Paper No. 3 



EFFECT OF TEMPERATURE ON MORPHOGENSIS l 



By Horton M. Laude 



Abstract 



The influence of heat or cold on the form, func- 

 tion, and life cycle of range plants is reviewed. 

 Particular attention is directed to those stress 

 conditions of temperature which evoke impair- 

 ment of function or visible injury. Investigations 

 on nonrange species, especially the cereal grains, 

 are included when the findings are deemed ap- 

 plicable to range vegetation. Several topics war- 

 ranting further study with relation to range spe- 

 cies are identified. 



Additional key words: Temperature stress, tem- 

 perature injury, critical stages 



Introduction 



Plant scientists recognize the importance of 

 temperature in regulating the rate of physiologi- 

 cal processes and in influencing growth and de- 

 velopment. The application of temperature re- 

 sponse specifically to the management of range 

 resources has received less attention. The influ- 

 ence of temperature on the form, function, and 

 growth of range species deserves consideration, 

 both to identify the more important responses 

 and to appraise their effect on the vegetation and 

 its use. 



Some limitations, however, deserve mention at 

 the outset. A number of responses are best illus- 

 trated or have been studied on species other than 

 those of rangelands. I have included these when 

 the findings might be applicable to range. Fur- 

 thermore, it must be remembered that tempera- 

 ture response is conditioned by the level of other 

 factors of the environment. For example, temper- 

 ature and moisture condition are closely associ- 



1 Contribution from the Department of Agronomy and 

 Range Science, University of California, Davis. 



2 Professor of Agronomy, University of California, 

 Davis, 95616. 



ated, as are radiant energy and temperature, and 

 others. I will, nevertheless, attempt to view tem- 

 perature in situations in which it is the primary 

 variable. Some difficulty will be encountered in 

 stating the precise temperature of different tis- 

 sues or organs of a plant, since authors in re- 

 porting experimentation often give only air tem- 

 peratures surrounding the plant. And lastly, what 

 levels of temperature deserve the greatest atten- 

 tion? An optimal temperature exists for a par- 

 ticular function or aspect of plant growth, but 

 environments continually fluctuate in nature and 

 plants experience temperatures above and below 

 this optimum for the greater part of their life 

 cycle. Near optimal temperatures do influence 

 growth, but often produce little visible indica- 

 tion of their effect. Temperatures further re- 

 moved from the optimal evoke more drastic re- 

 sponses, and visible symptoms become clearly ap- 

 parent. There is merit, therefore, in considering 

 those temperatures capable of producing definite 

 stress and visible symptoms, and I have empha- 

 sized them in my selections from the literature. 

 Some justification for this approach rests also on 

 the fact that rangelands occupy sites subject to 

 perhaps the most rigorous environment of any of 

 man's major agricultural areas. 



Temperature And Plant Form And 

 Function 



Although we recognize that cellular differences 

 underlie changes in tissues and organs, most 

 studies report responses at the tissue or organ 

 level. Went and Sheps (38) enumerate examples 

 of morphogenetic change induced by temperature. 

 The responses they noted in different species are 

 diverse and include number and size of floral 

 parts, flower color, leaf shape, seed visability, and 

 germination. 



Most studies have been conducted under some 



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