Photo: Platanus orientalis, Old World Sycamore or Plane tree, Beijing, China. © 2009 Delena Norris-Tull.
Research summary and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, March 2022.
Climate Change: Impacts of Increased CO2, NO, UV light, and Ozone on Native and Introduced Plants
Increased Ozone Levels and Increased UV-B Levels
Wang, et al., 2016, conducted an experiment on the effects of increased ozone and UV-B levels on Chinese tallow trees, Triadica sebifera. They compared the effects of varied amounts of ozone and UV-B light, on seedling plants grown from seeds collected from four different locations within the tree’s native range in China. And they compared these effects on seedlings grown from seeds collected from invasive tallow trees from four locations in the USA.
Chinese tallow trees were introduced into the USA in the 1700s as ornamental trees. In China, they are valued for their seed oil which is used in soaps, candles, as a drying oil in paints and varnishes, and as a fuel. Tallow trees are now considered invasive species throughout the Southeastern USA and into Texas and California.
Wang, et al., 2016, found that “In ambient UV-B, invasive plants had significantly higher mass than native plants... But negative effects of elevated UV-B were stronger for invasive plants such that invasive and native plants had comparable masses in elevated UV-B... Analyses of masses in different compartments indicated that invasive and native plants differed most strongly in plant stem mass (higher for invasive plants) that was reflected in significantly higher root to shoot ratios for native plants... The greater sensitivity of invasive plants to UV-B was driven by differences in leaf litter mass... Leaf litter mass increased with UV-B for native plants but decreased for invasive plants… as did the percent of leaf mass that fell as litter before harvest.
“Ozone and UV-B each decreased plant mass on average but they had significant interactive effects... In ambient UV-B, mass decreased as ozone increased... However, in elevated UV-B there was no additional impact of increasing ozone beyond the negative effect of UV-B and the lowest mass was in the highest ozone (150 ppb) with ambient UV-B. Increasing ozone decreased stem mass, leaf mass at harvest and aboveground mass in ambient UV-B but effects on root mass were weaker (not significant after Bonferroni correction) such that root to shoot ratio increased... Leaf area showed a similar pattern with significant decreases with ozone in ambient UV-B but not in elevated UV-B. However, UV-B did not decrease leaf area so SLA was significantly higher with elevated UV-B at intermediate (100 ppb) ozone... LAR showed a similar pattern with significant increases from UV-B at only the high (150 ppb) ozone level.”
Wang, et al., 2016, concluded that, “on average, invasive populations grew larger than native populations and they had greater plasticity such that they out performed natives in ambient UV conditions. However, this plasticity difference also means that invasive populations were more sensitive to increasing UV… Our study showed that invasive populations were more sensitive to UV-B radiation relative to native populations. Lower secondary metabolites in invasive populations, due to rapidly evolved trade-off between defense and growth when released from enemies, might be the reason reducing their competitiveness facing elevated UV-B radiation.”
Increased Ozone and CO2 Levels
Wang, et al., 2018, conducted similar experiments on the effects of increased ozone and CO2 levels on Chinese tallow trees (comparing trees from populations in China and the USA), and on pairs of related species of trees (cogeneric) native to the USA and China. They “manipulated ozone (control or 100 ppb) and CO2 (ambient or 800 ppm) in a factorial greenhouse experiment in replicated chambers. [They] investigated growth and defense (tannins) of seedlings of Triadica sebifera from invasive (USA) and native (China) populations and pairs of US and China tree species within three genera (Celtis, Liquidambar and Platanus).
Wang, et al., 2018, found that “The significant effect of CO2 × O3 … reflected increased leaf and stem masses with CO2 + O3, and root and total mass decreasing with O3 but increasing with CO2 + O3…. Root:shoot [ratio] was lower with O3 ... On average, plants from China had higher leaf, root, and total mass and more leaves but there was significant variation among genera for every one of the response variables and significant variation among species for leaf, root, and total mass … and leaf number as well... Compared to those from native populations, T. sebifera plants from invasive populations had greater stem mass, had greater root and total mass in control and CO2 + O3 …, had lower numbers of leaves in O3 or CO2 … and only plants from invasive populations had reductions in root:shoot with ozone... There was significant variation among populations for every response variable... Effects of CO2, O3 or CO2 × O3 did not vary among genera, species… or populations.”
