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Net ecosystem CO2 exchange is the result of net carbon uptake by plant photosynthesis and carbon loss by soil and plant respiration. Temperature increases due to climate change can modify the equilibrium between these fluxes and trigger ecosystem‐climate feedbacks that can accelerate climate warming. As these dynamics have not been well studied in dry shrublands, we subjected a Mediterranean shrubland to a 10‐year night‐time temperature manipulation experiment that analyzed ecosystem carbon fluxes associated with dominant shrub species, together with several plant parameters related to leaf photosynthesis, leaf morphology, and canopy structure. Under moderate night‐time warming (+0.9°C minimum daily temperature, no significant reduction in soil moisture), Cistus monspeliensis formed shoots with more leaves that were relatively larger and denser canopies that supported higher plant‐level photosynthesis rates. Given that ecosystem respiration was not affected, this change in canopy morphology led to a significant enhancement in net ecosystem exchange (+47% at midday). The observed changes in shoot and canopy morphology were attributed to the improved nutritional state of the warmed plants, primarily due to changes in nitrogen cycling and higher nitrogen resorption efficiency in senescent leaves. Our results show that modifications in plant morphology triggered by moderate warming affected ecosystem CO2 fluxes, providing the first evidence for enhanced daytime carbon uptake in a dry shrubland ecosystem under experimental warming. [ABSTRACT FROM AUTHOR]

Deicing agents cause soil salinization and degradation in urban areas. We assessed the capacity of urban lawns to maintain carbon sequestration and nutrient cycling with increasing soil salinity. The sensitivity to soil salinity of the main ecosystem players: plants and microorganisms were assessed considering their complex interactions between each other and environment. The effects of low and moderate soil salinization by common deicing agent (NaCl) were evaluated in mesocosms planted with two urban lawns: Lolium perenne and mixture of grasses. Mesocosm‐, plant‐, and soil‐level gas exchange were assessed on a short‐term (days) and long‐term (months) scales. Microbial response was characterized by analyzing the microbial properties and activities of nine enzymes. Carbon balance remained independent on the salinity due to cancelling effect of lowered gross primary production (GPP, −20%), decreased C input by plants into the soil (−40% for mixture) balanced by slower microbial decomposition of organic matter (−20%) and so, lower soil respiration (−35%). GPP declined as a long‐term response by a combination of stomatal constraint on photosynthesis with leaf respiration increase. Toxic effects of salinization on soil respiration were observed only for temperatures above 15°C. Microbial community with high C:N ratio (common for fungi) was the most sensitive to salinization. The death of microbial biomass (−31% for Lolium) and cell lysis increased soil enzyme activities (+38% for Lolium). We conclude that C balance of urban lawns remain homeostatic at secondary salinization. Temperature effects and plant‐microbial interactions will determine C and nutrients cycling under salinity stress in urban lawns. [ABSTRACT FROM AUTHOR]

Understanding how different combinations of plant functional traits contribute to species fitness is a question of considerable ecological interest, that can give insights into the mechanisms controlling community assembly, and into the processes by which climate change can modify plant community structure and composition. We investigated the changes in cover degree of three shrubs (Cistus monspeliensis, Dorycnium pentaphyllum and Helichrysum microphyllum) growing in a Mediterranean garrigue subjected for 11 years to a reduced rainfall regime, following a conceptual framework based on the two‐phase resource dynamic model: considering the seasonal drought typical of the Mediterranean climate, the two‐phases were identified based on high (pulse phase) and low (interpulse phase) soil water availability. We developed a parameter proportional to the whole plant photosynthesis (plant photosynthetic index, PPI), scaling up the leaf photosynthesis to canopy level, taking into account the different canopy densities and the fluctuations in leaf biomass due to summer leaf shedding. PPI was used to derive plant performance estimators for both pulse (maximum value reached by PPI, PPImax) and interpulse phase (duration of the exhaustion phase, Durep, when drought constrains PPI below the plant carbon compensation point determining carbon starvation). For each species the ratio between PPImax and Durep (named PPIred) was used as an index of plant performance. The reduced rainfall regime mainly decreased the performances of the dominant species C. monspeliensis, both limiting PPImax and extending Durep. Under both natural and the manipulated rainfall regime, PPIred was proportional to plant success, measured as the cover degree variation rate of the species. This result suggests that a mechanistic approach using functional traits to quantify the different performance of co‐occurring species can be used to investigate 1) the drivers of the medium‐term changes in species abundance and 2) the processes responsible for change in plant community composition under climate change. [ABSTRACT FROM AUTHOR]

Hydrological cycle is expected to become the primary cause of ecosystem's degradation in near future under changing climate. Rain manipulation experiments under field conditions provide accurate picture on the responses of biotic processes to changed water availability for plants. A field experiment, mimicking expected changes in rain patterns, was established in a Mediterranean shrub community at Porto Conte, Italy, in 2001. In November 2011 Cistus monspeliensis , one of the dominating shrub species in the Mediterranean basin, was 13 C labelled on plots subjected to extended rain shortage period and on control non manipulated plots. Carbon (C) allocation was traced by 13 C dynamics in shoots, shoot-respired CO 2 , roots, microbial biomass, K 2 SO 4 -extractable C and CO 2 respired from soil. Most of the recovered 13 C (60%) was respired by shoots within 2 weeks in control plots. In rain shortage treatment, 13 C remained incorporated in aboveground plant parts. Residence time of 13 C in leaves was longer under the rain shortage because less 13 C was lost by shoot respiration and because 13 C was re-allocated to leaves from woody tissues. The belowground C sink was weak (3–4% of recovered 13 C) and independent on rain manipulation. Extended rain shortage promoted C exudation into rhizosphere soil in expense of roots. Together with lowered photosynthesis, this “save” economy of new C metabolites reduces the growing season under rain shortage resulting in decrease of shrub cover and C losses from the system on the long-term. [ABSTRACT FROM AUTHOR]

