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Leaf adaptations of evergreen and deciduous trees of semi‐arid and humid savannas on three continents
Author(s) -
Tomlinson Kyle W.,
Poorter Lourens,
Sterck Frank J.,
Borghetti Fabian,
Ward David,
Bie Steven,
Langevelde Frank
Publication year - 2013
Publication title -
journal of ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.452
H-Index - 181
eISSN - 1365-2745
pISSN - 0022-0477
DOI - 10.1111/1365-2745.12056
Subject(s) - evergreen , deciduous , biology , phenology , transpiration , arid , agronomy , sclerophyll , photosynthesis , ecology , botany , mediterranean climate
SummaryDrought stress selects for a suite of plant traits at root, stem and leaf level. Two strategies are proposed for trees growing in seasonally water‐stressed environments: drought tolerance and drought avoidance. These are respectively associated with evergreen phenology, where plants retain their leaves throughout the year, and deciduous phenology, where plants drop their leaves during dry seasons. Evergreen species are thought to have leaf traits supporting lower photosynthesis and transpiration rates, in order to conserve water during dry periods. We evaluated 18 morphological, chemical and physiological leaf traits of 51 abundant savanna tree species that differed in leaf habit (deciduous and evergreen), selected from two climate types (semi‐arid and humid) in three continents ( A ustralia, A frica and S outh A merica) (annual rainfall range: 500–1550 mm), and grown in a common garden experiment. We hypothesised that evergreen species have more conservative water use and differ more across climate types than deciduous species because evergreen species are forced to endure extended water deficits during dry seasons. Trait shifts between semi‐arid and humid savannas did not differ between evergreen and deciduous species. Evergreen species had similar assimilation rates but lower photosynthetic water‐use efficiency ( PWUE ) than deciduous species, possibly to extend their leaf lifespans by protecting their photosynthetic machinery from overheating through evaporative cooling. Species of humid and semi‐arid environments did not differ with respect to assimilation rate or PWUE , but semi‐arid species did have smaller leaf sizes and greater leaf potassium and phosphorus concentrations. These traits may enable semi‐arid species to maximize growth during episodes of favourable moisture availability. Species from the three continents differed in their leaf traits. These probably reflect the greater proportion of evergreen species in A ustralia as compared to the other continents and generally infertile soils in the S outh A merican sampling sites compared to the wider fertility range in the A frican sites.Synthesis: Water stress in savannas does not select for more conservative water use, but may select for rapid adjustment to prevailing water conditions and for heat avoidance mechanisms.