Water stress and light intensity effects on growth and nocturnal acid accumulation in a terrestrial CAM bromeliad (Bromelia humilis Jacq.) under natural conditions

Abstract

Seasonal variations in CAM performance of sunexposed and partially shaded populations of Bromelia humilis were measured under natural conditions in a semi-arid region in northern Venezuela. The sun population consisted of smaller plants, with lower chlorophyll and total nitrogen contents per unit leaf area compared with plants from the partial-shade population. During the dry season CAM activity, assessed as nocturnal acid accumulation, was higher in the partial-shade population. Acid accumulation was stimulated by irrigation in both populations within 24 h after treatment. Daily changes in concentration of soluble sugars were opposite to leaf acidity indicating their role as carbon source for acid synthesis during the night. The change in nocturnal sugar concentration was always more than the amount required for acid accumulation, suggesting other carbohydrate-consuming processes such as transportation of sugars out of the leaf. CAM activity was higher during the rainy season, and differences between populations were smaller. At the end of the rainy season reduction of CAM activity caused by drought was first detected in the sun population. Measured ratios of glucan/soluble sugar show a higher proportion of readily utilizable sugars during periods of active CAM and growth. Under conditions of continuous high light intensity and air temperature leading to all year round high potential evaporation in semiarid tropical regions, fully exposed populations of B. humilis show a pronounced reduction of metabolic activity. Partial shade favours growth and CAM activity in this constitutive CAM species. It is concluded that water stress, and not light intensity, is the predominant limiting factor for growth of this species under natural conditions.

Effects of light stress on the growth of the epiphytic orchid Cattleya forbesii Lindl. X Laelia tenebrosa Rolfe

“…This fact agrees with the findings of Medina et al (1986) and Medina (1987) who demonstrated that some epiphytic orchids native to tropical and subtropical forests incorporate atmospheric CO 2 at night, and show During the period of observation, both groups of plants developed new leaves (figure 3). Plants maintained under 90% of PAR started to develop a new leaf (LF 5) after 80 days ( figure 3A), whereas under 22.5% of PAR the appearance of LF 5 occurred only after 103 days from the start of the experiment ( figure 3B).…”

Plantas medicinais: fatores de influência no conteúdo de metabólitos secundários

“…com os alcalóides de Catharanthus roseus 100 . O efeito da seca na concentração de metabólitos é, às vezes, dependente do grau de estresse e do período em que ocorre, sendo que efeitos a curto prazo parecem levar a uma produção aumentada, enquanto a longo prazo é observado um efeito oposto 6,95,98,101,102 . Outro fator é que a chuva contínua pode resultar na perda de substâncias hidrossolúveis das folhas e raízes por lixiviação; sabe-se que isto se aplica a algumas plantas produtoras de alcalóides, glicosídeos e até mesmo óleos voláteis 47,101 .…”

Global Environmental Change in Drylands: Ecohydrological Controls on Plant Communities

“…In contrast, other studies indicate that the indirect positive effect can be outweighed by the direct negative effect (Pagès et al, 2003 andPagès andMichalet, 2003), thus precluding the occurrence of indirect facilitation (Levin, 1999;Brooker et al, 2008). In my study, CAM plants are thought to be shade tolerant because of their photosynthetic plasticity and acclimation to shade, as confirmed by experimental evidence (Medina et al, 1986;Fetene et al, 1990;Ceusters et al, 2011).…”

“…In contrast, the photosynthetic plasticity of CAM plants and their acclimation to shade allows them to be shade tolerant (Medina et al, 1986;Fetene et al, 1990;Ceusters et al, 2011). Grasses and CAM plants are typically shallow rooted (Ogburn and Edwards, 2010; and thus they compete for soil water resources.…”