Plant Ecology最新文献

Functional traits offer insights into plant performance. However, linking traits to individual tree performance requires considering the overall phenotypic context and utilizing traits measured at the individual level. Tree growth rates are informative metrics about performance, however how it is measured provides different information on tree or community growth dynamics and structure and can alter the relationships or their strength with functional traits and individual phenotypes. Moreover, at the community level, trees can adjust their crown shapes and sizes to optimize canopy space utilization, and a high level of canopy packing can enhance the individual to community-level growth rate. In this study, we assessed the crown area of 1144 individual trees, a simple trait measured at the individual level, and the leaf mass per area (LMA), a common functional trait, to test trait-growth relationships, considering absolute and relative growth rate. The observed total photosynthetic mass (integrating crown area and LMA) positively explained absolute tree growth rates, interacting with tree height. As higher the trees, more intense was the effect. Importantly, this effect was not solely based on LMA or crown size. This implies that LMA’s predictive power could improve by integrating leaf-level traits with whole-plant allocation to leaf area. These variables, however, failed to predict the tree’s relative growth rates. Additionally, our study found that increased canopy packing levels raised the community-level growth rate within our plots. This overall community growth seems be facilitated by denser tree arrangements and efficient light interception in the forest due to the higher canopy packing level. We highlight the importance of considering crown area as a critical variable to be measured during floristic inventories and in studies focused on tree performance.

Just as plants attack heterospecific competitors with allelopathic phytotoxins, they also attack conspecifics with phytotoxins to inhibit seedling germination and growth (autotoxicity). As a result, for many plant species, autotoxicity limits offspring germination and growth proximate to parental plants—consequently reducing deleterious density dependent effects. Autotoxicity appears to vary across species, but it also may vary within species. We tested autotoxicity and variability in six ecotypes of the model plant, Arabidopsis thaliana, using allelopathy bioassays. We found that autotoxic impacts varied across the Eurasian and African ecotypes, and the negative effects on conspecific root growth were greater from above-than belowground exudate. In half the ecotypes, root growth decreased 71% in seedlings treated with exudate from the same ecotype than when treated with exudate from other ecotypes. That the ecotypes limited themselves more than they did other ecotypes is consistent with coexistence theory, which assumes species limit themselves more than others. Moreover, it is consistent with negative density dependent theories that suggest seedling mortality is highest near conspecific adults. Finally, the variation in autotoxicity across ecotypes suggests that intraspecific genetic variability and/or local habitat influence autotoxic intensity. It is well recognized that phytotoxic effect (allelopathy and autotoxicity) varies interspecifically but ecotype-level effects suggests that plants may exhibit greater intraspecific variation in autotoxicity than currently recognized.

Trianthema portulacastrum L. is an alien naturalized noxious summer weed belonging to Aizoaceae. Our field observations revealed that it was the dominant weed in the fields planted with maize and other summer crops, and on roadsides of wastelands and farmlands . This study was conducted to evaluate the potential allelopathic effects of the aqueous shoot extracts and mulching with different rates of air-dried shoots of T. portulacastrum collected from maize fields on two associating weeds namely, Corchorus olitorius and Euphorbia heterophylla. Seed germination and seedling growth of the test weeds decreased with increasing concentrations of the aqueous extract. The seeds bioassay experiments confirmed the autotoxicity of T. portulacastrum. We have found that the allelopathic effects of the target species on the two weeds, and the autotoxic effects on itself were mainly attributed to the presence of allelochemicals and not to the osmotic potential of the aqueous extracts. Mulching had inhibitory effects on the percentage of dry matter allocations and the growth parameters of the test weed species. The relative growth rate, the net assimilation rate, and the leaf area ratio of the non-mulched weeds were higher than those of mulched ones. The phytochemical screening of the dry shoots of T. portulacastrum indicated the presence of phenolic compounds, flavonoids, tannins, and alkaloids. The high concentration of alkaloids in the shoot deserves further research. The high-performance liquid chromatography confirmed the presence of 14 phenolic substances, which included 12 phenolic compounds, and 2 flavonoids. Evaluation of seed bioassay and mulching experiments revealed that the aqueous extract concentrations of 4 and 6 % of T. portulacastrum inhibited the germination of E. heterophylla, while the mulched plants showed tolerance at the juvenile-flowering stage. We conclude that tolerance to allelopathic stress varied among the tested weed species and the growth stages of the same species. The suitability of using either aqueous shoot extract or mulch of T. portulacastrum as a potential bioherbicide deserves further monitoring under field conditions.

