(Subproject 1.2.2)
by Libby Pinkard
Science
news
Effects of defoliation on tree productivity,
and the role of interacting stresses and mode of
defolation
- A defoliation experiment was established in 14 metre trees at
Pittwater, with the aim of investigating the effects of defoliation
on water relations and carbon uptake. It was logistically
difficult to run, requiring the use of a cherry picker to access
tree crowns. Carbon uptake, sap flow, stomatal conductance,
hydraulic conductance and foliar characteristics were examined over
a period of six months following removal of 45 per cent of leaf
area. The experiment is largely complete, and results suggest that
large trees experiencing defoliation respond differently in a
physiological sense compared to smaller trees. Biomass
harvest this winter will shed more light on possible reasons for
this, in terms of patterns of resource allocation. The work
has been done as part of Audrey Quentin’s PhD project (for
more about Audrey, please view her profile,
below).
- A new experiment was established at Pittwater to examine the
effects of interactions of abiotic stresses, in this case water and
nutrient, on responses to defoliation. Measurements commenced
in March, and have focused to date on quantifying carbon uptake of
defoliated and undefoliated plants. A detailed study of the
effects of the interaction of defoliation and stress (particularly
water) on plant water relations and implications for carbon uptake
will commence in spring, coinciding with the application of a
second defoliation event. In addition, the relative
contributions of leaf and stem photosynthesis on carbon uptake will
be examined. Biomass harvesting in August will provide
insights into the effects of stress interactions on root:shoot
allocation patterns, and patterns of nitrogen allocation within the
crown. Results will be used to improve our capacity to
quantify the effects of defoliation on tree growth.
- A number of our experiments rely on the use of artificial
defoliation to provide repeatable and controlled levels of
defoliation. The assumption in this approach is that
artificial defoliation has similar effects on physiological
processes and stem growth as does insect defoliation. Audrey
Quentin undertook an experiment to examine whether this presumption
is correct. She compared similar levels and patterns of
Chrysoptharta agricula and artificial defoliation in a pot
experiment. In general, there were similar responses in terms
of capacity for carbon uptake. However, insect defoliation
resulted in much higher levels of carotenoids and chlorophyll in
the foliage compared to artificial defoliation. It also
reduced height growth more than did artificial defoliation.
An examination of the effect of defoliation treatment on foliar
defence chemistry is ongoing.
Recent Workshops
- A mycosphaerella leaf disease workshop was held in April in
Hobart, and staff from 1.2.2 contributed four presentations
New staff
- Dr Karen Barry was appointed to replace Dr Libby Pinkard as the
Postdoctoral Research Fellow in this subproject. For more about
Karen, please view her profile below.
-
Dr Alieta Eyles was appointed as a 12-month Postdotoral Research
Fellow for this subproject to assist with the experimental
programme at Pittwater, and to undertake a study of induced
resistance in
E. globulus. Prior to returning to Tasmania
in January, Alieta was working with Pierluigi Bonello at The Ohio
State University, USA. She was involved in number of projects
related to chemical ecology and one of her major projects examined
the cross-effects of systemic induced resistance in Austrian pine
(
Pinus nigra) between a fungal pathogen and an insect
pest.
Publications
Pietrzykowski E, Stone C, Pinkard E, Mohammed CL
(2006) Effects of Mycosphaerella Leaf Disease on the
spectral reflectance of juvenile Eucalyptus globulus
foliage. Forest Pathology. 36,1-15.
Pinkard EA, Baillie CC, Patel V, Mohammed CL
(2006) Effects of fertilising with nitrogen and phosphorus on
growth and crown condition of Eucalyptus globulus Labill.
experiencing insect defoliation. Forest Ecology and
Management. 231, 131-137.
Pinkard EA, Gill WM, Mohammed CL (2006)
Physiology and anatomy of lenticel-like structures on leaves of
Eucalytpus nitens and E. globulus seedlings.
Tree Physiology. 26, 989 - 999.
Pinkard EA, Mohammed CL (2006) Photosynthesis of
Eucalyptus globulus Labill. with Mycosphaerella leaf
disease. New Phytologist. 170,
119-127.
Pinkard EA, Patel V, Mohammed CL (2006)
Chlorophyll and nitrogen determination for plantation-grown
Eucalyptus nitens and E. globulus using a
non-destructive meter. Forest Ecology and Management.
223, 211 - 217.
Pietrzykowski EA, Stone C, Pinkard EA, Mohammed
CL (2006) Effects of Mycosphaerella leaf disease on spectral
reflectance properties of juvenile Eucalyptus globulus
foliage. Forest Pathology. 36, 1-15.
Smith AH, Pinkard EA, Stone C, Battaglia M,
Mohammed CL (2006) Precision and accuracy of pest and pathogen
damage assessment in young eucalypt plantations. Environmental
Monitoring and Assessment 111, 243-256.
