Browsing by Author "Stefanski, Artur"
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Item Acclimation of photosynthetic temperature optima of temperate and boreal tree species in response to experimental forest warming(Wiley, 2015) Sendall, Kerrie M; Reich, Peter B; Zhao, Changming; Jihua, Hou; Wei, Xiaorong; Stefanski, Artur; Rice, Karen; Rich, Roy L; Montgomery, Rebecca A.Rising temperatures caused by climate change could negatively alter plant ecosystems if temperatures exceed optimal temperatures for carbon gain. Such changes may threaten temperature-sensitive species, causing local extinctions and range migrations. This study examined the optimal temperature of net photosynthesis (Topt) of two boreal and four temperate deciduous tree species grown in the field in northern Minnesota, United States under two contrasting temperature regimes. We hypothesized that Topt would be higher in temperate than co-occurring boreal species, with temperate species exhibiting greater plasticity in Topt, resulting in better acclimation to elevated temperatures. The chamberless experiment, located at two sites in both open and understory conditions, continuously warmed plants and soils during three growing seasons. Results show a modest, but significant shift in Topt of 1.1 ± 0.21 °C on average for plants subjected to a mean 2.9 ± 0.01 °C warming during midday hours in summer, and shifts with warming were unrelated to species native ranges. The 1.1 °C shift in Topt with 2.9 °C warming might be interpreted as suggesting limited capacity to shift temperature response functions to better match changes in temperature. However, Topt of warmed plants was as well-matched with prior midday temperatures as Topt of plants in the ambient treatment, and Topt in both treatments was at a level where realized photosynthesis was within 90–95% of maximum. These results suggest that seedlings of all species were close to optimizing photosynthetic temperature responses, and equally so in both temperature treatments. Our study suggests that temperate and boreal species have considerable capacity to match their photosynthetic temperature response functions to prevailing growing season temperatures that occur today and to those that will likely occur in the coming decades under climate change.Item Boreal and temperate trees show strong acclimation of respiration to warming(Nature Publishing Group, 2016) Reich, Peter B; Sendall, Kerrie M; Stefanski, Artur; Wei, Xiaorong; Rich, Roy L; Montgomery, Rebecca APlant respiration results in an annual flux of carbon dioxide (CO2) to the atmosphere that is six times as large as that due to the emissions from fossil fuel burning, so changes in either will impact future climate. As plant respiration responds positively to temperature, a warming world may result in additional respiratory CO2 release, and hence further atmospheric warming1, 2. Plant respiration can acclimate to altered temperatures, however, weakening the positive feedback of plant respiration to rising global air temperature3, 4, 5, 6, 7, but a lack of evidence on long-term (weeks to years) acclimation to climate warming in field settings currently hinders realistic predictions of respiratory release of CO2 under future climatic conditions. Here we demonstrate strong acclimation of leaf respiration to both experimental warming and seasonal temperature variation for juveniles of ten North American tree species growing for several years in forest conditions. Plants grown and measured at 3.4 °C above ambient temperature increased leaf respiration by an average of 5% compared to plants grown and measured at ambient temperature; without acclimation, these increases would have been 23%. Thus, acclimation eliminated 80% of the expected increase in leaf respiration of non-acclimated plants. Acclimation of leaf respiration per degree temperature change was similar for experimental warming and seasonal temperature variation. Moreover, the observed increase in leaf respiration per degree increase in temperature was less than half as large as the average reported for previous studies4, 7, which were conducted largely over shorter time scales in laboratory settings. If such dampening effects of leaf thermal acclimation occur generally, the increase in respiration rates of terrestrial plants in response to climate warming may be less than predicted, and thus may not raise atmospheric CO2 concentrations as much as anticipated.Item Data and code for remote spectral detection of biodiversity effects on forest biomass(2020-08-26) Williams, Laura J; Cavender-Bares, Jeannine; Townsend, Philip A; Couture, John J; Wang, Zhihui; Stefanski, Artur; Messier, Christian; Reich, Peter B; will3972@umn.edu; Williams, Laura JQuantifying how biodiversity affects ecosystem functions through time over large spatial extents is needed to meet global biodiversity goals yet is infeasible with field-based approaches alone. Imaging spectroscopy is a tool with potential to help address this challenge. In this study, we demonstrated a spectral approach to assess biodiversity effects in young forests that provides insight into its underlying drivers and could potentially be applied at large spatial scales. Using airborne imaging (NASA AVIRIS-NG) of a tree diversity experiment (IDENT-Cloquet in Cloquet, MN), spectral differences among plots enabled us to quantify net biodiversity effects on stem biomass and canopy nitrogen. In this repository, we present the spectral data and field data along with spectral