Abstract
ABSTRACT In the Amazon region, agroforestry systems (AFSs) are recommended as a sustainable production alternative for local communities. A common component in Amazonian AFSs are tropical fruit trees, which can form the canopy or grow in the understory. In this study, we evaluated the effect of high radiation on photosynthesis, growth and seedling survival of four Amazonian fruit-tree species: Theobroma cacao, Eugenia stipitata, Inga edulis and Psidium guajava. Growth, chlorophyll fluorescence, gas exchange, and leaf pigments were measured in seedlings of each species grown for 12 months inside shade houses with low (8%), medium (30%) and high relative illumination (100%). Eugenia stipitata and T. cacao had the lowest acclimation capacity to high solar radiation, followed by I. edulis. Therefore, these species must be grown under intermediate light levels in early growth stages, to protect them from direct sunlight. In contrast, P. guajava seedlings demonstrated high tolerance to elevated radiation, therefore, this species can be planted under full sunlight.
Highlights
Light intensity is a key factor for the establishment and growth of plants in agroforestry systems (AFSs), as the light environment below the canopy is variable and significantly affects the assimilation of CO2 and the development of plants growing in the understory (Charbonnier et al 2017)
This study aimed to evaluate the effect of intense radiation on photosynthesis, growth, and survival of young plants of four tropical fruit-tree species with different light requirements: T. cacao, E. stipitata, I. edulis, and P. guajava
In P. guajava, the relative growth rate (RGR), total biomass and foliar area increased as a function of the radiation level, with the highest values recorded at 100%, followed by 31% RI (Figure 2)
Summary
Light intensity is a key factor for the establishment and growth of plants in agroforestry systems (AFSs), as the light environment below the canopy is variable and significantly affects the assimilation of CO2 and the development of plants growing in the understory (Charbonnier et al 2017). Seedlings of an AFS can be exposed to high radiation, as in full sunlight, when canopy-trees are young or when the spacing among them is wide, which could negatively affect their growth and survival. Typical of open field conditions, may affect the establishment of canopy-tree seedlings, because radiation values usually exceed the light saturation point (LSP) of photosynthesis of many tropical fruit-tree species (Krause et al 2012). Since young plants of several species used in AFSs are vulnerable to light stress, intense radiation could cause photoinhibitory processes that affect their survival and growth, and the AFS productivity (Goh et al 2012). Photosynthesis, growth, and survival in seedlings of four tropical fruit-tree species under intense radiation.
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