Trophic transfer from aquatic to terrestrial ecosystems: a test of the biogeochemical niche hypothesis

Bartrons M., Sardans J., Hoekman D., Peñuelas J. (2018) Trophic transfer from aquatic to terrestrial ecosystems: a test of the biogeochemical niche hypothesis. Ecosphere. 9: 0-0.
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Doi: 10.1002/ecs2.2338

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Matter and energy flow across ecosystem boundaries. Transfers from terrestrial to aquatic ecosystems are frequent and have been widely studied, but the flow of matter from aquatic to terrestrial ecosystems is less known. Large numbers of midges emerge from some lakes in northern Iceland and fly to land. These lakes differ in their levels of eutrophication due to different intensities of geothermal warming and nutrient inputs. In the context of this material transfer from an aquatic to a terrestrial ecosystem, we investigated the relationships between the deposition of midges and the elemental composition and stoichiometry of organisms in low-productivity terrestrial ecosystems. We analyzed several terrestrial food webs in northeastern Iceland with similar food web compositions of terrestrial arthropods but different inputs of midges and analyzed the stoichiometric composition of the different trophic groups. Elemental composition differed among trophic groups and taxa much more than within each trophic group or taxa across the midge deposition gradient. Specifically, the change in N concentration was significant in plants (up to 70% increase in the site with maximum input) but not in predators, which had a more homeostatic elemental composition. These results thus show (1) a significant movement of matter and nutrients from an aquatic to a terrestrial habitat via the emergence of aquatic insects and the deposition of insect carcasses, (2) a larger impact on the elemental composition of plants than arthropods, and (3) support for the biogeochemical niche hypothesis, which predicts that different species should have a specific elemental composition, stoichiometry, and allocation as a consequence of their particular metabolism, physiology, and structure. © 2018 The Authors.

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Global trait–environment relationships of plant communities

Bruelheide H., Dengler J., Purschke O., Lenoir J., Jiménez-Alfaro B., Hennekens S.M., Botta-Dukát Z., Chytrý M., Field R., Jansen F., Kattge J., Pillar V.D., Schrodt F., Mahecha M.D., Peet R.K., Sandel B., van Bodegom P., Altman J., Alvarez-Dávila E., Arfin Khan M.A.S., Attorre F., Aubin I., Baraloto C., Barroso J.G., Bauters M., Bergmeier E., Biurrun I., Bjorkman A.D., Blonder B., Čarni A., Cayuela L., Černý T., Cornelissen J.H.C., Craven D., Dainese M., Derroire G., De Sanctis M., Díaz S., Doležal J., Farfan-Rios W., Feldpausch T.R., Fenton N.J., Garnier E., Guerin G.R., Gutiérrez A.G., Haider S., Hattab T., Henry G., Hérault B., Higuchi P., Hölzel N., Homeier J., Jentsch A., Jürgens N., Kącki Z., Karger D.N., Kessler M., Kleyer M., Knollová I., Korolyuk A.Y., Kühn I., Laughlin D.C., Lens F., Loos J., Louault F., Lyubenova M.I., Malhi Y., Marcenò C., Mencuccini M., Müller J.V., Munzinger J., Myers-Smith I.H., Neill D.A., Niinemets Ü., Orwin K.H., Ozinga W.A., Penuelas J., Pérez-Haase A., Petřík P., Phillips O.L., Pärtel M., Reich P.B., Römermann C., Rodrigues A.V., Sabatini F.M., Sardans J., Schmidt M., Seidler G., Silva Espejo J.E., Silveira M., Smyth A., Sporbert M., Svenning J.-C., Tang Z., Thomas R., Tsiripidis I., Vassilev K., Violle C., Virtanen R., Weiher E., Welk E., Wesche K., Winter M., Wirth C., Jandt U. (2018) Global trait–environment relationships of plant communities. Nature Ecology and Evolution. 2: 1906-1917.
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Doi: 10.1038/s41559-018-0699-8

