236 POWELL AND BOX

Foundation. M. S. Thesis. A & M MCINTYRE, G. A. 1952. A method for preference values of South Texas College of Texas. 88 p. unbiased selective sampling, using woody species for deer and cattle. LI, J. C. R. 1957. Introduction to ranked sets. Austral. J. Agr. Res. J. Range Manage. 19: 212-214. statistical inference. Edwards 3: 385-390. SNEDECOR, G. W. 1956. Statistical Brothers, Inc., Ann Arbor, Michi- POWELL, J., AND T. w. Box. 1966. methods. 5th Ed. The Iowa State gan. 568 p. Brush management influences Univ. Press, Ames, Iowa. 534 p.

Bud Activity in the Stem, Crown, and or low water supply prevent growth. Rest is the type of dor- Tissue of Switchgrassl mancy referred to when external conditions are favorable, but G. S. HEIDEMANN AND G. E. VAN RIPER= growth is limited by unfavor- Graduate Assistant and Associate Professor, Depar.t- able internal conditions. ment of Agronomy, University of Nebraska, Lincoln. Dormancy has been demon- strated primarily in and Highlight in the summer may severely seeds of horticultural crops. Co- activity appears fo be cyclic weaken the switchgrass ville (1920) found that dormancy in nafure in the switchgrass plant. and induce the invasion of Certain vegetative buds are dormant commonly occurred among trees weedy species. while others are active during the and shrubs of cold climatic re- growing season. This study suggests Axillary buds located on the fhaf swifchgrass should be grazed gions. , crown, and stem por- prior fo floral initiation so ihaf maxi- Evans and Ely (1935) studied mum forage production can be ob- tions of the plant are important the rhizomes of several species tained from acfivaied sfem buds. meristematic areas for vegeta- of grasses and found that both tive reproduction in switchgrass. Switchgrass, Panicum virga- below and above-ground The initiation and development turn (L.), is a perennial, native, develop, to a limited extent, at of these buds determine not only warm-season grass of North all times when weather condi- thickness of stand, but also the America. The warm-season tions were favorable for growth. revegetative potential of the growth habit of switchgrass is Laude (1953) reported that a grass under grazing conditions. advantageous for use in pasture number of perennial grasses in Preliminary investigations at rotation systems. It can be California become dormant dur- Lincoln, Nebraska have shown grazed during the hot summer ing the summer even though that these buds display a sea- months when most cool-season supplied with adequate water. sonal variation in activity. Al- grasses are dormant or semi- He associated summer dormancy though several other perennial dormant. However, early and with high temperature and a grasses also display dormancy medium maturing switchgrass long photoperiod. during the growing season, little decreases rapidly in nutritive In a study of quackgrass rhi- work has been done to charac- value and palatability with ma- zomes (Agropyron repens (L.) terize the nature of this dor- turation. On the other hand, Beauv.), Johnson (1962) found a mancy. when switchgrass is grazed so rest period in April and May The purpose of this study was that the growing point is re- which he described as “late- to determine the seasonal activ- moved before emergence from spring dormancy” rather than ity of buds located on the rhi- the boot, regrowth may be initi- the more common “summer dor- zome, crown, and stem portions ated from the uppermost 2 or 3 mancy.” This conclusion was of the switchgrass plant. axillary buds. Vegetative re- reached because prevailing growth in mid-summer provides Liierafure Review weather conditions before and palatable forage for cattle, and In a review by Samish (1954) during the period were relatively they continue to gain satisfac- the term “dormancy” is defined cool and moist and favorable for torily. Heavy grazing too early as the temporary suspension of quackgrass growth. visible growth; which he further The apical bud of nutgrass 1 Published with the approval of the breaks down into two main (Cyperus rotundus (L.)) has been Director as paper No. 1948, Journal “quiescence” and “rest .” reported to prevent growth of Series, Nebraska Agricultural Ex- types, Quiescence is the type of dor- other buds on the same tubers periment Station. mancy exhibited by the plant (Loustalot et al., 1954). This phe- 2 Now