How do microlocal environmental variations affect microbial activities of a Pinus halepensis litter in a Mediterranean coastal area?

Abstract

Mediterranean coastal ecosystems suffer many different types of natural and anthropogenic environmental pressure. Microbial communities, major conductors of organic matter decomposition are also subject to these environmental constraints. In this study, our aim was to understand how microbial activities vary at a small spatio-temporal scale in a Mediterranean coastal environment. Microbial activities were monitored in a Pinus halepensis litter collected from two areas, one close to (10 m) and one far from (300 m) the French Mediterranean coast. Litters were transferred from one area to the other using litterbags and studied via different microbial indicators after 2, 5 and 13 months. Microbial Basal Respiration, qCO₂, certain enzyme activities (laccase, cellulase, β-glucosidase and acid phosphatase) and functional diversity via Biolog microplates were assayed in litterbags left in the area of origin as well as in litterbags transferred from one area to the other. Results highlight that microbial activities differ significantly in this short spatial scale over time. The influence of microlocal conditions more intensified for litters situated close to the sea, especially during summer seems to have a stressful effect on microbial communities, leading to less efficient functional activities. However, microbial activities were more strongly influenced by temporal variations linked to seasonality than by location.

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“…This result reveals that the environmental conditions specific to the Mediterranean coastal area have a stronger effect than agriculture practices on soil functional diversity. This is consistent with previous research that has shown the significant contribution of micro‐local environmental conditions, such as exposure to salinity in coastal environments, to strong functional diversity (Qasemian et al ., ). Similarly, the selective adaptation of microbial populations to drought and osmotic stresses was responsible for the large functional diversity of microbes in a Greek Mediterranean grassland (Papatheodorou et al ., ).…”

Infra-red spectroscopy reveals chemical interactions driving water availability for enzyme activities in litters of typical Mediterranean tree species

“…above roughly 30% humidity. In previous studies, Qasemian et al (2012Qasemian et al ( , 2014 investigated litter microbial functioning in coastal habitats and showed that conductivity monitored in the field in Mediterranean coastal zones can be as high as 1500 mS cm À1 in summer. These studies revealed that, even at microlocal scales (from 10 to 300 m from shore), distance from the sea structures functional diversity, and that coastal constraints may limit microbial functioning by decreasing extracellular activities.…”

“…Qasemian et al (2014) showed that sea spray exposure can alter microbial activities: the influence of more intense salt exposure in litters close to the sea (and especially during summer drought) stresses microbial communities, leading to lower enzyme activities. However, salts can also directly impact enzymes by modifying their tridimensional conformation, interacting with their active site (which leads to inhibition of catalysis, Farnet et al, 2008) and limiting the quantity of water available.…”

“…The main environmental constraint in Mediterranean ecosystems is summer drought (Castro et al,2008;Sofo et al, 2008), but coastal zones also experience windy conditions, higher temperatures, and additional stresses, such as osmotic stress due to sea spray exposure, which can further impact litter functioning (Qasemian et al, 2014). Hydrolytic lipase activities were measured in litters both with and without added NaCl, and at different a w .…”