model coefficients and example code for fitting and applying spectral models to calculate spectral biodiversity effects.Item Data Supporting Reich et al 2022: Even modest climate change may lead to major transitions in boreal forests(2022-06-27) Reich, Peter, B.; Bermudez, Raimundo; Montgomery, Rebecca, A.; Rich, Roy, L.; Rice, Karen, E.; Hobbie, Sarah, E.; Stefanski, Artur; preich@umn.edu; Reich, Peter, B.To test the uncertainty of the sensitivity of forests to near–term warming and associated precipitation we used a five–year open–air experiment in southern boreal forest located at two research sites in northern Minnesota. The experiment used juveniles of nine temperate and boreal tree species that grew under ambient and seasonally warmed (+1.6C and +3.1C above- and belowground) and rainfall reduced (~30% less rainfall) conditions. Each year we surveyed all trees for their survival and growth and measured in situ light-saturated net photosynthesis (Anet) and leaf diffusive conductance (gs).Item Ectomycorrhizal fungal diversity and saprotrophic fungal diversity are linked to different tree community attributes in a field‐based tree experiment(Wiley, 2016) Nguyen, Nhu H; Williams, Laura J; Vincent, John B; Stefanski, Artur; Cavender‐Bares, Jeannine; Messier, Christian; Paquette, Alain; Gravel, Dominique; Reich, Peter B; Kennedy, Peter GExploring the link between above- and belowground biodiversity has been a major theme of recent ecological research, due in large part to the increasingly well-recognized role that soil microorganisms play in driving plant community processes. In this study, we utilized a field-based tree experiment in Minnesota, USA, to assess the effect of changes in plant species richness and phylogenetic diversity on the richness and composition of both ectomycorrhizal and saprotrophic fungal communities. We found that ectomycorrhizal fungal species richness was significantly positively influenced by increasing plant phylogenetic diversity, while saprotrophic fungal species richness was significantly affected by plant leaf nitrogen content, specific root length and standing biomass. The increasing ectomycorrhizal fungal richness associated with increasing plant phylogenetic diversity was driven by the combined presence of ectomycorrhizal fungal specialists in plots with both gymnosperm and angiosperm hosts. Although the species composition of both the ectomycorrhizal and saprotrophic fungal communities changed significantly in response to changes in plant species composition, the effect was much greater for ectomycorrhizal fungi. In addition, ectomycorrhizal but not saprotrophic fungal species composition was significantly influenced by both plant phylum (angiosperm, gymnosperm, both) and origin (Europe, America, both). The phylum effect was caused by differences in ectomycorrhizal fungal community composition, while the origin effect was attributable to differences in community heterogeneity. Taken together, this study emphasizes that plant-associated effects on soil fungal communities are largely guild-specific and provides a mechanistic basis for the positive link between plant phylogenetic diversity and ectomycorrhizal fungal richness.Item Effects of soil warming history on the performances of congeneric temperate and boreal herbaceous plant species and their associations with soil biota(2016) Thakur, Madhav P; Reich, Peter B; Wagg, Cameron; Fisichelli, Nicholas A; Ciobanu, Marcel; Hobbie, Sarah E; Rich, Roy L; Stefanski, Artur; Eisenhauer, NicoAims Climate warming raises the probability of range expansions of warm-adapted temperate species into areas currently dominated by cold-adapted boreal species. Warming-induced plant range expansions could partly depend on how warming modifies relationships with soil biota that promote plant growth, such as by mineralizing nutrients. Here, we grew two pairs of congeneric herbaceous plants species together in soil with a 5-year warming history (ambient, +1.7°C, +3.4°C) and related their performances to plant-beneficial soil biota. Methods Each plant pair belonged to either the mid-latitude temperate climate or the higher latitude southern boreal climate. Warmed soils were extracted from a chamberless heating experiment at two field sites in the temperate-boreal ecotone of North America. To isolate potential effects of different soil warming histories, air temperature for the greenhouse experiment was identical across soils. We hypothesized that soil with a 5-year warming history in the field would enhance the performance of temperate plant species more than boreal plant species and expected improved plant performances to have positive associations with plant growth-promoting soil biota (microbial-feeding nematodes and arbuscular mycorrhizal fungi). Important Findings Our main hypothesis was partly confirmed as only one temperate species performed better in soil with warming history than in soil with history of ambient temperature. Further, this effect was restricted to the site with higher soil water content in the growing season of the sampling year (prior to soil collection). One of the boreal species performed consistently worse in previously warmed soil, whereas the other species showed neutral responses to soil warming history. We found a positive correlation between the density of microbial-feeding nematodes and the performance of one of the temperate species in previously wetter soils, but this correlation was negative at the site with previously drier soil. We