Shielded environments reduce stress in alien Asteraceae species during hot and dry summers along urban‐to‐rural gradients (original) (raw)
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American Journal of Botany, 2003
Several environmental factors influence the distribution of plants in coastal salt marshes. Substrate salinity is among the major factors preventing several species from establishing near the water line. However, interspecific competition for light and nutrients is often significant in determining the upper limit of plants along the salt marsh gradient. In this study, we tested the effects of substrate salinity and light and nutrient availability on the performance of the annual Aster laurentianus (Asteraceae), an endangered species of eastern Canadian salt marshes. This species is typically found in a narrow band along the shores of shallow lagoons, cornered between the high water line and the dense, herbaceous community of the upper marsh. Low light availability was the most significant factor limiting plant performance. Salinity had little effect on A. laurentianus as, unexpectedly, did nutrient availability. Yet plants were able to absorb nutrients when these were made more available. Luxury consumption, the uptake of excess nutrients, may make sense for this annual plant because the habitat in which it grows is subject to frequent disturbances (e.g., sand accretion and salinity pulses) that may kill canopy species and release suppressed A. laurentianus individuals. These results suggest that interspecific competition for light may play a significant role in restraining A. laurentianus from the upper part of salt marshes. Luxury consumption may help the species to opportunistically take advantage of release from taller species, particularly towards the upper edge of the salt marsh gradient.
Floral Visitors of Three Asteraceae Species in a Xeric Environment in Central Mexico
We describe the spatial variation in the structure and composition of the communities of insects visiting the in-florescences of Flaveria ramosissima Klatt, Florestina pedata (Cav.) Cass., and Parthenium bipinnatifidum (Ort.) Rollins (Asteraceae) in a xeric environment in Central Mexico. Inflorescences of the three Asteraceae were visited by a total of 96 species of Hymenoptera, Diptera, Lepidoptera, Coleoptera, and Hemiptera. Total species richness of floral visitors to the three Asteraceae and total abundance of insects of Fl. pedata and P. bipinnatifi-dum did not differ between low and high vegetation cover sites. Total abundance of insects visiting the inflores-cences of F. ramosissima and abundance of Hymenoptera in all three Asteraceae were higher at the low vegetation coverage (LVC) site than at the high vegetation coverage (HVC) one. Diversity of insects of Fl. pedata and P. bipinnatifidum was higher at the HVC site. However, in F. ramosissima diversity was higher at the LVC site. The communities of insects of each Asteraceae were dissimilar between sites. These differences can be attributed to variation in the abundance of Lepidophora (Diptera: Bombyliidae), Miridae (Hemiptera), Melyridae (Coleoptera), Tiphiidae (Hymenoptera), Myrmecocystus mexicanus Wesmael, and Dorymyrmex grandulus (Forel) (Hymenoptera: Formicidae). The first three insect groups were sensitive to LVC, high temperature, and low humidity, whereas the last three tolerated those same environmental conditions. Changes in temperature, humidity, and resources associated with vegetation coverage seem to differentially affect each species of floral visitors of the three Asteraceae species studied.
African Journal of Plant Science
Ecological significance of Asteraceae in response to common colonizers due to the fast pace of urbanization in Lahore District was determined. The species are natural colonizers in this area. In order to gauge the response, sites from both urban and suburban areas were selected. A total of 28 species under 22 genera of the family Asteraceae were collected and identified. The results reveal that members of Asteraceae have highest diversity in suburban having richness of 18 species, followed by urban having only four species. The diversity index indicates that highest diversity was in suburban and rural wastelands of Raiwind. In comparison with the previous record, only 60% species of Asteraceae previously reported were found, out of which 50% species were present in suburban and rural and only 10% in urban areas. It appears that decline in the species number was due to the excessive growth of population, urbanization, industrialization, and invasive exotics like Parthenium hysterophorus and Pantanema vestitum.
Austral Ecology, 2005
Three experiments were conducted to verify if an increase in environmental stress level would affect the interactions between two species of nurse shrubs and seedlings of Aspidosperma quebracho-blanco. This is a mesic species with a generalist distribution over an extensive environments gradient. The relationship between Larrea divaricata and seedlings of A. quebracho-blanco was studied in two contrasting soils, a silty loam soil with higher surface clay content and a sandy loam soil. The effect of seasonal variability of rainfall on the initial establishment of seedlings under the shade of L. divaricata was evaluated in three consecutive years. The effect of nurse plant shade was tested comparing two shrub species with different types of leaf life span (sclerophyllousevergreen and leguminous-deciduous). The natural establishment of A. quebracho-blanco depended on shaded microsites, but not on the type of shade provided by different nurse shrubs. Emergence and initial establishment depended on interactions of soil type and seasonal rainfall variation with nurse plants. The importance of facilitation increased with clay soil (CS). Sandy soil was 'less humid' than CS under shrub shade. However, establishment success depends on opportune even rainfall distribution in interaction with nurse plant presence.
