The challenge of modern agriculture lies in sustaining high production rates while managing biotic and environmental pressures that reduce yield. In nature, environmental pressures are brought about by climatic changes, and in controlled environment production systems, they result from subsystem failures or poor control of key environmental parameters (Monje et al., 2003). Generally, high temperature stress reduces crop yield because it negatively affects several plant physiological processes, including photosynthesis, respiration, growth, development (phenology and morphology), and partitioning (White and Reynolds, 2003). However, quantifying crop responses to temperature has been difficult because different plant organs typically experience different thermal regimes (Monteith and Unsworth, 1990), the observed acclimatization responses vary according to the conditions a plant has been growing in, and the various physiological processes responding to temperature changes can interact to affect overall growth and yield (White and Reynolds, 2003).
It is important to measure temperature in a physiologically meaningful manner when studying plant development. In wheat, air temperature is a primary factor determining the phyllochron (e.g., the rate of leaf appearance) (McMaster et al., 2003), but soil temperature near the crown may better reflect shoot apex temperature than air temperature because the shoot apex of annual grass crops is located in the crown until the developmental stage of jointing (McMaster and Wilhelm, 2003). However, heating the shoot apex at crown depth of spring wheat by +3 °C does not speed up phenologic development or leaf appearance rates probably because leaf growth may occur above the soil surface (McMaster et al., 2003).
Several studies have examined root zone temperature (RZT) effects in lettuce (Lactuca sativa L.) (He et al., 2001), wheat (Guedira and Paulsen, 2002; Kirkham and Ahring, 1978), and creeping bentgrass (Agrostis stolonifera L.) (Rachmilevitch et al., 2006; Xu and Huang, 2000). Root zone temperature can alter shoot growth responses by influencing the temperature of the shoot apical meristem (McMaster et al., 2003), modifying hormonal balance (Tachibana et al., 1997; Wang et al., 2004), and altering water and nutrient uptake (Bowen, 1991). Although the most important factors responsible for reduced yield of wheat at high temperature are the reduction in the length of the growth cycle and the duration of grain fill (White and Reynolds, 2003), RZT has been reported to influence the response of plant growth rates to high air temperature.
Increasing RZT from 12 to 25 °C generally improves root functions related to supplying water and nutrients to shoots, leading to decreased root-to-shoot ratios, improved gas exchange, and increased chlorophyll content (Awal et al., 2003). Increasing RZT from 25 to 30 °C increases root-to-shoot ratios (Awal et al., 2003) and can increase photosynthetic rates (Ziska, 1998). However, further increases in RZT can lead to growth inhibition by reducing nutrient uptake and chlorophyll content (Du and Tachibana, 1994), disturbing plant water relations and reducing g S (Behboudian et al., 1994) or altering plant chemical signaling (Dodd et al., 2000; Tachibana et al., 1997; Wang et al., 2004).
Elevated RZT in the heat shock range (≈35 °C) appears to be more critical than air temperature in controlling plant growth. Earlier leaf senescence was observed in wheat exposed to 35 °C RZT and a 16-h photoperiod (Kuroyanagi and Paulsen, 1988). Tomato (Solanum lycopersicum L.) plants growing at 36 °C RZT for 20 d exhibited decreased shoot growth and P uptake compared with plants growing at 25 °C RZT (Klock et al., 1997). The probable causes for growth reductions at high RZT (37 °C) are increased respiratory costs for maintenance and ion uptake (Rachmilevitch et al., 2006).
Kirkham and Ahring (1978) studied the effect of RZT on leaf temperature and internal water status of wheat at a constant air temperature (25 °C) and ambient CO2 concentration (380 μmol·mol−1). Plant height and g S were greatest when air and root temperatures were similar, but plant height, water potential, and g S decreased when RZT exceeded air temperature. Guedira and Paulsen (2002) reported that applying differential shoot and root temperatures to maturing wheat plants affected kernel mass. Increasing shoot temperature to 30 °C and keeping the roots at 15 °C decreased kernel mass by 40%, whereas holding the shoots at 15 °C and increasing the roots to 30 °C decreased kernel mass by 57% compared with maintaining the whole plant at 15 °C. The greater reduction in kernel mass from higher root temperature than from high shoot temperature suggests that roots may regulate partitioning during grain filling. In another RZT study conducted with vegetative winter wheat grown in elevated CO2, the developmental stage of the crop determined the severity of damage experienced by the plant. Increases in RZT and N supply reduced allocation to roots and leaves and increased allocation to the stem, although an effect on carbon assimilation rate was not observed (Gavito et al., 2001). Furthermore, RZT affected mainly nutrient uptake and plant size during vegetative growth and its effects on root and shoot phenology became evident toward the end of vegetative growth.