Wang, et al., 2018, concluded that, “In this, the first study of population variation of an invader plant species in responses to ozone and elevated CO2, we found that ozone alone had negative effects on plant performance compared with the control treatment; however, ozone and CO2 together had positive effects. These results with invader, native and exotic tree species are consistent with previous findings which mainly focused on crops, as well as some tree species, such as pine, aspen, birch and beech (Kumari et al. 2015; Moran and Kubiske 2013; Talhelm et al. 2014; Vanhatalo et al. 2003), which found that elevated CO2 limited the negative effect of elevated ozone. Furthermore, most studies have posited that the positive effects of combined ozone and CO2 resulted from positive effects of elevated CO2 being larger than the negative effects of elevated ozone (Lindroth 2010; Sitch et al. 2007). However, in our study, there must have been an interactive effect of ozone and CO2 as plant performance did not increase with CO2 alone. An example of such an effect is when elevated CO2 decreases stomatal conductance and thus inhibits uptake of ozone into leaves (McKee et al. 2000). But, our finding was that ozone stimulated the ‘fertilization effect’ of CO2. Vanhatalo et al. (2003) reported the same pattern in height growth, needle dry weight and total biomass for Scots pine or Norway spruce seedlings... Their results and ours are consistent with a modeling study (Chen et al. 1994) which predicted that ozone might have little effects on plant biomass because of compensatory regrowth of more efficient younger tissues when ozone accelerated senescence. Lindroth et al. (2001) found that foliar C:N of birch and aspen had non-additive responses to elevated ozone and CO2 with large increases in C:N in combination. In addition, it is possible that soil microorganisms could have non-additive responses that shape plant responses which is consistent with mass being highest on average in CO2 + O3 for every species but we have no data to evaluate this possibility… This pattern of increased growth with the combination of ozone and CO2 was stronger for invasive populations of T. sebifera than for native populations. In addition, native and invasive populations varied in their responses to ozone or CO2 alone such that their performances were more similar in those conditions. Specifically, native populations were less sensitive to ozone for either mass or root:shoot compared to invasive populations that had significant decreases in mass and native populations had larger increases in response to elevated CO2.
“Our results… suggest that elevated ozone and CO2 will not have strong effects on competition between T. sebifera and US tree species. Compared to those species, T. sebifera had greater mass and lower tannins and elevated ozone and/or elevated CO2 did not have large enough effects on any of these species to change growth or defense of T. sebifera relative to these other species. Indeed, the patterns for growth and defense are suggestive of a trade-off between these traits… that may not be very sensitive to these abiotic drivers.”
Effects of increased CO2 and NO levels on soils
Deng, et al., 2016, conducted experiments comparing the effects of increased CO2 and NO levels on soils and various grasses and sedges in China. They “collected soils from degraded meadows and plots restored using three different plant species at Wugong Mountain (Jiangxi, China). [They] measured CO and NO emissions when soils were incubated at different temperatures (15, 25 or 35 °C) and levels of N addition (control vs. 4 gm) to understand their responses to warming and N deposition.”
They commented that, “Alpine meadows are degraded worldwide, but restorations are increasing. Because their soils represent large carbon (C) and nitrogen (N) pools, they may produce significant amounts of CO and NO depending on the plant species used in restorations. In addition, warming and N deposition may impact soil CO and NO emissions from restored meadows.”
Deng, et al., 2016, found that, “Dissolved organic C was higher in restored plots… compared to non-restored bare soils, and their soil inorganic N was lower. CO emission rates were increased by vegetation restorations, decreased by N deposition, and increased by warming. CO emission rates were similar for the three grass species at 15 and 25°C, but they were lower with Miscanthus floridulus at 35°C. Soils from [Fimbristylis] dichotoma and Carex chinensis plots had higher NO emissions than degraded or M. floridulus plots, especially at 25°C… These results show that the effects of restorations on soil greenhouse gas emissions depended on plant species. In addition, these differences varied with temperature suggesting that future climate should be considered when choosing plant species in restorations to predict soil CO and NO emissions and global warming potential.”