found no significant correlations between the performance of the other temperate species as well as the two boreal species and any of the studied soil biota. Our results indicate that soil warming can modify the relation between certain plant species and microbial-feeding nematodes in given soil edaphic conditions, which might be important for plant performance in the temperate-boreal ecotone.Item Fine-root biomass from Cloquet and Auclair IDENT sites(2022-03-14) Schuster, Michael J.; Williams, Laura J; Stefanski, Artur; Bermudez, Raimundo; Messier, Christian; Belluau, Michaël; Paquette, Alain; Gravel, Dominique; Reich, Peter B; schuster@umn.edu; Schuster, Michael JMean fine-root biomass data gathered from the IDENT experiments in Cloquet, MN and Auclair, Quebec.Item Geographic range predicts photosynthetic and growth response to warming in co-occurring tree species(Nature Publishing Group, 2015) Reich, Peter B; Sendall, Kerrie M; Rice, Karen; Rich, Roy L; Stefanski, Artur; Hobbie, Sarah E; Montgomery, Rebecca APopulations near the warm edge of species ranges may be particularly sensitive to climate change, but lack of empirical data on responses to warming represents a key gap in understanding future range dynamics. Herein we document the impacts of experimental warming on the performance of 11 boreal and temperate forest species that co-occur at the ecotone between these biomes in North America. We measured in situ net photosynthetic carbon gain and growth of >4,100 juvenile trees from local seed sources exposed to a chamberless warming experiment that used infrared heat lamps and soil heating cables to elevate temperatures by +3.4 °C above- and belowground for three growing seasons across 48 plots at two sites. In these ecologically realistic field settings, species growing nearest their warm range limit exhibited reductions in net photosynthesis and growth, whereas species near their cold range limit responded positively to warming. Differences among species in their three-year growth responses to warming parallel their photosynthetic responses to warming, suggesting that leaf-level responses may scale to whole-plant performance. These responses are consistent with the hypothesis, from observational data and models, that warming will reduce the competitive ability of currently dominant southern boreal species compared with locally rarer co-occurring species that dominate warmer neighbouring regions. © 2015 Macmillan Publishers Limited. All rights reserved.Item Is it getting hot in here? Adjustment of hydraulic parameters in six boreal and temperate tree species after 5 years of warming(Wiley, 2016) Mculloh, Katherine A; Petitmermet, Joshua; Stefanski, Artur; Rice, Karen E; Rich, Roy L.; Montgomery, Rebecca A; Reich, Peter BGlobal temperatures (T) are rising, and for many plant species, their physiological response to this change has not been well characterized. In particular, how hydraulic parameters may change has only been examined experimentally for a few species. To address this, we measured characteristics of the hydraulic architecture of six species growing in ambient T and ambient +3.4 °C T plots in two experimentally warmed forest sites in Minnesota. These sites are at the temperate–boreal ecotone, and we measured three species from each forest type. We hypothesized that relative to boreal species, temperate species near their northern range border would increase xylem conduit diameters when grown under elevated T. We also predicted a continuum of responses among wood types, with conduit diameter increases correlating with increases in the complexity of wood structure. Finally, we predicted that increases in conduit diameter and specific hydraulic conductivity would positively affect photosynthetic rates and growth. Our results generally supported our hypotheses, and conduit diameter increased under elevated T across all species, although this pattern was driven predominantly by three species. Two of these species were temperate angiosperms, but one was a boreal conifer, contrary to predictions. We observed positive relationships between the change in specific hydraulic conductivity and both photosynthetic rate (P = 0.080) and growth (P = 0.012). Our results indicate that species differ in their ability to adjust hydraulically to increases in T. Specifically, species with more complex xylem anatomy, particularly those individuals growing near the cooler edge of their range, appeared to be better able to increase conduit diameters and specific hydraulic conductivity, which permitted increases in photosynthesis and growth. Our data support results that indicate individual's ability to physiologically adjust is related to their location within their species range, and highlight that some wood types may adjust more easily than others.Item Phenological data (2009-2013) for ten tree species grown under experimental warming in northern Minnesota, USA(2020-03-27) Montgomery, Rebecca A; Stefanski, Artur; Reich, Peter B; Rice, Karen E; rebeccam@umn.edu; Montgomery, Rebecca A; University of Minnesota Forest Ecology GroupThis dataset contains five years of data on time of budburst, growing degree days at the time of budburst, time of senescence and phenological growing season length phenology data for ten tree species native to Minnesota, USA. Data were collected in a long-term open-air warming experiment located a the Cloquet Forestry Center, Cloquet, MN, USA and the Hubachek Wilderness Research Center, Ely, MN, USA. The design was