Impact of poplar on soil organic matter quality and microbial communities in arable soils

Poplars grown in short rotation coppice on agricultural land are a promising bioenergy crop. This study aimed to evaluate the soil organic matter (SOM) quality and viable microbial consortium under six-years-old poplar (Populus maximowiczii) and under wheat (Triticum aestivum) at a test site in central Germany. The SOM molecular composition and stability was determined by pyrolysis-field ionization mass spectrometry (Py-FIMS). The microbial consortium was assessed in terms of microbial phospholipid fatty acid (PLFA) profiles. Py-FIMS and the PLFAs agreed in showing crop-specific differences in the SOM quality and in the associated microbial communities. Higher proportions of carbohydrates, long-chained fatty acids, sterols and suberins at the expense of N-containing compounds under poplar than under wheat were associated with lower concentrations of microbial PLFAs in the organic matter. A higher ratio of total fungal to bacterial (f/b) PLFAs, a lower ratio of Gram-positive to Gram-negative bacterial PLFAs and lower biomass of arbuscular mycorrhizal fungi in the organic matter were revealed under poplar than under wheat. Lower N- and increased C-availability in the SOM promoted fungal vs. bacterial colonization, increased the SOM stability by a lower decomposability and caused SOM accumulation under poplar.