Flowering phenology and height growth pattern are associated with maximum plant height, relative growth rate and stem tissue mass density in herbaceous grassland species

1. We hypothesize that flowering phenology correlates with plant height growth pattern and that the pattern is associated with functional traits including maximum plant height (Hmax), RGR, stem tissue mass density (SD), hollow ratio (proportion of central hollow of stem cross-sectional area) and leaf mass per area (LMA) in grassland herbaceous species. 2. We investigated plant height growth trajectories and flower phenology, and measured LMA, SD and hollow ratio for 25 herbaceous species including 20 dicot forb species and five monocot species in an old-field grassland of New England, USA. Hmax, RGR, T10 and T90 (Julian day when plant height was 10% and 90%Hmax respectively) were derived from a logistic function for each species and were analysed in relation to LMA and SD. 3. Hmax was positively correlated with T10, T90 and flowering onset time (Julian day when the first 10% of flowers were blossoming) across species and across evolutionary-correlated divergences. Early growing and flowering species were shorter than late ones, and species reaching Hmax earlier flowered earlier than their counterparts. 4. There was a positive relationship between T90 and RGR, in which early growing species were usually at mid-to-high levels of RGR, while late-growing ones had widely varied RGR. A similar relationship was found between flowering onset time and RGR. RGR was significantly negatively correlated with SD and LMA but positively with hollow ratio, as indicated by correlation analysis and phylogenetically independent comparative analysis. 5. Based on the above results, we propose that herbaceous species have two major dimensions of height growth strategies (early vs. late and fast vs. slow growth), collectively resulting in three extreme cases (early and fast, late and slow, and late and fast). Different height growth trajectories resulting from these strategies may reduce asymmetric competition among co-existing species in dense grasslands. 6. Synthesis. Flowering phenology and height growth patterns are significantly associated with functional traits such as RGR, LMA and hollow ratio in herbaceous grassland species. The difference in height growth trajectories and associated functional traits may allow species coexistence possibly at both plant and consumer trophic levels.