Riparian forest transpiration under the current and projected Mediterranean climate: Effects on soil water and nitrate uptake

Poblador S., Thomas Z., Rousseau-Gueutin P., Sabaté S., Sabater F. (2019) Riparian forest transpiration under the current and projected Mediterranean climate: Effects on soil water and nitrate uptake. Ecohydrology. 12: 0-0.
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Doi: 10.1002/eco.2043

Resumen:

Vegetation plays a key role in riparian area functioning by controlling water and nitrate (N─NO3 −) transfers to streams. We investigated how spatial heterogeneity modifies the influence of vegetation transpiration on soil water and N─NO3 − balances in the vadose soil of a Mediterranean riparian forest. On the basis of field data, we simulated water flow and N─NO3 − transport in three riparian zones (i.e., near-stream, intermediate, and hillslope) using HYDRUS-1D model. We investigated spatiotemporal patterns across the riparian area over a 3-year period and future years using an IPCC/CMIP5 climate projection for the Mediterranean region. Potential evapotranspiration was partitioned between evaporation and transpiration to estimate transpiration rates at the area. Denitrification in the forest was negligible, thus N─NO3 − removal was only considered through plant uptake. For the three riparian zones, the model successfully predicted field soil moisture (θ). The near-stream zone exchanged larger volumes of water and supported higher θ and transpiration rates (666 ± 75 mm) than the other two riparian zones. Total water fluxes, θ, and transpiration rates decreased near the intermediate (536 ± 46 mm transpired) and hillslope zones (406 ± 26 mm transpired), suggesting that water availability was restricted due to deeper groundwater. Transpiration strongly decreased θ and soil N─NO3 − in the hillslope and intermediate zones. Our climate projections highlight the importance of groundwater availability and indicate that soil N─NO3 − would be expected to increase due to changes in plant-root uptake. Lower water availability in the hillslope zone may reduce the effectiveness of N─NO3 − removal in the riparian area, increasing the risk of excess N─NO3 − leaching into the stream. © 2018 John Wiley & Sons, Ltd.

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Growth and water use performance of four co-occurring riparian tree species in a Mediterranean riparian forest

Nadal-Sala D., Sabaté S., Sánchez-Costa E., Poblador S., Sabater F., Gracia C. (2017) Growth and water use performance of four co-occurring riparian tree species in a Mediterranean riparian forest. Forest Ecology and Management. 396: 132-142.
Enlace
Doi: 10.1016/j.foreco.2017.04.021

Resumen:

Mediterranean riparian zones act as vegetation shelters for several deciduous tree species at the edge of their bioclimatic distribution, e.g. alder (Alnus glutinosa), black poplar (Populus nigra) or ash (Fraxinus excelsior). Current global warming and human induced disturbances may worsen their growing conditions. Under such circumstances, black locust (Robinia pseudoacacia) is outcompeting autochthonous tree species. Here, we provide evidences of black locust better growth and water use performance than alder and ash. We compare the temporal and spatial patterns of transpiration and the stem basal area increments of alder, black poplar, common ash and black locust, all of them co-occurring in a mixed riparian Mediterranean forest. Black locust presented the lowest transpiration values per basal area unit (4.0 mm·m−2·growing season−1). Although tree transpiration was mainly driven by energy availability instead of water, ash transpiration was constrained by water availability at soil water contents below 0.08 cm3·cm−3. Black locust was the only tree species growing all over the water availability gradient present in the study site, and it did not present any significant difference in sap flow values across this gradient. Furthermore, black locust and black poplar were the species with higher growth-based water use efficiency (5.4 g·cm−1·m−3 and 3.6 g·cm−1·m−3, respectively); ash and alder were the less efficient ones (2.8 g·cm−1·m−3 and 1.9 g·cm−1·m−3respectively). The good performance of black locust is relevant to understand its great successful invasion of Mediterranean riparian forests, particularly after human-induced disturbances, as forest management. © 2017 Elsevier B.V.

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Soil water content drives spatiotemporal patterns of CO2 and N2O emissions from a Mediterranean riparian forest soil

Poblador, S., Lupon, A., Sabaté, S., Sabater, F. (2017) Soil water content drives spatiotemporal patterns of CO2 and N2O emissions from a Mediterranean riparian forest soil. Biogeosciences. 14: 4195-4208.
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Doi: 10.5194/bg-14-4195-2017

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Are forest disturbances amplifying or canceling out climate change-induced productivity changes in European forests?

