Influence of maternal environment in developing different levels of physical dormancy and its ecological significance

There is considerable literature on the ecology of seeds with impermeable coats, i.e., physical dormancy (PY), but the factors controlling the development of PY and their ecological importance have received little study. The differences in relative humidity, temperature, and rainfall of the maternal environment during seed development, which vary within year at different sites or between years within the same site, contribute to the number and level of PY are reviewed. These factors all influence the development of PY by lowering the level of moisture content in the seeds. Based on moisture content reached during maturation drying, two levels of PY can be recognized: (1) shallow and (2) absolute. Seeds with shallow PY are shed at higher water content, while seeds with absolute PY have lower moisture content at the time of shedding. However, if the moisture content maintained is higher than the 'shallow dormant' level, the seed coat remains permeable to water. It is suggested that this variation in the level of PY subsequently affects the dormancy loss mechanisms and determines the ability of seeds to establish a long-term persistent seed bank or germinate within few years of shedding.