Does greater night-time, rather than constant, warming alter growth of managed pasture under ambient and elevated atmospheric CO2?

This study examined the effects of warming, elevated atmospheric CO2 and cutting regimen on the growth of Phalaris aquatica cv. Holdfast swards. Six temperature gradient tunnels (TGT) were used to manipulate both air temperature and atmospheric CO2 concentrations (ambient and 750 ppm). Within each tunnel, there were three temperature treatments: no warming, constant warming of +3.0degreesC and a daytime warming of 2.2degreesC combined with a night-time warming of 4.0degreesC and two defoliation frequencies. Averaged across 20 months of growth, there was a positive effect of elevated atmospheric CO2 (+11%), no effect of either warming treatment and a negative effect of frequent cutting (-19%) on total above ground biomass production. The responses to all treatments, however, were strongly seasonal. Positive responses to CO2 were statistically significant only in the spring, when plant growth was strongest. No evidence was found that high night-time warming had different effects on plant growth and plant responses to elevated atmospheric CO2, than constant warming.