Área de Botánica, Departamento de Ciencias Agroforestales, Escuela de Ingenierías Agrarias, Univ. de Valladolid, Los Pajaritos s/n, ES-42003 Soria, Spain.
Ann Bot. 2012 Jan;109(1):299-307. doi: 10.1093/aob/mcr260. Epub 2011 Oct 16.
Seed banks are critical in arid ecosystems and ensure the persistence of species. Despite the importance of seed banks, knowledge about their formation and the extent to which a seed bank can recover after severe perturbation remains scarce. If undisturbed, soil seed banks reflect a long vegetation history; therefore, we would expect that new soil seed banks and those of undisturbed soils require long periods to become similar with respect to both density and composition. In contrast, if soil seed banks are only a short- to mid-term reservoir in which long-term accumulation constitutes only a tiny fraction, they will recover rapidly from the vegetation. To shed light on this question, we evaluated seed bank formation in a semi-arid gypsum community.
Soils from 300 plots were replaced with sterilized soil in an undisturbed semi-arid Mediterranean community. Seasonal changes in seed bank density and composition were monitored for 3 years by comparing paired sterilized and control soil samples at each plot.
Differences in seed bank density between sterilized and control soil disappeared after 18 months. The composition of sterilized seed banks was correlated with that of the control plots from the first sampling date, and both were highly correlated with vegetation. Nearly 24 % of the seed bank density could be attributed to secondary dispersal. Most seeds died before emergence (66·41-71·33 %), whereas the rest either emerged (14·08-15·48 %) or persisted in the soil (14·59-18·11 %).
Seed banks can recover very rapidly even under the limiting and stressful conditions of semi-arid environments. This recovery is based mainly on the seed rain at small scales together with secondary dispersal from intact seed banks in the vicinity. These results emphasize the relevance of processes occurring on short spatial scales in determining community structure.
种子库在干旱生态系统中至关重要，可确保物种的存续。尽管种子库非常重要，但有关其形成以及种子库在受到严重干扰后能够恢复的程度的知识仍然匮乏。如果不受干扰，土壤种子库反映了长期的植被历史；因此，我们预计新的土壤种子库和未受干扰土壤的种子库在密度和组成方面需要很长时间才能变得相似。相比之下，如果土壤种子库只是一个短期到中期的储库，长期积累仅构成一小部分，那么它们将从植被中迅速恢复。为了阐明这个问题，我们评估了半干旱石膏群落中的种子库形成。
在未受干扰的半干旱地中海群落中，用无菌土壤替换了 300 个样地的土壤。通过在每个样地比较配对的无菌和对照土壤样本，监测了 3 年内种子库密度和组成的季节性变化。
无菌土壤和对照土壤之间的种子库密度差异在 18 个月后消失。无菌种子库的组成与对照样地的第一个采样日期相关，且两者都与植被高度相关。种子库密度的近 24%可归因于二次扩散。大多数种子在萌发前死亡（66.41-71.33%），其余的要么萌发（14.08-15.48%），要么在土壤中存活（14.59-18.11%）。
即使在半干旱环境的限制和压力条件下，种子库也可以迅速恢复。这种恢复主要基于小尺度上的种子雨，以及附近完整种子库的二次扩散。这些结果强调了短空间尺度上发生的过程在确定群落结构方面的重要性。
