Annals of Botany 37: 553-563, 1973
© 1973 Annals of Botany Company
RESEARCH-ARTICLE |
The Influences of Seasonal Changes in Solar Radiation and Air Temperature on the Growth in the Early Vegetative Phase of Zea mays
Department of Agricultural Science, University of Oxford
1 Research Station, Canadian Department of Agriculture Ottawa, Canada
2 Department of Forestry, University of Oxford
Received: 21 August 1972
At weekly intervals from May to September over 2 years the growth of separate batches of Zea mays (Swiss hybrid Orla 266) was recorded for individual plants in pot experiments, together with the corresponding weekly means of solar radiation and the mean, maximum, and minimum diurnal air temperatures. To reduce sampling errors the plants were ranked on the bases of initial grain size and leaf number. To minimize differences in stage of development at the end of 21 days from sowing the size was adjusted in 1965 by switching the pots in and out of a glasshouse: in 1966 the plants were kept for the first 11 days in a controlled environment and then hardened off in the open. Between 21 and 28 days when the second sample was taken half the plants were subjected to light shade (0.65–0.70 daylight).
Multiple regression analysis showed that the relative growth rate of the whole plant (RGR), the rate of increase in leaf area (RLGR), and the net assimilation rate (NAR) were positively dependent on both radiation and mean air temperature. In 1965 there were negative effects of minimum temperature on RGR and NAR and a positive response of RLGR to leaf number. In 1966 an increase in leaf number led to a higher RGR and LAR but depressed RLGR, while minimal temperature had no significant effects. In all these regressions the variation accounted for was high, ranging from 80 to 89 per cent.
At the second sampling occasion the leaf-area ratio (LARf) was inversely related to radiation, negatively dependent on day temperature, but positively linked with night temperature. The order of the initial LAR exerted no influence. The RGRs of the shoot and the root were positively associated with both radiation and mean temperature. In 1965 there were small negative responses of the shoot to both minimum temperature and leaf number and for the root only leaf number. The variation accounted for was least for LARf (59–62 per cent) and intermediate for RGRa and RGRr (77–89 per cent).
For RGR, NAR, and RLGR the calculated partial regression coefficients for mean temperature in 1965 were larger than those for radiation but in 1966, apart from RLGR, they were equalled by radiation. The discrepancies between years can be ascribed to a higher correlation coefficient between radiation and temperature in 1965 (0.53) as against 1966 (0.33).
The value of multiple regression analysis in the evaluation of the environment by carefully designed field experiments is emphasized in relation to other investigations of light and temperature undertaken under controlled conditions.