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Herbaceous Plant Community (herbaceous + plant_community)
Selected AbstractsWinners and losers in herbaceous plant communities: insights from foliar carbon isotope composition in monocultures and mixturesJOURNAL OF ECOLOGY, Issue 6 2005A. JUMPPONEN Summary 1We established monocultures and 16 unique mixed communities of 12 native grasses, legumes and non-N2 -fixing forbs. We identified species having a greater or lesser yield in the mixed communities than expected from monoculture data as winners and losers, respectively. To test our hypothesis that performance of the subordinate species (losers) is mainly controlled by light availability, whereas the dominant species (winners) are sensitive to the availability of below-ground resources, we traced the effects of number of species, light transmission in the community and foliar N concentration on plant photosynthesis through leaf C isotope composition (,13C). 2Phalaris arundinacea and Phleum pratense, the two tallest grass species, yielded more in mixtures than expected, as, initially, did Dactylis glomerata. Festuca ovina, the smallest grass, and Ranunculus acris, a forb, had smaller yield in mixtures than expected. For most species, observed mixture yields did not deviate significantly from those expected. 3Decreases in transmitted light decreased ,13C in D. glomerata, Lotus corniculatus and Rumex acetosa. The ,13C of Trifolium pratense and L. corniculatus was affected by increasing number of species in the plant community even after accounting for the transmitted light. In P. arundinacea, ,13C increased with increasing foliar %N, as expected for the tallest, dominant species. 4Species showing a positive, significant relationship between ,13C and transmitted light were relatively low growing and unable to establish dominance in multispecies communities due to shading by larger dominants. 5We conclude that above-ground competition is crucial in determining C isotope composition among the subordinate species, whereas the dominant species are more strongly affected by below-ground resources. Different factors thus dictate the physiological performance of species according to the size-distribution hierarchy in the community. [source] Fertilization effects on species density and primary productivity in herbaceous plant communitiesOIKOS, Issue 3 2000Laura Gough Fertilization experiments in plant communities are often interpreted in the context of a hump-shaped relationship between species richness and productivity. We analyze results of fertilization experiments from seven terrestrial plant communities representing a productivity gradient (arctic and alpine tundra, two old-field habitats, desert, short- and tall-grass prairie) to determine if the response of species richness to experimentally increased productivity is consistent with the hump-shaped curve. In this analysis, we compared ratios of the mean response in nitrogen-fertilized plots to the mean in control plots for aboveground net primary productivity (ANPP) and species density (D; number of species per plot of fixed unit area). In general, ANPP increased and plant species density decreased following nitrogen addition, although considerable variation characterized the magnitude of response. We also analyzed a subset of the data limited to the longest running studies at each site (,4 yr), and found that adding 9 to 13 g N m,2 yr,1 (the consistent amount used at all sites) increased ANPP in all communities by approximately 50% over control levels and reduced species density by approximately 30%. The magnitude of response of ANPP and species density to fertilization was independent of initial community productivity. There was as much variation in the magnitude of response among communities within sites as among sites, suggesting community-specific mechanisms of response. Based on these results, we argue that even long-term fertilization experiments are not good predictors of the relationship between species richness and productivity because they are relatively small-scale perturbations whereas the pattern of species richness over natural productivity gradients is influenced by long-term ecological and evolutionary processes. [source] Contrasting effects of cattle and wildlife on the vegetation development of a savanna landscape mosaicJOURNAL OF ECOLOGY, Issue 5 2010Kari E. Veblen Summary 1.,Through their effects on plant communities, herbivores can exert strong direct and indirect effects on savanna ecosystems and have the potential to create and maintain savanna landscape heterogeneity. Throughout much of sub-Saharan Africa, periodic creation and abandonment of livestock corrals leads to landscape mosaics of long-term ecosystem hotspots that attract both cattle and large ungulate wildlife. 2.,The development and maintenance of vegetation in these types of hotspots may be controlled in part by herbivory. Cattle and wildlife may have different, potentially contrasting effects on plant succession and plant,plant interactions. We ask how cattle and wild herbivores affect the maintenance and vegetation development of corral-derived landscape heterogeneity (0.25,1.0 ha treeless ,glades') in Laikipia, Kenya, through their effects on long-term successional and short-term plant,plant dynamics. 