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Browsing by Author "Sendall, Kerrie M"

Now showing 1 - 4 of 4
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    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.
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    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 A
    Plant 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.
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    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 A
    Populations 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.
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    Trade‐offs in juvenile growth potential vs. shade tolerance among subtropical rain forest trees on soils of contrasting fertility
    (Wiley, 2016) Sendall, Kerrie M; Lusk, Christopher H; Reich, Peter B
    Plant adaptation to gradients of light availability involves a well-studied functional trade-off, as does adaptation to gradients of nutrient availability. However, little is known about how these two major trade-offs interact, and thus, it remains unclear whether and how the nature of the growth–shade tolerance trade-off differs on soils of contrasting fertility. We asked whether juvenile growth–shade tolerance trade-offs differed in slope and elevation between tree assemblages on nutrient-rich basalt and nutrient-poor rhyolite soils in an Australian subtropical rain forest. We measured the growth of, and the range of light environments occupied by, juveniles (40–120 cm tall) of eight basalt specialists, six rhyolite specialists, and one generalist that was common on both substrates. In situ minimum light requirements were estimated from the 5th percentile of the distribution of naturally regenerated juveniles in relation to daily light transmittance. Stem growth was measured for 12–16 months across a wide range of light environments to estimate the light compensation point of growth of each species. Light compensation points of growth showed nearly a 1 : 1 correspondence with in situ minimum light requirements of species, indicating that whole-plant carbon balance is a key driver of ecological success in low light. Minimum light requirements were negatively correlated with relative growth rate in low light, but correlated positively with growth in high light. Soil type had no effect on either the slope or the elevation of this trade-off, all species aligning around a common growth–shade tolerance trade-off, but our results do show a wider range of growth rates and shade tolerance on the nutrient-rich basalt soil than on the nutrient-poor rhyolite. Our results suggest that adaptation to light availability involves fundamentally similar trade-offs on these two substrates of differing fertility. However, a wider range of growth rates and shade tolerance on the nutrient-rich basalt soil than on the nutrient-poor rhyolite may help to explain the higher species richness and greater structural complexity of forest stands on the former substrate.