Global change factors affect plant carbon uptake in concert. In order to investigate the response directions and
potential interactive effects, and to understand the underlying mechanisms, multifactor experiments are needed.
The focus of this study was on the photosynthetic response to elevated CO2 [CO2; free air CO2 enrichment
(FACE)], drought (D; water-excluding curtains), and night-time warming (T; infrared-reflective curtains) in
a temperate heath. A/Ci curves were measured, allowing analysis of light-saturated net photosynthesis (Pn), lightand
CO2-saturated net photosynthesis (Pmax), stomatal conductance (gs), the maximal rate of Rubisco
carboxylation (Vcmax), and the maximal rate of ribulose bisphosphate (RuBP) regeneration (Jmax) along with leaf
d13C, and carbon and nitrogen concentration on a monthly basis in the grass Deschampsia flexuosa. Seasonal
drought reduced Pn via gs, but severe (experimental) drought decreased Pn via a reduction in photosynthetic
capacity (Pmax, Jmax, and Vcmax). The effects were completely reversed by rewetting and stimulated Pn via
photosynthetic capacity stimulation. Warming increased early and late season Pn via higher Pmax and Jmax.
Elevated CO2 did not decrease gs, but stimulated Pn via increased Ci. The T3CO2 synergistically increased plant
carbon uptake via photosynthetic capacity up-regulation in early season and by better access to water after
rewetting. The effects of the combination of drought and elevated CO2 depended on soil water availability, with
additive effects when the soil water content was low and D3CO2 synergistic stimulation of Pn after rewetting. The
photosynthetic responses appeared to be highly influenced by growth pattern. The grass has opportunistic water
consumption, and a biphasic growth pattern allowing for leaf dieback at low soil water availability followed by
rapid re-growth of active leaves when rewetted and possibly a large resource allocation capability mediated by the
rhizome. This growth characteristic allowed for the photosynthetic capacity up-regulations that mediated the
T3CO2 and D3CO2 synergistic effects on photosynthesis. These are clearly advantageous characteristics when
exposed to climate changes. In conclusion, after 1 year of experimentation, the limitations by low soil water
availability and stimulation in early and late season by warming clearly structure and interact with the
photosynthetic response to elevated CO2 in this grassland species.