Effects of long-term exposure to elevated CO2 and increased nutrient supply on bracken (Pteridium aquilinum)

1. Bracken (Pteridium aquilinum) is an important fern with a global distrib ution. Little is known of the response of this species to elevated CO2. We investigated the effects of high CO2 (570 compared with 370 mu mol mol(-1)) with and without an increased nutrient supply (a combined N, P, K applicat ion) on the growth and physiology of bracken, growing in containers in cont rolled-environment glasshouses, over two full growing seasons. Results of g rowth and physiology determinations are reported for the second season. 2. Elevated CO2 had little impact on the growth or allocation of dry mass i n bracken. No significant changes were detected in dry mass of the total pl ant or any of the organs: rhizomes, roots and fronds. In contrast to the sm all effects of high CO2 the high nutrient treatment caused a three-fold sti mulation of total plant dry mass and an increase in the allocation of dry m ass to above ground when compared with low nutrient controls. 3. Net photosynthetic rates in saturating light were increased by both high CO2 and nutrient treatments, particularly in spring months (May and June). Growth in elevated CO2 did not cause a down-regulation in light-saturated rates of photosynthesis. The increased carbon gain in the high CO2 treatmen ts was accompanied, in the low-nutrient plants, by higher concentrations of carbohydrates. However, in high-nutrient plants the CO2 treatment did not cause an accumulation of carbohydrates. The absence of a growth response to elevated CO2 in bracken despite significant increases in photosynthesis re quires further investigation.