Beier C., Emmett B.A., Tietema A., Schmidt I.K., Penũelas J., Láng E.K., Duce P., De Angelis P., Gorissen A., Estiarte M., De Dato G.D., Sowerby A., Kröel-Dulay G., Lellei-Kovács E., Kull O., Mand P., Petersen H., Gjelstrup P., Spano D. (2009) Carbon and nitrogen balances for six shrublands across Europe. Global Biogeochemical Cycles. 23: 0-0.EnllaçDoi: 10.1029/2008GB003381
Shrublands constitute significant and important parts of European landscapes providing a large number of important ecosystem services. Biogeochemical cycles in these ecosystems have gained little attention relative to forests and grassland systems, but data on such cycles are required for developing and testing ecosystem models. As climate change progresses, the potential feedback from terrestrial ecosystems to the atmosphere through changes in carbon stocks, carbon sequestration, and general knowledge on biogeochemical cycles becomes increasingly important. Here we present carbon and nitrogen balances of six shrublands along a climatic gradient across the European continent. The aim of the study was to provide a basis for assessing the range and variability in carbon storage in European shrublands. Across the sites the net carbon storage in the systems ranged from 1,163 g C m-2 to 18,546 g C m-2, and the systems ranged from being net sinks (126 g C m -2 a-1) to being net sources (-536 g C m-2 a-1) of carbon with the largest storage and sink of carbon at wet and cold climatic conditions. The soil carbon store dominates the carbon budget at all sites and in particular at the site with a cold and wet climate where soil C constitutes 95% of the total carbon in the ecosystem. Respiration of carbon from the soil organic matter pool dominated the carbon loss at all sites while carbon loss from aboveground litter decomposition appeared less important. Total belowground carbon allocation was more than 5 times aboveground litterfall carbon which is significantly greater than the factor of 2 reported in a global analysis of forest data. Nitrogen storage was also dominated by the soil pools generally showing small losses except when atmospheric N input was high. The study shows that in the future a climate-driven land cover change between grasslands and shrublands in Europe will likely lead to increased ecosystem C where shrublands are promoted and less where grasses are promoted. However, it also emphasizes that if feedbacks on the global carbon cycle are to be predicted it is critically important to quantify and understand belowground carbon allocation and processes as well as soil carbon pools, particularly on wet organic soils, rather than plant functional change as the soil stores dominate the overall budget and fluxes of carbon. Copyright 2009 by the American Geophysical Union.
Blanch J.-S., Peñuelas J., Sardans J., Llusià J. (2009) Drought, warming and soil fertilization effects on leaf volatile terpene concentrations in Pinus halepensis and Quercus ilex. Acta Physiologiae Plantarum. 31: 207-218.EnllaçDoi: 10.1007/s11738-008-0221-z
The changes in foliar concentrations of volatile terpenes in response to water stress, fertilization and temperature were analyzed in Pinus halepensis and Quercus ilex. The most abundant terpenes found in both species were α-pinene and Δ3-carene. β-Pinene and myrcene were also abundant in both species. P. halepensis concentrations were much greater than those of Q. ilex in agreement with the lack of storage in the latter species (15205.60 ± 1140.04 vs. 0.54 ± 0.08 μg g-1 [d.m.]). The drought treatment (reduction to 1/3 of full watering) significantly increased the total terpene concentrations in both species (54% in P. halepensis and 119% in Q. ilex). The fertilization treatment (addition of either 250 kg N ha-1 or 250 kg P ha-1 or both) had no significant effects on terpene foliar concentrations. The terpene concentrations increased from 0.25 μg g-1 [d.m.] at 30°C to 0.70 μg g-1 [d.m.] at 40°C in Q. ilex (the non-storing species) and from 2,240 μg g-1 [d.m.] at 30°C to 15,621 μg g-1 [d.m.] at 40°C in P. halepensis (the storing species). Both species presented negative relationship between terpene concentrations and relative water contents (RWC). The results of this study show that higher terpene concentrations can be expected in the warmer and drier conditions predicted for the next decades in the Mediterranean region. © 2008 Franciszek Górski Institute of Plant Physiology, Polish Academy of Sciences.
