190 research outputs found
Performance-based inference of selection on stomatal length and specific leaf area varies with climate-of-origin of the forest tree, Eucalyptus ovata
Understanding how functional traits affect plant performance and fitness is a key step in unravelling the role of
natural selection in shaping the evolutionary trajectory of populations. We examined early-age selection acting
on leaf traits via their effects on growth performance and fitness, measured in Eucalyptus ovata trees planted in a
common-garden field trial embedded in a reforestation planting in Tasmania, Australia. We focused on two
important leaf traits - stomatal length and specific leaf area (SLA) - measured two years after planting, and
compared interplanted E. ovata groups originating from dry and wet home-site climates, with the trial site having
intermediate long-term mean annual rainfall. Two-year height growth was used as the performance attribute,
and the time-averaged tree survival over the subsequent six years as the fitness component. There was evidence
for performance-based selection on the leaf traits, with the strength and form of selection depending on the trait
and climate group being considered. In this sense, selection in the dry group operated mainly on stomatal length
where a combination of directional (favouring longer stomata) and stabilizing selection was detected, whereas
selection in the wet group acted only on SLA and was purely stabilizing. Estimates of performance-based
correlational selection were not statistically significant. For both climate groups, estimates of fitness-based selection
gradients provided evidence for significant directional (but not quadratic) selection on height performance,
favouring individuals with faster growth, but did not indicate statistical support for direct effects of the
leaf traits on tree survival, conditional on measured performance. These results validated qualitative inferences
of selection from the performance-based analysis, and suggested that selection on the leaf traits appeared to be
mediated by their effects on early-age height performance, which in turn directly influenced later-age survival.
We discuss the mechanisms by which the focal traits may have affected height performance, and likely factors
contributing to the different patterns of phenotypic selection observed in the two groups experiencing the same
environment. We also provide expressions of analytical derivatives that were developed for the estimation of
selection gradients based on a logistic regression model relating a binary fitness response to linear and nonlinear
covariate terms for the target regressor variables.info:eu-repo/semantics/publishedVersio
Linking leaf economic and hydraulic traits with early-age growth performance and survival of Eucalyptus pauciflora
Selection on plant functional traits may occur through their direct effects on
fitness (or a fitness component), or may be mediated by attributes of plant
performance which have a direct impact on fitness. Understanding this link is
particularly challenging for long-lived organisms, such as forest trees, where
lifetime fitness assessments are rarely achievable, and performance features
and fitness components are usually quantified from early-life history stages.
Accordingly, we studied a cohort of trees from multiple populations of
Eucalyptus pauciflora grown in a common-garden field trial established at
the hot and dry end of the species distribution on the island of Tasmania,
Australia. We related the within-population variation in leaf economic (leaf
thickness, leaf area and leaf density) and hydraulic (stomatal density, stomatal
length and vein density) traits, measured from two-year-old plants, to two-year
growth performance (height and stem diameter) and to a fitness component
(seven-year survival). When performance-trait relationships were modelled for
all traits simultaneously, statistical support for direct effects on growth
performance was only observed for leaf thickness and leaf density.
Performance-based estimators of directional selection indicated that
individuals with reduced leaf thickness and increased leaf density were
favoured. Survival-performance relationships were consistent with size-
dependent mortality, with fitness-based selection gradients estimated for
performance measures providing evidence for directional selection favouring
individuals with faster growth. There was no statistical support for an effect
associated with the fitness-based quadratic selection gradient estimated for
growth performance. Conditional on a performance measure, fitness-based
directional selection gradients estimated for the leaf traits did not provide
statistical support for direct effects of the focal traits on tree survival. This
suggested that, under the environmental conditions of the trial site and time
period covered in the current study, early-stage selection on the studied leaf
traits may be mediated by their effects on growth performance, which in turn has a positive direct influence on later-age survival. We discuss the potential
mechanistic basis of the direct effects of the focal leaf traits on tree growth, and
the relevance of a putative causal pathway of trait effects on fitness through
mediation by growth performance in the studied hot and dry environmentinfo:eu-repo/semantics/publishedVersio
Directional Selection on Tree Seedling Traits Driven by Experimental Drought Differs Between Mesic and Dry Populations
Original ResearchWe evaluated population differences and drought-induced phenotypic selection on four
seedling traits of the Australian forest tree Eucalyptus pauciflora using a glasshouse drydown
