Due to increased reserves available to face adverse conditions, drought tolerance should increase with seed size. This has been confirmed in the laboratory, but under field conditions the pattern has not yet been found. We tested whether drought tolerance increases with seed size under field conditions in a semiarid grassland. We recorded the performance (germination, survival, and growth) of 12 species with different-sized seeds sown under conditions associated with hydric stress: along a natural stress gradient related to soil depth, and under experimentally manipulated irradiance levels that affected evaporation and thus soil humidity. We estimated drought tolerance indices for each performance metric, as well as a multivariate tolerance index that integrated the different components of performance. Each index was regressed on seed size accounting for phylogenetic effects. Seed size had little effect on individual metrics, but the joint evidence from all tests revealed a clear positive correlation with seed size. The multivariate tolerance index also increased with seed size, confirming the expected relationship. This suggests that comprehensive measures encompassing the whole life cycle may be required to characterize drought tolerance properly and may explain why this pattern has remained elusive in most studies. Also, we used a narrow range of seed sizes, so there is the possibility that the relationship between seed size and tolerance holds only for small-seeded species.

由于可用于应对不利条件的储备增加，因此抗旱性应随种子大小而增加。这已经在实验室中得到证实，但是在野外条件下还没有发现这种模式。我们测试了半干旱草原上田间条件下的耐旱性是否随种子大小的增加而增加。我们记录了在与水胁迫相关的条件下播种的12种不同大小种子的性能（发芽，存活和生长）：沿着与土壤深度相关的自然应力梯度，以及在实验控制的辐照度水平下影响蒸发并因此影响土壤湿度。我们估算了每个性能指标的干旱耐性指数，以及综合了不同性能成分的多元耐性指数。每个指标都根据种子大小回归，以反映系统发育效应。种子大小对个体指标影响不大，但是所有测试的联合证据显示，种子大小与种子大小呈明显正相关。多元耐受指数也随种子大小而增加，证实了预期的关系。这表明可能需要采用涵盖整个生命周期的综合措施来正确表征耐旱性，并且可以解释为什么这种模式在大多数研究中仍然难以捉摸。另外，我们使用的种子大小范围很窄，因此有可能种子大小和耐受性之间的关系仅适用于小种子物种。多元耐受指数也随种子大小而增加，证实了预期的关系。这表明可能需要采用涵盖整个生命周期的综合措施来正确表征耐旱性，并且可以解释为什么这种模式在大多数研究中仍然难以捉摸。另外，我们使用的种子大小范围很窄，因此有可能种子大小和耐受性之间的关系仅适用于小种子物种。多元耐受指数也随种子大小而增加，证实了预期的关系。这表明可能需要采用涵盖整个生命周期的综合措施来正确表征耐旱性，并且可以解释为什么这种模式在大多数研究中仍然难以捉摸。另外，我们使用的种子大小范围很窄，因此有可能种子大小和耐受性之间的关系仅适用于小种子物种。