Craine J.M., Elmore A.J., Aidar M.P.M., Bustamante M., Dawson T.E., Hobbie E.A., Kahmen A., MacK M.C., McLauchlan K.K., Michelsen A., Nardoto G.B., Pardo L.H., Peñuelas J., Reich P.B., Schuur E.A.G., Stock W.D., Templer P.H., Virginia R.A., Welker J.M., Wright I.J. (2009) Global patterns of foliar nitrogen isotopes and their relationships with climate, mycorrhizal fungi, foliar nutrient concentrations, and nitrogen availability. New Phytologist. 183: 980-992.EnllaçDoi: 10.1111/j.1469-8137.2009.02917.x
Ratios of nitrogen (N) isotopes in leaves could elucidate underlying patterns of N cycling across ecological gradients. To better understand global-scale patterns of N cycling, we compiled data on foliar N isotope ratios (δ15N), foliar N concentrations, mycorrhizal type and climate for over 11 000 plants worldwide. Arbuscular mycorrhizal, ectomycorrhizal, and ericoid mycorrhizal plants were depleted in foliar δ15N by 2‰, 3.2‰, 5.9‰, respectively, relative to nonmycorrhizal plants. Foliar δ15N increased with decreasing mean annual precipitation and with increasing mean annual temperature (MAT) across sites with MAT ≥ -0.5°C, but was invariant with MAT across sites with MAT < -0.5°C. In independent landscape-level to regional-level studies, foliar δ15N increased with increasing N availability; at the global scale, foliar δ15N increased with increasing foliar N concentrations and decreasing foliar phosphorus (P) concentrations. Together, these results suggest that warm, dry ecosystems have the highest N availability, while plants with high N concentrations, on average, occupy sites with higher N availability than plants with low N concentrations. Global-scale comparisons of other components of the N cycle are still required for better mechanistic understanding of the determinants of variation in foliar δ15N and ultimately global patterns in N cycling.
Díaz-de-Quijano M., Peñuelas J., Ribas A. (2009) Increasing interannual and altitudinal ozone mixing ratios in the Catalan Pyrenees. Atmospheric Environment. 43: 6049-6057.EnllaçDoi: 10.1016/j.atmosenv.2009.08.035
Interannual, seasonal, daily and altitudinal patterns of tropospheric ozone mixing ratios, as well as ozone phytotoxicity and the relationship with NOx precursors and meteorological variables were monitored in the Central Catalan Pyrenees (Meranges valley and Forest of Guils) over a period of 5 years (2004-2008). Biweekly measurements using Radiello passive samplers were taken along two altitudinal transects comprised of thirteen stations ranging from 1040 to 2300 m a.s.l. Visual symptoms of ozone damage in Bel-W3 tobacco cultivars were evaluated biweekly for the first three years (2004-2006). High ozone mixing ratios, always above forest and vegetation protection AOT40 thresholds, were monitored every year. In the last 14 years, the AOT40 (Apr-Sept.) has increased significantly by 1047 μg m-3 h per year. Annual means of ozone mixing ratios ranged between 38 and 67 ppbv (38 and 74 ppbv during the warm period) at the highest site (2300 m) and increased at a rate of 5.1 ppbv year-1. The ozone mixing ratios were also on average 35-38% greater during the warm period and had a characteristic daily pattern with minimum values in the early morning, a rise during the morning and a decline overnight, that was less marked the higher the altitude. Whereas ozone mixing ratios increased significantly with altitude from 35 ppbv at 1040 m-56 ppbv at 2300 m (on average for 2004-2007 period), NO2 mixing ratios decreased with altitude from 5.5 ppbv at 1040 m-1 ppbv at 2300 m. The analysis of meteorological variables and NOx values suggests that the ozone mainly originated from urban areas and was transported to high-mountain sites, remaining aloft in absence of NO. Ozone damage rates increased with altitude in response to increasing O3 mixing ratios and a possible increase in O3 uptake due to more favorable microclimatic conditions found at higher altitude, which confirms Bel-W3 as a suitable biomonitor for ozone concentrations during summer time. Compared to the valley-bottom site the annual means of ozone mixing ratios are 37% larger in the higher sites. Thus the AOT40 for the forest and vegetation protection threshold is greatly exceeded at higher sites. This could have substantial effects on plant life at high altitudes in the Pyrenees. © 2009 Elsevier Ltd. All rights reserved.
