row and threshing in the lab. Roots were harvested to a l0-cm depth immediately beneath the plants using a 7.6-cm-diameter root core; two subsamples were ...
NOTES
EFFECTS OF FUMIGATION ON GROWTH, PHOTOSYNTHESIS, WATER RELATIONS AND MYCORRHIZAL DEVELOPMENT OF WINTER WHEAT IN THE FIELD Winter wheat (Triticum aestivum L.) was grown in methyl bromide fumigated and nonfumigated soils in the field. Fumigation increased growth of wheat in the winter but depressed growth later in the spring. Growth depression of winter wheat in fumigated soils coincided with VAM-fungal colonization of wheat roots in nonfumigated soils. In the spring, wheat plants growing in fumigated soils were more chlorotic than those
Can. J. Plant Sci. Downloaded from pubs.aic.ca by 183.224.77.75 on 12/01/15 For personal use only.
in
nonfumigated soils. Plants grown
in
fumigated soils produced 18-21% less
aboveground biomass during grain hlling, and 42% less grain at final harvest than controls. In May, photosynthesis, stomatal conductance, and transpiration of flag leaves were reduced 40-52,4l-55, and24-36%, respectively, in fumigated plots when compared to nonfumigated plots. Wheat was colonized by VAM only 2O% of the growth period; however, VAM colonization may occur at a period critical to grain production of winter wheat.
Key words: Titicum aestivure, fumigation, rnycorrhizae, photosynthesis, water relations, wheat lwinter.;
IEffets de Ia fumigation sur la croissance, la photosynthdse, I'utilistion de I'eau et le d6veloppement des mycorhizes dans le bl6 d'hiver au champ.l Titre abr6g6: Effets de la fumigation sur la physiologie du bl6. Nous avons cultiv6 du bl6 d'hiver (Triticum aestivum L.) en plein champ, dans des sols fumig6s au bromure de m6thyle ou non fumig6s. La fumigation a entrain6 une augmentation de la croissance du bI6 pendant l'hiver mais a limit6 cette croissance plus tard, au printemps. Cette baisse de la croissance du bl6 d'hiver en sols fumig6s coincidait avec la colonisation, par les champignons mycorhiziens v6siculaires arbusculaires (VAM), des racines du bl6 cultiv6 en sols non fumig6s. Au printemps, les plants de bl6 cultiv6s en sols fumig6s 6taient plus chlorotiques que ceux cultiv6s en sols non fumigds. Les plantes cultiv6es en sols fumig6s ont produit de 18 d 2l% de moins de biomasse au-dessus du sol pendant l'6tape de gonflement des grains, et 42Vo de moins
de grains ir la rdcolte finale, comparativement aux plants t6moins. En mai, la photosynthdse, la conductance stomatale et la transpiration de la dernidre feuille ont 6t6 r6duites de 40 ir 52%, 4l it 55% et24 d36% respectivement dans les parcelles fumig6es, comparativement aux parcelles non fumigds. Le bl6 n'a 6t6 colonis6 par les VAM que pendant2O% de la pdriode de croissance. Toutefois, il est possible que cette colonisation survienne )r une p6riode critique pour la production des grains chez le bl6 d'hiver. Mots cl6s: Triticum aestivum, fumigation, mycorhize, phytosynthdse, utilisation de I'eau,
bld d'hiver
Vesicular-arbuscular mycorrhizal
(VAM)
fungi can enhance plant water relations (Safrr et al. 1972). Wheat colonized by VAM fungi was shown to have higher stomatal conductances than non-VAM plants in both wet and dry soils (Allen and Boosalis 1983). Also, plants colonized before anthesis had twice the
plants (Ellis et
al. 1985). Colonization of
winter wheat roots in the freld does not occur until head emergence (Hayman 1970). The delayed colonization has been attributed to the effect of soil temperature on spore germination (Hetrick et al. 1984). Since colonization
occurs for only a small portion of winter biomassandgrainproductionof noncolonized wheats total growth cycle, the benefits of VAM fungal colonization in the field have Can. J. Plant Sci.69:535-540 (Apr. 1989) been considered doubtful (Hetrick et al. 535
CANADIAN JOURNAL OF PLANT SCIENCE
Can. J. Plant Sci. Downloaded from pubs.aic.ca by 183.224.77.75 on 12/01/15 For personal use only.