a 2 (site) X 2 (habitat) x 3 (warming treatment) factorial, with 6 replicates (2 per block) for a total of 72 7.1 m2 circular plots. Species include: Quercus rubra, Quercus macrocarpa, Pinus banksiana, Pinus strobus, Populus tremuloides, Betula papyrifera, Abies balsamea, Picea glauca, Acer rubrum, Acer saccharum. These data are released in conjunction with a publication.Item Phenology matters: Extended spring and autumn canopy cover increases biotic resistance of forests to invasion by common buckthorn (Rhamnus cathartica)(Forest Ecology and Management, 2020) Schuster, Michael J.; Wragg, Peter D.; Williams, Laura J.; Butler, Ethan E.; Stefanski, Artur; Reich, Peter B.Forest light availability strongly regulates understory community composition, and low availability may confer resistance to invasion by exotic species, yet common buckthorn (Rhamnus cathartica L.) invades North American temperate forests with a broad range of light habitats. It is unclear to what extent buckthorn’s success is due to high mid-season shade tolerance versus shade avoidance permitted by early leaf out and late senescence. We used buckthorn seedlings planted into a forest diversity experiment in Cloquet, Minnesota, USA and a combined buckthorn physiology-canopy light model to test (1) how buckthorn germination, growth, and survival depend on canopy shading and (2) how canopy species richness and phenology affect light availability and buckthorn performance. Based on the mean of May, August, and October light measurements, we found that canopies that permitted ≤3% transmission of incoming light had almost complete mortality of buckthorn and that growth of surviving buckthorn was strongly tied to light availability, but not canopy richness. Compared to deciduous canopies or deciduous-evergreen mixtures, evergreen canopies restricted light availability the most and led to the smallest and least likely to survive buckthorn. Our canopy models further indicated a tight linkage between buckthorn performance and spring and autumn light availability, but not summer light availability. We conclude that spring and autumn light availability are key regulators of buckthorn performance and that buckthorn relies on shade avoidance via an extended phenology to succeed in temperate forests. Consequently, we suggest species with extended spring or autumn canopy cover offer the greatest resistance to invasion, and communities which are often leafless during such periods are most vulnerable to invasion by buckthorn and similar invasive shrubs.Item The photosynthetic process will shape how tree species from the boreal-temperate ecotone will fare in the future climate(2021-08) Stefanski, ArturPhotosynthesis is a physiological process, without which, life as we know it would not be possible—period. Photosynthesis allows plants to harvest and store energy in carbon bonds; however, like any biological process, it is constrained by several abiotic and biotic conditions. This dissertation was inspired by my fascination with the process of photosynthesis, as I sought insights into: i) its complexity and whether and how the fast pace of changing climate might affect it, and ii) understanding whether signals of plant responses to an ecologically realistic in situ warming and reduced rainfall experiment are consistent across multiple years with varying climatic conditions (e.g., wet vs. dry and hot vs. cold years) warranting confidence and generalization of findings.Leveraging the B4WarmED (Boreal Forest [4] Warming at an Ecotone in Danger) experiment, my collaborators and I investigated whether and how the photosynthetic process of tree species from the boreal-temperate ecotone—as a whole and its subcomponents—will be affected by future climate. B4WarmED is an experimental platform that implements ecologically realistic open-air warming and summer rainfall reduction in juvenile tree species native to the boreal-temperate ecotone in North America. My dissertation is in three parts, i.e., three chapters. First, I show that juvenile tree species reveal a surprising lack of sensitivity of the biochemical limitation of the photosynthetic process in response to warming and water limitation. Second, I demonstrate that stomatal behavior changes under warming such that plants become more prolific water users but only when water is ample. The stomatal behavior becomes more conservative when water becomes more limiting and marginal water cost of carbon gain increases due to either rainfall reduction or an increase of evaporative demand caused by warming. Moreover, the weak effect of elevated temperatures becomes detectable, but only when thermal effects are separated from indirect effects of warming on soil water content. Third, I examine a complex set of interactions that act together to shape carbon assimilation, including its component processes and climatic variables on a long-time scale. As a result, I demonstrate that carbon assimilation of tree species from the boreal-temperate ecotone will be affected by future climate change where temperate species will have a primarily positive response while the boreal will have a negative response. This change in carbon assimilation will be dictated by the alleviating effect that warming will have on photosynthetic enzymes especially, for temperate species, and reduction of stomatal conductance that reduces water loss resulting in increased water use efficiency in all species. Further, I also show that the effects are directionally consistent within