Microhabitats, germination, and establishment for Mammillaria gaumeri (Cactaceae), a rare species from Yucatan

Mammillaria gaumeri is a rare cactus endemic to northern Yucatan that has a low rate of seedling establishment. We evaluated the effect of different light microhabitats on germination and seedling survival for this species in the field. Microclimatic requirements for seed germination are synchronized with those typical of the rainy season: germination was optimal at a soil water potential of -0.2 to 0.0 MPa and at a diurnal/nocturnal temperature of 30 degrees/20 degrees C. Low photon fluxes are necessary for seed germination; maximal germination (91.5% +/- 0.38%) and seedling survival (210 d) occurred in microhabitats receiving 20% of total ambient photosynthetic photon flux density (PPFD). Seedlings growing under this condition had a greater volume/surface area relationship (more water stored within their tissues) than those receiving 50% of total ambient PPFD. Water availability is the limiting factor for seedling establishment in arid and semiarid environments; however, because M. gaumeri seedlings had a low tolerance to extreme temperatures, a combination of microclimatic factors determined where a seedling could establish and survive.