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12 páginas, 5 figuras, 2 tablas.-- et al., [Background and Aims]: Genome size is a function, and the product, of cell volume. As such it is contingent on ecological circumstance. The nature of ‘this ecological circumstance’ is, however, hotly debated. Here, we investigate for angiosperms whether stomatal size may be this ‘missing link’: the primary determinant of genome size. Stomata are crucial for photosynthesis and their size affects functional efficiency. [Methods]: Stomatal and leaf characteristics were measured for 1442 species from Argentina, Iran, Spain and the UK and, using PCA, some emergent ecological and taxonomic patterns identified. Subsequently, an assessment of the relationship between genome-size values obtained from the Plant DNA C-values database and measurements of stomatal size was carried out. [Key Results]: Stomatal size is an ecologically important attribute. It varies with life-history (woody species < herbaceous species < vernal geophytes) and contributes to ecologically and physiologically important axes of leaf specialization. Moreover, it is positively correlated with genome size across a wide range of major taxa. [Conclusions]: Stomatal size predicts genome size within angiosperms. Correlation is not, however, proof of causality and here our interpretation is hampered by unexpected deficiencies in the scientific literature. Firstly, there are discrepancies between our own observations and established ideas about the ecological significance of stomatal size; very large stomata, theoretically facilitating photosynthesis in deep shade, were, in this study (and in other studies), primarily associated with vernal geophytes of unshaded habitats. Secondly, the lower size limit at which stomata can function efficiently, and the ecological circumstances under which these minute stomata might occur, have not been satisfactorally resolved. Thus, our hypothesis, that the optimization of stomatal size for functional efficiency is a major ecological determinant of genome size, remains unproven., A considerable quantity of the data used in this project was collected during projects funded by respectively NERC (UK), the Research Institute of Forests and Rangelands (RIFR, Iran), Universidad Nacional de Córdoba, Comisión Interministerial de Ciencia y Tecnología (Spain) and the Darwin Initiative for the Survival of Species (DEFRA, UK).

The soil seed-banks in the main natural vegetation patches that make up mountain grasslands on granite substrates in central Argentina were studied. The main natural vegetation types are moist swards, tall-tussock grasslands and stony grasslands. Ten compound soil samples from each community at two soil depths (0-5 and 5-10 cm) were taken. The density of soil seed-banks was highest in moist swards, intermediate in stony grasslands and lowest in tall-tussock grasslands. Low levels of similarity were found between the established vegetation and total soil seed-bank in tall-tussock grasslands and stony grasslands, but the similarity was higher in swards. In all three communities the seed-bank was most frequently transient in nature. Short-term persistent and long-term persistent seed-banks were less frequent. Regeneration from the seed-banks after disturbance is expected to differ among communities on different edaphic patches. On the basis of the density and longevity of the soil seed-banks and the similarity to the established vegetation, potential for in sitar regeneration should be lower in tall-tussock grasslands, intermediate in stony grasslands and higher in moist swards.

We tested whether seed mass and shape are good predictors of seed persistence in the soil of subhumid temperate montane grasslands of central Argentina. We plotted seed mass against variance of seed dimensions of 71 herbaceous species and obtained information on their persistence in the soil from a previous experiment on germinable seed banks. We identified a certain seed mass/shape combination beyond which no seed was persistent in the soil, with the exception of the annualTagetes minuta. Our results confirmed the patterns previously reported for British species: small and compact seeds tend to persist in the soil for a longer time than big and elongated or flattened seeds. We suggest that the value of seed mass and shape as predictors of persistence in the soil can be extended beyond the British flora to herbaceous floras from other humid temperate regions.