The contribution of Portuguese agriculture to the climate change,

mitigation and adaptation strategies for the sector

CORINA CARRANCA

INRB, I.P./INIA Unidade de Ambiente e Recursos Naturais

Quinta do Marquês, Av. República, Nova Oeiras, 2784-505 Oeiras CEER, Instituto Superior de Agronomia, Tapada da Ajuda, 1349-017 Lisboa

PORTUGAL e.mail: corina.carranca@inrb.pt

Abstract: - Agriculture in Portugal contributes for less than 10% of total greenhouse gas (GHGs) emissions, where 34% comes from methane (CH4) in animal husbandry, 64% comes from nitrogen (N) oxides (NOx and N2O) by the intensive use of mineral fertilizers, the incomplete nitrification and denitrification processes, the waterlogged rice fields, the addition of organic compounds to the soil, the drip fertigation, the N2 fixation by legumes, particularly, the pastures, and the sediments, by the alternate wetting and drying processes and the presence of soil organisms such as worms. Animal husbandry is the main responsible (71%) for total emission coming from agriculture, particularly the dairy cows housed. Methane emissions from the animal housing are mainly caused by enteric fermentation. During storage and after spreading of farmyard manure in the soil substantial differences concerning CH4 and N2O emissions occur with composted and anaerobically stacked farmyard manure. In agriculture, forests are the main responsible for CO2 emission (4 Mt CO2 equivalent year-

1) by the respiration process, and the double amount can be reached in presence of fires. However, forests have an important role on CO2 capture during the photosynthetic process, by C accumulation in the plant biomass and soil organic matter. The Portuguese forest can sequester about 80 t CO2 ha-1 year-1 and contributed to about 18% of C sequestration in 2010. The eucalyptus has a very efficient capacity to use water and nutrients and can accumulate C in the biomass and soil more efficiently than other plant species in temperate climate. Microbial activity is also responsible for CO2 emissions, particularly under soil disturbance. This is the case of pastures conversion to annual crops. On the other hand, if soil conservation practices have been used, such as for permanent pastures, C sequestration in the soil is appreciable. “Montado” is a Portuguese extensive farming system consisting of cork and holms-oak trees, several shrubs and improved pastures. This is a very sustainable agricultural system where pasture may consist of biodiverse crops with more than twenty species and include several legumes. They can sequester more than 4 t C ha-1 year-1, particularly in the soil since the crops are used for animal feeding (-4.5 t C km−2 year-1). Supposing an increase from 10 to 30 g organic matter kg-1 soil, an accumulation of 33 t C ha-1 in a 15 cm layer is expected, corresponding to a sequestration of the order of 128 t CO2 ha-1. These data show that 200,000 ha of permanent pastures will largely meet the Kyoto Protocol Commitment (1997). About 80% of cultivated plants can be associated with mycorrhizal soil fungi. This symbiosis allows a better performance and health for most efficiently mycorrhized plants, particularly under biotic and abiotic stress, such as drought, high temperatures, saline and contaminants. These plants can capture more CO2 from the atmosphere by the photosynthetic process, producing higher levels of photo assimilates which are exuded by the roots enriching the mycorrhizosphere and contributing for the C sequestration. Key-Words: -arable crop, forest, greenhouse gases, impact, modeling, nutrient and water use efficiency, productivity, rainfall, soil microbial diversity, temperature.

1 Introduction Climate change variables including precipitation (amount and distribution), temperature and atmospheric carbon dioxide (CO2) concentration are expected to alter agricultural productivity pattern worldwide. Carbon is a plant nutrient and CO2 atmospheric enrichment has the potential to enhance plant productivity through the photosynthetic process. Higher global temperatures and altered precipitation patterns are expected to accompany the higher CO2 levels and these factors may lessen or negate any production (Brouder and Volenec, 2008). The chemical transformations of

atmospheric pollutants such as volatile organic compounds (VOCs), nitrogen oxides (NOx) and other ozone (O3) precursors must also be investigated to better understand, in the light of climate change, the continuously increasing of O3

background concentrations and the contribution from changing biogenic and anthropogenic sources. Concomitant increases in the biogenic gases methane (CH4) and NOx have been observed (Brouder and Volenec, 2008). Extreme events have been registered worldwide, namely the high temperatures, water deficit and fires in Russia, the intensive rainfall events in central and east Europe,

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the floods in India and Pakistan, and the landslides in China.

