Plant responses to atmospheric CO2 enrichment with emphasis on roots and the rhizosphere.

Plant root response to atmospheric C02 enrichment can be great. Results from this controlled environment investigation demonstrate substantial effects on root system architecture, micromorphology and physiology. The most pronounced effects were an increase in root length (110%) and root dry weight (143%). Root diameter, stele diameter, cortex width, roovshoot and root weight ratios all increased; root numbers did not increase. The long-term implications for belowground processes could be enormous.

Response of plant roots to elevated atmospheric carbon dioxide

Carbon dioxide is rising in the global atmosphere, and this increase can be expected to continue into the foreseeable future. This compound is an essential input to plant life. Crop function is affected across all scales from biochemical to agro-ecosystem. An array of methods (leaf cuvettes, field chambers, free-air release systems) are available for experimental studies of CO2 effects. Carbon dioxide enrichment of the air in which crops grow usually stimulates their growth and yield. Plant structure and physiology are markedly altered. Interactions between CO2 and environmental factors that influence plants are known to occur. Implications for crop growth and yield are enormous. Strategies designed to assure future global food security must include a consideration of crop responses to elevated atmospheric CO2. Future research should include these targets: search for new insights, development of new techniques, construction of better simulation models, investigation of belowground processes, study of interactions, and the elimination of major discrepancies in the scientific knowledge base.

Crop responses to CO2 enrichment

Published in Agron. J. 105:657–669 (2013) doi:10.2134/agronj2013.0018 Copyright © 2013 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. G climate change has emerged as an important environmental challenge due to its potential impact on biological systems on Earth. Atmospheric concentrations of CO2 have steadily increased from approximately 315 μmol mol–1 in 1959 to a current atmospheric concentration of approximately 385 μmol mol–1 which converts to an average annual increase rate of nearly 2 μmol mol–1 (Keeling and Whorf, 2005). At this rate of increase, concentrations are projected to reach levels between 500 and 1000 μmol mol–1 by 2100 (IPCC, 2007). Carbon dioxide is not only a major greenhouse gas, but essential to plant growth (Kramer, 1981; Dahlman et al., 1985; Warrick, 1988; Kimball, 2011). The flow of C from photosynthesizing tissues of higher plants, through the roots and into the soil is one of the key processes in terrestrial ecosystems. Increases in atmospheric CO2 concentration will have direct and indirect effects on crop plants and increases in CO2 will generally increase plant productivity and water-use efficiency (Drake and Gonzalez-Meier, 1997; IPCC, 2007). The long-term response to CO2 remains uncertain and will depend on environmental constraints. Yields of most agricultural crops will increase under elevated CO2 with productivity increases in the range 15 to 41% for C3 crops and 5 to 10% for C4 crops (Cure, 1985; Kimball, 1983; IPCC, 2007; LotzeCampen and Schellnhuber, 2009). Analyses of plant responses to elevated atmospheric CO2 have focused largely on aboveground processes; however, understanding the effects on photosynthesis are insufficient to answer questions about overall plant response to a changing atmosphere. A whole-plant perspective is required to understand the critical feedbacks and adjustments occurring within a plant and between plants and soil. An overlooked and under studied aspect of plant response to rising CO2 is on belowground processes. The vital role of roots as an interface between the lithosphere and biosphere is necessary to understand plant response to elevated CO2. Despite the important role roots play, they have been an understudied component of agricultural research since they exist underground. Root health in crop plants will play a major role in providing sustainable highly productive crops with the ability to cope with climate changes; however, the effect of increasing CO2 on root growth and development is poorly understood. Climate change is expected to increase the incidence of extreme weather events, such as drought, heat waves, and heavy precipitation and floods, causing crop production to become more variable (IPCC, 2001, 2007; Hatfield et al., 2011). Under these conditions, many of the environmental factors, for example, water, temperature, light, nutrition, salinity, air pollutants, and competition have significant interactions with CO2 concentration on root responses for numerous species as summarized by Rogers et al. (1994). Understanding of dynamics of crop roots is important from the point of view of management of available resources to increase the productivity of crops and resilience of crops to climate stress. AbstRAct

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Dynamics of Plant Root Growth under Increased Atmospheric Carbon Dioxide

Climate change and its impact on agricultural production is being debated in economic literature in context of different regions. The geographical location of Pakistan is assumed to be vulnerable to climate change. Concentration of greenhouse gases (GHGs) like carbon dioxide, methane and nitrous oxide through human activities has altered the composition of climate. These gases have increased temperature on earth by trapping sun light. This higher temperature in tropical regions may negatively affect the growth process and productivity of wheat. This study aims to look at the impact of climate change on wheat production in Pakistan. The study uses Autoregressive Distributed Lag (ARDL) model to evaluate the impact of global climate change on the production of wheat in Pakistan. The study considers annual data from 1960 to 2009. On the basis of this historical data the study tries to capture the impact of climate change on wheat production up to now. The results of estimation reveal that global climate change doesn’t influence the wheat production in Pakistan. However, on the basis of the results some appropriate adaptative measures are proposed to confront any adverse shock to wheat production in Pakistan.

Climate Change and Wheat Production in Pakistan: An Autoregressive Distributed Lag Approach

INCREASING CONCENTRATIONS of atmospheric carbon dioxide (C02) and other radiatively active 'greenhouse' gases may lead to large changes in the global climate, possibly with profound effects on global ecosystems. If the results of climate models are correct, the world will, in the matter of a century, become warmer than at any time during the last 100000 years or more. Recently, the International Meteorological Institute (IMI) in Stockholm, with joint support from the World Meteorological Organization (WMO), the United Nations Environment Programme (UNEP) and the International Council of Scientific Unions (ICSU) carried out a scientific review (Bolin et al., 1986) of the 'greenhouse effect' and its environmental consequences. The purpose of this article is to summarize the results of that review with respect to the possible effects on agriculture. Agriculture can be affected in two broad (but not necessarily mutually exclusive) ways: by the direct effects of C02 on plants, and by the effects of changes in climate. For each, what information do we have for impact assessment? What do the results of existing studies tell us? Let us examine the direct effects of C02 first.

R. A. Warrick

Papers

Carbon dioxide, climatic change and agriculture