Showing papers by "David C. Hartnett published in 2015"
TL;DR: Despite the effects of drought and grazing on aboveground net primary productivity and community structure, this work suggests that grasses stabilize tallgrass prairie plant communities because their rhizomes and associated buds persist through co-occurring disturbances.
Abstract: While the effects of drought and grazing are often studied separately, these disturbances co-occur in grasslands worldwide and interactively influence population, community, and ecosystem processes. The effects of drought and grazing on the belowground bud bank may dictate the trajectory of community recovery because new shoots arise from belowground buds after disturbance in perennial grasslands. We therefore investigated the separate and interactive effects of severe drought and grazing on the belowground bud bank and aboveground vegetation in the tallgrass prairie of northeast Kansas, USA. Contrary to our expectations, we observed changes in community structure and declines in species richness both above and below ground in response to drought and grazing. We also hypothesized that drought would reduce bud bank density of all taxonomic groups, but found that grass bud and shoot densities remained constant across all drought and grazing treatment combinations. While sedge and forb bud and shoot densities were reduced by drought, only sedge bud density declined to a greater extent when grazed under drought conditions. Live rhizome biomass did not vary by treatment and was highly correlated with bud bank density, suggesting that bud demography is tightly linked to the production and senescence of rhizomes. Despite the effects of drought and grazing on aboveground net primary productivity and community structure, our work suggests that grasses stabilize tallgrass prairie plant communities because their rhizomes and associated buds persist through co-occurring disturbances.
45 citations
TL;DR: The tiller and bud bank dynamics of P. smithii, a dominant rhizomatous grass of the northern mixed-grass prairie, were examined in South Dakota throughout an annual cycle to assess the investment in guerilla versus phalanx growth and the role of different bud populations in renewal versus regenerative functions and vegetative spread via rhizomes.
Abstract: Recruitment of rhizomatous perennial grass ramets primarily occurs from the belowground bud bank. Investment in guerilla versus phalanx growth is determined by bud availability, development, and spatial distribution. The tiller and bud bank dynamics of Pascopyrum smithii, a dominant rhizomatous grass of the northern mixed-grass prairie, were examined in South Dakota throughout an annual cycle to assess the investment in guerilla versus phalanx growth and the role of different bud populations in renewal versus regenerative functions and vegetative spread via rhizomes. Pascopyrum smithii invested substantially in both phalanx and guerilla tiller production. However, investment in rhizome production before tiller recruitment prioritized guerilla over phalanx growth. Annual tiller recruitment of P. smithii was capable of flexible timing, occurring in either spring or fall. Renewal buds, from which rhizomes and tillers were recruited, primarily consisted of the youngest generation of buds borne at the base of tillers. Although rhizome axillary buds and older tiller axillary buds were rarely used in annual tiller recruitment, they provided a sizable reserve (regenerative) bud bank. The spatial distribution of bud development produced the mixed guerrilla–phalanx growth pattern and flexible tiller recruitment timing of P. smithii. Therefore, P. smithii is capable of employing both conservative and foraging growth strategies which will facilitate its persistence under local neighborhood variability and changing resource availability associated with environmental change. Understanding the spatial distribution of buds as determined by rhizome architecture is essential to understanding the distribution and composition of species within plant communities dominated by clonal species.
22 citations
TL;DR: Co-occurring C3 caespitose grasses had similar bud-bank and tiller dynamics contributing to genet persistence but differed in bud characteristics that could affect genet longevity and species coexistence.
Abstract: PREMISE OF THE STUDY: Tiller recruitment from the belowground bud bank of caespitose grasses infl uences their ability to monopolize local resources and, hence, their genet fi tness. Diff erences in bud production and outgrowth among tiller types within a genet and among species may explain co-occurrence of caespitose grasses. This study aimed to characterize genet bud-bank and tiller production and dynamics in two co-occurring species and compare their vegetative reproductive strategies. METHODS: Bud-bank and tiller dynamics of Hesperostipa comata and Nassella viridula , dominant C 3 caespitose grasses in the northern mixed-grass prairie of North America, were assessed throughout an annual cycle. KEY RESULTS: The two species showed similar strategies, maintaining polycyclic tillers and thus creating mixed-age genet bud banks comprising multiple bud cohorts produced in diff erent years. Vegetative tillers produced the majority of buds, whereas fl owering tillers contributed little to the bud bank. Buds lived for at least 2 yr and were maintained in multiple developmental stages throughout the year. Because bud longevity rarely exceeded tiller longevity, tiller longevity drove turnover within the bud bank. Tiller population dynamics, more than bud production per tiller, determined the diff erential contribution of tiller types to the bud bank. Nassella viridula had higher bud production per tiller, a consistent annual tiller recruitment density, and greater longevity of buds on senesced and fl owering tillers than H. comata . CONCLUSIONS: Co-occurring C 3 caespitose grasses had similar bud-bank and tiller dynamics contributing to genet persistence but diff ered in bud characteristics that could aff ect genet longevity and species coexistence.
18 citations
TL;DR: The results indicate that mycorrhizal symbiosis has diverse consequences, influencing the abundance and the quality of host plants in tallgrass prairie, as well as their responses to consumers.
Abstract: Plant–herbivore interactions and mycorrhizal symbiosis are important associations in grasslands that may interact due to their relationships with a common host plant and its resources. However, few studies have explored the effect of mycorrhizal symbiosis on plant–herbivore interactions. An understanding of the complex interactions between host plants, mycorrhizal fungi, and insect herbivores is enhanced by in situ examinations of the three parties acting simultaneously. The objective of this study was to quantify the effects of mycorrhizal symbiosis on insect herbivory and the host-plant community in tallgrass prairie. We used long-term mycorrhizal and fungicide-treated plots at Konza Prairie Biological Station (Manhattan, KS) to determine whether insect herbivory is altered by suppression of mycorrhizal fungi. Herbivory on plants in mycorrhizal control plots was greater than in fungicide-treated plots, and for one plant guild, C3 graminoids, the difference was significant. In fungicide-treated plots, plant diversity was significantly greater and herbivory was negatively correlated with plant species diversity. Differences in productivity of plant functional groups due to mycorrhizal symbiosis may be a key factor in patterns of insect herbivory. The results indicate that mycorrhizal symbiosis has diverse consequences, influencing the abundance and the quality of host plants in tallgrass prairie, as well as their responses to consumers.
14 citations
TL;DR: The vegetative reproduction and dynamics of Andropogon gerardii, a dominant C4 perennial grass of the Great Plains of North America, were compared between tallgrass and northern mixedgrass prairie habitats and similar population growth rates occurred in both habitats.
Abstract: Plant species with wide distributions may differ in their population dynamics across their range, especially in contrasting habitats. Most tiller recruitment of perennial grasses occurs vegetatively from the belowground bud bank rather than from seed. Seed reproduction often occurs under a narrower range of environmental conditions than vegetative reproduction. As a result flowering and seedling recruitment patterns of a species often differ between contrasting habitats and across its range. How vegetative reproduction and bud bank dynamics of a species vary between contrasting habitats has not been well studied and could explain the differences in its persistence and productivity between habitats. Therefore, the vegetative reproduction and dynamics of Andropogon gerardii, a dominant C4 perennial grass of the Great Plains of North America, were compared between tallgrass and northern mixedgrass prairie habitats. Bud production and tiller recruitment in 10 populations were examined throughout an a...
12 citations