Smith N.G., Keenan T.F., Colin Prentice I., Wang H., Wright I.J., Niinemets Ü., Crous K.Y., Domingues T.F., Guerrieri R., Yoko Ishida F., Kattge J., Kruger E.L., Maire V., Rogers A., Serbin S.P., Tarvainen L., Togashi H.F., Townsend P.A., Wang M., Weerasinghe L.K., Zhou S.-X. (2019) Global photosynthetic capacity is optimized to the environment. Ecology Letters. : 0-0.EnllaçDoi: 10.1111/ele.13210
Earth system models (ESMs) use photosynthetic capacity, indexed by the maximum Rubisco carboxylation rate (Vcmax), to simulate carbon assimilation and typically rely on empirical estimates, including an assumed dependence on leaf nitrogen determined from soil fertility. In contrast, new theory, based on biochemical coordination and co-optimization of carboxylation and water costs for photosynthesis, suggests that optimal Vcmax can be predicted from climate alone, irrespective of soil fertility. Here, we develop this theory and find it captures 64% of observed variability in a global, field-measured Vcmax dataset for C3 plants. Soil fertility indices explained substantially less variation (32%). These results indicate that environmentally regulated biophysical constraints and light availability are the first-order drivers of global photosynthetic capacity. Through acclimation and adaptation, plants efficiently utilize resources at the leaf level, thus maximizing potential resource use for growth and reproduction. Our theory offers a robust strategy for dynamically predicting photosynthetic capacity in ESMs. © 2019 John Wiley & Sons Ltd/CNRS
Asbjornsen H., Campbell J.L., Jennings K.A., Vadeboncoeur M.A., McIntire C., Templer P.H., Phillips R.P., Bauerle T.L., Dietze M.C., Frey S.D., Groffman P.M., Guerrieri R., Hanson P.J., Kelsey E.P., Knapp A.K., McDowell N.G., Meir P., Novick K.A., Ollinger S.V., Pockman W.T., Schaberg P.G., Wullschleger S.D., Smith M.D., Rustad L.E. (2018) Guidelines and considerations for designing field experiments simulating precipitation extremes in forest ecosystems. Methods in Ecology and Evolution. 9: 2310-2325.EnllaçDoi: 10.1111/2041-210X.13094
Precipitation regimes are changing in response to climate change, yet understanding of how forest ecosystems respond to extreme droughts and pluvials remains incomplete. As future precipitation extremes will likely fall outside the range of historical variability, precipitation manipulation experiments (PMEs) are critical to advancing knowledge about potential ecosystem responses. However, few PMEs have been conducted in forests compared to short-statured ecosystems, and forest PMEs have unique design requirements and constraints. Moreover, past forest PMEs have lacked coordination, limiting cross-site comparisons. Here, we review and synthesize approaches, challenges, and opportunities for conducting PMEs in forests, with the goal of guiding design decisions, while maximizing the potential for coordination. We reviewed 63 forest PMEs at 70 sites world-wide. Workshops, meetings, and communications with experimentalists were used to generate and build consensus around approaches for addressing the key challenges and enhancing coordination. Past forest PMEs employed a variety of study designs related to treatment level, replication, plot and infrastructure characteristics, and measurement approaches. Important considerations for establishing new forest PMEs include: selecting appropriate treatment levels to reach ecological thresholds; balancing cost, logistical complexity, and effectiveness in infrastructure design; and preventing unintended water subsidies. Response variables in forest PMEs were organized into three broad tiers reflecting increasing complexity and resource intensiveness, with the first tier representing a recommended core set of common measurements. Differences in site conditions combined with unique research questions of experimentalists necessitate careful adaptation of guidelines for forest PMEs to balance local objectives with coordination among experiments. We advocate adoption of a common framework for coordinating forest PME design to enhance cross-site comparability and advance fundamental knowledge about the response and sensitivity of diverse forest ecosystems to precipitation extremes. © 2018 The Authors. Methods in Ecology and Evolution © 2018 British Ecological Society
Craine J.M., Elmore A.J., Wang L., Aranibar J., Bauters M., Boeckx P., Crowley B.E., Dawes M.A., Delzon S., Fajardo A., Fang Y., Fujiyoshi L., Gray A., Guerrieri R., Gundale M.J., Hawke D.J., Hietz P., Jonard M., Kearsley E., Kenzo T., Makarov M., Marañón-Jiménez S., McGlynn T.P., McNeil B.E., Mosher S.G., Nelson D.M., Peri P.L., Roggy J.C., Sanders-DeMott R., Song M., Szpak P., Templer P.H., Van der Colff D., Werner C., Xu X., Yang Y., Yu G., Zmudczyńska-Skarbek K. (2018) Isotopic evidence for oligotrophication of terrestrial ecosystems. Nature ecology & evolution. 2: 1735-1744.EnllaçDoi: 10.1038/s41559-018-0694-0
Human societies depend on an Earth system that operates within a constrained range of nutrient availability, yet the recent trajectory of terrestrial nitrogen (N) availability is uncertain. Examining patterns of foliar N concentrations and isotope ratios (δ15N) from more than 43,000 samples acquired over 37 years, here we show that foliar N concentration declined by 9% and foliar δ15N declined by 0.6-1.6‰. Examining patterns across different climate spaces, foliar δ15N declined across the entire range of mean annual temperature and mean annual precipitation tested. These results suggest declines in N supply relative to plant demand at the global scale. In all, there are now multiple lines of evidence of declining N availability in many unfertilized terrestrial ecosystems, including declines in δ15N of tree rings and leaves from herbarium samples over the past 75-150 years. These patterns are consistent with the proposed consequences of elevated atmospheric carbon dioxide and longer growing seasons. These declines will limit future terrestrial carbon uptake and increase nutritional stress for herbivores.
