The morphological and physiological responses of perennial ryegrass (Lolium perenne L.), cocksfoot (Dactylis glomerata L.) and tall fescue (Festuca arundinacea Schreb.; syn. Schedonorus phoenix Scop.) to variable water availability
2012
There is a growing interest in the use of deficit irrigation
and perennial pasture species other than perennial
ryegrass ( Lolium perenne L.) in temperate agriculture, in
response to the decreasing availability of irrigation
water. Deficit irrigation requires an understanding of
plant responses to drought stress to ensure maximum
dry-matter return on water applied. A glasshouse study
was undertaken to investigate some of the morphological
and physiological responses of perennial ryegrass,
cocksfoot ( Dactylis glomerata L.) and tall fescue ( Festuca
arundinacea Schreb.; syn. Schedonorus phoenix Scop.) to
varied moisture availability. One water treatment
involved frequent applications of water to maintain a
soil water potential of approximately )10 kPa (100%
treatment), and three other treatments involved applications
at the same frequency, but using 33, 66 or
133% of the water applied in the 100% treatment. The
water treatments continued over two plant regrowth
cycles, followed by a ‘recovery’ phase of a single
regrowth cycle during which all plants received the
same water allocation as the 100% treatment. Depletion
and replenishment of stubble water-soluble carbohydrate
(WSC) differed between the three species in
response to soil moisture availability. By the second
regrowth cycle, stubble WSC concentration and content
in moisture-stressed cocksfoot plants had increased,
followed by a decrease during the subsequent recovery
phase when the stored WSC reserves were utilized to
support regrowth. The changes in stubble WSC reserves
corresponded to the maintenance of relatively stable
(i.e. the smallest reduction in leaf DM in response to
moisture stress), but consistently lower DM production
for cocksfoot compared with the other species. In
contrast, moisture stress had no effect on the stubble
WSC reserves of perennial ryegrass and tall fescue, with
the exception of a significant decrease in WSC concentration
under the 33% water treatment for perennial
ryegrass. Perennial ryegrass achieved an intermediate
DM yield and maintained positive growth rates
throughout the study, even when watered at 33% of
the requirement for optimal soil moisture levels. However,
a more pronounced reduction in leaf DM in plants
under moisture stress compared with the other species,
combined with declining WSC reserves and the death of
daughter tillers, highlighted the vulnerability of perennial
ryegrass to poor persistence under prolonged
drought conditions. Tall fescue appeared to have the
greatest scope under moisture stress in terms of maintaining
productivity and displaying attributes that contribute
to persistence. Its leaf DM was consistently
greater than that of the other species, displaying a
smaller decline in growth under water stress compared
to perennial ryegrass and an ability to recover faster
upon re-watering. This study has expanded the information
available that compares and defines the potential
of each species under moisture stress and
emphasizes the importance of balancing short-term
DM production with long-term persistence in choice of
pasture species.
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