While the effects of seed size on survival and early seedling growth have been demonstrated in Quercus spp., there is a knowledge gap regarding these effects under water limiting conditions. To address this need, we studied cork oak (Quercus suber L.) seedling development among treatments including three acorn classes (small: < 4 g, intermediate: 4–6 g), and large: ≥ 6 g) and two water regimes (well-watered versus water stressed). The following hypotheses were proposed: the reserve effect (larger seeds retain a larger proportion of reserves after germinating), the metabolic effect (seedlings from larger seeds have slower relative growth rates), the seedling-size effect (larger seeds produce larger seedlings), and that plant tolerance to water stress increases with increasing seed size. Acorn size had no effect on duration and rate of acorn germination nor on seedling survival, but it significantly affected almost all growth parameters, excepting the number of growth unit and leaves and leaf area. Seedlings coming from large acorns always showed the highest values for the affected growth parameters, followed by those coming from acorns of intermediate size; seedlings coming from small acorns always exhibited the lowest values. Water stress significantly affected survival rate (88.2% for well-watered seedlings versus 64.7% for water stressed seedlings) and biomass of fine roots and stems, but independently of acorn size. Our results are in line with both hypothesizes of the reserve effect and seedling-size effect, but not for the metabolic effect nor the plant tolerance to water stress increases with increasing seed size hypotheses. In general, our results show that large acorns had no advantage in survival or seedling growth under water stress comparatively to intermediate or small acorns, at least under the conditions of our experiment.

中文翻译：

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橡子大小对水分胁迫下栎树幼苗存活和生长的影响

虽然已经在栎属植物中证明了种子大小对存活和早期幼苗生长的影响，但在水分限制条件下，关于这些影响存在知识空白。为了满足这一需求，我们研究了软木橡树 (Quercus suber L.) 幼苗在处理中的发育情况，包括三个橡子类（小：< 4 克，中：4-6 克）和大：≥ 6 克）和两种水制度（充分浇水与水压力）。提出了以下假设：储备效应（较大的种子在发芽后保留较大比例的储备）、代谢效应（较大种子的幼苗相对生长速度较慢）、幼苗大小效应（较大的种子产生较大的幼苗）、并且植物对水分胁迫的耐受性随着种子大小的增加而增加。橡子大小对橡子发芽的持续时间和速率以及幼苗存活率没有影响，但它显着影响几乎所有生长参数，除了生长单位和叶数和叶面积。来自大橡子的幼苗总是显示出受影响的生长参数的最高值，其次是来自中等大小的橡子；来自小橡子的幼苗总是表现出最低值。水分胁迫显着影响存活率（水分充足的幼苗为 88.2%，水分胁迫的幼苗为 64.7%）和细根和茎的生物量，但与橡子大小无关。我们的结果符合储备效应和幼苗大小效应的假设，但不是因为代谢效应或植物对水分胁迫的耐受性随着种子大小的增加而增加。总的来说，我们的结果表明，至少在我们的实验条件下，与中等或小橡子相比，大橡子在水分胁迫下在存活或幼苗生长方面没有优势。