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Plant functional traits directly affect ecosystem functions. At the species level, trait combinations depend on trade-offs representing different ecological strategies, but at the community level trait combinations are expected to be decoupled from these trade-offs because different strategies can facilitate co-existence within communities. A key question is to what extent community-level trait composition is globally filtered and how well it is related to global versus local environmental drivers. Here, we perform a global, plot-level analysis of trait–environment relationships, using a database with more than 1.1 million vegetation plots and 26,632 plant species with trait information. Although we found a strong filtering of 17 functional traits, similar climate and soil conditions support communities differing greatly in mean trait values. The two main community trait axes that capture half of the global trait variation (plant stature and resource acquisitiveness) reflect the trade-offs at the species level but are weakly associated with climate and soil conditions at the global scale. Similarly, within-plot trait variation does not vary systematically with macro-environment. Our results indicate that, at fine spatial grain, macro-environmental drivers are much less important for functional trait composition than has been assumed from floristic analyses restricted to co-occurrence in large grid cells. Instead, trait combinations seem to be predominantly filtered by local-scale factors such as disturbance, fine-scale soil conditions, niche partitioning and biotic interactions. © 2018, The Author(s), under exclusive licence to Springer Nature Limited.

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Foliar C, N, and P stoichiometry characterize successful plant ecological strategies in the Sonoran Desert

Castellanos A.E., Llano-Sotelo J.M., Machado-Encinas L.I., López-Piña J.E., Romo-Leon J.R., Sardans J., Peñuelas J. (2018) Foliar C, N, and P stoichiometry characterize successful plant ecological strategies in the Sonoran Desert. Plant Ecology. 219: 775-788.
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Doi: 10.1007/s11258-018-0833-3

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Ecological processes are centered to water availability in drylands; however, less known nutrient stoichiometry can help explain much of their structure and ecological interactions. Here we look to the foliar stoichiometry of carbon (C), nitrogen (N), and phosphorus (P) of 38 dominant plant species from the Sonoran Desert, grouped in four different functional types to describe ecological characteristics and processes. We found that foliar N, C:N, C:P, and N:P stoichiometric ratios, but not P, were higher than those known to most other ecosystems and indicate P but not N limitations in leaves. Biological N fixers (BNF) had even higher leaf N concentrations, but bio-elemental concentrations and stoichiometry ratios were not different to other non-N-fixing legume species which underscores the need to understand the physiological mechanisms for high N, and to how costly BNF can succeed in P-limiting drylands environments. Stoichiometry ratios, and to lesser extent elemental concentrations, were able to characterize BNF and colonizing strategies in the Sonoran Desert, as well as explain leaf attribute differences, ecological processes, and biogeochemical niches in this dryland ecosystem, even when no direct reference is made to other water-limitation strategies. © 2018, Springer Science+Business Media B.V., part of Springer Nature.

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Root exudate metabolomes change under drought and show limited capacity for recovery

Gargallo-Garriga A., Preece C., Sardans J., Oravec M., Urban O., Peñuelas J. (2018) Root exudate metabolomes change under drought and show limited capacity for recovery. Scientific Reports. 8: 0-0.
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Doi: 10.1038/s41598-018-30150-0

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Root exudates comprise a large variety of compounds released by plants into the rhizosphere, including low-molecular-weight primary metabolites (particularly saccharides, amino acids and organic acids) and secondary metabolites (phenolics, flavonoids and terpenoids). Changes in exudate composition could have impacts on the plant itself, on other plants, on soil properties (e.g. amount of soil organic matter), and on soil organisms. The effects of drought on the composition of root exudates, however, have been rarely studied. We used an ecometabolomics approach to identify the compounds in the exudates of Quercus ilex (holm oak) under an experimental drought gradient and subsequent recovery. Increasing drought stress strongly affected the composition of the exudate metabolome. Plant exudates under drought consisted mainly of secondary metabolites (71% of total metabolites) associated with plant responses to drought stress, whereas the metabolite composition under recovery shifted towards a dominance of primary metabolites (81% of total metabolites). These results strongly suggested that roots exude the most abundant root metabolites. The exudates were changed irreversibly by the lack of water under extreme drought conditions, and the plants could not recover. © 2018, The Author(s).

