Results and discussion
The mean air temperature for the period of June 1 through
September 30 was 22.2 ◦C in 2009, and 23.6 ◦C in 2011, compared
with a 20 year mean of 22.8 ◦C. Precipitation for that period totaled
310 mm in 2009, and 438 mm in 2011, compared with the longterm
mean of 409 mm. Photosynthetically active radiation over the
same period averaged 26.0 mol m−2 d−1 in 2009 and 25.1 in 2011,
compared with the 20-year mean of 25.6 mol m−2 d−1. Thus neither
year was substantially abnormal for the region in terms of temperature,
rainfall or radiation. Dates for the measurement of leaf gas
exchange were chosen such that soil moisture was not limiting