PLANT MORPHOGENESIS FOR SCIENTIFIC MANAGEMENT T)F RANGE RESOURCES 



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DRY WEIGHT 



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8 16 32 



LIGHT INTENSITY, K LUX 



Figure 2. — Dry weight accumulation in red clover seed- 

 lings after a 4-week growing period at five illumination 

 periods and three leight levels, average of three 

 cultivars (2). 



ing stems when grown at a low light intensity. 

 Increasing light intensity to 16,000 or 32,000 lux 

 resulted in over 80 percent of the plant flower- 

 ing, but only when grown under the long illum- 

 ination periods. It is interesting to note that es- 

 sentially the same percentage of plants of 'Dol- 

 lard' red clover flowered under the three intensity 

 levels. However, the percentage of flowering 

 plants was considerably lower than noted for 

 the Pennscott plants when grown at the higher 

 intensities. 



The relationship between light intensity and 

 length of the illumination period in the plants 

 of Pennscott red clover appears to be one of 

 providing a maximal growth rate until the plants 

 have developed sufficiently to respond to the 

 flowering stimulus. However, a segment of the 

 Dollard red clover plant population appears to 

 have additional environmental requirements for 

 floral development than simply seedling growth. 



High light levels during the early stages of 

 seedling growth favor development of the root 

 system since root growth is reduced to a greater 

 extent under low light conditions than is growth 

 of aerial tissue. The ratio of aerial tissue to root 

 tissue of 14-day-old alfalfa seedlings decreased 

 from near 4.0 to slightly under 3.0 when grown 



under light intensities of 8,000 and 16,000 lux, 

 respectively (fig. 3). Likewise, Matches and 

 others (13) reported that shading reduced dry 

 weight of alfalfa root tissue to a greater extent 

 than that of the aerial tissue. 



Rapid seedling growth insures adequate root 

 development which in turn increases competitive 

 capacity of the seedling. Rhodes (15) reported 

 that grasses with high competitive capacity 

 (Lolium spp.) produced more root tissue during 

 seedling development than species of low com- 

 petitive capacity (Dactylis spp.). The time at 

 which nodal roots emerged was suggested to be 

 an important seedling characteristic determining 

 the competitive capacity of several grass species. 

 In view of the close association between root 

 growth and light intensity, it is unfortunate that 

 light levels under which these experiments were 

 conducted were not defined. Since the experiments 

 were conducted under greenhouse conditions, it 

 would seem that light levels were low. It is not 

 clear to what extent competitive capacity, as re- 

 flected by root growth characteristics, of the 

 species evaluated may have been affected by low 

 light intensity. However, these studies emphasize 

 the importance of recognizing that vigorous root 

 growth is essential for optimum seedling growth 

 and development- 

 Temperature, being a major parameter of the 

 natural environment and closely associated with 

 radiation intensity, obviously has an important 

 effect on seedling growth and development. A 



Table 1. — Percentage of -flowering plants of red 

 clover cultivars grown at three light intensity 

 levels and five illumination periods (2) 



Illumination period (hours) 



Cultivar 



14 16 



is 



20 



8,000 lux intensity 



Pennscott 

 Dollard 



Pennscott 

 Dollard 



Pennscott 

 Dollard 



II 







27 



2 s 



11 







20 



.-,:, 



lli.OMO 



lux 



intensity 









i» 



36 



S3 











;-,<> 



42 



32,000 



lux 



intensity 









10 



45 



S'J 











45 



40 