Wiseman D, Smethurst P, Pinkard L, Wardlaw T,
Beadle C, Hall MF, Baillie CC, Mohammed CL (2006) Pruning and
fertiliser effects on branch size and decay in two Eucalyptus
nitens plantations. Forest Ecology and Management
225 (1-3), 123-133.
Publications - in
press
Glen M, Smith A, Langrell SRH, Mohammed CL
(2006) Nested PCR detection of Mycosphaerella species in
leaf disease of Eucalyptus plantations.
Phytopathology (in press)
Glen M, Alfenas AC, Zauza EAV, Wingfield MJ,
Mohammed CL (2006) Puccinia psidii – the
threat to Australia’s environment and economy.
Australasian Plant Pathology (in press) (invited
review)
Medhurst JL, Pinkard EA, Beadle CL, Worledge D
(2006) Increases in photosynthetic capacity of plantation-grown
Acacia melanoxylon after form pruning. Forest Ecology
and Management (in press)
Pinkard EA, Battaglia M, Mohammed CL (2007)
Defoliation and nitrogen effects on photosynthesis and growth of
Eucalyptus globulus. Tree Physiology (in
press)
Wiseman D, Hall MF, Baillie CC, Smethurst PJ,
Pinkard L, Wardlaw T, Beadle CL, , Mohammed CL (2006) The effects
of tree nutrition on tree attributes and decay from pruning in
Eucalyptus nitens plantations. Forest Ecology and
Management (in press)
Meet
incoming postdoctoral researcher Dr Karen
Barry
 |
Dr Karen Barry has been appointed to replace Dr Libby Pinkard as
the Postdoctoral Research Fellow in the Forest Health sub-project
(1.2.2). Karen will take up the 50 per cent full time equivalent
position in January 2008. She is currently completing an
ARC-funded project examining the effects of different stresses on
leaf- and crown-level factors (biochemistry, physiology, leaf area)
and spectral reflectance determined at the leaf and crown-level, to
enable development of spectral indices which will characterise
stress.
Meet PhD candidate Audrey
Quentin
I moved to Australia from France for the first
time in 2005 to undertake a six-month Honours project, researching
the impacts on eucalypt physiology of the fungal diseases
Mycosphaerella sp. and Phaeophleoposra
eucalypti.
To read more about my background please click here.
For an update on how my project is progressing,
please read on…
Field and glasshouse experiments incorporated
into this project seek to examine the hypotheses:
- plants under water or nutrient stress seek to maintain current
rates of physiological activity and carbon gain when experiencing
pest attack
- the capacity of physiological processes to respond to pest
attack is influenced by resource availability and environmental
stress
In the initial stage of the project, I explored the response of
individual 13 metre trees that I submitted to 45 per cent
artificial defoliation in a trial plot at Pittwater in southern
Tasmania. An elevated work platform was used to access the tree
crowns for measurements. The aim is to investigate whether
defoliation changes the efficiency of photosynthesis and water
transport in the stem and leaf, and evaluate the impact on biomass
allocation below- and above-ground. I also used a glasshouse
experiment to compare the effects of artificial and chewing larvae
(
Chrysophtharta agricola Chap.) defoliation on the
photosynthetic capacity, growth rates and biomass allocation of
young
Eucalyptus globulus. Artificial defoliation has been
broadly used in numerous studies to simulate defoliation by insect
pest, despite of differences existing between snipping and chewing.
Both stress treatments consisted of 25 per cent removal of total
leaf area. Spatial pattern of natural defoliation has been
respected in the artificial treatment.
efoliation stress resulted in photosynthetic
up-regulation and reduction in biomass, especially leaf production
of the damaged and newly formed apical zones. Natural and
artificial defoliation reduced by 32 percent and 40 per cent
respectively in height growth increment. However, artificial
defoliation did not affect diameter growth rate although insect
chewing reduced it by 40 per cent. We concluded that artificial
snipping of leaf area mimicked the effects of C. agricola
larval feeding and that careful artificial defoliation may induce
similar effects as insect chewing defoliation on photosynthetic
capacity and total biomass of E. globulus seedlings -
although these two defoliation types did not have equal effects on
photosynthesis’ increase in intensity and diameter growth
rate.
To date, no investigations of combined effects
of defoliation and drought on morphological and ecophysiological
parameters of eucalypt species have been conduced. In a series of
experiments to be performed with young eucalypt trees at the new
plantation at Pittwater and in pot experiments, I will explore the
effects of repeated defoliation and drought stress. I aim to
investigate tree responses to the combination of stress factors,
which will result in contrasting effects when they are applied
separately. These experiments will start in spring.
I am very thankful to the people I work with,
who are extremely helpful assisting me with my research topic and I
feel that I am gaining a valuable amount of benefit, knowledge and
skill in the area of forest health and sustainable management
through these experiences.
