Response of Crops to Environmental Change Conditions

Abstract

Numbers of people and their fossil fuel consumption are increasing, also land use is changing, contributing to increasing atmospheric carbon dioxide (CO2) concentrations and probably increasing global temperatures: by 2100 these may reach 700μmol/mol and 4°C respectively. The consequences for growth and production of the main foods - the cereals wheat and rice (with C3 photosynthesis) and maize, sorghum and millet (with C4 photosynthesis)-and the mainly C3 root and pulse crops will be considerable for food production on local and global scales. To assess the effects on agricultural production, experiments which analyse the effects of CO2 concentration and air temperature and their interaction, and the effects of altered rainfall on crops, are assessed. Studies at IACR-Rothamsted o wheat and sugar beet are specifically discussed. Plants with C3 photosynthesis will respond positively to elevated CO2; C4 crops less so. Wheat and rice respond with ca. 25% increase in yield with CO2 doubling, equivalent to an increase of ca. +2.5% per decade over the next century. Root crops respond with larger increases. Adequate water and nutrition are essential for increased production to be expressed. Increasing temperatures will probably decrease production of most crops except where they are currently limited by cool conditions. Wheat and rice yields decrease about 25% for a 4°C increase and sugar beet about 8% (-2.5 and -1% per decade respectively). Production will increase most with good nutrition, water, etc, and least in poor growth conditions. Effects of changing environment on photosynthetic acclimation and production are considered. Acclimation is related to assimilate production and the “sink strength” of growing organs for assimilates, and to the feedback mechanisms between carbohydrate accumulation and development of the photosynthetic system. Complex source-sink and plant-environment interactions may explain variability of acclimation in crops. Use of experimental results to assess food production over large areas suggests a beneficial effect of elevated CO2 where water and nutrients are adequate but as in much of world agriculture this is not so, gains will be modest and possibly offset by negative effects of elevated CO2 under resource limitation. The needs for plant breeding and genetic manipulation in order for staple foods to a more efficiently produced under global environmental change conditions are considered.