Comportamento estomático e crescimento de plantas de faveleira (Cnidoscolus quercifolius pohl.) em função de doses de potássio e níveis de água.

Abstract

This study aimed to investigate the gas exchange, growth and biomass production of faveleira samplings fertilized with potassium and exposed to different water conditions. The experiment was conducted in a completely randomized design, with 4 replications and two plants per experimental unit, with treatments arranged in factorial scheme 4 x 3, corresponding to three doses of potassium (0 (control), 97.5 and 195 mg dm-3 K) and four levels of water (100% (control), 75% and 50% and 25% of pot capacity (cv). The plants were kept in black plastic bags containing 5 kg of soil, for 150 days. Increase in potassium doses promoted rise in leaf water potential, stomatal conductance, and transpiration and photosynthetic rates. However, there was no influence of potassium fertilizer on height, diameter, leaf area and dry matter production of plants, except in the roots. Reduction in water levels reduced leaf water potential, the parameters stomatal, growth and dry matter production of plants. It is recommended that the substrate moisture level of 75% of the vessel capacity in the early growth stages of faveleira saplings. This work aimed to evaluate the physiological behaviour of faveleira plants grown in the field, in an a area of Caatinga, during the rainy season and early dry period. Adult plants grown in the Nupeárido Experimental Farm, at the Federal University of Campina Grande, Patos, Paraíba, Brazil, were selected for evaluation during the months of March and April (wet season) and May and June (dry season), in the year 2016. We evaluated the soil moisture content, water potential (ψw), osmotic potential (ψπ), relative water content (RWC), stomatal conductance (gs), transpiration rate (E), photosynthetic rate (A), intercellular CO2 concentration (Ci), instantaneous water use efficiency (A/E) and carboxylation efficiency (A/Ci). The reduction in water availability in the soil promoted a marked decrease in soil water potential, which was more affected than the relative water content. The opening of the stomata was affected by the decrease in soil moisture content, reducing the stomatal conductance, transpiration rate, photosynthesis rate, instantaneous water use efficiency and carboxylation efficiency. The photosynthesis was more affected than transpiration by reduction in soil moisture content.