Irwin N. Forseth

Bio: Irwin N. Forseth is an academic researcher from University of Maryland, College Park. The author has contributed to research in topics: Stomatal conductance & Population. The author has an hindex of 24, co-authored 43 publications receiving 1714 citations.

Kudzu (Pueraria montana): History, Physiology, and Ecology Combine to Make a Major Ecosystem Threat

Abstract: Kudzu, Pueraria montana (Lour.) Merr. variety lobata (Willd.) was introduced into the United States at the 1876 Centennial Exposition in Philadelphia, PA. Subsequently, it was planted widely to reduce soil erosion by the Soil Erosion Service and Civilian Conservation Corp. Over 85 million seedlings of kudzu were provided to landowners by government agencies in the southeast in the first half of the 20th century. In 1953, kudzu was removed from the list of approved plants for erosion control, in 1970 it was officially labeled a weed, and in 1997 it was placed on the Federal Obnoxious Weed List. Its rapid elongation rates, high leaf area indices, high photosynthetic rates, and frequent rooting at stem nodes make kudzu an aggressive competitor with native shrubs and trees. Estimates are that kudzu currently covers 3 million hectares throughout the eastern United States and is spreading by 50,000 ha per year. Despite widespread anecdotal statements, little quantitative information is available regarding the e...

Physiological response curve analysis using nonlinear mixed models

Abstract: Nonlinear response curves are often used to model the physiological responses of plants. These models are preferable to polynomials because the coefficients fit to the curves have biological meaning. The response curves are often generated by repeated measurements on one subject, over a range of values for the environmental variable of interest. However, the typical analysis of differences in coefficients between experimental groups does not include a repeated measures approach. This may lead to inappropriate estimation of error terms. Here, we show how to combine mixed model analysis, available in SAS, that allows for repeated observations on the same experimental unit, with nonlinear response curves. We illustrate the use of this nonlinear mixed model with a study in which two plant species were grown under contrasting light environments. We recorded light levels and net photosynthetic response on anywhere from 8 to 10 points per plant and fit a Mitscherlich model in which each plant has its own coefficients. The coefficients for the photosynthetic light-response curve for each plant were assumed to follow a multivariate normal distribution in which the mean was determined by the treatment. The approach yielded biologically relevant coefficients and unbiased standard error estimates for multiple treatment comparisons.

Effects of below- and aboveground competition from the vines Lonicera japonica and Parthenocissus quinquefolia on the growth of the tree host Liquidambar styraciflua

Abstract: Detrimental effects of vines on tree growth in successional environments have been frequently reported. Little is known, however, about the relative importance of below and aboveground competition from vines on tree growth. The objective of this study was to quantify and compare the growth responses of Liquidambar styraciflua saplings to below and/or aboveground competition with the exotic evergreen vine, Lonicera japonica (Japanese honeysuckle), and the native deciduous vine, Parthenocissus quinquefolia (Virginia creeper). Soil trenching and/or vine-trellising were used to control the type of vine competition experienced by trees. Comparisons among untrenched treatments tested for effects of belowground competition. Comparisons among trenched treatments tested for effects of aboveground competition. After two growing seasons, Lonicera japonica had a greater effect on the growth of L. styraciflua than did P. quinquefolia. This effect was largely due to root competition, as canopy competition only had a negative effect on tree growth when it occurred in combination with root competition. Leaf expansion was consistently and similarly affected by all treatments which involved belowground competition.

Interactive effects of water stress and xylem-limited bacterial infection on the water relations of a host vine.

Abstract: Xylella fastidiosa, a xylem-limited bacterial pathogen that causes bacterial leaf scorch in its hosts, has a diverse and extensive host range among plant species worldwide. Previous work has shown that water stress enhances leaf scorch symptom severity and progression along the stem in Parthenocissus quinquefolia infected by X. fastidiosa. The objective here was to investigate the mechanisms underlying the interaction of water stress and infection by X. fastidiosa. Using the eastern deciduous forest vine, P. quinquefolia, infection and water availability were manipulated while measuring leaf water potentials (psi(L)), stomatal conductance (g(s)), whole shoot hydraulic conductance (K(h)), per cent xylem embolism, and xylem vessel dimensions. No significant differences in any of the physiological measurements were found between control and infected plants prior to drought. Drought treatment significantly reduced psi(L) and g(s) at all leaf positions throughout the day in late summer in both years of the study. In addition, infection significantly reduced psi(L) and g(s) in the most basal leaf positions in late summer in both years. Whole shoot hydraulic conductance was reduced by both low water and infection treatments. However, per cent embolized vessels and mean vessel diameter were affected by drought treatment only. These results imply that the major effect of infection by X. fastidiosa occurs due to reduced hydraulic conductance caused by clogging of the vessels, and not increased cavitation and embolism of xylem elements. The reduced K(h) caused by X. fastidiosa infection acts additively with the water limitation imposed by Drought stress.

