For comparison of seedling growth competitive responsa~ in a controlled environment, monocultures (intraspecific) and 2 species mixtures (interspecific) of mountain rye (Secuk mou&mum), crested wheatgrass (Agropyron cristatum x deseftorlmr 'Hycrest~, and downy brome (Bromus tectorum) were established. Seedling dry root and sboot weights, shoot area, and maximum root length were compared at 1,2,4, and 6 weeks of growth in shoot roots boxes under a growth chamber environment (16 hr @ 14" C, 1,060 PE m-2 set-1; 8 hr @ 100 C, dark). Soil moisture depletion was monitored gavimetrically. Dry root and shoot weight, sboot area, and root length of mountain rye was greater tban that of both downy brome and Hycrest crested wheatgrass at every sampiing period over the 6-week study when grown in two-species mixtures. No difference was obtained for these seedling growth characters between downy brome and Hycrest mixtures, except for a 6.4 cm vs. 4.8 cm maximum root length at 1 week of growth. Similarly, in monoculture, mountain rye generally produced greater seediing growth than the other 2 species, although exceptions occurred for root weight, shoot area, and root length by 6 weeks of growth. Mountain rye depleted soil moisture in tire growth boxes more rapidly and to a lower potentiai than tire other 2 species. The results of this study indicate mountain rye provide vigorous competition asaseedllhg.
A soil and root system sampling technique that accurately measures root distribution within the soil profile without causing excessive damage to experimental plots would improve the efficiency of root system research. A monolith mapping root sampling technique is described that combines the positive attributes of the soil monolith and profile wall methods with a less destructive hand tool sampling protocol. The objective of this field study was to compare monolith mapping with a standard monolith washing technique for the purpose of measuring root distribution in the upper 30 cm of the root zone. Root systems of maize (Zea mays L.) (V6 stage of development) from plots (Vienna loams oils; fine‐loamy, mixed Udic Haploborolls) treated with broadcast or banded P were sampled using the modified monolith method. The roots present in the soil monolith were mapped (monolith mapping method), and the maps used to represent two‐dimensional root distribution. The soil monolith was then grid‐sectioned into 5.1 by 5.1 by 7.6 cm rectangular blocks and washed to separate roots from the soil. Root length was then measured using a line‐intersect method (monolith washing method). Monolith mapping and monolith washing methods both detected differences in root system distribution in the soil profile. A significant linear relationship (r = 0.87) between root length density and root number as measured by the two methods allows conversion of the numerical data collected by the monolith mapping method into root length density values. We conclude that monolith mapping works well for determining the spatial differences in root distribution in the upper 30 cm of the root zone. The relative time requirements, accuracy, and less destructive nature of the technique (compared with the trench profile and framed monolith methods) result in more efficient collection of data on root system characteristics.
Inhibition of net photosynthesis of jointed goatgrass and downy brome protoplasts by metribuzin and its ethylthio analog (ethyl-metribuzin) was greater at 25 than at 10 C. As temperature increased from 10 to 25 C, the concentration of ethyl-metribuzin required to inhibit net photosynthesis 50% (I50) decreased by a factor of 3.5 and 4.3, respectively, in jointed goatgrass and downy brome. I50values for metribuzin decreased by a factor of 1.5 and 2.5 in jointed goatgrass and downy brome, respectively, for the same 15 C increase in temperature. Based on I50values at 10 C, metribuzin was nine times more inhibitory than ethyl-metribuzin in jointed goatgrass and eight times more inhibitory in downy brome. At 25 C, metribuzin was only 4.7 and 3.9 times more inhibitory than ethyl-metribuzin in jointed goatgrass and downy brome, respectively. Thus, cold temperatures reduced the activity of ethyl-metribuzin more than metribuzin. The activity of both herbicides was reduced less in protoplasts of jointed goatgrass than in protoplasts of downy brome over the 15 C range.
Root absorption of subtoxic levels of metribuzin and its ethylthio analog (ethyl-metribuzin) by downy brome, jointed goatgrass, and winter wheat increased by a factor of three to five times as temperature increased from 10 to 20 C. Absorption of ethyl-metribuzin per gram dry weight was similar for all three species. Absorption and distribution of ethyl-metribuzin, but not metribuzin, were similar per gram dry weight in downy brome and jointed goatgrass. Absorption of metribuzin per gram dry weight was lower for winter wheat than for the other two species at 20 C. In general, the ratio of absorbed ethyl-metribuzin detected in shoots to that in roots was less in winter wheat and jointed goatgrass than in downy brome. The absorption by roots of14C-herbicides relative to water was similar for winter wheat and jointed goatgrass. Absorption of both14C-herbicides by winter wheat and jointed goatgrass was nonpreferential with respect to water absorption at 10 and 15 C. However, at 20 C14C-herbicide absorption was reduced 5 to 30% with respect to water absorption. Downy brome absorption of14C-herbicides with respect to water was 30 to 50% less than that of the other two species.
In thls study WC determined th8t mount8ln rye (Se& mont8am), cre8ted wheatgr8ss (Agropyron criatum X desertorum 'Hycreet'), 8nd downy brome (2?romus tectorum) h8ve slmllu germlnatlon temperature requirements and thus have tbc potentlal to germinate under slmllu soil temperature regimes, I future which could be rdv8at8geous for subsequent seedling competition of mount8ln rye or crested whe8tgr8ss 8giinst downy brome. Germhutlon tempenture profiles were compared uslng a thenno-gr8dlent germlrmtlon pl8te. Flfty-elx d&rent d8y/nlght tempenture reglmea were utlllzed for the comp8rlsons. The blvuirte spllne model WM found to be the best model for predlctlng germln8tlon-temper8ture response of the 3 species. Mountain rye 8nd downy brome produced high germhutlon under widely fluctu8tlng (20-300 C, 16 hr d8y/5-10" C, 8 hr nlgbt) temperature regimes with era&d whatgr8ss demonstmtlng 8n optimum genninrtlon temper rture over 8 10-20" C dry/250 C night regime. One of the 2 downy brome sources ev8lurted exhibited 8 much broader optimum germination tempenture nnge. However, the differences in germlnrtlon temperature profiles obtrined were not of 8 magnitude likely to be blologlc8lly or ecologlc8lly slgnlfiant due to the rel8tlvely high germln8tlon obt8lned over 8 wide nnge of fluctuating day/night temperrturea for 8ll3 species.
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