The effects of nutrient addition on floral characters and pollination in two subalpine plants, Ipomopsis aggregata and Linum lewisii

Abstract

The availability of soil and pollination resources are main determinants of fitness in many flowering plants, but the degree to which each is limiting and how they interact to affect plant fitness is unknown for many species. We performed resource (water and nutrients) and pollination (open and supplemental) treatments on two species of flowering plants, Ipomopsis aggregata and Linum lewisii, that differed in life-history, and we measured how resource addition affected floral characters, pollination, and reproduction (both male and female function). We separated the direct effects of resources versus indirect effects on female function via changes in pollination using a factorial experiment and path analysis. Resource addition affected I. aggregata and L. lewisii differently. Ipomopsis aggregata, a monocarp, responded to fertilization in the year of treatment application, increasing flower production, bloom duration, corolla width, nectar production, aboveground biomass, and pollen receipt relative to control plants. Fertilization also increased total seed production per plant, and hand-pollination increased seeds per fruit in I. aggregata, indicating some degree of pollen limitation of seed production. In contrast, fertilization had no effect on growth or reproductive output in the year of treatment on L. lewisii, a perennial, except that fertilization lengthened bloom duration. However, delayed effects of fertilization were seen in the year following treatment, with fertilized plants having greater aboveground biomass, seeds per fruit, and seeds per plant than control plants. In both species, there were no effects of resource addition on male function, and the direct effects of fertilization on female function were relatively stronger than the indirect effects via changes in pollination. Although we studied only two plant species, our results suggest that life-history traits may play an important role in determining the reproductive responses of plants to soil nutrient and pollen additions.

Plant genotype, nutrients, and G × E interactions structure floral visitor communities

“…We added fertilizer as dry, slow-release pellets (nitrogen was added in the form of urea, N 2 H 4 CO, and phosphorus was added as triple super phosphate, P 2 O 5 ) which released nitrogen and phosphorus into the soil during rainfall events. These levels of enrichment have been shown to double nutrient availability in similar systems (Goldberg andMiller 1990, Sanders et al 2007) and are comparable to several local oldfield studies manipulating nutrients to examine effects on plant community dynamics (Sanders et al 2007, Blue et al 2011, Souza et al 2011a, as well as other studies examining nutrient enrichment effects on floral traits and pollinators (e.g., Campbell and Halama 1993, Asikainen and Mutikainen 2005, Munoz et al 2005, Burkle and Irwin 2009a, Burkle and Irwin 2010. We crossed Solidago altissima genotype identity and genotypic diversity with these nutrient treatments such that there were two monoculture plots of each v www.esajournals.org genotype for each nutrient treatment and three genotype mixture plots for each nutrient treatment.…”

“…Also, the variability within floral visitor communities (i.e., dispersion) was lower in phosphorus-enriched plots. As nutrient treatments did not consistently alter floral abundance, the effects on the floral visitor community were likely driven by changes in the quality and quantity of floral rewards like nectar and pollen (e.g., Lau and Stephenson 1993, Burkle and Irwin 2009a.…”

“…One key environmental factor for plants and their associated floral visitors is soil nutrient availability, as nutrients can vary considerably at a local level and are known to influence flower production and bloom duration (e.g., Campbell and Halama 1993, Asikainen and Mutikainen 2005, Munoz et al 2005, Burkle and Irwin 2009a. In fact, pollination ecologists have documented the role of floral traits, such as floral display size (the number of open flowers) and flowering phenology (timing and duration of bloom period) in explaining pollinator preferences (e.g., Stang et al 2006, Olesen et al 2008, Burkle and Irwin 2009b).…”

Abiotic conditions affect floral antagonists and mutualists of Impatiens capensis (Balsaminaceae)

“…Previous work indicates ( Heil et al, 2001 ) herbivory. The effects of nutrients on pollinators has not been examined as frequently, but range from positive ( Muñoz et al, 2005 ;Burkle and Irwin, 2009 ) to negative ( Muñoz et al, 2005 ) to neutral ( Burkle and Irwin, 2009 ). In this study, however, the effects of fertilizer on plantinsect interactions were remarkably consistent, leading to increased interactions with both mutualists and antagonists.…”

Landscape scale variation in nectar amino acid and sugar composition in a Lepidoptera pollinated orchid species and its relation with fruit set

“…How nectar composition naturally varies at a true landscape scale remains unknown. Experimental studies have reported that litter availability may affect nectar sugar content (Baude et al 2011), whereas soil nutrient levels were shown to influence both nectar production (Burkle & Irwin 2009) and nectar AA content (Gardener & Gillman 2001b). Therefore, it can be expected that landscape scale environmental variation leads to nectar composition variation across populations and that this may on its turn contribute to variation in fruiting success among populations.…”