Glyphosate Resistance of C3 and C4 Weeds under Rising Atmospheric CO2

The present paper reviews current knowledge on how changes of plant metabolism under elevated CO 2 concentrations (e[CO 2 ]) can affect the development of the glyphosate resistance of C 3 and C 4 weeds. Among the chemical herbicides, glyphosate, which is a non-selective and post-emergence herbicide, is currently the most widely used herbicide in global agriculture. As a consequence, glyphosate resistant weeds, particularly in major field crops, are a widespread problem and are becoming a significant challenge to future global food production. Of particular interest here it is known that the biochemical processes involved in photosynthetic pathways of C 3 and C 4 plants are different, which may have relevance to their competitive development under changing environmental conditions. It has already been shown that plant anatomical, morphological, and physiological changes under e[CO 2 ] can be different, based on (i) the plant’s functional group, (ii) the available soil nutrients, and (iii) the governing water status. In this respect, C 3 species are likely to have a major developmental advantage under a CO 2 rich atmosphere, by being able to capitalize on the overall stimulatory effect of e[CO 2 ]. For example, many tropical weed grass species fix CO 2 from the atmosphere via the C 4 photosynthetic pathway, which is a complex anatomical and biochemical variant of the C 3 pathway. Thus, based on our current knowledge of CO 2 fixing, it would appear obvious that the development of a glyphosate-resistant mechanism would be easier under an e[CO 2 ] in C 3 weeds which have a simpler photosynthetic pathway, than for C 4 weeds. However, notwithstanding this logical argument, a better understanding of the biochemical, genetic, and molecular measures by which plants develop glyphosate resistance and how e[CO 2 ] affects these measures will be important before attempting to innovate sustainable technology to manage the glyphosate-resistant evolution of weeds under e[CO 2 ]. Such information will be of essential in managing weed control by herbicide use, and to thus ensure an increase in global food production in the event of increased atmospheric [CO 2 ] levels.