Plant Life History Traits Research Articles

Soil salinity regulates spatial-temporal heterogeneity of seed germination and seedbank persistence of an annual diaspore-trimorphic halophyte in northern China

Background and aimsSeed heteromorphism is a plant strategy that an individual plant produces two or more distinct types of diaspores, which have diverse morphology, dispersal ability, ecological functions and different effects on plant life history traits. The aim of this study was to test the effects of seasonal soil salinity and burial depth on the dynamics of dormancy/germination and persistence/depletion of buried trimorphic diaspores of a desert annual halophyte Atriplex centralasiatica.MethodsWe investigated the effects of salinity and seasonal fluctuations of temperature on germination, recovery of germination and mortality of types A, B, C diaspores of A. centralasiatica in the laboratory and buried diaspores in situ at four soil salinities and three depths. Diaspores were collected monthly from the seedbank from December 2016 to November 2018, and the number of viable diaspores remaining (not depleted) and their germinability were determined.ResultsNon-dormant type A diaspores were depleted in the low salinity “window” in the first year. Dormant diaspore types B and C germinated to high percentages at 0.3 and 0.1 mol L-1 soil salinity, respectively. High salinity and shallow burial delayed depletion of diaspore types B and C. High salinity delayed depletion time of the three diaspore types and delayed dormancy release of types B and C diaspores from autumn to spring. Soil salinity modified the response of diaspores in the seedbank by delaying seed dormancy release in autum and winter and by providing a low-salt concentration window for germination of non-dormant diaspores in spring and early summer.ConclusionsBuried trimorphic diaspores of annual desert halophyte A. centralasiatica exhibited diverse dormancy/germination behavior in respond to seasonal soil salinity fluctuation. Prolonging persistence of the seedbank and delaying depletion of diaspores under salt stress in situ primarily is due to inhibition of dormancy-break. The differences in dormancy/germination and seed persistence in the soil seedbank may be a bet-hadging strategy adapted to stressful temporal and spatial heterogeneity, and allows A. centralasiatica to persist in the unpredictable cold desert enevironment.

Time since first naturalization is key to explaining non‐native plant invasions on islands

AbstractAimInvestigating the extent of insular invasions by non‐native species (i.e., the number of islands they occupy) is central to island conservation. However, interrelationships among plant life history traits, naturalization histories, and island characteristics in determining island occupancy by non‐native plant species are poorly understood. We investigated whether island occupancy by different non‐native plant species declines in relation to their year of first naturalization and whether periods of first naturalization differ among growth forms, dispersal modes, and biogeographic origins. Then, we asked if non‐native plants that naturalized more recently occur more frequently on islands that are large, less isolated, and close to urban areas. We contrasted trends across growth forms, dispersal modes, and biogeographic origins.Location264 offshore islands in northern Aotearoa New Zealand.TaxaVascular plant species.MethodsWe combined field surveys and published data for 767 non‐native plant species on the islands. We categorized each species according to its growth form (n = 3), dispersal mode (n = 4) and biogeographic origin (n = 5) and identified its year of first naturalization in Aotearoa New Zealand. We tested our hypotheses using ANCOVA and generalized linear models (GLMs).ResultsThere were similar declines in island occupancy in relation to the year of first naturalization in Aotearoa New Zealand across all trait and biogeographic origin categories. First naturalization times of herbaceous species, those with unspecialized dispersal modes, and those originating from Eurasia and the Mediterranean basin were disproportionately earlier than other categories. Non‐native plants with more recent first naturalization occur more frequently on large islands close to urban areas, but not on less isolated ones. Relationships with island characteristics did not differ among trait and biogeographic origin categories.Main ConclusionsOverall, time of first naturalization was more important than trait and biogeographic origin categories in explaining non‐native plant invasion patterns on islands. Since there were similar relationships between island occupancy and the year of first naturalization in Aotearoa New Zealand for all categories, management bodies should focus on non‐native plant species of trait and biogeographic origin categories that have naturalized recently (e.g., woody species from other regions within Oceania), and on large islands close to urban areas. Introduction and naturalization histories provide essential context for interpreting the role of plant traits and biogeographic origin in understanding plant invasions on islands.

Genome-wide association study of aphid abundance highlights a locus affecting plant growth and flowering in Arabidopsis thaliana.

