Do Plants Prevent Atmospheric CO2 Levels from Falling Too Far?

by Emil Morhardt

A recent paper discussed in the previous post (Galbraith and Eggleston, 2017) claims that during the past 800,000 years when the Earth has been in a glacial condition with the occasional interglacial period (such as now), there is a strong correlation between global temperature and atmospheric CO2 levels, and that they tend to go to the same low point again and again and stay there. These authors argue that if CO2 were to go lower, so would the temperature, and that therefore something is keeping the CO2 level from going any lower then 190 ppm. One intriguing possibility they bring up comes from a paper (Pagani et al., 2009) by Mark Pagani at Yale, and his colleagues at the Carnegie Institution in Stanford and at the University of Sheffield who claim that plants stop effective photosynthesis if CO2 levels fall below 190 ppm, depriving the carbon cycle of two sources of removal of atmospheric CO2; photosynthesis, and a more subtle plant activity called biologically enhanced silicate chemical weathering. The mechanisms of these two processes are interesting. Continue reading

CO2 Impacts Tropical Forest Resistance to Climate Change

by Leta Ames

It is well known that fire can play a crucial role in the reproduction and development of plant populations. The availability of water and CO2 also impact plant growth, especially of larger species. It is believed that the interactions of climate, fire, and CO2 greatly influence the shift between savanna and tropical forest ecosystems and their permanence thereafter. Previous research has relied on data collected from intact tropical forests, but although useful, these data only provide a snapshot of the impact of CO2, fire, and climate on these ecosystems. To gain a better understanding of what factors influence tropical ecosystems Shanahan et al. (2016) used the concentrations of carbon and hydrogen stable isotopes from sedimentary leaf wax n-alkanes (δ13Cwax and δDwax) and the frequency of charcoal layers from sediment obtained from Lake Bosumtwi in Ghana to construct a history of changes in vegetation and hydrology, as well as to estimate the annual fire frequency. Continue reading

Fertilizing the Ocean to Trap CO2

by Emil Morhardt

One of the ways scientists have hoped to suck CO2 out of the atmosphere is by adding nutrients to the ocean that are limiting the growth of photosynthetic phytoplankton. The idea is that with the proper nutrients (iron being the main one experimented with so far) the plankton would capture CO2 photosynthetically, convert it to biomass, die, then sink to the ocean floor, “exporting” the new carbon in their bodies to a place where it couldn’t have any effect on global warming. There are a number of posts in this blog dealing with those experiments under the category “Ocean Fertilization”; they haven’t worked very well because, among other things, instead of sinking to seafloor, the phytoplankton get eaten by zooplankton which metabolically convert them back into energy and CO2 which can then diffuse back to the atmosphere, or at least contribute to ocean acidification.

A fascinating paper just published in Science, examines the nutrients limiting the growth of the photosynthetic marine cyanobacterium, Prochlorococcus, in a much more interesting and comprehensive way than previously possible, and although it doesn’t directly speak to the feasibility of fertilizing the ocean to trap CO2 (sorry about the somewhat misleading title to this post) it greatly increases the potential sophistication with which such a goal could be pursued. Continue reading

Cutting Climate Costs of Nitrogen Fertilizer Production

by Emil Morhardt

Nitrogen fertilizer, crucial for growing commercial crops, is based on ammonia made in factories using the energy- and CO2-intensive Haber-Bosch process; hydrogen is stripped off natural gas using steam, then reacted with nitrogen in the air. The process uses repeated cycling at high temperature and pressure, and consumes 2% of the world’s energy production. Stuart Licht and colleagues at George Washington University noticed, however, that a recently developed fuel cell using ammonia as a fuel and producing electricity as an output might be run in reverse: electricity in, ammonia out, with a whole lot less temperature and pressure (and energy) required. Even better, it wouldn’t need natural gas as a hydrogen source—with its attendant CO2 production—being able to get it from air and steam at a temperature lower than a household oven baking bread and at ambient pressure. Furthermore only simple materials would be required; molten sodium and potassium hydroxide (inexpensive commodity chemicals), nickel electrodes, and an iron oxide catalyst, all in a single pot.

