Plant Ecology最新文献

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.

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.

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.