Área foliar, assimilação de carbono e fotoquímica da fotossíntese de duas cultivares de mangueira (Mangifera indica L.) sob diferentes intensidades de sombreamento ou temperatura
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2006-02-23Autor
Araújo, Eugênio Celso Emérito
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The physiology of mango is little known in relation to other fruit trees. There are gaps about
estimation of mango leaf area using no destructive methods or concern photosynthetic responses
under temperatures above 10oC, carbon assimilation, leaf and bud productions inr shade. The aims
of present work were to shed light on these gaps determining on mango cultivars Tommy Atkins
and Haden a) Indexes and equations for fast and no-destructive estimate leaf area (AF) just using
length (C), maximum width (L), or both; b) Photosynthetic capacity, leaf and bud production
growing under 0, 65 and 85% of shade and, c) The photosynthetic responses (photochemical and
photosynthetic capacities) under temperatures between 17-32o C. The leaf area (AF) could be
estimated multiplying length x width x 0,74 (for Tommy cultivar) or 0,78 (for Haden) as well using
equations: AF = 4,96349 C - 33,429 (R2=0,86); AF = 17,02964 L - 18,88065 (R2=0,85) and AF =
0,73499 (CxL) + 0,59459 (R2=0,92) for Tommy or AF = 5,35282C - 33,17061(R2=0,88); AF =
19,09951L - 24,61777(R2=0,89) and AF = 0,76015(CxL) + 0,43257(R2=0,99) for Haden. In shade
the cultivars presented same values of maximum net photosynthesis (Amax) obtained under full
solar irradiance, decreasing the light compensation point and/or increasing the chlorophyll content.
Besides, until 65% of shade, both cultivars maintained the same leaf and bud production in relation
to full solar irradiance treatment, enabling them for plantation under high densities until middle
shade intensities (around 65%). The optimum temperature range for Amax was 23-29oC in
Tommy and 23-26oC in Haden. Both cultivars presented an unbalance between photochemical and
biochemical phases of the photosynthesis in between 17-32o C, especially Haden. Under regular
atmospheric concentration of CO2 the net photosynthesis of Haden, in general, was smaller than
Tommy, while under CO2 saturation the opposite happened, possibly because Haden used its largest
capacity of electron transport to increase the carbon assimilation, and, at the same time, decreasing
its susceptibility to oxidative stress. Both cultivars presented high temperature adaptation
maintaining almost constant the intensities of dark respiration (Rd) in Tommy and the
photorespiration (Pr) in Haden. In Tommy Pr induced increases in light saturation (LS) and
compensation (LCP) points, and reductions in apparent quantum yield (α). In Haden increases in
Rd, LS stability and α reductions with temperature did not keep relationship with Pr nor with RE
probably because the rupture of the cellular homeostasis caused by high electron excess.