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The Competitive Advantage of Crops Over Weeds at Elevated CO2 Concentrations

Paper Reviewed
Kaciene, G., Kiksaityte, A., Januskaitiene, I., Miskelyte, D., Zaltauskaite, J., Sujetoviene, G., Sakalauskiene, S., Miliauskiene, Juozapaitiene, G. and Juknys, R. 2017. Different crop and weed performance under single and combined effects of elevated CO2 and temperature. Crop Science 57: 935-944.

One of the tactics utilized by climate alarmists in their attempt to disparage or downplay the growth-enhancing benefits of atmospheric CO2 enrichment is to suggest that weeds will become ever more aggressive in the future as the air's CO2 content continues to climb, making them greater threats to the wellbeing of both natural ecosystems and farming operations. But is this contention correct?

Hoping to provide some knowledge in this regard, Kaciene et al. (2017) set out to investigate this subject, noting that "few studies have dealt with single and combined effects of elevated CO2 and temperature on both crop and weed species." Therefore, it became their purpose to examine "whether elevated CO2 and air temperature, projected by the end of this century, differentially affect crop and weed species."

To answer their research question, the team of ten Lithuanian scientists grew two crop (pea, Pisum sativum; barley, Hordeum vulgare) and one weed (wild mustard, Sinapis arvensis) species in controlled environment chamber conditions under ambient (400 ppm) or elevated (700 ppm or 1400 ppm) CO2 at either ambient (21/14°C) or elevated (25/18°C) day/night temperatures, while evaluating a number of growth related parameters.

In describing their findings, Kaciene et al. report that elevated CO2 had a positive effect on photosynthesis and biomass for both pea and barley plants, whereas "low and statistically insignificant growth stimulation was noticed for wild mustard seedlings." Both crop species also experienced large gains in plant water use efficiency (70-140%), whereas "a several-fold lower effect on water use efficiency was detected in wild mustard." With respect to temperature, the authors found that "in most cases, elevated 4°C above ambient air temperature alone did not have a significant effect on plant growth and physiological and biochemical parameters except increased transpiration rate and reduced water use efficiency in all plant species."

Commenting on these and other of their findings, Kaciene et al. conclude that "crops, especially legumes, take a considerably higher advantage from elevated [CO2] compared with weed species, as can be seen from significantly greater stimulation of biomass production and photosynthetic rate, a lower degree of photosynthetic downregulation, and higher water use efficiency," adding that "apart from this, [the] combined treatment with elevated (700 ppm) CO2 concentration and air temperature elevated 4°C above ambient leads to even higher stimulation of plant growth and photosynthetic performance." And thus it is that "these findings suggest that the investigated crop species, especially pea plants, have high advantage than weed under rising [CO2], and this benefit is detected to be even higher under elevated [CO2] and temperature."

Posted 31 July 2017