Filella I., Peñuelas J., Seco R. (2009) Short-chained oxygenated VOC emissions in Pinus halepensis in response to changes in water availability. Acta Physiologiae Plantarum. 31: 311-318.EnllaçDoi: 10.1007/s11738-008-0235-6
Short-chained oxygenated VOC (oxVOCs) emissions from Pinus halepensis saplings were monitored in response to changes in water availability. Online measurements were made with a proton transfer reaction-mass spectrometer under controlled conditions, together with CO2 and H2O exchange measurements. Masses corresponding to methanol and acetone were the most emitted oxVOCs. All the oxVOC exchanges, except that of acetone (M59), were significantly related to stomatal conductance and transpiration. Acetaldehyde (M45) emission showed, moreover, a strong dependence on the concentration of acetaldehyde in the ambient: stomatal opening (stomatal conductance above 75 mmol m-2 s-1) only allowed increased emissions when external concentration were below 6 ppb. Acetone (M59) presented an important peak of emission following light and stomatal opening in the morning when plants were water stressed. Thus, the alterations in oxVOC emissions in P. halepensis caused by the water deficit seem to be mainly driven by water stress effect on stomatal closure and oxVOC air concentrations. © 2008 Franciszek Górski Institute of Plant Physiology, Polish Academy of Sciences, Kraków.
Filella I., Porcar-Castell A., Munné-Bosch S., Bäck J., Garbulsky M.F., Peñuelas J. (2009) PRI assessment of long-term changes in carotenoids/chlorophyll ratio and short-term changes in de-epoxidation state of the xanthophyll cycle. International Journal of Remote Sensing. 30: 4443-4455.EnllaçDoi: 10.1080/01431160802575661
The Photochemical Reflectance Index (PRI), an index based on leaf reflectance at 531 nm, has been found suitable for tracking variations in photosynthetic activity from leaf to ecosystem levels. This suitability has been attributed to PRI correlation with xanthophyll interconversion and photosynthetic radiation-use efficiency. However, other pigments and factors may be involved in such relationships. We studied the relationship between PRI and xanthophylls and other carotenoids in saplings of two widely distributed evergreen species (Scots pine and Holm oak) submitted to experimentally changing light conditions in a field experiment. PRI was strongly correlated with the de-epoxidation state of xanthophylls (DEPS, an expression of the relative concentration of the three xanthophyll cycle pigments), but also with carotenoids/chlorophyll ratio and β-carotene/chlorophyll ratio in both species. However, following momentary decreases in light due to clouds, PRI changed following the DEPS changes, while the carotenoids/chlorophyll ratio remained constant. The results show that PRI was able to reveal short-term changes in de-epoxidation state, i.e. the signal of xanthophyll interconversion, but it also tracked long-term changes in carotenoids/chlorophyll. Carotenoids other than xanthophylls, e.g. β-carotene, are also related to photoprotective processes, thus also making PRI effective as a measure of changes in photosynthetic light-use efficiency in response to stress on a long-term level. © 2009 Taylor & Francis.
Terradas J, Peñuelas J, Lloret F (2009) The Fluctuation Niche in Plants. International Journal of Ecology doi: 10.1155/2009/959702. Article ID 959702.
Sardans J, Peñuelas J, Ogaya R (2009) Climate change and drought: a threat for Mediterranean ecosystem. UAB DIVULGA 2009/02.
Hallik L, Kull O, Nilson T, Peñuelas J (2009) Spectral reflectance of multispecies herbaceous and moss canopies in the boreal forest understory and open field. Canadian Journal of Remote Sensing 35: 474-485.
Peñuelas J, Llebot JE, Cacho I (2009) Una diagnosi pionera del canvi climàtic a Catalunya. A "Les veus del CADS. 10 anys del Consell Assessor per al Desenvolupament Sostenible de Catalunya". Consell Assessor per al Desenvolupament Sostenible de Catalunya. pp. 19-30
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