Does cladode inclination restrict microhabitat distribution for Opuntia puberula (Cactaceae)?

Area of Science:

• Plant Biology
• Ecology
• Botany

Background:

• Opuntia species typically exhibit vertical cladodes.
• Opuntia puberula predominantly displays horizontal cladodes.
• The adaptive significance of horizontal cladodes in Opuntia puberula is largely unknown.

Purpose of the Study:

• Investigate if horizontal cladodes in Opuntia puberula are an adaptation for increased light interception in understory environments.
• Determine if this trait limits the plant's distribution in full sun habitats.
• Characterize the effects of cladode inclination on light interception, temperature, and carbon gain.

Main Methods:

• Quantified cladode inclination angles across varying light availabilities.
• Measured light interception, cladode temperature, and carbon gain (nocturnal acid accumulation).
• Described anatomical and physiological traits of upper and lower cladode surfaces.

Main Results:

• 95% of Opuntia puberula cladodes had inclination angles below 50°, with lower angles correlating with decreased light availability.
• Nocturnal acid accumulation increased with intercepted photosynthetically active photon flux density (PPFD).
• Chlorophyll content varied between upper and lower cladode surfaces, but chlorenchyma thickness, stomatal conductance, and nocturnal acid accumulation were similar between surfaces.

Conclusions:

• The horizontal cladode position in Opuntia puberula is anatomically determined and restricts the species to shaded habitats.
• This trait prevents overheating in shaded environments but does not appear to enhance carbon gain.
• The horizontal orientation may limit the distribution of Opuntia puberula in full sun environments.