Abstract preview
EGF 2008
Overwintering of timothy and perennial ryegrass in Norway from a climate
change perspective
Höglind M.1, Jørgensen M.2, Østrem L.3, Bakken A. K.4 and Thorsen S. M.1
Norwegian Institute for Agricultural and Environmental Research (Bioforsk)
1
Horticulture and Urban Greening Division, Særheim, Klepp, Norway1
2
Arctic Agriculture and Land Use Division, Holt, Tromsø, Norway
3
Horticulture and Urban Greening Division, Fureneset, Hellevik i Fjaler, Norway
4
Grassland and Landscape Division, Kvithamar, Stjørdal, Norway
Corresponding author: mats.hoglind@bioforsk.no
Abstract
In a comprehensive research programme, WINSUR, we are currently investigating the effect
of climate change on overwintering of Phleum pratense L. and Lolium perenne L., two
important forage grasses. We summarize results from different studies in the field and
controlled environments. Increased CO2 concentration in the atmosphere (+170 ppm) had no
effect on frost hardening in an open-top chamber experiment, whereas a temperature increase
of 2 C in the autumn reduced the frost tolerance by 1 C. Plants transferred from the field to
a phytothrone in January dehardened rapidly. The most winter hardy cultivar dehardened from
-26 to -18 C during one week of exposure to 3 C, and to -15 C during one week exposure
to 9 C. The data suggest that winter-hardy cultivars of northern origin may be as prone to
dehardening as less winter-hardy cultivars of southern origin. Ice encasement and frost
tolerance were highly correlated. The results are discussed from a climate change perspective.
Key words: forage grasses, climate change, winter survival, ice encasement, frost, CO2
Introduction
Climate change scenarios for Norway (RegClim, 2005; http://regclim.met.no) indicate that the
temperature will increase, especially in the winter (up to 3.5 C) and in the northern parts of
the country. There will be more frequent events of extreme precipitation, especially along the
coast, more precipitation as rain and less as snow, and more variable weather in general,
although the extent of variation is under debate. What will be the yields and winter
persistency of swards with perennial grasses in the future climate? In a comprehensive
research programme in Bioforsk, WINSUR, we are currently investigating the winter
persistency of timothy (Phleum pratense L.) and perennial ryegrass (Lolium perenne L.), two
important forage grasses with different growth strategies and winter hardiness, in the
predicted future climate. We summarize results from different experiments carried out in the
field and controlled environments.
Materials and methods
Two contrasting cultivars of timothy and two of perennial ryegrass were compared with
respect to growth and development of frost and ice encasement tolerance. The experimental
sites were Holt (69.65°N, 18.91°E), Kvithamar (63.49°N, 10.88°E), Fureneset (61.29°N,
5.04°E) and Særheim (58.76°N, 5.65°E). The effect of increased autumn temperature (ca. 2
C above the ambient temperature) and CO2 concentration (ca. + 170 ppm) on growth and
hardening was investigated in open top chambers at Særheim in 2005/2006 using pot grown
plants. The ambient daily mean temperature was 8 C for the period 1 September to 15
December. The development of frost tolerance was studied at Holt and Særheim in 2005/2006
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Abstract preview
EGF 2008
using pot grown plants with the pots placed close to each other in the field to mimic normal
sward conditions. There were 10 plants per pot and 20 pots per m2. Tillers were sampled at
various points in time to determine their frost tolerance which was expressed as LT50 (the
temperature below which at least 50% of the population was killed) (Larsen, 1978). The
simultaneous development of frost and ice encasement tolerance was studied at Holt,
Kvithamar and Særheim in 2006/2007 in field plots. To facilitate sampling in periods with
frozen soil, turfs for later sampling were dug up in the end of autumn and placed in growth
containers (30 cm x 40 cm x 17 cm) adjacent to the field (Holt) or placed back in their
original position in the field with a 3 mm felt underneath (Kvithamar). At Særheim, all
sampling could be done directly in the field due to limited soil frost. Tillers were sampled to
determine their frost tolerance (as described above) together with their ice encasement
tolerance which was expressed as LD50 (the number of days required to kill 50% of the
population when the tillers were completely encapsulated in ice and stored in darkness at
-2 C) (Gudleifsson and Björnsson, 1989). A dehardening experiment was carried out at Holt
in 2006. Plants grown outdoors in pots were brought indoors in January, tested for LT50 and
grown in a phytothrone at different temperatures for subsequent LT50 tests. The day length
was 12 h. All the LT50 and LD50 values presented were estimated using probit analysis.
Results and discussion
Increased CO2 concentration stimulated the accumulation of biomass in autumn (total dry
weight above ground 18.5 and 22.6 g pot-1 at ambient and elevated CO2, respectively, on 21
November; P<0.05) but had no effect on the frost tolerance (average LT50 -12.2 C on 15
December) or the density of tillers in spring (average 123 pot-1 on 6 April). There was no
interaction between CO2 and temperature for any parameter. In a corresponding experiment
carried out at the same location in a previous year, there was similarly no effect of CO2 on the
frost tolerance of winter wheat (Mortensen and Hanslin, 2007).