experiment. We compared dry and mesic populations and tested for directional
selection on lamina length (reflecting leaf size), leaf shape, the node of ontogenetic
transition to the petiolate leaf (reflecting the loss of vegetative juvenility), and lignotuber
size (reflecting a recovery trait). On average, the dry population had smaller and broader
leaves, greater retention of the juvenile leaf state and larger lignotubers than the mesic
population, but the populations did not differ in seedling survival. While there was
statistical support for directional selection acting on the focal traits in one or other
population, and for differences between populations in selection gradient estimates
for two traits, only one trait—lamina length—exhibited a pattern of directional selection
consistent with the observed population differences being a result of past adaptation to
reduce seedling susceptibility to acute drought. The observed directional selection for
lamina length in the mesic population suggests that future increases in drought risk in the
wild will shift the mean of the mesic population toward that of the dry population. Further,
we provide evidence suggesting an early age trade-off between drought damage and
recovery traits, with phenotypes which develop larger lignotubers early being more
susceptible to drought death. Such trade-offs could have contributed to the absence of
population mean differences in survival, despite marked differentiation in seedling traitsinfo:eu-repo/semantics/publishedVersio
Recent climate-driven ecological change across a continent as perceived through local ecological knowledge
Documenting effects of climate change is an important step towards designing mitigation and adaptation responses. Impacts of climate change on terrestrial biodiversity and ecosystems have been well-documented in the Northern Hemisphere, but long-term data to detect change in the Southern Hemisphere are limited, and some types of change are generally difficult to measure. Here we present a novel approach using local ecological knowledge to facilitate a continent-scale view of climate change impacts on terrestrial biodiversity and ecosystems that people have perceived in Australia. We sought local knowledge using a national web-based survey, targeting respondents with close links to the environment (e.g. farmers, ecologists), and using a custom-built mapping tool to ask respondents to describe and attribute recent changes they had observed within an area they knew well. Results drawn from 326 respondents showed that people are already perceiving simple and complex climate change impacts on hundreds of species and ecosystems across Australia, significantly extending the detail previously reported for the continent. While most perceived trends and attributions remain unsubstantiated, \u3e35 reported anecdotes concurred with examples in the literature, and \u3e20 were reported more than once. More generally, anecdotes were compatible with expectations from global climate change impact frameworks, including examples across the spectrum from organisms (e.g. increased mortality in \u3e75 species), populations (e.g. changes in recruitment or abundance in \u3e100 species, phenological change in \u3e50 species), and species (e.g. \u3e80 species newly arriving or disappearing), to communities and landscapes (e.g. \u3e50 examples of altered ecological interactions). The overarching pattern indicated by the anecdotes suggests that people are more often noticing climate change losers (typically native species) than winners in their local areas, but with observations of potential ‘adaptation in action’ via compositional and phenological change and through arrivals and range shifts (particularly for native birds and exotic plants). A high proportion of climate change-related anecdotes also involved cumulative or interactive effects of land use. We conclude that targeted elicitation of local ecological knowledge about climate change impacts can provide a valuable complement to data-derived knowledge, substantially extending the volume of explicit examples and offering a foundation for further investigation
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Arbuscular mycorrhizal communities respond to nutrient enrichment and plant invasion in phosphorus‐limited eucalypt woodlands
Arbuscular mycorrhizal fungi (AMF) facilitate ecosystem functioning through provision of plant hosts with phosphorus (P), especially where soil P is limiting. Changes in soil nutrient regimes are expected to impact AMF, but the direction of the impact may depend on context. We predicted that nitrogen (N)-only enrichment promotes plant invasions and exacerbates their P limitation, increasing the utility of AMF and promoting AMF diversity. We expected that enrichment with N, P and other nutrients similarly promotes plant invasions, but decreases the benefit and diversity of AMF because P is readily available for both native and exotic plants.
We tested these hypotheses in eucalypt woodlands of south-western Australia, that occur on soils naturally low in P. We evaluated AMF communities within three modified ground-layer states representing different types of nutrient enrichment and associated plant invasions. We compared these modified states to near-natural reference woodlands.
AMF richness varied across ground-layer states. The moderately invaded/N-enriched state showed the highest AMF richness, while the highly invaded/NP-enriched state showed the lowest AMF richness. The reference state and the weakly invaded/enriched state were intermediate. AMF richness and colonisation were higher in roots of exotic than native plant species.
