Germination data for nurse-plant effects on the seed biology and germination of desert annuals

Simplified data for the Austral Ecology paper here: http://onlinelibrary.wiley.com/doi/10.1111/aec.12144/abstract AbstractNurse-plants generally have positive effects on understorey species by creating more suitable conditions for stress-intolerant plants relative to open micro-habitats. However, long-term effects of this plant–plant facilitation system have been rarely examined. Seeds of five desert annual species from Atiquipa coastal desert in Southern Peru were used to examine whether different microenvironmental conditions under the nurse-plants Caesalpinia spinosa Molina (Kuntze) lead to differences in seed biology and germinability of annual plants relative to open, canopy-free conditions. Seeds collected from plants associated with nurse-plants were predicted to be (i) larger due to more favourable growing conditions, (ii) more viable and with greater germination rates, (iii) less variable in size and viability due to reduced environmental heterogeneity, and (iv) to germinate faster to avoid apparent competition with other annuals. Seed attribute measurements and germination trials in growth chambers were used to test these predictions. Although the plant abundance of only 2 of 5 species was strongly facilitated by the nurse-plant, no significant differences were found in seed mass, viability or relative variability between understorey and open micro-habitats for any of the species. Contrary to our predictions, final seed germination rates of seeds from open micro-habitats were higher, and the open micro-habitat treatment was more favourable for germination of seeds from both open and understorey environments. Taken together, these results suggest that plant–plant facilitation does not necessarily affect seed biology traits. Further studies addressing larger distribution ranges and/or density gradients of understorey species will illuminate the potential evolutionary effects of nurse-plants.本数据集为《Austral Ecology》期刊论文的简化数据，原文链接：http://onlinelibrary.wiley.com/doi/10.1111/aec.12144/abstract。【摘要】护助植物（nurse plants）通常通过为不耐胁迫植物创造比开阔微生境（open micro-habitats）更适宜的生存条件，对下层植物（understorey species）产生正向促进作用。然而，该植物间促进作用（plant–plant facilitation）系统的长期效应却鲜有研究。本研究以秘鲁南部阿蒂基帕沿海沙漠的5种沙漠一年生植物种子为材料，探究护助植物刺云实（Caesalpinia spinosa Molina (Kuntze)）下方的微环境与无冠层的开阔微生境之间的差异，是否会导致一年生植物的种子生物学特性及发芽能力（germinability）产生不同。我们针对从护助植物伴生植株上采集的种子提出以下假设：其一，由于生长条件更优越，种子体积更大；其二，种子活力（viability）更高、发芽率（germination rates）更强；其三，因环境异质性（environmental heterogeneity）降低，种子大小与活力的变异程度更低；其四，种子发芽速度更快，以规避与其他一年生植物的表观竞争（apparent competition）。本研究通过测定种子属性指标，并在人工气候箱（growth chambers）中开展发芽试验，对上述假设进行验证。尽管5个物种中仅2种的植株丰度（plant abundance）受到护助植物的显著促进，但所有物种的种子质量、活力以及相对变异程度，在下层生境与开阔微生境之间均未呈现显著差异。与我们的假设相悖的是，来自开阔微生境的种子最终发芽率更高，且开阔微生境处理对取自开阔生境与下层生境的种子发芽均更为有利。综合来看，本研究结果表明，植物间的促进作用未必会对种子生物学特性产生影响。未来可针对下层植物更大的分布范围及/或密度梯度（density gradients）开展研究，以进一步阐明护助植物的潜在进化效应（evolutionary effects）。