Spatial and temporal deployment of crop roots in CO₂‐enriched environments

Abstract

 Growth of crops in CO# -enriched atmospheres typically results in significant changes in root growth and development. Increased root carbohydrates stimulate root growth either directly (functioning as substrates) or indirectly (functioning as signal molecules) by enhancing cell division or cell expansion, or both. Although highly variable, the literature suggests that, generally, initiation and stimulation of lateral roots is favored over the elongation of primary roots, leading to more highly branched, shallower root systems. Such architectural shifts can render root systems less efficient, perhaps contributing to the lower specific root activities often reported. Allocation of carbon (C) to roots fluctuates through the life of the plant ; root functional and growth responses should therefore not be viewed as static. In annual crops, C allocation to belowground processes changes as vegetative growth switches to reproduction and maturation. Reductions in C allocation to roots over time might cause temporal shifts in root deployment, perhaps affecting root demography. However, significant changes in root turnover (defined here as root flux or mortality relative to total root pool size) as a result of decreased root longevities in crop plants are unlikely. Consideration of changing C allocation to roots, a more thorough understanding of the mechanistic controls on root longevity, and a better characterization of the rooting habits (life histories) of different crop species will further our understanding of how increasing atmospheric [CO # ] will affect root demography. This knowledge will lead the way toward a more thorough understanding of the linkage of atmosphere with belowground plant function and also that of plant function with soil biology and structure. Ultimately, successful modeling of global C and nitrogen (N) cycles will require empirical data concerning spatial and temporal deployment of roots for a range of crop species grown under different agricultural management systems.

Plant water relations at elevated CO2– implications for water‐limited environments

“…Fine roots at the soil surface may be beneficial in capturing water after a dry soil is rewetted (Kosola & Eissenstat 1994). Several experiments suggest that crop plants in a higher CO 2 atmosphere will have larger root systems that are more highly branched, especially at shallow depths, and this should increase the capacity for resource acquisition, but at lower efficiency (Pritchard & Rogers 2000). CO 2 enrichment of a grassland community led to an upward shift in root length density with a greater proportion of roots in the top 6 cm soil layer (Arnone et al .…”

“…1999;Pritchard & Rogers 2000). In general, elevated [CO 2 ] increases plant biomass, root mass and total leaf area (Rogers, Runion & Krupa 1994;Curtis & Wang 1998) and alters leaf net photosynthetic rates, stomatal conductance and water-use efficiency (WUE) (Gunderson & Wullschleger 1994;Saxe, Ellsworth & Heath 1998).…”

Root dynamics and global change: seeking an ecosystem perspective

“…In an annual crop system, the important research questions are more likely to revolve around root deployment and resource capture rather than equilibrium responses and C flux (Fitter et al, 1991). Root turnover is likely to be impacted by CO # differently in annual versus perennial plants (Pritchard & Rogers, 2000).…”

“…In discussing the responses of crop roots to elevated CO # , Pritchard & Rogers (2000) emphasize the importance of cell expansion and cell division and suggest that a key to understanding how root growth will change in a high-CO # environment is to understand how carbohydrates, especially sucrose, functions both as a substrate for growth and as a regulatory molecule. From this perspective, they review the literature and conclude that roots in a high CO # environment will be larger and more highly branched, but less efficient in nutrient and water uptake (also see Berntson & Bazzaz, 1996 ;Rogers et al, 1999).…”

Intra-specific variation in response of Neem (Azadirachta indica A. Juss) to elevated CO2 levels and biochemical characterization of differently responding plants

“…With regard to increased root length under elevated CO 2 environment, it is reported that the responses of roots to CO 2 are dependent on experimental conditions (Ceulemans & Mousseau 1994). When the plants exposed to increased CO 2 , root have observed to become more numerous, longer, thicker and faster growing in crops (Chandhuri et al 1990) with increased root length in many plant species (Norby 1994, Pritchard & Rogers 2000, Bernecchi et al 2000. Lengths and volumes of tap root and fine roots were higher for CO 2 enhanced cotton plants (Rogers et al 1993).…”