Seasonal and diurnal variations of plant isoprenoid emissions from two dominant species in Mediterranean shrubland and forest submitted to experimental drought

Mu Z., Llusià J., Liu D., Ogaya R., Asensio D., Zhang C., Peñuelas J. (2018) Seasonal and diurnal variations of plant isoprenoid emissions from two dominant species in Mediterranean shrubland and forest submitted to experimental drought. Atmospheric Environment. 191: 105-115.
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Doi: 10.1016/j.atmosenv.2018.08.010

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We tested the effect of increasing drought conditions in the Mediterranean Basin on isoprenoid emissions for the coming decades by analyzing their effect experimentally on the dominant Mediterranean species Erica multiflora in a Garraf shrubland and Quercus ilex in a Prades forest in Catalonia (Spain). Drought was simulated in Garraf using automatically sliding curtains to decrease the amount of soil moisture by 5% and in Prades by partial rainfall exclusion and runoff exclusion for a 25% decrease. We measured photosynthetic rates (A), stomatal conductance (gs) and rates of isoprenoid emission in the morning and at midday for four seasons and determined the relationship of emission rates with environmental conditions. Terpenes were emitted by both species, but only E. multiflora emitted isoprene. α-Pinene and limonene were the most abundant terpenes. Isoprenoid emissions increased with air temperature and generally decreased as the amount of soil moisture increased. The results of this study suggest that higher isoprenoid emissions can be expected in the warmer and drier conditions predicted for the coming decades in the Mediterranean region. © 2018

Llegeix més

Ecosystem thresholds, tipping points, and critical transitions

Munson S.M., Reed S.C., Peñuelas J., McDowell N.G., Sala O.E. (2018) Ecosystem thresholds, tipping points, and critical transitions. New Phytologist. 218: 1315-1317.
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Doi: 10.1111/nph.15145

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[No abstract available]

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Thirsty tree roots exude more carbon

Preece C., Farré-Armengol G., Llusià J., Peñuelas J. (2018) Thirsty tree roots exude more carbon. Tree Physiology. 38: 690-695.
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Doi: 10.1093/treephys/tpx163

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Root exudation is an important input of carbon into soils and affects plant and soil communities, but little is known about the effect of climatic factors such as drought on exudation, and its ability to recover. We studied the impact of increasing drought on root exudation and its subsequent recovery in the Mediterranean tree species Quercus ilex L. in a greenhouse study by measuring the amount of total organic carbon in exudates. The amount of exudation per unit root area increased with drought duration and was 21% higher under the most extreme drought scenario compared with the non-droughted control. The amount of root exudation did not differ between the treatments following 6 weeks of re-watering, indicating a strong capacity for recovery in this species. We concluded that drought could affect the amount of root exudation, which could in turn have a large impact on microbial activity in the rhizosphere, and alter these microbial communities, at least in the short term. This tree species may be able to return to normal levels of root exudation after a drought event, but long-term exudate-mediated impacts on Mediterranean forest soils may be an unforeseen effect of drought. © The Author(s) 2018. Published by Oxford University Press. All rights reserved.

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Critical temperature and precipitation thresholds for the onset of xylogenesis of Juniperus przewalskii in a semi-arid area of the north-eastern Tibetan Plateau

Ren P., Rossi S., Camarero J.J., Ellison A.M., Liang E., Peñuelas J. (2018) Critical temperature and precipitation thresholds for the onset of xylogenesis of Juniperus przewalskii in a semi-arid area of the north-eastern Tibetan Plateau. Annals of Botany. 121: 617-624.
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Doi: 10.1093/aob/mcx188