AMF community composition differed among ground-layer states, with the highly invaded/NP-enriched state being most distinct. Distinctions among states were often driven by family-level patterns. Reference and moderately invaded/N-enriched states each supported distinct groups of zero-radius operational taxonomic units (zOTUs) in Acaulosporaceae, Gigasporaceae and Glomeraceae, whereas Gigasporaceae and Glomeraceae were nearly absent from the highly invaded/NP-enriched state. Further, Diversisporaceae and Glomeraceae were most diverse in the moderately invaded/N-enriched state.
Synthesis. Both the nature of soil nutrient enrichment and plant provenance matter for AMF. N-only enrichment of low-P soils increased AMF richness, likely due to the introduction of AMF-dependent exotic plant species and exacerbation of their P limitation. In contrast, multi-nutrient enrichment, decreased AMF richness potentially due to a decrease in host dependence on AMF, regardless of host provenance. The changes in AMF community composition with nutrient enrichment and plant invasion warrant further research into predicting the functional implications of these changes
Genomic Scans across Three Eucalypts Suggest that Adaptation to Aridity is a Genome-Wide Phenomenon
Widespread species spanning strong environmental (e.g., climatic) gradients frequently display morphological and physiological adaptations to local conditions. Some adaptations are common to different species that occupy similar environments. However, the genomic architecture underlying such convergent traits may not be the same between species. Using genomic data from previous studies of three widespread eucalypt species that grow along rainfall gradients in southern Australia, our probabilistic approach provides evidence that adaptation to aridity is a genome-wide phenomenon, likely to involve multiple and diverse genes, gene families and regulatory regions that affect a multitude of complex genetic and biochemical processes
Climate-adjusted provenancing: A strategy for climate-resilient ecological restoration
Investments in ecological restoration are estimated at $US 2 trillion per annum worldwide and are increasing rapidly (Cunningham, 2008; Williams et al., 2014). These investments are occurring in an environment of accelerated climate change that is projected to continue into the next century, yet they currently take little account of such change. This has significant implications for the long-term success of restoration plantings across millions of hectares, with germplasm used in current restoration efforts potentially poorly-adapted to future climates. New approaches that optimize the climate-resilience of these restoration efforts are thus essential (Breed et al., 2013; Williams et al., 2014; Havens et al., 2015)..
Leaf Economic and Hydraulic Traits Signal Disparate Climate Adaptation Patterns in Two Co-Occurring Woodland Eucalypts
With climate change impacting trees worldwide, enhancing adaptation capacity has become
an important goal of provenance translocation strategies for forestry, ecological renovation, and
biodiversity conservation. Given that not every species can be studied in detail, it is important
to understand the extent to which climate adaptation patterns can be generalised across species,
in terms of the selective agents and traits involved. We here compare patterns of genetic-based
population (co)variation in leaf economic and hydraulic traits, climate–trait associations, and genomic
differentiation of two widespread tree species (Eucalyptus pauciflora and E. ovata). We studied 2-yearold
trees growing in a common-garden trial established with progeny from populations of both
species, pair-sampled from 22 localities across their overlapping native distribution in Tasmania,
Australia. Despite originating from the same climatic gradients, the species differed in their levels of
population variance and trait covariance, patterns of population variation within each species were
uncorrelated, and the species had different climate–trait associations. Further, the pattern of genomic
differentiation among populations was uncorrelated between species, and population differentiation
in leaf traits was mostly uncorrelated with genomic differentiation. We discuss hypotheses to
explain this decoupling of patterns and propose that the choice of seed provenances for climatebased
plantings needs to account for multiple dimensions of climate change unless species-specific
information is availableinfo:eu-repo/semantics/publishedVersio
Sensitivity of global soil carbon stocks to combined nutrient enrichment
Soil stores approximately twice as much carbon as the atmosphere and fluctuations in the size of the soil carbon pool directly influence climate conditions. We used the Nutrient Network global change experiment to examine how anthropogenic nutrient enrichment might influence grassland soil carbon storage at a global scale. In isolation, enrichment of nitrogen and phosphorous had minimal impacts on soil carbon storage. However, when these nutrients were added in combination with potassium and micronutrients, soil carbon stocks changed considerably, with an average increase of 0.04 KgCm−2 year−1 (standard deviation 0.18 KgCm−2 year−1). These effects did not correlate with changes in primary productivity, suggesting that soil carbon decomposition may have been restricted. Although nutrient enrichment caused soil carbon gains most dry, sandy regions, considerable absolute losses of soil carbon may occur in high‐latitude regions that store the majority of the world's soil carbon. These mechanistic insights into the sensitivity of grassland carbon stocks to nutrient enrichment can facilitate biochemical modelling efforts to project carbon cycling under future climate scenarios
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