Dataset Information

Shrubs indirectly increase desert seedbanks through facilitation of the plant community.

ABSTRACT: The mechanisms supporting positive ecological interactions are important. Foundation species can structure desert biodiversity by facilitating seedbanks of annual plants, but the direct and indirect mechanisms of shrub effects on seedbank have not been experimentally decoupled. We conducted the first test of shrubs increasing seedbank densities through direct effects on the seedbank (i.e. shrub seed-trapping, animal-mediated dispersal) and indirect effects by facilitating the annual plant community (i.e. seed deposition, annual seed-trapping). Two distinct desert ecosystems were used to contrast transient seedbank densities in shrub and open microsites by manipulating annual plant density and the presence of the persistent seedbank. We measured transient seedbank densities at the end of the growing season by collecting soil samples and extracting seeds from each respective treatment. Transient seedbank densities were greatest in shrub canopies and with relatively higher annual plant densities. The persistent seedbank contributed to transient seedbank densities only in one desert and in the open microsite. Shrubs indirectly increased seedbank densities by facilitation the seed production of the annual plants. Therefore, shrubs are increasing seedbank independently of the annual plant community, likely through trapping effects, and dependently by facilitating seed production of the annuals. These findings provide evidence for a previously undescribed mechanism that supports annual seedbanks and thus desert biodiversity. We also identify shrubs as being significant drivers of desert plant communities and emphasize the need to consider multiple mechanisms to improve our ability to predict the response of ecosystems to change.

SUBMITTER: Filazzola A

PROVIDER: S-EPMC6481865 | biostudies-literature | 2019

REPOSITORIES: biostudies-literature

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Shrubs indirectly increase desert seedbanks through facilitation of the plant community.

Filazzola Alessandro A Liczner Amanda Rae AR Westphal Michael M Lortie Christopher J CJ

PloS one 20190424 4

The mechanisms supporting positive ecological interactions are important. Foundation species can structure desert biodiversity by facilitating seedbanks of annual plants, but the direct and indirect mechanisms of shrub effects on seedbank have not been experimentally decoupled. We conducted the first test of shrubs increasing seedbank densities through direct effects on the seedbank (i.e. shrub seed-trapping, animal-mediated dispersal) and indirect effects by facilitating the annual plant commun ...[more]

PMID: 31017967

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Project description:The magnet species hypothesis proposes that flowering plants that are attractive to pollinators can increase the relative pollination rates of neighbouring plants by acting as 'magnets.' Here, we test the hypothesis that insect-pollinated shrub species Larrea tridentata and wind-pollinated shrub species Ambrosia dumosa act as magnets for the pollinator visitation of understory annual plant species in an arid ecosystem. As an extension to the magnet species hypothesis, we propose the double magnet species hypothesis in which we further test for reciprocity by the floral island created in the understory of the benefactor shrubs as an additional pollinator magnet for the shrub itself. We used an annual plant placed near each shrub and the open to measure the effect of shrubs on annuals. The double magnet species hypothesis was tested using L. tridentata with and without surrounding annuals. We measured pollinator visitation and visit duration using video and in-situ observation techniques to test whether shrubs increase pollinator visitation to understory annual plants, if insect-pollinated shrubs act as better pollinator magnets than wind-pollinated shrubs (to determine the effects of the floral resource itself), and whether shrubs with annuals in their understory have higher pollinator visitation rates relative to shrubs without annuals. We found that insect-pollinated shrubs increased the visitation rate and duration of visits by pollinators to their understory plants and that wind-pollinated shrubs decreased the duration of visits of some insect visitors, but these relationships varied between years. While the presence of annuals did not change the visitation rate of all possible pollinators to L. tridentata flowers, they did decrease the visitation duration of specifically bees, indicating a negative reciprocal effect of the understory on pollination. Thus, the concentrated floral resources of flowers on insect-pollinated shrubs can act as a magnet that attract pollinators but that in turn provide a cost to pollination of the shrub. However, while wind-pollinated shrubs may provide other benefits, they may provide a cost to the pollination of their understory. These findings support the magnet species hypothesis as an additional mechanism of facilitation by insect-pollinated shrubs to other plant species within arid ecosystems.

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Project description:Plant facilitation has a pivotal role in regulating species coexistence, particularly under arid environments. The present study aimed to evaluate the facilitative effect of Calligonum polygonoides L. on its understory plants in coastal habitat. Forty Calligonum shrubs were investigated and the environmental data (soil temperature, moisture, pH, salinity, carbon and nitrogen content, and light intensity), vegetation composition, and diversity of associated species were recorded under- and outside canopies. Eight of the most frequent understory species were selected for evaluating their response to the facilitative effect of C. polygonoides. Bioactive ingredients of Calligonum roots were analyzed using gas chromatography-mass spectrometry (GC-MS), and mycorrhizal biodiversity in their rhizosphere soil was also assessed. The effect of Calligonum on understory plants ranged between facilitation and inhibition in an age-dependent manner. Old shrubs facilitated 18 and inhibited 18 associated species, while young shrubs facilitated 13 and inhibited 9 species. Calligonum ameliorated solar radiation and high-temperature stresses for the under canopy plants. Moreover, soil moisture was increased by 509.52% and 85.71%, while salinity was reduced by 47.62% and 23.81% under old and young shrubs, respectively. Soil contents of C and N were increased under canopy. This change in the microenvironment led to photosynthetic pigments induction in the majority of understory species. However, anthocyanin, proline contents, and antioxidant enzyme activities were reduced in plants under canopy. Thirteen mycorrhizal fungal species were identified in the rhizospheric soil of Calligonum with the predominance of Funneliformis mosseae. Thirty-one compounds were identified in Calligonum root extract in which pyrogallol and palmitic acid, which have antimicrobial and allelopathic activities, were the major components. The obtained results demonstrated that facilitation provided by Calligonum is mediated with multiple mechanisms and included a set of interrelated scenarios that took place in a species-specific manner.

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Dataset Information

Shrubs indirectly increase desert seedbanks through facilitation of the plant community.

Publications

Shrubs indirectly increase desert seedbanks through facilitation of the plant community.

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