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Background and Aims The onset of xylogenesis plays an important role in tree growth and carbon sequestration, and it is thus a key variable in modelling the responses of forest ecosystems to climate change. Temperature regulates the resumption of cambial activity, but little is known about the effect of water availability on the onset of xylogenesis in cold but semi-arid regions. Methods The onset of xylogenesis during 2009-2014 was monitored by weekly microcoring Juniperus przewalskii trees at upper and lower treelines on the north-eastern Tibetan Plateau. A logistic regression was used to calculate the probability of xylogenic activity at a given temperature and a two-dimensional reverse Gaussian model to fit the differences between the observed and estimated days of xylogenesis onset at given temperatures and precipitation within a certain time window. Key Results The thermal thresholds at the beginning of the growing season were highly variable, suggesting that temperature was not the only factor initiating xylem growth under cold and dry climatic conditions. The onset of xylogenesis was well predicted for climatic thresholds characterized by a cumulative precipitation of 17.0 ± 5.6 mm and an average minimum temperature of 1.5 ± 1.4 °C for a period of 12 d. Conclusions Xylogenesis in semi-arid regions with dry winters and springs can start when both critical temperature and precipitation thresholds are reached. Such findings contribute to our knowledge of the environmental drivers of growth resumption that previously had been investigated largely in cold regions without water shortages during early growing seasons. Models of the onset of xylogenesis should include water availability to improve predictions of xylem phenology in dry areas. A mismatch between the thresholds of temperature and moisture for the onset of xylogenesis may increase forest vulnerability in semi-arid areas under forecasted warmer and drier conditions. © 2017 The Author(s). Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved.

Llegeix més

Coping with iron limitation: a metabolomic study of Synechocystis sp. PCC 6803

Rivas-Ubach A., Poret-Peterson A.T., Peñuelas J., Sardans J., Pérez-Trujillo M., Legido-Quigley C., Oravec M., Urban O., Elser J.J. (2018) Coping with iron limitation: a metabolomic study of Synechocystis sp. PCC 6803. Acta Physiologiae Plantarum. 40: 0-0.
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Doi: 10.1007/s11738-018-2603-1

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Iron (Fe) is a key element for all living systems, especially for photosynthetic organisms because of its important role in the photosynthetic electron transport chain. Fe limitation in cyanobacteria leads to several physiological and morphological changes. However, the overall metabolic responses to Fe limitation are still poorly understood. In this study, we integrated elemental, stoichiometric, macromolecular, and metabolomic data to shed light on the responses of Synechocystis sp. PCC 6803, a non-N2-fixing freshwater cyanobacterium, to Fe limitation. Compared to Synechocystis growing at nutrient replete conditions, Fe-limited cultures had lower growth rates and amounts of chlorophyll a, RNA, RNA:DNA, C, N, and P, and higher ratios of protein:RNA, C:N, C:P, and N:P, in accordance with the growth rate hypothesis which predicts faster growing organisms will have decreased biomass RNA contents and C:P and N:P ratios. Fe-limited Synechocystis had lower amounts Fe, Mn, and Mo, and higher amount of Cu. Several changes in amino acids of cultures growing under Fe limitation suggest nitrogen limitation. In addition, we found substantial increases in stress-related metabolites in Fe-limited cyanobacteria such antioxidants. This study represents an advance in understanding the stoichiometric, macromolecular, and metabolic strategies that cyanobacteria use to cope with Fe limitation. This information, moreover, may further understanding of changes in cyanobacterial functions under scenarios of Fe limitation in aquatic ecosystems. © 2018, Franciszek Górski Institute of Plant Physiology, Polish Academy of Sciences, Kraków.

Llegeix més

Characterisation of functional-trait dynamics at high spatial resolution in a mediterranean forest from sentinel-2 and ground-truth data

Schauman S., Verger A., Filella I., Peñuelas J. (2018) Characterisation of functional-trait dynamics at high spatial resolution in a mediterranean forest from sentinel-2 and ground-truth data. Remote Sensing. 10: 0-0.
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Doi: 10.3390/rs10121874

