putting seed traits into pellets: using seed mass data to improve seed encapsulation technology for native plant revegetation

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 ten 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 ten 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.

幼苗出苗率低下常常制约生态修复直接播种的成效。为实现联合国生态修复十年（UN Decade on Restoration）计划中的全球自然修复目标，亟需开发可提升种子利用效率与幼苗出苗率的新技术。挤出丸粒化种子（extruded pellets）在农业中应用广泛，亦是基于种子的生态修复领域极具前景的技术进展。然而，针对拥有不同种子大小与形态型的多样本土物种，仍需对挤出丸粒化种子进行优化适配。

本研究旨在探究，在用于植被恢复的挤出丸粒化种子包衣处理下，种子质量如何影响本土植物种子的出苗表现（幼苗总出苗率）。研究采用30种澳大利亚本土植物的种子开展了两项温室试验：试验1中将种子包埋于丸粒中心，以明确种子质量与出苗率之间的关联；试验2中将种子包埋于更接近丸粒边缘的位置，针对10个小种子物种子集，探究种子位置（中心 vs 边缘）对出苗率的影响。两项试验均将丸粒化种子的出苗表现与最优裸籽对照组进行对比，以明确水分充足条件下种子包衣的潜在限制因素。

试验1结果显示，当种子被包埋于丸粒中心时，裸籽对照组的出苗率普遍高于丸粒化种子。但当种子包埋于丸粒中心时，种子质量可显著预测出苗率（R²=0.32，p=0.002），即大种子物种的出苗率往往高于小种子物种。

试验2结果表明，将种子包埋于更接近丸粒边缘的位置（相较于中心位置），可使全部10个小种子物种的平均出苗率提升28倍。在受试的小种子物种中，有一半物种在丸粒边缘包埋处理下的出苗率与裸籽对照组相当。

综合与应用：本研究结果整体表明：① 种子中心包埋条件下，种子质量与出苗率呈正相关关系；② 将小种子物种的种子包埋于更接近丸粒边缘的位置，可显著提升其出苗率。将本研究发现转化为实践应用，有助于优化不同种子大小、且萌发需求存在细微差异的本土物种的出苗效果。