ABSTRACT Banded iron formations (BIF) have a particular vegetation type and provide a good model system for testing theories related to leaf phenology, due to unique stressful environmental conditions. As a consequence of the stressful conditions of BIF environment, we hypothesize that most species would retain at least some significant canopy cover, even at the end of the dry season, independently of growth form - trees, shrubs, and sub-shrubs. Considering the strong seasonality, we also hypothesize that photoperiod and rainfall act as triggers for leaf fall and leaf flushing in these environments. The majority of the fifteen studied species had a semi-deciduous behavior and shed their leaves mainly during the dry season, with a recovery at the end of this season. In general, leaf flushing increased around the spring equinox (end of the dry season and start of the rainy season). A trade-off between leaf loss and leaf maintenance is expected in a community in which most plants are naturally selected to be semi-deciduous. Our results suggest photoperiod as a dominant factor in predicting leaf phenology.

Ecophysiological responses of plants are useful for monitoring the success of ecological restoration projects that target species conservation. In this study we evaluated the ecophysiological traits of individuals of Chamaecrista semaphora from a natural population and from a site under restoration. Water potential and chlorophyll a fluorescence parameters were measured both in adult and young plants of the two populations. No difference in water potential was found between sites, but individuals in the restored site had higher water potential at predawn. Adults in the natural site presented lower daily values of potential quantum yield, indicating the occurrence of photoinhibition. Individuals in the restored site also presented higher maximum relative electron transport rate (ETRMAX). No difference was found in leaf carbon isotope discrimination values (σ13C) between plants growing in restored and natural sites, suggesting similar water use efficiency. These results indicate that C. semaphora individuals in the restored site had similar or better photosynthetic and water economy performances than individuals at the natural site. Methodologies traditionally employed to assess stress response of plants, such as chlorophyll a fluorescence and procedures used to evaluate the efficiency of water use, allowed us to verify the success of restoration procedures using an endangered species.

O objetivo do estudo foi avaliar a performance fotossintética em populações de duas leguminosas arbóreas, Stryphnodendron adstringens (Mimosoideae), uma espécie típica do Cerrado e Cassia ferruginea (Caesalpinoideae), que ocorre na Mata Atlântica. Os parâmetros de fotossíntese foram obtidos por medições de fluorescência da clorofila em progênies de plantas naturalmente polinizadas provenientes de três populações de S. adstringens e de uma população de C. ferruginea. Plantas de S. adstringens crescendo sob as mesmas condições que plantas de C. ferruginea, demandaram, comparativamente, valores mais elevados de luz para a saturação da fotossíntese, respectivamente 600 µmol.m-2.s-1 e 350 µmol.m-2.s-1, e apresentaram uma mais elevada eficiência intrínseca do fotossistema II, Fv/Fm de 0,814 versus 0,783 em C. ferruginea. Os maiores valores de Fv/Fm observados em S. adstringens podem explicar as maiores taxas relativas de transporte de elétrons (ETR). Não foram encontradas diferenças significativas entre progênies das árvores de C. ferruginea, nem entre populações de S. adstringens, e apenas algumas poucas diferenças entre progênies dentro de populações de S. adstringens. O fato de parâmetros da fluorescência da clorofila distinguir espécies, mas não populações ou progênies pode estar relacionado à baixa variação genética destes caracteres de fluorescência da clorofila ou devido a ausência da expressão das diferenças genéticas em plantas sob condições não estressantes.

The aim of this study was to investigate the photosynthetic performance in populations of two legume tree species, Stryphnodendron adstringens (Mimosoideae), typical from Cerrado, and Cassia ferruginea (Caesalpinoideae) from the Atlantic Rain Forest. The photosynthetic traits were assessed by measures of chlorophyll fluorescence in progenies of naturally pollinated plants from three populations of S. adstringens and a population of C. ferruginea. Plants of S. adstringens growing under similar conditions of C. ferruginea plants demanded higher light values for photosynthesis saturation, 600 µmol.m-2.s-1 and 350 µmol.m-2.s-1 respectively, and showed higher intrinsic photosynthetic efficiency of photosystem II, Fv/Fm of 0.814 versus 0.783 in C. ferruginea. The highest values of Fv/Fm observed in S. adstringens can explain the highest electron transport rates (ETR) obtained for this species. No significant differences were found among progenies from different C. ferruginea trees nor among populations of S. adstringens, and only in few cases, variation among progenies within populations were found for S. adstringens plants. The fact that fluorescence parameters distinguished species but not populations or most of progenies may be related to low intraspecific genetic variation of these chlorophyll fluorescence traits or due to lack of expression on genetic differences in plants under no stressful conditions.