Commentary by Dr. Delena Norris-Tull: It is very concerning that very little research has been conducted on the potential impacts of the above climate change factors on native and introduced plants, particularly as the research indicates that the impacts vary by species.
References:
Next Sections:
Research summary and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, March 2022.
Climate Change: Impacts of Increased CO2, NO, UV light, and Ozone on Native and Introduced Plants
Increased Ozone Levels and Increased UV-B Levels
Wang, et al., 2016, conducted an experiment on the effects of increased ozone and UV-B levels on Chinese tallow trees, Triadica sebifera. They compared the effects of varied amounts of ozone and UV-B light, on seedling plants grown from seeds collected from four different locations within the tree’s native range in China. And they compared these effects on seedlings grown from seeds collected from invasive tallow trees from four locations in the USA.
Chinese tallow trees were introduced into the USA in the 1700s as ornamental trees. In China, they are valued for their seed oil which is used in soaps, candles, as a drying oil in paints and varnishes, and as a fuel. Tallow trees are now considered invasive species throughout the Southeastern USA and into Texas and California.
Wang, et al., 2016, found that “In ambient UV-B, invasive plants had significantly higher mass than native plants... But negative effects of elevated UV-B were stronger for invasive plants such that invasive and native plants had comparable masses in elevated UV-B... Analyses of masses in different compartments indicated that invasive and native plants differed most strongly in plant stem mass (higher for invasive plants) that was reflected in significantly higher root to shoot ratios for native plants... The greater sensitivity of invasive plants to UV-B was driven by differences in leaf litter mass... Leaf litter mass increased with UV-B for native plants but decreased for invasive plants… as did the percent of leaf mass that fell as litter before harvest.
“Ozone and UV-B each decreased plant mass on average but they had significant interactive effects... In ambient UV-B, mass decreased as ozone increased... However, in elevated UV-B there was no additional impact of increasing ozone beyond the negative effect of UV-B and the lowest mass was in the highest ozone (150 ppb) with ambient UV-B. Increasing ozone decreased stem mass, leaf mass at harvest and aboveground mass in ambient UV-B but effects on root mass were weaker (not significant after Bonferroni correction) such that root to shoot ratio increased... Leaf area showed a similar pattern with significant decreases with ozone in ambient UV-B but not in elevated UV-B. However, UV-B did not decrease leaf area so SLA was significantly higher with elevated UV-B at intermediate (100 ppb) ozone... LAR showed a similar pattern with significant increases from UV-B at only the high (150 ppb) ozone level.”
Wang, et al., 2016, concluded that, “on average, invasive populations grew larger than native populations and they had greater plasticity such that they out performed natives in ambient UV conditions. However, this plasticity difference also means that invasive populations were more sensitive to increasing UV… Our study showed that invasive populations were more sensitive to UV-B radiation relative to native populations. Lower secondary metabolites in invasive populations, due to rapidly evolved trade-off between defense and growth when released from enemies, might be the reason reducing their competitiveness facing elevated UV-B radiation.”
Increased Ozone and CO2 Levels
Wang, et al., 2018, conducted similar experiments on the effects of increased ozone and CO2 levels on Chinese tallow trees (comparing trees from populations in China and the USA), and on pairs of related species of trees (cogeneric) native to the USA and China. They “manipulated ozone (control or 100 ppb) and CO2 (ambient or 800 ppm) in a factorial greenhouse experiment in replicated chambers. [They] investigated growth and defense (tannins) of seedlings of Triadica sebifera from invasive (USA) and native (China) populations and pairs of US and China tree species within three genera (Celtis, Liquidambar and Platanus).
