Biomedical subjects

Catherine A Gehring

Publications and source records attributed to Catherine A Gehring.

9 recordsLinked to original sources

PubMed2007

Shifts from competition to facilitation between a foundation tree and a pioneer shrub across spatial and temporal scales in a semiarid woodland.

* Theoretical and empirical research has supported the hypothesis that plant-plant interactions change from competition to facilitation with increasing abiotic stress. However, the consistency of such changes has been questioned in arid and semiarid ecosystems. * During a drought in the semiarid south-western USA, we used observations and a field experiment to examine the interactions between juveniles of a foundation tree (Pinyon pine, Pinus edulis) and a common shrub (Apache plume, Fallugia paradoxa) in replicated areas of high and low stress. * The presence of F. paradoxa reduced P. edulis performance at low-stress sites, but had the opposite effect at high-stress sites. However, the intensity of the interactions depended on temporal variation in climate and age of P. edulis. Both above- and below-ground factors contributed to competition, while only above-ground factors contributed to facilitation. * These results support the hypothesis that interactions can change from competition to facilitation as abiotic stress increases in semiarid environments. A shift from competition to facilitation may be important for the recovery of P. edulis and other foundation species that have experienced large-scale mortality during recent droughts.

Adaptation, Physiological↗

PubMed2006

Environmental and genetic effects on the formation of ectomycorrhizal and arbuscular mycorrhizal associations in cottonwoods.

Although both environment and genetics have been shown to affect the mycorrhizal colonization of host plants, the impacts of these factors on hosts that can be dually colonized by both ectomycorrhizal (EM) and arbuscular mycorrhizal (AM) fungi are less understood. We examined the influence of environment and host crosstype on the EM and AM colonization of cottonwoods (Populus angustifolia and natural hybrids) by comparing levels of colonization of trees growing in common gardens that differed in elevation and soil type. We also conducted a supplemental watering experiment to determine the influence of soil moisture on AM and EM colonization. Three patterns emerged. First, garden location had a significant impact on mycorrhizal colonization, such that EM colonization was 30% higher and AM colonization was 85% lower in the higher elevation garden than the lower elevation garden. Second, crosstype affected total (EM + AM) colonization, but did not affect EM or AM colonization. Similarly, a significant garden x crosstype interaction was found for total colonization, but not for EM or AM colonization. Third, experimental watering resulted in 33% higher EM colonization and 45% lower AM colonization, demonstrating that soil moisture was a major driver of the mycorrhizal differences observed between the gardens. We conclude that environment, particularly soil moisture, has a larger influence on colonization by AM versus EM fungi than host genetics, and suggest that environmental stress may be a major determinant of mycorrhizal colonization in dually colonized host plants.

Altitude↗

PubMed2006

A framework for community and ecosystem genetics: from genes to ecosystems.

Can heritable traits in a single species affect an entire ecosystem? Recent studies show that such traits in a common tree have predictable effects on community structure and ecosystem processes. Because these 'community and ecosystem phenotypes' have a genetic basis and are heritable, we can begin to apply the principles of population and quantitative genetics to place the study of complex communities and ecosystems within an evolutionary framework. This framework could allow us to understand, for the first time, the genetic basis of ecosystem processes, and the effect of such phenomena as climate change and introduced transgenic organisms on entire communities.

Animals↗

PubMed2006

The promise and the potential consequences of the global transport of mycorrhizal fungal inoculum.

