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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]

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]