climate change has been a public discussion topic for several years. It is
difficult to predict changes in climate and sea level due to the enhancement of
the so-called greenhouse effect (including temperature rise, CO2
increase, and nitrogen deposition) but atmospheric CO2 concentration
is measurably increasing and is expected to double current levels during the
next century with marked effects on current agroclimatic conditions. Man has
effectively accelerated global respiration about 10 million! times by the
combustion of several billion years worth of accumulated photosynthate and
other organic carbon in the course of a few hundred years. Aside global
warming, shifts in rates and distribution of precipitation and increases in
surface level ultraviolet (UV)-B radiation due to a depletion of the
stratospheric ozone layer are among the likely alterations. Since actions and
interactions of climatic factors and man-induced changes in for instance
vegetation structure are very complex and oceans can act as large buffers on
more radical short-term (years) changes, there is great uncertainty about what
to expect over the next century. In contrast to research on natural terrestrial
ecosystems and some agricultural crops, possible effects of a change in climate
on grapevines have largely been ignored.
Possible consequences of increased
temperature and altered precipitation patterns on Viticulture in Europe
several simulation models, it is generally agreed that global mean surface
temperature could rise between 1–4,5 °C depending on the future development of
industrial emissions with a best estimate of a near 1,8–2,5 °C warming by the
middle of the next century (Carter et al., 1991,
Intergovernmental panels on climate change (IPCC) 1992, 1994, 1998, 2001).
An increase in temperature of this magnitude in Europe would have profound
effects on Viticulture.
current temperature development in the northern hemisphere clearly shows a
gradual warming trend in all seasons (fig.
1), especially over the last twenty years (Jones et
al., 2001). This warming has been less pronounced than that in the
southern hemisphere over the same time period. However, global circulation
models (GCM) currently predict a more rapid warming in the northern hemisphere
over the next 50 years (Evans, 1996). This would
considerably change the margins of suitability for grape growing shifting the
northern boundary for Viticulture under this scenario on the order of 10–30 km
per decade up to 2020 with a predicted doubling of this rate between 2020 and
2050 (Kenny and Harrison, 1993). This would also
profoundly change the distribution of suitable varieties within Europe.
Calculations using the Huglin climate index classification (Huglin,
1986) for varietal suitability in Geisenheim, Germany (50 ° latitude North)
shows that Riesling, Pinot gris and Pinot noir are suitable cultivars for this
location (fig. 2) based on the
average climatic conditions over the past 30 years. If suitability would be
based on the average temperature development over the next 50 years, cultivars
such as Merlot or Cabernet franc become a possible choice (fig. 2). The warming trend can also be
demonstrated through the large decrease in the frequency of autumn (October)
frost events over the past 100 years (Hoppmann and Hüster,
1988). Indirect estimates of the growth of terrestrial vegetation by use of
satellite data from measurements of the normalised difference vegetation index
(NDVI) have recently confirmed that plant growth and growing season length is
significantly increasing especially in the northern high latitudes (> 45 °N)
(Myneni et al., 1997).
to global warming are predictions on altered (annual, seasonal) precipitation
patterns. For central Europe higher incidence of strong precipitation events in
winter, higher frequency of extreme temperatures and less precipitation in
summer are among the expected effects (Schönwiese and Rapp,
1997). Significant changes have already occurred over all continents and
are predicted to continue based on GCMs for a doubling in CO2
concentration (Hulme et al., 1992). Even if actual precipitation
rates and/or their distribution would be unaffected, water evaporation rates
will increase due to higher surface temperatures of oceans and land masses. For
land masses, changes in evaporation rates may reduce soil moisture on the long
term. Some earlier predictions estimated 20-30% reduction in soil moisture in
northern Europe, 30 to 50% in western Europe, 20 to 40% in central Europe, 20
to 30% for most of the Mediterranean region and even more for the Iberian
peninsula (Stigliani and Salomons, 1992) but these
estimates have been doubted recently based on past and current climatic trends (Schönwiese and Rapp, 1997). The impact on Viticulture and
the socio-economic consequences would nevertheless be dramatic, especially in
southern Europe where water is a scarce resource and irrigation is often not
possible. Predictions based on past climatic trends between 1960 and 1990 (not
models) show that coastal regions and western Europe in general will receive
more precipitation in winter (fig. 3)
but less in summer (fig. 4),
but these scenarios are not uniform over Europe.
precipitation patterns may necessitate introduction of cover crops over winter
in order to minimise soil erosion and to maximise water and nutrient storage. Favis-Mortlock (1994)
has shown that an increase in 8-15% rainfall in winter will increase erosion
by 27 to 35%. On the other hand, higher frequency of extreme temperatures in
summer will automatically lead to increased evapo-transpiration and, coupled
with reduced precipitation in summer rainfall areas, may render full or partial
use of cover crops impossible in countries such as Germany, Switzerland, or
northern Italy where this is currently common practice. In recent years,
off-flavour problems in white wine have been linked to competition problems for
water and nitrogen between cover crop and grapevines in dry years (Rapp et al., 1993). However, soil erosion and
nitrogen leaching coupled to reduced water quality for human consumption may
preclude going back to clean cultivation. In other viticultural areas with no
summer rain, like the ‘La Mancha’ area south of Madrid in Spain, soil tillage
systems also may have to be changed completely. Common practice in these and
other comparable regions in Europe is very frequent tillage to avoid capillary
rise of water from deeper soil layers and subsequent unproductive evaporation,
yet at low soil water content going to a no-tillage system may actually
conserve more water.
soil water is not the only ‘soil’-parameter affected through changes in
temperature and precipitation. Soil respiration is positively correlated with
an increase in these variables and soil organic matter content will be altered
in the long term and may require different ways of soil management practices.