Advances in ecology during the past decade have led to a much more detailed understanding of the potential negative consequences of species' introductions. Moreover, recent studies of mycorrhizal symbionts have led to an increased knowledge of the potential utility of fungal inoculations in agricultural, horticultural and ecological management. The intentional movement of mycorrhizal fungal species is growing, but the concomitant potential for negative ecological consequences of invasions by mycorrhizal fungi is poorly understood. We assess the degree to which introductions of mycorrhizal fungi may lead to unintended negative, and potentially costly, consequences. Our purpose is to make recommendations regarding appropriate management guidelines and highlight top priority research needs. Given the difficulty in discerning invasive species problems associated with mycorrhizal inoculations, we recommend the following. First, careful assessment documenting the need for inoculation, and the likelihood of success, should be conducted prior to inoculation because inoculations are not universally beneficial. Second, invasive species problems are costly and often impossible to control by the time they are recognized. We recommend using local inoculum sources whenever possible. Third, non-sterile cultures of inoculum can result in the movement of saprobes and pathogens as well as mutualists. We recommend using material that has been produced through sterile culture when local inoculum is not available. Finally, life-history characteristics of inoculated fungi may provide general guidelines relative to the likelihood of establishment and spread. We recommend that, when using non-local fungi, managers choose fungal taxa that carry life-history traits that may minimize the likelihood of deleterious invasive species problems. Additional research is needed on the potential of mycorrhizal fungi to spread to non-target areas and cause ecological damage.

Agriculture↗

PubMed2006

Below-ground interactions with arbuscular mycorrhizal shrubs decrease the performance of pinyon pine and the abundance of its ectomycorrhizas.

Few studies have examined how below-ground interactions among plants affect the abundance and community composition of symbiotic mycorrhizal fungi. Here, we combined observations during drought with a removal experiment to examine the effects of below-ground interactions with arbuscular mycorrhizal (AM) shrubs on the growth of pinyon pines (Pinus edulis), and the abundance and community composition of their ectomycorrhizal (EM) fungi. Shrub density was negatively correlated with pinyon above- and below-ground growth and explained 75% of the variation in EM colonization. Consistent with competitive release, pinyon fine-root biomass, shoot length and needle length increased with shrub removal. EM colonization also doubled following shrub removal. EM communities did not respond to shrub removal, perhaps because of their strikingly low diversity. These results suggest that below-ground competition with AM shrubs negatively impacted both pinyons and EM fungi. Similar competitive effects may be observed in other ecosystems given that drought frequency and severity are predicted to increase for many land interiors.

Ecosystem↗

PubMed2005

Arbuscular mycorrhizal fungi in the tree seedlings of two Australian rain forests: occurrence, colonization, and relationships with plant performance.

The roots of rain forest plants are frequently colonized by arbuscular mycorrhizal fungi (AMF) that can promote plant growth in the nutrient poor soils characteristic of these forests. However, recent studies suggest that both the occurrence of AMF on rain forest plants and the dependence of rain forest plants on AMF can be highly variable. We examined the occurrence and levels of AMF colonization of some common seedling species in a tropical and a subtropical rain forest site in Queensland, Australia. We also used a long-term database to compare the growth and mortality rates of seedling species that rarely formed AMF with those that regularly formed AMF. In both forests, more than one-third of the seedling species rarely formed AMF associations, while 40% of species consistently formed AMF in the tropical site compared to 27% in the subtropical site. Consistent patterns of AMF occurrence were observed among plant families at the two sites. Variation among seedling species in AMF occurrence or colonization was not associated with differences in seed mass among species, variation in seedling size and putative age within a species, or lack of AMF inoculum in the soil. Comparisons of four seedling species growing both in the shaded understory and in small canopy gaps revealed an increase in AMF colonization in two of the four species in gaps, suggesting that light limitation partially explains the low occurrence of AMF. Seedling survival was significantly positively associated with seed biomass but not with AMF colonization. Furthermore, seedling species that regularly formed AMF and those that did not had similar rates of growth and survival, suggesting that mycorrhizal and nonmycorrhizal strategies were equivalent in these forests. Furthermore, the high numbers of seedlings that lacked AMF and the overall low rate of seedling growth (the average seedling required 6 years to double its height) suggest that most seedlings did not receive significant indirect benefits from AMF through connection to canopy trees via a common mycorrhizal network.

Australia↗

PubMed2005

Evidence for mutualist limitation: the impacts of conspecific density on the mycorrhizal inoculum potential of woodland soils.