species across years and vary in magnitude on an intra and interannual scale due to realized climatic conditions. Together, this dissertation research adds to our understanding of when and how climatic change—in terms of elevated temperatures and altered precipitation—will affect the photosynthetic process and its components. This provides additional insight to basic plant physiology, carbon cycle modeling in response to climate change, and demonstrates how tree species from the boreal-temperate forests will fare in the future climate.Item Responses of two understory herbs, Maianthemum canadense and Eurybia macrophylla, to experimental forest warming: early emergence is the key to enhanced reproductive output(Botanical Society of America, 2015) Jacques, Marie-Hélène; Lapointe, Line; Rice, Karen; Montgomery, Rebecca A; Stefanski, Artur; Reich, Peter BUnderstory herbs might be the most sensitive plant form to global warming in deciduous forests, yet they have been little studied in the context of climate change. A field experiment set up in Minnesota, United States simulated global warming in a forest setting and provided the opportunity to study the responses of Maianthemum canadense and Eurybia macrophylla in their natural environment in interaction with other components of the ecosystem. Effects of +1.7° and +3.4°C treatments on growth, reproduction, phenology, and gas exchange were evaluated along with treatment effects on light, water, and nutrient availability, potential drivers of herb responses. Overall, growth and gas exchanges of these two species were modestly affected by warming. They emerged up to 16 (E. macrophylla) to 17 d (M. canadense) earlier in the heated plots than in control plots, supporting early-season carbon gain under high light conditions before canopy closure. This additional carbon gain in spring likely supported reproduction. Eurybia macrophylla only flowered in the heated plots, and both species had some aspect of reproduction that was highest in the +1.7°C treatment. The reduced reproductive effort in the +3.4°C plots was likely due to reduced soil water availability, counteracting positive effects of warming. Global warming might improve fitness of herbaceous species in deciduous forests, mainly by advancing their spring emergence. However, other impacts of global warming such as drier soils in the summer might partly reduce the carbon gain associated with early emergence.Item Temperature and leaf nitrogen affect performance of plant species at range overlap(Wiley, 2015) Fisichelli, Nicholas A; Stefanski, Artur; Frelich, Lee E; Reich, Peter BPlant growth and survival near range limits are likely sensitive to small changes in environmental conditions. Warming temperatures are causing range shifts and thus changes in species composition within range-edge ecotones; however, it is often not clear how temperature alters performance. Through an observational field study, we assessed temperature and nitrogen effects on survival and growth of co-occurring temperate (Acer saccharum) and boreal (Abies balsamea) saplings across their overlapping range limits in the Great Lakes region, USA. Across sampled ranges of soil texture, soil pH, and precipitation, it appears that temperature affects leaf nitrogen for A. saccharum near its northern range limit (R2 = 0.64), whereas there was no significant leaf N ~ temperature relationship for A. balsamea. Higher A. saccharum leaf N at warm sites was associated with increased survival and growth. Abies balsamea survival and growth were best modeled with summer temperature (negative relationship); performance at warm sites depended upon light availability, suggesting the shade-tolerance of this species near its southern range limits may be mediated by temperature. The ranges of these two tree species overlap across millions of hectares, and temperature and temperature-mediated nitrogen likely play important roles in their relative performance.Item Warming shifts 'worming': effects of experimental warming on invasive earthworms in northern North America(2014) Eisenhauer, Nico; Stefanski, Artur; Fisichelli, Nicholas A; Rice, Karen; Rich, Roy; Reich, Peter BClimate change causes species range shifts and potentially alters biological invasions. The invasion of European earthworm species across northern North America has severe impacts on native ecosystems. Given the long and cold winters in that region that to date supposedly have slowed earthworm invasion, future warming is hypothesized to accelerate earthworm invasions into yet non-invaded regions. Alternatively, warming-induced reductions in soil water content (SWC) can also decrease earthworm performance. We tested these hypotheses in a field warming experiment at two sites in Minnesota, USA by sampling earthworms in closed and open canopy in three temperature treatments in 2010 and 2012. Structural equation modeling revealed that detrimental warming effects on earthworm densities and biomass could indeed be partly explained by warming-induced reductions in SWC. The direction of warming effects depended on the current average SWC: warming had neutral to positive effects at high SWC, whereas the opposite was true at low SWC. Our results suggest that warming limits the invasion of earthworms in northern North America by causing less favorable soil abiotic conditions, unless warming is accompanied by increased and temporally even distributions of rainfall sufficient to offset greater water losses from higher evapotranspiration.