Plant life-history traits, such as size and flowering, contribute to shaping variation in herbivore abundance. Although plant genes involved in physical and chemical traits have been well studied, less is known about the loci linking plant life-history traits and herbivore abundance. Here, we conducted a genome-wide association study (GWAS) of aphid abundance in a field population of Arabidopsis thaliana. This GWAS of aphid abundance detected a relatively rare but significant variant on the third chromosome of A. thaliana, which was also suggestively but non-significantly associated with the presence or absence of inflorescence. Out of candidate genes near this significant variant, a mutant of a ribosomal gene (AT3G13882) exhibited slower growth and later flowering than a wild type under laboratory conditions. A no-choice assay with the turnip aphid, Lipaphis erysimi, found that aphids were unable to successfully establish on the mutant. Our GWAS of aphid abundance unexpectedly found a locus affecting plant growth and flowering.

Life History Traits of Exotic and Native Species Determine Grassland Management Outcomes Following Prescribed Fire

<h3>ABSTRACT</h3> Disturbance regimes, including the historical timing of disturbance, are important components of natural ecosystems and greatly influence ecosystem structure and functioning. Consequently, disturbance timing can be an important component of biodiversity management. We evaluated the effect of prescribed fires ignited during the warm and cool seasons (summer and spring, respectively) on the plant community of a calcareous grassland in northern Mississippi (USA). We found that fire season influenced plant community composition by having differential impacts on species with different life history traits. Differences among species were primarily driven by the dichotomy between cool-season (C₃) and warm-season (C₄) plants, independent of species native status. Spring burns reduced the cover of cool-season C₃ graminoids, but had the opposite effect on C₄ graminoids, which likely benefited from increases in resource availability due to the reduction of C₃ species. However, summer burns decreased the abundance of C₄ graminoids, as summer burns were ignited during the active growing and reproductive period for the C₄ species. We found the same patterns for the number of inflorescences of the most abundant C₃ and C₄ graminoids. Summer burns also increased overall species diversity and the abundance of native C₃ graminoids, forbs, and vines, resulting in significant differences in plant community composition between spring- and summer-burned areas. Programs that aim to restore native grassland communities in the short-term using prescribed fire should consider the life history traits of target plants (including invasive species) to determine the best time for prescribed fire implementation.

Biochar-fertilizer mixture: does plant life history trait determine fertilizer application rate?

ABSTRACT The annual cumin and perennial fennel are economically important medicinal crops of cold dry regions of Pakistan. We hypothesized that the cumin, which produces 2–3 times less biomass, will respond to lower rates of mixture of biochar with synthetic NPK fertilizer or manure, compared to fennel. The NPK, poultry manure and their mixture with wood-derived or cow manure-derived biochars were applied for three consecutive years. No positive relation between application rate of biochar-mixed fertilizers and yield of both crops was observed over three years of study, except that manure-derived biochar-NPK mixture had a positive relation (R2 = 0.99, P = 0.01) with the yield of fennel only during the third year. Significant positive influences of biochar-based fertilizers compared to control were observed for cumin and fennel of third year cropping. The co-amendment of NPK (0.14 kg ha−1) with manure-derived biochar (6.6 t ha−1) consistently increased the yield of cumin during the first two years of cropping, as opposed to NPK fertilizer. Cumin had a greater seed:stover biomass ratio when it received the co-amendment of wood-derived biochar with NPK or poultry manure. Our findings indicate that there is some potential for biochar-fertilizer amendments to improve the growth of these high-value medicinal crops.

Effects of Seed Endophytic Bacteria on Life History and Reproductive Traits in a Cosmopolitan Weed, Capsella bursa-pastoris.

Diverse bacteria inhabit plant seeds, and at least some of them can enhance plant performance at the early developmental stage. However, it is still inconclusive whether seed bacteria can influence post-germination traits and their contribution to plant fitness. To explore the evolutionary and ecological consequences of seed endophytic bacteria, we isolated four bacterial strains from the seeds of an annual weedy plant species, Capsella bursa-pastoris, and conducted a common garden experiment using seeds inoculated by isolated bacteria. Seeds infected by bacteria tended to germinate in spring rather than in autumn. Bacterial treatment also altered the expression of plant life history and reproductive traits, including flowering dates, rosette diameter at bolting, number of inflorescences, and fruit production. The results of the path analyses suggested that such effects of bacterial treatments were due to bacterial inoculation as well as germination delayed until spring. Spring germinants with bacterial infection showed a weaker association between post-germination traits and relative fitness than those without bacterial infection. These results suggest that seed bacteria likely affect the expression of post-germination traits directly or indirectly by delaying the germination season. An altered contribution of plant traits to relative fitness implies the influence of seed bacteria on the strength of natural selection.

