Análise sistêmica da fotossíntese de cultivares de Coffea arabica L. em condições de campo e de laboratório
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Date
2008-03-03Author
Bortolin, Livia Haik Guedes de Camargo
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On the first chapter, photosyntehsis network global connectance analysis (Cg) and
principal components analysis (PCA) indicate, respectively, that decrease on net
photosynthesis (PN) was accompanied by reduced autonomy in relation to environment and
reduced variation of answers of all physiological network variables in clear day. High
synchronization among physiological and meteorological parameters (reduced autonomy of
cultivars in relation to environment) on clear day was considered the main cause of PN drop.
This causal relationship was highlighted by results from PCA pointing out simultaneously: 1
- a clear contrast among physiological and meteorological vectors, 2 - reduced physiological
variation of grafted and non-grafted individuals on clear day, and 3 - distribution of symbols
representing clear and cloudy days close to meteorological and physiological vectors,
respectively. Therefore, autonomy was strong parameter of stress condition of Coffea arabica
on clear and cloudy days under field conditions in growing season.
On the second chapter, young plants of C. arabica cultivars presented higher net
carbon assimilation and quantum efficiency when treated for 14 hours at 17-23ºC (reduced
temperatures) than when treated for 14 hours at 26-32ºC (elevated temperatures). At 17-23ºC,
electron transport rate was not excessive, negative components of photosynthetic process are
reduced, and biochemical and photochemical processes of photosynthesis are in equilibrium.
The principal component analyses (PCA) showed that at reduced temperatures (17-23ºC)
there was similar physiological behavior among cultivars. On the other hand, at elevated
temperatures (26-32ºC), the cultivars displayed broader physiological variation and strong
inhibition of photosynthesis at leaf temperature of 32ºC. On this extreme temperature it was
brought about a decrease of carboxylation efficiency and an increase of mesophyll limitation
of photosynthesis. Photosynthesis network of C. arabica was tightly adjusted at elevated
temperatures (Cg values higher than at reduced temperatures). Network analysis and PCA in C. arabica were appropriate tools to discriminate the impact of stressing temperatures and the
kind of responses of each cultivar under changing environment.