Sardans J., Alonso R., Carnicer J., Fernández-Martínez M., Vivanco M.G., Peñuelas J. (2016) Factors influencing the foliar elemental composition and stoichiometry in forest trees in Spain. Perspectives in Plant Ecology, Evolution and Systematics. 18: 52-69.LinkDoi: 10.1016/j.ppees.2016.01.001
Concentrations of nutrient elements in organisms and in the abiotic environment are key factors influencing ecosystem structure and function. We studied how concentrations and stoichiometries of nitrogen (N), phosphorus (P) and potassium (K) in leaves of forest trees are related to phylogeny and to environmental factors (mean annual precipitation, mean annual temperature, forest type, and nitrogen deposition). Using data for 4691 forest plots from across Spain, we tested the following hypotheses: (i) that foliar stoichiometries of forest trees are strongly influenced by phylogeny, (ii) that climate, as an important driver of plant uptake and nutrient use efficiency, affects foliar stoichiometry, (iii) that long-term loads of N influence N, P and K concentrations and ratios in natural vegetation, and (iv) that sympatric species are differentiated according to their foliar stoichiometry, thereby reducing the intensity of resource competition. Our analyses revealed that several factors contributed to interspecific variation in elemental composition and stoichiometry. These included phylogeny, forest type, climate, N deposition, and competitive neighborhood relationships (probably related to niche segregation effect).These findings support the notion that foliar elemental composition reflects adaptation both to regional factors such as climate and to local factors such as competition with co-occurring species. © 2016 Elsevier GmbH.
Campioli M., Vicca S., Luyssaert S., Bilcke J., Ceschia E., Chapin Iii F.S., Ciais P., Fernández-Martínez M., Malhi Y., Obersteiner M., Olefeldt D., Papale D., Piao S.L., Peñuelas J., Sullivan P.F., Wang X., Zenone T., Janssens I.A. (2015) Biomass production efficiency controlled by management in temperate and boreal ecosystems. Nature Geoscience. 8: 843-846.LinkDoi: 10.1038/ngeo2553
Plants acquire carbon through photosynthesis to sustain biomass production, autotrophic respiration and production of non-structural compounds for multiple purposes. The fraction of photosynthetic production used for biomass production, the biomass production efficiency, is a key determinant of the conversion of solar energy to biomass. In forest ecosystems, biomass production efficiency was suggested to be related to site fertility. Here we present a database of biomass production efficiency from 131 sites compiled from individual studies using harvest, biometric, eddy covariance, or process-based model estimates of production. The database is global, but dominated by data from Europe and North America. We show that instead of site fertility, ecosystem management is the key factor that controls biomass production efficiency in terrestrial ecosystems. In addition, in natural forests, grasslands, tundra, boreal peatlands and marshes, biomass production efficiency is independent of vegetation, environmental and climatic drivers. This similarity of biomass production efficiency across natural ecosystem types suggests that the ratio of biomass production to gross primary productivity is constant across natural ecosystems. We suggest that plant adaptation results in similar growth efficiency in high- and low-fertility natural systems, but that nutrient influxes under managed conditions favour a shift to carbon investment from the belowground flux of non-structural compounds to aboveground biomass. © 2015 Macmillan Publishers Limited.
Fernandez-Martinez M., Garbulsky M., Penuelas J., Peguero G., Espelta J.M. (2015) Temporal trends in the enhanced vegetation index and spring weather predict seed production in Mediterranean oaks. Plant Ecology. 216: 1061-1072.LinkDoi: 10.1007/s11258-015-0489-1
The extremely year-to-year variable production of seeds (masting) is an extended plant reproductive behaviour important for forest dynamics and food webs. The dependence of these episodes of massive seed production on recently or long-term photosynthesised carbohydrates, however, remains controversial. In this paper, we explore whether vegetation (tree canopy) changes, detected using EVI as a proxy of leaf area and photosynthetic capacity, can provide a reliable estimation of seed production. To complete this analysis, we also explored the effect of weather both in the trends of EVI and in acorn crop size. To this end, we compared the trends of the EVI and acorn production over 10 years (2000–2009) in five stands of Quercus ilex L. in Barcelona (Catalonia, NE Spain). We found that acorn production was mainly driven by a combination of: (i) a minimum initial threshold in the EVI values, (ii) an increase in EVI in the 9 ± 4 months prior to reproduction, and (iii) appropriate weather conditions (low water stress) during spring. These results indicated, apparently for the first time, that reproduction in masting species could be detected and partly predicted by remotely sensed vegetative indices. Our results suggested that this particular reproductive behaviour in Mediterranean oaks was driven by a combination of two factors, i.e. good and improving vegetation conditions, as shown by a minimum initial threshold and the increase in EVI needed for large seed crops, and the need of wet weather conditions during spring. Moreover, our results fully supported recent studies that have associated short-term photosynthate production with seed production. © 2015, Springer Science+Business Media Dordrecht.
