Studies of variation in plant environmental factors of Kinnow mandarin for at Agriculture Research Station, SriGanganagar district of Rajasthan state in India during 2002-04 with respect to three differential irrigation treatments revealed that overall maximum carboxylation efficiency (A) was estimated at 70% Etc treatment from April to June with a linear trend. It showed depression in September and October followed by a steady rise in November and December months. Stomatal conductance revealed oscillating trend with maximum in 70% Etc treatment for April and May months followed by steep rise in 40% Etc treatment for June-July. It remained static in August and September, but a trend reversal occurred in October-November with maximum stomatal conductance in 100% Etc treatment. The cumulative overall high stomatal resistance in 40% treatment might have attributed to low photosynthetic rates followed by 100% treatment and the better assimilation rates were observed under 70% treatment and were correlated with low rates of stomatal resistance. The daily course of transpiration in all the three irrigation treatments was not closely linked to solar irradiation but rather to leaf temperature. Temperatures of 25-30degreesC are optimal for photosynthesis but temperatures above 30degreesC definitely reduce photosynthetic activity. The annual trend for three consecutive years' data revealed occurrence of cyclic oscillations in photosynthesis, stomatal conductance, stomatal resistance, transpiration rate and photosynthetic active radiation under field conditions. Citrus belong to C3 plants, with photosynthetic rates lower than C4 plants. Assimilation rates ranging from 1.28 to 7.93 mmol m -2 s -1 observed under differential irrigation treatments seem realistic under optimal irrigated conditions of Western Rajasthan.
