Seed Hydration Memory in Sonoran Desert Cacti and Its Ecological Implication

Abstract

Cactus seeds on the soil surface in the desert are subjected to periods of drought that last for up to a few months, and thus they are typically under discontinuous hydration (or discontinuous dehydration). Apparently, they can tolerate long periods of dehydration after single or multiple hydration events and subsequently germinate in accordance with the previous hydration experience. This was verified in three cactus species from the Sonoran Desert. Seeds of Stenocereus thurberi hydrated for 72 or 80 h followed by a dehydration period lasting for 4, 14, 70, 120 or 181 d germinated 2–3 d earlier and had 1.4–2 times shorter mean germination time (MGT) than untreated seeds. Seeds given shorter hydration periods also began to germinate sooner than the controls. MGT was shorter only when the hydration period was 48 h or longer. Final germination percentages were not affected by these treatments, only the MGT. Except for differences in germination percentages, similar results were found for Pachycereus pecten-aboriginum and Ferocactus peninsulae. When the cycle of 24 h hydration followed by 4 d dehydration was repeated one or two times, the effect was cumulative: MGT was equal to 48 and 72 h hydration, respectively. These results suggest a phenomenon of “seed hydration memory,” the ability of seeds to retain during dehydration periods those physiological changes that result from seed hydration. Thus, treated seeds subsequently germinated earlier then untreated seeds, regardless of the duration of dehydration period. This led to a greater biomass accumulation and thus to higher survival in seedlings from treated than from untreated seeds.