It was noted in previous posts that for crops with C3 photosynthetic pathway the current levels of atmospheric carbon dioxide are limiting to plant growth. Crops are currently starved of CO2 in a similar way to being starved of water, nitrogen, phosphorus, light etc. Current atmospheric levels of CO2 can thus be regarded as a plant stress, which weakens them and makes them inefficient. At higher levels of CO2 this stress is reduced, and the plant copes better with all other types of stress, including heat and cold, atmospheric pollution, root pathogens, as well as shortages of water, minerals etc.
Sylvan Wittwer (Professor emeritus at Michigan State University, who directed the Michigan Agricultural Experiment Station for 20 years and chaired the Board on Agriculture of the National Research Council) has remarked:
There has been and still remains, a great reluctance on the part of many climatologists and ecologists, and especially environmentalists, to accept the concept that the rising level of atmospheric CO2 could be more beneficial than harmful for plant growth, food production, and the overall biosphere…Yet the scientific evidence is overwhelming.
Summary data from 279 published studies is shown below in which plants of all types were grown under paired stress (red) and unstressed (blue) conditions. For resource-limited plants the benefits of increased CO2 are astounding.
Wittwer points out that of the hundreds of scientific reports documenting the benefits, Al Gore carefully selected five reports and a personal communication to emphasize possible negative aspects to enhanced CO2 on plants. Gore knew what he was doing, of course – he either deliberately rejected the facts, or gave instructions to researchers for his book only to cherry pick papers that support his alarmist agenda. Again we see him as a lying propagandist.
In Physiological plant ecology: ecophysiology and stress physiology of funcional groups (Springer, 2003), Walter Larcher writes:
According to over 3000 scientific publications on the biology of CO2 effects, a broad spectrum of growth responses to CO2 enrichment exists. Since elevated CO2 often reduces the plants’ demands for other resources, CO2 effects on growth do not simply follow Liebig’s law of the minimum. Plants exposed to elevated CO2 need less enzymes (and thus lower quantities of leaf proteins and nitrogen), lose less water (can cope with less soil moisture and often operate at smaller stomata openings) and need less light (because of a shift in the light compensation point for photosynthesis) to reach the equivalent, or even higher photosynthetic rates than plants growing under control conditions with “normal” CO2 concentrations.
We will show from the literature the tremendous benefits of enhanced atmospheric CO2. The benefits are much more marked in crops that are subject to resource limitation. Under ideal conditions, where there is no shortage of water, light, nutrients, trace elements etc, the benefit of doubling atmospheric CO2 may be 40%. However, where plants are resource limited a doubling of CO2 can enhance growth of crops by over 100% in some cases. This is particularly important in regions of the world where the soil is poor for many reasons, since increasing atmospheric CO2 will enable crops to be grown efficiently where they currently cannot be grown without first improving the soil and irrigation. In this post we will briefly mention minerals and other essential nutrients (nitrogen, phosphorus, iron etc).
For example, iron deficiency is severely limiting to crop growth in calcareous soils, which represent 30% of global land area. Increased atmospheric CO2 enables plants to extract higher levels of iron from the soil. Jin et al in Elevated Carbon Dioxide Improves Plant Iron Nutrition through Enhancing the Iron-Deficiency-Induced responses under Iron-Limited Conditions in Tomato (Plant Physiology, May 2009) demonstrated
Plant growth was increased by elevated CO2 in both Fe-sufficient and Fe-limited media. Shoot fresh weight was increased by 22% and 44%, respectively, and root fresh weight by 43% and 97%, respectively, compared with plants grown in ambient CO2…
Improved nutrient and water uptake has in some cases been traced to greater root mycorrhization (a symbiotic fungal extension of roots). Mycorrhizae also improve plant health by protecting roots from pathogenic microorganisms.
In Effect of Carbon Dioxide Concentration on Growth and Dry Matter Production of Crop Plants (Japan. Jour. Crop Sci, 1978) Imai and Murata showed that after 10 days of treatment with nitrogen at 350ppm and 1000ppm CO2 the dry weight (DW) of rice plants was as follows:
350ppm CO2, 30 mg nitrogen per plant DW = 835 mg per plant
350ppm CO2, 120 mg nitrogen per plant DW = 1,081 mg per plant
1000ppm CO2, 30 mg nitrogen per plant DW = 1,199 mg per plant
1000ppm CO2, 120 mg nitrogen per plant DW = 1,862 mg per plant
This demonstrates that at higher levels of atmospheric CO2, food crops have considerably lower requirements for fixed nitrogen for the same growth; alternatively, for the same nitrogen treatment they achieve considerably enhanced growth.
Higher levels of atmospheric CO2 lead to greater biological nitrogen fixation from the atmosphere, so less is required to be added as fertilizer. This is especially important in legumes, which are also able to improve their uptake and usage of phosphorus with increased CO2. Legume /bacterial symbiosis leading to nitrogen fixation is significantly increased at elevated CO2 levels (Reddy et al, 1989; Reardon et al, 1990). Philips et al (1976) demonstrated increased nitrogen fixation in peas, and Sherwood (1978) found the same in clover. A classic study by Hardy and Havelka (1975) showed that a tripling of atmospheric CO2 results in a six-fold increase in biological nitrogen fixation (from 75 to 425 kg per hectare) by rhizobial bacteria in nodules attached to the roots of soybeans.
Increasing atmospheric CO2 is an unmixed blessing – it will bring currently unproductive land into use and bring greater yield from existing land without additional fertilizer use. This is a wonderful benefit in being able to feed an increasing world population. These effects can be subjected to routine experiment and observation, can be demonstrated and reproduced, and so are sound science, unlike the specious pseudo-science underpinning the supposed effects of CO2 on climate.