Fungual competition of Auriscalpium andStrobilurus on pinecones
Successive decomposition may be affected by fungul competition. Fungal competitions of Auriscalpium and Strobilurus on substrates correspond to the two functional types: primary resource capture and secondary resource capture, respectively (Boddy, 2000), so that the two genera appear orderly on the cones. On newly fallen cones, there may be hundreds of fungi competing to colonize cones on the surface, which is similar to the situation reported in woods (Coates & Rayner, 1985). However, the most obvious obstacles for fungi on newly fallen cones are the lack of easily assimilated nutrient matrixs such as lignin and hemicellulose, and the presences of inhibitory substances such as resin, etc. (Abad, Ansuategui, & Bermejo, 2006). Because of their ability to breakdown these resistant substances, Auriscalpium can gain a competitive edge with other microorganisms in microbial community on newly fallen cones.
With the increase of the decomposition levels, the competitive pressures on the cones gradually increase attributed to the disappearance or reduction of antibacterial or antifungal substances. On one hand, the cones decomposed by the Auriscalpium provide suitable conditions for Strobilurus growth. During this period, the fruitbodies ofStrobilurus and Auriscalpium can co-exist on the same cone (Figure S5f). On the other hand, fungi of Strobilurus , as aggressive competitors, produce toxins (e.g. strobilurin) to enhance its competitiveness with Auriscalpium and other microorganisms (Figure S5a–f). For nutrients and spaces, the antagonists can either interact directly with the competitors (Lima, Arru, De Curtis, & Arras, 1999), or secrete antibiotics to suppress competitors (Wilson et al., 1991). Some studies on antifungal SMs and enzymes produced by fungi with antagonists have been conducted extensively in vitro (Alves, Ferreira, Martins, & Pintado, 2012; Jonkers et al., 2012). Through SM clusters analyses, we find that the number of SM clusters of the genusAuriscalpium is fewer than that of Strobilurus (Table 3), while all fungi of Strobilurus contain a fungicidal strobilurin cluster whose derivatives have broad spectrum antifungal activity, and, thus, are widely used as biological fungicide (Niego et al., 2021). In addition, the number of NRPS-like in the genomes of Strobilurusis higher than those in Auriscalpium (Table 3). Most of the NRPS, PKS and their combinations have antibacterial and antifungal activities (Fernandes, Costa, Sousa, Zalocha, & Almeida, 2019), which indicates that the fungi in Strobilurus have stronger antibacterial and antifungal activities than those in Auriscalpium . Aside from the SMs, other factors such as microclimate, the size and quality of nutrient sources can shift the balance between fungal decomposer groups (Boddy, 2000). Thus, in the natural environment, the outcomes of interactions between fungi are variable, leading to differences in community structures.