Pereskiopsis porteri

Nomenclature and structure

The accepted name is Pereskiopsis porteri (Brandegee ex F.A.C.Weber) Britton & Rose. P. gatesii is now its synonym. The plants studied have persistent, flat, fleshy leaves and relatively hard green stems. These organs differ in the intensity and temporal distribution of assimilation. [2-WWW] [Martin and Wallace 2000]

The transition from day to night

In the 1987 study at 25/15°C under a twelve-hour day, the nocturnal share of daily leaf CO₂ uptake was about 6% in well-hydrated plants. After seven days of drought, it rose to 92%, and after fourteen to 97%. Daytime assimilation declined by about 94% and 99% respectively relative to the initial state. [Nobel and Hartsock 1987]

The balance expressed per unit leaf area was initially 108 mmol CO₂ m⁻² during the day and 7 mmol m⁻² at night. After seven days of drought, values were 6 and 72, and after fourteen days 1 and 35. The increase in nocturnal contribution therefore represents a change in gas-exchange strategy with declining total daily carbon gain. [Nobel and Hartsock 1987, tab. 1, p. 116]

Comparison with a later experiment

Martin and Wallace measured at 30/20°C under a fourteen-hour photoperiod. Leafy shoots of P. porteri showed similar total CO₂ uptake by day and night, while the daytime phase more often predominated in other Pereskiopsis samples. The results illustrate physiological plasticity associated with conditions and plant state. [Martin and Wallace 2000]

Nocturnal acidification also occurred in stems. Some acids formed from respiratory CO₂, so acidity determination supplements measurement of exchange with the atmosphere. Together, the two measurements show how much carbon a plant acquires from its surroundings and how much it temporarily recovers within tissues. [Martin and Wallace 2000]