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Afforestation neutralizes soil pH

Hong, S., Piao, S., Chen, A., Liu, Y., Liu, L., Peng, S., Sardans, J., Sun, Y., Peñuelas, J., Zeng, H. (2018) Afforestation neutralizes soil pH. Nature Communications. 9: 0-0.
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Doi: 10.1038/s41467-018-02970-1

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Stoichiometry patterns of plant organ N and P in coastal herbaceous wetlands along the East China Sea: implications for biogeochemical niche

Hu M., Peñuelas J., Sardans J., Sun Z., Wilson B.J., Huang J., Zhu Q., Tong C. (2018) Stoichiometry patterns of plant organ N and P in coastal herbaceous wetlands along the East China Sea: implications for biogeochemical niche. Plant and Soil. : 0-0.
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Doi: 10.1007/s11104-018-3759-6

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Background and aims: Nitrogen (N) and phosphorus (P) are essential nutrients for plant growth, and their availability and stoichiometry play pivotal roles in trophic dynamics and community composition. The biogeochemical niche (BN) hypothesis claims that each species should have an optimal elemental composition and stoichiometry as a consequence of its optimal function in its specific ecological niche. Little attention, however, has been given to N and P stoichiometric patterns and test the BN hypothesis in coastal wetland communities from the perspective of organ and species-specific comparisons. Methods: We investigated factors responsible for changes in N and P stoichiometry patterns in different functional groups in coastal wetlands and tested the BN hypothesis by evaluating N and P composition in whole aboveground plants and organs. Results: Both plant N and P concentrations were high in coastal wetlands, indicating that N and P were not likely limiting, although the N:P ratio was slightly lower than the ratio reported in global and Chinese terrestrial flora. N and P concentrations and N:P ratios varied strongly between C3 and C4 species, among species, and among organs within species. N and P concentrations were not correlated with latitude, mean annual temperature and precipitation, although N:P ratio was weakly correlated with these factors. The differences in N and P concentrations and N:P ratios along the wetland gradients were mainly because of the species-specific community composition of each site. Conclusions: The results are consistent with the BN hypothesis. First, N and P composition is species-specific (homeostatic component of BN), each species tends to maintain its own composition even growing in different sites with different species composition. Second, different species, despite maintaining their own composition, have distinct degree of composition phenotypic flexibility (flexibility component of BN); this different size of “biogeochemical space” was observed when comparing different species living in the same community and the shifts in species BN space and size was observed when comparing populations of the same species living in different sites. © 2018, Springer Nature Switzerland AG.

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Remote sensing of canopy nitrogen at regional scale in Mediterranean forests using the spaceborne MERIS terrestrial chlorophyll index

Loozen Y., Rebel K.T., Karssenberg D., Wassen M.J., Sardans J., Peñuelas J., De Jong S.M. (2018) Remote sensing of canopy nitrogen at regional scale in Mediterranean forests using the spaceborne MERIS terrestrial chlorophyll index. Biogeosciences. 15: 2723-2742.
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Doi: 10.5194/bg-15-2723-2018

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Canopy nitrogen (N) concentration and content are linked to several vegetation processes. Therefore, canopy N concentration is a state variable in global vegetation models with coupled carbon (C) and N cycles. While there are ample C data available to constrain the models, widespread N data are lacking. Remotely sensed vegetation indices have been used to detect canopy N concentration and canopy N content at the local scale in grasslands and forests. Vegetation indices could be a valuable tool to detect canopy N concentration and canopy N content at larger scale. In this paper, we conducted a regional case-study analysis to investigate the relationship between the Medium Resolution Imaging Spectrometer (MERIS) Terrestrial Chlorophyll Index (MTCI) time series from European Space Agency (ESA) Envisat satellite at 1ĝ€km spatial resolution and both canopy N concentration (%N) and canopy N content (Nĝ€gĝ€mĝ'2, of ground area) from a Mediterranean forest inventory in the region of Catalonia, in the northeast of Spain. The relationships between the datasets were studied after resampling both datasets to lower spatial resolutions (20, 15, 10 and 5ĝ€km) and at the original spatial resolution of 1ĝ€km. The results at higher spatial resolution (1ĝ€km) yielded significant log-linear relationships between MTCI and both canopy N concentration and content: r2ĝ€ Combining double low line ĝ€0.32 and r2ĝ€ Combining double low line ĝ€0.17, respectively. We also investigated these relationships per plant functional type. While the relationship between MTCI and canopy N concentration was strongest for deciduous broadleaf and mixed plots (r2ĝ€ Combining double low line ĝ€0.24 and r2ĝ€ Combining double low line ĝ€0.44, respectively), the relationship between MTCI and canopy N content was strongest for evergreen needleleaf trees (r2ĝ€ Combining double low line ĝ€0.19). At the species level, canopy N concentration was strongly related to MTCI for European beech plots (r2ĝ€ Combining double low line ĝ€0.69). These results present a new perspective on the application of MTCI time series for canopy N detection. © Author(s) 2018.