Reyer, C.P.O., Bathgate, S., Blennow, K., Borges, J.G., Bugmann, H., Delzon, S., Faias, S.P., Garcia-Gonzalo, J., Gardiner, B., Gonzalez-Olabarria, J.R., Gracia, C., Hernández, J.G., Kellomäki, S., Kramer, K., Lexer, M.J., Lindner, M., Van Der Maaten, E., Maroschek, M., Muys, B., Nicoll, B., Palahi, M., Palma, J.H.N., Paulo, J.A., Peltola, H., Pukkala, T., Rammer, W., Ray, D., Sabaté, S., Schelhaas, M.-J., Seidl, R., Temperli, C., Tomé, M., Yousefpour, R., Zimmermann, N.E., Hanewinkel, M. (2017) Are forest disturbances amplifying or canceling out climate change-induced productivity changes in European forests?. Environmental Research Letters. 12: 0-0.
Enlace
Doi: 10.1088/1748-9326/aa5ef1

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Mitigating the stress of drought on soil respiration by selective thinning: Contrasting effects of drought on soil respiration of two oak species in a mediterranean forest

Chang, C.-T., Sperlich, D., Sabaté, S., Sánchez-Costa, E., Cotillas, M., Espelta, J.M., Gracia, C. (2016) Mitigating the stress of drought on soil respiration by selective thinning: Contrasting effects of drought on soil respiration of two oak species in a mediterranean forest. Forests. 7: 0-0.
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Doi: 10.3390/f7110263

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Aboveground and belowground biomass allocation patterns in two Mediterranean oaks with contrasting leaf habit: an insight into carbon stock in young oak coppices

Cotillas M., Espelta J.M., Sánchez-Costa E., Sabaté S. (2016) Aboveground and belowground biomass allocation patterns in two Mediterranean oaks with contrasting leaf habit: an insight into carbon stock in young oak coppices. European Journal of Forest Research. 135: 243-252.
Enlace
Doi: 10.1007/s10342-015-0932-9

Resumen:

In the last decades, the global interest in the role of forests as carbon sinks has grown, and thus, studies aimed at estimating tree biomass have progressively increased. However, few surveys have focused on young coppices, although they are abundant worldwide in areas regenerating after disturbance (e.g. wildfire, clearcutting). In the Mediterranean Basin, young coppices are very frequent, and most of them are formed by evergreen and deciduous oaks (Quercus spp.). In this survey, we have studied the biomass allocation patterns of two oaks coexisting in coppices, the evergreen Quercus ilex and the deciduous Quercus cerrioides, comparing them in the light of their different leaf habit, which may influence their physiological performance in the context of climate change. We have also obtained allometric equations for each species and its components, which we have used to calculate the carbon stock in the sampled area, as an insight into the potential of young oak coppices to sequester carbon. The results indicate a higher biomass investment of Q. ilex in the stump and a higher leafiness and allocation to roots in Q. cerrioides. In the light of these differences, the evergreen Q. ilex could be defined as a “resource-saving” species in comparison with the more “resource-demanding” Q. cerrioides. The allometric equations were able to predict from 78 to 99 % of the variation in biomass using diameter as predictor variable for all the tree components aside of the stump. Overall carbon stock estimation in the young coppice of our study area was 43.2 Mg ha−1, of which 62 % is stored belowground. These results highlight the importance of biomass allocation in the belowground compartment in Mediterranean young oak coppices as a temporal carbon sink. Moreover, they provide evidence that these forests may store a relevant amount of carbon, often ignored in forest inventories. © 2016, Springer-Verlag Berlin Heidelberg.

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Assessment of the impacts of climate change on Mediterranean terrestrial ecosystems based on data from field experiments and long-term monitored field gradients in Catalonia

Peñuelas, J., Sardans, J., Filella, I., Estiarte, M., Llusià, J., Ogaya, R., Carnicer, J., Bartrons, M., Rivas-Ubach, A., Grau, O., Peguero, G., Margalef, O., Pla-Rabés, S., Stefanescu, C., Asensio, D., Preece, C., Liu, L., Verger, A., Rico, L., Barbeta, A., Achotegui-Castells, A., Gargallo-Garriga, A., Sperlich, D., Farré-Armengol, G., Fernández-Martínez, M., Liu, D., Zhang, C., Urbina, I., Camino, M., Vives, M., Nadal-Sala, D., Sabaté, S., Gracia, C., Terradas, J. (2016) Assessment of the impacts of climate change on Mediterranean terrestrial ecosystems based on data from field experiments and long-term monitored field gradients in Catalonia. Environmental and Experimental Botany. : 0-0.
Enlace
Doi: 10.1016/j.envexpbot.2017.05.012

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Balance between carbon gain and loss under long-term drought: Impacts on foliar respiration and photosynthesis in Quercus ilex L

Sperlich D., Barbeta A., Ogaya R., Sabaté S., Peñuelas J. (2016) Balance between carbon gain and loss under long-term drought: Impacts on foliar respiration and photosynthesis in Quercus ilex L. Journal of Experimental Botany. 67: 821-833.
Enlace
Doi: 10.1093/jxb/erv492

Resumen:

