Effect of compost amendment on rhizosphere bacterial communities and yield of lettuce in soilless substrate

The use of organic matter from the recycling of wastes, as compost, has been proposed in soilless substrates as an amendment to improve the growth of plants and as an alternative to peat. Compost is a renewable material, not as peat, subjected to fast depletion. We have evaluated the effect of two doses of amendment with compost in soilless substrate on the yield and diversity of rhizosphere bacterial communities of lettuce in a growing chamber. Plants were grown in 300 mL containers with a soilless mix of perlite and coconut fiber, and compost obtained from food waste was added at 5 and 10% v/v. The compost treatments produced a significant increase of the fresh weight of the aerial part of the plants. The functional diversity of the rhizosphere communities was evaluated by community level physiological profiling (CLPP) using the Biolog EcoPlatesT and the principal component analysis (PCA) of profiles that indicated the effect of the amendment level on the grouping of the samples. A total higher substrate metabolism was detected, as indication of a functional and numerical diversity. The genetic profiles of bacterial communities were obtained from DNA of the rhizosphere by amplicon length heterogeneity (ALH)-PCR of the 16S rDNA and the PCA indicated a significant effect of each treatment, based on relative abundancy of the amplicons. Bacterial isolates from the rhizosphere were identified by 16S rDNA sequencing and the predominant taxa were affiliated to Bosea sp., Curtobacterium flaccumfaciens, Cupriavidus campinensis, Bacillus licheniformis, Rhodococcus jalingiae, Pseudomonas sp., Mycobacterium sp. and Variovorax sp. In conclusion, the level of nutrients in the compost amendment produced an increase of yield and significantly affected the diversity of rhizosphere communities evaluated by metabolic and genetic profiling.