Miroslava Rakocevic ^1,2,3* Eunice Reis ² Rafael Leonardo De Almeida ¹ Ivar Wendling ³ Rafael Vasconcelos Ribeiro ¹

• ¹ State University of Campinas, Campinas, São Paulo, Brazil
• ² Embrapa Meio Ambiente, Jaguariuna, São Paulo, Brazil
• ³ Embrapa Florestas, Colombo, Brazil

Plants have developed specific mechanisms to tackle environmental challenges. During one annual period, a dioecious yerba mate with rhythmic growth can present two growth units (GU1, GU2) intercalated with two rest periods (R1, R2). We hypothesized that photosynthetic performance will be much higher under monoculture (MO, high light) than under agroforestry system (AFS, low light) over annual growth and that secondary sexual dimorphism (SSD) will be more expressed during rests than during growth periods. We evaluated the maximum net photosynthesis (Amax), apparent quantum efficiency of CO2 assimilation (Ф), respiration rate in the dark (Rd), and in the light (RL), RL/Rd ratio, maximum apparent rate of electron transport (Jmax), maximum apparent RuBisCO carboxylation rate (Vcmax), Jmax/Vcmax ratio, and chlorophyll indexes in four clones (two males and two females). Light was reduced by 92-95% in AFS compared to MO. Photosynthetic traits generally varied over the annual rhythmic growth and revealed higher photosynthetic performance under MO than AFS. Lower Amax and Rd in all clones under AFS as compared to MO occurred together with higher inhibition of respiration by light (low RL/Rd) under AFS than MO. Despite the strong effect of cultivation systems and growth rhythmicity on photosynthetic traits, our data did not suggest that frequency of SSD in photosynthetic performance (with exception of Jmax/Vcmax ratio) was related to cultivation system or period of rhythmic growth. The SSD was expressed in higher Chl b index and lower Chl a/b ratio in females than males during R2 and GU2, indicating lower sensitivity of females to extreme light conditions of two cultivation systems as compared to males. Higher Amax, and similar respiration rates (Rd and RL) in females than in males in early vegetative phases after pruning (herein R1 and GU1) could be considered as a fitness strategy of female plants in their additional effort to produce fruits and seeds in latter phases. Our results additionally revealed the importance of the period of evaluation for assessing photosynthesis in plant species with rhythmic growth.