Higher winter temperatures coupled with higher relative precipitation in winter
as compared to summer will cause large increases in organic matter decay rates.
It must also be kept in mind, that concomitantly to the increase in ambient
temperature and CO2, some sources predict a large additional deposition
of nitrogen, particular in the northern hemisphere.
Influence of elevated
carbon dioxide concentration
the CO2 concentration may have been close to 20 times the current
level at certain times in earth’s history, it remained relatively stable at
around 270 ppm over the last 5 centuries (Ehleringer and
Cerling, 1995), beginning to rise only after the industrial revolution when
human caused CO2 release became significant. The oldest continuous
record of direct measurements of CO2 comes from the top of Mauna
Loa, Hawaii, which started in 1957 (fig.
5A). The current level of near 370 ppm is more than 30% higher since
the industrial revolution 200 years ago and nearly 20% higher since direct
measurements began (fig. 5A).
Fossil fuel consumption will further increase through the increase in world
population, land use, and higher energy consumption per capita. Currently, a
person in the United States of America, on average, uses 22 tons of carbon per
year, whereas a person in India, for example, uses only 0.7 tons of carbon per
year (Bazzaz, 1998), yet it is the developing nations who
will contribute dramatically to future CO2 emissions through their
development (for a complete list see internet data bank of Carbon Dioxide
Information Analysis Centre at Oak
Ridge National Laboratory, Tennessee, USA). The global increase in CO2
is thought to occur much faster than plants are capable of genetically adapting
to the change and photosynthesis will inevitably be affected. Predictions of
how much atmospheric CO2 concentration will rise during the next
century differ between different model analyses but most agree on an
approximate doubling by the end of this century (fig. 5B), with some scientists
speculating that atmospheric CO2 concentration could actually exceed
1000 ppm (Bazzaz, 1998). The direct response of
grapevines to a rise in CO2 concentration seems to be similar to the
results obtained in most of the studies conducted on annual and perennial
plants, where an increase in net photosynthesis, biomass, crop yield, light
–nutrient– and water-use efficiency is found (Bindi et
al., 1996a). In the short term, photosynthesis and water-use efficiency
(ratio of photosynthesis to water consumption) is stimulated by increased CO2
(Schultz, 2000).Grapes grown in arid regions like Spain
may therefore be expected to benefit from increased CO2 and may be
able to at least partly overcome some of the adverse conditions created by
increases in likelyhood and severity of drought events. But on the whole plant
level, long term elevated CO2 exposure may have very different
effects. The initial increase in photosynthesis may be partly or completely
down-regulated if sinks for the manufactured photosynthate are not sufficient
so that over a period of days, weeks or months of growth in elevated CO2,
the acclimation response may be substantial enough that the photosynthetic
rates of plants grown and measured in elevated CO2 may even become
equal to those grown at current ambient concentrations (Bazzaz,
regulation at the biochemical, physiological and the molecular level of
photosynthesis, and judging from the large differences in vegetative and
reproductive development between grape cultivars (Champagnol,
1984), it is likely that sink size and activity will largely affect the
responses of different varieties to elevated CO2. Bindi et al. (1996a) in
a study using a FACE-system (free air carbon dioxide enrichment in the field)
with the variety Sangiovese over several months, found a stronger increase in
leaf area (+ 35%) and vegetative dry weight (+ 49%), than in reproductive dry
weight (+21%) when CO2 concentration was increased to 700 ppm. The
increase in vegetative dry matter was confirmed when simultaneous changes in
temperature and solar radiation were additionally considered in running several
climate change scenarios and GCMs, but yield response was negative in most
cases and more so for Cabernet Sauvignon than for Sangiovese (Bindi
et al., 1996b). Faster development of larger leaf areas may in turn
have important consequences for water consumption and canopy management, which
just points to the difficulty in predicting the combined action of several
changing environmental factors.
Can increasing Ultraviolet radiation levels affect
grapevine physiology and grape composition?