This study was conducted in preparation for the Photosynthesis Experiment Subsystem Testing and Operation (PESTO) spaceflight experiment. PESTO examined the effects of microgravity on photosynthetic and growth rates using 21-d-old crop stands of ‘USU-Apogee’ wheat (Monje et al., 2005; Stutte et al., 2005). ‘USU-Apogee’ was grown aboard the International Space Station (ISS) in the Biomass Production System [BPS (Orbitec, Madison, Wis.)]. The BPS consists of four automated plant growth chambers providing active control of air temperature, relative humidity, CO2 concentration, root zone moisture, and light level during spaceflight. Like in most spaceflight plant growth chambers, RZT was not controlled because of power limitations to the BPS imposed by the ISS (Morrow and Crabb, 2000). Although gravity does not change RZT directly, the lack of gravity in space reduces buoyancy-driven heat transfer, and even well-ventilated hardware (e.g., root modules) is expected to be hotter than on earth (Monje et al., 2003). Therefore, the effects of elevated RZT on the vegetative growth of ‘USU-Apogee’ were studied to determine if increased RZT might confound growth responses observed in PESTO. The objectives were to determine the RZTs at which plant growth and carbon partitioning are affected as well as determine which physiological and morphologic responses might occur when these RZTs are exceeded.
Araus, J.L. , Slafer, G.A. , Reynolds, M.P. & Royo, C. 2002 Plant breeding and drought in C3 cereals: What should we breed for? Ann. Bot. (Lond.) 89 925 940
Awal, M.A. , Ikeda, T. & Itoh, R. 2003 The effect of soil temperature on source-sink economy in peanut (Arachis hypogaea) Environ. Exp. Bot. 50 41 50
Behboudian, M.H. , Graves, W.R. , Walsh, C.S. & Korcak, R.F. 1994 Water relations, mineral nutrition, growth and 13C discrimination in two apple cultivars under daily episodes of high root-medium temperature Plant Soil 162 125 133
Bowen, G.D. 1991 Soil temperature, root growth, and plant function 309 330 Waisel Y. , Eshel A. & Kafkafi U. Plant roots—The hidden half Marcel Dekker N.Y
Bugbee, B. & Koerner, G. 1997 Yield comparisons and unique characteristics of the dwarf wheat cultivar ‘USU-Apogee’ Adv. Space Res. 20 1891 1894
Dodd, I.C. , He, J. , Turnbull, C.G.N. , Lee, S.K. & Critchley, C. 2000 The influence of supra-optimal root-zone temperatures on growth and stomatal conductance in Capsicum annuum L J. Expt. Bot. 51 239 248
Du, Y.C. & Tachibana, S. 1994 Photosynthesis, photosynthate translocation and metabolism in cucumber roots held at supraoptimal temperature J. Jpn. Soc. Hort. Sci. 63 401 408
Gavito, M.E. , Curtis, P.S. , Mikelsen, T.N. & Jakobsen, I. 2001 Interactive effects of soil temperature, atmospheric CO2 and soil N on root development, biomass and nutrient uptake of winter wheat during vegetative growth J. Expt. Bot. 52 1913 1923
- Search Google Scholar
- Export Citation
Gavito, M.E. Curtis, P.S. Mikelsen, T.N. Jakobsen, I. 2001 Interactive effects of soil temperature, atmospheric CO2 and soil N on root development, biomass and nutrient uptake of winter wheat during vegetative growthJ. Expt. Bot. 52 1913 1923 10.1093/jexbot/52.362.1913
Guedira, M. & Paulsen, G.M. 2002 Accumulation of starch in wheat grain under different shoot/root temperatures during maturation Funct. Plant Biol. 29 495 503
He, J. , Lee, S.K. & Dodd, I.C. 2001 Limitations to photosynthesis of lettuce grown under tropical conditions: Alleviation by root-zone cooling J. Expt. Bot. 52 1323 1330
Huang, B. & Gao, H. 2000 Growth and carbohydrate metabolism of creeping bentgrass cultivars in response to increasing temperatures Crop Sci. 40 1115 1120
Kirkham, M.B. & Ahring, R.M. 1978 Leaf temperature and internal water status of wheat grown at different root temperatures Agron. J. 70 657 662
Klock, K.A. , Taber, H.G. & Graves, W.R. 1997 Root respiration and phosphorous nutrition of tomato plants grown at a 36°C root-zone temperature J. Amer. Soc. Hort. Sci. 122 175 178