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Global and regional phosphorus budgets in agricultural systems and their implications for phosphorus-use efficiency

Lun, F., Liu, J., Ciais, P., Nesme, T., Chang, J., Wang, R., Goll, D., Sardans, J., Peñuelas, J., Obersteiner, M. (2018) Global and regional phosphorus budgets in agricultural systems and their implications for phosphorus-use efficiency. Earth System Science Data. 10: 1-18.
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Doi: 10.5194/essd-10-1-2018

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Higher capability of C3 than C4 plants to use nitrogen inferred from nitrogen stable isotopes along an aridity gradient

Luo W., Wang X., Sardans J., Wang Z., Dijkstra F.A., Lü X.-T., Peñuelas J., Han X. (2018) Higher capability of C3 than C4 plants to use nitrogen inferred from nitrogen stable isotopes along an aridity gradient. Plant and Soil. : 1-11.
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Doi: 10.1007/s11104-018-3661-2

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Background and aims: The nitrogen isotope composition (δ15N) of plants in arid and semiarid grasslands is affected by environmental factors, especially water availability. Nevertheless, it is unclear whether the response of δ15N to water availability differs between C3 and C4 photosynthetic pathways. Methods: We investigated plant δ15N of coexisting C3 and C4 species as a function of aridity along a 3200 km aridity gradient across the arid and semi-arid grasslands of northern China. Results: Aridity was positively correlated with plant δ15N values in both C3 and C4 plants and also in the entire plant community, whereas soil bulk δ15N values increased first and then decreased along the aridity gradient. The N uptake by C4 plants appeared to be more affected by competition pressure of neighboring plants and soil microbes than for C3 plants along the transect. Conclusions: The decoupled relationship between plant and soil δ15N values indicated that variations in vegetation and soil δ15N values were driven by differential biogeochemical processes, while different soil N sources were used for plant growth along the climatic gradient. The advantage of C3 plants in the use of N may counteract the competitive advantage that C4 plants have over C3 plants due to their higher water use efficiency under drier conditions. These findings can help understand why C4 plants do not completely replace C3 plants in drier environments despite their higher water use efficiency. © 2018 Springer International Publishing AG, part of Springer Nature

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Effects of extreme drought on plant nutrient uptake and resorption in rhizomatous vs bunchgrass-dominated grasslands

Luo W., Xu C., Ma W., Yue X., Liang X., Zuo X., Knapp A.K., Smith M.D., Sardans J., Dijkstra F.A., Peñuelas J., Bai Y., Wang Z., Yu Q., Han X. (2018) Effects of extreme drought on plant nutrient uptake and resorption in rhizomatous vs bunchgrass-dominated grasslands. Oecologia. : 0-0.
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Doi: 10.1007/s00442-018-4232-1

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Both the dominance and the mass ratio hypotheses predict that plant internal nutrient cycling in ecosystems is determined by the dominant species within plant communities. We tested this hypothesis under conditions of extreme drought by assessing plant nutrient (N, P and K) uptake and resorption in response to experimentally imposed precipitation reductions in two semiarid grasslands of northern China. These two communities shared similar environmental conditions, but had different dominant species—one was dominated by a rhizomatous grass (Leymus chinensis) and the other by a bunchgrass (Stipa grandis). Results showed that responses of N to drought differed between the two communities with drought decreasing green leaf N concentration and resorption in the community dominated by the rhizomatous grass, but not in the bunchgrass-dominated community. In contrast, negative effects of drought on green leaf P and K concentrations and their resorption efficiencies were consistent across the two communities. Additionally, in each community, the effects of extreme drought on soil N, P and K supply did not change synchronously with that on green leaf N, P and K concentrations, and senesced leaf N, P and K concentrations showed no response to extreme drought. Consistent with the dominance/mass ratio hypothesis, our findings suggest that differences in dominant species and their growth form (i.e., rhizomatous vs bunch grass) play an important nutrient-specific role in mediating plant internal nutrient cycling across communities within a single region. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature.

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