Trocas gasosas e qualidade de mudas de Microdesmia rigida (Benth.) Sothers & Prance sob déficit hídrico e adubação potássica.

Abstract

The plant species of the caatinga have several mechanisms of adaptability to drought, and this capacity is linked to various factors, such as mineral nutrition. The use of potassium (K) added to the substrate can be an alternative to potentiate the effects of rustification of seedlings and so reducing the irrigation blade throughout the production process. Thus, this study aimed to evaluate the attenuating effects of potassium on gas exchange and seedling quality of Microdesmia rigida seedlings under water deficiency. The experiment was conducted in a shaded environment, with 50% light interception, in the Forest Nursery of UAEF/UFCG. The treatments were distributed in an entirely randomized design (DIC), in a 4 x 4 factorial scheme, being four potassium (K) levels (0, 50, 100 and 150 mg dm-3 K) and four irrigation shifts (daily irrigation (control), and every 5, 10 and 15 days). Relative water content (RWC), transpiration (E) and photosynthesis (A) rates, stomatal conductance (gs), internal CO2 concentration (Ci), intrinsic water use efficiency (WUEi), carboxylation efficiency (A/Ci), absolute growth rate (AGR), plant height, stem diameter, dry mass, height/diameter ratio (HDR), and Dickson quality index (DQI) were evaluated. There was no significant effect of treatments on DQI and HDR. The variables Ci, A/Ci, plant height, stem diameter, AGR and dry matter production were affected in isolation by irrigation shift, while TRA, E, gs, A and WUEi were affected by both factors. Irrigating the plants daily or every five days provided the maintenance of higher water status and better stomatal behavior, and the plants were sensitive to water stress provided by longer irrigation shifts (every 10 and 15 days). Potassium fertilization proved to be effective in attenuating the negative effects caused by water deficiency on gas exchange and WUEi of the plants, especially the doses of 100 and 150 mg dm-3 of K. The increase in the irrigation shift negatively affected the growth and dry mass production of the plants.