The ability of seedlings to establish can depend on the availability of appropriate mycorrhizal fungal inoculum. The possibility that mycorrhizal mutualists limit the distribution of seedlings may depend on the prevalence of the plant hosts that form the same type of mycorrhizal association as the target seedling species and thus provide inoculum. We tested this hypothesis by measuring ectomycorrhizal (EM) fine root distribution and conducting an EM inoculum potential bioassay along a gradient of EM host density in a pinyon-juniper woodland where pinyon is the only EM fungal host while juniper and other plant species are hosts for arbuscular mycorrhizal (AM) fungi. We found that pinyon fine roots were significantly less abundant than juniper roots both in areas dominated aboveground by juniper and in areas where pinyon and juniper were co-dominant. Pinyon seedlings establishing in pinyon-juniper zones are thus more likely to encounter AM than EM fungi. Our bioassay confirmed this result. Pinyon seedlings were six times less likely to be colonized by EM fungi when grown in soil from juniper-dominated zones than in soil from either pinyon-juniper or pinyon zones. Levels of EM colonization were also reduced in seedlings grown in juniper-zone soil. Preliminary analyses indicate that EM community composition varied among sites. These results are important because recent droughts have caused massive mortality of mature pinyons resulting in a shift towards juniper-dominated stands. Lack of EM inoculum in these stands could reduce the ability of pinyon seedlings to re-colonize sites of high pinyon mortality, leading to long-term vegetation shifts.

Arizona↗

PubMed2005

Chronic herbivory negatively impacts cone and seed production, seed quality and seedling growth of susceptible pinyon pines.

Although herbivory often reduces the reproduction of attacked trees, few studies have examined how naturally occurring insect-resistant and susceptible trees differ in their reproduction, nor have these effects been experimentally examined through long-term herbivore removals. In addition, few studies have examined the effects of herbivory on the quality of seeds produced and the implications of reduced seed quality on seedling establishment. We evaluated the impact of chronic herbivory by the stem-boring moth, Dioryctria albovittella, on cone and seed production of the pinyon pine (Pinus edulis) during two mast years. Three patterns emerged. First, moth herbivory was associated with reductions in cone production, viable seed production and seed mass. Specifically, pinyons susceptible to moth attack had 93-95% lower cone production, and surviving cones produced 31-37% fewer viable seeds, resulting in a 96-97% reduction in whole tree viable seed production. In addition, surviving seeds from susceptible trees had 18% lower mass than resistant trees. Second, long-term experimental removal of the herbivore resulted in increased rates of cone and seed production and quality, indicating that moth herbivory was the driver of these reductions. Third, seed size was positively associated with seed germination and seedling biomass and height, suggesting that trees suffering chronic herbivory produce poorer quality offspring. Thus, the resistance traits of pinyons can affect the quality of offspring, which in turn may affect subsequent seedling establishment and population dynamics.

Analysis of Variance↗

PubMed2003

Soil community composition and the regulation of grazed temperate grassland.

The effect of the community composition of soil microbes on ecosystem processes has received relatively little attention. Here we examined the variation in soil microbial composition in a Yellowstone National Park grassland and the effect of that variation on the growth, in a greenhouse, of the dominant grass in the community. Plants and their rhizospheric soil were collected from paired, Poa pratensis-dominated grassland plots located inside and outside a 40-year-old exclosure. P. pratensis aboveground, belowground, and whole plant growth were greater in pots with soil communities from grazed grassland compared to fenced grassland, indicating (1) soil microbial communities differed, and (2) this difference influenced the growth of the plant that dominated both grasslands. Treating pots with fungicide (benomyl) suppressed the soil community influence, indicating that different fungal communities caused the soil microbe effect. In addition, two lines of evidence are consistent with the hypothesis that arbuscular mycorrhizal fungal (AMF) species composition affected P. pratensis: (1) a divergence in AMF spore communities in the two field soils, and (2) little evidence of pathogenic fungi. These findings emphasize the need to examine the role that the composition of the soil microbial community plays in controlling terrestrial ecosystems.

Climate↗