Inflorescences contribute more than rosettes to lifetime carbon gain in Arabidopsis thaliana (Brassicaceae)

Abstract

A metamorphosis from rosette to inflorescence in many annuals shifts photosynthetic tissue from a two-dimensional array in the soil boundary layer during cool months to a three-dimensional structure in the troposphere as spring progresses. We propose that this shift allows escape from both self-shading and an increasingly stressful boundary layer microclimate, permitting continued increases in growth. As a first step in exploring this hypothesis, we compared the lifetime C gain, water loss, and instantaneous water use efficiency (WUE) of five Arabidopsis thaliana genotypes by measuring gas exchange across the life cycle. On average, the inflorescence contributed 55% (± 5% SE) of lifetime C gain, but only 25% of lifetime water loss. Mean inflorescence WUE was nearly fourfold that of the rosette. The inflorescence continued to fix C after rosette senescence. The percentage inflorescence: total C gain varied among genotypes, from 36% to 93%. Genotypes differed in WUE for both structures. We suggest that local climates may have selected for divergence in these traits. For many annuals and winter annuals, understanding C and water budgets and their evolution must include measures of both rosette and inflorescence gas exchange.

Ontogenetic changes in tolerance to herbivory in Arabidopsis

“…Similarly, stems may contribute to tolerance by providing additional photosynthetic area directly or through the cauline leaves they support, which, in turn, provide continuous assimilation during the reproductive stage of plants (Mooney et al 1995;Stevens et al 2008;Tiffin 2000). In fact, it was shown recently that the inflorescence contributes 36-93% of the lifetime C gain in Arabidopsis (Earley et al 2009), depending on the accession. This partly explains the positive association between stem biomass and compensatory ability, and the differences among accessions found in our study, since most of the stem mass of Arabidopsis corresponds to the inflorescence, and accessions vary in their inflorescence:rosette size ratio.…”

“…Greater tolerance at the 1st-flower stage could be achieved through the translocation of stored resources from stem to reproductive tissue elicited by the combined demand of resources from the developing reproductive tissue and the loss of foliar tissue to herbivores. Alternatively, it could be explained by the lower fitness value of the older (rosette) leaves at a time at which cauline leaves are already contributing most of the C (and presumably the transpiration that drives mineral nutrient acquisition) needed for the production of reproductive tissue (Barto and Cipollini 2005;Earley et al 2009). …”

The evolution of competitive strategies in annual plants

“…The green inflorescence stems of Arabidopsis can account for a significant proportion of total photosynthesis (Earley et al 2009). Arabidopsis growth form mutants that produce small rosettes but high allocation to leaves on upright inflorescences had high fitness under simulated competition for light, but low fitness in high-light environments (Bonser and Geber 2005).…”

Is ‘peak N’ key to understanding the timing of flowering in annual plants?

“…Flowering is therefore defined as the switch from the production of leaves to the production of reproductive tissues and can be equated roughly with bolting. For simplicity, we assume that reproductive tissues are nonphotosynthetic and hence do not contribute to C fixation (although we acknowledge that this assumption is violated by at least some annual species; Earley et al, 2009). After flowering, the plant's growth rate will, as before, be the smaller of the rootand leaf-limited growth rates G root (t) and G leaf (t), although all of this growth is now invested in reproductive mass.…”