An official website of the United States government
Abstract Warming shifts the thermal optimum of net photosynthesis (ToptA) to higher temperatures. However, our knowledge of this shift is mainly derived from seedlings grown in greenhouses under ambient atmospheric carbon dioxide (CO2) conditions. It is unclear whether shifts inToptAof field-grown trees will keep pace with the temperatures predicted for the 21stcentury under elevated atmospheric CO2concentrations. Here, using a whole-ecosystem warming controlled experiment under either ambient or elevated CO2levels, we show thatToptAof mature boreal conifers increased with warming. However, shifts inToptAdid not keep pace with warming asToptAonly increased by 0.26–0.35 °C per 1 °C of warming. Net photosynthetic rates estimated at the mean growth temperature increased with warming in elevated CO2spruce, while remaining constant in ambient CO2spruce and in both ambient CO2and elevated CO2tamarack with warming. Although shifts inToptAof these two species are insufficient to keep pace with warming, these boreal conifers can thermally acclimate photosynthesis to maintain carbon uptake in future air temperatures.
more »
« less
This content will become publicly available on December 1, 2025
Photosynthetic capacity in middle‐aged larch and spruce acclimates independently to experimental warming and elevated CO 2
Abstract Photosynthetic acclimation to both warming and elevated CO2of 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 CO2on photosynthetic capacity (VcmaxandJmax) in mature trees of two North American boreal conifers, tamarack and black spruce. We show thatVcmaxandJmaxat a standard temperature of 25°C did not change with warming, whileVcmaxandJmaxat their thermal optima (Topt) and growth temperature (Tg) increased. Moreover,VcmaxandJmaxat either 25°C,ToptorTgdecreased with elevated CO2. TheJmax/Vcmaxratio decreased with warming when assessed at bothToptandTgbut did not significantly vary at 25°C. TheJmax/Vcmaxincreased with elevated CO2at either reference temperature. We found no significant interaction between warming and elevated CO2on all traits. If this lack of interaction between warming and elevated CO2on theVcmax,JmaxandJmax/Vcmaxratio is a general trend, it would have significant implications for improving photosynthesis representation in vegetation models. However, future research is required to investigate the widespread nature of this response in a larger number of species and biomes.
more »
« less
- Award ID(s):
- 2021898
- PAR ID:
- 10589851
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Plant, Cell & Environment
- Volume:
- 47
- Issue:
- 12
- ISSN:
- 0140-7791
- Page Range / eLocation ID:
- 4886 to 4902
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Summary Nitrogen (N) limitation has been considered as a constraint on terrestrial carbon uptake in response to rising CO2and climate change. By extension, it has been suggested that declining carboxylation capacity (Vcmax) and leaf N content in enhanced‐CO2experiments and satellite records signify increasing N limitation of primary production. We predictedVcmaxusing the coordination hypothesis and estimated changes in leaf‐level photosynthetic N for 1982–2016 assuming proportionality with leaf‐levelVcmaxat 25°C. The whole‐canopy photosynthetic N was derived using satellite‐based leaf area index (LAI) data and an empirical extinction coefficient forVcmax, and converted to annual N demand using estimated leaf turnover times. The predicted spatial pattern ofVcmaxshares key features with an independent reconstruction from remotely sensed leaf chlorophyll content. Predicted leaf photosynthetic N declined by 0.27% yr−1, while observed leaf (total) N declined by 0.2–0.25% yr−1. Predicted global canopy N (and N demand) declined from 1996 onwards, despite increasing LAI. Leaf‐level responses to rising CO2, and to a lesser extent temperature, may have reduced the canopy requirement for N by more than rising LAI has increased it. This finding provides an alternative explanation for declining leaf N that does not depend on increasing N limitation.more » « less
-
Abstract Tropical forest canopies cycle vast amounts of carbon, yet we still have a limited understanding of how these critical ecosystems will respond to climate warming. We implemented in situ leaf‐level + 3°C experimental warming from the understory to the upper canopy of two Puerto Rican tropical tree species,Guarea guidoniaandOcotea sintenisii. After approximately 1 month of continuous warming, we assessed adjustments in photosynthesis, chlorophyll fluorescence, stomatal conductance, leaf traits and foliar respiration. Warming did not alter net photosynthetic temperature response for either species; however, the optimum temperature ofOcoteaunderstory leaf photosynthetic electron transport shifted upward. There was noOcotearespiratory treatment effect, whileGuarearespiratory temperature sensitivity (Q10) was down‐regulated in heated leaves. The optimum temperatures for photosynthesis (Topt) decreased 3–5°C from understory to the highest canopy position, perhaps due to upper canopy stomatal conductance limitations.Guareaupper canopyToptwas similar to the mean daytime temperatures, whileOcoteacanopy leaves often operated aboveTopt. With minimal acclimation to warmer temperatures in the upper canopy, further warming could put these forests at risk of reduced CO2uptake, which could weaken the overall carbon sink strength of this tropical forest.more » « less
-
Thermal sensitivity in ectothermic organisms is often contingent upon environmental factors. Nutrient availability in particular is believed to influence the physiological responses of primary producers to global warming and is thus relevant to consider when forecasting the structure and functioning of future marine ecosystems. This study measured the effect of nutrient enrichment on the thermal sensitivity of 4 genera of Galápagos seaweeds (Ulva,Caulerpa,Padina, andOchtodes), estimated as the thermal optimum (Topt), performance maximum (Pmax), activation energy, and deactivation energy. These parameters were quantified by modeling thermal performance curves for net photosynthesis under ambient and nutrient-enriched conditions. Our findings revealed variation inToptamong genera, ranging from 27.6° to 36.0°C. Nutrient additions enhancedToptby ~2°C for 2 (PadinaandCaulerpa) of the 4 taxa and also significantly increasedPmaxinPadina, suggesting the ability for warming-induced ocean stratification and associated effects (i.e. decreasing nutrient availability) to reduce the capacities of these populations to maintain and support new growth. No significant differences inToptorPmaxwere observed for eitherUlvaorOchtodeswith enrichment. Ambient net photosynthesis and respiration rates were also compared across genera;Pmaxrates for net photosynthesis were consistently higher than those for respiration (i.e. until just beyondTopt); however, photosyntheticToptvalues were lower. Thus, this study suggests that further warming could reduce overall net primary productivity, with potentially far-reaching implications for marine food webs.more » « less
-
Summary Leaf dark respiration (Rd) acclimates to environmental changes. However, the magnitude, controls and time scales of acclimation remain unclear and are inconsistently treated in ecosystem models.We hypothesized thatRdand Rubisco carboxylation capacity (Vcmax) at 25°C (Rd,25,Vcmax,25) are coordinated so thatRd,25variations supportVcmax,25at a level allowing full light use, withVcmax,25reflecting daytime conditions (for photosynthesis), andRd,25/Vcmax,25reflecting night‐time conditions (for starch degradation and sucrose export). We tested this hypothesis temporally using a 5‐yr warming experiment, and spatially using an extensive field‐measurement data set. We compared the results to three published alternatives:Rd,25declines linearly with daily average prior temperature;Rdat average prior night temperatures tends towards a constant value; andRd,25/Vcmax,25is constant.Our hypothesis accounted for more variation in observedRd,25over time (R2 = 0.74) and space (R2 = 0.68) than the alternatives. Night‐time temperature dominated the seasonal time‐course ofRd, with an apparent response time scale ofc.2 wk.Vcmaxdominated the spatial patterns.Our acclimation hypothesis results in a smaller increase in globalRdin response to rising CO2and warming than is projected by the two of three alternative hypotheses, and by current models.more » « less
