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

Abstract

Summary1. 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. 2. 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. 3. 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. 4. 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. 5. 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.

How does climate influence xylem morphogenesis over the growing season? Insights from long-term intra-ring anatomy inPicea abies

“…Stronger and more defined associations emerged when the climatic data were aligned according to the DD temperature thresholds at high elevation (especially for CD in the first ring sectors; Figs 6 and 7), but not at lower elevations (see Cuny et al, 2015). These add additional evidence and further confirm that late-spring temperature controls the onset of cambial activity and the kinetics of cell formation in cold environments (Kirdyanov et al, 2003;Seo et al, 2008;Thibeault-Martel et al, 2008;Moser et al, 2010;Olano et al, 2013). However, we also observed waterrelated constraints on tracheid morphogenesis.…”

Sequence of plant responses to droughts of different timescales: lessons from holm oak (Quercus ilex) forests

“…Mediterranean summer drought stops growth in Q. ilex, resulting in bimodal secondary growth patterns (Lempereur et al 2015). A transient quiescence of growth has also been reported for Mediterranean conifers (Camarero et al 2010;Vieira et al 2014) and forbs (Olano et al 2013). Large below-and above-ground bud banks are also characteristically associated with Mediterranean vegetation (Canadell and Lopez-Soria 1998;Klimešová and Klimeš 2007) and its capacity to recover from fires but are also relevant after extreme droughts (Zeppel et al 2015).…”

Comparative analysis of annual rings of perennial forbs in the Loess Plateau, China

“…von found that annual ring widths of forbs in the Wallowa Mountains (northeastern Oregon, USA) declined linearly with age at low and intermediate altitudes, but increased for the first few years and then declined in later years at high altitudes. In addition, Olano et al (2013) showed that ring width of the alpine forb, Silene ciliate, decreased with plant age at all altitudinal zones (from 1986 to 2413m) in Mediterranean high mountains. On the contrary, Liu and Zhang (2007) found that ring widths of forbs in the Mongolia grassland indicated a linear increasing trend with age.…”

“…Previous studies have suggested that annual growth rings are widespread among perennial forbs in the regions located at rather higher latitudes (above 40 • N), such as the central European lowlands (Dietz and Ullmann, 1997;Dietz and Fattorini, 2002), North America (Dietz and Schweingruber, 2002;Dietz and von Arx, 2005;, Mediterranean (Olano et al, 2013) and Inner Mongolia grassland (Liu and Zhang, 2007). In contrast, we detected distinguishable growth rings of many perennial forbs at the Loess Plateau located at comparatively lower latitudes (from 35 to 39 • N), and we hypothesized those perennial forbs with annual rings might widespread in the temperate seasonal zones of the Northern Hemisphere.…”

“…The patterns of growth rings in forbs may vary in different environmental conditions, and growth rings may be missing or false under the extremely adverse growth conditions (Dietz and Ullmann, 1998;Dietz and Fattorini, 2002;Moloney et al, 2009). In addition, annual rings of forbs can respond rapidly and sensitively to climatic fluctuations (Dietz and von Arx, 2005;Liu and Zhang, 2010), as well as other environmental factors, such as alti-tudinal gradients Olano et al, 2013) and anthropogenic disturbances (Dietz and Fattorini, 2002;Dietz and Schweingruber, 2002). Consequently, growth rings of forbs can be considered as a useful approach to study growth forms and life history strategies of forbs across a wide environmental range (Moloney et al, 2009;von Arx et al, 2012;Olano et al, 2013).…”