Dustin F. Haines

Allocation, stress tolerance and carbon transport in plants: how does phloem physiology affect plant ecology?

Despite the crucial role of carbon transport in whole plant physiology and its impact on plant-environment interactions and ecosystem function, relatively little research has tried to examine how phloem physiology impacts plant ecology. In this review, we highlight several areas of active research where inquiry into phloem physiology has increased our understanding of whole plant function and ecological processes. We consider how xylem-phloem interactions impact plant drought tolerance and reproduction, how phloem transport influences carbon allocation in trees and carbon cycling in ecosystems and how phloem function mediates plant relations with insects, pests, microbes and symbiotes. We argue that in spite of challenges that exist in studying phloem physiology, it is critical that we consider the role of this dynamic vascular system when examining the relationship between plants and their biotic and abiotic environment.

Joshua tree (Yucca brevifolia) seeds are dispersed by seed-caching rodents

ABSTRACT Joshua tree (Yucca brevifolia) is a distinctive and charismatic plant of the Mojave Desert. Although floral biology and seed production of Joshua tree and other yuccas are well understood, the fate of Joshua tree seeds has never been studied. We tested the hypothesis that Joshua tree seeds are dispersed by seed-caching rodents. We radioactively labelled Joshua tree seeds and followed their fates at five source plants in Potosi Wash, Clark County, Nevada, USA. Rodents made a mean of 30.6 caches, usually within 30 m of the base of source plants. Caches contained a mean of 5.2 seeds buried 3–30 mm deep. A variety of rodent species appears to have prepared the caches. Three of the 836 Joshua tree seeds (0.4%) cached germinated the following spring. Seed germination using rodent exclosures was nearly 15%. More than 82% of seeds in open plots were removed by granivores, and neither microsite nor supplemental water significantly affected germination. Joshua tree produces seeds in indehiscent pods or capsules, which rodents dismantle to harvest seeds. Because there is no other known means of seed dispersal, it is possible that the Joshua tree–rodent seed dispersal interaction is an obligate mutualism for the plant.

Desert Tortoise Hibernation: Temperatures, Timing, and Environment

Abstract This research examined the onset, duration, and termination of hibernation in Desert Tortoises (Gopherus agassizii) over several years at multiple sites in the northeastern part of their geographic range, and recorded the temperatures experienced by tortoises during winter hibernation. The timing of hibernation by Desert Tortoises differed among sites and years. Environmental cues acting over the short-term did not appear to influence the timing of the hibernation period. Different individual tortoises entered hibernation over as many as 44 days in the fall and emerged from hibernation over as many as 49 days in the spring. This range of variation in the timing of hibernation indicates a weak influence at best of exogenous cues hypothesized to trigger and terminate hibernation. There do appear to be regional trends in hibernation behavior as hibernation tended to begin earlier and continue longer at sites that were higher in elevation and generally cooler. The emergence date was generally more similar among study sites than the date of onset. While the climate and the subsequent timing of hibernation differed among sites, the average temperatures experienced by tortoises while hibernating differed by only about five degrees from the coldest site to the warmest site.

The making of giant pumpkins: How selective breeding changed the phloem of Cucurbita maxima from source to sink

Despite the success of breeding programmes focused on increasing fruit size, relatively little is known about the anatomical and physiological changes required to increase reproductive allocation. To address this gap in knowledge, we compared fruit/ovary anatomy, vascular structure and phloem transport of two varieties of giant pumpkins, and their smaller fruited progenitor under controlled environmental conditions. We also modelled carbon transport into the fruit of competitively grown plants using data collected in the field. There was no evidence that changes in leaf area or photosynthetic capacity impacted fruit size. Instead, giant varieties differed in their ovary morphology and contained more phloem on a cross-sectional area basis in their petioles and pedicels than the ancestral variety. These results suggest that sink activity is important in determining fruit size and that giant pumpkins have an enhanced capacity to transport carbon. The strong connection observed between carbon fixation, phloem structure and fruit growth in field-grown plants indicates that breeding for large fruit has led to changes throughout the carbon transport system that could have important implications for how we think about phloem transport velocity and carbon allocation.

Leafy spurge (Euphorbia esula) affects vegetation more than seed banks in mixed-grass prairies of the northern Great Plains.