Terrestrial carbon exchange is a key process of the global carbon cycle consisting of a delicate balance between photosynthetic carbon uptake and respiratory release. We have, however, a limited understanding how long-term decreases in precipitation induced by climate change affect the boundaries and mechanisms of photosynthesis and respiration. We examined the seasonality of photosynthetic and respiratory traits and evaluated the adaptive mechanism of the foliar carbon balance of Quercus ilex L. experiencing a long-term rainfall-exclusion experiment. Day respiration (R d) but not night respiration (R n) was generally higher in the drought treatment leading to an increased R d/R n ratio. The limitation of mesophyll conductance (g m) on photosynthesis was generally stronger than stomatal limitation (g s) in the drought treatment, reflected in a lower g m/g s ratio. The peak photosynthetic activity in the drought treatment occurred in an atypical favourable summer in parallel with lower R d/R n and higher g m/g s ratios. The plant carbon balance was thus strongly improved through: (i) higher photosynthetic rates induced by g m; and (ii) decreased carbon losses mediated by R d. Interestingly, photosynthetic potentials (V c,max, J max, and TPU) were not affected by the drought treatment, suggesting a dampening effect on the biochemical level in the long term. In summary, the trees experiencing a 14-year-long drought treatment adapted through higher plasticity in photosynthetic and respiratory traits, so that eventually the atypical favourable growth period was exploited more efficiently. © 2015 The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology.

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Direct and indirect impacts of climate and socio-economic change in Europe: a sensitivity analysis for key land- and water-based sectors

Kebede A.S., Dunford R., Mokrech M., Audsley E., Harrison P.A., Holman I.P., Nicholls R.J., Rickebusch S., Rounsevell M.D.A., Sabate S., Sallaba F., Sanchez A., Savin C., Trnka M., Wimmer F. (2015) Direct and indirect impacts of climate and socio-economic change in Europe: a sensitivity analysis for key land- and water-based sectors. Climatic Change. 128: 261-277.
Enlace
Doi: 10.1007/s10584-014-1313-y

Resumen:

Integrated cross-sectoral impact assessments facilitate a comprehensive understanding of interdependencies and potential synergies, conflicts, and trade-offs between sectors under changing conditions. This paper presents a sensitivity analysis of a European integrated assessment model, the CLIMSAVE integrated assessment platform (IAP). The IAP incorporates important cross-sectoral linkages between six key European land- and water-based sectors: agriculture, biodiversity, flooding, forests, urban, and water. Using the IAP, we investigate the direct and indirect implications of a wide range of climatic and socio-economic drivers to identify: (1) those sectors and regions most sensitive to future changes, (2) the mechanisms and directions of sensitivity (direct/indirect and positive/negative), (3) the form and magnitudes of sensitivity (linear/non-linear and strong/weak/insignificant), and (4) the relative importance of the key drivers across sectors and regions. The results are complex. Most sectors are either directly or indirectly sensitive to a large number of drivers (more than 18 out of 24 drivers considered). Over twelve of these drivers have indirect impacts on biodiversity, forests, land use diversity, and water, while only four drivers have indirect effects on flooding. In contrast, for the urban sector all the drivers are direct. Moreover, most of the driver–indicator relationships are non-linear, and hence there is the potential for ‘surprises’. This highlights the importance of considering cross-sectoral interactions in future impact assessments. Such systematic analysis provides improved information for decision-makers to formulate appropriate adaptation policies to maximise benefits and minimise unintended consequences. © 2015, Springer Science+Business Media Dordrecht.

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Seasonal variability of foliar photosynthetic and morphological traits and drought impacts in a Mediterranean mixed forest

Sperlich D., Chang C.T., Penuelas J., Gracia C., Sabate S. (2015) Seasonal variability of foliar photosynthetic and morphological traits and drought impacts in a Mediterranean mixed forest. Tree Physiology. 35: 501-520.
Enlace
Doi: 10.1093/treephys/tpv017

Resumen:

The Mediterranean region is a hot spot of climate change vulnerable to increased droughts and heat waves. Scaling carbon fluxes from leaf to landscape levels is particularly challenging under drought conditions. We aimed to improve the mechanistic understanding of the seasonal acclimation of photosynthesis and morphology in sunlit and shaded leaves of four Mediterranean trees (Quercus ilex L., Pinus halepensis Mill., Arbutus unedo L. and Quercus pubescens Willd.) under natural conditions. Vc,max and Jmax were not constant, and mesophyll conductance was not infinite, as assumed in most terrestrial biosphere models, but varied significantly between seasons, tree species and leaf position. Favourable conditions in winter led to photosynthetic recovery and growth in the evergreens. Under moderate drought, adjustments in the photo/biochemistry and stomatal/mesophyllic diffusion behaviour effectively protected the photosynthetic machineries. Severe drought, however, induced early leaf senescence mostly in A. unedo and Q. pubescens, and significantly increased leaf mass per area in Q. ilex and P. halepensis. Shaded leaves had lower photosynthetic potentials but cushioned negative effects during stress periods. Species-specificity, seasonal variations and leaf position are key factors to explain vegetation responses to abiotic stress and hold great potential to reduce uncertainties in terrestrial biosphere models especially under drought conditions. © The Author 2015. Published by Oxford University Press.

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