Abstract Many ecosystems can abruptly shift between states, and shallow lakes are a classic example. Biomanipulation via the removal of benthivores can shift a shallow lake from a turbid to a clear-water macrophyte-dominated state, but the limited number of long-term studies indicates that persistence in this state rarely lasts beyond 5–10 years. We analyzed 12 years of pre-removal (1996–2007) and 17 years of post-removal (2008–2024) data to assess the ecological impacts of a common carp ( Cyprinus carpio ) removal from Lake Wingra, a shallow eutrophic lake in Madison, Wisconsin, USA. Summer water clarity abruptly increased following the winter 2008 carp removal, resulting in a 64% increase in mean Secchi depth in post-removal summers and a major expansion of the littoral zone. Fast growing submerged macrophytes (for example, Ceratophyllum demersum and invasive Myriophyllum spicatum ) rapidly expanded into deeper zones, reaching the maximum colonization depth of 3.96 m within four summers. Post-removal nutrient concentrations declined by 24–34% and became more correlated with precipitation, suggesting a shift from internal to external regulation of nutrient loading. Three likely interacting mechanisms for maintaining water clarity include predation by centrarchids maintaining low carp populations, the high and stable coverage of submerged macrophytes, and abundant filamentous algae that provide an additional nutrient sink. However, high biomass of invasive species and filamentous algae can degrade ecosystem services and function, and increased variability of precipitation-driven nutrient inputs may destabilize the macrophyte-dominated state in the future. We demonstrate with long-term data the sustained shift of a shallow eutrophic lake out of the turbid state with a single biomanipulation.

Abstract Mycorrhizal associations are key drivers of soil biogeochemistry, but previous studies have focused almost exclusively on ectomycorrhizal (EcM) and arbuscular mycorrhizal (AM) associations. Ericoid mycorrhizal (ErM) shrubs frequently occur in forest understories and are expanding in response to disturbance, but are rarely considered in biogeochemical frameworks. We investigated the relationships of understory ErM shrubs and overstory trees on carbon (C) and nitrogen (N) in soil organic matter fractions in a southern Appalachian temperate forest. We sampled the 0–10 cm mineral soil layer from 43 plots at the Coweeta Hydrologic Laboratory, across gradients in overstory EcM dominance and understory ErM shrub biomass. Soil C:N ratios increased with both increasing EcM dominance and increasing ErM shrub biomass. However, total particulate organic matter (POM) C, and the proportion of C and N held in POM increased with increasing ErM shrub biomass, but not with increasing EcM dominance. In contrast, mineral-associated organic matter (MAOM) C and N were negatively associated with EcM dominance, but were not related to ErM shrubs. Our findings suggest that ErM shrubs facilitate POM formation while AM trees promote MAOM formation. Because ErM shrub biomass represents a small fraction of total forest biomass, our work provides evidence that ErM shrubs have an outsized effect on soil organic matter, which advocates for their inclusion in mechanistic studies and biogeochemical frameworks.

Abstract By causing widespread tree mortality, spruce budworm outbreaks significantly affect the structural and functional dynamics of northeastern boreal forests. This study examined the understory plant community’s response during the 2005–2020 outbreak in the northeastern boreal forest of Canada. Using a trait-based approach, we analyzed functional diversity, dominance, and resilience across fir-dominated, mixed, and spruce-dominated stands. Results revealed an increase in functional diversity and a decrease in Simpson dominance, particularly in fir-dominated and mixed stands. Changes in soil fertility, light availability, and tree basal area, driven by defoliation and tree mortality, were identified as key factors influencing understory vegetation. Trait shifts, especially the increase in shade-tolerant, mesic, and medium nutrient species and the decline of hydric water preferences and non-vascular growth form, reflected niche-based selection processes under altered conditions. However, the variability in trait distributions and species turnover across stand types also pointed to the role of neutral processes, such as stochastic colonization and dispersal limitation. Functional redundancy varied across stand types, with fir-dominated stands showing greater resilience, likely due to higher trait plasticity and pre-disturbance composition. These findings highlight the complex interplay between niche-driven and stochastic mechanisms in shaping understory dynamics and provide insights for sustainable forest management during and after spruce budworm outbreaks.

Nitrogen (N) availability is known to interact with the drought tolerance in plants, but its effects on the morphological acclimation of forest trees to low precipitation have rarely been investigated. Based on a Germany-wide field-study design covering different combinations of climatic conditions and atmospheric N deposition, we harvested young trees up to 70 cm in height of Fagus sylvatica, Quercus petraea, Pseudotsuga menziesii, and Abies alba. We tested the hypothesis that high N deposition decreases the root/shoot ratio, alters fine root morphology (for example, by reducing specific root length of absorptive roots) and reduces mycorrhizal colonization rate, which are factors that would reduce the capacity for water uptake under drought. European beech showed reduced root/shoot ratios at high N deposition and reduced specific root length and mycorrhizal colonization of absorptive roots at sites with both high N deposition and low precipitation. These observations were consistent with the optimal portioning theory, as less investment in belowground biomass was required to meet the N demand at high N deposition. Sessile oak showed no effect of N deposition or mean annual precipitation on the parameters studied, indicating that the gradients studied were not large enough to cause changes. Douglas-fir and silver fir expanded their root systems with increasing N deposition, with higher specific root length in Douglas-fir and a trend towards higher root tip abundance in silver fir. Thus, in contrast to European beech, we found no indication that the tree's ability to cope with drought was reduced by high N deposition in sessile oak, Douglas-fir, and silver fir. The combined negative effect of drought and high N deposition on the root system in European beech as Central Europe’s most dominant tree species in the natural vegetation emphasizes the need for curtailing N emissions, especially from agriculture.

Flow regimes of river ecosystems worldwide have undergone substantial changes because of water resource development, altering the way in which organic matter is generated and cycled throughout entire river catchments. Flow–ecology studies have focused on structural variables measured at small spatial scales. This creates a challenging mismatch when applying adaptive flow management for ecosystem functioning at a catchment or regional scale. Here, we sought to inform flow management by evaluating the drivers of ecosystem metabolism in a regulated river and assessing our ability to predict metabolism at unmonitored locations. We estimated rates of ecosystem metabolism from high-frequency monitoring of dissolved oxygen concentration at eight sites on the Lachlan River of Australia’s Murray–Darling Basin. We then applied a spatio-temporal stream network model to predict metabolism at unmonitored locations using only remotely sensed and gauging station predictor variables. Gross primary productivity (GPP) was higher at sites with lower mean annual discharge, and strong seasonal patterns in rates of productivity tended to be disrupted by rising flows. Similarly, ecosystem respiration (ER) was higher at sites with lower mean annual discharge and lower annual flow variation, but increased slightly in response to higher daily flows. Predictions at validation sites were generally accurate, albeit with substantial site-to-site variation. Our results suggest that flow changes may have altered metabolic rates from conditions prior to water abstraction and dam construction. These findings will assist in managing flows for ecosystem function outcomes and support extrapolation from monitored sites to the broad scales required for evaluating catchment-scale outcomes of river management.