Physiological behavior of four species of young trees from the caatinga during two cycles of water stress

Four species from the semi-arid region of Pernambuco State, Northeast Brazi l, known as "caatinga", were subjected to two watering cycles in a greenhou se, in order to compare their physiological behaviour and drought resistanc e during the initial stage of growth. Senna martiana (Benth) H. S. Irwin & Barneby; Senna spectabilis (DC.) H.S. Irwin & Barneby var. excelsa (Schrad) , H. S. Irwin & Barneby; Caesalpinia ferrea Mart. ex Tul, and Caesalpinia p yramidalis Tul. were grown in pots with normal watering until 90 days after planting, after which watering continued for the control plants and was su ppressed from the others (for 7 or 14 days). Transpiration (E), diffusive r esistance (Rs), leaf temperature (Tf) and leaf water potential (Psiw) were evaluated. Under normal conditions Caesalpinia pyramidalis showed the highe st E (7.31 mmol.m(-2).s(-1)), followed by Caesalpinia ferrea (5.23 mmol.m(- 2).s(-1)), Senna martiana (4.52 mmol.m(-2).s(-1)) and Senna spectabilis (4. 42 mmol.m(-2).s(-1)). Under of stress conditions 14 days, E dropped to 0.66 ; 0.65; 0.54 and 0.66 mmol.m(-2).s(-1), respectively. Water stress for 7 da ys increased R and decreased water potential for the four species in the ab ove order, with variations from 9.47 to 12.08 s.cm(-1) and from -1.83 to -3 .95 MPa, respectively. Siginificant differences were observed among the spe cies and among the water treatments for all the variables studied.