Foliar nutrients in relation to growth, allocation and leaf traits in seedlings of a wide range of woody plant species and types

Abstract

This study aimed to identify functional correlates of seedling leaf nutrient content among woody species and to characterise functional species groups with respect to leaf nutrient attributes. Seedlings of 81 woody species from the temperate zone of western Europe were grown in a standard laboratory environment with standard, near-optimal nutrient availability. Weight-based leaf N content (N_wght) was positively correlated with mean relative growth rate (RGR), but the correlation with mean RGR was tighter when leaf N was expressed on a whole-plant weight basis: leaf nitrogen weight ratio (LNWR). Area-based leaf N content (N_area) was not associated with mean RGR, but was closely correlated with the quotient of saturated leaf weight and leaf area. Weight-based leaf K content (K_wght) was a close correlate of the saturated/dry weight ratio of the foliage. Within the lower range, K_wght corresponded with growth-related nutrient attributes, but higher values appeared to indicate succulence or remobilisable stored water. Functional groups of species and genera could be distinguished with respect to seedling leaf nutrient attributes. Deciduous woody climbers and scramblers had consistently higher leaf N_wght, LNWR and (apparently) leaf K_wght than other deciduous species or genera, and shrubs had higher values than trees. These differences seemed due partly to variation in specific leaf area. Evergreens had consistently higher leaf N_area than deciduous plants, but there were no significant differences in weight-based leaf nutrient attributes between these two groups, possibly because of `luxury nutrient consumption' by the slow-growing evergreens. Another functional group was that of the nitrogen-fixing species, which had consistently high innate leaf N_wght compared to non-N-fixers. The ecological significance of the leaf nutrient attributes in this study is discussed by comparing the seedling data with those from field-collected material, and by brief reference to the natural habitats of the species.