ASPECTOS FISIOLÓGICOS, ANATÔMICOS E PRODUTIVOS EM PLANTAS DE SOJA SOB DUAS CONDIÇÕES DE IRRADIÂNCIA E UMIDADE DO SOLO

Abstract

The objective of this study was to determine the water deficit (WD) and contrasting irradiance effects on physiology, anatomy and grain yield of soybean plants at the R1 development stage. The experimental design was a randomized block with five replications in a growth chamber and a 2 x 2 factorial treatment arrangement: 90 and 40% (WD) field capacities (FC); and 750 and 1500 µmol (photons) m-2 s-1 irradiance. The WD caused lower investment in shoot biomass, reduced pollen grain germination, which associated with the reduced CO2 assimilation, promoted lower grain yield. In response to WD, there was an increasing in the non-photochemical energy dissipation, as well as a higher concentration of total soluble sugars, proline and malonaldehyde. In the WD condition under lower irradiance, the plants developed larger spongy parenchyma thickness (related to higher mesophilic conductance of CO2). In the well-watered condition and higher irradiance, there was a greater palisade parenchyma thickness, conferring the photosynthetic efficiency maintenance. In addition, there was an increase in the activity of superoxide dismutase, catalase, peroxidase and ascorbate peroxidase antioxidant enzymes in leaves due to higher light availability. This gave higher energy expenditure by plants, reflecting in reduction of leaf area, number and dry mass of leaves, number of branches and dry mass of stem in well-watered condition. Interestingly, these strategies of osmotic adjustment, photoprotection and antioxidant defenses act together in the WD and higher irradiance condition.