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The characterisation of functional-trait dynamics of vegetation from remotely sensed data complements the structural characterisation of ecosystems. In this study we characterised for the first time the spatial heterogeneity of the intra-annual dynamics of the fraction of absorbed photosynthetically active radiation (FAPAR) as a functional trait of the vegetation in Prades Mediterranean forest in Catalonia, Spain. FAPAR was derived from the Multispectral Instrument (MSI) on the Sentinel-2 satellite and validated by comparison with the ground measurements acquired in June 2017 at the annual peak of vegetation activity. The validation results showed that most of points were distributed along the 1:1 line, with no bias nor scattering: R2 = 0.93, p < 0.05; with a root mean square error of 0.03 FAPAR (4.3%). We classified the study area into nine vegetation groups with different dynamics of FAPAR using a methodology that is objective and repeatable over time. This functional classification based on the annual magnitude (FAPAR-M) and the seasonality (FAPAR-CV) from the data on one year (2016-2017) complements structural classifications. The internal heterogeneity of the FAPAR dynamics in each land-cover type is attributed to the environmental and to the specific species composition variability. A spatial autoregressive (SAR) model for the main type of land cover, evergreen holm oak forest (Quercus ilex), indicated that topographic aspect, slope, height, and the topographic aspect x slope interaction accounted for most of the spatial heterogeneity of the functional trait FAPAR-M, thus improving our understanding of the explanatory factors of the annual absorption of photosynthetically active radiation by the vegetation canopy for this ecosystem. © 2018 by the authors.

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Moisture-mediated responsiveness of treeline shifts to global warming in the Himalayas

Sigdel S.R., Wang Y., Camarero J.J., Zhu H., Liang E., Peñuelas J. (2018) Moisture-mediated responsiveness of treeline shifts to global warming in the Himalayas. Global Change Biology. 24: 5549-5559.
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Doi: 10.1111/gcb.14428

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Among forest ecosystems, the alpine treeline ecotone can be considered to be a simplified model to study global ecology and climate change. Alpine treelines are expected to shift upwards in response to global warming given that tree recruitment and growth are assumed to be mainly limited by low temperatures. However, little is known whether precipitation and temperature interact to drive long-term Himalayan treeline dynamics. Tree growth is affected by spring rainfall in the central Himalayan treelines, being good locations for testing if, in addition to temperature, precipitation mediates treeline dynamics. To test this hypothesis, we reconstructed spatiotemporal variations in treeline dynamics in 20 plots located at six alpine treeline sites, dominated by two tree species (birch, fir), and situated along an east–west precipitation gradient in the central Himalayas. Our reconstructions evidenced that treelines shifted upward in response to recent climate warming, but their shift rates were primarily mediated by spring precipitation. The rate of upward shift was higher in the wettest eastern Himalayas, suggesting that its ascent rate was facilitated by spring precipitation. The drying tendency in association with the recent warming trends observed in the central Himalayas, however, will likely hinder an upslope advancement of alpine treelines and promote downward treeline shifts if moisture availability crosses a critical minimum threshold. Our study highlights the complexity of plant responses to climate and the need to consider multiple climate factors when analyzing treeline dynamics. © 2018 John Wiley & Sons Ltd

Llegeix més

Soil microbial CNP and respiration responses to organic matter and nutrient additions: Evidence from a tropical soil incubation

Soong J.L., Marañon-Jimenez S., Cotrufo M.F., Boeckx P., Bodé S., Guenet B., Peñuelas J., Richter A., Stahl C., Verbruggen E., Janssens I.A. (2018) Soil microbial CNP and respiration responses to organic matter and nutrient additions: Evidence from a tropical soil incubation. Soil Biology and Biochemistry. 122: 141-149.
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Doi: 10.1016/j.soilbio.2018.04.011

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Soil nutrient availability has a strong influence on the fate of soil carbon (C) during microbial decomposition, contributing to Earth's C balance. While nutrient availability itself can impact microbial physiology and C partitioning between biomass and respiration during soil organic matter decomposition, the availability of labile C inputs may mediate the response of microorganisms to nutrient additions. As soil organic matter is decomposed, microorganisms retain or release C, nitrogen (N) or phosphorus (P) to maintain a stoichiometric balance. Although the concept of a microbial stoichiometric homeostasis has previously been proposed, microbial biomass CNP ratios are not static, and this may have very relevant implications for microbial physiological activities. Here, we tested the hypothesis that N, P and potassium (K) nutrient additions impact C cycling in a tropical soil due to microbial stoichiometric constraints to growth and respiration, and that the availability of energy-rich labile organic matter in the soil (i.e. leaf litter) mediates the response to nutrient addition. We incubated tropical soil from French Guiana with a 13C labeled leaf litter addition and with mineral nutrient additions of +K, +N, +NK, +PK and +NPK for 30 days. We found that litter additions led to a ten-fold increase in microbial respiration and a doubling of microbial biomass C, along with greater microbial N and P content. We found some evidence that P additions increased soil CO2 fluxes. Additionally, we found microbial biomass CP and NP ratios varied more widely than CN in response to nutrient and organic matter additions, with important implications for the role of microorganisms in C cycling. The addition of litter did not prime soil organic matter decomposition, except in combination with +NK fertilization, indicating possible P-mining of soil organic matter in this P-poor tropical soil. Together, these results point toward an ultimate labile organic substrate limitation of soil microorganisms in this tropical soil, but also indicate a complex interaction between C, N, P and K availability. This highlights the difference between microbial C cycling responses to N, P, or K additions in the tropics and explains why coupled C, N and P cycle modeling efforts cannot rely on strict microbial stoichiometric homeostasis as an underlying assumption. © 2018

