Search

Controlled burning is a common management technique used to control invasive understory plants and promote oak regeneration throughout the prairie-forest ecotone and across eastern deciduous forests. However, prescribed burning effects on oak forest and woodland soils remain largely unknown. As fire has significant and often disproportionate impacts on soil carbon (C), nitrogen (N), and phosphorus (P), evaluating the impacts of repeated, low-intensity prescribed burning on oak forest soil is fundamental for understanding and predicting burning effects on vegetation dynamics and ecosystem functions. The goal of this study was to evaluate relative changes in soil C and nutrient dynamics in response to three decades of annual, low-intensity controlled burning in an oak-dominated forest in northern Illinois. We found that annual burning increased soil organic and inorganic N availability and microbial biomass N. Burning also increased N cycling rates and N-degrading enzyme activity in the 5–15 cm soil layer. Surprisingly, annual burning had little effect on soil P pools and fluxes, likely due to intrinsically high soil P availability. Similarly, though total soil C increased, burning did not alter available C concentrations, microbial biomass C, C-degrading enzyme activities, or C mineralization rates. As such, annual burning created a positive feedback on inorganic N production, altering relationships among C, N, and P. In contrast with management goals, controlled burning often fails to enhance oak proliferation or decrease the abundance of invasive plants. As Eastern forests were historically N-limited, our study suggests a potential mechanism behind these restoration outcomes: frequent, low-intensity burning may produce soil environments that are incompatible with restoration goals. [ABSTRACT FROM AUTHOR]

Saprotrophic fungi are the dominant producers of organic matter-degrading extracellular enzymes in forest soils, but the extent to which they drive spatio-temporal variation in enzyme activities is unclear. We quantified the relationships between saprotrophic fungal biomass and enzyme activities in a mature temperate hardwood forest by placing soil-filled ingrowth bags inside trenches. Trenches were located in replicate stands (n = 7) dominated by either arbuscular mycorrhizal (AM)- or ectomycorrhizal (ECM)-associated tree species, which reflect differences in soil substrate quality and nutrient availability. Additionally, we assessed the extent to which the relationships between saprotrophic fungal biomass and enzyme activities varied across seasons and were altered by experimental nitrogen (N) addition. Overall, both fungal production and enzyme activities differed between mycorrhizal types and across seasons, but were unaffected by N addition. Additionally, enzyme activities exhibited strong, positive relationships with saprotrophic fungal biomass. However, the relative production of carbon (C)-degrading enzymes was greater in stands dominated by AM-associated trees in the late growing season, and the relative production of N-degrading enzymes was greater in the late growing season across both AM- and ECM-dominated forest stands. These patterns reflected tree- and season-driven changes in microbial C and N limitation. As such, while the common assumption that microbial biomass and enzyme activities are positively correlated is robust for saprotrophic fungi, enzyme produced per unit biomass may not be consistent among stands and across seasons. • Saprotroph mycelia production rates are greater in ECM forests than in AM forests. • Extracellular enzyme activities are linearly related to saprotrophic fungal biomass. • Relationships between enzymes and saprotrophs vary across seasons and forests. [ABSTRACT FROM AUTHOR]

Soil invertebrates are abundant and diverse members of forest ecosystems, contributing in large parts to ecosystem functioning. Understanding drivers of soil invertebrate diversity, density, and community composition is critical to inform management practices as forests face rapid changes in land use and climate. Tree community metrics may help predict invertebrate communities due to their large role in shaping microhabitat and soil conditions. Ground beetles are a large family of soil-dwelling invertebrates comprised of multiple functional groups ideal for tying tree communities to invertebrate communities broadly. Methods Here, we evaluated the effects of tree diversity, density, and functional groups on ground beetle (Carabidae) diversity, density, and community composition in four eastern US temperate forest sites in the National Ecological Observatory Network. Results We found little evidence to support our hypothesis that higher tree diversity and density would, respectively, lead to higher diversity and density ground beetle communities. Instead, evergreen tree abundance strongly shaped ground beetle density and community composition. Specifically, evergreen stands contained a lower density of ground beetles than deciduous stands. Similarly, the relative abundance of predatory ground beetles increased as the relative abundance of evergreen trees increased. Conclusions Our results show that the resource environments created by trees with varying leaf habits are a dominant force driving ground beetle community diversity and density patterns and suggest that future research exploring mechanisms driving this pattern could improve our understanding of plant-soil interactions. • The goal of this study was to understand drivers of soil invertebrate composition. • We evaluated tree composition on ground beetle (Carabidae) composition. • Evergreen tree abundance predicted ground beetle density and community composition. • Trees with varying leaf habits are a dominant force driving ground beetle patterns. • This study improves our understanding of plant-soil interactions. [ABSTRACT FROM AUTHOR]