GROWTH-CHARACTERISTICS OF NEWLY INITIATED CLADODES OF OPUNTIA-FICUS-INDICA AS AFFECTED BY SHADING, DROUGHT AND ELEVATED CO2

Biomass accumulation and area expansion of newly initiated cladodes of Opuntia ficus-indica were studied to help understand the high product ivity of this Crassulacena acid metabolism species. In a glasshouse, b oth dry weight and area increased more and more rapidly for about 30 d ays and then increased linearly with time up to 63 days. The relative growth rate averaged 0.12 day-1, comparable to values for productive C 3 and C, plants. New cladodes initiated on basal cladodes with 2-fold higher initial dry weight grew twice as fast. Drought reduced biomass accumulation and area expansion of new cladodes by 62 and 52%, respect ively. A 70% reduction in irradiation decreased biomass accumulation o f new cladodes by 17% and their thickness by 11%. In a growth chamber containing 720 mumol CO2 (mol air)-1, biomass of newly initiated clado des was 7% higher, area was 8% less, specific mass was 16% higher and less carbohydrate was translocated from basal cladodes than for 360 mu mol CO2 mol-1. The large capacity for storage of carbohydrate and wate r in basal cladodes of O. ficus-indica apparently buffered environment al stresses, thereby reducing their effects on growth of daughter clad odes.