Llegeix més

Quantifying soil moisture impacts on light use efficiency across biomes

Stocker B.D., Zscheischler J., Keenan T.F., Prentice I.C., Peñuelas J., Seneviratne S.I. (2018) Quantifying soil moisture impacts on light use efficiency across biomes. New Phytologist. 218: 1430-1449.
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Doi: 10.1111/nph.15123

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Terrestrial primary productivity and carbon cycle impacts of droughts are commonly quantified using vapour pressure deficit (VPD) data and remotely sensed greenness, without accounting for soil moisture. However, soil moisture limitation is known to strongly affect plant physiology. Here, we investigate light use efficiency, the ratio of gross primary productivity (GPP) to absorbed light. We derive its fractional reduction due to soil moisture (fLUE), separated from VPD and greenness changes, using artificial neural networks trained on eddy covariance data, multiple soil moisture datasets and remotely sensed greenness. This reveals substantial impacts of soil moisture alone that reduce GPP by up to 40% at sites located in sub-humid, semi-arid or arid regions. For sites in relatively moist climates, we find, paradoxically, a muted fLUE response to drying soil, but reduced fLUE under wet conditions. fLUE identifies substantial drought impacts that are not captured when relying solely on VPD and greenness changes and, when seasonally recurring, are missed by traditional, anomaly-based drought indices. Counter to common assumptions, fLUE reductions are largest in drought-deciduous vegetation, including grasslands. Our results highlight the necessity to account for soil moisture limitation in terrestrial primary productivity data products, especially for drought-related assessments. © 2018 The Authors. New Phytologist © 2018 New Phytologist Trust

Llegeix més

Coupling of ecosystem-scale plant water storage and leaf phenology observed by satellite

Tian F., Wigneron J.-P., Ciais P., Chave J., Ogée J., Peñuelas J., Ræbild A., Domec J.-C., Tong X., Brandt M., Mialon A., Rodriguez-Fernandez N., Tagesson T., Al-Yaari A., Kerr Y., Chen C., Myneni R.B., Zhang W., Ardö J., Fensholt R. (2018) Coupling of ecosystem-scale plant water storage and leaf phenology observed by satellite. Nature Ecology and Evolution. 2: 1428-1435.
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Doi: 10.1038/s41559-018-0630-3

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Plant water storage is fundamental to the functioning of terrestrial ecosystems by participating in plant metabolism, nutrient and sugar transport, and maintenance of the integrity of the hydraulic system of the plant. However, a global view of the size and dynamics of the water pools stored in plant tissues is still lacking. Here, we report global patterns of seasonal variations in ecosystem-scale plant water storage and their relationship with leaf phenology, based on space-borne measurements of L-band vegetation optical depth. We find that seasonal variations in plant water storage are highly synchronous with leaf phenology for the boreal and temperate forests, but asynchronous for the tropical woodlands, where the seasonal development of plant water storage lags behind leaf area by up to 180 days. Contrasting patterns of the time lag between plant water storage and terrestrial groundwater storage are also evident in these ecosystems. A comparison of the water cycle components in seasonally dry tropical woodlands highlights the buffering effect of plant water storage on the seasonal dynamics of water supply and demand. Our results offer insights into ecosystem-scale plant water relations globally and provide a basis for an improved parameterization of eco-hydrological and Earth system models. © 2018, The Author(s).

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