Effect of domestication on phenotypic plasticity in chaya (Cnidoscolus aconitifolius (Mill) I.M. Johnstone)

It is widely recognized that phenotypic plasticity may increase the survival of plants in environmentally variable habitats. However, the manner in which artificial selection affects the phenotypic plasticity of crops is poorly understood and there is no previous study in clonally propagated crops. The goal of this study was to assess the effect of domestication on phenotypic plasticity in leaf traits, growth rates and allocation patterns, under contrasting light environments, in the clonally propagated crop chaya (Cnidoscolus aconitifolious (Mill) I.M. Johnstone). Leaf area, leaf perimeter, leaf specific area, leaf production, trichome density, growth in height, growth in stem diameter and slenderness were measured in 97 clones belonging to 20 genotypes (10 wild and 10 domesticated). The clones were allocated to two contrasting light environments: fully exposed to sun vs. placement beneath a shade cloth. Reaction norms for each trait were compared between wild and domesticated clones. Results suggest that domestication and light environment had a non-additive effect on phenotypic plasticity in leaf production and slenderness. Reduced plasticity in these traits was observed in domesticated plants compared to that of their wild relatives. Leaf production and slenderness are associated with the shade avoidance syndrome, which is evident in wild plants but not manifested in domesticated plants. Reduced plasticity in leaf production also suggests yield stability, since the leaves form the edible part of chaya. I conclude that artificial selection reduces phenotypic plasticity in the yield of chaya and in its response to variation in the light environment.

ASPECTOS ANATÔMICOS E FISIOLÓGICOS DE FOLHAS DE Mimosa scabrella DE ÁREAS COM DIFERENTES GRAUS DE SUCESSÃO

O objetivo deste trabalho foi verificar a influência de diferentes condições de luminosidade presentes em folhas de Mimosa scabrella Benthan plantadas em áreas com diferentes graus de sucessão nas margens do Reservatório Iraí, PR. Foram avaliados aspectos morfológicos (área foliar, peso seco, área foliar específica), anatômicos (espessuras de cutícula, epiderme adaxial, parênquima paliçádico, parênquima lacunoso, epiderme adaxial e espessura total), fisiológicos (taxa de fotossíntese, condutância estomática e transpiração) e desenvolvimento das plantas (altura, diâmetro e sobrevivência até os 18 meses). Para os parâmetros morfológicos, M. scabrella apresentou diferença significativa para a área foliar específica, que foi maior para os indivíduos da capoeira. Diferenças significativas foram encontradas para a espessura da epiderme adaxial e do parênquima paliçádico. A epiderme adaxial foi maior na área de capoeira, enquanto que o parênquima paliçádico maior na área aberta. Indivíduos da área aberta apresentaram maior taxa de transpiração e condutância estomática. Tanto a altura quanto o diâmetro não mostraram diferença significativa entre as áreas. A sobrevivência foi considerada insatisfatória para ambas as áreas, porém foi ligeiramente maior na capoeira. Esses resultados, aliados ao comportamento natural da espécie, sugerem que M. scabrella deve ser implantada em densidades maiores.Palavras-chave: Morfoanatomia foliar; fisiologia, variação de luz; recuperação de área degradada; silvicultura de espécies nativas. AbstractAnatomical and physiological features of Mimosa scabrella leaves growing on areas with different succession stages This study aims to evaluate the influence of light conditions at different stages of succession in leaves of Mimosa scabrella Benthan planted in Iraí’s water reservoir margins, State of Paraná, Brazil. We evaluated leaf morphology (area, dry weight, specific area), anatomy (cuticle thickness, adaxial epidermis, palisade parenchyma, parenchyma spongy, adaxial epidermis and total thickness), physiology (photosynthesis rate, stomatal conductance, transpiration) and plant growth (height, diameter) and survival up to age of 18 months. Plants of Mimosa scabrella of natural regeneration showed greater leaf specific area than those of planted individuals. Significant differences were found on thickness of the adaxial epidermis and palisade parenchyma. The adaxial epidermis was higher in regenerating area, whereas the palisade parenchyma was higher in open field. Plants of open field presented higher values of transpiration and stomatal conductance. Concerning height and diameter growth, plants of both areas showed no significant differences. Survival was considered unsatisfactory for both areas, but was slightly higher in regenerating area. According to M. scabrella behavior in natural conditions, the results suggest that this species must be implanted in greater densities.Keywords: Leaf morphology; leaf anatomy; physiology; light; land recuperation; native tree species.

Sclerophylly and Foliar Nutrient Status of Mediterranean-Climate Plant Communities in Southern Australia

An increase (percentage dry weight) in both lignin and cellulose (with a greater proportion of cellulose than lignin being formed) is associated with a decrease in the concentration of phosphorus (and of other related elements) per unit dry weight in the leaves of sunlit overstorey species, of both sclerophyll and savannah communities in the mediterranean climate of southern Australia. Simultaneously, crude protein decreases. Leaves become increasingly sclerophyllous (with a higher Sclerophyll Index), with lower crude protein (cytoplasm) per unit dry weight; thicker leaves with lower leaf specific area result. The degree of sclerophylly per unit foliar phosphorus content is a little higher in understorey species which are partially shaded by the overstorey canopy.