Two adaptive strategies to face variable environments have been proposed for annual plants in deserts: delayed and plastic (predictive) germination. All theories and models have been formulated based on studies on winter annuals, although half of the world deserts have summer annuals. We conducted an experiment to quantify the response of summer annual communities located along an altitudinal gradient (proxy for aridity gradient) to simulated precipitation levels. We expected to find increasingly lower germination fractions (more conservative) as we moved from the highest (less arid) area to the lowest (more arid) area, and also higher germination thresholds in the more arid end of the gradient. The experiment was implemented with two variables: altitude (2900, 3150, 3400 and 3600 m a.s.l.) and simulated precipitation (20, 40, 60, and 80 mm). The full generalized linear model showed that the number of seedlings was related to precipitation, altitude, and their interaction. The number of seedlings was positively related to the precipitation: more seedlings germinated in the less arid sites, and their slopes were steeper, suggesting stronger effects of precipitation in less arid areas. These results supported our first prediction: seed banks from the drier area tend to have more conservative germination responses. We also found a plastic behavior in all four altitudes. Our results show that summer-annuals may utilize both survival strategies as a way to cope with environmental uncertainty.

已经针对沙漠中的一年生植物提出了两种面对可变环境的适应性策略：延迟发芽和可塑性（预测性）发芽。所有理论和模型都是根据对冬季年的研究得出的，尽管世界上一半的沙漠都有夏季年。我们进行了一项实验，以量化沿海拔梯度（干旱梯度的代理人）的夏季年度群落对模拟降水水平的响应。随着我们从最高（干旱程度）最低的区域移到最低（干旱程度最高）的区域，并且在梯度更干旱的末端也出现了较高的发芽阈值，我们期望发现发芽分数越来越低（更保守）。实验使用两个变量进行：海拔高度（2900、3150、3400和3600 m asl）和模拟降水量（20、40、60和80 mm）。完全的广义线性模型表明，幼苗的数量与降水，海拔及其相互作用有关。幼苗的数量与降水量成正比：在较少干旱的地区发芽的幼苗更多，它们的坡度更陡，表明在较少干旱的地区降雨的影响更大。这些结果支持了我们的第一个预测：干燥地区的种子库往往具有更保守的发芽反应。我们还发现了在所有四个高度上的塑性行为。我们的结果表明，夏季每年可能会利用两种生存策略来应对环境不确定性。干旱少的地方发芽的种子更多，其坡度更陡，表明干旱少的地区降雨的影响更大。这些结果支持了我们的第一个预测：干燥地区的种子库往往具有更保守的发芽反应。我们还发现了在所有四个高度上的塑性行为。我们的结果表明，夏季每年可能会利用两种生存策略来应对环境不确定性。干旱少的地方发芽的种子更多，其坡度更陡，表明干旱少的地区降雨的影响更大。这些结果支持了我们的第一个预测：干燥地区的种子库往往具有更保守的发芽反应。我们还发现了在所有四个高度上的塑性行为。我们的结果表明，夏季年度可能将两种生存策略都用作应对环境不确定性的一种方式。