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The effect of cactus spines on light interception and Photosystem II for three sympatric species of Opuntia from the Mojave Desert
Author(s) -
Loik Michael E.
Publication year - 2008
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.2008.01110.x
Subject(s) - photosynthesis , xanthophyll , biology , botany , thylakoid , photosystem , photosystem ii , chloroplast , biochemistry , gene
Cactus spines reduce herbivory, direct water toward roots and reduce the impacts of high‐ and low‐temperature extremes. Yet, shading of stems by spines reduces incident photosynthetic photon flux density (PFD), photosynthesis and growth. This study compared spinescence, PFD interception, stem temperature, Photosystem II (PSII) photochemistry and xanthophyll pigment composition for three species of cacti from the Mojave Desert, CA. The species vary in spinescence: Opuntia basilaris , which has no central or radial spines; Opuntia erinacea , which is densely covered with spines; and Opuntia phaeacantha , which has an intermediate coverage of spines. The role of spines was tested by removing spines from stems of O. erinacea . PFD interception was similar for both O. basilaris and O. phaeacantha , and about three times that for densely spined O. erinacea ; removal of spines increased incident PFD three‐fold. There were no effects of spines on stem temperatures. Steady‐state light‐response curves of chlorophyll a fluorescence from PSII indicated that ΦPSII, photochemical quenching (qP) and electron flux within PSII were lower, and non‐photochemical quenching was higher, for O. erinacea in comparison to the other two species with less spines. After 2 months, qP was higher and electron flux lower, and xanthophyll pigment pool size was higher, for stems from which spines had been removed compared with intact stems. These three species allocate different amounts of biomass to spines, resulting in species‐specific PFD interception, PSII photochemistry and xanthophyll pigment pool size, which may help maintain rates of photosynthesis during the hot, dry Mojave Desert summer.