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Calfapietra C.,CNR Institute of Agro-environmental and Forest Biology | Calfapietra C.,Academy of Sciences of the Czech Republic | Penuelas J.,Global Ecology Unit CREAF CSIC UAB | Niinemets T.,Estonian University of Life Sciences | Niinemets T.,Estonian Academy of Sciences
Trends in Plant Science

Urban environments that are stressful for plant function and growth will become increasingly widespread in future. In this opinion article, we define the concept of 'urban plant physiology', which focuses on plant responses and long term adaptations to urban conditions and on the capacity of urban vegetation to mitigate environmental hazards in urbanized settings such as air and soil pollution. Use of appropriate control treatments would allow for studies in urban environments to be comparable to expensive manipulative experiments. In this opinion article, we propose to couple two approaches, based either on environmental gradients or manipulated gradients, to develop the concept of urban plant physiology for assessing how single or multiple environmental factors affect the key environmental services provided by urban forests. © 2014 Elsevier Ltd. Source

Fu Y.H.,Peking University | Fu Y.H.,University of Antwerp | Zhao H.,Peking University | Piao S.,Peking University | And 18 more authors.

Earlier spring leaf unfolding is a frequently observed response of plants to climate warming. Many deciduous tree species require chilling for dormancy release, and warming-related reductions in chilling may counteract the advance of leaf unfolding in response to warming. Empirical evidence for this, however, is limited to saplings or twigs in climate-controlled chambers. Using long-term in situ observations of leaf unfolding for seven dominant European tree species at 1,245 sites, here we show that the apparent response of leaf unfolding to climate warming (S T, expressed in days advance of leaf unfolding per °C warming) has significantly decreased from 1980 to 2013 in all monitored tree species. Averaged across all species and sites, S T decreased by 40% from 4.0 ± 1.8 days °C-1 during 1980-1994 to 2.3 ± 1.6 days °C-1 during 1999-2013. The declining S T was also simulated by chilling-based phenology models, albeit with a weaker decline (24-30%) than observed in situ. The reduction in S T is likely to be partly attributable to reduced chilling. Nonetheless, other mechanisms may also have a role, such as 'photoperiod limitation' mechanisms that may become ultimately limiting when leaf unfolding dates occur too early in the season. Our results provide empirical evidence for a declining S T, but also suggest that the predicted strong winter warming in the future may further reduce S T and therefore result in a slowdown in the advance of tree spring phenology. © 2015 Macmillan Publishers Limited. All rights reserved. Source

Sanchez-Lorenzo A.,University of Girona | Sanchez-Lorenzo A.,CSIC - Pyrenean Institute of Ecology | Vicente-Serrano S.M.,CSIC - Pyrenean Institute of Ecology | Wild M.,ETH Zurich | And 3 more authors.
Climate Research

Interest is growing in the trends of atmospheric evaporation demand, increasing the need for long-term time series. This work describes, for the first time, the development of a dataset on evaporation in Spain based on long-term series of Piché and pan measurement records. Piché measurements have been reported for >50 stations since the 1960s. Measurements of pan evaporation, which is a much more widely studied variable in the literature, are also available, but only since 1984 for 21 stations. Particular emphasis was placed on the homogenization of this dataset. Both the mean annual Piché and pan series over Spain showed evaporative increases during the common study period (1985?2011), by a rate of around +0.1 mm d?1 decade?1. Furthermore, using the annual Piché records since the 1960s, an evaporation decline was detected from the 1960s to the mid-1980s, which resulted in a non-significant trend over the entire 1961?2011 period. Our results indicate agreement between the decadal variability of reference evapotranspiration and the surface solar radiation previously reported and the evaporation from Piché and pan measurements, especially during summer. The suitability of Piché records compared to pan evaporation data to represent past trends is discussed. © 2014 Inter-Research. Source

Sardans J.,Global Ecology Unit CREAF CSIC UAB | Penuelas J.,Global Ecology Unit CREAF CSIC UAB
Global Ecology and Biogeography

Aim: Potassium (K) is the second most abundant nutrient in plant photosynthetic tissues after nitrogen (N). Thousands of physiological and metabolic studies in recent decades have established the fundamental role of K in plant function, especially in water-use efficiency and economy, and yet macroecological studies have mostly overlooked this nutrient. Methods: We have reviewed available studies on the content, stoichiometry and roles of K in the soil-plant system and in terrestrial ecosystems. We have also reviewed the impacts of global change drivers on K content, stoichiometry and roles. Conclusions: The current literature indicates that K, at a global level, is as limiting as N and phosphorus (P) for plant productivity in terrestrial ecosystems. Some degree of K limitation has been seen in up to 70% of all studied terrestrial ecosystems. However, in some areas atmospheric K deposition from human activities is greater than that from natural sources. We are far from understanding the K fluxes between the atmosphere and land, and the role of anthropogenic activities in these fluxes. The increasing aridity expected in wide areas of the world makes K more critical through its role in water-use efficiency. N deposition exerts a strong impact on the ecosystem K cycle, decreasing K availability and increasing K limitation. Plant invasive success is enhanced by higher soil K availability, especially in environments without strong abiotic stresses. The impacts of other drivers of global change, such as increasing atmospheric CO2 or changes in land use, remain to be elucidated. Current models of the responses of ecosystems and carbon storage to projected global climatic and atmospheric changes are now starting to consider N and P, but they should also consider K, mostly in arid and semi-arid ecosystems. © 2015 John Wiley & Sons Ltd. Source

Zechmeister-Boltenstern S.,University of Natural Resources and Life Sciences, Vienna | Keiblinger K.M.,University of Natural Resources and Life Sciences, Vienna | Mooshammer M.,University of Vienna | Penuelas J.,Global Ecology Unit CREAF CSIC UAB | And 3 more authors.
Ecological Monographs

Elemental stoichiometry constitutes an inherent link between biogeochemistry and the structure and processes within food webs, and thus is at the core of ecosystem functioning. Stoichiometry allows for spanning different levels of biological organization, from cellular metabolism to ecosystem structure and nutrient cycling, and is therefore particularly useful for establishing links between different ecosystem compartments. We review elemental carbon : nitrogen : phosphorus (C:N:P) ratios in terrestrial ecosystems (from vegetation, leaf litter, woody debris, and dead roots, to soil microbes and organic matter). While the stoichiometry of the plant, litter, and soil compartments of ecosystems is well understood, heterotrophic microbial communities, which dominate the soil food web and drive nutrient cycling, have received increasing interest in recent years. This review highlights the effects of resource stoichiometry on soil microorganisms and decomposition, specifically on the structure and function of heterotrophic microbial communities and suggests several general patterns. First, latitudinal gradients of soil and litter stoichiometry are reflected in microbial community structure and function. Second, resource stoichiometry may cause changes in microbial interactions and community dynamics that lead to feedbacks in nutrient availability. Third, global change alters the C:N, C:P, and N:P ratios of primary producers, with repercussions for microbial decomposer communities and critical ecosystem services such as soil fertility. We argue that ecological stoichiometry provides a framework to analyze and predict such global change effects at various scales. © 2015 by the Ecological Society of America. Source

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