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Gas exchange characteristics of giant cacti species varying in stem morphology and life history strategy
Author(s) -
Huber John,
Dettman David L.,
Williams David G.,
Hultine Kevin R.
Publication year - 2018
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/ajb2.1166
Subject(s) - biology , photosynthesis , transpiration , stomatal conductance , relative growth rate , botany , perennial plant , growth rate , geometry , mathematics
Premise of the Study Giant cacti species possess long cylindrical stems that store massive amounts of water and other resources to draw on for photosynthesis, growth, and reproduction during hot and dry conditions. Across all giant cacti taxa, stem photosynthetic surface area to volume ratio (S:V) varies by several fold. This broad morphological diversity leads to the hypothesis that giant cacti function along a predictable resource use continuum from a “safe” strategy reflected in low S:V, low relative growth rates ( RGR ), and low net assimilation rates ( A net ) to a high‐risk strategy that is reflected in high S:V, RGR , and A net . Methods To test this hypothesis, whole‐plant gas exchange, chlorophyll fluorescence, and whole‐spine‐tissue carbon isotope ratios (δ 13 C) were measured in four giant cacti species varying in stem morphology and RGR . Measurements were conducted on five well‐watered, potted plants per species. Key Results Under conditions of mild diel temperatures and low atmospheric vapor pressure deficit, A net , transpiration ( E ), and stomatal conductance ( G s ) were significantly higher, and water‐use efficiency ( A net : G s ) was lower in fast‐growing, multi‐stemmed species compared to the slower growing, single‐stemmed species. However, under warmer, less optimal conditions, gas exchange converged between stem types, and neither δ 13 C nor chlorophyll fluorescence varied among species. Conclusions The results add to a growing body of evidence that succulent‐stemmed plants function along a similar economic spectrum as leaf‐bearing plants such that functional traits including stem RGR , longevity, morphology, and gas exchange are correlated across species with varying life‐history strategies.