Effects of increased nitrogen availability on the structure and functioning of a mediterranean Basin maquis
Year: 2012
Type: dissertation
Abstract: Increased N availability, resulting from agro-industrial activities, affects ecosystems’ stability. Mediterranean Basin ecosystems are biodiversity hotspots threatened by N deposition, however, little or no information is available on their responses to increased N. The general aim of this thesis was to develop an integrated system-level approach to study the responses of a Mediterranean Basin maquis to increased N availability. Since 2007, the form and dose of N available at the experimental site (ambient N deposition 5.2 kg ha-1 yr-1 and soil N 0.1%) was modified by addition of 40 kg NH4 +-N ha-1 yr-1, 40 and 80 kg NH4NO3-N ha-1 yr-1. The structure and functioning of above- and below-ground communities were monitored for 4.5 years. Over the first year, the added N was retained by the system and detected in the autumn as soil inorganic N. The increased N promoted plant and soil microbial diversity. Exposure to 40 kg NH4 +-N ha-1 yr-1 (solely or with nitrate) increased plant diversity but not productivity, while exposure to 40 kg NH4NO3-N ha-1 y-1 increased productivity but not diversity. The Nbenefited species were small short-lived plants, from disturbed and/or eutrophied sites, while N-affected plants were perennial shrubs characteristic of very poor sites. After 2.5 years of treatments, soils from the control and litter from the four treatments were collected for a laboratory decomposition study. The leaf litter produced under the high N treatment was enriched in N and lignin. This study suggested that increasing N in Mediterranean maquis selected for plants with lower litter decomposability, potentially increasing soil organic matter. In agreement, after 4.5 years, soil organic matter and inorganic N had increased under the higher N dose. The dataset permitted the first estimation of an N critical load for this habitat (20-30 kg N ha-1 yr-1). Data suggest that agriculture, a source of NH4 +-N, may decrease the permanent plant cover and increase soil erosion, while industrial and urban activities, sources of NO3 --N, may promote productivity and increase fire risk. This is of significant importance for land-use management in biodiverse and fragmented ecosystems such as the Mediterranean ones, especially in Natura 2000 sites. However, longer-term studies are needed to explore the applicability of the findings and the interaction of N availability with other global change drivers.
Author: Maria Teresa Machado Dias
Language: English
Subfield: Soil Science
Domain: Life Sciences
SDGs: Life on land, Zero hunger
Open Access status: green
OpenAlex ID: W2246427282