The functional morphology of juvenile plants tolerant of strong summer drought in shaded forest understories in southern Spain
| Autor: | Lawren Sack, Grubb, Pj, Maranon, T. |
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| Přispěvatelé: | Dirección General de Investigación Científica y Técnica, DGICT (España), Natural Sciences and Engineering Research Council of Canada, Cambridge Commonwealth Trust, University of Cambridge |
| Jazyk: | angličtina |
| Rok vydání: | 2003 |
| Předmět: | |
| Zdroj: | Digital.CSIC. Repositorio Institucional del CSIC instname ResearcherID |
| Popis: | 25 pages, 5 figures, 9 tables, 118 references. We thank David Coomes, Bill Davies, Chris Gilligan, Taylor Feild, Michael Huston, Bill Platt, Ed Tanner, Fernando Valladares and Rafael Villar for helpful comments. It has been hypothesized that plants cannot tolerate combined shade and drought, as a result of morphological trade-offs. However, numerous plant species are reportedly widespread in shaded forest understories that face drought, whether seasonal or occasional. We studied juveniles of six plant species that cope with strong summer drought in the understoreys of mixed Quercus forests in southern Spain: the tall-shrubs Phillyrea latifolia and Viburnum tinus, the perennial herb Rubia peregrina, the small shrub Ruscus aculeatus, and climbers Hedera helix and Smilax aspera. All of these species persist in evergreen shade (c. 3% daylight). Two other species were studied as comparators, Ruscus hypoglossum, less tolerant of drought, and Ceratonia siliqua, less tolerant of shade. Morphological and chemical variables relevant to shade and drought tolerance were measured for juveniles in a range of sizes, and also for the leaves of mature plants. The species converge in features that confer tolerance of shade plus drought by reducing demand for resources. Demand for water is reduced through a moderate to high below-ground mass fraction and low to moderate specific leaf area (respectively 0.22-0.52 and 112-172 cm2 g(-1) at 1.00 g total dry mass). Demand for both irradiance and water is reduced through a low to moderate foliar nitrogen concentration and long-lived, physically protected leaves (greater than or equal to 2 yr). The species also converge in features that confer tolerance of either low irradiance or drought through specialized capture of resource, without precluding the other tolerance. These features include deep roots relative to shoot size, moderately higher specific leaf area in shade (1.2-2.0 x that in sun) and higher chlorophyll:nitrogen ratio in shade. Foliar chlorophyll per unit mass was higher in shade, but chlorophyll was not necessarily synthesized in greater amounts; rather, it was higher apparently due to shade effects on structural features linked with specific leaf area. In contrast, N per unit mass was higher in sun leaves independently of specific leaf area. Despite these convergences, the species diverge considerably in their root mass allocation and architecture, leaf saturated water content, density of stomata and guard cell size. No single narrowly defined functional type is needed for tolerance of shade plus drought. The project was supported by scholarships to L.S. from NSERC (Canada), the Cambridge Commonwealth Trust, and the Cambridge University Department of Plant Sciences (Frank Smart Fund), and by Spanish DGICYT project grants to T.M. (PB97-1177 and 1FD97-0743-C03-03). |
| Databáze: | OpenAIRE |
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