Fyllas N.M., Bentley L.P., Shenkin A., Asner G.P., Atkin O.K., Díaz S., Enquist B.J., Farfan-Rios W., Gloor E., Guerrieri R., Huasco W.H., Ishida Y., Martin R.E., Meir P., Phillips O., Salinas N., Silman M., Weerasinghe L.K., Zaragoza-Castells J., Malhi Y. (2017) Solar radiation and functional traits explain the decline of forest primary productivity along a tropical elevation gradient. Ecology Letters. : 0-0.EnllaçDoi: 10.1111/ele.12771
One of the major challenges in ecology is to understand how ecosystems respond to changes in environmental conditions, and how taxonomic and functional diversity mediate these changes. In this study, we use a trait-spectra and individual-based model, to analyse variation in forest primary productivity along a 3.3 km elevation gradient in the Amazon-Andes. The model accurately predicted the magnitude and trends in forest productivity with elevation, with solar radiation and plant functional traits (leaf dry mass per area, leaf nitrogen and phosphorus concentration, and wood density) collectively accounting for productivity variation. Remarkably, explicit representation of temperature variation with elevation was not required to achieve accurate predictions of forest productivity, as trait variation driven by species turnover appears to capture the effect of temperature. Our semi-mechanistic model suggests that spatial variation in traits can potentially be used to estimate spatial variation in productivity at the landscape scale. © 2017 John Wiley & Sons Ltd/CNRS.
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., Barbeta, A., Achotegui-Castells, A., Gargallo-Garriga, A., Sperlich, D., Farré-Armengol, G., Fernández-Martínez, M., Liu, D., Zhang, C., Urbina, I., Camino-Serrano, M., Vives-Ingla, M., Stocker, B.D., Balzarolo, M., Guerrieri, R., Peaucelle, M., Marañón-Jiménez, S., Bórnez-Mejías, K., Mu, Z., Descals, A., Castellanos, A., Terradas, J. (2017) Impacts of global change on Mediterranean forests and their services. Forests. 8: 0-0.EnllaçDoi: 10.3390/f8120463
Bahar N.H.A., Ishida F.Y., Weerasinghe L.K., Guerrieri R., O'Sullivan O.S., Bloomfield K.J., Asner G.P., Martin R.E., Lloyd J., Malhi Y., Phillips O.L., Meir P., Salinas N., Cosio E.G., Domingues T.F., Quesada C.A., Sinca F., Escudero Vega A., Zuloaga Ccorimanya P.P., del Aguila-Pasquel J., Quispe Huaypar K., Cuba Torres I., Butrón Loayza R., Pelaez Tapia Y., Huaman Ovalle J., Long B.M., Evans J.R., Atkin O.K. (2016) Leaf-level photosynthetic capacity in lowland Amazonian and high-elevation Andean tropical moist forests of Peru. New Phytologist. : 0-0.EnllaçDoi: 10.1111/nph.14079
We examined whether variations in photosynthetic capacity are linked to variations in the environment and/or associated leaf traits for tropical moist forests (TMFs) in the Andes/western Amazon regions of Peru. We compared photosynthetic capacity (maximal rate of carboxylation of Rubisco (Vcmax), and the maximum rate of electron transport (Jmax)), leaf mass, nitrogen (N) and phosphorus (P) per unit leaf area (Ma, Na and Pa, respectively), and chlorophyll from 210 species at 18 field sites along a 3300-m elevation gradient. Western blots were used to quantify the abundance of the CO2-fixing enzyme Rubisco. Area- and N-based rates of photosynthetic capacity at 25°C were higher in upland than lowland TMFs, underpinned by greater investment of N in photosynthesis in high-elevation trees. Soil [P] and leaf Pa were key explanatory factors for models of area-based Vcmax and Jmax but did not account for variations in photosynthetic N-use efficiency. At any given Na and Pa, the fraction of N allocated to photosynthesis was higher in upland than lowland species. For a small subset of lowland TMF trees examined, a substantial fraction of Rubisco was inactive. These results highlight the importance of soil- and leaf-P in defining the photosynthetic capacity of TMFs, with variations in N allocation and Rubisco activation state further influencing photosynthetic rates and N-use efficiency of these critically important forests. © 2016 New Phytologist Trust.