Abstract Exotic plants have the ability to modify soil seed banks in habitats they invade, but little is known about the legacy of invasion on seed banks once an exotic plant has successfully been controlled. Natural areas previously invaded by leafy spurge in the northern Great Plains typically have one of two fates following its removal: a return of native plants, or a secondary invasion of other exotic plants. It is unknown, however, if this difference in plant communities following leafy spurge control is due to seed bank differences. To answer this question, we monitored seed banks and standing vegetation for 2 yr in mixed-grass prairies that were previously invaded by leafy spurge but controlled within 5 yr of our study. We found that native plant seed banks were largely intact in areas previously invaded by leafy spurge, regardless of the current living plant community, and leafy spurge invasion history had a larger impact on cover and diversity of the vegetation than on the seed banks. Differences in plant communities following leafy spurge control do not appear to be related to the seed banks, and soil conditions may be more important in determining trajectories of these postinvasion communities. Nomenclature: Leafy spurge, Euphorbia esula L. EPHES Management Implications: Leafy spurge is an invasive exotic plant of great concern in the northern Great Plains. Control efforts have been successful in recent years, but previously invaded areas either experience a return of native plants (a desirable outcome), or a secondary invasion of other exotic plants (an undesirable outcome). Little is known about the impact of leafy spurge invasion on seed banks, and if seed banks differ between areas with varying invasion histories and vegetation trajectories following leafy spurge control. Our investigation of these seed banks revealed that native species were common in the seed banks of all invasion histories, and that the seed banks were not significantly different among invasion histories and vegetation trajectories. These differences did not appear to be a reflection of the current standing vegetation, but rather resulted either from seeds that arrived at the soil before the invasion, or that were dispersed to invaded sites from nearby native-dominated areas. We conclude that native plant restoration in areas previously invaded by leafy spurge is probably not hindered by the seed banks, and that seed banks appear to be relatively resilient after leafy spurge invasion and control. However, the ubiquitous presence of the aggressively invasive grasses smooth brome and Kentucky bluegrass may necessitate active restoration efforts that simultaneously reduce invasive grass presence and promote native plant recruitment. Additional experimentation would help determine if popular management methods, such as seed addition, are effective in achieving these restoration goals in habitats that already have intact native seed banks.

Regional Patterns of Floristic Diversity and Composition in Forests Invaded by Garlic Mustard (Alliaria petiolata)

Abstract The impacts of invasive species on native plant communities are often studied on small spatial scales but may vary across regionally heterogeneous landscapes. Comparisons of vegetation across several similar sites with and without an invasive species present can be logistically challenging but highly informative to both scientists and land managers. We examined regional geographic variation in the diversity and composition of 8 replicate northeastern forest-understory plant communities invaded by the non-native species Alliaria petiolata (Garlic Mustard). Despite variation in underlying soil conditions and horizon development, several native species and their associated functional groups were either negatively or positively associated with Garlic Mustard invasion at the regional scale, and soil moisture and pH were higher in invaded plots across all sites. Most tree species were less common at invaded sites, but high tree-seedling abundances at some sites led to regionally higher seedling abundance in the presence of Garlic Mustard. Our study highlights the importance of species-specific responses, as well as site-specific soil conditions, for better understanding potential impacts of invasion.

Allocation, stress tolerance and carbon transport in plants

Despite the crucial role of carbon transport in whole plant physiology and its impact on plant-environment interactions and ecosystem function, relatively little research has tried to examine how phloem physiology impacts plant ecology. In this review, we highlight several areas of active research where inquiry into phloem physiology has increased our understanding of whole plant function and ecological processes. We consider how xylem-phloem interactions impact plant drought tolerance and reproduction, how phloem transport influences carbon allocation in trees and carbon cycling in ecosystems and how phloem function mediates plant relations with insects, pests, microbes and symbiotes. We argue that in spite of challenges that exist in studying phloem physiology, it is critical that we consider the role of this dynamic vascular system when examining the relationship between plants and their biotic and abiotic environment.

Allocation, stress tolerance and carbon transport in plants: how does phloem physiology affect plant ecology?: Phloem ecophysiology

Despite the crucial role of carbon transport in whole plant physiology and its impact on plant-environment interactions and ecosystem function, relatively little research has tried to examine how phloem physiology impacts plant ecology. In this review, we highlight several areas of active research where inquiry into phloem physiology has increased our understanding of whole plant function and ecological processes. We consider how xylem-phloem interactions impact plant drought tolerance and reproduction, how phloem transport influences carbon allocation in trees and carbon cycling in ecosystems and how phloem function mediates plant relations with insects, pests, microbes and symbiotes. We argue that in spite of challenges that exist in studying phloem physiology, it is critical that we consider the role of this dynamic vascular system when examining the relationship between plants and their biotic and abiotic environment.