important determinant of plant ecological strategies. One potential driver of leaf tensile resistance is growing ...season length. When growing seasons are long, strong leaves, which often require more time and resources to construct than weak leaves, may be more advantageous than when growing seasons are short. Growing season length and other ecological conditions may also impact the morphological traits that underlie leaf tensile resistance.
Methods
To understand variation in leaf tensile resistance, we measured size‐dependent leaf strength and size‐independent leaf toughness in diverse genotypes of the widespread perennial grass Panicum virgatum (switchgrass) in a common garden. We then used quantitative genetic approaches to estimate the heritability of leaf tensile resistance and whether there were genetic correlations between leaf tensile resistance and other morphological traits.
Results
Leaf tensile resistance was positively associated with aboveground biomass (a proxy for fitness). Moreover, both measures of leaf tensile resistance exhibited high heritability and were positively genetically correlated with leaf lamina thickness and leaf mass per area (LMA). Leaf tensile resistance also increased with the growing season length in the habitat of origin, and this effect was mediated by both LMA and leaf thickness.
Conclusions
Differences in growing season length may promote selection for different leaf lifespans and may explain existing variation in leaf tensile resistance in P. virgatum. In addition, the high heritability of leaf tensile resistance suggests that P. virgatum will be able to respond to climate change as growing seasons lengthen.
Plant community succession is structured by initial richness, plant consumer pressure and soil resource supply. These drivers influence species' trait trade‐offs that underlie temporal changes in ...plant community diversity. Importantly, how these drivers interact with each other and through time and whether they act on different facets of plant community diversity by promoting different plant trade‐off strategies remains poorly understood.
We experimentally manipulated initial plant richness, consumer pressure via pesticide spraying and soil resource supply via fertilization across 4 years of old field succession. We then allowed natural colonization and extinction to occur and examined how the three drivers influenced succession. Specifically, we examined changes in temporal dynamics by conducting yearly taxonomic cover surveys and measuring light penetration to the ground. In the third year, we measured vegetative height and specific leaf area (SLA), and investigated seed mass using a trait database.
Higher initial richness, lower consumer pressure and increased soil resource supply all decreased colonizing species richness and light availability and variably altered species evenness. These effects generally acted additively rather than interactively in driving community diversity during succession. However, soil resource supply suppressed consumer pressure effects on species richness and light availability, while consumer pressure and soil resource supply modified initial richness effects on light availability. Treatments acted on different trait identities, revealing different mechanisms underlying taxonomic responses. Initial richness effects on seed mass of colonizing species were modified by soil resource supply. Decreased consumer pressure increased intraspecific community height and decreased interspecific SLA. Increased soil resource supply increased community height, SLA and seed mass.
Synthesis. Our results suggest species' resource strategies underlie plant diversity responses to consumer pressure and soil resource supply. Resource addition promoted resource‐acquisitive species; consumer pressure disadvantaged resource‐conservative species. Meanwhile, initial richness altered subsequent community composition primarily through persistence of early residents. We show that community responses to drivers of succession depend on underlying trait trade‐offs of resident species, and these trade‐offs influence community diversity across succession.
Initial richness, consumer pressure, and soil resource supply structure plant community succession. Species’ resource strategies underlie plant diversity responses to consumer pressure and soil resource supply. Resource addition promoted resource‐acquisitive species; consumer pressure disadvantaged resource‐conservative species. Initial richness altered subsequent community composition primarily through persistence of early residents. Community responses to drivers of succession depend on underlying species’ trait tradeoffs, which influence community diversity across succession.
Light limitation is a major driver of succession and an important determinant of the performance of shade-intolerant tree seedlings. Shade intolerance may result from a resource allocation strategy ...characterized by rapid growth and high metabolic costs, which may make shade-intolerant species particularly sensitive to nutrient limitation and pathogen pressure. In this study, we evaluated the degree to which nitrogen availability and fungal pathogen pressure interact to influence plant performance across different light environments. To test this, we manipulated nitrogen availability (high, low) and access by foliar fungal pathogens (sprayed with fungicide, unsprayed) to seedlings of the shade-intolerant tree, Liquidambar styraciflua, growing at low and high light availability, from forest understory to adjacent old field. Foliar fungal damage varied with light and nitrogen availability; in low light, increasing nitrogen availability tripled foliar damage, suggesting that increased nutrient availability in low light makes plants more susceptible to disease. Despite higher foliar damage under low light, spraying fungicide to exclude pathogens promoted 14% greater plant height only under high light conditions. Thus, although nitrogen availability and pathogen pressure each influenced aspects of plant performance, these effects were context dependent and overwhelmed by light limitation. This suggests that failure of shade-intolerant species to invade closed-canopy forest can be explained by light limitation alone.
Premise
Herbivore pressure can vary across the range of a species, resulting in different defensive strategies. If herbivory is greater at lower latitudes, plants may be better defended there, ...potentially driving a latitudinal gradient in defense. However, relationships that manifest across the entire range of a species may be confounded by differences within genetic subpopulations, which may obscure the drivers of these latitudinal gradients.
Methods
We grew plants of the widespread perennial grass Panicum virgatum in a common garden that included genotypes from three genetic subpopulations spanning an 18.5° latitudinal gradient. We then assessed defensive strategies of these plants by measuring two physical resistance traits—leaf mass per area (LMA) and leaf ash, a proxy for silica—and multiple measures of herbivory by caterpillars of the generalist herbivore fall armyworm (Spodoptera frugiperda).
Results
Across all genetic subpopulations, low‐latitude plants experienced less herbivory than high‐latitude plants. Within genetic subpopulations, however, this relationship was inconsistent—the most widely distributed and phenotypically variable subpopulation (Atlantic) exhibited more consistent latitudinal trends than either of the other two subpopulations. The two physical resistance traits, LMA and leaf ash, were both highly heritable and positively associated with resistance to different measures of herbivory across all subpopulations, indicating their importance in defense against herbivores. Again, however, these relationships were inconsistent within subpopulations.
Conclusions
Defensive gradients that occur across the entire species range may not arise within localized subpopulations. Thus, identifying the drivers of latitudinal gradients in herbivory defense may depend on adequately sampling the diversity within a species.
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