Distance from the sea as a driving force of microbial communities under water potential stresses in litters of two typical Mediterranean plant species

Abstract

Though many studies have focused on the incidence of drought, little attention has been paid to osmotic stress and to how the interaction of the two stresses impacts microbial functioning. Moreover, deciphering how certain environmental factors such as distance from the sea or type of litter may shape microbial responses to these stresses is of huge importance. The objective of this study is to shed light on the impact of matric and osmotic stresses (combined or not) on litter microbial communities potentially shaped differently by either plant species or distance from the sea. Two Mediterranean plant species, Cistus albidus L. and Pistacia lentiscus L., collected from both inland and coastal areas, were used to set up a total of 72 mesocosms (4 mesocosms×3 types of litters (pure or mixed)×2 sites (coastal and inland)×3 types of stress). A first set of twenty four mesocosms ‘control’ (4 mesocosms×3 types of litters (pure or mixed)×2 sites (coastal and inland)) were maintained under favourable conditions for 60days (25°C, 600g·kg−1 water content). For matric stress, twenty four mesocosms were subjected to 5 drying/rewetting cycles (7days at 25°C/7days at 600g·kg−1 water content and 25°C). For osmotic stress, twenty four mesocosms received 10mg of chlorine ions per g of litter using NaCl and then were incubated at 600g·kg−1 water content and 25°C for 60days. The last twenty four mesocosms were subjected to the combined drought and salt stresses for 60days. Resistance to added osmotic stress was also tested. Catabolic diversity assessed via Biolog Ecoplates, was higher in coastal than in inland areas after drought and combined stresses. Moreover, catabolic profiles were shaped differently after stresses depending on the litter type. Basal respiration withstood an added severe drought stress better in microbial communities previously subjected to combined stresses. Resistance to an added osmotic stress was higher in inland litters previously subjected to salt stress. Microbial communities from the coastal area were more able to maintain their catabolic potential and thus to withstand these stresses. Combined stresses and osmotic stress reinforced resistance to added severe drought or osmotic stress respectively. Thus our findings reveal that microbial communities previously subjected to water potential stresses were more capable to overcome additional stresses of similar nature, suggesting adaptation mechanisms to such type of stresses.