536
1984). However, moisture stress during grain-filling can have a major impact on grain
planted 20 Sept. Rainfall received during the growing season was as follows: September,
yield (Passioura 1977), and thus VAM colonization may occur at a critical phase of wheat growth. Methyl bromide fumigation has been used extensively as a control procedure in the study of VAM-fungal colonization. Fumigation is nonselective in that all microbes are initially
0.4 cm; October, 5.3 cm; November, 4.3 cm, December, 14.6 cm; JanuarY, 2.4 cm; February, 8.4 cm; March, 15.1 cm; April, 12.8 cm; and May,2.1 cm. Average daily air temperatures were 2, 11, 16, and 20"C for February, March, April, and May, respectively.
reduced (Menge 1982); unfortunately, no procedure for selective eliminating VAM
Plant biomass samples were taken 28 Feb., 13 Mar., 10 May, and 21 May. These dates corresponded to developmental stages 4, 6,
fungi is currently available. The objectives of this study were to compare growth of winter wheat in fumigated and nonfumigated field plots. Measured parameters included VAMfu ngal coloni zation, growth characters, yield, leaf nutrients, photosynthesis, stomatal conductance, transpiration, and leaf xylem potential. The study was conducted at the USDA Forage and Livestock Research Laboratory in El Reno, Oklahoma. Soils were fine silty Haplustolls of the Dale Series. The field was previously an Old World Bluestem (Botftriochloa sp.) pasture that was planted to winter wheat (Triticum aestivum L. 'Tam l0l') beginning the fall of 1983. Prior to
fumigation the experimental area was
ploughed and disced. The experiment was a randomized complete block with four replicates. Experimental units were 2.5 x 3.0 m plots which were either fumigated (FUM) or nonfumigated (NIL) on 12 Sept. 1984. BromO-Gas (Great Lakes Chemical Corporation, West Lafayette, Ind.) was the fumigant and contained 98% methyl bromide and2% chloropicrin. The resultant rate was 593 kg ha-l methyl bromide, which is slightly higher than rates recommended for rapid dissipation of the
gas (Menge 1982). Experimental plot perimeters were trenched to a depth of about 30 cm. Plastic was placed over each plot and buried to a depth of 30 cm around the borders. After 24 h of fumigation the tarps were cut open; the plastic borders remained as a barrier to mycorrhizal contamination from surrounding nonfumigated soils. The fields were fertilized with ammonium nitrate
at ll2 ks
N
ha I and winter
wheat was
10.1 and
ll.1 of the Feekes scale (Large
1954). Aboveground biomass was harvested
from 13 cm of drill row; there was one
sub-
sample per experimental unit. Drill rows were 20 cm apart, hence the area harvested was 0.026 m'. Each sample was separated into flower heads and live leaves. Leaves taken 10 and 2l May were scanned for leaf area with a LI-3000 portable area meter (Li Cor, Inc., Lincoln, Nebr.). The plant parts were dried at 60"C in a forced-air oven for at least 48 h. Grain was harvested from each plot by hand clipping 2-mJong sections of row and threshing in the lab. Roots were harvested to a l0-cm depth immediately beneath the plants using a 7.6-cm-diameter
root core; two subsamples were collected per experimental unit. The roots were washed
free of soil with a hydropneumatic elutria-
system (Gillison's Inc., Benzonia, Mich.), floated in water, and skimmed free
tion of
debris.
About 10% of each root sample was prepared and scored for VAM colonization. Roots were cleared and stained using a modified Phillips and Hayman (1970) method. Random selection was accomplished by cutting roots into l-cm-long segments, spreading the segments on a grid, and using a random-
numbers table to select a portion of the segments. Mycorrhizal root colonization was determined microscopically at 100x (Bierman and Linderman 1981). Photosynthesis, stomatal conductance,
transpiration, photosynthetically active radiation (PAR), and leaf temperature were measured on two flag leaves per experimental unit
TRENT ET AL.
-
FUMIGATION EFFECTS ON WHEAT PHYSIOLOGY
during 8 May, 9 May, 15 May, and 23 May
However, the trend was for higher shoot mass in the FUM plots compared to the NIL plots in late winter and early spring, and higher
xylem poitential was measured on the same leaves with a Scholander pressure bomb (Soil
values
Moisture Corp., Santa Barbara, Calif.).
plots although differences were significant only in late May, when live leaves were absent from plants in NIL plots. Leaf area index was 6.2 and 5.0 on 10 May, and2.3 and 0 on 2l May for FUM and NIL plots, respectively. Mass of flower heads was higher for NIL plots, although the differences were again not sig-
with an LI-6000 portable photosynthesis meter (Li Cor, Inc., Lincoln, Nebr.). Leaf
Flag leaves were taken from plants of each
treatment
Can. J. Plant Sci. Downloaded from pubs.aic.ca by 183.224.77.75 on 12/01/15 For personal use only.
53'7
on 10 May when plants from
fumigated plots began to exhibit chlorosis. Two subsamples per experimental unit were ground with a cyclone mill (Udy Corp., Ft. Collins, Colo.) and leaf tissue was digested with a Tecator digestion system using a modified Parkinson and Allen (1975) procedure.
Nitrogen was determined using an Orion
for NIL plants during grain-filling
(May). Leaf mass tended to be higher in FUM
nificant. Grain yield from FUM plots (217 g m ') was significantly lower (P
z
+ot@O€N€ OO-*rC:rd
D
o+ F-€-\Od*S 6NO-*@--
J
a Ez FLC
i=yd;i
Nn
^2,,=
';E 9^
>z :e €hoh ll^;
oi
l-i
3'
=4 6-_ :.1
v-l roq rq i'? NOT
p
