Net leaf photosynthetic and transpiration rates were determined, on cloudless days, by
enclosing a leaf held horizontally in a transparent cuvette (1000 cm 3) of the Li-COR
6200 Portable System (Nebraska, USA). Readings were repeated on six leaves per plot,
and measurements were repeated three times per leaf. Air temperature data provided by
the photosynthesis equipment were equivalent to values measured with a portable
Rotronich thermohygrometer (Switzerland) placed 1.3 m above the ground.