Manager, Department of Agronomy, Engineering Research, when unfavorable external con- nomenon is commonly referred Deere & Company, Moline, Illinois. ditions such as high temperature to as apical dominance. Another SWITCHGRASS BUD ACTIVITY example of apical dominance is Table 1. Elongation and dry weight of rhizome, crown, and stem buds of swifchgrass grown in ihe dark af 28 C for 14 days during 1962.1 that found in the potato tuber. -_ When the intact potato tuber Rhizome Crown buds Stem buds becomes active after a rest pe- Sampling Dry Dry DYY riod, one or more apical buds dates Lengths Weight Length” Weight Length2 Weight cm elongate, but the lateral buds 1962 cm mg cm mg mg usually fail to grow. If, however, 3-10 5.32 - 9.94 - 0.55 - lateral buds and apical buds are 3-22 3.66 - 11.14 - 0.13 - 5.25 98 11.69 325 0.74 cut out and grown separately, 4-5 31 5.39 95 12.26 310 0.42 5 both start growing at the same 4-19 5-3 4.39 64 7.34 115 0.60 13 time (Michener, 1942). 5-17 2.65 28 0 0 2.32 100 It is believed that the dor- 5-31 3.30 45 1.07 6 2.18 35 mancy of buds in woody , 6-14 0.61 7 3.78 32 2.16 21 tubers, and herbaceous perenni- 6-28 2.07 32 5.30 75 2.93 31 als have similar fundamental 7-12 2.68 48 6.72 101 2.90 44 processes (Samish, 1954). There- 7-26 4.13 66 7.69 157 4.29 95 fore, since there are few basic 8-9 1.72 34 10.60 304 1.84 40 differences between the buds of 8-23 0.32 6 9.87 240 1.63 38 1.99 34 9.34 342 0.50 12 an underground stem and the 9-6 1.81 38 6.85 244 0.23 5 buds of its above-ground coun- 9-20 10-4 3.30 64 7.16 243 0.75 23 terpart, findings of any of these lo-18 3.87 70 6.46 170 0.76 16 various forms may well be re- 11-15 1.98 37 5.17 214 0.28 9 lated to the others. 1 Implanted in agar and each bud value based on 25 sections for each Materials and Methods sampling date. The experimental area (3200 fts) 2 An average of the longest elongated bud of several which occurred on was located on the Agronomy farm each rhizome or stem-crown section. at Lincoln, Nebraska. Nebraska-28 switchgrass was seeded in April, 1959. A uniform stand was ready for Table 2. Elongation and dry weight of rhizome, crown, and stem buds of swifchgrass grown in the dark ai 28 C for 14 days during 1963.1 sampling in the spring of 1962. The ~__ ~_ ~____ -___ soil was a well-drained Sharpsburg Rhizome buds Crown buds Stem buds silty clay loam which was fertilized Sampling Dry Dry =Y annually with 55 lb/acre of elemental dates Lengths Weight Lengths Weight Length2 Weight N as NH4NOs. The pH of the soil 1963 cm mg cm mg cm mg was 6.0. Seventy-one lb/acre of ele- 3-12 4.67 96 mental P were applied as 42% con- 10.72 312 1.62 24 3-26 5.42 87 10.17 centrated superphosphate on Febru- 214 1.96 28 4-9 4.82 93 8.53 190 1.63 ary 20, 1962. 30 4-23 4.26 63 0 Axillary bud activity of rhizome, 0 1.78 37 5-7 2.42 34 0 1.19 30 crown, and stem was determined by 0 5-21 1.61 16 0 0 2.47 57 using an in vitro method similar to 6-4 2.09 27 1.84 15 0.30 10 that described by Johnson (1961). 6-18 1.48 24 7.96 122 0.42 3 Plant tissue was obtained bi-weekly 7-2 1.56 31 6.39 99 3.53 48 by digging up 2 to 3 ft2 of sod to a 7-16 1.30 20 9.41 220 5.76 152 depth of three to four inches (Tables 7-30 1.85 29 10.54 247 2.58 57 1 and 2). Plants obtained from the 8-13 0.89 20 9.45 258 3.82 83 field were washed free of soil with 8-27 0.82 13 8.65 273 4.00 84 cold tap water. The plants were kept 9-10 0.83 16 11.18 449 2.06 65 moist during the trip to the labora- 9-24 2.49 51 5.04 241 0 0 tory by first wrapping them in a __ -- _- moistened burlap sack, and then 1 Implanted in agar and each bud value based on 25 sections for each placing the entire bundle in a plas- sampling date. tic bag. In the laboratory, the plant 2 An average of the longest elongated bud which occurred on each rhizome material was placed in a refrigera- or stem-crown section. tor at 5 C and removed as needed during processing. Plant material was again washed with tap water, nodes with at least one noticeable activity was variable, but that sec- and adventitious roots and scale bud and a root. The root was cut tions with an attached root(s) con- on the rhizomes were re- free of the rhizome during the sec- sistently had the highest bud ac- moved. The rhizomes were cut into tioning process. A preliminary ex- tivity. 