Wang, et al., 2018, found that “The significant effect of CO2 × O3 … reflected increased leaf and stem masses with CO2 + O3, and root and total mass decreasing with O3 but increasing with CO2 + O3…. Root:shoot [ratio] was lower with O3 ... On average, plants from China had higher leaf, root, and total mass and more leaves but there was significant variation among genera for every one of the response variables and significant variation among species for leaf, root, and total mass … and leaf number as well... Compared to those from native populations, T. sebifera plants from invasive populations had greater stem mass, had greater root and total mass in control and CO2 + O3 …, had lower numbers of leaves in O3 or CO2 … and only plants from invasive populations had reductions in root:shoot with ozone... There was significant variation among populations for every response variable... Effects of CO2, O3 or CO2 × O3 did not vary among genera, species… or populations.”
Wang, et al., 2018, concluded that, “In this, the first study of population variation of an invader plant species in responses to ozone and elevated CO2, we found that ozone alone had negative effects on plant performance compared with the control treatment; however, ozone and CO2 together had positive effects. These results with invader, native and exotic tree species are consistent with previous findings which mainly focused on crops, as well as some tree species, such as pine, aspen, birch and beech (Kumari et al. 2015; Moran and Kubiske 2013; Talhelm et al. 2014; Vanhatalo et al. 2003), which found that elevated CO2 limited the negative effect of elevated ozone. Furthermore, most studies have posited that the positive effects of combined ozone and CO2 resulted from positive effects of elevated CO2 being larger than the negative effects of elevated ozone (Lindroth 2010; Sitch et al. 2007). However, in our study, there must have been an interactive effect of ozone and CO2 as plant performance did not increase with CO2 alone. An example of such an effect is when elevated CO2 decreases stomatal conductance and thus inhibits uptake of ozone into leaves (McKee et al. 2000). But, our finding was that ozone stimulated the ‘fertilization effect’ of CO2. Vanhatalo et al. (2003) reported the same pattern in height growth, needle dry weight and total biomass for Scots pine or Norway spruce seedlings... Their results and ours are consistent with a modeling study (Chen et al. 1994) which predicted that ozone might have little effects on plant biomass because of compensatory regrowth of more efficient younger tissues when ozone accelerated senescence. Lindroth et al. (2001) found that foliar C:N of birch and aspen had non-additive responses to elevated ozone and CO2 with large increases in C:N in combination. In addition, it is possible that soil microorganisms could have non-additive responses that shape plant responses which is consistent with mass being highest on average in CO2 + O3 for every species but we have no data to evaluate this possibility… This pattern of increased growth with the combination of ozone and CO2 was stronger for invasive populations of T. sebifera than for native populations. In addition, native and invasive populations varied in their responses to ozone or CO2 alone such that their performances were more similar in those conditions. Specifically, native populations were less sensitive to ozone for either mass or root:shoot compared to invasive populations that had significant decreases in mass and native populations had larger increases in response to elevated CO2.
“Our results… suggest that elevated ozone and CO2 will not have strong effects on competition between T. sebifera and US tree species. Compared to those species, T. sebifera had greater mass and lower tannins and elevated ozone and/or elevated CO2 did not have large enough effects on any of these species to change growth or defense of T. sebifera relative to these other species. Indeed, the patterns for growth and defense are suggestive of a trade-off between these traits… that may not be very sensitive to these abiotic drivers.”
Effects of increased CO2 and NO levels on soils
Deng, et al., 2016, conducted experiments comparing the effects of increased CO2 and NO levels on soils and various grasses and sedges in China. They “collected soils from degraded meadows and plots restored using three different plant species at Wugong Mountain (Jiangxi, China). [They] measured CO and NO emissions when soils were incubated at different temperatures (15, 25 or 35 °C) and levels of N addition (control vs. 4 gm) to understand their responses to warming and N deposition.”
They commented that, “Alpine meadows are degraded worldwide, but restorations are increasing. Because their soils represent large carbon (C) and nitrogen (N) pools, they may produce significant amounts of CO and NO depending on the plant species used in restorations. In addition, warming and N deposition may impact soil CO and NO emissions from restored meadows.”
