Plastic Phenotypic Response to Light of 16 Congeneric Shrubs From a Panamanian Rainforest

The comparative phenotypic plasticity of 16 species of tropical rainforest shrubs (genus Psychotria, Rubiaceae) was investigated by growing plants in three light environments on Barro Colorado Island (BCI, Panama). The three light environments gave daily photon flux densities (PPFD) similar to the natural light gradient from shaded forest understory to small and large canopy gaps. Six of the species are principally found in gaps or forest edge environments, whereas the other ten species are principally found in shaded understories. Interactions between light treatment and species resulted in unpredictable mean phenotypic expression across light treatments. Shoot relative growth rates (RGR) were similar for understory and gap species in the low light treatment. Gap species had significantly greater shoot RGR in the intermediate light treatment than in the high light treatment. Mean plasticity was significantly lower for morphological variables when com- pared to physiological variables, while variation in plasticity was significantly greater for structural variables. Significant differences between gap and understory species were found in the plasticity of six out of the seven variables. The mean phenotypic plasticity of the seven variables was significantly greater for gap than for understory species. The high plasticity of gap species was consistent with the hypothesis that specialization in a more favorable environment increases plasticity. The species exhibited a wide range of leaf longevities, from four to 29 months, with gap species having, on average, shorter leaf life- span than understory species. Mean phenotypic plasticity decreased with increasing leaf longevity. Selection for greater plasticity may be stronger in the gap species because gaps exhibit a relatively predictable decrease in PPFD for which plasticity could be adaptive. While we have found a significant correlation between phenotypic plasticity and habitat affiliation, phylogeny (subgenus ascription) was not correlated with plasticity or with plant performance in any given PPFD treatment, reinforcing the hypothesis that phenotypic plas- ticity has evolved through natural selection in this diverse genus.

[1]  F. Valladares,et al.  Exploring Phenotypic Plasticity in the LichenRamalina capitata: Morphology, Water Relations and Chlorophyll Content in North- and South-facing Populations , 1997 .

[2]  Robert W. Pearcy,et al.  Photosynthetic responses to dynamic light under field conditions in six tropical rainforest shrubs occuring along a light gradient , 1997, Oecologia.

[3]  K. Kitajima,et al.  Seasonal leaf phenotypes in the canopy of a tropical dry forest: photosynthetic characteristics and associated traits , 1997, Oecologia.

[4]  S. Løvtrup,et al.  What has survived of Darwin's theory? , 1997 .

[5]  M. Press,et al.  PHOTOSYNTHESIS IN RELATION TO GROWTH AND SEEDLING ECOLOGY OF TWO DIPTEROCARP RAIN FOREST TREE SPECIES , 1996 .

[6]  Peter Ryser,et al.  The importance of tissue density for growth and life span of leaves and roots: a comparison of five ecologically contrasting grasses , 1996 .

[7]  Troy D. Sadler,et al.  Evolution of a Generalist Genotype: Multivariate Analysis of the Adaptiveness of Phenotypic Plasticity , 1996, The American Naturalist.

[8]  F. Bazzaz.  Plants in Changing Environments: Linking Physiological, Population, and Community Ecology , 1996 .

[9]  E. Veenendaal,et al.  Responses of West African Forest Tree Seedlings to Irradiance and Soil Fertility , 1996 .

[10]  Christopher J. Lortie,et al.  The Specialization Hypothesis for Phenotypic Plasticity in Plants , 1996, International Journal of Plant Sciences.

[11]  H. Huber.  Plasticity of internodes and petioles in prostrate and erect Potentilla species , 1996 .

[12]  C. Field,et al.  Ecophysiological Constraints on the Distribution of Piper Species , 1996 .

[13]  S. Mulkey,et al.  Influence of Seasonal Drought on the Carbon Balance of Tropical Forest Plants , 1996 .

[14]  F. Bazzaz,et al.  Photosynthetic Characteristics of Tropical Trees Along Successional Gradients , 1996 .

[15]  R. Monson.  The use of phylogenetic perspective in comparative plant physiology and developmental biology , 1996 .

[16]  H. Lambers,et al.  The causes of inherently slow growth in alpine plants : an analysis based on the underlying carbon economies of alpine and lowland Poa species , 1996 .

[17]  G. Neuner,et al.  Frost resistance and susceptibility to ice formation during natural hardening in relation to leaf anatomy in three evergreen tree species from New Zealand. , 1995, Tree physiology.