20 mm sections, each having several periment indicated that rhizome bud Lower stem buds and basal crown 238 HEIDEMANN AND VAN RIPER buds are commonly located within 1.5 inches of each other on the aver- age switchgrass plant (Fig. 1). There- fore, sections 1.5 inches in length were also sectioned for studying bud activity of the lower stem bases and basal crown buds. Stem and crown bud material consists of the lower 1.5 inches of the culm. Stem buds are referred to as the aerial section and crown buds as the basal portion of the 1.5 inch sections. Bud activity of the lower stem bases and basal crown buds were studied separately on the same section. The rhizome and stem-crown sec- tions were kept moist before im- planting in agar by placing them on moistened blotters in plastic trays. I NTErPM EDlATE Twenty-five sections of both the rhizome and stem-crown sections FIG. 1. A typical switchgrass plant showing the parent plant, its subsequent were selected at random each sam- rhizome growth, the current culm, new rhizome growth, and crown and stem pling date for determining bud ac- buds. tivity. Erlenmeyer flasks with a 125 ml capacity served as culture vessels. were then transferred to a 28 C dark Results Each flask contained 50 ml of a room for 14 days. The percentage bud activity, solidified 0.8% agar medium. Five Upon completion of the 14 day elongation, and dry weights of sections were implanted per flask growth period, the implanted rhi- resulting in five replications for zome and stem-crown sections were switchgrass rhizome, crown, and each type of plant material. The removed from the flasks. Rhizome stem buds were studied by using agar had been previously adjusted or stem-crown sections having no- tissue culture teclmiques during to a pH of 5.0 with 0.1 NH2SOh. ticeable new growth were counted as two years, 1962 and 1963. Prior to implanting, the plugged having active buds. Bud activity The average percentage rhi- flasks (Fig. 2 and 3) containing the was expressed as a percentage based zome bud activity (a-year aver- medium were autoclaved for 30 min. on the number of active sections age) was highest in the spring at 15 psi. The rhizome and stem- from the 25 sections originally im- and in the fall (Fig. 4). Rhizome crown sections were rinsed several planted. The longest elongated bud bud activity generally decreased times with distilled water, but no on each section was measured and further attempts were made to steri- was expressed as growth in centi- from mid-April to mid-June lize them. Flaming of each flask at meters. The total weight of all when the plants were in the the time of implanting aided in re- elongated buds was obtained after early boot stage of growth, A ducing mold contamination. The the excised buds had been dried in general increase was noted in flasks containing the plant material an oven at 70 C for 72 hours. July as new rhizome growth was

FIG. 2. Tissue cultures of 20 mm rhizome sections after 14 days FIG. 3. Tissue cultures of stem-crown sections after 14 days of of growth in the dark at 28 C. growth in the dark at 28 C. SWITCHGRASS BUD ACTIVITY 239

bud elongation (0 to 0.42 cm) was

90 L noted during June and on Sep- c tember 24. ._ 80 .-> CROWN Dry matter production from - ?m -c, 70 .iC’iT,vIrv elongated rhizome, crown, and S 60 stem buds during 1963 is also % m 50 presented in Table 2. Maximum weights from rhizome buds (51 to 96 mg) occurred from March 12 to April 23 and on September STm 24. Minimum weights (13 to 34 ~~~ WrJ ACl’IV-IT’Y mg) were recorded the rest of the season. Minimum weights I arch April PIB~ June JOY Aug. Sept. oct.-- Nov. from crown buds (0 to 99 mg)

SN'F'LINOIlATE were recorded from April 23 to FIG. 4. The two-year average trend of axillary bud activity of rhizome, crown and June 4 and on July 2. Heavier stem buds of switchgrass. weights (122 to 449 mg) were recorded throughout the remain- also observed in the field. Dur- cm) occurred during the early der of the sampling period. Max- ing August and early September spring and fall. imum dry weights from stem a definite dormancy period was Dry matter determinations of buds (48 to 152 mg) were re- noted. elongated rhizome buds during corded on May 21 and from July Crown and stem bud activity 1962 (Table 1) indicated the most 2 to September 10. Minimum were inversely related to each dry matter production (64 to 98 weights (0 to 10 mg) were re- other (Fig. 4). During March, mg) occurred from April 5 to corded during June and on Sep- crown bud activity was above May 3, and on July 26, and dur- tember 24. 