Is Partitioning of Dry Weight and Leaf Area Within Dactylis glomerata Affected by N and CO2Enrichment?

Abstract

We examined changes in dry weight and leaf area within Dactylis glomerata L. plants using allometric analysis to determine whether observed patterns were truly affected by [CO2] and N supply or merely reflect ontogenetic drift. Plants were grown hydroponically at four concentrations of<$>{\\rm NO}^{\\minus}_{3}<$>in controlled environment cabinets at ambient (360μll−1) or elevated (680μll−1) atmospheric [CO2]. Both CO2and N enrichment stimulated net dry matter production. Allometric analyses revealed that [CO2] did not affect partitioning of dry matter between shoot and root at high N supply. However, at low N supply there was a transient increase in dry matter partitioning into the shoot at elevated compared to ambient [CO2] during early stages of growth, which is inconsistent with predictions based on optimal partitioning theory. In contrast, dry matter partitioning was affected by N supply throughout ontogeny, such that at low N supply dry matter was preferentially allocated to roots, which is in agreement with optimal partitioning theory. Independent of N supply, atmospheric CO2enrichment resulted in a reduction in leaf area ratio (LAR), solely due to a decrease in specific leaf area (SLA), when plants of the same age were compared. However, [CO2] did not affect allometric coefficients relating dry weight and leaf area, and effects of elevated [CO2] on LAR and SLA were the result of an early, transient stimulation of whole plant and leaf dry weight, compared to leaf area production. We conclude that elevated [CO2], in contrast to N supply, changes allocation patterns only transiently during early stages of growth, if at all.