Alleviating Nitrogen Limitation in Mediterranean Maquis Vegetation Leads to Ecological Degradation

Abstract

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.

Shrub Invasion Overrides the Effect of Imposed Drought on the Photosynthetic Capacity and Physiological Responses of Mediterranean Cork Oak Trees

“…The values of V cmax and J max observed in our study are in agreement with previous studies reported for cork oak with contrasting water availabilities [36,37] or in studies with other Quercus or sclerophylls [26,38,39]. Similarly, the observed values of V cmax and J max for gum rockrose in our study were like those reported for gum rockrose during the summer in the only study that we are aware of [40], but also for other sclerophyllous shrubs [26,39,41].…”

“…However, mesophyll conductance was also observed to decrease under drought conditions, potentially contributing to the reduction in apparent V cmax [4,26,37]. Despite cork oak showing high mesophyll conductance values (around 0.1 mol CO 2 m −2 s −1 ) compared to other evergreen oaks [26,37,53], the mesophyll conductance in gum rockrose [40] and other malacophylls is about double (> 0.2 mol CO 2 m −2 s −1 [26,37,41]. The contribution of mesophyll limitations for the whole non-stomatal limitations in each species remains to be clarified.…”

Integrating Ecological Principles for Addressing Plant Production Security and Move beyond the Dichotomy ‘Good or Bad’ for Nitrogen Inputs Choice

“…The low NUE may increase as the external concentrations of N, particularly nitrate, are reduced. Under natural Mediterranean conditions, a long-term N-manipulation study (since 2007) shows that N availability (and ammonium in particular) is a driving force for biodiversity changes above- [51,52] and belowground [53][54][55], suggesting that the biotic compartments (living plants, plant litter, soil biota) have a crucial role in preventing N losses [50]. Whether low NUE is actually a feature of plant species' response according to the availability of different N sources under natural environments [51,52] is still rather difficult to generalize, particularly for agro-ecosystems.…”

Changes in reflectance of rice seedlings during planthopper feeding as detected by digital camera: Potential applications for high-throughput phenotyping

“…Thus, this paper presents a novel approach for using multivariate statistics of combined red, green and blue values to evaluate resistance to planthoppers. Previous studies have used similar methods for environmental assessments, such as evaluating phytotoxicity to grassland plants [64] or the impact of nitrogen enrichment on Mediterranean maquis vegetation [65].…”