Suchergebnisse

In the Mediterranean, mixed forests of Aleppo pine and holm oak are widespread. Generally considered a transition stage in the succession towards climax oak communities, niche segregation may also contribute to the prevalence of these communities. So far, there is increasing evidence of hydrological niche segregation, with the two species showing complementary water use and seasonal growth patterns. However, it remains unknown whether interspecific interactions affect the response to climate and the mid-term (decadal) growth and water-use efficiency of pines and oaks in mixed stands. Here, we combined tree-ring chronologies, built on different competition classes within a mixed stand, with a spatially explicit assessment of individual growth and wood carbon isotope discrimination (∆13C), as a proxy of intrinsic water-use efficiency, and compared these results with previously reported water uptake patterns. We found that competition with pines modulated the climate response of oaks, whereas pine climate response was insensitive to competition. On the other hand, pine density affected only pine growth, whereas oak competition affected both species. We conclude that the presence of pines had negligible or even positive effects on the oaks, but competition with neighbor oaks limited their ability to recover after drought. Conversely, pines experienced greater drought stress under competition, with both oaks and pines ; This research was funded by the Spanish Government through Projects CGL2011-26654 and RTI2018-094691-B-C31 (MCIU/AEI/FEDER, EU). J.P.F. was supported by Reference Group H09_20R (Gobierno de Aragón, Spain).

In the Mediterranean, mixed forests of Aleppo pine and holm oak are widespread. Generally considered a transition stage in the succession towards climax oak communities, niche segregation may also contribute to the prevalence of these communities. So far, there is increasing evidence of hydrological niche segregation, with the two species showing complementary water use and seasonal growth patterns. However, it remains unknown whether interspecific interactions affect the response to climate and the mid-term (decadal) growth and water-use efficiency of pines and oaks in mixed stands. Here, we combined tree-ring chronologies, built on different competition classes within a mixed stand, with a spatially explicit assessment of individual growth and wood carbon isotope discrimination (∆13C), as a proxy of intrinsic water-use efficiency, and compared these results with previously reported water uptake patterns. We found that competition with pines modulated the climate response of oaks, whereas pine climate response was insensitive to competition. On the other hand, pine density affected only pine growth, whereas oak competition affected both species. We conclude that the presence of pines had negligible or even positive effects on the oaks, but competition with neighbor oaks limited their ability to recover after drought. Conversely, pines experienced greater drought stress under competition, with both oaks and pines. ; This research was funded by the Spanish Government through Projects CGL2011-26654 and RTI2018-094691-B-C31 (MCIU/AEI/FEDER, EU). J.P.F. was supported by Reference Group H09_20R (Gobierno de Aragon, Spain).

Stable isotopes in tree rings provide climatic information with annual resolution dating back for centuries or even millennia. However, deriving spatially explicit climate models from isotope networks remains challenging. Here we propose a methodology to model regional precipitation from carbon isotope discrimination (Δ13C) in tree rings by (1) building regional spatial models of Δ13C (isoscapes) and (2) deriving precipitation maps from Δ13C-isoscapes, taking advantage of the response of Δ13C to precipitation in seasonally dry climates. As a case study, we modeled the spatial distribution of mean annual precipitation (MAP) in the northeastern Iberian Peninsula, a region with complex topography and climate (MAP = 303–1086 mm). We compiled wood Δ13C data for two Mediterranean species that exhibit complementary responses to seasonal precipitation (Pinus halepensis Mill., N = 38; Quercus ilex L.; N= 44; pooling period: 1975–2008). By combining multiple regression and geostatistical interpolation, we generated one Δ13 C-isoscape for each species. A spatial model of MAP was then built as the sum of two complementary maps of seasonal precipitation, each one derived from the corresponding Δ13C-isoscape (September–November from Q. ilex; December–August from P. halepensis). Our approach showed a predictive power for MAP (RMSE = 84 mm) nearly identical to that obtained by interpolating data directly from a similarly dense network of meteorological stations (RMSE = 80–83 mm, N= 65), being only outperformed when using a much denser meteorological network (RMSE=56–57 mm, N=340). This method offers new avenues for modeling spatial variability of past precipitation, exploiting the large amount of information currently available from tree-ring networks. ; This work was funded by the Marie Curie project SMARTREES (MC-ERG-246725, European Union, FP7), and Spanish project PALEOISOTREE (CGL2009-13079-C02-01). J.d.C. is supported by a FPI fellowship (MCINN, Spain). JPF is supported by the Ramón y Cajal programme (RYC-2008-02050, MCINN, Spain).

Molecular clocks drive oscillations in leaf photosynthesis, stomatal conductance, and other cell and leaf-level processes over ~24 h under controlled laboratory conditions. The influence of such circadian regulation over whole-canopy fluxes remains uncertain; diurnal CO2 and H2O vapor flux dynamics in the field are currently interpreted as resulting almost exclusively from direct physiological responses to variations in light, temperature and other environmental factors. We tested whether circadian regulation would affect plant and canopy gas exchange at the Montpellier European Ecotron. Canopy and leaf-level fluxes were constantly monitored under field-like environmental conditions, and under constant environmental conditions (no variation in temperature, radiation, or other environmental cues). ; This study benefited from the CNRS human and technical resources allocated to the Research Infrastructure Ecotrons, as well as from the state allocation 'Investissement d'Avenir' ANR-11-INBS-0001; ExpeER Transnational Access program; Ramón y Cajal fellowships (RYC-2012-10970 to VRD and RYC-2008-02050 to JPF); the Erasmus Mundus Master Course Mediterranean Forestry and Natural Resources Management (MEDfOR); and internal grants from the Leibniz Centre for Agricultural Landscape Research to AG, and from the Western Sydney University's Hawkesbury Institute for the Environment and the Spanish Government (AGL2015-69151-R) to VRD.