Deng, et al., 2016, found that, “Dissolved organic C was higher in restored plots… compared to non-restored bare soils, and their soil inorganic N was lower. CO emission rates were increased by vegetation restorations, decreased by N deposition, and increased by warming. CO emission rates were similar for the three grass species at 15 and 25°C, but they were lower with Miscanthus floridulus at 35°C. Soils from [Fimbristylis] dichotoma and Carex chinensis plots had higher NO emissions than degraded or M. floridulus plots, especially at 25°C… These results show that the effects of restorations on soil greenhouse gas emissions depended on plant species. In addition, these differences varied with temperature suggesting that future climate should be considered when choosing plant species in restorations to predict soil CO and NO emissions and global warming potential.”
Commentary by Dr. Delena Norris-Tull: It is very concerning that very little research has been conducted on the potential impacts of the above climate change factors on native and introduced plants, particularly as the research indicates that the impacts vary by species.
References:
- Chen, C.W., Tsai, W.T., Gomez, L.E. (May, 1994). Modeling responses of Ponderosa Pine to interacting stresses of ozone and drought. Forest Science, 40(2): 267–28.
- Deng, B., Li, Z., Zhang, L, Ma, Y., Li, Z., Zhang, W., Guo, X., Niu, D., & Siemann, E. (March, 2016). Increases in soil CO and NO emissions with warming depend on plant species in restored alpine meadows of Wugong Mountain, China. Journal of Soils & Sediments: Protection, Risk Assessment, & Remediation, 16(3): 777-784.
- Kumari, S., Agrawal, M., & Singh, A. (2015). Effects of ambient and elevated CO2 and ozone on physiological characteristics, antioxidative defense system and metabolites of potato in relation to ozone flux. Environmental and experimental botany, 109: 276-287.
- Lindroth, R. L., Kopper, B. J., Parsons, W. F., Bockheim, J. G., Karnosky, D. F., Hendrey, G. R., Pregitzer, K.S., Isebrands, J.G., & Sober, J. (2001). Consequences of elevated carbon dioxide and ozone for foliar chemical composition and dynamics in trembling aspen (Populus tremuloides) and paper birch (Betula papyrifera). Environmental Pollution, 115(3): 395-404.
- Lindroth, R. L. (2010). Impacts of elevated atmospheric CO2 and O3 on forests: phytochemistry, trophic interactions, and ecosystem dynamics. Journal of chemical ecology, 36(1): 2-21.
- McKee, I. F., Mulholland, B. J., Craigon, J., Black, C. R., & Long, S. P. (2000). Elevated concentrations of atmospheric CO2 protect against and compensate for O3 damage to photosynthetic tissues of field‐grown wheat. New Phytologist, 146(3): 427-435.
- Moran, E. V., & Kubiske, M. E. (2013). Can elevated CO 2 and ozone shift the genetic composition of aspen (Populus tremuloides) stands? New Phytologist, 198(2): 466-475.
- Sitch, S., Cox, P. M., Collins, W. J., & Huntingford, C. (2007). Indirect radiative forcing of climate change through ozone effects on the land-carbon sink. Nature, 448(7155): 791-794.
- Talhelm, A. F., Pregitzer, K. S., Kubiske, M. E., Zak, D. R., Campany, C. E., Burton, A. J., Dickson, R.E., Hendrey, G.R., Isebrands, J.G., Nagy, J., & Karnosky, D. F. (2014). Elevated carbon dioxide and ozone alter productivity and ecosystem carbon content in northern temperate forests. Global change biology, 20(8): 2492-2504. https://onlinelibrary.wiley.com/doi/10.1111/gcb.12564
- Vanhatalo, M., Bäck, J., & Huttunen, S. (2003). Differential impacts of long-term (CO2) and O3 exposure on growth of northern conifer and deciduous tree species. Trees, 17(3): 211-220.
- Wang, H., Zhang, L., Ma, X., Zou, J., & Siemann, E. (April, 2018). The effects of elevated ozone and CO2 on growth and defense of native, exotic and invader trees. Journal of Plant Ecology, 11(2): 266-272. https://doi.org/10.1093/jpe/rtw142
- Wang, H., Ma, X., Zhang, L., Siemann, E., & Zou, J. (Feb., 2016). UV-B has larger negative impacts on invasive populations of Triadica sebifera but ozone impacts do not vary. Journal of Plant Ecology, 9(1): 61-68. doi:10.1093/jpe/rtv045
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