3.,We used the Kenya Long-term Exclosure Experiment to exclude from glades different combinations of cattle, large ungulate wildlife (i.e. zebras, gazelles and other antelopes), and mega-herbivore wildlife (i.e. giraffes and elephants). We first assessed long-term changes in cover of the dominant grass species, Cynodon plectostachyus and Pennisetum stramineum (the early- and late-dominant species, respectively). We then used a neighbour removal experiment to test the effects of different herbivores on competition and facilitation between the two glade grass species. 4.,In the long-term experiment, we found that large ungulate wildlife reinforced landscape heterogeneity over time by helping maintain glades in their early C. plectostachyus -dominated form. Cattle and mega-herbivore wildlife, on the other hand, appeared to reduce the positive effects through forage preference for C. plectostachyus. 5.,In the neighbour removal experiment, we found that each grass species benefited from facilitation when it was the preferred forage for the dominant grazer. Facilitation of C. plectostachyus by P. stramineum was strongest when cattle co-occurred with wildlife, whereas facilitation of P. stramineum by C. plectostachyus was strongest when cattle were absent. 6.,Synthesis. Our results demonstrate that different combinations of cattle and wildlife have different effects, largely via contrasting forage preferences, on the persistence of landscape heterogeneity in this savanna landscape. More generally, we provide evidence for contrasting effects of cattle and wildlife on short-term plant interactions (facilitation) and successional processes within the herbaceous plant community. [source] Photon flux partitioning among species along a productivity gradient of an herbaceous plant communityJOURNAL OF ECOLOGY, Issue 6 2006ANNE AAN Summary 1We studied light partitioning among species along the natural productivity gradient of herbaceous vegetation with an above-ground dry mass of 150,490 g m,2. The aim was to investigate how the light capturing ability per above-ground biomass and leaf nitrogen changes in an entire community and to reveal whether different species respond similarly to changes in soil conditions and competition. 2Species becoming dominant at high soil resources have intrinsically low leaf area ratios (LAR) and lower tissue nitrogen concentration, and hence relatively high nitrogen use efficiency. These traits lead to dominance when soil resources allow rapid growth so that benefits arising from the ability to locate leaves above neighbours and thereby increasing asymmetry of competition, become more crucial. 3In contrast to our expectations, above-ground efficiency of nitrogen use on the community level (aNUE) increased along the productivity gradient. Species level nitrogen use efficiency was unaffected by variation in site productivity; the increase in community aNUE was solely as a consequence of changes in species composition. 4Light absorption per unit of above-ground mass, ,M, declined significantly at the community level and also in most species, indicating that light use efficiency increased with increased site productivity and LAI. 5Light absorption per unit of leaf nitrogen, ,N, as an indicator of the ratio NUE/LUE showed no clear pattern on the community level because both NUE and LUE tend to increase with increased productivity. At the species level, ,N tends to decrease because NUE did not change with stand productivity. 6Some subordinate species responded by enlarging their LAR to increased competition. Additionally, these species were the most responsive in their leaf chlorophyll/nitrogen ratio to changes in light conditions, which shows that physiological plasticity is important for species that are unable to compete for light with the ability to position their leaves above those of other species. 7This study shows how plasticity in above-ground growth pattern and nitrogen allocation differs between species with respect to increased soil fertility and competition, leading to distinctive strategies of survival. Light partitioning analysis reveals that increased competition for light, resulting in changes in species composition, is the key factor that leads to decoupling of species and community level acclimation. [source] Kaempferol Glycosides from Lobularia maritima and Their Potential Role in Plant InteractionsCHEMISTRY & BIODIVERSITY, Issue 2 2009Antonio Fiorentino Abstract Six kaempferol glycosides, four of them characterized for the first time, were isolated from the leaf extract of Lobularia maritima. The structural elucidation was performed by a combined approach using Electrospray-Ionization Triple-Quadrupole Mass-Spectrometric (ESI/TQ/MS) techniques, and 1D- and 2D-NMR experiments (1H, 13C, DEPT, DQ-COSY, TOCSY, ROESY, NOESY, HSQC, HMBC, and HSQC-TOCSY). The isolated kaempferol derivatives have different disaccharide substituents at C(3) and four of them have a rhamnose unit at C(7). To evaluate their potential allelopathic role within the herbaceous plant community, the compounds, as well as the aglycone obtained from enzymatic hydrolysis, have been tested in vitro on three coexisting plant species, Dactylis hispanica, Petrorhagia velutina, and Phleum subulatum. The results obtained allow us to hypothesize that the type of the sugar modulates the biological response. The bioassay data, analyzed by a multivariate approach, and grouping the compounds on the basis of the number of sugar units and the nature of carbohydrates present in the disaccharide moiety, indicate a structure,activity relationship. [source] | ||||||||||