Analyses of soils sampled on Madagascar Highlands following temperature and rainfall gradients in 2014

Priming effect (PE) in soil is proposed to be generated by two distinct mechanisms: “stoichiometric decomposition” and/or “nutrient mining” theories. Each mechanism gets its own dynamics, involves its own microbial actors and targets different soil organic matter (SOM) pools. The present study aims to evaluate how climatic parameters drive the intensity of each PE generation mechanism via the modification of microbial and physicochemical soil properties. Soils were sampled (May 2014) in the center of Madagascar, along climatic gradients designed to distinguish temperature from rainfall effects. Abiotic soil descriptors were Bulk Density, granulometry (clay silt and sand %), soil humidity, pH, CEC, oxydable Aluminium and Iron (estimation from spectral data) Kaolinite and Gibbsite content (estimations from spectral data), Total C, N and P, mineral N (addition of NH3 and NH4 data), available P. Biotic descriptors were microbial biomass phosphorus (MBP), molecular microbial biomass (MMB), 16S and 18S copy numbers per g of soil (qPCR), and bacterial and fungal communities composition (at the phylum level) obtained by 454 pyrosequencing methodology. DNA sequences were deposited in the European Nucleotide Archive, under the study accession number PRJEB19651. Soil respiration, wheat straw mineralization, and induced Priming effect have been recorded after a 7 and 42 days of soils laboratory incubation. All methodologies are described in the attached paper.