This glasshouse study was undertaken to determine the effect of temperature
and defoliation on the regrowth of prairie grass
(Bromus willdenowii Kunth cv. Matua) in comparison with
perennial ryegrass (Lolium perenne L. cv. Dobson).
Individual plants of prairie grass and perennial ryegrass were grown in 2
mini-swards with one half as prairie grass and the other as ryegrass. From
H0 (13 weeks after sowing) to the completion of the
experiment at H3, one sward was maintained at a
day/night temperature of 18/10˚C and the other at
25/15˚C. From H0 to H1,
prairie grass was defoliated 4 times at the time taken to regrow 1 new leaf
per tiller (1-leaf stage), 2 times at the 2-leaf stage, or once at the 4-leaf
stage to 60, 90, or 120 mm stubble height. Similarly, ryegrass was defoliated
3 times at the 1- leaf stage, once at the 1-leaf stage then once at the 2-leaf
stage, or once at the 3-leaf stage to 30, 60, or 90 mm stubble height. Plants
were subsequently harvested at H1,
H2, and H3, being the
commencement, mid-point, and completion of the full regrowth cycle (4- and
3-leaf stage for prairie grass and ryegrass, respectively).
Prairie grass was more adversely affected by frequent defoliation than
ryegrass. The combination of high temperature and frequent defoliation reduced
growth rates by 66 v. 54%, stubble dry matter
(DM) by 50 v. 11%, root DM by 62
v. 45%, and stubble water-soluble carbohydrate
(WSC) by 52 v. 21% for prairie grass and
ryegrass, respectively.
In contrast, ryegrass was more affected by defoliation height than prairie
grass, particularly at the higher temperature. Close defoliation and high
temperature reduced growth rate by 35 v. 25%,
root DM by 18 v. 0%, and stubble WSC by
84% v. 36% for ryegrass and prairie grass,
respectively. The number of tillers per plant was reduced by close
defoliation, more so at the high temperature in ryegrass but not in prairie
grass.
Defoliating prairie grass to 90 mm stubble height at the 4-leaf per tiller
stage compared with the 1-leaf per tiller led to maximum restoration of
stubble WSC reserves as well as maximising leaf and root growth. The higher
stubble WSC and greater root DM of prairie grass, together with its ability to
maintain growth rates and tillering under high temperature, are attributes
which explain why prairie grass appears to be more productive and persistent
than ryegrass in a subtropical environment.
Effects of the Fungal Endophyte, Neotyphodium lolii, on Net Photosynthesis and Growth Rates of Perennial Ryegrass (Lolium perenne) are Independent of In Planta Endophyte Concentration
