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Effects of environmental and physiological factors on photosynthetic
characteristics in ''Irwin'' mango leaves were investigated by open gas analysis
system. Dark respiration rate, light compensation point, light saturation point
and quantum yield (Φ) were 0.65μmol.m-2s-1, 25-50μmol.m-2s-1, 700-800μmol.
m-2s-1 and 0.032μmol CO2/μmol PPF, respectively. Maximum net photosynthetic
rate was about 10-12μmol.m-2s-1 under light intensity above 800μmol.m-2s-1,
leaf temperature between 26-33℃ and vapor pressure deficit (VPD) below 1.5
KPa in ambient CO2 concentration. Besides, CO2 compensation point, CO2
saturation point and carboxylation efficiency were about 50μmol.mol-1, 1000μ
mol.mol-1 and 0.068 mol.m-2s-1, respectively, and light saturation point
increased as leaf maturated until leaf age reached 60-70 days. Diurnal changes
of photosynthetic characteristics of mature leaves in potted plants and field-
grown ones were also investigated. Tree age did not affect diurnal changes,
but mature leaves with similar age of older trees had higher maximum net
photosynthetic rate. Under sunny and hot day, diurnal changes showed two peaks
with midday depression whereas only one peak under sunny but not hot day.
Prior to attainment of the second peak, frequent irrigation on the
experimental date showed higher net photosynthetic rate. Diurnal changes of
mature leaves in field-grown plants did not show midday depression. In
addition, mature leaves on terminal part of flush had higher net photosynthetic
rate than lower parts of the same flush. Mature leaves on current flushes which
age younger than 3 months had similar photosynthetic capacity or stomatal
conductance whereas those older than 12 months had only about one half of the
capacity or conductance.
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