Response of Portulaca olearacea and its rhizospheric microbiome to the application of slumgum from beekeeping industry transformed with Penicillium chrysogenum

Abstract

In the beekeeping industry, “slumgum” is generated as a solid organic waste during the beeswax-rendering process from old scraped honeycombs. This bio-waste could be considered as a novel organic fertilizer due to its high content in organic matter and nutrients. As a novelty in this study, we analysed the effect of application of solid and liquid slumgum transformed or not with Penicillium chrysogenum on purslane (Portulaca oleracea) yield and its relationship with soil rhizosphere. For this purpose, nutritional composition, enzymatic activities involved in the P, N and C cycles, fungal and bacterial community composition, diversity and potential functionality in the rhizosphere were measured. The application of solid and liquid slumgum transformed with P. chrysogenum (TS and TL, respectively) and slumgum liquid (L) significantly increased purslane shoot biomass and foliar P content, compared to the non-transformed solid slumgum (S). The different types of slumgum tested resulted in changes in the composition of both bacteria and fungi communities, resulting in distinct communities for each treatment. Moreover, changes in the functional fungal guilds were observed, with increased abundances of saprotrophs and reduced number of plant pathogens under the TS, TL, and L treatments. Solid slumgum transformed with P. chrysogenum (TS) was also the most effective in enhancing enzymatic activities related with C, N and P cycles in the rhizosphere. Conversely, the use of solid slumgum (S) led to an increase in the abundance of bacterial genes primarily associated with the denitrification process. Our preliminary results suggest that solid and liquid slumgum transformed with P. chrysogenum, as well as liquid non-transformed slumgum (TS, TL, and L, respectively), could be considered as novel organic fertilizers, amendments or additives within the circular economy context and the sustainable use of natural resources. Nevertheless, further studies are necessary to validate the positive outcomes observed, particularly under field conditions and with a variety of species.