Nutrient availability induces contrasting allocation and starch formation in resprouting and obligate seeding shrubs

1. Woody plant responses to crown removal in fire-prone vegetation are of two types: resprouting (resprouters) or killed (obligate seeders). Obligate seeders maximize their fitness by ensuring they are reproductively mature before the next fire; resprouters invest in structures that increase their chance of surviving the next fire. 2. We tested whether seven congeneric pairs of resprouter and obligate seeder shrubs differ in plant size, leaf traits, water relations, biomass allocation and root starch formation in response to resource availability. This was tested by examining the interactive effects of water and nutrient availability in a factorial experiment. 3. Plant size (dry mass and shoot length), leaf area and stomatal conductance did not differ consistently among resprouters and obligate seeders, but were affected by water and nutrient availability. Leaf-area ratio and specific leaf area were not affected consistently by nutrient or water availability, and did not differ among obligate seeders and resprouters. 4. Biomass allocation responded to resource availability and differed between resprouter and obligate seeder pairs. Nutrient addition reduced allocation to root mass, and resprouters consistently allocated more than obligate seeders to root mass. Leaf mass ratios were higher in obligate seeders, and were maintained at the expense of stem mass when nutrients limited growth. 5. Starch concentrations in the roots of resprouters were higher than in obligate seeders. Resprouters increased the concentration of starch in their roots when growth was limited by nutrients, but obligate seeders did not. Resprouters appear to develop a starch-storage capacity through both reserve formation and accumulation mediated by nutrient availability. 6. Allocation, rather than growth differences, provide some insight into why resprouters are often more common than obligate seeders, especially on fertile sites. Seedlings of resprouters may be advantaged at fertile sites because allocation to roots and starch reserve formation enable them to be better competitors after fire. We predict that the interplay of biomass allocation, reproduction, starch storage and disturbance frequency provide a framework for patterns of coexistence in shrubs in fire-prone ecosystems.