No abstract

An understanding of variations in morphophysiological leaf traits of plant models in dry tropical forests is essential for quantifying C fluxes from forest ecosystems in response to climate changes. The present study evaluated the influences of seasonal rainfall and different light conditions on the gas exchange, nutrients, organic compounds and morphological traits in Croton blanchetianus Baill. trees within a fragment of Caatinga forest. Stomatal conductance (gs) and net photosynthesis (PN) demonstrated variations within the diurnal cycle, with maximum values at approximately midday and minimum values at predawn. The PN and the diurnal integrated CO2 assimilation were lower during the dry season than in the rainy season. Water use efficiency was positively correlated with PN (r = 0.73) during the dry season only. However, the correlation between PN and gs was observed during the rainy season only (r = 0.60). Thus we demonstrated that C. blanchetianus has a remarkable ability to adapt to global climatic changes and could be considered a model in studies exploring water relationships in woody plants; consequently, this species may be important in future reforestation studies.

RESUMO: Neste trabalho se objetivou avaliar a técnica de espectroscopia no infravermelho próximo (NIR) e a análise multivariada para a diferenciação de cultivares de girassol utilizando sementes e óleo. As amostras foram submetidas à análise no NIR e os espectros foram gerados por meio do detector FT-IR. Para a construção do modelo de calibração foi utilizado o método de classificação multivariada por mínimos quadrados parciais com análise discriminante (PLS-DA), em que as classes (y) são as variáveis dependentes e os espectros obtidos das amostras as variáveis independentes. As cultivares de girassol foram diferenciadas, tanto óleo quanto semente. Por óleo obteve-se 100% de acerto na calibração, 92% no teste de y-randomization, 86% na validação cruzada e 92% na validação externa, em que se testa 25% das amostras para validar o modelo. E por sementes 100% de acerto na calibração, 87% no teste de y-randomization, 100% na validação cruzada e 100% na validação externa. Portanto, conclui-se que a técnica de espectroscopia no infravermelho próximo, associada à análise multivariada, diferencia cultivares de girassol, tanto por meio do óleo, extraído de semente com pericarpo e de semente sem pericarpo, quanto por semente, com e sem pericarpo.

No abstract

Plant species of the Brazilian Caatinga experience seasonal wet and dry extremes, requiring seasonally different leaf characteristics for optimizing water availability. We investigated if Croton blanchetianus Baill exhibits leaf morphoanatomical traits across seasons and positioning in sunlight/natural shade. Leaves of ten 1-3 m tall plants in full sunlight and ten in natural shade were assessed in May, July (wet season), October and December (dry season) 2015 for gas exchange, leaf size, lamina and midrib cross sections (14 parameters), and chloroplast structure (5 parameters). Net photosynthesis was greater during the wet season (21.6 µm−2 s−1) compared to the dry season (5.8 µm−2 s−1) and was strongly correlated with almost all measured parameters (p < 0.01). Shaded leaves in the wet season had higher specific leaf area (19.9 m2 kg−1 in full-sun and 23.1 m2 kg−1 in shade), but in the dry season they did not differ from those in full sun (7.5 m2 kg−1 and 7.2 m2 kg−1). In the wet season, the expansion of the adaxial epidermis and mesophyll lead to larger and thicker photosynthetic area of leaves. Furthermore, chloroplast thickness, length and area were also significantly larger in full sunlight (2.1 μm, 5.1 μm, 15.2 μm2; respectively) and shaded plants (2.0 μm, 5.2 μm, 14.8 μm2; respectively) during wetter months. Croton blanchetianus exhibits seasonal plasticity in leaf structure, presumably to optimize water use efficiency during seasons of water abundance and deficit. These results suggest that the species is adaptable to the increased drought stress projected by climate change scenarios.

Physiological conditioning is a technique that consists in controlling the speed of water uptake by seeds, with osmotic solutions, aiming to improve their quality, reducing time and increasing germination rate. Eremanthus erythropappus (D.C.) MacLeish seeds were subjected to priming with polyethylene glycol 6000 (PEG), potassium nitrate (KNO3) and the combination of the two at the concentrations of 0.4; -0.8; -1.0; -1.2 and -1.4 MPa for four, six and eight days. Germination, germination speed index (GSI), emergence, emergence speed index (ESI) and expression of superoxide dismutase (SOD), catalase (CAT) and peroxidase (PO) enzymes were assessed. E. erythropappus seed priming in polyethylene glycol solution with potentials between -0.8 MPa and -1.4 MPa is not satisfactory because it adversely affects germination and reduces the activity of peroxidase and catalase enzymes. The other substances were not significant so there is a need for further research with other substances and / or concentrations