90% while stem bud activity was ing October. Minimum dry mat- In general, field observations below 30%. However, in mid- ter production (6 to 7 mg) was on each sampling date during May, crown bud activity was noted June 14 and August 23. both years indicated that termi- nonexistent whereas 66% of the Crown bud weight was the nal rhizome buds were actively stem buds were active. Crown greatest (170 to 342 mg) during producing aerial shoots during bud activity averaged from 64% April and after August 9. Lower late April and early May, and to 90% throughout the remain- weights (0 to 157 mg) were noted that elongation of new rhizomes der of the sampling period while during May, June and July. Dry occurred during midsummer stem bud activity generally de- weight from stem buds was high from July to mid-August. Crown creased from 58% during late (35 to 100 mg) on May 17 and 31, buds appeared to be active only June to 6% in mid-September. and from July 12 to August 23. during two periods. The first Rhizome bud elongation mea- Lower weights were recorded was in late April when a major- surements taken during 1962 during the spring and fall and ity of the crown buds produced (Table l), indicated that maxi- in June. tillers, and the second period was mum growth (3.66 to 5.39 cm) Measurement of rhizome bud in late June when crown buds generally occurred during elongation during 1963 (Table 2) initiated new rhizome growth. March, April, and early May. indicated maximum elongation Stem buds appeared inactive Minimum elongation (0.61 and (4.26 to 5.42 cm) occurred from throughout the entire sampling 0.32 cm) was noted on June 14 March 12 to April 23, and that period. and August 23, respectively. minimum elongation (0.82 to Discussion Maximum elongation (9.94 to 0.89 cm) occurred from August Bud activity appears to be 12.26 cm) of crown bud shoots 13 to September 10. Minimum cyclic in nature in the switch- was noted from March 10 to elongation of crown buds (0 to grass plant. In general, activity April 19. Minimal elongation (0 1.84 cm) occurred from April 23 appears to move upward (late to 3.78 cm) occurred from May to June 4 while longer measure- April and early May) from the 17 to June 14. Medium elonga- ments (5.04 to 11.18 cm) were rhizome and basal crown areas tion was generally noted the recorded throughout the remain- into the stem until floral initia- rest of the season. Stem bud der of the sampling period. Max- tion in late June, then from the elongation was greatest (1.63 to imum stem bud elongation (1.19 stem back down into the basal 4.29 cm) between May 17 and to 5.76 cm) occurred from March crown area, and finally into the August 23. A minimum amount to late May and from July 2 to rhizome late in the growing sea- of stem bud elongation (<0.76 September 10. Minimum stem son. 240 HEIDEMANN AND VAN RIPER

Rhizome and crown buds pos- buds were largely inactive dur- late summer when carbohydrate sessed the highest potential for ing the sampling period, except reserves seemingly should be new initiation during early for two instances. The first was high, they appear to be unavail- spring in in vitro studies. And in late spring when a majority able in that dry matter produc- in field observations, in late of the crown buds elongated and tion was reduced as well as bud April and early May, apical buds formed new tillers. The second activity. This suggests that re- of rhizomes and basal crown period of activity in the field was spiratory enzymes may be in- buds became active and initiated noted when new rhizome growth hibited by certain mechanisms aerial shoots. High activity (in was initiated from crown buds and causes food reserves to be- vitro) was found in the axillary during late June. come unavailable and conse- stem buds of these aerial shoots The lack of continuity between quently dormancy occurs. until seed heads began emerging field observations and tissue cul- Theoretically it appears that from the boot in late June. At ture studies of bud activity the grazing of switchgrass should the same time, (in vitro) crown serves to point out differences begin in late May and early June buds were largely absent and in types of dormancy. It is ob- prior to floral initiation in late rhizome buds were semi-dor- vious that tissue cultures