Under pressure: how a Mediterranean high‐mountain forb coordinates growth and hydraulic xylem anatomy in response to temperature and water constraints

• Published in: Functional ecology 2013-12, Vol.27 (6), p.1295-1303
• Main Authors: Olano, Jose Miguel, Almería, Iván, Eugenio, Màrcia, Arx, Georg, Tjoelker, Mark
• Format: Article
• Language: English
• Subjects: Altitudinal gradient; Animal and plant ecology; Animal, plant and microbial ecology; annual root rings; Autoecology; Biological and medical sciences; Ciliata; Climate change; Climate models; climatic change; climatic double stress; climatic factors; Climatology. Bioclimatology. Climate change; Drought; Earth, ocean, space; equations; Exact sciences and technology; External geophysics; forbs; functional xylem anatomy; Fundamental and applied biological sciences. Psychology; General aspects; genome; herb‐chronology; Human ecology; Mediterranean high mountains; Meteorology; mountains; Plant age; Plant ecology; Plant growth; Plant physiological ecology; plant reproduction; Plants; seed quality; Silene; Species; spring; summer; water stress; Xylem
• ISSN: 0269-8463; 1365-2435
• DOI: 10.1111/1365-2435.12144

Plant growth in Mediterranean high mountains is limited by the double climatic stress of low winter temperatures and summer drought. Elevational shifts in response to climate change may be complex for species whose distribution is constrained by several climatic factors. We used herb‐chronology, that is, the analysis of annual rings in the secondary root xylem of perennial forbs, to evaluate life‐long factors constraining secondary growth and xylem hydraulic anatomy along an elevational gradient from the upper to the lower distribution limits of the alpine forb Silene ciliata at its southernmost distribution range. Generalized additive models (GAM) showed that annual ring width (RW) in S. ciliata was greatest at intermediate elevations and smallest at the upper and lower limits of its elevational range. In contrast, maximal vessel area (MVA) was greatest at lower elevations. RW responded to climatic conditions in early spring and late summer, suggesting the presence of a bimodal xylogenesis. Structural equation modelling (SEM) indicated a positive influence of MVA on RW in the same year; improved hydraulic efficiency seemed to promote higher secondary growth. The observed greatest secondary growth (RW) and maximal vessel area (MVA) at intermediate and intermediate‐low elevations, respectively, contrasts with previous evidence of an improvement in plant reproduction and recruitment with increasing elevation for S. ciliata. However, our results are in agreement with other indicators suggesting that best conditions occur at intermediate elevations, such as better seed quality or larger genome size. This study reinforces the evidence that the response of high‐mountain plants to climatic change under simultaneous temperature and drought stress is complex and that models that simply assume an increase in elevation as a response to higher temperatures may fail to predict future responses to climate change.