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BRANCHING PATTERNS OF COLUMNAR CACTI: INFLUENCES ON PAR INTERCEPTION AND CO 2 UPTAKE
Author(s) -
Geller Gary N.,
Nobel Park S.
Publication year - 1986
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1986.tb08565.x
Subject(s) - interception , gigantea , shading , biology , photosynthetically active radiation , volume (thermodynamics) , botany , ramification , horticulture , photosynthesis , mathematics , physics , ecology , art , quantum mechanics , combinatorics , visual arts
Field measurements and a computer model were used to determine how stem shape and arrangement of stems in space affect interception of photosynthetically active radiation (PAR) and CO 2 uptake under otherwise optimal conditions for four species of columnar cacti ( Carnegiea gigantea, Lophocereus schottii, Pachycereus pringlei, and Stenocereus thurberi ). In simulations where the number of widely spaced stems was increased from 1 to 19 but plant volume remained constant, surface area and PAR interception increased, leading to 3‐fold increases in whole‐plant CO 2 uptake. Increasing the distance between stems from 0 cm to infinity decreased self‐shading and increased predicted CO 2 uptake 4‐fold. Stem length, diam, ribbing characteristics, and spine coverage also influenced PAR interception. The model indicated that the observed higher frequency of branches on the south side of the trunk of C. gigantea had only a slight, though positive, effect on CO 2 uptake for single‐branched plants. Because of its greater surface area (A), a five‐stemmed plant of C. gigantea typical for a field site near Tucson, Arizona was predicted to have 52% more CO 2 uptake than a single‐stemmed plant of the same volume (V). Although large A/V decreases water storage per unit transpiring area, whole‐plant CO 2 uptake can be increased when A/V is increased by branching for these constant‐volume plants. However, the stems must be arranged to avoid excessive self‐shading and thus keep the area below PAR compensation small.