Influence of mechanical root restriction on gas-exchange of four papaya genotypes

four papaya genotypes, two from the ？solo？ group (sunrise solo tj and improved sunrise solo line 72/12) and two from the ？formosa？ group (tainung 02 and know you 01) grown in ultisol under field conditions in macaé, rj, brazil, were used in this study. two different effective depths (ed) were determined in the area using a penetrographer with average soil moisture of 11.2%. the area with ed of 0.35 m with a maximum pressure of 4.12 mpa for penetration was defined as an area with restriction (wr) to root growth, while, the area with minimum ed of 0.60 m and a pressure lower than 2.30 mpa as an area with no restriction (nr). the net co2 assimilation rate (a), stomatal conductance (gs), leaf temperature (tl), intercellular partial pressure of co2 (ci) and intrinsic water use efficiency (iwue) were evaluated for three consecutive days after irrigation. mechanical root restriction affected gas exchange of the four papaya genotypes. all genotypes grown in the wr area had lower a, gs and ci and higher tl than the same genotypes in the nr area. all genotypes grown in the wr area had high iwue and sunrise solo tj had the highest iwue.