Photosynthetic capacity in middle-aged larch and spruce acclimates independently to experimental warming and elevated CO.

Photosynthetic acclimation to both warming and elevated CO of boreal trees remains a key uncertainty in modelling the response of photosynthesis to future climates. We investigated the impact of increased growth temperature and elevated CO on photosynthetic capacity (V and J) in mature trees of two North American boreal conifers, tamarack and black spruce. We show that V and J at a standard temperature of 25°C did not change with warming, while V and J at their thermal optima (T) and growth temperature (T) increased.

Effects of plant diversity on productivity strengthen over time due to trait-dependent shifts in species overyielding.

Plant diversity effects on community productivity often increase over time. Whether the strengthening of diversity effects is caused by temporal shifts in species-level overyielding (i.e.

Reduced global plant respiration due to the acclimation of leaf dark respiration coupled with photosynthesis.

Leaf dark respiration (R ) acclimates to environmental changes. However, the magnitude, controls and time scales of acclimation remain unclear and are inconsistently treated in ecosystem models. We hypothesized that R and Rubisco carboxylation capacity (V ) at 25°C (R , V ) are coordinated so that R variations support V at a level allowing full light use, with V reflecting daytime conditions (for photosynthesis), and R /V reflecting night-time conditions (for starch degradation and sucrose export).

Climate change-induced stress disrupts ectomycorrhizal interaction networks at the boreal-temperate ecotone.

The interaction networks formed by ectomycorrhizal fungi (EMF) and their tree hosts, which are important to both forest recruitment and ecosystem carbon and nutrient retention, may be particularly susceptible to climate change at the boreal-temperate forest ecotone where environmental conditions are changing rapidly. Here, we quantified the compositional and functional trait responses of EMF communities and their interaction networks with two boreal ( and ) and two temperate ( and ) hosts to a factorial combination of experimentally elevated temperatures and reduced rainfall in a long-term open-air field experiment. The study was conducted at the B4WarmED (Boreal Forest Warming at an Ecotone in Danger) experiment in Minnesota, USA, where infrared lamps and buried heating cables elevate temperatures (ambient, +3.

Boreal conifers maintain carbon uptake with warming despite failure to track optimal temperatures.

Warming shifts the thermal optimum of net photosynthesis (T) to higher temperatures. However, our knowledge of this shift is mainly derived from seedlings grown in greenhouses under ambient atmospheric carbon dioxide (CO) conditions. It is unclear whether shifts in T of field-grown trees will keep pace with the temperatures predicted for the 21 century under elevated atmospheric CO concentrations.

Stomatal behaviour moderates the water cost of CO acquisition for 21 boreal and temperate species under experimental climate change.

The linkage of stomatal behaviour with photosynthesis is critical to understanding water and carbon cycles under global change. The relationship of stomatal conductance (g ) and CO assimilation (A ) across a range of environmental contexts, as represented in the model parameter (g ), has served as a proxy of the marginal water cost of carbon acquisition. We use g to assess species differences in stomatal behaviour to a decade of open-air experimental climate change manipulations, asking whether generalisable patterns exist across species and climate contexts.

Even modest climate change may lead to major transitions in boreal forests.

The sensitivity of forests to near-term warming and associated precipitation shifts remains uncertain. Herein, using a 5-year open-air experiment in southern boreal forest, we show divergent responses to modest climate alteration among juveniles of nine co-occurring North American tree species. Warming alone (+1.

Assessing the relevant time frame for temperature acclimation of leaf dark respiration: A test with 10 boreal and temperate species.

Plants often adjust their leaf mitochondrial ("dark") respiration (R ) measured at a standardized temperature such as 20°C (R ) downward after experiencing warmer temperatures and upward after experiencing cooler temperatures. These responses may help leaves maintain advantageous photosynthetic capacity and/or be a response to recent photosynthate accumulation, and can occur within days after a change in thermal regime. It is not clear, however, how the sensitivity and magnitude of this response change over time, or which time period prior to a given measurement best predicts R .

Enhanced light interception and light use efficiency explain overyielding in young tree communities.

Diverse plant communities are often more productive than mono-specific ones. Several possible mechanisms underlie this phenomenon but their relative importance remains unknown. Here we investigated whether light interception alone or in combination with light use efficiency (LUE) of dominant and subordinate species explained greater productivity of mixtures relative to monocultures (i.

Remote spectral detection of biodiversity effects on forest biomass.

Quantifying how biodiversity affects ecosystem functions through time over large spatial extents is needed for meeting global biodiversity goals yet is infeasible with field-based approaches alone. Imaging spectroscopy is a tool with potential to help address this challenge. Here, we demonstrate a spectral approach to assess biodiversity effects in young forests that provides insight into its underlying drivers.

Short- and long-term responses of photosynthetic capacity to temperature in four boreal tree species in a free-air warming and rainfall manipulation experiment.

High latitude forests cope with considerable variation in moisture and temperature at multiple temporal scales. To assess how their photosynthetic physiology responds to short- and long-term temperature variation, we measured photosynthetic capacity for four tree species growing in an open-air experiment in the boreal-temperate ecotone `Boreal Forest Warming at an Ecotone in Danger' (B4WarmED). The experiment factorially manipulated temperature above- and below-ground (ambient, +3.