Do Southern Hemisphere tree rings record past volcanic events? A case study from New Zealand

Abstract. Much of our knowledge about the impacts of volcanic eruptions on climate comes from proxy records. However, little is known about their impact on the low to mid-latitudes of the Southern Hemisphere. Using superposed epoch analysis, we investigated whether volcanic signals could be identified in annual tree-ring series from eight New Zealand dendrochronological species. We found that most species are reliable recorders of volcanic cooling and that the magnitude and persistence of the post-event response can be broadly linked to plant life history traits. Across species, site-based factors, particularly altitude and exposure to prevailing conditions, are more important determinants of the strength of the volcanic response than species. We then investigated whether chronology selection impacts the magnitude of post-volcanic cooling in tree-ring-based temperature reconstructions by developing two new multispecies reconstructions of New Zealand summer (December–February) temperature with one reconstruction from the pool of all available chronologies, and the other from a selected subset shown to be sensitive to volcanic eruptions. Both reconstructions record temperature anomalies that are remarkably consistent with studies based on instrumental temperature and the ensemble mean response of climate models, demonstrating that New Zealand ring widths are reliable indicators of regional volcanic climate response. However, we also found that volcanic response can be complex, with positive, negative, and neutral responses identified – sometimes within the same species group. Species-wide composites thus tend to underestimate the volcanic response. This has important implications for the development of future tree-ring and multiproxy temperature reconstructions from the Southern Hemisphere.

Growth, morphology and C/N metabolism responses of a model submersed macrophyte, Vallisneria natans, to various light regimes

Decreased underwater light availability is one of the most important environmental factors leading to the decline in submersed macrophytes in lakes. However, previous studies mostly focused on a relatively short time scale and lack data on the continuous monitoring of plant life history traits under different light conditions. The present experiment studied the growth, morphology and C/N metabolism of a representative submersed macrophyte, Vallisneria natans, in response to various light regimes (2.8%, 7.1%, 17.1%, and 39.5% ambient light intensity) over a period of 12 months. The results showed that the total biomass and ramet number increased with increased light intensity; in contrast, individual biomass, leaf number and maximum leaf length decreased with increased light intensity. The C/N metabolism indices of V. natans indicated that leaves were the most sensitive to light availability, stems were moderately sensitive, and roots were the least sensitive. V. natans grown in an extremely low-light environment exhibited decreased soluble carbohydrate (SC) and starch and increased free amino acid (FAA) and total nitrogen (TN) levels. The increasing function of the ramet number under different light regimes was fitted. The obtained maximum environmental capacity of the ramet number (K) and the days that the ramet number reached K/2 in each treatment are useful for lake V. natans restoration and seedling cultivation in similar limited-resource environments. Harvesting partial ramets properly and maintaining the ramet number near K/2 could ensure the maximum increase rate of the population to satisfy the demand of V. natans seedlings for lake restoration. The results obtained in this study can be used for lake water level management to achieve specific purposes during submerged macrophyte recovery, such as plant height elongation or plant population quantity expansion.

RNase-based self-incompatibility in cacti.

Approximately one-half of all flowering plants express genetically based physiological mechanisms that prevent self-fertilisation. One such mechanism, termed RNase-based self-incompatibility, employs ribonucleases as the pistil component. Although it is widespread, it has only been characterised in a handful of distantly related families, partly due to the difficulties presented by life history traits of many plants, which complicate genetic research. Many species in the cactus family are known to express self-incompatibility but the underlying mechanisms remain unknown. We demonstrate the utility of a candidate-based RNA-seq approach, combined with some unusual features of self-incompatibility-causing genes, which we use to uncover the genetic basis of the underlying mechanisms. Specifically, we assembled transcriptomes from Schlumbergera truncata (crab cactus or false Christmas cactus), and interrogated them for tissue-specific expression of candidate genes, structural characteristics, correlation with expressed phenotype(s), and phylogenetic placement. The results were consistent with operation of the RNase-based self-incompatibility mechanism in Cactaceae. The finding yields additional evidence that the ancestor of nearly all eudicots possessed RNase-based self-incompatibility, as well as a clear path to better conservation practices for one of the most charismatic plant families.