Fernández-Martínez M., Vicca S., Janssens I.A., Sardans J., Luyssaert S., Campioli M., Chapin F.S., Ciais P., Malhi Y., Obersteiner M., Papale D., Piao S.L., Reichstein M., Rodà F., Peñuelas J. (2015) Reply to 'Uncertain effects of nutrient availability on global forest carbon balance' and 'Data quality and the role of nutrients in forest carbon-use efficiency'. Nature Climate Change. 5: 960-961.LinkDoi: 10.1038/nclimate2794
[No abstract available]
Sardans J., Alonso R., Janssens I.A., Carnicer J., Vereseglou S., Rillig M.C., Fernández-Martínez M., Sanders T.G.M., Peñuelas J. (2015) Foliar and soil concentrations and stoichiometry of nitrogen and phosphorous across European Pinus sylvestris forests: Relationships with climate, N deposition and tree growth. Functional Ecology. : 0-0.LinkDoi: 10.1111/1365-2435.12541
This study investigated the factors underlying the variability of needle and soil elemental composition and stoichiometry and their relationships with growth in Pinus sylvestris forests throughout the species' distribution in Europe by analysing data from 2245 forest stands. Needle N concentrations and N:P ratios were positively correlated with total atmospheric N deposition, whereas needle P concentrations were negatively correlated. These relationships were especially pronounced at sites where high levels of N deposition coincided with both higher mean annual temperature and higher mean annual precipitation. Trends towards foliar P deficiency were thus more marked when high N deposition coincided with climatic conditions favourable to plant production. Atmospheric N deposition was positively correlated with soil solution NO3- , SO42- , K+, P and Ca2+ concentrations, the soil solution NO3-:P ratio, total soil N and the total soil N:Olsen P ratio and was negatively correlated with soil Olsen P concentration. Despite these nutrient imbalances, during the period studied (1990-2006), N deposition was positively related with Pinus sylvestris absolute basal diameter (BD) growth, although only accounting for the 10% of the total variance. However, neither N deposition nor needle N concentration was related with relative annual BD growth. In contrast, needle P concentration was positively related with both absolute and relative annual BD growth. These results thus indicate a tendency of European P. sylvestris forests to store N in trees and soil in response to N deposition and unveil a trend towards increased nutrient losses in run-off as a consequence of higher soil solution N concentrations. Overall, the data show increasing ecosystem nutrient imbalances with increasingly limiting roles of P and other nutrients such as K in European P. sylvestris forests, especially in the centre of their distribution where higher levels of N deposition are observed. Thus, although the data show that N deposition has had an overall positive effect on P. sylvestris growth, the effect of continuous N deposition, associated with decreasing P and K and increasing N:P in leaves and in soil, may in the future become detrimental for the growth and competitive ability of P. sylvestris trees. © 2015 British Ecological Society.