Kuroyanagi, T. & Paulsen, G.M. 1988 Mediation of high-temperature injury by roots and shoots during reproductive growth of wheat Plant Cell Environ. 11 517 523
Liu, X. & Huang, B. 2005 Root physiological factors involved in cool-season grass response to high soil temperature Environ. Exp. Bot. 53 233 245
Liu, X. , Huang, B. & Banowetz, G. 2002 Cytokinin effects in creeping bentgrass responses to heat stress. I. Shoot and root growth Crop Sci. 42 457 465
Long, S.P. & Bernacchi, C.J. 2003 Gas exchange measurements, What can you tell us about the underlying limitations to photosynthesis? Procedures and sources of error J. Expt. Bot. 54 2393 2401
McMaster, G.S. & Wilhelm, W.W. 2003 Phenological responses of wheat and barley to water and temperature: Improving simulation models J. Agr. Sci. 141 129 147
McMaster, G.S. , Wilhelm, W.W. & Frank, A.B. 2005 Developmental sequences for simulating crop phenology for water-limiting conditions Austral. J. Agr. Res. 56 1277 1288
McMaster, G.S. , Wilhelm, W.W. , Palic, D.B. , Porter, J.R. & Jamieson, P.D. 2003 Spring leaf appearance and temperature: Extending the paradigm? Ann. Bot. (Lond.) 91 697 705
Monje, O. & Bugbee, B. 1998 Adaptation to high CO2 concentration in an optimal environment: Radiation capture, canopy quantum yield and carbon use efficiency Plant Cell Environ. 21 315 324
Monje, O. , Stutte, G.W. & Chapman, D. 2005 Microgravity does not alter plant stand gas exchange of wheat at moderate light levels and saturating CO2 concentration Planta 222 336 345
Monje, O. , Stutte, G.W. , Goins, G.D. , Porterfield, D.M. & Bingham, G.E. 2003 Farming in Space: Environmental and biophysical concerns Adv. Space Res. 31 151 167
Monje, O. , Stutte, G.W. , Wang, H.T. & Kelly, C.J. 2001 NDS water pressures affect growth rate by changing leaf area, not single leaf photosynthesis Soc. Automotive Eng. Tech. Paper 2001-01-2277
Rachmilevitch, S. , Lambers, H. & Huang, B. 2006 Root respiratory characteristics associated with plant adaptation to high soil temperature for geothermal and turf-type Agrostis species J. Expt. Bot. 57 623 631
Richards, R.A. 1988 A tiller inhibitor gene in wheat and its effect on plant growth Austral. J. Agr. Res. 39 749 757
Stutte, G.W. , Monje, O. , Goins, G.D. & Chapman, D.K. 2000 Measurement of gas exchange characteristics of developing wheat in the Biomass Production Chamber Soc. Automotive Eng. Tech. Paper 2000-01-2292
Stutte, G.W. , Monje, O. , Goins, G.D. & Tripathy, B.C. 2005 Microgravity effects on thylakoid, single leaf, and whole canopy photosynthesis of dwarf wheat Planta 223 46 56
Tachibana, S. , Du, Y.C. , Wang, Y.H. & Kitamura, F. 1997 Implication of endogenous cytokinins in the growth inhibition of cucumber plants by supraoptimal root-zone temperature J. Jpn. Soc. Hort. Sci. 66 549 555
Wang, Z. , Pote, J. & Huang, B. 2003 Responses of cytokinins, antioxidant enzymes, and lipid peroxidation in shoots of creeping bentgrass to high root-zone temperatures J. Amer. Soc. Hort. Sci. 128 648 655
Wang, Z. , Xu, Q. & Huang, B. 2004 Endogenous cytokinin levels and growth responses to extended photoperiods for creeping bentgrass under heat stress Crop Sci. 44 209 213
White, J.W. & Reynolds, M.P. 2003 A physiological perspective on modeling temperature response in wheat and maize crops 8 17 White J.W. Modeling temperature response in wheat and maize: Proc. of a workshop Intl. Maize and Wheat Improvement Center El Batan, Mexico 23–25 Apr. 2001 Natural Resources Group Geographic Information Systems Series 03-01.
- Search Google Scholar
- Export Citation
White, J.W. Reynolds, M.P. 2003 A physiological perspective on modeling temperature response in wheat and maize crops 8 17 White J.W. Intl. Maize and Wheat Improvement Center El Batan, Mexico 23–25 Apr. 2001 Natural Resources Group Geographic Information Systems Series 03-01.
Xu, Q. & Huang, B. 2000 Effects of differential air and soil temperatures on carbohydrate metabolism in creeping bentgrass Crop Sci. 40 1368 1374
Ziska, L.H. 1998 The influence of root zone temperature on photosynthetic acclimation to elevated carbon dioxide concentrations Ann. Bot. (Lond.) 81 717 721