Photosynthetic limitation of several representative subalpine species in the Catalan Pyrenees in summer

Abstract

Information on the photosynthetic process and its limitations is essential in order to predict both the capacity of species to adapt to conditions associated with climate change and the likely changes in plant communities. Considering that high-mountain species are especially sensitive, three species representative of subalpine forests of the Central Catalan Pyrenees: mountain pine (Pinus uncinata Mill.), birch (Betula pendula Roth) and rhododendron (Rhododendron ferrugineum L.) were studied under conditions associated with climate change, such as low precipitation, elevated atmospheric [CO2 ] and high solar irradiation incident at Earth's surface, in order to detect any photosynthetic limitations. Short-term high [CO2 ] increased photosynthesis rates (A) and water use efficiency (WUE), especially in birch and mountain pine, whereas stomatal conductance (gs ) was not altered in either species. Birch showed photosynthesis limitation through stomatal closure related to low rainfall, which induced photoinhibition and early foliar senescence. Rhododendron was especially affected by high irradiance, showing early photosynthetic saturation in low light, highest chlorophyll content, lowest gas exchange rates and least photoprotection. Mountain pine had the highest A, photosynthetic capacity (Amax ) and light-saturated rates of net CO2 assimilation (Asat ), which were maintained under reduced precipitation. Furthermore, maximum quantum yield (Fv /Fm ), thermal energy dissipation, PRI and SIPI radiometric index, and ascorbate content indicated improved photoprotection with respect to the other two species. However, maximum velocity of carboxylation of RuBisco (Vcmax ) indicated that N availability would be the main photosynthetic limitation in this species.

Aged but withstanding: Maintenance of growth rates in old pines is not related to enhanced water-use efficiency

“…In the case of AIG and ORD sites, the iWUE improvement during the industrial period may be caused by an increase in A given that δ 18 O-derived g s was maintained rather stable from the 1850s onwards (Scheidegger et al 2000). Similarly, Fernández-Martínez & Fleck (2016) found increased photosynthetic rates and iWUE for Mountain pine withouth changes in g s under elevated c a . Thus, sufficient water availability, higher c a and warm temperatures may enhance A and lead to increased C inputs in these high-elevation forests (Streit et al 2014).…”

“…Furthermore, the use of different source waters along the growing season could be influencing wood δ 18 O (Roden & Siegwolf 2012). We further acknowledge that other local factors such as the contrasting nutrient availability in the soil (basic soils in ORD and PED vs. acid ones in AIG) could also be responsible for contrasting tree responses at site level given that Mountain pine photosynthesis can be constrained in sites with poor soils and low N concentration (Fernández-Martínez & Fleck 2016). Therefore, growth fertilization could also be expected if N loads increase in the future, albeit current N deposition rates are relatively low in these areas (Badeau et al 1996; but see Boutin et al 2015).…”

Testing annual tree-ring chemistry by X-ray fluorescence for dendroclimatic studies in high-elevation forests from the Spanish Pyrenees

“…This means that wet and cool summer conditions could enhance the cell expansion and xylem differentiation in this site leading to increased Ca concentrations in the cell walls (Brett and Waldron, 1996). We further acknowledge that other local factors such as the contrasting nutrient availability in the soil (basic soils in Ordesa vs. acid soils in Aigüestortes) or site differences (wider rings and higher MXD values in the drier Ordesa site compared with the cool-wet Aigüestortes site) could also be responsible for contrasting responses between sites given that mountain pine photosynthesis can be constrained in sites with poorly developed soils having low N concentrations (Fernández-Martínez and Fleck, 2016). Therefore, growth fertilization could also be expected if N loads increase in the future, albeit current N deposition rates are relatively low in most Pyrenean high-elevation areas (Badeau et al, 1996;but see Boutin et al, 2015).…”

Adjustment of photosynthetic carbon assimilation to higher growth irradiance in three-year-old seedlings of two Tunisian provenances of Cork Oak (Quercus suber L.)

“…However, it does highlight that additional, non-diffusive limitations affect photosynthesis in Feija leaves compared to those of Gaâfour for seedlings transferred to HL condition. It is widely assumed that Jmax and Vcmax parameters represent the major limitations to light-saturated photosynthesis (Long & Bernacchi 2003) and that the decrease in biochemical capacity (Jmax and Vcmax) can limit An at high light, possibly by affecting nitrogen partitioning to Rubisco with increasing relative irradiance (Grassi & Bagnaresi 2001, Katahata et al 2007, Fernàndez & Fleck 2016. Mechanistic photosynthetic models may be used to determine the impact of varying environmental conditions -including those predicted to be affected by climate change -on the biochemistry of photosynthesis and carbon acquisition at the leaf and plant levels (Patrick et al 2009).…”