Comparative responses of soybean (Glycine max), sicklepod (Senna obtusifolia), and Palmer amaranth (Amaranthus palmeri) to root zone and aerial temperatures
Sr. Wright et al., Comparative responses of soybean (Glycine max), sicklepod (Senna obtusifolia), and Palmer amaranth (Amaranthus palmeri) to root zone and aerial temperatures, WEED SCI, 47(2), 1999, pp. 167-174
Experiments were conducted to compare germination efficiencies and vegetati
ve growth of soybean and the competing weed species, sicklepod and Palmer a
maranth, over a range of temperatures in the root zone and aerial environme
nts. From genetic origins we hypothesized that the weeds would have a highe
r temperature optimum, which would help explain competitive interactions se
en in the southeastern U.S. Germination experiments indicated that germinat
ion efficiency of the weeds was much more sensitive to low temperature than
soybean, being markedly inhibited below 18 C. Similarly, experiments in an
automated, temperature-controlled hydroponic system revealed that the weed
species were less tolerant of low root zone temperature but more tolerant
of high root zone temperature than soybean. At 16 C, dry weight of soybean
was 74% of the control dry weight at 24 C, whereas dry weights of sicklepod
and Palmer amaranth were 5 and 20% of the control, respectively. At 32 C,
soybean root dry weight was only 80% of the 24 C treatment, whereas root dr
y weight of the weed species was not significantly different. When plants w
ere grown at a low aerial temperature, growth of all plants was strongly in
hibited, but the negative effects were somewhat more severe in the weed spe
cies than with soybean. An increase in aerial temperature from 26/22 C to 3
4/30 C (day/night) had a positive influence on dry matter accumulation of t
he weed species, stimulating sicklepod 150 to 200% and Palmer amaranth 150
to 1,600% compared to their respective controls, whereas soybean remained a
t about 80 to 90% of the control. All species grew taller with increasing t
emperature. Leaf area of the weeds increased but leaf area of soybean did n
ot increase. Consistent with our original hypothesis, the results clearly s
how that the weeds, which originate from warm geographical regions, respond
more negatively than soybean to low temperatures in the growth environment
but more positively to high temperatures. The temperature characteristics
help to explain why the intensity of weed pressure increases as the soybean
growing season progresses, even after canopy closure.