Abstract
Tropical dry forests are characterized by a high diversity of tree communities and extremely heterogeneous water availability. The tree Alvaradoa amorphoides is a pioneer species of the tropical dry forest found in Xochicalco, Morelos, Mexico. To determine the water requirements for this species to germinate, we evaluated the seed germination rates under field and laboratory conditions. In the field, the seeds had an overall mean germination rate of 42%, but the rate varied between the different sites independent of the soil relative humidity and landscape. Alvaradoa amorphoides seeds exposed to a water potential of -0.5 MPa delayed germination, extending Phase II. At the -1.0 and -1.5 MPa water potentials, germination was inhibited by 80 and 100%, respectively, but the seeds remained viable. Although, the oxygen consumption did not differ between the treatments, the respiration profiles did not show the same triphasic curve as the control. The H2O2 and O2- levels were not significantly different in the seeds at the evaluated low-water potentials (-0.5 and -1.0 MPa), nor were the catalase, superoxide dismutase, and glutathione reductase activity. Only ascorbate peroxidase activity was inhibited at these two water potentials. Our data showed that the A. amorphoides seeds remained in phase II during low water potentials without high levels of Reactive Oxygen Species (ROS) production and continued to be viable; this latter fact might explain the low influence of the humidity and landscape on the germination performance in the field.