## 1 Introduction  
Volatile compounds (VCs) are low-molecular-weight substances, encompassing both inorganic and organic compounds that diffuse through air, soil, or water, enabling them to interact with organisms and influence biological functions [1, 2]. Many organisms emit VCs and interact with each other, and in this study, we focus on the effects of VCs emitted by edible mushroom fungi beds (FBs) on crops. Previous research has consistently demonstrated that fungal VCs act as signaling molecules that promote plant growth, enhance stress tolerance, and improve overall plant health [3, 4]  
The potential of fungal VCs as plant growth promoters was first highlighted by [PERSON] et al. (2003), who demonstrated that VCs emitted by fungal mycelia could stimulate plant growth without direct physical contact [5]. Subsequent studies corroborated these findings across diverse fungal and plant species. For instance, [PERSON] et al. (2021) found that VCsfrom _Cladosporium halotolerans_ NGPF1 significantly improved the growth of horticultural crops, while [PERSON] et al. (2022) reported that _Trichoderma_-derived VCs enhanced tomato seedling growth by promoting root branching and suppressing diseases [6; 7]. Similarly, [PERSON] et al. (2022) demonstrated that _Trichoderma koningiopsis_ T-51 VCs improved both the quality of tomato fruits and the biomass of _Arabidopsis thaliana_[8]. A variety of exposure methods have been developed to study the effects of fungal VCs on plant growth. These methods typically involve creating a shared atmosphere between the fungal source and target plants without direct physical contact. Chamber-based co-cultivation systems using Petri dishes, where fungi and plants are grown in separate compartments that share the same headspace, are commonly employed [3]. Additionally, innovative experimental setups such as the modified square Petri dish system introduced by [PERSON] et al. (2013) [9], the extensively used sandwich methods [10; 11; 12; 13; 14; 15; 16; 17], single-plate systems without physical divisions [18; 19], split-plate assays [20; 21; 22; 23; 24; 25], and plate-within-plate configurations used by [PERSON] et al. (2015) to investigate the effect of fungal aging on VOCs production [26] have been explored. While these methods have been crucial for understanding fungal VCs-plant interactions, challenges remain in scaling up their application for agricultural use. Ensuring stability and efficacy under field conditions, optimizing exposure techniques, and identifying low-cost sources of fungal VCs are critical obstacles [27; 28; 29; 30; 31]. Despite the demonstrated potential of fungal VCs to promote plant growth, the complexity of cultivating fungi and extracting these VCs from mycelia continues to hinder their widespread practical application. Current approaches often require controlled laboratory conditions, making large-scale implementation challenging. On the other hand, edible mushroom cultivating substrates, also known as FBs, could provide a readily available alternative source of fungal VCs. These FBs, typically made from agricultural by-products such as sawdust or rice straw, are widely available but often discarded as waste after mushroom harvesting. Recent studies suggest that bioactive volatiles released from waste edible mushroom FBs can have protective effects on plants, even after their primary use in mushroom production [32; 33]. However, their biostimulatory functions remain largely unvalidated, and no systematic study has assessed their effectiveness as plant growth promoters. The main aim of this study was to evaluate the potential of mushroom FBs as a direct source of bioactive fungal VCs to promote plant growth. To achieve this, we studied a novel non-contact exposure method for applying the VCs to rice seedlings (_Oryza sativa_ L.).