A series of studies were conducted to examine the antioxidant
status, drought and disease tolerance, and growth response
to foliar application of soluble seaweed (Ascophyllum
nodosum) extracts (SE) and humic acid (HA; 25% active HA or
2.9% active HA) in tall fescue (Festuca arundinacea Schreb),
Kentucky bluegrass (Poa pratensis L.) and creeping
bentgrass (Agrostis palusttis Huds.) grown under low
(-0.5 MPa) and high (-0.03 MPa) soil moisture environments.
Foliar application of humic acid (2.9 % active HA) at
23.7 and 47.4 l/ha improved leaf water status, shoot and
root development in tall fescue, Kentucky bluegrass and
creeping bentgrass grown under drought. Humic acid (2.9%
active HA) at 15.5 l/ha or SE at 326 g/ha significantly
reduced dollarspot incidence and improved turf quality in
creeping bentgrass.
Drought stress induced an increase of antioxidants
alpha-tocopherol and ascorbic acid concentrations in the
three turfgrass species. In the experiment with Kentucky
bluegrass, drought stress increased beta-carotene concentration,
but did not significantly influence superoxide dismutase
(SOD) activity.
Foliar application of humic acid (25% active HA) at
5 l/ha and/or SE at 326 g/ha consistently
enhanced alpha-tocopherol and ascorbic acid concentrations,
leaf water status, and growth in the three cool-season
turfgrass species grown under low and high soil moisture
environments. In the experiment with Kentucky bluegrass,
application of HA at 5 l/ha plus SE at 326 g/ha also
increased beta-carotene content and SOD activity under low
and high soil moisture environments. There were close positive correlations between the
antioxidant status and shoot or root growth in the three turfgrass
species regardless of soil moisture levels.
The antioxidant SOD activity, photosynthetic
capacity in terms of Fvm690, and chlorophyll content in
terms of Fm730/Fm690 exhibited a seasonal fluctuation in
endophyte [Neotiphodium coenophialum (Morgan Jones and Gams)
Glenn, Bacon, Price and Hanlin] -free and endophyte-infected
tall fescue. Application of SE enhanced SOD activity,
photosynthetic capacity, and chlorophyll content in tall
fescue, especially at 4 weeks after SE treatment. The SOD
activity, photosynthetic capacity and chlorophyll content
were not significantly influenced by the endophyte
infection. A close positive correlation between SOD and
photosynthetic capacity during the summer was found in
endophyte-free and endophyte-infected tall fescue.