Increased autumn temperature, on the other hand, delayed hardening and reduced the frost
tolerance. This was evident both in the open top chamber experiment at Særheim, although
the effect was modest (LT50 on 15 Dec. -12.7 and -11.7 C at ambient and high temperature,
respectively, P<0.05) and when comparing the development of frost tolerance in plants grown
outdoors under contrasting weather conditions (Table 1).
Table 1. Frost tolerance (LT50; C) in timothy and perennial ryegrass at the end of
November/beginning of December, together with the autumn temperature (daily mean air temperature
in the previous month,C ). Averages for two cultivars of each species are given. 95% Feducial limits
for LT50 were within ±1 C except for the ryegrass at Holt in 2005 (±2 C).
Year
2005
2006
Holt
Autumn temp.
5.6
2.3
LT50 timothy
-17.4
<-20
LT50 ryegrass
-10.8
<-17
Særheim
Autumn temp.
5.8
7.4
LT50 timothy
-19.9
-17.6
LT50 ryegrass
-12.2
-9.8
Thus, unusually mild autumn conditions led to poorer frost tolerance at Holt in 2005 than in
2006 when the conditions were more normal (colder). Similarly, at Særheim the poorest frost
tolerance was obtained after the warmest autumn (2006). At the same time, it is evident that
other factors also play a role in the development of frost tolerance. Differences in day length
and radiation during the autumn most likely contributed to the differing results between Holt
and Særheim. The presence or absence of snow modifying the conditions around the apex is
also an important factor for frost hardening. Mild weather in mid-winter may melt the snow
and promote dehardening. Plants at Holt transferred from the field to a phytotrone with
temperatures between 3 and 9 C in January 2007 dehardened rapidly (Table 2).
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EGF 2008
Table 2. Frost tolerance (LT50, C) in two timothy cultivars in the field and one week after they had
been transfer to a phytothrone and subjected to three different growing temperatures. The upper and
lower 95% Feducial limits of the LT50 values are presented in brackets.
Engmo
Gindstad
In the field
-26.0 (-23.9/-30.4)
-15.5 (-13.6/-16.7)
One week after transfer to phytothrone at
+3 C
+6 C
-17.6 (-16.9/-18.3)
-15.6 (-14.9/-16.4)
-14.2 (-13.2/-15.6)
-12.0 (-11.2/-12.8)
+9 C
-14.7 (-14.0/-15.4)
-8.6 (-7.4/-9.6)
Substantial dehardening was observed even at the lowest growing temperature 3 C. Both
ryegrass cultivars similarly dehardened rapidly (data not shown). The results confirm earlier
findings (Jørgensen et al., 2006) and suggest that rapid hardening may occur in periods of
mild weather, even in mid-winter, and that northern, winter-hardy cultivars like Engmo may
be as prone to dehardening as less winter-hardy cultivars like Grindstad.
There was a large genetic variation in frost tolerance. The lowest LT50 value observed in the
different experiments together was -27, - 23, -18, and was -16 C for Engmo, Grindstad,
Riikka and Gunne, respectively. There was similarly a large variation in ice encasement
tolerance, with Engmo reaching a maximum LD50 greater than 9 weeks, followed by 7, 3 and
2 weeks for Grindstad, Riikka, and Gunne, respectively. Furthermore, LD50 varied between
locations and time of season (Table 3), generally with the highest values at Holt and the
lowest at Særheim. The LD50 values were highly correlated with the LT50 values measured
at the onset of ice encasement. Since the LT50 can be modelled with good precision, the close
correlation may facilitate modelling of LD50 and ice encasement injury.
Table 3. Ice encasement tolerance (LD50; days) in Grindstad timothy and Gunne perennial ryegrass at
three different locations in 2006/2007. 95% Feducial limits for LD50 were within ±2 days for ryegrass
and ±3 days for timothy except for at Særheim in March (±8 days).
Location
Holt
Kvithamar
Særheim
Timothy
December
>44
41
35
January
46
41
30
March
32
29
30
Ryegrass
December
14
9
10
January
15
>12
<4
March
11
8
n.a.
Conclusions
The predicted temperature increase in autumn temperatures will delay the hardening and
reduce the frost tolerance of the genotypes presently grown. Increased CO2 concentration in
the atmosphere will have limited effect on frost hardening. Rapid dehardening may occur as a
result of mild weather in mid-winter, even in winter-hardy cultivars of northern origin.
Modelling work is in progress that will give more detailed estimates of how timothy and
perennial ryegrass will perform in the future winter climate.
References
Gudleifsson B. and Björnsson H. (1989) Methods for estimating ice encasement tolerance of grasses in the
laboratory. Icelandic Agricultural Sciences, 2, 99-103.
Jørgensen M, Østrem L. and Höglind M. (2006) Dehardening in timothy and perennial ryegrass during winter
and spring. Proceedings of NJF Seminar 384 10-12 August 2006, Akureyri, Iceland. Agricultural University of
Iceland, AUI Publication 10, pp. 111-114.
Larsen A. (1978) Freezing tolerance in grasses. Methods for testing in controlled environments. Meld. Norges
Landbrukshøgskole, 57, 56pp.
Mortensen L. and Hanslin HM. (2007) Effekter av klimaendring på høsttilvekst og overvintring: Hvete. Bioforsk
Fokus, 1, 28-29.
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