Multi-factor control of seed mass of species on the eastern part of the Qinghai-Tibetan Plateau: Integration of environmental filters, local adaptation and correlated evolution

Seed mass is a central plant life history trait that varies and evolves due to selection by biotic or abiotic factors. To determine the factors affecting seed mass variation among species and phylogeny, we used linear and regression tree analyses of three biotic traits and four niche traits to quantify the relative importance of each trait on seed mass for 1340 angiosperm species from the eastern part of the Qinghai-Tibetan Plateau. Dispersal mode was the strongest predictor of both species and phylogenetic seed mass variation, whereas life form only had a small impact. These results suggest that seed mass has responded to dispersers rather than the life history or available stored resources. Moreover, in both inter-specific and phylogenetic comparisons, species with similar light, moisture and disturbance niche positions tended to have similar seed mass, indicating that adaptation to local environments is a second force driving species-level seed mass variation. The lack of any relationship between thermal niche and seed mass in the phylogenetic analysis implies that seed mass variation along thermal gradients may be a result of regional species sorting, or alternatively, a plastic response to the variation in plant size. All species and phylogenetic multivariate models showed that both dispersal mode and species light/moisture niche explain seed mass variation, suggesting the importance of coevolution or covariation between seeds and vertebrates and the selection or filter effect of habitats on early life-history stages of plants in affecting individual seed development. Lastly, our results imply that phylogenetic constraints and niche conservatism may operate simultaneously in determining regional patterns of seed mass variation.

Fire and functional traits: Using functional groups of birds and plants to guide management in a fire‐prone, heathy woodland ecosystem

AbstractAimMany dry forests and woodlands worldwide are fire‐prone and support bird and plant communities shaped by fire. Changes in fire regimes, including the time between fires, have important implications for population trajectories. We studied the responses of bird and plant communities of heathy woodlands to time since the last fire, a key measure underpinning fire management, to evaluate whether current management strategies will enhance conservation of multiple taxa.LocationOtway Ranges, south‐eastern Australia.MethodsWe surveyed birds and plants at 38 sites, stratified by an 80‐year post‐fire chronosequence, and modelled the responses of individual species, functional groups and community composition to fire history. Model outputs were used to evaluate the impacts of fire management as guided by (a) domains of tolerable fire intervals, a concept based on plant life history traits, and (b) the spatial arrangement of post‐fire age classes, a surrogate for animal habitats.ResultsBird and plant communities both responded to time since fire. Notable relationships included the following: a high reporting rate of ground‐foraging birds and high cover and species richness of shrubs immediately after fire; and a gradual increase up to ~50 years and ~20 years post‐fire of birds that forage in the mid‐storey and facultative‐resprouting plants, respectively. Post‐fire age classes had distinct bird and plant assemblages. Tolerable fire intervals currently used by land managers (min 12–max 45 years between fires) encompassed the peak in richness of most plant functional groups but not the preferred habitat of lower‐mid‐storey foraging birds.Main conclusionsFire management based solely on birds or plants risks population declines in other biota. Use of functional groups can help guide strategic planning, such as spatial representation of post‐fire age classes across the landscape. Maintaining late‐successional vegetation will provide habitat for several groups of birds, while fire is needed at sufficient frequency to prevent loss of plants and ground‐foraging birds.

Among-population variation in seed mass for 190 Tibetan plant species: Phylogenetic pattern and ecological correlates

It is widely assumed that seed mass, as a proxy of both dispersability and competitiveness, can affect community composition and diversity. Numerous studies have validated the influence of seed mass at the interspecific level. However, little is known about patterns of among-population variation in seed mass (APVSM), which may influence a species’ persistence under climate change. We characterized the naturally occurring variation in seed mass among populations across 190 Tibetan plant species (2503 populations). We tested for relationships between APVSM and plant life-history traits (mean seed mass, seed dormancy type, seed dispersal mode, life form, and pollination system) and an environmental factor, elevation. We also tested patterns of phylogenetic signal in APVSM and identified the lineages (clades) with an exceptionally high or low APVSM. We found that APVSM varied > 5-fold among species, ranging from 0.085 in Bromus sinensis to 0.447 in Anaphalis flavescens. Furthermore, wind-dispersed species tended to have greater APVSM. Finally, we found that APVSM exhibited a significant phylogenetic signal (i.e., closely related species were more or less variable in their seed size than would be expected by chance) that was driven by a few major lineages. Clades with significantly less APVSM included Brassicaceae, Campanulaceae, Ranunculaceae (including Thalictrum, Trollius, Aconitum and Anemone), Roegneria, Rumex. Clades with significantly greater APVSM included Bignoniaceae, Lamiaceae, Orobanchaceae, Anaphalis, Cotoneaster and Sorbus. In summary, our study suggested that APVSM is partly due to trade-offs in evolutionary history and its associations with other life-history traits.

