## 3 Results and Discussion
### TEM Examination of the Inoculated A. saligna Wood with Fungi  
TEM studies show that erosion and losing parts of the secondary wall occurred. The middle lamella remained intact in the majority of samples. The formation of cavities in the cell walls was the dominant feature. The formation of cavities within the S\({}_{1}\), S\({}_{2}\), or S\({}_{3}\) layers and erosion depend on the fungus type [11; 12].  
As it can be seen from the TEM micrographs, the most affected samples were those infested with _A. niger_, where the effect of the fungus on the wood cells appeared in the presence of soft-rot cavities, especially within the secondary cell walls of the S\({}_{1}\) and S\({}_{3}\) layers (Figure 2b-e) compared to control (Figure 2a). Soft-rot decay type II (erosion) was obvious in the samples infested with _A. flavus_, starting from the S\({}_{2}\) layer and extending to the S\({}_{1}\) layer. An increase in the electron-lucent appearance of some regions in the middle lamella and secondary wall layers suggests a loss of wood substance (Figure 3a,c). In addition, checks and splits were frequently noted within the secondary cell wall regions (Figure 2b).  
The wood samples infected with _F. culmorum_ showed general laceration in the wood tissue because of sectioning, which indicates the weakness of the sample. In addition, soft-rot decay type II (erosion) starting from the S\({}_{2}\) layer and extending to the S\({}_{1}\) layer was apparent (Figure 4). _A. tenuissima_ caused ultrastructure alterations in the wood samples similar to soft-rot fungi, regarding cavities (soft-rot decay type I) within the S\({}_{3}\) layer (Figure 5). Moreover, _T. harzianum_ caused two types of soft-rot decay in wood samples, namely: cavities within the S\({}_{3}\) and S\({}_{1}\) layers and erosion within the S\({}_{3}\) layer (Figure 6). These results, regarding the patterns and mechanisms of degradation, are consistent with previous studies [11; 12].  
Figure 2: _Cont._Figure 3: _Cont._  
Figure 2: Transmission electron microscope (TEM) photos of control treatment (**a**) and wood samples infected with _A. niger_ (**b–e**), showing the effect of the fungus on the wood cells, which appears in the presence of soft-rot cavities, especially within the \(S_{1}\) and \(S_{3}\) layers. ML—middle lamella; \(S_{1}\), \(S_{2}\), \(S_{3}\)—secondary cell wall layers of wood.  
Figure 4: TEM photos (**a**,**b**) of wood samples infected with _Fusarium_ showing soft-rot decay type II (erosion), starting from the S\({}_{2}\) layer and extending to the S\({}_{1}\) layer. The general apparent lacerations result from sectioning.  
Figure 5: TEM photos of wood samples infected with _A. tenuissima_, showing cavities within the S\({}_{3}\) layer similar to soft-rot decay type I (**a**). Furthermore, checks and fissures (shown by arrows), are found within the S\({}_{1}\) and S\({}_{2}\) layers, with extensive erosion of the middle lamellae region (**b**).  
Figure 3: TEM photos of wood samples infected with _A. flavus_, showing soft-rot decay type II (erosion), starting from the S\({}_{2}\) layer and extending to the S\({}_{1}\) layer. Increasing the electron-lucent appearance of some regions in middle lamella and secondary wall layers suggests a loss of wood substance (**a**,**c**). In addition, checks (CH) and splits are frequently noted within the secondary cell wall regions (**b**).