Growth characteristics of newly initiated cladodes of Opuntia ficusindica 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 productivity of this Crassulacean acid metabolism species. In a glasshouse, both dry weight and area increased more and more rapidly for about 30 days and then increased linearly with time up to 63 days. The relative growth rate averaged 0. 12 day^-1, comparable to values for productive C₃ and C₄ 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%, respectively. A 70% reduction in irradiation decreased biomass accumulation of new cladodes by 17% and their thickness by 11%. In a growth chamber containing 720 μmol Co₂ (mol air)^-1, biomass of newly initiated cladodes was 7% higher, area was 8% less, specific mass was 16% higher and less carbohydrate was translocated from basal cladodes than for 360 μmol Co₂ mol^-1. The large capacity for storage of carbohydrate and water in basal cladodes of O. ficus-indica apparently buffered environmental stresses, thereby reducing their effects on growth of daughter cladodes