Ecological drivers of plant life-history traits: Assessment of seed mass and germination variation using climate cues and nitrogen resources in conifers

Abstract Understanding plant-environment interactions is an important link to studying the impact of climate change on community assemblies and population dynamics, especially for tree species that define the ecosystem they occupy. Based on seed mass and germination data of three conifers over six decades (1955–2015) across British Columbia, Canada, we performed pairwise correlation analysis between focal traits and the environment (climates in crop year and four prior-years and nitrogen resources). Using key environmental correlates, we constructed a linear mixed model to assess both traits and performed linear discrimination analysis to predict trait tendencies under future climate scenarios. Findings showed that seed mass variation was considerably ascribed to nitrogen deposition and climate in prior-years preceding seed crop. Climate in crop year had higher correlations with seed germination than in prior-years, but germination-climate correlations were much weaker than seed mass-climate counterparts. Both seed mass and germination had high correlations with temperature-based climate variables, such as evapotranspiration, degree-days above 5 °C (positive) and below 18 °C (negative); however, some climate variables had high but opposite correlations with the same trait between species. Across the study region, ecological trade-offs between species were similar for the aspect of temperature but differed between precipitation-based variables, indicating the important role of precipitation in ecological constraints. Finally, we predicted that climate change would result in more spatially homogeneous traits and make them shift towards intermediate or low levels. These results have important implications for the natural seedling regeneration of forest trees under climate change, which potentially cascades to influence trait expression, plant fitness and population persistence.

Reaching similar goals by different means – Differences in life-history strategies of clonal and non-clonal plants

Clonality is a largely underexplored plant life-history trait with possibly profound effects on plant demography. Clonal growth constitutes an alternative reproductive pathway, which should provide clonal species with an advantage over non-clonal ones under disturbance regimes unfavourable to regeneration from seeds.We investigated how clonal and non-clonal species differ in their life histories (other than clonality) and how this relates to disturbance regimes where the studied species occur. Further, we focused on the contribution of clonality to fluctuations in the populations of species and the importance of clonality for the life cycle of a species in relation to its other life-history characteristics. We achieved this through phylogenetically informed analyses of the matrix population models available from the COMPADRE database coupled with information on species clonality from the CLO-PLA database.The phylogenetic principal component analysis revealed that plant life-history characteristics could be aligned along two gradients. The gradient of generation time and individual turnover in populations was more important and corresponded to the frequency of habitat disturbance. Clonal species on average had populations with lower overall rates of individual turnover and disturbance frequencies. The second gradient was correlated with disturbance severity and plant ability to regenerate after the loss of biomass. The importance of clonal growth for the life cycle of a clonal species increased with more severe disturbance events. The fluctuation of population growth rates depended on the life-history characteristics of a species but not on clonality. The net effect of clonal growth on the fluctuations of the populations of a species was positive.In general, clonality seems to provide an important alternative for adjusting plant life history to the disturbance regime and other site conditions allowing a plant to circumvent its morphological or developmental constraints. Clonal growth turned out to be mainly a mechanism that enables population expansion under favourable conditions rather than a mechanism that buffers the effects of adverse conditions.

Disentangling the influence of ecological and historical factors on seed germination and seedling types in a Neotropical dry forest.