Depending on the strength of the relationship between biodiversity and aboveground biomass (AGB), diversity loss could lead to varied declines in carbon storage, compromising the role of forests as carbon sink. This study assesses different factors affecting the diversity–AGB relationship, including small trees (diameter < 7.5 cm) and considering different diversity metrics (Hill numbers), plot sizes (80, 400 and 1000 m²) and successional age categories (8–22, 23–30 and > 60 years). The study compares these relationships across three types of tropical dry forests: deciduous, semi-deciduous, and semi-evergreen. Results reveal the highest deviance values in plots with large trees in the 400 m² size (d² = 40.4), decreasing when small trees were included (d² = 25.8). Higher deviance values show the major contribution of large trees to diversity and AGB of 400 m² plots, while lower deviance values indicate the high contribution of small trees to diversity but limited contribution to AGB. When analyzing only large trees, deviance decreased with the order of Hill numbers. However, incorporating small trees increased deviance for higher Hill numbers. This is because abundance of small and large trees together has a greater influence on AGB. The diversity–AGB relationship was more prevalent and stronger in the semideciduous forest, which had marked orographic and successional age variation. The strongest diversity–AGB effect occurred in early successional ages, weakening in older stages. Our results show that accuracy in estimating the diversity–AGB relationship varies with plant size, diversity parameters, plot size and forest type.

In the context of ongoing global changes, long-term demographic monitoring data is crucial to assess the viability of natural populations. Such data is particularly important when large fluctuations in population size obfuscate background demographic trajectories. Here, we report results from the first 5 years of a long-term monitoring of a moonwort (Botrychium, Ophioglossaceae) community in Bic National Park, eastern Canada. Our objectives were to provide a first estimate of the composition, size, and demography of the moonwort colonies and to evaluate the putative influence of meteorological and microenvironmental variables on the density of aboveground sporophytes and sporophyte trait variability. Individuals were identified to the species level and tallied in each colony (n = 16 colonies) for the first 3 years (2019–2021) and then marked, monitored, and measured in permanent sample plots (n = 27 plots) for the last 3 years (2021–2023). Although colonies did not vary in composition (n = 8 Botrychium species), the number of emerged individuals differed yearly. Moonwort abundance, re-emergence, and trophophore height were associated with rainfall during the period of sporophyte emergence. Post-drought recovery occurred readily, which might reflect rapid recruitment or dormancy in Botrychium. Moonwort abundance declined as shrub cover and herbaceous vegetation height increased whereas trophophore size was smaller under closed tree canopy. Our results suggest spring rainfall as the limiting factor in opened habitats, whereas competition for sunlight may be limiting under closed canopy. The sizable and species-rich moonwort community of the Bic National Park provides key insights into Botrychium ecology and community dynamics.

We assessed the effect of grazing and plant patchiness on the perennial grass seed bank in litter patches in relation to co-occurring shrub, annual grass, and forb seed banks in disturbed rangelands of the Patagonian Monte. We hypothesized that litter patches in disturbed rangelands have a perennial grass seed bank but co-occurring seed banks of annual lifeforms reduce the opportunities for perennial grass reestablishment at these patches. We evaluated the effect of microsite (bare soil vs. vegetated) and grazing (grazed vs, non-grazed) on the (1) size (seeds m⁻²) of the four seed banks, (2) frequency of microsites with the respective seeds, and (3) frequency of co-occurrence of the perennial grass with shrub, annual grass and forb seed banks in litter patches at 5 dates (2009–2011). We found the smallest perennial grass and annual grass seed banks in litter patches under grazing and in bare soil microsites. The shrub and forb seed banks in litter patches were smaller at vegetated than at bare soil microsites under grazing and the reverse occurred in non-grazed conditions. The sizes of all seed banks were positively related to the frequency of litter patches with the respective seeds. In these litter patches, the size of perennial grass and shrub seed banks did not vary with grazing, and/or microsite while the size of annual grass and forb seed banks decreased with grazing and increased in vegetated microsites. The perennial grass seed bank in litter patches co-occurred mostly with forb and annual grass seed banks (several times larger). This is probably a constraint for the reestablishment of perennial grasses. However, although scarce, litter patches with exclusive perennial grass seed bank or co-occurring perennial grass and shrub seed banks could be an opportunity for perennial grass reestablishment.

