Photosynthesis data for Calluna vulgaris, Vaccinium myrtillus and Empetrum nigrum at the Climoor field site in Clocaenog Forest (2001 - 2007)

Photosynthesis was measured with a CIRAS-2 infrared gas analyser between 11 am and 3 pm using a standard leaf cuvette with a light source. The tip was inserted in the cuvette and remained there until photosynthesis and transpiration rates were seen to equilibrate.

Two of the three plant species have three dimensional leaves, and data on leaf mass is included to facilitate the standardization of measurements between differently sized leaves (determining leaf area is not possible currently for three dimensional leaves). The plant leaves/branches photosynthesis was measured on were sampled and dried at 65 degrees Celsius to determine the leaf mass and area. Non-flowering and non-fruiting, sun-exposed tips were used for all measurements.

Data is recorded in the CIRAS in the field, and downloaded into excel files which were stored in CEH Bangors shared file area.

1) Photosynthesis response curves were measured in 2002 and 2003 on Calluna vulgaris and Vaccinium myrtillus. For light response curves (Photosynthesis vs. light (PAR) response), photosynthetic active radiation (PAR) was reduced from 1200 or 1000 photons m-2 s-1 to 20 photons m-2 s-1 at constant Ci (internal CO2 concentration). For A/Ci responses (Photosynthesis vs. internal CO2 concentration), Ci was reduced starting between 800 and 400 µmol mol-1. On 04/04/2002, three light response curves were measured in each plot. After that, only one response curve was measured in each plot.
In the dataset ?Photosynthesis_response_Clocaenog.csv?, values for ?Stomatal conductance? (mmol m-2 s-1) and ?Internal CO2 concentration? (Ci, µmol mol-1) above 1000 are considered unreliable.

2) Photosynthesis was measured at a fixed Ci and PAR by different members of CEH staff in 2001, 2002, 2003, 2005 and 2007. In 2001, photosynthesis was measured on C. vulgaris, V. myrtillus and Empetrum nigrum. PAR was 1000 µmol photons m-2 s-1 from ambient light or from halogen lamps if ambient PAR was lower. Data from 2002 and 2003 were extracted from photosynthesis response curves measured on C. vulgaris and V. myrtillus at 1000 µmol photons m-2 s-1. Data from 2005 were measured for only control and drought treatments on all 3 plant species at 1000 µmol photons m-2 s-1 and a CO2 concentration of 350 ppm. In 2005, photosynthesis was measured in all climate treatments on healthy, fungal infected or herbivory affected V. myrtillus leaves. Herbivory is reflected in the leaf mass and area. Measurements were taken at a PAR of 800 µmol photons m-2 s-1 and near ambient CO2 concentration of 400 ppm.