In a controlled environment, we artificially induced drought during flowering of Epilobium angustifolium, an animal-pollinated plant. Leaf water potential (ψ(l)) and floral traits were monitored over a 12-d period of soil moisture depletion. Soil moisture depletion induced drought stress over time, as revealed by significant treatment × day interactions for predawn and midday ψ(l). Nectar volume and flower size showed significant negative responses to drought stress, but nectar sugar concentration did not vary between treatments. Floral traits were more buffered from drought than leaf water potentials. We used path analysis to examine direct and indirect effects of ψ(l) on floral traits for plants in well-watered (control) vs. drought treatments. According to the best-fit path models, midday ψ(l) has significant positive effects on flower size and nectar volume in both environments. However, for controls midday ψ(l) also had a significant negative effect on nectar sugar concentration. Results indicate that traits influencing floral attractiveness to pollinators in E. angustifolium vary with plant water status, such that pollinator-mediated selection could indirectly target physiological or biochemical controls on ψ(l). Moreover, under mesic conditions selection for greater nectar sugar reward may be constrained by the antagonistic effects of plant water status on nectar volume and sugar concentration.

Water loss through inflorescences may place extreme demands on plant water status in arid environments. Here we examine how corolla size, a trait known to influence pollination success, affects the water cost of flowering in the alpine skypilot, Polemonium viscosum. In a potometry experiment, water uptake rates of inflorescences were monitored during bud expansion and anthesis. Corolla volume of fully expanded flowers predicted water uptake during bud expansion (R =0.61, P=0.0375) and corolla surface area predicted water uptake during anthesis (R=0.59, P=0.044). To probe mechanisms underlying the relationship between corolla size and water uptake, cell dimensions and densities were measured in several regions of fully expanded corollas. Corolla length was positively correlated with cell length in the middle of the corolla tube and cell diameter in the corolla lobe (Pearson's r from 0.26-0.33, n=86, P ≤ 0.05). Cell density was negatively correlated with cell dimensions in the upper corolla tube and lobe (Pearson's r from -0.39 to -0.42, P ≤ 0.0015). These findings suggest that more water may be required to maintain turgor in large corollas in part because their tissues have lower cell wall densities. The carbon cost of water use by flowers was assessed in krummholz and tundra habitats for P. viscosum flowering, respectively, during dry and wet portions of the growing season. For plants in full flower, average leaf water potentials were significantly more negative (P=0.0079) at mid-day in the krummholz (June) than in the tundra (July), but were similar before dawn (P=0.631). Photosynthetic rate at the time of flowering declined significantly with increasing corolla size in the krummholz (P=0.0376), but was unrelated to corolla size on the tundra (P>0.72). Plants losing water through large corollas may close leaf stomata to maintain turgor. If photosynthesis limits growth in this perennial species, then the water cost of producing large flowers should exacerbate the cost of reproduction under dry conditions. Such factors could select for flowers with smaller corollas in the krummholz, countering pollinator-mediated selection and helping maintain genetic variation in corolla size components of P. viscosum.

A combination of microcosm studies, polymerase chain reaction (PCR) analysis, and site data was used to assess the indigenous reductive dechlorinating potential in a trichloroethene (TCE)-contaminated aquifer at Cape Canaveral Air Station, Florida. Sediment and groundwater were obtained from two distinct locations approximately 10 m apart. Microcosm studies were performed to assess dechlorinating activity under a variety of nutrient and electron donor amendment conditions. Most live microcosms constructed using material from the first location, near well 9 (W09), were negative for dechlorination. All live microcosms constructed using material from the second location (W06) exhibited dechlorination of TCE to vinyl chloride (VC) and ethene (ETH). DNA encoding 16S ribosomal RNA (rDNA) with a sequence nearly identical with that from Dehalococcoides ethenogenes strain 195 was detected in the active microcosms and in the sediment from W06 with polymerase chain reaction (PCR) using primers targeted to unique regions of Dehalococcoides 16S rDNA. Dehalococcoides was not detected in the autoclaved microcosms from W06, nor in sediment and most microcosms from W09. The results of the microcosm studies and PCR analysis were supported by field data, which indicated significant accumulation of cis-1,2-dichloroethene (cisDCE) and VC at W06, but not at W09. The different microcosm results obtained for the two locations and the spatial variation of positive PCR results indicates heterogeneous distribution of dechlorinating activity and a specific dechlorinating organism, Dehalococcoides, at the site. As both Dehalococcoides and dechlorination activity were similarly, heterogeneously distributed, this suggests that molecular-probing (which could and should be extended in the future to include virtually all known dechlorinators and/or dehalogenases) can provide a relatively quick and facile method for investigating spatial distributions of dechlorinators on-site.

Polygonum viviparum is widely distributed in arctic and alpine regions of the northern hemisphere. Fruit set has never been observed in North American populations and has been reported only very rarely in Europe. Although this species is extremely well studied, the impediments to successful fruit production are unknown. We investigated the sexual reproductive process in P. viviparum growing in the southern Colorado Rocky Mountains. For comparison, we also examined this process in the sympatric congener P. bistortoides, in which reproduction is exclusively sexual. Lack of viable fruit production in P. viviparum has no single developmental explanation; defects occur in each of the processes and structures associated with sexual reproduction studied, yet, these processes and structures also appear to function normally in at least some flowers or individuals. Development is abnormal in many ovules of P. viviparum, however, comparison with P. bistortoides shows that these abnormalities do not contribute to differences in seed production between the two species. The virtual absence of sexual reproduction in P. viviparum appears to be due largely to a low rate of fertilization and to embryo/fruit abortion.