may June. Since maximum stem bud mant. As the seed heads emerged have removed apical dominance activity exists at this time, pro- in late June in the field, newly thus promoting aerial shoots duction of new palatable lateral developed crown buds became (Michener, 1942). The vertical shoots from the axillary buds on active, and initiated new rhi- implantation of normally hori- the stems should produce more zome growth. The new rhizomes zontal rhizome material in vitro forage over a longer period of elongated and stem bud activity may have also resulted in pro- time. Additional fertilizer cou- (in vitro) decreased until mid- motion of aerial shoots (Palmer, pled with adequate rainfall or August when rhizomes became 1954). However, high rhizome supplemental irrigation during dormant. During late Septem- and crown bud activity noted in this period of regrowth should ber, high bud activity (in vitro) tissue cultures during the spring prevent the switchgrass plants was once again evident primarily and fall from buds which were from becoming severely weak- in the rhizome and crown buds previously inactive in the fields ened. Further management stu- with little activity found in stem suggested that “quiescence” may dies should be designed to test buds. have resulted from an unfavor- the findings from this study. Results of the field observa- able external condition such as Summary tions and the in vitro bud activ- low temperature. When soil tem- The percentage bud activity, ity study failed to coincide dur- peratures were favorable for shoot elongation, and dry shoot ing several periods of the grow- growth during late spring and weights of switchgrass rhizome, ing season. For instance, new midsummer, a p i c a 1 dominance crown, and stem buds were stu- rhizome growth in the field was may have been present, causing died using tissue culture tech- initiated largely from crown buds to remain inactive in the niques during 1962 and 1963. buds, and these rhizomes grew field. Induced crown and stem Bud activity appears to be actively throughout July and bud activity may also be at- cyclic in nature in the switch- early August. Rhizome elonga- tributed to a p i c a 1 dominance. grass plant. During early spring, tion was not noted at other times Since little rhizome bud activity rhizome and crown buds are during the growing season. How- was noted in both the field and active while axillary stem buds ever, in vitro studies indicated in tissue cultures during late are inactive. During late spring, that rhizome buds were most ac- August and early September an stem buds become active and the tive during early spring and fall, internal factor alone may be sug- rhizome and crown buds are less In vitro studies did substantiate gested as the reason for dor- active. Subsequent to flowering, field observations in that the mancy during this time. This rhizome and crown buds are re- least activity was noted during type of bud dormancy could be activated and the stem buds once late August and early Septem- the true “rest” referred to by more become inactive. ber. Samish (1954). Several types of dormancy Stem base and crown tissue Dry matter determinations were apparent in switchgrass cultures indicated that crown from shoots produced by rhizome rhizomes during the growing buds possessed high activity buds prior to forage initiation in season. During early spring and throughout the sampling period, late April supports the supposi- late fall “quiescence” (due to except during the late spring tion of Weaver (1963) that high external environmental condi- period after the aerial shoots had carbohydrate reserves are avail- tions i.e., low temperatures) was emerged. However, field obser- able for new shoot growth in apparent. During late spring, vations indicated that crown early spring. However, during mid-summer, and early fall api- SWITCHGRASS BUD ACTIVITY 241

