Variation in light intensity, air temperature and relative air humidity leads to diurnal variations of photosynthetic rate
and leaf relative water content. In order to determine the diurnal changes in net photosynthetic rate of vine plants and
influence of the main environmental factors, gas exchange in the vine leaves were measure using a portable plant CO2
analysis package. The results show that diurnal changes in photosynthetic rate could be interpreted as single-peak
curve, with a maximum at noon (10.794 μmol CO2 m-2 s-1). Leaf relative water content has maximum value in the
morning; the values may slightly decrease during the day (day of June, with normal temperature, no rain, no water
restriction in soil).