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Chapter 7 examines the biological effects of rising CO2 concentrations and warmer temperatures. This is the largely unreported side of the global warming debate, perhaps because it is unequivocally good news. Rising CO2 levels increase plant growth and make plants more resistant to drought and pests. It is a boon to the world’s forests and prairies, as well as to farmers and ranchers and the growing populations of the developing world.
Chapter 7 Key Findings
- A 300-ppm increase in the air’s CO2 content typically raises the productivity of most herbaceous plants by about one-third; and this positive response occurs in plants that utilize all three of the major biochemical pathways (C3, C4, CAM) of photosynthesis. For woody plants, the response is even greater. The productivity benefits of CO2 enrichment are also experienced by aquatic plants, including freshwater algae and macrophytes, and marine microalgae and macroalgae.
- The amount of carbon plants gain per unit of water lost-or water-use efficiency-typically rises as the CO2 content of the air rises, greatly increasing their ability to withstand drought. In addition, the CO2-induced percentage increase in plant biomass production is often greater under water-stressed conditions than it is when plants are well watered.
- Atmospheric CO2 enrichment helps ameliorate the detrimental effects of several environmental stresses on plant growth and development, including high soil salinity, high air temperature, low light intensity and low levels of soil fertility. Elevated levels of CO2 have additionally been demonstrated to reduce the severity of low temperature stress, oxidative stress, and the stress of herbivory. In fact, the percentage growth enhancement produced by an increase in the air’s CO2 concentration is often even greater under stressful and resource-limited conditions than it is when growing conditions are ideal.
- As the air’s CO2 content continues to rise, plants will likely exhibit enhanced rates of photosynthesis and biomass production that will not be diminished by any global warming that might occur concurrently. In fact, if the ambient air temperature rises, the growth-promoting effects of atmospheric CO2 enrichment will likely also rise, becoming more and more robust.
- The ongoing rise in the air’s CO2 content likely will not favor the growth of weedy species over that of crops and native plants.
- The growth of plants is generally not only enhanced by CO2-induced increases in net photosynthesis during the light period of the day, it is also enhanced by CO2-induced decreases in respiration during the dark period.
- The ongoing rise in the air’s CO2 content, as well as any degree of warming that might possibly accompany it, will not materially alter the rate of decomposition of the world’s soil organic matter and will probably enhance biological carbon sequestration. Continued increases in the air’s CO2 concentration and temperature will not result in massive losses of carbon from earth’s peatlands. To the contrary, these environmental changes-if they persist-would likely work together to enhance carbon capture.
- Other biological effects of CO2 enhancement include enhanced plant nitrogen-use efficiency, longer residence time of carbon in the soil, and increased populations of earthworms and soil nematodes.
- The aerial fertilization effect of the ongoing rise in the air’s CO2 concentration (which greatly enhances vegetative productivity) and its anti-transpiration effect (which enhances plant water-use efficiency and enables plants to grow in areas that were once too dry for them) are stimulating plant growth across the globe in places that previously were too dry or otherwise unfavorable for plant growth, leading to a significant greening of the Earth.
- Elevated CO2 reduces, and nearly always overrides, the negative effects of ozone pollution on plant photosynthesis, growth and yield. It also reduces atmospheric concentrations of isoprene, a highly reactive non-methane hydrocarbon that is emitted in copious quantities by vegetation and is responsible for the production of vast amounts of tropospheric ozone.
Chapter 7. Biological Effects of Carbon Dioxide Enrichment (PDF, 1,453 kb)
7.1. Plant Productivity Responses (PDF, 351 kb)
7.1.1. Herbaceous Plants
7.1.2. Woody Plants
7.1.3. Aquatic Plants
7.2. Water Use Efficiency (PDF, 74 kb)
7.2.1. Agricultural Species
7.2.2. Grassland Species
7.2.3. Woody Species
7.3. Amelioration of Environmental Stresses (PDF, 464 kb)
7.3.1. Disease
7.3.2. Herbivory
7.3.3. Insects
7.3.4. Shade
7.3.5. Ozone
7.3.6. Low Temperatures
7.3.7. Nitrogen Deficiency
7.3.8. High Salinity
7.3.9. Elevated Temperature
7.3.10. UV-B Radiation
7.3.11. Water Stress
7.4. Acclimation (PDF, 86 kb)
7.4.1. Agricultural Species
7.4.2. Chaparral and Desert Species
7.4.3. Grassland Species
7.4.4. Tree Species
7.5. Competition (PDF, 67 kb)
7.5.1. C3 vs. C4 Plants
7.5.2. N-Fixers vs. Non-N-Fixers
7.5.3. Weeds vs. Non-Weeds
7.6. Respiration (PDF, 77 kb)
7.6.1. Herbaceous Plants
7.6.2. Woody Plants
7.7. Carbon Sequestration (PDF, 165 kb)
7.7.1. CO2 Enhancement and Carbon Sequestration
7.7.2. Decomposition
7.7.3. Temperature and Carbon Sequestration
7.8. Other Benefits (PDF, 255 kb)
7.8.1. Nitrogen-Use Efficiency
7.8.2. Nutrient Acquisition
7.8.3. Pathogens
7.8.4. Parasitic Plants
7.8.5. Roots
7.8.6. Seeds
7.8.7. Tannins
7.8.8. Transgenic Plants
7.8.9. Isoprene
7.8.10. Microorganisms
7.8.11. Worms
7.9. Greening of the Earth (PDF, 196 kb)
7.9.1. Africa
7.9.2. Asia
7.9.3. Europe
7.9.4. North America
7.9.5. Oceans
7.9.6. Global
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