Species-specific flowering phenology responses to experimental warming and drought alter herbaceous plant species overlap in a temperate-boreal forest community.

Background And Aims: Warmer temperatures and altered precipitation patterns are expected to continue to occur as the climate changes. How these changes will impact the flowering phenology of herbaceous perennials in northern forests is poorly understood but could have consequences for forest functioning and species interactions. Here, we examine the flowering phenology responses of five herbaceous perennials to experimental warming and reduced summer rainfall over 3 years.

Warming and disturbance alter soil microbiome diversity and function in a northern forest ecotone.

The response to global change by soil microbes is set to affect important ecosystem processes. These impacts could be most immediate in transitional zones, such as the temperate-boreal forest ecotone, yet previous work in these forests has primarily focused on specific subsets of microbial taxa. Here, we examined how bacterial and fungal communities respond to simulated above- and below-ground warming under realistic field conditions in closed and open canopy treatments in Minnesota, USA.

Phenological responses of temperate and boreal trees to warming depend on ambient spring temperatures, leaf habit, and geographic range.

Changes in plant phenology associated with climate change have been observed globally. What is poorly known is whether and how phenological responses to climate warming will differ from year to year, season to season, habitat to habitat, or species to species. Here, we present 5 y of phenological responses to experimental warming for 10 subboreal tree species.

Surprising lack of sensitivity of biochemical limitation of photosynthesis of nine tree species to open-air experimental warming and reduced rainfall in a southern boreal forest.

Photosynthetic biochemical limitation parameters (i.e., V , J and J :V ratio) are sensitive to temperature and water availability, but whether these parameters in cold climate species at biome ecotones are positively or negatively influenced by projected changes in global temperature and water availability remains uncertain.

Effects of climate warming on photosynthesis in boreal tree species depend on soil moisture.

Climate warming will influence photosynthesis via thermal effects and by altering soil moisture. Both effects may be important for the vast areas of global forests that fluctuate between periods when cool temperatures limit photosynthesis and periods when soil moisture may be limiting to carbon gain. Here we show that the effects of climate warming flip from positive to negative as southern boreal forests transition from rainy to modestly dry periods during the growing season.

Experimental warming advances phenology of groundlayer plants at the boreal-temperate forest ecotone.

Premise Of The Study: Changes to plant phenology have been linked to warmer temperatures caused by climate change. Despite the importance of the groundlayer to community and forest dynamics, few warming experiments have focused on herbaceous plant and shrub phenology.

Methods: Using a field study in Minnesota, United States, we investigated phenological responses of 16 species to warming over five growing seasons (2009-2013) at two sites, under two canopy covers, and in three levels of simultaneous above- and belowground warming: ambient temperature, ambient +1.

Reduced feeding activity of soil detritivores under warmer and drier conditions.

Anthropogenic warming is projected to trigger positive feedbacks to climate by enhancing carbon losses from the soil1. While such losses are, in part, owing to increased decomposition of organic matter by invertebrate detritivores, it is unknown how detritivore feeding activity will change with warming2, especially under drought conditions. Here, using four year manipulation experiments in two North American boreal forests, we investigate how temperature (ambient, +1.

Warming alters the energetic structure and function but not resilience of soil food webs.

Climate warming is predicted to alter the structure, stability, and functioning of food webs1-5. Yet, despite the importance of soil food webs for energy and nutrient turnover in terrestrial ecosystems, warming effects on these food webs-particularly in combination with other global change drivers-are largely unknown. Here, we present results from two complementary field experiments testing the interactive effects of warming with forest canopy disturbance and drought on energy fluxes in boreal-temperate ecotonal forest soil food webs.

Effect of Simulated Climate Warming on the Ectomycorrhizal Fungal Community of Boreal and Temperate Host Species Growing Near Their Shared Ecotonal Range Limits.

Ectomycorrhizal (ECM) fungi can influence the establishment and performance of host species by increasing nutrient and water absorption. Therefore, understanding the response of ECM fungi to expected changes in the global climate is crucial for predicting potential changes in the composition and productivity of forests. While anthropogenic activity has, and will continue to, cause global temperature increases, few studies have investigated how increases in temperature will affect the community composition of ectomycorrhizal fungi.

Consistent leaf respiratory response to experimental warming of three North American deciduous trees: a comparison across seasons, years, habitats and sites.

Most vascular plants acclimate respiration to changes in ambient temperature, but explicit tests of these responses in field settings are rare, and how acclimation responses vary in space and time is relatively unstudied, hindering our ability to predict respiratory release of carbon under future climatic conditions. We measured temperature response curves of leaf respiration for three deciduous tree species from 2009 to 2012 in a field warming experiment (+3.4 °C above ambient) in both open and understory conditions at two sites in the southern boreal forest in Minnesota, USA.

Ectomycorrhizal fungal response to warming is linked to poor host performance at the boreal-temperate ecotone.

Rising temperatures associated with climate change have been shown to negatively affect the photosynthetic rates of boreal forest tree saplings at their southern range limits. To quantify the responses of ectomycorrhizal (EM) fungal communities associated with poorly performing hosts, we sampled the roots of Betula papyrifera and Abies balsamea saplings growing in the B4Warmed (Boreal Forest Warming at an Ecotone in Danger) experiment. EM fungi on the root systems of both hosts were compared from ambient and +3.