## 3 Results
### Dynamics of Microbial Populations  
The heatmap in Figure 3 depicts the evolution of microbial communities represented as changes in the distribution of the 73 dominant OTUs. D1 exhibited a stable profile, where the most relevant variations are associated with the first months of the year, showing a change in OTUs abundance from January (D1_JAN) to March (D1_MAR). These fluctuations were followed by a stabilization period up to September (D1_SEP), followed by an alteration in November (D1_NOV). These changes were in agreement with the variation in the macromolecular composition of digestates (Figure 1a). Specifically, the bacterial OTUs were the most significantly affected by the change between D1_JAN and D1_MAR. Bacteroidetes sp. OTU02, Thermoanaerobacterales sp. OTU13, _Syntrophacheticus schinkii_ OTU15, _Atopostes suicolaalis_ OTU21, and Lactobacillus DTU36  
Figure 3: Heatmap of the relative abundance of the most abundant OTUs in the sampled reactors. The color scale changes from blue to red for lower to higher abundant OTUs. are all decreased in D1_MAR, while _D. tunisiensis_ OTU05 and Dysgonomonadaceae sp. OTU03 increased in this same period and then reduced their abundance in the later sampling D1_NOV. This suggests that the mentioned OTUs are responsible for the hydrolysis of abundant recalcitrant polysaccharides (i.e., cellulose and hemicellulose) and the fermentation of their monomers along the whole year [34; 35], replacing the metabolic activity of the previous OTUs. Furthermore, it has been found that members of Dysgonomonadaceae participate in the hydrolysis of complex protein substrates [36], as such, the fluctuations of Dysgonomonadaceae sp. OTU03 and Synergistaceae sp. OTU06 in the same period, are likely due to the competition for the same substrate, since both families are known for the efficient utilization of sugars and proteins [37; 38]. Competitive effects are among the most important microbial interactions and have a very important role in shaping the anaerobic digestion systems [4; 30]. Interestingly, the hydrolytic Clostrridiaceae sp. OTU01, although fluctuating along the year, showing a peak in March (27.0%) and a trough in July (17.6%) in D1, was the prevalent microbe also in the other reactors (Figure 3). In fact, similar abundances and metabolic activities are reported when cellulose and hemicellulose are the main components of the AD feedstocks [39], as for D1, D2, and D3 digesters (Figure 1a). Moreover, it is widely reported in the literature that members of this family, such as _C. thermocellum_ or _C. cellulolyticum_, are involved in recalcitrant lignocellulosic compounds degradation supported by cellulolytic and hemicellulose enzymes such as endoglucanases and glycoside hydrolases [40; 41; 42]. Bacteriades sp. OTU02 underwent a slight reduction in March but gradually increased again from May onwards (D1_MAY), highlighting its crucial involvement in the anaerobic degradation of the processed agricultural substrates. On the same line, the hydrolytic and homoacetogenic _D. tunisiensis_ OTU05 increased 12-fold during March, and reached 21.2% of the community in May (D1_MAY), but then exhibited a fall to 6.5% in December. The unexpected development of this species is likely due to its metabolic flexibility since the fermentative activity of _D. tunisiensis_ enables the utilization of simple sugars as well as cellulose, chitin, and xylan [43]. Additionally, the genome analysis of _D. tunisiensis_ underscores the potential for syntrophic interactions with methanogenic archaea, as this bacterium is predicted to produce acetate, CO2, and H2 as fermentation end-products [34]. Finally, variations in the microbial structure in D1_NOV were related to the bacterial Halanaerobiaceae sp. OTU04 and the methanogenic species _M. bourgensis_ OTU11. This can be explained considering a positive interaction established between homoacetogenic bacteria and their hydrogenotrophic partners determined a significant increase in archaeal abundance, leading to an increment of _M.