The presence of American beech litter can alter the growth response of sugar maple seedlings to drought

In late successional forests of North America, sugar maple (Acer saccharum Marsh.) and American beech (Fagus grandifolia Ehrh.) form a complex ecosystem with intricate interactions. Over the last few decades, several studies have reported a marked increase in American beech dominance relative to sugar maple. Recent evidence suggests that extreme events such as drought could accelerate sugar maple's maladaptation to climate change and favor American beech in its replacement dynamics. In this study, we conducted a greenhouse experiment to investigate the effects of soil water stress and American beech presence on sugar maple seedling growth, structural physiology, leaf nitrogen, and chlorophyll. The seedlings were subjected to the following treatments independently and in combination for 82 days: soil water stress; soil originating from stands with American beech proliferation; soil sterilization; and presence of American beech litter. The results revealed that soil water stress was the primary factor significantly reducing sugar maple seedling growth, which also resulted in an increased root-to-shoot ratio. The presence of soil from stands with American beech proliferation did not exacerbate this negative effect. Soil sterilization, initially expected to reduce seedling growth by eliminating mycorrhizal associations, actually improved seedling growth. This suggests that adverse biotic processes, such as pathogens, were present in the soils regardless of their origin, and their negative effects outweighed the potential benefits from mycorrhization. The addition of American beech litter mitigated the effects of soil water stress but also introduced allelopathic compounds that hindered seedling growth. Overall, this study highlighted the complex interactions affecting sugar maple seedling growth, emphasizing that drought is a major limiting factor.