Photosynthetic Adaptation of Solanum dulcamara L. to Sun and Shade Environments: II. Physiological Characterization of Phenotypic Response to Environment

Phenotypic plasticity and genetic variation in leaf traits of Yushania niitakayamensis (Bambusoideae; Poaceae) in contrasting light environments

Yushania niitakayamensis (Bambusoideae; Poaceae), a perennial grass distributed from mid to high elevations in Taiwan, is often found growing in exposed grassland or shaded forest understories. To answer the question how does Y. niitakayamensis cope with contrasting light availability of habitats, we compared (1) leaf ecophysiological traits between populations of Y. niitakayamensis growing in exposed and shaded habitats in four seasons, and (2) plasticity patterns of transplanted plants to two light treatments (full-sun and 70 % shading) in a phytotron. Significant differences in leaf morphological (leaf length, width, specific leaf area, stomatal density), anatomical (leaf thickness (LT), the frequency of cavity formed by collapsed fusoid cells), and biochemical (chlorophyll contents, nitrogen contents per unit area ([N]_area) and stable carbon isotope ratio) features were found between populations across seasons. Common garden experiments suggested that most of the trait variations in field growing plants can be explained by the effect of growth light treatment but not by that of population. However, variations between the two populations in LT, [N]_area, gas exchange parameters, and the degree of plasticity in LT and [N]_area in responding to growth light regimes might have genetic basis. In comparison between transplants from different origins grown under same light regime, plants from the exposed population grown under full-sun expressed significantly higher LT, [N]_area and light-saturated photosynthetic rates, whereas plants from the shaded population grown under shading had significantly higher water use efficiency. Accordingly, local specialization in populations of Y. niitakayamensis to particular environmental conditions might have arisen.

A meta-analysis of plant responses to light intensity for 70 traits ranging from molecules to whole plant performance

By means of meta-analyses we determined how 70 traits related to plant anatomy, morphology, chemistry, physiology, growth and reproduction are affected by daily light integral (DLI; mol photons m^-2  d^-1 ). A large database including 500 experiments with 760 plant species enabled us to determine generalized dose-response curves. Many traits increase with DLI in a saturating fashion. Some showed a more than 10-fold increase over the DLI range of 1-50 mol m^-2  d^-1 , such as the number of seeds produced per plant and the actual rate of photosynthesis. Strong decreases with DLI (up to three-fold) were observed for leaf area ratio and leaf payback time. Plasticity differences among species groups were generally small compared with the overall responses to DLI. However, for a number of traits, including photosynthetic capacity and realized growth, we found woody and shade-tolerant species to have lower plasticity. We further conclude that the direction and degree of trait changes adheres with responses to plant density and to vertical light gradients within plant canopies. This synthesis provides a strong quantitative basis for understanding plant acclimation to light, from molecular to whole plant responses, but also identifies the variables that currently form weak spots in our knowledge, such as respiration and reproductive characteristics.

PHENOTYPIC PLASTICITY IN POLYGONUM PERSICARIA. I. DIVERSITY AND UNIFORMITY IN GENOTYPIC NORMS OF REACTION TO LIGHT

Several aspects of genotype-environment interaction may act to modulate natural selection in populations that encounter variable environments. In this study the norms of reaction (phenotypic responses) of 20 cloned genotypes from two natural populations of the annual plant Polygonum persicaria were determined over a broad range of controlled light environments (8%-100% full sun). These data reveal both the extent of functionally adaptive phenotypic plasticity expressed by individual genotypes, and the patterns of diversity among genotypes for characters relevant to fitness, in response to an environmental factor that is both highly variable within populations and critical to growth and reproduction.

A revision of the Dulcamaroid Clade of Solanum L. (Solanaceae)

The Dulcamaroid clade of Solanum contains 45 species of mostly vining or weakly scandent species, including the common circumboreal weed Solanum dulcamara L. The group comprises members of the previously recognised infrageneric groupings sect. Andropedas Rusby, sect. Californisolanum A. Child, sect. Dulcamara (Moench) Dumort., sect. Holophylla (G.Don) Walp., sect. Jasminosolanum (Bitter) Seithe, sect.Lysiphellos (Bitter) Seithe, subsect. Nitidum A.Child and sect. Subdulcamara Dunal. These infrageneric groups are not monophyletic as traditionally recognised, and the complex history of the classification of the dulcamaroid solanums is reviewed. Many of the species in the clade are quite variable morphologically; plants are shrubs, herbaceous vines or woody canopy lianas, and habits can vary between these states in a single locality. Variation in leaf shape and pubescence density and type is also extreme and has lead to the description of many minor morphological variants as distinct species. The flowers of members of the group are generally very showy, and several species (e.g., Solanum crispum Ruiz & Pav., Solanum laxum Spreng., Solanum seaforthianum Andrews) are popular ornamental plants that have occasionally escaped from cultivation and become naturalised. The clade is here divided into five morphologically and geographically delimited species groups to facilitate further study. One new species from southern Ecuador, Solanum agnoston S.Knapp sp. nov., is described here. Full descriptions and synonymies (including designations of lectotypes or neotypes), preliminary conservation assessments, illustrations, distribution maps, and an extensive list of localities are provided for all species.

