Effects of atmospheric ammonia (NH3) on terrestrial vegetation: a review.

Genetic structuring of plant populations is strongly influenced by both common ancestry and current patterns of interpopulation genetic exchange. The interaction of these two forces is particularly confounding and hence interesting in plants. This complexity of plant genetic structures is due in part to a diversity of reproductive ecologies affecting genetic exchange and the fact that reproductive barriers are often weak between otherwise morphologically well-defined species. Phylogeographic methods provide a means of examining the history of genetic exchange among populations, with the potential to distinguish biogeographic patterns of genetic variation caused by gene flow from those caused by common ancestry. With regard to plants, phylogeography will be most useful when applied broadly across the entire spectrum of potential genetic exchange. Although current phylogeographic studies of plants show promise, widespread application of this approach has been hindered by a lack of appropriate molecular variation; this problem is discussed and possible solutions considered.

Phylogeographic studies in plants: problems and prospects

functional diversity, which underlies variation in growth rates, productivity, population and community dynamics, and ecosystem function. The broad congruence of these variations with climatic and environmental conditions on local, regional, and global scales has fostered the concept that plant ecophysiological characteristics are well adapted to their local circumstances. For example, the repeated occurrence of plants with CAM (Crassulacean Acid Metabolism) photosynthesis and succulent leaves or stems in severely water-limited environments, and the independent evolution of these traits in numerous plant lineages, provides compelling evidence of the physiological evolution of these water-conserving traits under the influence of natural selection (Ehleringer and Monson 1993). Similarly, studies of the evolution of heavy metal tolerance confirm that natural selection may cause rapid ecophysiological evolution in just a few generations, leading to local adaptation in populations just a few meters apart (Antonovics et al. 1971). Many ecophysiological traits—considered here as all aspects of resource uptake and utilization, including biochemistry, metabolism, gas exchange, leaf structure and function, nutrient and biomass allocation, canopy structure, and growth—are likely to influence fitness and undergo adaptive evolution. Traits affecting the assimilation and use of resources such as carbon, water, and nutrients directly influence plant growth. Patterns of resource allocation to growth, reproduction, defense, and stress tolerance are also likely to be under strong selection. Phenotypic plasticity, the expression of different phenotypes by

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The Evolution of Plant Ecophysiological Traits: Recent Advances and Future Directions

Weeds are often more competitive with crops at higher soil nutrient levels. This can result in increased de- pendency on herbicides and tiliage to maintain adequate weed control. A number of studies have shown weeds accu- mulate higher concentrations of nitrogen, phosphorus, po- tassium, calcium, and magnesium than crops, thus depleting soil nutrient levels more quickly and reducing crop yield. Understanding basic mechanisms and timing of nutrient uptake in weeds and crops can lead to fertilization strategies which will enhance the competitive ability of crops while reducing interference from weeds. Such strategies can in- clude deep band application of fertilizers to the crop row, as opposed to broadcast applications. Banding techniques also reduce the potential for nitrate contamination of surface or groundwater. The addition of nitrification inhibitors or in- creasing the proportion of nitrogen as ammonium or urea in fertilizer mixtures can restrict growth of ammonium- or urea-sensitive weeds. The timing of fertilizer applications can take advantage of maximal rates of nutrient uptake into crop roots at specific developmental stages. In addition, nutrient use efficiency can be enhanced by choosing appropriate crop cultivars, maintaining effective weed control practices, or altering row spacing or seeding rate to increase accumulation of nitrogen, phosphorus, and potassium in crops. Additional index words. Banding, competition, ecophysiology, fertilizers, nitrogen, nutrient uptake.