Guerrieri, R., Lepine, L., Asbjornsen, H., Xiao, J., Ollinger, S.V. (2016) Evapotranspiration and water use efficiency in relation to climate and canopy nitrogen in U.S. forests. Journal of Geophysical Research G: Biogeosciences. : 0-0.EnllaçDoi: 10.1002/2016JG003415
Malhi, Y., Girardin, C.A.J., Goldsmith, G.R., Doughty, C.E., Salinas, N., Metcalfe, D.B., Huaraca Huasco, W., Silva-Espejo, J.E., del Aguilla-Pasquell, J., Farfán Amézquita, F., Aragão, L.E.O.C., Guerrieri, R., Ishida, F.Y., Bahar, N.H.A., Farfan-Rios, W., Phillips, O.L., Meir, P., Silman, M. (2016) The variation of productivity and its allocation along a tropical elevation gradient: A whole carbon budget perspective. New Phytologist. : 0-0.EnllaçDoi: 10.1111/nph.14189
Guerrieri R., Vanguelova E.I., Michalski G., Heaton T.H.E., Mencuccini M. (2015) Isotopic evidence for the occurrence of biological nitrification and nitrogen deposition processing in forest canopies. Global Change Biology. 21: 4613-4626.EnllaçDoi: 10.1111/gcb.13018
This study examines the role of tree canopies in processing atmospheric nitrogen (Ndep) for four forests in the United Kingdom subjected to different Ndep: Scots pine and beech stands under high Ndep (HN, 13-19 kg N ha-1 yr-1), compared to Scots pine and beech stands under low Ndep (LN, 9 kg N ha-1 yr-1). Changes of NO3-N and NH4-N concentrations in rainfall (RF) and throughfall (TF) together with a quadruple isotope approach, which combines δ18O, Δ17O and δ15N in NO3 - and δ15N in NH4 +, were used to assess N transformations by the canopies. Generally, HN sites showed higher NH4-N and NO3-N concentrations in RF compared to the LN sites. Similar values of δ15N-NO3 - and δ18O in RF suggested similar source of atmospheric NO3 - (i.e. local traffic), while more positive values for δ15N-NH4 + at HN compared to LN likely reflected the contribution of dry NHx deposition from intensive local farming. The isotopic signatures of the N-forms changed after interacting with tree canopies. Indeed, 15N-enriched NH4 + in TF compared to RF at all sites suggested that canopies played an important role in buffering dry Ndep also at the low Ndep site. Using two independent methods, based on δ18O and Δ17O, we quantified for the first time the proportion of NO3 - in TF, which derived from nitrification occurring in tree canopies at the HN site. Specifically, for Scots pine, all the considered isotope approaches detected biological nitrification. By contrast for the beech, only using the mixing model with Δ17O, we were able to depict the occurrence of nitrification within canopies. Our study suggests that tree canopies play an active role in the N cycling within forest ecosystems. Processing of Ndep within canopies should not be neglected and needs further exploration, with the combination of multiple isotope tracers, with particular reference to Δ17O. © 2015 John Wiley & Sons Ltd.
Ripullone F., Rivelli A.R., Baraldi R., Guarini R., Guerrieri R., Magnani F., Peñuelas J., Raddi S., Borghetti M. (2011) Effectiveness of the photochemical reflectance index to track photosynthetic activity over a range of forest tree species and plant water statuses. Functional Plant Biology. 38: 177-186.EnllaçDoi: 10.1071/FP10078
In this study, we investigated the potential of the photochemical resistance index (PRI) to track photosynthetic activity under water stress conditions by measuring PRI, leaf fluorescence, the xanthophyll cycle and photosynthetic activity in different forest tree species subjected to progressive drought. The PRI declined with pre-dawn water potential and a significant relationship between PRI and the xanthophyll de-epoxidation state (DEPS) was observed, although with large interspecific variability in the sensitivity of PRI to changes in DEPS. For single tree species, a strong relationship was observed on either PRI light saturated photosynthesis or PRI maximum photochemical efficiency of PSII (ΔF/Fm′); a larger variability in both relationships was apparent when data from different species were pooled together. However, an improved correlation was shown only in the former relationship by plotting the PRI (dawn PRI minus the midday PRI values). Thus, we conclude that PRI is able to provide a good estimate of maximum CO2 assimilation at saturating light and ΔF/F m′ for single tree species, despite the severe drought conditions applied. PRI should be applied more cautiously when dealing with multispecific forests because of confounding factors such as the strong interspecific differences in the initial value of PRI and in the sensitivity of PRI to changes in DEPS in response to drought. © 2011 CSIRO.
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