After considerable experimentation with different temperatures, voltages, forms of iron oxide, Continue reading

The Other Ocean Acidification Problem: CO2 as a Resource

by Dawn Barlow

This study addresses the effects of enhanced CO2 levels in the ocean by looking at how increased acidity might indirectly cause phase shifts in community structure of coral reef and kelp forest ecosystems in temperate and tropical waters. Under elevated acidity and temperature conditions, productivity of certain photosynthetic organisms such as mat-forming algae (low-profile ground-covering macroalgal and turf communities) can increase, making CO2 not only a direct stressor but also an indirect stressor by being a resource for certain competitive organisms, creating enormous potential for shifts in species dominance. Additionally, ocean acidification acts together with other environmental stressors and primary consumers, and these factors also influence community response to acidic conditions. Connell et al. (2013) investigate the prevalence of mat-forming algae in three different scenarios where CO2 levels were either ambient or elevated: in the laboratory, in mesocosms in the field, and at naturally occurring CO2 vents that locally alter the seawater chemistry. They find that in all the scenarios, the algae mats respond positively to the elevated conditions, increasing growth rate and cover to so that the algae became a majority space holder regardless of any herbivory. This is likely because the new environmental conditions favor species with fast growth and colonization rates and short generation times, and these are the species that are capable of completely… Continue reading

Use of Computer Systems to Tailor Slurry Application to Specific Agricultural Fields Proves Effective

Schellberg and Lock (2009) conducted a study that designed software and hardware systems to control the application of slurry to grasslands and agricultural crops. They theorized that if the application process of the slurry, utilized as a crop fertilizer, could be controlled to a high degree of accuracy based on a fertilizer application map, specific to the field of cultivation, large N losses to the environment and over-fertilization of the crops would be avoided. This study did not evaluate the effectiveness of their site-specific slurry application techniques in the form of crop yield or spatial distribution of N. Instead, the effectiveness of the software and hardware systems to work together and produce the accurate application levels as determined in the application map were of concern in the study. — <!–[if supportFields]> CONTACT _Con-3EF86BDE1 \c \s \l <![endif]–>Maria Harwood<!–[if supportFields]><![endif]–>
Schellberg, J., Lock, R., 2009. A Site-specific Slurry Application Technique on Grassland and on Arable Crops. Bioresource Technology 100, 280–286.

 Schellberg and Lock used cattle slurry in their two field application experiments on a grassland used for forage and a field of corn. The key issues in applying this technique lay in the ability to determine the local nutrient demand of the plants and the need for an advanced on-field monitoring system tracking the release of the slurry. The authors tackled the latter problem by creating a software and hardware system to actively control the flow rate of the slurry during application. The various parameters that they measured include the dry matter yield, the dry matter content in the harvested material, the plant N content, the estimated N extraction by plants, the mineralized N in the fields, and the calculated N fertilizer. These data were used as input parameters to their software system to ultimately determine the correct amount of N fertilizer, or slurry, to be applied to the varying locations within the field.
This article pointed to the accuracy of the application map as the key to the site-specific application of slurry, although they noted that the size of the grid cells within the field for slurry application have to be significantly small to produce accurate results. There also was a time lag noted within the equipment as it attempted to adjust as it entered a geographic region of the field that required a varying amount of slurry.

15N Content Found in Plants Can Be Used as an Indicator of Excess Compost Application

Yun and Ro (2009) conducted an experiment using Chinese cabbage plants to determine whether the amount of 15N within the plant tissues can be used to indicate the overuse of compost in soil. Compost is an important inexpensive alternative to chemical fertilizers, although the overuse of compost can lead to the same environmental impacts that overuse of N fertilizers have. The amount of nutrients in compost varies depending upon the source, therefore the concentrations of N and P need to be determined before application to soils in order to avoid overuse. Four different amounts of compost were used in the experiment and three areas of plant tissue and the soil were analyzed for 15N content. They determined the amount of 15N found in the plants along with the soil nitrate content can be used to tell if the level of compost application was too high. — <!–[if supportFields]> CONTACT _Con-3EF86BDE1 \c \s \l <![endif]–>Maria Harwood<!–[if supportFields]><![endif]–>
Yun, S., Ro, H., 2009. Natural 15N abundance of plant and soil inorganic-N as evidence for over-fertilization with compost. Soil Biology and Biochemistry 41, 1541–1547.

 Yun and Ro used potted Chinese cabbage plants grown for 42 days in soil amended with a compost made of pig manure mixed with sawdust. Four different rates of compost were applied to the soil; 0, 500, 1000, 1500 mg N/kg. The outer, middle, and inner leaves of the Chinese cabbage plants were analyzed for N content to determine whether the source of N found in the plants was from the compost or the indigenous N soil content. This distinction is key to figuring out if 15N can be used as an indicator of the amount of compost used or if it is only showing the N usage from the soil.
Compost application increased the amount of dry mass accumulation of the cabbage with the lowest application rate, but successive increasing amounts of compost produced no increase in dry mass. Although the amount of dry mass did not increase with added compost, the uptake of N by the cabbage plants did increase in proportion to the amount of compost. The increasing compost amounts also produced greater amounts of 15N found in the cabbage for all applications except the lowest. The inner, younger leaves of the cabbage showed a strong correlation of the 15N levels being derived from the compost, therefore the authors determined the 15N levels found in plants can be used as an indicator of the amount of compost being applied to the soil.