Field comparisons of photosynthesis and leaf conductance in Ziziphus mauritiana and other fruit tree species in Zimbabwe.
Clifford S. C., Kadzere I., Jones H. G., Jackson J. E.
Author Affiliation: Horticulture Research International, Wellesbourne, Warwick CV35 9EF, UK.
Trees: Structure and Function 11 : 449-454
Abstract : Z. mauritiana has potential as a drought tolerant fruit crop. Data are presented for gas exchange in exposed leaves in field-grown Z. mauritiana at a highland site and potted seedlings at a hotter lowland site in tropical Zimbabwe, together with indigenous and locally-grown commercial fruit crops. The field trial at the highland site included local Z. mauritiana (known as Musau), introduced Indian Z. mauritiana (cv. Umran), figs and peaches. The lowland trial included Musau, indigenous crops, mangoes (cv. Irwin), Strychnos spinosa and Sclerocarya birrea. Assimilation was highest early in the morning, followed by a gradual decline throughout the remainder of the day. Leaf conductance followed the same trend as assimilation for figs and peaches, but in both Z. mauritiana accessions, conductance tracked irradiance, reaching a maximum in the middle of the day. Substomatal CO2 concentrations increased with declining assimilation indicating that during high irradiance, assimilation was mainly controlled by mesophyll limitations rather than conductance. At the highland site both Z. mauritiana accessions were highly productive, with light saturated assimilation significantly higher than in either figs or peaches. At the warmer lowland site, assimilation and conductance in Musau were higher than in the other indigenous fruit species growing under similar conditions. Despite increased assimilation in Z. mauritiana when compared to the other species, there was no increase in the assimilation ratio (ratio of assimilation/conductance) which was offset by the high conductance values. Under conditions where water was not limiting, young Z. mauritiana plants showed no enhanced stomatal control over water loss, but were highly productive (per unit leaf area) relative to the other species.