Trait divergence along the rainfall gradient
Eight traits showed significant clinal trends across the natural rainfall gradient, suggesting an adaptive role for these traits with rainfall. Towards drier sites, plants decreased in germination fraction, days to flowering, stomata density, height, and biomass, and they increased in reproductive allocation and seed production (Table 2, Fig. 1). Furthermore, flowering started at smaller plant size (fewer leaves) in drier sites, although at MM, plants invested less in lateral branches and thus possessed fewer but larger leaves along the main stem (Petrů et al . 2006; pers. obs.). There was a marginally significant tendency towards lowerδ 13C in arid sites (p=0.08, Fig. 1) and no clinal trend for diaspore weight despite significant differences among sites (Table 2, Fig. 1).
The clinal trends across sites in flowering time, leaf number at flowering and reproductive allocation matched the direction of their rapid evolutionary response within ten years climate manipulation. In contrast, five traits showed clines along the natural rainfall gradient but no rapid evolution under climate manipulations (germination fraction, stomata density, height, biomass, seed number).
The five water levels in the greenhouse affected all traits (Table 1 & 2; Fig. S1 supp. information), indicating plasticity in response to water. Clearly significant site × water interactions for all traits except reproductive allocation (p=0.08) indicated genetic variation in trait plasticity among sites (Table 2).