Effects of Water Stress on Symptomatology and Growth of Parthenocissus quinquefolia Infected by Xylella fastidiosa

Abstract: A greenhouse study was conducted to test the hypothesis that bacterial leaf scorch symptoms, caused by Xylella fastidiosa, are more severe during periods of drought stress. A two-by-two complete factorial design with two pathogen treatments (control and infected) and two soil moisture levels (high and low) was used with Parthenocissus quinquefolia vines in 1999 and 2000. In each year, a high percentage of P. quinquefolia plants inoculated with X. fastidiosa expressed typical bacterial leaf scorch symptoms, with the outer scorched portion of the leaf separated from green tissue by a chlorotic halo. X. fastidiosa was detected in all symptomatic plants using an immunomagnetic capture and nested polymerase chain reaction technique, and was reisolated and cultured in modified periwinkle wilt liquid media. In both years, symptoms progressed further along the stem and were more severe at corresponding leaf positions in low-water-infected plants compared to high-water-infected plants. Total leaf area, shoot length, and number of nodes on the longest shoot per plant were all reduced due to drought and X. fastidiosa infection. This study is the first to verify the hypothesis that bacterial leaf scorch symptoms are enhanced during drought stress. Maintaining plant vigor with regular watering can be used to sustain plants infected by X. fastidiosa, particularly during periods of water stress.

Understanding plant responses to drought — from genes to the whole plant

Abstract: In the last decade, our understanding of the processes underlying plant response to drought, at the molecular and whole-plant levels, has rapidly progressed. Here, we review that progress. We draw attention to the perception and signalling processes (chemical and hydraulic) of water deficits. Knowledge of these processes is essential for a holistic understanding of plant resistance to stress, which is needed to improve crop management and breeding techniques. Hundreds of genes that are induced under drought have been identified. A range of tools, from gene expression patterns to the use of transgenic plants, is being used to study the specific function of these genes and their role in plant acclimation or adaptation to water deficit. However, because plant responses to stress are complex, the functions of many of the genes are still unknown. Many of the traits that explain plant adaptation to drought - such as phenology, root size and depth, hydraulic conductivity and the storage of reserves - are those associated with plant development and structure, and are constitutive rather than stress induced. But a large part of plant resistance to drought is the ability to get rid of excess radiation, a concomitant stress under natural conditions. The nature of the mechanisms responsible for leaf photoprotection, especially those related to thermal dissipation, and oxidative stress are being actively researched. The new tools that operate at molecular, plant and ecosystem levels are revolutionising our understanding of plant response to drought, and our ability to monitor it. Techniques such as genome-wide tools, proteomics, stable isotopes and thermal or fluorescence imaging may allow the genotype-phenotype gap to be bridged, which is essential for faster progress in stress biology research.

The interaction of plant biotic and abiotic stresses: from genes to the field

Abstract: Plant responses to different stresses are highly complex and involve changes at the transcriptome, cellular, and physiological levels. Recent evidence shows that plants respond to multiple stresses differently from how they do to individual stresses, activating a specific programme of gene expression relating to the exact environmental conditions encountered. Rather than being additive, the presence of an abiotic stress can have the effect of reducing or enhancing susceptibility to a biotic pest or pathogen, and vice versa. This interaction between biotic and abiotic stresses is orchestrated by hormone signalling pathways that may induce or antagonize one another, in particular that of abscisic acid. Specificity in multiple stress responses is further controlled by a range of molecular mechanisms that act together in a complex regulatory network. Transcription factors, kinase cascades, and reactive oxygen species are key components of this cross-talk, as are heat shock factors and small RNAs. This review aims to characterize the interaction between biotic and abiotic stress responses at a molecular level, focusing on regulatory mechanisms important to both pathways. Identifying master regulators that connect both biotic and abiotic stress response pathways is fundamental in providing opportunities for developing broad-spectrum stress-tolerant crop plants.

Invasive species, ecosystem services and human well-being.

Abstract: Although the effects of invasive alien species (IAS) on native species are well documented, the many ways in which such species impact ecosystem services are still emerging. Here we assess the costs and benefits of IAS for provisioning, regulating and cultural services, and illustrate the synergies and tradeoffs associated with these impacts using case studies that include South Africa, the Great Lakes and Hawaii. We identify services and interactions that are the least understood and propose a research and policy framework for filling the remaining knowledge gaps. Drawing on ecology and economics to incorporate the impacts of IAS on ecosystem services into decision making is key to restoring and sustaining those life-support services that nature provides and all organisms depend upon.

Plant competition underground

Abstract: Belowground competition occurs when plants decrease the growth, survival, or fecundity of neighbors by reducing available soil resources. Competition belowground can be stronger and involve many more neighbors than aboveground competition. Physiological ecologists and population or community ecologists have traditionally studied belowground competition from different perspectives. Physiologically based studies often measure resource uptake without determining the integrated consequences for plant performance, while population or community level studies examine plant performance but fail to identify the resource intermediary or mechanism. Belowground competitive ability is correlated with such attributes as root density, surface area, and plasticity either in root growth or in the properties of enzymes involved in nutrient uptake. Unlike competition for light, in which larger plants have a disproportionate advantage by shading smaller ones, competition for soil resources is apparently more symmetric. Below...

The ecology of lianas and their role in forests

Abstract: Recent studies have demonstrated the increasingly important role of lianas (woody vines) in forest regeneration, species diversity and ecosystem-level processes, particularly in the tropics. Mechanisms responsible for the maintenance of liana species diversity could yield new insights into the maintenance of overall species diversity. Lianas contribute to forest regeneration and competition, not only by competing directly with trees, but also by differentially affecting tree species and thus changing how trees compete among themselves. In addition, they contribute considerably to ecosystem-level processes, such as whole-forest transpiration and carbon sequestration. As the rate of tropical forest disturbance increases, they are likely to increase in relative abundance throughout the tropics and the importance of lianas to many aspects of forest dynamics will grow.