cal dominance appeared to cause LITERATURE CITED LOUSTALOT,A. J., T. J. MUZIK, AND dormancy because buds which COVILLE,F. V. 1920. The influence of H. J. CRUZADO. 1954. Studies on nutgrass (Cyperus rotundus, L.) were inactive in the field initi- cold in stimulating the growth of plants. J. Agr. Res. 20: 151-160. and its control. P. R. (Mayaguez) ated shoots under laboratory EVANS, M. W., AND J. E. ELY. 1935. Fed. Expt. Sta. Bull. 52. 30 p. conditions when apical domi- The rhizomes of certain species of MICHENER,D. H. 1942. Dormancy and nance was removed. A period of grasses. J. Am. Sot. Agron. 27: 791- apical dominance in potato tubers. “rest” was observed in late sum- 797. Am. Jour. Bot. 29: 558-562. JOHNSON,B. G., ANDK. P. BUCHHOLTZ. mer in that buds were dormant MUELLER,I. M. 1941. An experimental 1961. An in vitro method of evalu- study of rhizomes of certain prairie both under laboratory conditions ating the activity of buds on the plants. Ecol. Monog. 11: 165-188. and in the field. rhizomes of quackgrass (Agropy- PALMER, J. H. 1954. Effect of shoot ran repens). Weeds 9: 600-606. This study suggests that JOHNSON,B. G., ANDK. P. BUCHHOLTZ. orientation on and shoot de- switchgrass should be grazed 1962. The natural dormancy of velopment. Nature 174: 85-87. prior (late May and early June) vegetative buds on the rhizomes of SAMISH, R. M. 1954. Dormancy in woody plants. Ann. Rev. Plant to floral initiation (late june) so quackgrass (Agropyron repens). Weeds 10: 53-57. Physiol. 5: 183-204. that maximum forage production LAUDE, H. M. 1953. The nature of WEAVER, J. E. 1963. The wonderful from activated stem buds may summer dormancy in perennial prairie sod. J. Range Manage. 16: be attained. grasses. Bot. Gaz. 114: 284-292. 165-171.

5it 9 8

Bowie silt loam but with some Influences of Grazing and Fire on Vegetation Beauregard silt loam. Internal drain- and Soil of Longleaf Pine-Bluestem Range age is moderate to slow. Annual rainfall averages 58 inches; all VINSON L. DUVALL AND NORWIN E. LINNARTZl months except October exceed 4 inches. Principal Range Scientist, Southern Forest Experiment Station, Forest Service, U.S.D.A., Alexandria, Lousi- The longleaf pine (Pinus palus- ana; and Associate Professor of Forestry, School of tris) forest was cut more than 20 Forestry and Wildlife Management, Louisiana Agricul- years before the study described tural Experiment Station, Baton Rouge. here began in 1952, leaving rela- tively open grassland. Slender blue- stem (Andropogon tener) and pine- Highlight bell et al., 1954). Grasses are hill bluestem (A. divergens) were Herbage yield and density of cover generally utilized heavily the dominant grasses. Panicums (Pani- were greater on moderately or first year after burning, but less heavily grazed than on ungrazed cum spp.) , paspalums (Paspalum range. Botanical composiiion re- intensely during the second. spp.) , and miscellaneous bluestems mained relaiively constant under xffects of grazing pressures were also prominent. Carpetgrass moderate use but changed markedly on ungrazed and heavily grazed and burning on forage vegeta- (Axonopus affinis) inhabited small, ranges. Grazing compacted soils, but tion and soils were assessed in heavily grazed areas. insufficiently fo impair herbage a la-year study on Louisiana Before 1951, the range was open growih or accelerate erosion. Fire to unregulated grazing, and wild- had liffle long-range effect. range. Influences of experimen- tal treatments on herbage yield fires were frequent. Effects of prior burning and grazing were indeter- A fire in late winter or early and litter accumulation during minable. spring has been reported to im- the first 8 years were published For this study, eighteen 1/s-acre prove accessibility, stimulate in an earlier issue of the Journal paddocks were constructed on a site growth, and increase nutrient (Duvall, 1962). This paper pre- that had been burned by wildfire a content of new herbage on long- sents final results and reports year previously. Intermittent graz- leaf pine-bluestem range (Camp- changes in ground cover, botani- ing by cows and calves began in cal composition, and physical April 1952, and averaged 140 days properties of soil as induced by a year. Through 1960, six paddocks grazing. were grazed heavily, six were grazed 1 We are indebted to Chung-Yun moderately, and six were ungrazed. Hse, formerly Research Assistant, Procedure School of Forestry and Wildlife Moderate grazing aimed at utilizing Management, Louisiana State Uni- The area of study, on the Palustris 40 to 50% of current herbage aver- versity, for soil property determi- Experimental Forest in central Lou- aged 15 animal-unit days per pad- nations and statistical analyses of siana, slopes 2 to 5% and has deep, dock per year, while heavy grazing a portion of the study data. medium-textured soils chiefly of averaged 30 animal-unit days.