Seasonality and the control of longevity and dormancy in macaúba palm diaspores

Abstract

The persistence of diaspores in soil seed banks (SB) will depend on their ability to remain viable (longevity) without germinating (dormancy). Changes in longevity and dormancy are governed by interactions between both intrinsic and environmental factors, and which determine the dynamics of SB. Our understanding of those dynamics will be important for the commercial propagation and conservation of natural populations, but remains incipient for tropical species. We evaluated the effects of climatic seasonality on the longevity and dormancy of diaspores of the neotropical oleaginous macaúba palm (Acrocomia aculeata). Pyrenes (seeds enveloped by the endocarp) of the species were kept in simulated SB under nursery conditions for two years. Morphological, biomechanical, cytological and physiological evaluations were carried out, every 90 days. The longevity of macaúba pyrenes is related to the maintenance of the structural protection of the embryo, tolerance to water deficits, and the control of oxidative stress. Dormancy level is reduced by changes in the biomechanics of the micropylar region: the gradual weakening of resistance tissues (the operculum and germination pore plate) and the increasing growth force of the embryo. Diaspores gradually become competent at perceiving environmental stimuli (especially high temperatures), which favors germination during windows of climatic opportunity in the late austral spring and early summer. Diaspores persisting in the SB contribute to the resilience of natural populations and will be important to the management and enrichment of areas where the species is exploited through extractivism.