In tropical dry forests, although seed germination and seedling establishment are in general limited by the seasonal availability of water, high interspecific variability, nonetheless, exists in terms of seedling traits and germination dynamics. Differences among species in seed germination and seedling traits may be related to other plant life-history traits, such that assessing these relationships may increase our understanding of factors influencing plant establishment, which would affect the regeneration pathways of tropical dry forest communities. In this study, taking into consideration the effect species' phylogeny, we evaluated the relationships of seed germination metrics (percentage, lag time, and rate of germination) and seedling types (i.e. cotyledons functional morphology), with plant life-history traits (growth form, seed mass, dispersal syndrome and dispersal phenology) for 110 species in a Neotropical dry forest in Mexico. A total of 92% of the species studied disperse their seeds during the dry season, mainly at the beginning of this season (66%), a strategy mostly associated with autochorous herbs. Seed germination was more frequent in species that dispersed seeds at the end of the dry season. Germination percentage was not related to any of the traits studied. However, germination lag time and rate were negatively related to seed mass, a trait that in turn depended on growth form and dispersal syndrome. The dominant seedling type in the community was phanerocotylar epigeal with foliaceous cotyledons (56%), which was mostly associated with small seed mass and herbaceous growth form. Our results provide evidence that several plant life-history traits explain an important part of the variation in seed germination and seedling characteristics observed among species. Therefore, these plant life-history traits may be useful for grouping species in terms of their establishment strategies and roles on the regeneration of tropical dry communities.

Trade-offs between host tolerances to different pathogens in plant-virus interactions.

Although accumulating evidence indicates that tolerance is a plant defence strategy against pathogens as widespread as resistance, how plants evolve tolerance is poorly understood. Theory predicts that hosts will evolve to maximize tolerance or resistance, but not both. Remarkably, most experimental works failed in finding this trade-off. We tested the hypothesis that the evolution of tolerance to one virus is traded-off against tolerance to others, rather than against resistance and identified the associated mechanisms. To do so, we challenged eighteen Arabidopsis thaliana genotypes with Turnip mosaic virus (TuMV) and Cucumber mosaic virus (CMV). We characterized plant life-history trait modifications associated with reduced effects of TuMV and CMV on plant seed production (fecundity tolerance) and life period (mortality tolerance), both measured as a norm of reaction across viral loads (range tolerance). Also, we analysed resistance-tolerance and tolerance-tolerance trade-offs. Results indicate that tolerance to TuMV is associated with changes in the length of the pre-reproductive and reproductive periods, and tolerance to CMV with resource reallocation from growth to reproduction; and that tolerance to TuMV is traded-off against tolerance to CMV in a virulence-dependent manner. Thus, this work provides novel insights on the mechanisms of plant tolerance and highlights the importance of considering the combined effect of different pathogens to understand how plant defences evolve.

Plant density and life history traits of Aconitum spicatum in North-central Nepal: effects of elevation and anthropogenic disturbances.

Increasing cross-border trade of medicinal and aromatic plants (MAPs) has put heavy pressure on a considerable number of species in the Himalayas. One of the threatened species in Nepal is Aconitum spicatum. Unfortunately for this species and for many others, our knowledge on population ecology and performance across the distribution range is insufficient, hindering the formulation of species-specific management plans. We therefore studied density and population structure of A. spicatum and assessed variation in its life history traits among three populations (subalpine, lower alpine and alpine) along an elevation gradient (3,000–4,200 m a.s.l.) in Annapurna Conservation Area, north-central Nepal. The results show that human disturbances and topographic factors contributed to the variation in density and life history traits. The overall density ranged between 0.56 ± 0.09 (Mean ± SE) and 2.48 ± 0.24 plants/m2 with highest mean density in the lower alpine and lowest in the subalpine population. The subalpine population was also characterized by lower investment in reproductive structures with lowest seed mass and low seed viability and fecundity. Among the environmental variables tested, harvesting, animal droppings and fire appeared to be the most important factors affecting density of different life stages of A. spicatum. The prevailing harvesting pattern is destructive as it involves uprooting of the whole plant and this appears to be a main reason for low recruitment and reduced density of the subalpine population. The level of disturbance decreased with increasing elevation. In terms of reproductive effort, the alpine population performed best. Our results indicate that the viability of A. spicatum populations depends on controlling over-harvesting and pre-mature harvesting of tubers and protecting younger life stages from grazing, trampling and fire. We therefore recommend that when formulating management guidelines, measures aiming to mitigate such anthropogenic disturbances should be considered.

Alterations in Life-History Associated With Non-target-site Herbicide Resistance in Alopecurus myosuroides.

