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Gas exchange and chlorophyll fluorescence responses of three south‐western Yucca species to elevated CO 2 and high temperature
Author(s) -
Huxman T. E.,
Hamerlynck E. P.,
Loik M. E.,
Smith S. D.
Publication year - 1998
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1046/j.1365-3040.1998.00396.x
Subject(s) - yucca , photosynthesis , stomatal conductance , perennial plant , botany , chlorophyll fluorescence , arid , diurnal temperature variation , horticulture , desert climate , biology , ecology , atmospheric sciences , geology
The ability of seedlings to tolerate temperature extremes is important in determining the distribution of perennial plants in the arid south‐western USA, and the manner in which elevated CO 2 impacts the ability of plants to tolerate high temperatures is relatively unknown. Whereas the effects of chronic high temperature (30–38°C) and elevated CO 2 are comparatively well understood, little research has assessed plant performance in elevated CO 2 during extreme (> 45 °C) temperature events. We exposed three species of Yucca to 360 and 700 μ mol CO 2 mol –1 for 8 months, then 9 d of high temperature (up to 53 °C) to evaluate the impacts of elevated CO 2 on the potential for photosynthetic function during external high temperature. Seedlings of a coastal C 3 species ( Yucca whipplei ), a desert C 3 species ( Yucca brevifolia ), and a desert CAM species ( Yucca schidigera ), were used to test for differences among functional groups. In general, Yuccas exposed to elevated CO 2 showed decreases in carboxylation efficiency as compared with plants grown at ambient before the initiation of high temperature. The coastal species ( Y . whipplei ) showed significant reductions (33%) in CO 2 saturated maximum assimilation rate ( A max ), but the desert species ( Y . brevifolia and Y . schidigera ) showed no such reductions in A max . Stomatal conductance was lower in elevated CO 2 as compared with ambient throughout the temperature event; however, there were species‐specific differences over time. Elevated CO 2 enhanced photosynthesis in Y. whipplei at high temperatures for a period of 4 d, but not for Y. brevifolia or Y. schidigera . Elevated CO 2 offset photoinhibition (measured as F v / F m ) in Y. whipplei as compared with ambient CO 2 , depending on exposure time to high temperature. Stable F v / F m in Y. whipplei occurred in parallel with increases in the quantum yield of photosystem II ( ΦPSII ) at high temperatures in elevated CO 2 . The value of ΦPSII remained constant or decreased with increasing temperature in all other treatment and species combinations. This suggests that the reductions in F v / F m resulted from thermal energy dissipation in the pigment bed for Y. brevifolia and Y. schidigera . The greater efficiency of photosystem II in Y. whipplei helped to maintain photosynthetic function at high temperatures in elevated CO 2 . These patterns are in contrast to the hypothesis that high temperatures in elevated CO 2 would increase the potential for photoinhibition. Our results suggest that elevated CO 2 may offset high‐temperature stress in coastal Yucca , but not in those species native to drier systems. Therefore, in the case of Y. whipplei , elevated CO 2 may allow plants to survive extreme temperature events, potentially relaxing the effects of high temperature on the establishment in novel habitats.