Growth, resource storage, and adaptation to drought in California and eastern Mediterranean oak seedlings

Abstract

Low recruitment of new plants as currently observed in several California oak species might partly result from insufficient storage of vital resources (reduced ability to regrow after disturbance) or from low adaptation to environmental stress, such as drought. We conducted two studies under divergent environmental conditions to compare seedlings of California oaks with ecologically equivalent species from the eastern Mediterranean region, where recruitment has been substantial over the past 25–30 years. Resource concentrations (nonstructural carbohydrates and nitrogen) in taproots and the ratio of root resource content to shoot biomass did not provide evidence that Californian oak seedlings have smaller reserves for resprouting than eastern Mediterranean species in these studies. However, we observed lower seedling survival among California species, when compared with Mediterranean species, under conditions of higher drought stress. In the California deciduous Quercus douglasii Hook. & Arn., water-use efficiency as measured by leaf gas exchange and leaf δ13C was lower compared with its Mediterranean equivalent Quercus ithaburensis Decne. In addition, stomatal conductance in the California evergreen Quercus agrifolia Née appeared to be less sensitive to vapor pressure deficit than in its Mediterranean equivalent Quercus calliprinos Webb. Our results suggest lower adaptation to drought in the California species tested here as compared with Mediterranean species, which will negatively impact recruitment of oaks from California under the currently drier soil conditions.

Photosynthesis, stomatal conductance and terpene emission response to water availability in dry and mesic Mediterranean forests

“…Photosynthesis and stomatal conductance A and gs patterns observed during the spring and summer in this study were consistent with previous studies of the Mediterranean species P. halepensis and Quercus ilex (Baquedano and Castillo 2007;Peñuelas and Llusià 1999;Llusià and Peñuelas 2000), and Q. calliprinos and Q. ithaburensis (Klein et al 2013;Schiller et al 2010;Grünzweig et al 2008). A and gs showed the seasonal trend expected in a Mediterranean climate (Llusià and Peñuelas 2000) except under the near-desertic conditions of Yatir forest (Maseyk et al 2008) where values were extremely low both in spring and summer ( Figs.…”

“…These species are Pinus halepensis L., Quercus calliprinos and Quercus ithaburensis Webb. In this Mediterranean region these species undergo periods of drought and high temperature frequently (Atzmon et al 2004;Grünzweig et al 2008). We measured them in Yatir (in the south, arid) Birya (located north, Mediterranean sub-humid conditions) and Solelim (located north, Mediterranean conditions).…”

Shrinking windows of opportunity for oak seedling establishment in southern California mountains

“…, Grünzweig et al. ). Numerous studies in California foothill oak woodlands have documented increased rates of oak seedling establishment in wetter years (Griffin , Borchert et al.…”

Cork oak physiological responses to manipulated water availability in a Mediterranean woodland

“…Leaf surface reduction is a further protective mechanism of dehydration avoidance restraining water loss while maximizing carbon gain, and keeping minimum « md above the threshold of xylem embolism under increasing drought intensity. Lower SLA has long been shown to be an adaptive response to drought (Abrams, 1994;Cunningham et al, 1999;Grünzweig et al, 2008) or an indicator of resource conditions (Cornelissen et al, 2003). Ramírez-Valiente et al (2011) found that cork oak's SLA was negatively correlated with annual shoot growth and positively related to annual growth.…”