Effect of phosphorus and potassium on gas exchanges of Tachigali vulgaris

Tachigali vulgaris L. G. Silva & H. C. Lima is a pioneer species with great potential for reforestation. The inadequate supply of phosphorus and potassium results in nutritional disorders, requiring nutritional complementation. This study aimed to evaluate the effect of phosphorus (P) and potassium (K) doses on Tachigali vulgaris gas exchange. Three doses of P (0, 26.7 and 53.5 kg-1 ha) and three doses of K (0, 50 and 100 kg-1 ha) were applied in a 3x3 factorial scheme as randomized block design. The data were submitted to analysis of variance using the Tukey 1% test and Pearson's linear correlation test. Potassium fertilization provided increases of approximately 30% in the rate of liquid photosynthesis (PN). Stomata conductance (GS), internal CO2 concentration (Ci), perspiration (E), instantaneous caboxilation efficiency (ΦC), water use efficiency (EWU) and intrinsic water use efficiency (iEWU) were also favored at dose of 78.2 g kg-1 K, suggesting their role in regulating essential physiological processes for plant growth. The highest PN values were observed with application of 33.1 g kg-1 P and 78.2 g kg-1 K, with rates of 4.28 and 4.86 μmol CO2 m-2 s-1, respectively, which also occurred with E, ΦC, EWU and iEWU. It was observed that P exerted antagonistic effects on K absorption, which may also have impaired Mg2+ absorption due to the fact that Ca2+ is an accompanying ion of potassium fertilizer