## 5 Discussion  
Our study provides compelling evidence that VCs derived from edible mushroom FBs significantly enhance rice seedling growth and biomass accumulation. By utilizing a non-contact exposure method, we demonstrated that FBs-derived volatiles can act as effective plant growth-promoting biostimulants. These findings corroborate previous research on fungal volatile-mediated plant growth enhancement while addressing key challenges associated with their practical application on a large scale. The role of fungi-derived VCs in plant growth stimulation has gained increasing attention in recent years. Fungal volatiles modulate not only plant development but also stress tolerance and defense mechanisms through airborne signaling, eliminating the need for direct plant-fungi interactions [5, 6, 7]. Our study expands these findings by introducing edible mushroom FBs as a sustainable alternative to mycelial-based volatile production. Unlike conventional fungal cultivation systems, FBs offer a readily available, cost-effective, and scalable method for harnessing bioactive volatiles. Notably, our results confirm previous reports suggesting that waste FBs retain bioactive volatile activity even after mushroom harvesting [32, 33]. Additionally, the wider agricultural benefits of FBs extend beyond VCs production. These materials have been explored for soil amendment, composting, and bioenergy applications, highlighting their broader sustainability potential [39, 40]. By integrating waste mushroom FBs into circular agricultural practices, we can simultaneously enhance plant productivity and environmental sustainability. _Application of mushroom FBs for short-term seedling cultivation_  
Short-term exposure of rice seedlings to VCs from shitake and enokitake FBs resulted in significant biomass increases. Results showed that shitake FBs led to the highest dry weight and plant height and enokitake FBs provided a moderate increase in biomass but suppressed root elongation. This aligns with previous studies indicating that fungal VCs vary by species and can exert contrasting effects on plant morphology [26]. Moreover, previous studies have linked fungal volatile organic compounds (VOCs) to hormonal pathway modulation, nutrient uptake, and stress response regulation [3, 31]. The ability of shitake FBs to enhance seedling biomass suggests their potential as a natural alternative to synthetic growth enhancers. _Dose-dependent effects of fungal volatiles on plant growth_  
One of the most significant findings of this study was the dose-dependent response of rice seedlings to FBs-derived VCs. At 30 g and 60 g of shitake FBs, results showed maximum biomass accumulation, while at 1 g and 5 g had negligible effects, and 15 g led to partial growth inhibition. This non-linear response aligns with previous research demonstrating that while low concentrations of fungal VCs promote growth, excessive exposure may trigger stress-related pathways leading to growth inhibition [8]. Similarly, [PERSON] et al. (2013) reported that high doses of 1-octen-3-ol could activate plant stress defense responses, ultimately suppressing growth [34]. Experiments using synthetic organic compounds further confirmed this phenomenon, whereby 1-Octen-3-one and 3-octanol promoted biomass accumulation at 1 \(\upmu\)L but former inhibited growth at 10 \(\upmu\)L. These results suggest that careful optimization of fungal VCs concentrations is essential to maximize their beneficial effects. _Optimization of non-contact exposure methods_One of the primary objectives of this study was to develop and evaluate different non-contact exposure methods for fungal VCs. Our results indicate that the Open Petri Dish (OPD) exposure method yielded the highest biomass accumulation and plant height, while FBs wrapped in gas-permeable polymer films (PVC and HDPE) regulated volatile diffusion and influenced plant responses. These findings align with studies by [PERSON] et al.