Variability in functional traits mediates plant interactions along stress gradients
Journal of Ecology, 2013
1. Environmental gradients may influence a plant's physiological status and morphology, which in turn may affect plant-plant interactions. However, little is known about the relationship between environmental variation, physiological and morphological variability of plants and variation in the balance between competition and facilitation. 2. Mountain ranges in dry environments have opposing altitudinal environmental gradients of temperature and aridity, which limit plant growth at high and low elevations. This makes them particularly suitable for exploring the relationships between environmental conditions, plant phenotype and plant-plant interactions. We hypothesized that different environmental stressors will differently affect the physiological status of a nurse plant. This, then, manifests itself as variation in nurse plant morphological traits, which in turn mediates plant-plant interactions by altering microhabitat conditions for the nurse and associated species. 3. In an observational study, we measured a series of functional traits of Arenaria tetraquetra cushions as indicators of its physiological status (e.g. specific leaf area, relative water content) and morphology (e.g. cushion compactness, size). Measurements were taken along the entire elevation range where A. tetraquetra occurs. Furthermore, we analysed how these functional traits related to soil properties beneath cushions and the number of associated species and individuals compared with open areas. 4. Cushions at high elevation showed good physiological status; they were compact and large, had higher soil water and organic matter content compared with open areas and showed the strongest facilitation effect of the whole elevation gradientthat is, the highest increase in species richness and abundance of beneficiaries compared with open areas. Physiological data at low elevation indicated stressful abiotic conditions for A. tetraquetra, which formed loose and small cushions. These cushions showed less improved soil conditions and had reduced facilitative effects compared with those at high elevation. 5. Synthesis. Functional traits of the nurse species varied distinctively along the two opposing stress gradients, in parallel to the magnitude of differences in microenvironmental conditions between cushions and the surrounding open area, and also to the facilitation effect of cushions. Our data, therefore, provides a strong demonstration of the generally overlooked importance of a nurse plant's vigour and morphology for its facilitative effects.
Plant Systematics and Evolution, 2009
Flowering-time, plant longevity and size of capitulum were studied in a common garden experiment on seven populations of annual Chaetanthera moenchioides derived from a strong latitudinal aridity gradient in the mediterranean climate area of Chile. Populations derived from the drier northern part of the latitudinal gradient showed significantly shorter flowering and fruiting phenology and smaller capitula under uniform growing conditions. Water stress experiments performed in the greenhouse induced further phenological hastening and a reduction in number of ray florets per capitulum. Population differentiation and the reaction norms in C. moenchioides agree with the predictions of geneticassimilation given that the plastic response of the species under water stress mimics phenotypic differentiation that has evolved along the environmental gradient.
Plant responses to abiotic stress in their natural habitats
The study of plant responses to abiotic stress is one of the most active research topics in plant biology, due to its unquestionable academic interest, but also because of its practical implications in agriculture, since abiotic stress (mainly draught and high soil salinity) is the major cause for the reduction in crop yields worldwide. Studies in model systems, such as Arabidopsis thaliana, have allowed to define general, basic molecular mechanisms of stress responses (regulation of osmotic balance and ion homeostasis, synthesis of protective metabolites and proteins, activation of antioxidant systems, etc.). However, these responses, in most cases, do not lead to stress tolerance; in fact, Arabidopsis, like most wild plants, and all important crops are rather sensitive, while some specialised plants (halophytes, gypsophytes, xerophytes…) are resistant to drastic abiotic stress conditions in their natural habitats. Therefore, the response mechanisms in plants naturally adapted to stress must be more efficient that those which operate in non-tolerant plants, although both may share the same molecular basis. We propose that these quantitative differences are dependent on, and modulated by the edafoclimatic properties of the habitat where plants develop, and by spatial and temporal changes of those properties. In this paper we describe our multidisciplinar approach to study the mechanisms of tolerance to abiotic stress, based on the determination of the levels of several molecular markers, characteristic of different pathways of stress responses, in tolerant wild plants under natural conditions; the results obtained will be then correlated with climatological data and with those derived from edafological assays, performed on samples collected simultaneously with the plant material. This strategy may contribute to our knowledge on stress response mechanisms, providing complementary information to that obtained from more common studies in this field, which use non-tolerant model species and laboratory or greenhouse artificial conditions.