Fernandez-Martinez M., Vicca S., Janssens I.A., Luyssaert S., Campioli M., Sardans J., Estiarte M., Penuelas J. (2014) Spatial variability and controls over biomass stocks, carbon fluxes, and resource-use efficiencies across forest ecosystems. Trees - Structure and Function. 28: 597-611.LinkDoi: 10.1007/s00468-013-0975-9
Key message: Stand age, water availability, and the length of the warm period are the most influencing controls of forest structure, functioning, and efficiency. We aimed to discern the distribution and controls of plant biomass, carbon fluxes, and resource-use efficiencies of forest ecosystems ranging from boreal to tropical forests. We analysed a global forest database containing estimates of stand biomass and carbon fluxes (400 and 111 sites, respectively) from which we calculated resource-use efficiencies (biomass production, carbon sequestration, light, and water-use efficiencies). We used the WorldClim climatic database and remote-sensing data derived from the Moderate Resolution Imaging Spectroradiometer to analyse climatic controls of ecosystem functioning. The influences of forest type, stand age, management, and nitrogen deposition were also explored. Tropical forests exhibited the largest gross carbon fluxes (photosynthesis and ecosystem respiration), but rather low net ecosystem production, which peaks in temperate forests. Stand age, water availability, and length of the warm period were the main factors controlling forest structure (biomass) and functionality (carbon fluxes and efficiencies). The interaction between temperature and precipitation was the main climatic driver of gross primary production and ecosystem respiration. The mean resource-use efficiency varied little among biomes. The spatial variability of biomass stocks and their distribution among ecosystem compartments were strongly correlated with the variability in carbon fluxes, and both were strongly controlled by climate (water availability, temperature) and stand characteristics (age, type of leaf). Gross primary production and ecosystem respiration were strongly correlated with mean annual temperature and precipitation only when precipitation and temperature were not limiting factors. Finally, our results suggest a global convergence in mean resource-use efficiencies. © 2013 Springer-Verlag Berlin Heidelberg.
Fernandez-Martinez M., Vicca S., Janssens I.A., Sardans J., Luyssaert S., Campioli M., Chapin Iii F.S., Ciais P., Malhi Y., Obersteiner M., Papale D., Piao S.L., Reichstein M., Roda F., Penuelas J. (2014) Nutrient availability as the key regulator of global forest carbon balance. Nature Climate Change. 4: 471-476.LinkDoi: 10.1038/nclimate2177
Forests strongly affect climate through the exchange of large amounts of atmospheric CO 2 (ref.). The main drivers of spatial variability in net ecosystem production (NEP) on a global scale are, however, poorly known. As increasing nutrient availability increases the production of biomass per unit of photosynthesis and reduces heterotrophic respiration in forests, we expected nutrients to determine carbon sequestration in forests. Our synthesis study of 92 forests in different climate zones revealed that nutrient availability indeed plays a crucial role in determining NEP and ecosystem carbon-use efficiency (CUEe; that is, the ratio of NEP to gross primary production (GPP)). Forests with high GPP exhibited high NEP only in nutrient-rich forests (CUEe = 33 ± 4%; mean ± s.e.m.). In nutrient-poor forests, a much larger proportion of GPP was released through ecosystem respiration, resulting in lower CUEe (6 ± 4%). Our finding that nutrient availability exerts a stronger control on NEP than on carbon input (GPP) conflicts with assumptions of nearly all global coupled carbon cycle-climate models, which assume that carbon inputs through photosynthesis drive biomass production and carbon sequestration. An improved global understanding of nutrient availability would therefore greatly improve carbon cycle modelling and should become a critical focus for future research. © 2014 Macmillan Publishers Limited.
Fernández-Martínez M., Belmonte J., Maria Espelta J. (2012) Masting in oaks: Disentangling the effect of flowering phenology, airborne pollen load and drought. Acta Oecologica. 43: 51-59.LinkDoi: 10.1016/j.actao.2012.05.006
Quercus species exhibit an extreme inter-annual variability in seed production often synchronized over large geographical areas (masting). Since this reproductive behavior is mostly observed in anemophilous plants, pollination efficiency is suggested as one hypothesis to explain it, although resource-based hypotheses are also suggested as alternatives. We analyzed the effect of flowering phenology, airborne pollen presence and meteorological conditions in the pattern of acorn production in mixed evergreen-deciduous oak forests (Quercus ilex and Quercus pubescens) in NE Spain for twelve years (1998-2009). In both oaks, higher temperatures advanced the onset of flowering and increased the amount of airborne pollen. Nevertheless, inter-annual differences in pollen production did not influence acorn crop size. Acorn production was enhanced by a delay in flowering onset in Q. ilex but not in Q. pubescens. This suggests that in perennial oaks a larger number of photosynthates produced before flowering could benefit reproduction while the lack of effects on deciduous oaks could be because these species flush new leaves and flowers at the same time. Notwithstanding this effect, spring water deficit was the most relevant factor in explaining inter-annual variability in acorn production in both species. Considering that future climate scenarios predict progressive warmer and dryer spring seasons in the Mediterranean Basin, this might result in earlier onsets of flowering and higher water deficits that would constrain acorn production. © 2012 Elsevier Masson SAS.
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