Approaches for Improving Crop Competitiveness Through the Manipulation of Fertilization Strategies

9 – Many Little Hammers: Ecological Management of Crop-Weed Interactions

The ecological, morphological, and physiological diversity of species in the Hawaiian silversword alliance is exceptional. The 28 species, which belong to the endemic genera Argyroxiphium, Dubautia, and Wilkesia, have a wide variety of geographical distributions and elevational ranges within the archipelago. They grow in habitats as varied as dry scrub and woodland, wet scrub and forest, cinder and lava, and bog. Ecological diversity is also evident among sympatric species. At a site of sympatry on the island of Hawaii, for example, D. ciliolata and D. scabra are restricted to different lava flows, even though individuals of the two species may grow within a meter of one another. The 28 species have growth forms as varied as rosette shrubs, shrubs, trees, and lianas. They have a wide range of leaf sizes and shapes, with the Dubautia species exhibiting significant variation in leaf turgor maintenance capacities. Morphological and physiological diversity is also evident among sympatric species. At a site of sympatry on the island of Maui, for example, A. sandwicense and D. menziesii exhibit different suites of morphological and physiological traits enabling them to cope with the severe environmental conditions. The patterns of diversity and the genomic relationships among the 28 species suggest that a variety of factors may have played important roles in their adaptive radiation. The Hawaiian silversword alliance is a premier example of adaptive radiation in plants (Carlquist, 1980; Carr et al., 1989). The alliance includes 28 species in three endemic genera: Argyroxiphium, Dubautia, and Wlilkesia (Carr, 1985). The species grow in a wide range of habitats and have a wide variety of growth forms. They are also closely related, as evidenced by the high frequency of spontaneous interspecific and intergeneric hybrids in nature, coupled with the ease of production of artificial hybrids in the laboratory (Carr & Kyhos, 1981, 1986). The detailed analysis of the hybrids and parental taxa using cytogenetic, electrophoretic, and molecular approaches has provided compelling evidence that the silversword alliance is a genetically cohesive group whose origin and diversification probably trace to a single colonizing ancestor (Baldwin et al., 1988; Carr et al., 1989). Our objective in this review is to provide insight into the ecological, morphological, and physiological diversity of species in the silversword alliance. With respect to ecological diversity, we compare the geographical distributions, habitats, and elevational ranges of the 28 species, then analyze the local distributions of several sympatric Dubautia species. With respect to morphological and physiological diversity, we compare the growth forms, leaf sizes, and leaf shapes of the 28 species, then examine the turgor maintenance capacities of the Dubautia species and the water and temperature balances of two sympatric Argyroxiphium and Dubautia species. Our primary theme is that the ' This paper is dedicated to Dr. Sherwin Carlquist in honor of his pioneering research on the Hawaiian silversword alliance. The research was supported by NSF Grant DEB-82064 11 and a gift from the Atlantic Richfield Foundation to the senior author. We thank Lani Stemmermann for invaluable companionship, botanical insight, and technical assistance in the field. We also thank the staff of Haleakala National Park, particularly R. Nagata and L. Loope, for critical logistical support, and J. Canfield and N. Friedman for generous photographic assistance. 2 Department of Ecology & Evolutionary Biology, University of Arizona, Tucson, Arizona 85721, U.S.A. < Department of Botany, University of Hawaii, Honolulu, Hawaii 96822, U.S.A. 4 Department of Plant & Soil Sciences, University of Maine, Orono, Maine 04469, U.S.A. Department of Botany, University of California, Davis, California 95616, U.S.A. ANN. MISSOURI BOT. GARD. 77: 64-72. 1990. This content downloaded from 152.1.161.146 on Thu, 27 Mar 2014 19:39:59 PM All use subject to JSTOR Terms and Conditions Volume 77, Number 1 Robichaux et al. 65 1990 Adaptive Radiation of Hawaiian Silversword Alliance

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Matt Liebman

Papers

Adaptive Radiation of the Hawaiian Silversword Alliance (Compositae- Madiinae): Ecological, Morphological, and Physiological Diversity

Effects of nitrogen fertilizer, irrigation, and crop genotype on canopy relations and yields of an intercrop/weed mixture

Competition by barley and pea against mustard : effects on resource acquisition, photosynthesis and yield