Soils are being degraded at an alarming rate and thereby also crucial ecosystem goods and services. Nitrogen (N) enrichment is a major driver of this degradation. While the negative impacts of N enrichment on vegetation are well known globally, those on various ecological interactions, and on ecosystem functioning, remain largely unknown. Because Mediterranean ecosystems are N limited, they are good model systems for evaluating how N enrichment impacts not only vegetation but also ecological partnerships and ecosystem functioning. Using a 7-year N-manipulation (dose and form) field experiment running in a Mediterranean Basin maquis located in a region with naturally low ambient N deposition (<4 kg N ha−1 y−1), we assessed the impacts of the N additions on (i) the dominant plant species (photosynthetic N-use efficiency); (ii) plant-soil ecological partnerships with ectomycorrhiza and N-fixing bacteria; and (iii) ecosystem degradation (plant-soil cover, biological mineral weathering and soil N fixation). N additions significantly disrupted plant-soil cover, plant-soil biotic interactions, and ecosystem functioning compared with ambient N deposition conditions. However, the higher the ammonium dose (alone or with nitrate), the more drastic these disruptions were. We report a critical threshold at 20-40 kg ammonium ha−1 y−1 whereby severe ecosystem degradation can be expected. These observations are critical to help explain the mechanisms behind ecosystem degradation, to describe the collective loss of organisms and multifunction in the landscape, and to predict potential fragmentation of Mediterranean maquis under conditions of unrelieved N enrichment. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Water availability, together with temperature, represents the most limiting abiotic factor regulating soil CO2 efflux (SR). Besides the direct effect of water limitation, drought also influences plant activity, determining changes in the quality and quantity of root exudates, thus indirectly affecting soil microbial activity. To determine how the seasonal changes of plant activity and soil microbial metabolism and structure affect SR response to drought, we investigated the correlation between leaf gas exchange, soil carbon pools and soil respiration sources and the role of soil carbon pools on microbial populations and soil respiration, in a summer deciduous Mediterranean (SDS) and a winter deciduous temperate (WDS) shrublands, experiencing a dry summer period. In both sites, drought reduced photosynthesis, but affected SR differently: in SDS, SR decreased, although microbial heterotrophic respiration (SRh) remained unchanged; in WDS, SR did not vary but SRh was reduced. While in SDS the microbial community was able to respire more complex substrates, in WDS it was strongly dependent on easily decomposable molecules, thus on plant activity. Therefore, the response of soil CO2 efflux to water limitation is not exclusively influenced by climate as it is modulated by the degree of adaptation of the microbial community to drought. [ABSTRACT FROM AUTHOR]

A transient state canopy-chamber was developed to monitor CO2 exchange of shrubland ecosystems. The chamber covered 0.64 m² and it was modular with a variable height. Several tests were carried out to check the potential errors in the flux estimates due to leakages and the environment modifications during the measurements inside the chamber. The laboratory leakages test showed an error below 1% of the flux; the temperature increases inside the chamber were below 1.3 °C at different light intensity and small pressure changes. The radial blowers inside the chamber created different wind speed at different chamber height, with faster speed at the top of the chamber and the minimum wind speed that was recorded at soil level, preventing detectable effects on soil CO2 emission rates. Moreover, the chamber was tested for two years in a semi-arid Mediterranean garrigue, identifying a strong seasonality of CO2 fluxes with the highest rates during spring and lowest rates recorded during the hot dry non-vegetative summer. [ABSTRACT FROM AUTHOR]

Above- and belowground carbon (C) stores of terrestrial ecosystems are vulnerable to environmental change. Ecosystem C balances in response to environmental changes have been quantified at individual sites, but the magnitudes and directions of these responses along environmental gradients remain uncertain. Here we show the responses of ecosystem C to 8-12 years of experimental drought and night-time warming across an aridity gradient spanning seven European shrublands using indices of C assimilation (aboveground net primary production: aNPP) and soil C efflux (soil respiration: Rs). The changes of aNPP and Rs in response to drought indicated that wet systems had an overall risk of increased loss of C but drier systems did not. Warming had no consistent effect on aNPP across the climate gradient, but suppressed Rs more at the drier sites. Our findings suggest that above- and belowground C fluxes can decouple, and provide no evidence of acclimation to environmental change at a decadal timescale. aNPP and Rs especially differed in their sensitivity to drought and warming, with belowground processes being more sensitive to environmental change. [ABSTRACT FROM AUTHOR]

Highlights: [•] We analysed Cistus monspeliensis spring-leaf functioning under experimental drought. [•] Assimilation rates were reduced only before leaf morphological adaptations occurred. [•] These adaptations were adopted earlier under experimental dry conditions. [•] When natural summer aridity occurred, leaf morphology also changed in the control. [•] Leaf shedding was anticipated under experimental drought to reduce water losses. [Copyright &y& Elsevier]