Análise sistêmica da fotossíntese de cultivares de Coffea arabica L. em condições de campo e de laboratório

Abstract

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.