The leaf economics spectrum of Poaceae reflects variation in survival strategies

Leaf morphology reflects a trade-off between maximising resource acquisition and investment in structural/metabolic durability, and continuous variation in such leaf economics is apparent even within traditional plant functional type categories such as 'grasses'. We hypothesised that the leaf economics spectrum of 'grasses' reflects a spectrum of survival strategies, with functional divergence apparent both within and between ecozones. CSR classification and histology of 30 Poaceae with ranges restricted to either the southern Alps or Po plain of Italy demonstrated that alpine species were predominantly stress-tolerators (mean C:S:R = 26.7:46.1:27.2%) but included some competitive ruderals (e.g. Agrostis schraderana). Lowland species were predominantly competitive ruderals but included some stress-tolerators (e.g. Stipa pennata). Functional relationships were confirmed by PCA: PCA1 represented a trade-off between high SLA, high foliar N, rapid phenology (competitive ruderals) and high foliar C:N and dry matter content (stress-tolerators). Stress-tolerance was negatively correlated with the extent of intercellular airspace, and positively with mesophyll, schlerenchyma and vascular tissues (a trade-off between internal conductivity and durability). The leaf economics spectrum of Poaceae reflects a spectrum of whole plant function, but only the overall plant strategy can elucidate the extent to which vegetative or reproductive phases are critical for survival.