Abstract
Organic wastes have the potential to be used as soil organic amendments after undergoing a process of stabilization such as composting or as a resource of renewable energy by anaerobic digestion (AD). Both composting and AD are well-known, eco-friendly approaches to eliminate and recycle massive amounts of wastes. Likewise, the application of compost amendments and digestate (the by-product resulting from AD) has been proposed as an effective way of improving soil fertility. The study of microbial communities involved in these waste treatment processes, as well as in organically amended soils, is key in promoting waste resource efficiency and deciphering the features that characterize microbial communities under improved soil fertility conditions. To move beyond the classical analyses of metataxonomic data, the application of co-occurrence network approaches has shown to be useful to gain insights into the interactions among the members of a microbial community, to identify its keystone members and modelling the environmental factors that drive microbial network patterns. Here, we provide an overview of essential concepts for the interpretation and construction of co-occurrence networks and review the features of microbial co-occurrence networks during the processes of composting and AD and following the application of the respective end products (compost and digestate) into soil.
Highlights
The implementation of sustainable agricultural practices such as the addition of organic amendments into soil needs to assess the impact of such practices, on soil physicochemical properties, and on soil microbial communities since they play a pivotal role in the functioning of the entire ecosystem [45]
It reinforces the potential of co-occurrence networks as useful tools to understand how microbe–microbe interactions change throughout the composting process in response to environmental parameters, and how these changes might influence the quality of the end product by identifying the keystone OTUs that have a large influence in the community
This was explained by the authors in relation to the highly diverse type of nutrients provided by liquid digestate, which counterweigh the influence of niche partitioning in the microbial community assembly by allowing more stochastic processes to occur, while niche overlap introduces more relationships and interactions
Summary
The activity of the ever-increasing human population generates millions of tons of solid organic wastes (that is, any material that is biodegradable and comes from living organisms) [1]. Organic wastes have the potential to be used as a resource for renewable energy production and as a source of soil nutrients, which helps to reduce our dependence on inorganic fertilizers, and represents an ecologically-sound and economically attractive alternative to landfill disposal and incineration [4]. Microorganisms 2021, 9, 1165 such as exhausted seeds, hoof and horn meal, animal feathers and fur, wastes from sugar extraction, distillery waste and biosolids from paper mills; and (iv) biosolids: treated wastewater residues from municipal wastewater treatment plants [6,7] Some of these have the potential to be used as soil organic amendments and/or as a raw material to generate energy by anaerobic digestion (AD) [2]. The application of compost and digestate into soil has been proposed as an effective way of improving soil quality and fertility, while at the same time, protecting the environment because their use could be part of a strategy to eliminate and recycle massive amounts of waste [8]
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