Environmental selection during early ontogeny influences plant species representation in mature vegetation. Chief amongst these selective forces is the interplay of herbivore selection and seedling defence/tolerance. Although some species can recover from almost complete cotyledon loss, it remains unclear whether tolerance is impacted by other critical early life-history hazards like competition. This study examines early seedling tolerance of two sympatric Plantago species (P. lanceolata and P. major) for individuals grown in isolation, monoculture (i.e., with conspecifics) and mixed assemblages (with congenerics). The effects of 95 and 50% cotyledon removal at 14-d-old on plant growth and root:shoot allocation was established in 28-d and 100-d old plants. Although damage and neighbour environment consistently limited subsequent growth of P. major, there was no interaction between these factors. Nonetheless, individuals subjected to 95% defoliation in mixed assemblages were substantially smaller than those without neighbours. A similar response to cotyledon removal was evident for P. lanceolata at 28-d, although plants with conspecific neighbours tended to be larger. The defoliation effect disappeared at 100-d, and plants grown with neighbours were now smaller. Mortality and root:shoot allocation did not vary across treatments. While we underscore the negative impact that early ontogenetic damage and the influence of neighbour environment has on subsequent plant growth, we failed to elucidate obvious interactions between these factors. Nonetheless, we highlight how the remarkable tolerance of Plantago seedlings to almost complete defoliation in the face of intra-/inter-specific competition, may yet be impacted by anthropogenic disruption of environmental filters operating at the regeneration stage.

There are reports suggesting that leaf-cutting ants can act as a biotic filter, selecting plant traits according to foraging preferences, and consequently affecting the species composition of plant communities. In order to test this hypothesis, we evaluated the relationship between the floristic and functional diversity of woody plants in fragments of Semideciduous Seasonal Atlantic Forest (SAF) with the presence or absence of Atta sexdens (Linnaeus, 1758) nests. We expected that, in places where A. sexdens nests is present, 1) floristic diversity is lower and 2) the plant community is dominated by species characterized by greater investment in anti-herbivore defenses and lower nutritional content. For this, we sampled nine SAF fragments in the north of Paraná state, in Brazil. The diversity of woody regenerants (> 1 m in height, < 2 cm diameter) was estimated and 10 functional traits were evaluated: gap dependence, deciduousness, leaf nitrogen and carbon content, leaf C/N ratio, presence of leaf trichomes, leaf thickness, specific leaf area, presence of latex and condensed tannins, for the 28 most abundant woody species. Contrary to expectations, there were no differences in floristic diversity between sites with or without A. sexdens, and functional diversity was also similar, reflecting the floristic similarity. We suggest that the herbivory pressure by A. sexdens on the woody regenerants of SAF fragments is not strong enough to cause significant mortality in individual species and, consequently, affect plant diversity and composition. This may in part be related to the fact that most nests of A. sexdens were established in the edges of the fragments and that ants from these nests forage not only in the forest but also in the agricultural matrix where food resources are abundant. We also suggest that longer-term studies are still needed to fully elucidate the effects of A. sexdens on the plant community of Atlantic Forest fragments.

This study examines the recovery of late-successional forests in the Acadian Forest Region of northeastern North America after anthropogenic canopy disturbance. Tree species were sampled in a chronosequence of post-clearcut (3–54 years) and remnant late-successional forests (100–165 years) in four demographic size classes in Nova Scotia, Canada: seedlings, small saplings, large saplings, and canopy trees. Clearcut forests acquired late-successional canopy species composition within five decades after logging disturbance. Resilience to clearcutting was due principally to the persistence of residual shade-tolerant coniferous species, mostly red spruce (Picea rubens Sarg.) and eastern hemlock (Tsuga canadensis (L.) Carrière) in recovering stands. Redundancy analysis (RDA) revealed that most residual canopy species responded positively to canopy removal as small saplings, but not as seedlings. Seedlings of all residual canopy species exhibited strong associations with stand age, canopy cover, and microhabitats characteristic of older forests, such as rotting logs and smaller pieces of decayed wood. These results show that managed late-successional Acadian forests can recover quickly after clearcutting if advance tree regeneration (seedlings and saplings) is present and protected in the understory during canopy removal. Such Careful Logging methods focused on advance regeneration remain under-utilized in Acadian forests, though our results indicate they could better address silvicultural objectives such as maintaining a viable conifer component throughout stand development, as well as broader biodiversity goals in the management of late-successional forest types.

Fire is a natural component in tropical open ecosystems. Therefore, species are adapted to and thrive in post-fire conditions. In these fire-prone ecosystems smoke is one of the fire products that can stimulate seed germination. Here, we evaluated if and how smoke influences the germination of 44 Cerrado ground layer species, including grasses, forbs, subshrubs, and shrubs. Specifically, we aimed to answer the following questions: (1) How does smoke affect the germination of the Cerrado ground layer species? (2) Does smoke concentration influence the response? (3) Does this response differ according to growth form? (4) Are there differences in response between savanna and wet grassland communities? Considering all species together, smoke did not affect the germination of the study species. However, we found species having positive or negative responses, depending on the smoke concentration. When considering growth forms, grasses had a reduction in mean germination time. Smoke also reduced the mean germination time of savanna species, whereas, for wet grassland species, there was no effect of smoke. Thus, smoke has an asymmetric effect on cue germination in the Cerrado, depending on the species, growth form, and habitat. This effect can play a role in community post-fire responses, mostly related to faster germination.