Putting seed traits into pellets: using seed mass data to improve seed encapsulation technology for native plant revegetation.
Abstract
Poor seedling emergence often limits the success of direct seeding in ecological restoration. New techniques for maximising seed use efficiency and seedling emergence are needed to help meet global targets for nature repair in the UN Decade on Restoration. Extruded pellets are widely used in agriculture and represent a promising advancement in seed-based restoration. However, extruded pellets must be optimised for diverse suites of native species that possess a range of seed sizes and morphotypes. We investigated how seed mass affects the performance of native plant seeds (total % seedling emergence) when encapsulated in extruded pellets designed for revegetation. Two glasshouse trials were undertaken using seeds from 30 native Australian plant species. In Trial 1, we encapsulated seeds in the centre of pellets and determined the relationship between seed mass and emergence. In Trial 2, we encapsulated seeds nearer the periphery of pellets and determined whether the position of seeds (central vs. peripheral) affected emergence for a subset of 10 small-seeded species. In both trials, emergence from pellets was compared to an optimal, bare-seeded control to identify any barriers to seed encapsulation under well-watered conditions. In Trial 1, when seeds were centrally encapsulated, emergence was generally higher for bare-seeded controls relative to pelleted seeds. However, seed mass predicted emergence when seeds were encapsulated in the pellet centre (R2 = 0.32, p = 0.002), such that larger-seeded species tended to have higher emergence than smaller-seeded species. In Trial 2, encapsulating seeds nearer the pellet periphery (relative to the centre) resulted in an average 28-fold increase in emergence for all 10 small-seeded species. For half of the small-seeded species trialled, emergence from the pellet periphery was equivalent to that of bare-seeded controls. Synthesis and applications: Collectively, our results demonstrate: (1) a positive relationship between seed mass and emergence under central-encapsulation, and (2) that emergence can be significantly improved for small-seeded species when seeds are positioned nearer the pellet periphery. Translation of these findings into practice can help optimise emergence outcomes for native species with different sized seeds and nuanced germination requirements.