Efficiency and allometry of seed production in grassland forbs: site and year comparative study in the Italian Eastern Pre-Alps

Forbs are important biodiversity components of grasslands and are often threatened by management intensification. As most forbs propagate predominantly by seed, knowledge of their seed regenerative traits would improve the conservation and restoration of forb-rich ecosystems. The main seed production traits of six forbs that are common in European species-rich grasslands were studied by collecting fertile shoots from different sites and over several years. Among sites and years, variability was high, particularly in the number of inflorescences per shoot, which affected ovule production more than any other trait. Relationships between inflorescence size and the number of ovules were mainly negatively allometric or almost so, with lower flower densities in larger inflorescences. The average ovule-to-seed transformation efficiency was 58%. There was significant variation among collections of the same species, and even more between species. Species with a low ovule-to-seed transformation efficiency generally exhibited compensatory, high seed viability. Large inflorescences had high ovule to seed utilization values, probably because of better nutrient conditions. Seed germinability (average, 30%) was much lower than seed viability (average, 54%); therefore, seed dormancy was an important feature of the species studied.

杂类草（forbs）是草原生态系统生物多样性的核心组成部分，且常因管理集约化措施而面临生存威胁。鉴于多数杂类草主要通过种子进行繁殖，明晰其种子更新性状，有助于优化以杂类草为主的生态系统的保护与修复工作。本研究针对欧洲物种丰富草原中常见的6种杂类草，通过跨多个年份、多个样地采集其结实枝条，对其主要种子生产性状开展了系统研究。研究发现，样地与采集年份间的性状变异程度较高，其中单枝花序数的变异最为突出，其对胚珠产量的影响远超其余所有性状。花序大小与胚珠数量之间的关系主要呈负异速生长或近似负异速生长，即更大的花序其花朵密度更低。供试物种的平均胚珠向种子转化效率为58%。同一物种的不同采集批次间存在显著性状差异，且物种间的差异更为显著。胚珠向种子转化效率较低的物种，通常会表现出补偿性的高种子生活力。大型花序的胚珠转结种子利用率更高，这可能与其所处的更优越的营养条件有关。种子萌发率（平均为30%）远低于种子生活力（平均为54%），由此可见，种子休眠是本研究涉及物种的重要特征之一。