PLANT MORPHOGENESIS FOR SCIENTIFIC MANAGEMENT OF RANGE RESOURCES 



35 



after that time. The relative change of PR with 

 leaf age was unaffected by the temperature. 



Low light intensities reduce tillering (5, 22, 

 41, 73) and effects of temperature on tillering 

 cannot be considered in isolation from such fac- 

 tors. Templeton and others (68) found tillering 

 to be influenced by photoperiod, temperature, and 

 age of plant. Mitchell (45, 46) found greater 

 tillering with high light intensity at equivalent 

 leaf stages. 



Peters (50) and Knievel and Smith (33) found 

 the time of tiller initiation to be critical in its 

 growth and survival. Summer tillers produced 

 significantly more secondary tillers than did win- 

 ter tillers. Lambert (35, 36, 37) found the ma- 

 jority of orchardgrass and timothy seed heads 

 were produced by autumn initiated tillers and 

 production of floral tillers was influenced by 

 plant density and tiller competition. He stated 

 that aerial competition reduced the number of 

 ears while edaphic competition affected the num- 

 ber of tillers per plant. Anslow (4) found that 

 leaf removal at progressively younger stages re- 

 stricted the growth of grass and that this effect 

 was buffered by a higher net assimilation rate 

 per area of leaf in a sward of predominantly 

 young leaves. Part of the higher net photosyn- 

 thesis could result from improved illumination 

 of the younger leaves after removal of the older 

 tissue but, as he pointed out, the rates of assimi- 

 lation by foliage may depend on the demands 

 created by the plant, and it is here that environ- 

 ment plays a big role. Reviews by Langer (39) 

 and Black (8) gave excellent summaries of light 

 effects on tillering. 



Tied in closely with tiller, root, and crown 

 growth is the carbohydrate status of the plant. 

 Here, environmental factors and management 

 play major roles. Researchers, looking at this 

 problem, have credited carbohydrate level at a 

 critical growth stage as a major factor in produc- 

 tion and stand persistence (5, 9, 10, 12, 17, 65, 

 75). Davidson and Milthorpe (21) suggested that 

 carbohydrates form only part of a labile pool 

 supplying energy for regrowth and that nitrogen 

 compounds are involved. Carlson (16) concluded 

 from studies with ladino clover that carbohydrate 

 reserves are chiefly used as a respiratory sub- 

 strate and the degree to which they provide 

 actual regrowth metabolites is yet unknown. 



Sheard (58) suggested that high plant produc- 

 tion requires carbohydrates for energy and 

 readily available protein for synthesis of new 

 protoplasm; if either is lacking regrowth will 

 be slowed. Darrow (18) found root weights of 

 bluegrass grown at 35° C. to be about half those 

 at 15° or 25°. Top growth and rhizome numbers 

 were also less. Higher concentrations of water 

 soluble carbohydrates are generally found in cool- 

 season species grown at low temperature (2, 7. 9. 

 20, 23, 59, 65). Temperature appears to particu- 

 larly influence fructosans, the principle nonstruc- 

 tural polysaccharide of these grasses. 



Soil temperatures can affect nutrient uptake by 

 plants. Power and others (51) reported lower N 

 and P uptake by barley at higher soil tempera- 

 ture, provided samples were taken at a specific 

 stage of development. Smith (60) found low K 

 content in plants grown at low temperature 

 regimes. Walker (71) reported that, for different 

 elements, the uptake by corn seedlings peaked at 

 different soil temperatures, and Ca deficiency was 

 present at soil temperatures above 27° C He also 

 found alternating soil temperatures to be more 

 influential than those held constant. Apparently 

 soil temperature influences growth most during 

 the light period when plants are photosynthesiz- 

 ing (72). Hunsigi and Ketcheson (31) reported 

 P uptake by corn to be initially high at 24° and 

 32° C but, with a subsequent reduction in the 

 number of lateral roots, P uptake declined at 

 these temperatures. Sharma and others (57) re- 

 ported P appeared to interfere with the translo- 

 cation of Zn at 15°. 



Optimum soil temperatures can indeed be 

 found for specific species as pointed out by 

 Walker (71) and, since it has been demonstrated 

 that changes in field soil temperatures are possi- 

 ble by mulching, irrigation, and so forth (1, 3, 

 27) , more knowledge is needed regarding the opti- 

 mum soil temperature for plants. 



Much research dealing with soil temperature 

 and plant responses has been conducted in growth 

 chambers. These have proved valuable in the 

 study of specific responses to single or multiple 

 environmental factor variations. However, ob- 

 served plant responses in growth chambers are 

 not always comparable with those seen in the 

 field. Complete simulation of ambient environ- 