UV-B radiation can be damaging for terrestrial organisms. The UV-B wavelength
band ranges from 280 nm to 320 nm, though only wavelengths greater than 290 nm
can reach the Earth’s surface. In sunlight, the ratio of UV-B to
photosynthetically active radiation (PAR; 400-700 nm) fluctuates, primarily
caused by changes in solar angle and thickness of the ozone layer. Depletion of
the ozone layer results from emissions of halogenated chemicals, such as
chlorofluorocarbons (also called halocarbons) and decreases the effectiveness
for UV-B screening (Tevini, 1996). Stratospheric ozone
levels are near their lowest point since measurements began. Changes over the
past decades are difficult to quantify because of lack of suitable historical
data. Estimates range from an average increase of about 8% per decade (Blumthaler and Ambach, 1990) at high altitudes to 4-7%
since 1970 for the Northern Hemisphere and 130% for the Antarctica in spring (Madronich et al., 1998). However, the temporal and
spatial variation due to cloud cover, atmospheric pollutants and surface albedo
is very large. Based on satellite observations monthly deviations from these
mean values can reach up to near +40% under clear sky conditions for latitudes
between the 30th and 50th degree North (McPeters
et al., 1996), where almost all grapes are grown in Europe.
Additionally, seasonal fluctuations may largely exceed the average increase in
UV-radiation and are likely to cause significant biological damage.
UV-B can be damaging to terrestrial organisms including plants and microbes,
but these organisms also have protective and repair mechanisms. The impact of
UV-B on the morphological, physiological and biochemical features of higher plants
has been extensively studied and foremost decreases of leaf expansion (Tevini and Teramura, 1989), fresh and dry weight, total
biomass and photosynthetic capacity have been noted (Krupa
and Jäger, 1996). UV-B responses
may not remain instantaneous and effects could accumulate from year to year in
long-lived perennial plants such as trees (Madronich et
al., 1998) and thus there is a chance that this may also occur in grapevines.
in UV-absorbing compounds seem to be a general reaction to increased UV-B
radiation (Tevini, 1996; Jansen et al., 1998). The
stimulation of these compounds is primarily intended to reduce UV-radiation
penetration into plants and other organisms. For instance the formation of
yellow and red pigments has been shown to significantly reduce the penetration
of UV-light into nectarine fruit (Blanke, 1996). Some
key-enzymes involved in flavonoid biosynthesis (chalcone synthase) and the
phenyl-propanoid pathway (phenylalanine ammonium-lyase) have been shown to be
upregulated by UV-radiation, as are levels of key antioxidants glutathione and
ascorbate (Jansen et al., 1998), whereas
carotenoid pigment formation and the incorporation of nitrogen into amino acids
(AA) can be inhibited (Döhler et al., 1995; Jansen et
al., 1998). Since components such as flavonoids, amino acids and
carotenoids are important constituents of grapes with a marked effect on
flavour development, some influence of UV-B radiation on grape composition can
be expected (Schultz et al., 1998) (table 1).
Table 1 Some known effects of UV-B radiation and their
possible relevance for grape production
Possible relevance for grape
• activation of genes of the phytopropanoid pathway
– accumulation of flavonoids and anthocyanins (colour
formation, wine composition)
• inactivation (damage) of photosystem II and of
– decreased photosynthesis
• reduced chlorophyll and
– decreased photosynthesis,
– altered aroma compounds?
1,1,6-trimethyl-1,2-dihydronaphtalene, TDN, ß-damascenone)?
– xanthophylls, leaf and berry energy balance?
• effects on nitrogen metabolism (via carbon supply
or direct effects on key enzymes)
– decreased amino acid concentration (yeast
metabolism, fermentation kinetics, higher alcohol formation, secondary aromatic
• thicker leaves, wax
• photo-oxidation of indole acetic acid (IAA,
auxin), UV-B absorption by tryptophan
– possible formation of o-aminoacetophenone (off-flavour in white wines)
• increase in ascorbic acid and glutathione content
through the formation of free radicals
– photoprotection, sulfur metabolism, induction of
enzyme activities (important for yeast metabolism)?
• flowering and phenology
– may be affected in some varieties
• alterations in soil
microflora and fauna
– nutrient availability
on the molecular level, UV-B can destruct peptides and lipids and can
photo-degrade the plant hormone auxin which absorbs in the UV-B range and may
play a significant role in the formation of an off-flavour in white wines
increasingly found over the last decade in Central Europe (Geßner
et al., 1999) (table 1).
In a field
trial with different levels of UV-radiation we found both amino acid (AA) and carotenoid
concentration at harvest to be substantially reduced under current level
ambient UV-B radiation in berry skins of the cultivar White Riesling (Schultz et al., 1998). Additionally, AA composition
was altered under UV-B radiation, exhibiting lower levels of arginine and
glutamine, the main sources of AA for yeast metabolism. Several authors
suggested that the difference between the carotenoid level at the onset of
ripening and that at harvest indicates the formation of norisoprenoids (Razungles et al., 1993; Bureau et al., 1998).
These compounds have been linked to the ageing flavour of wines (vitispirane,
1,1,6-trimethyl-1,2-dihydronaphtalene, TDN) and the fruity character of must
and wine (damascenone). Thus the response to UV-light may not be exclusively
negative, but our current knowledge on this subject is still very limited. The
great challenge in the future will be to predict the responses of grapevines to
simultaneously changing climatic components and to develop adequate strategies
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