The evolution of resistance to herbicides is a classic example of rapid contemporary adaptation in the face of a novel environmental stress. Evolutionary theory predicts that selection for resistance will be accompanied by fitness trade-offs in environments where the stress is absent. Alopecurus myosuroides, an autumn-germinating grass weed of cereal crops in North-West Europe, has evolved resistance to seven herbicide modes-of-action, making this an ideal species to examine the presence and magnitudes of such fitness costs. Here, we use two contrasting A. myosuroides phenotypes derived from a common genetic background, one with enhanced metabolism resistance to a commercial formulation of the sulfonylurea (ALS) actives mesosulfuron and iodosulfuron, and the other with susceptibility to these actives (S). Comparisons of plant establishment, growth, and reproductive potential were made under conditions of intraspecific competition, interspecific competition with wheat, and over a gradient of nitrogen deprivation. Herbicide dose response assays confirmed that the two lines had contrasting resistance phenotypes, with a 20-fold difference in resistance between them. Pleiotropic effects of resistance were observed during plant development, with R plants having a greater intraspecific competitive effect and longer tiller lengths than S plants during vegetative growth, but with S plants allocating proportionally more biomass to reproductive tissues during flowering. Direct evidence of a reproductive cost of resistance was evident in the nitrogen deprivation experiment with R plants producing 27% fewer seed heads per plant, and a corresponding 23% reduction in total seed head length. However, these direct effects of resistance on fecundity were not consistent across experiments. Our results demonstrate that a resistance phenotype based on enhanced herbicide metabolism has pleiotropic impacts on plant growth, development and resource partitioning but does not support the hypothesis that resistance is associated with a consistent reproductive fitness cost in this species. Given the continued difficulties associated with unequivocally detecting costs of herbicide resistance, we advocate future studies that adopt classical evolutionary quantitative genetics approaches to determine genetic correlations between resistance and fitness-related plant life history traits.

Springs ecosystems: vulnerable ecological islands where environmental conditions, life history traits, and human disturbance facilitate non-native plant invasions

Ecosystem invasion by non-native plants depends on plant life history characteristics that influence the species’ invasiveness, as well as environmental factors that determine site invasibility. Small, insular ecosystems are thought be especially vulnerable to invasion but evidence for this pattern has been mixed. Freshwater springs form island-like ecosystems, allowing for a test of this proposal. Here, we investigated the effects of physical environmental factors, human disturbance, and plant life history traits on the occurrence of native and non-native plant species at 55 springs across different biomes in Alberta, Canada. A total of 526 plants were identified, 12.5% of which were non-native. Among these, species richness and abundance were greater at springs within biomes subject to increased land use intensity, especially livestock grazing, as compared to springs in parks and protected areas with limited land use. Subsequently, springs with higher human impact supported greater richness (r2 = 0.13) and abundance (r2 = 0.31) of non-native species, while native species abundance declined with increasing human impact (r2 = 0.14). Common native and non-native plant taxa exhibited life history traits that confer greater tolerance to human disturbance, such as that arising from livestock production that can disperse propagules, including clonal capacity and physical and chemical herbivory defenses. Our results indicated that springs ecosystems with greater human disturbance were more vulnerable to invasion by non-native plants, and this can reduce plant biodiversity and the ecological services provided by these distinctive, insular ecosystems.

Leaf mechanical strength and photosynthetic capacity vary independently across 57 subtropical forest species with contrasting light requirements

Leaf mechanical strength and photosynthetic capacity are critical plant life-history traits associated with tolerance and growth under various biotic and abiotic stresses. In principle, higher mechanical resistance achieved via higher relative allocation to cell walls should slow photosynthetic rates. However, interspecific relationships among these two leaf functions have not been reported. We measured leaf traits of 57 dominant woody species in a subtropical evergreen forest in China, focusing especially on photosynthetic rates, mechanical properties, and leaf lifespan (LLS). These species were assigned to two ecological strategy groups: shade-tolerant species and light-demanding species. On average, shade-tolerant species had longer LLS, higher leaf mechanical strength but lower photosynthetic rates, and exhibited longer LLS for a given leaf mass per area (LMA) or mechanical strength than light-demanding species. Depending on the traits and the basis of expression (per area or per mass), leaf mechanical resistance and photosynthetic capacity were either deemed unrelated, or only weakly negatively correlated. We found only weak support for the proposed trade-off between leaf biomechanics and photosynthesis among co-occurring woody species. This suggests there is considerable flexibility in these properties, and the observed relationships may result more so from trait coordination than any physically or physiologically enforced trade-off.