Shade tolerance, photoinhibition sensitivity and phenotypic plasticity of Ilex aquifolium in continental Mediterranean sites

Abstract

Shade tolerance, plastic phenotypic response to light and sensitivity to photoinhibition were studied in holly (Ilex aquifolium L.) seedlings transported from the field to a greenhouse and in adult trees in the field. All plants were growing in, or originated from, continental Mediterranean sites in central Spain. Seedlings tolerated moderate but not deep shade. Mortality was high and growth reduced in 1% sunlight. Survival was maximal in 12% sunlight and minimal in full sunlight, although the relative growth rate of the seedlings surviving in high light was similar to that of plants in moderate shade. Maximum photochemical efficiency at predawn was significantly lower in sun plants than in shade plants in the field, revealing chronic photoinhibition that was most pronounced in winter. Plasticity in response to available light varied according to the variable studied, being low for photosynthetic capacity and stomatal conductance, and high for specific leaf area, root:shoot ratio and leaf area ratio, particularly in seedlings. Differences in water relations and hydraulic features between sun and shade plants in the field were marginal. High water potential at the turgor loss point of field-grown plants suggested that holly is sensitive to drought during both the seedling and the adult stage. Low relative growth rates in both high and low light with low physiological plasticity in response to light indicate the existence of a stress-tolerance mechanism. We conclude that holly is a facultative understory plant in areas of oceanic and relatively mild climate, but an obligate understory plant in dry continental areas such as the study site. The impact of abandonment of traditional management practices and climate change on these Mediterranean populations is discussed.

Morphological and physiological adjustments of Brazilwood (Caesalpinia echinata Lam.) to direct solar radiation

“…Physiological adjustments are mediated by primary and secondary messengers. Among the primary messengers, the carbohydrates of low molecular weight such as glucose, fructose and sucrose are considered important molecular flags (Gibson, 2004;Nishizawa et al, 2008) associated with osmoregulation in leaf tissue under intense irradiance (Aranda et al, 2001;Valladares et al, 2005).…”

“…The specific leaf area (SLA) is also subject to variations in the concentration of soluble carbohydrates combined with intense irradiance (Lambers and Poorter, 2004). In some trees, SLA (Valladares et al, 2005) and the concentration of carbohydrates (Marenco et al, 2001) increased in plants under full sunlight.…”

“…Under intense irradiance, some trees present inhibition of photosystem II (PSII) electron transport associated with the higher concentration of carbohydrates (Valladares et al, 2005;Melgar et al, 2009) and increased levels of flavonoids (Tattini et al, 2006).…”

“…Morphological and physiological changes in response to variations in irradiance intensity are well documented for leaves of trees in temperate zones (Matsuki et al, 2003;Valladares et al, 2005;Urban et al, 2007;Wyka et al, 2007). For the tropical trees, especially those native to Brazilian forests, there are increasing ongoing investigations which will bring answers in the medium term (Souza and Válio, 2003;Mengarda et al, 2009).…”

Adaptações estruturais de sete espécies ciófitas arbustivas de Floresta Ombrófila Densa

“…Entre as características morfológicas foliares estudadas, a AEF é tida como um dos principais indicadores da taxa de crescimento e de estratégias do uso de recursos pelas plantas (Vendramini et al 2002), sendo que o seu incremento pode traduzir-se como um mecanismo que permite aumentar a interceptação total da luz pelas plantas que se desenvolvem em ambientais mais sombreados (Niinemets & Fleck 2002). Este padrão de resposta funcional tem sido observado em diferentes espécies submetidas ao sombreamento, como em Schinus terenbitifolius Raddi (Anacardiaceae) submetido à sombra em área de capoeira, com valor de AEF superior a 80 cm 2 .g -1 (Sabbi et al 2009); em Ilex aquifolium L. (Aquifoliaceae) (Valladares et al 2005); e em Mikania glomerata Spreng (Asteraceae) (Espíndola Jr. et al 2009). Em trabalho com espécies medicinais, Boeger et al (2009) demonstraram que a AEF está negativamente relacionada com a intensidade luminosa e, assim, há um maior investimento em tecido fotossintético para maximizar o aproveitamento da luz difusa recebida em ambientes sombreados.…”