Differential performance of tropical soda apple and its biological control agent Gratiana boliviana (Coleoptera: Chrysomelidae) in open and shaded habitats

The leaf feeding beetle Gratiana boliviana Spaeth has been released since 2003 in the southeastern United States for biological control of tropical soda apple, Solanum viarum Dunal. In Florida, G. boliviana can be found on tropical soda apple growing in open pastures as well as in shady wooded areas. The objectives of this study were to determine the effect of light intensity on the performance of tropical soda apple and G. boliviana under greenhouse conditions, and to determine the abundance and mortality of G. boliviana in open and shaded habitats. Leaves growing in the shade were less tough, had higher water and nitrogen content, lower soluble sugars, and less dense and smaller glandular trichomes compared with leaves growing in the open. Plants grew slightly taller and wider under shaded conditions but total biomass was significantly reduced compared with plants grown in the open. In the greenhouse, G. boliviana had higher immature survival, greater folivory, larger adult size, and higher fecundity when reared on shaded plants compared with open plants. Sampling of field populations revealed that the overall abundance of G. boliviana was lower but leaf feeding damage was higher in shaded habitats compared with the open habitats. The percentage of eggs surviving to adult was greater in shaded compared with open habitats. The abundance of predators was higher in the open pasture and was positively correlated with the abundance of G. boliviana. These results indicate that not only plant quality but also habitat structure are important to the performance of weed biological control agents.

Estimation of the light distribution between photosystems I and II in intact wheat leaves by fluorescence and photoacoustic measurements

Usisng intact leaves, the extent of the decrease in chlorophyll a fluorescenece caused by the addition of continuous 710 nm light superimposed on modulated (20 Hz) 550 nm light was used to determine the distribution of this absorbed light between photosystems I (α) and II (β). The Fo and Fm levels, which defined the total variable fluorescenece, were taken as equal to those obtained with excess 710 nm light and with saturating blue-green light, respectively.An analogous procedure was used with a photoacoustic detector, saturating white light defining a base line for oxygen yield, the levels with an without 710 nm light being used to define β and α respectively.The two methods gave similar values for the distribution of light between the two photosystems for the experimental conditions used, β averaging 0.55 for a range of Triticum genotypes and Brachypodium sylvaticum grown in high or low light.

Photosynthetic adaptation of Solanum dulcamara L. to sun and shade Environments : IV. A comparison of North American and European genotypes

Clonal replicates of six genotypes of Solanum dulcamara L. grown in eight different environments were compared for photosynthesis and growth. Four of the genotypes were native to shaded habitats, two to sun habitats. The experimental growth environments differed in light level, daily temperature amplitude and substrate moisture availability. Treatments elicited large differences in lightsaturated photosynthetic rates and growth. Genotypic differences in response to the treatments were identified. However, when genotypes native to sun and shade habitats were compared, there were no consistent differences in photosynthesis or total plant dry weight. It was concluded that previously reported differences in the photosynthetic response of genotypes native to sun and shade habitats to treatment light level may have been the result of the persistent after-effects to changes in leaf water potential and not an adaptive response to growth light level.

The effects of light and nitrogen on photosynthesis, leaf characteristics, and dry matter allocation in the chaparral shrub, Diplacus aurantiacus

Plants of Diplacus aurantiacus, a successional shrub common in California chaparral, were grown under controlled conditions in which either quantum flux density or nitrogen availability was varied. Photosynthesis and leaf nitrogen content were determined on a leaf area and a leaf weight basis, and whole plant growth was monitored.There was a direct relationship between photosynthesis and leaf nitrogen content on both area and weight bases. Reduced light intensity of the growth environment resulted in reductions in light-saturated photosynthesis and nitrogen content on an area basis, but not on a weight basis. With reduced nitrogen availability, photosynthesis and leaf nitrogen content per unit leaf weight decreased.Resource use efficiency increased as the resource became more limiting. The results are consistent with a model of plant growth in which net carbon gain of the leaf is maximized.