[18]  Robert W. Pearcy,et al.  Exploitation of environmental heterogeneity by plants: ecophysiological processes above- and belowground , 1994 .

[19]  J. Coleman,et al.  Interpreting phenotypic variation in plants. , 1994, Trends in ecology & evolution.

[20]  O. O. Osunkoya,et al.  Influence of seed size and seedling ecological attributes on shade-tolerance of rain-forest tree species in northern Queensland , 1994 .

[21]  D. Sims,et al.  5 – Photosynthetic Acclimation to Changing Light Environments: Scaling from the Leaf to the Whole Plant , 1994 .

[22]  F. Stuart Chapin,et al.  Evolution of Suites of Traits in Response to Environmental Stress , 1993, The American Naturalist.

[23]  P. Reich.  Reconciling apparent discrepancies among studies relating life span, structure and function of leaves in contrasting plant life forms and climates: the blind men and the elephant retold' , 1993 .

[24]  S. Scheiner.  Genetics and Evolution of Phenotypic Plasticity , 1993 .

[25]  D. Sims,et al.  Response of leaf anatomy and photosynthetic capacity in Alocasia macrorrhiza (Araceae) to a transfer from low to high light. , 1992 .

[26]  P. Reich,et al.  Leaf Life‐Span in Relation to Leaf, Plant, and Stand Characteristics among Diverse Ecosystems , 1992 .

[27]  Hendrik Poorter,et al.  Inherent Variation in Growth Rate Between Higher Plants: A Search for Physiological Causes and Ecological Consequences , 1992 .

[28]  S. Wright.  Seasonal Drought and the Phenology of Understory Shrubs in a Tropical Moist Forest , 1991 .

[29]  S. Wright,et al.  DROUGHT ACCLIMATION OF AN UNDERSTORY SHRUB (PSYCHOTRIA LIMONENSIS; RUBIACEAE) IN A SEASONALLY DRY TROPICAL FOREST IN PANAMA , 1991 .

[30]  F. Stuart Chapin,et al.  Integrated Responses of Plants to Stress , 1991 .

[31]  C. W. Hamilton.  A Revision of Mesoamerican Psychotria Subgenus Psychotria (Rubiaceae), Part II: Species 17-47 , 1989 .

[32]  C. W. Hamilton.  A Revision of Mesoamerican Psychotria Subgenus Psychotria lRubiaceaerc Part Ic Introduction and Species 1-16 , 1989 .

[33]  C. Uhl,et al.  Vegetation Dynamics in Amazonian Treefall Gaps , 1988 .

[34]  Charles D. Canham,et al.  Growth and Canopy Architecture of Shade‐Tolerant Trees: Response to Canopy Gaps , 1988 .

[35]  E. Nordheim,et al.  Estimating Gap Origin Probabilities for Canopy Trees , 1988 .

[36]  C. Field.  On the Role of Photosynthetic Responses in Constraining the Habitat Distribution of Rainforest Plants , 1988 .

[37]  A. Gentry,et al.  Contribution of nontrees to species richness of a tropical rain forest , 1987 .

[38]  Christopher B. Field,et al.  Plant Responses to Multiple Environmental FactorsPhysiological ecology provides tools for studying how interacting environmental resources control plant growth , 1987 .

[39]  T. Hirose.  A vegetative plant growth model : adaptive significance of phenotypic plasticity in matter partitioning , 1987 .

[40]  J. Denslow.  TROPICAL RAINFOREST GAPS AND TREE SPECIES DIVERSITY , 1987 .

[41]  Carl D. Schlichting,et al.  The Evolution of Phenotypic Plasticity in Plants , 1986 .

[42]  David J. Hicks,et al.  The Ecology of Leaf Life Spans , 1982 .

[43]  S. Pickett,et al.  PHYSIOLOGICAL ECOLOGY OF TROPICAL SUCCESSION: A Comparative Review , 1980 .

[44]  F. S. Chapin,et al.  The Mineral Nutrition of Wild Plants , 1980 .

[45]  F. Bazzaz.  The Physiological Ecology of Plant Succession , 1979 .

[46]  T. Croat.  Flora of Barro Colorado Island , 1978 .

[47]  A. D. Bradshaw,et al.  Evolutionary Significance of Phenotypic Plasticity in Plants , 1965 .