Altering root temperature does not directly effect photosynthetic rates in a temperate grassland community

Abstract

Air and soil temperatures are expected to rise by 1-3°C during the next century. Warmer soil temperatures could potentially alter both root growth and nutrient uptake, with consequent effects on shoot physiology, including carbon acquisition. A soil warming system was set up at the University of York experimental gardens and used to alter soil temperatures, independently of insolation, in a semi-natural temperature grassland ecosystem. Soil temperatures in the heated plots tracked ambient values, but were raised by 3°C. Shade treatments were also applied giving a total of 6 treatments each consisting of 4 replicates. The system was run continuously for 12 months. At intervals throughout this period photosynthetic rates of two species in the system, Plantago lanceolata and Holcus lanatus, were measured under saturating light (Asat). Additionally, CO2 and light curves were also measured during summer. Root growth was reduced in plots subjected to a shade treatment. Shoot responses of the two species to shade varied. Both species exhibited an increase in specific leaf area, with Plantago also exhibiting reduced stomatal conductance and transpiration. Despite the shoot responses to shade there was no effect of shading on Asat results for either species. Heating had no significant effect on any measured parameter. Both root growth and respiration acclimated to the increases in soil temperatures. There were also no shoot responses to temperature, neither in morphology nor in photosynthetic parameters. Light and CO2 curves indicated that capacity and efficiency were not effected by the different soil temperature regimes. These results will be discussed.