Plant size is related to biomass partitioning and stress resistance in water-limited annual plant communities

Plant functional traits are used increasingly for linking environmental conditions, community structure and ecosystem function. Traits associated with rapid resource capture may come at the expense of those related to stress resistance. In annual plants, such a tradeoff may be reflected through plant size (biomass) vs. biomass partitioning patterns, as the former represents resource capture rate while the latter represents reorganization to cope with resource stress. In a water-limited annual plant community we investigated: 1) the effects of water and nitrogen availability on plant size and biomass partitioning, i.e., biomass partitioning between organs (root to shoot ratio, R/S, and reproductive effort, Rep/Veg), and biomass partitioning in space (specific leaf area, SLA), 2) the relationship between plant size and biomass partitioning at both the interspecific and intraspecific level, and 3) the relationships between plant size and biomass partitioning strategy and stress resistance. Eight key species varying in their natural size range were grown under variable water and nitrogen availability and their size and biomass partitioning were monitored throughout their growth and at fixed phenological phases. In all species, reduced water and/or nitrogen availability was associated with smaller size, increased R/S, and decreased SLA while Rep/Veg remained constant. At the intraspecific level, plant size was negatively related to R/S and positively related to SLA. At the interspecific level, no relationship was found between size or stress resistance and any of the biomass-partitioning traits or their plasticity. However, species size was negatively related to stress resistance. This tradeoff between species size and stress resistance emerges as a consistent property of fundamental importance in shaping annual plant communities along resource gradients.