Effects of elevated CO₂, nitrogen and phosphorus on the growth and photosynthesis of two upland perennials: Calluna vulgaris and Pteridium aquilinum

Abstract

Bracken (Pteridium aquilinum (L.) Kuhn) and heather (Calluna vulgaris (L.) Hull) are important upland species which often grow in close proximity in the UK. The effects of factorial treatments of elevated atmospheric CO₂ (539 μmol mol⁻¹ as opposed to ambient atmospheric CO₂ concentrations of 355 μmol mol⁻¹), added N (50 kg N ha⁻¹ as NH₄NO₃) and added P (20 kg P ha⁻¹ as NaH₂PO₄) on the performance of these two species were studied under controlled environmental conditions using container-grown plants. Plants grown and measured at high CO₂ had higher rates of net photosynthesis than those grown and measured in ambient CO₂ . This increase was greater in heather than in bracken and resulted in a large stimulation of growth in the former. In bracken there was no significant change in plant size or phenology. The increase in biomass of heather in high CO₂ was greatest in the absence of added nutrients and lowest when both N and P were supplied. The growth and photosynthesis of both plants responded positively to the supply of P alone or P with N (in both CO₂ atmospheres), but there was little response to N alone. The implications of these findings for bracken and heather growing in the field under conditions of an elevated CO₂ atmosphere and greater nutrient availability are discussed.