The actual main challenge is to attack the origin of the problem (mitigation), i.e., to reduce the anthropogenic greenhouse gases (GHGs) emissions and prepare the society for the biophysics and socio-economic impacts of climate change (adaptation). European Union (EU) defined climate change as a priority area for research, innovation and development in agriculture. European Union put emphasis on prediction of climate ecological, earth and ocean systems changes, on tools and on technologies for monitoring, preventing and mitigating of environmental pressures, risks including on health and for the sustainability of the natural and man-made environment, and adaptation strategies. Models should include climate projections, the hydrological and biogeochemical cycles, the stratosphere and troposphere chemical interactions, the interactions between climate and aerosols, the representation of land surface processes, the interactions between climate and ecosystems, the improvement of the representation of cryospheric processes, the sea level change, critical processes in ocean and atmosphere interactions, and the reduction of bias corrections at the interface between regional climate models and climate impact models.

Studies on global climate change and mineral nutrition remain relatively sparse, with nitrogen (N) being the primary focus of research. Existing literature reviews have examined N and climate change emphasizing the soil biodiversity (Swift et al., 1998; Chapin, 2003; Carranca et al., 2009a,b), water cycling (Pendall et al., 2004; Gonçalves et al., 2006), root uptake kinetics (BassiriRad, 2000) and soil C/N cycling in extreme environments (Hobbie et al., 2002). The potential for global climate change factors to influence the physiological use efficiency of plant nutrient and nutrient availability and transport through soil and across root membranes are new questions addressed. Experimentation has not found conclusive evidence that physiological plant nutrient use efficiency is altered in high CO2 environments (Brouder and Volenec, 2008).

Research should explore the stress on vegetation and the impact on biomass including soil organic matter (OM). Scientifically sound thresholds for protecting plant ecosystems, as well as soil biota from atmospheric pollutants and for maintaining productivity and the carbon (C) sink strength should be developed.

Schulp et al. (2008) estimated that the EU-27 will sequester 90-111 Tg C year−1 in 2030, in the terrestrial biosphere. In three of the four scenarios used in the Land Use Change (LUC) model, they found that net C sequestration will increase, mainly due to a decrease in cropland area.

1.1 Greenhouse gases and climate change

The current concentrations of GHGs are believed to have already altered global climate and there is some evidence that warming has negatively impacted crop yield. The rate of increase in GHGs concentrations is expected to accelerate and a CO2 level of 550 µmol mol-1 can be reached by 2050 (Raven and Karley, 2006). Likewise, rate of increase in temperature within the next century is supposed to be markedly higher than the changes that occurred in the past. It is advisable to stabilize the CO2 concentration at a maximum of 500 µmol mol-1 in order to stabilize the global temperature rise at 2–3 ºC during the XXI century.

Temperature records from the northern hemisphere showed a temperature rise of approximately 0.6 ºC within a 150-year period (Mann et al., 1998; Brouder and Volenec, 2008). In the XX century, mean air temperature in Portugal showed three patterns of variation: an elevation in the 1910-1945 period, followed by a reduction by 1946-1975, and a more accelerated increase in the 1976-2000 period. In the last period of this century, the minimum temperatures have risen, reducing the temperature range. In this period, mean temperature in the Iberian Peninsula increased by 1 ºC. In the Portuguese continent, rainfall decreased in February and March.

Schlenker et al. (2006) reported that temperature will increase from 2.0 to 2.4 ºC between 2020 and 2049 in USA relatively to the present conditions, and can dramatically increase (3.6 to 7.4 ºC) between 2070 and 2099. According to Southworth et al. (2000), the mean annual global surface temperature is projected to increase 1-3.5 ºC by 2100, but unlike CO2 the magnitude of temperature increase will vary regionally and will be accompanied by altered precipitation pattern (Brouder and Volenec, 2008).

SIAM, SIAM II and CLIMAAT II Portuguese models for climate change for the 2080-2100 period estimated a significant increase in the mean air temperature, with an increase of about 4 ºC for the maximum temperature in summer in coastal areas and 7 ºC in the interior, and an increase of heat waves frequency and intensity, fire risks, and land-use changes. Precipitation in the mainland will be reduced by 100 mm, especially in spring, summer and autumn, with an increase in winter. In Madeira and Azores islands, temperature will increase more moderately (1-3 ºC).

Temperature has been considered as an important ecological factor that determines a variety of structural and functional characteristics in managed and natural ecosystems, but the exact mechanism for temperature-induced changes in nutrient uptake capacity is not clearly understood (BrassiriRad, 2000). Potentially, if soils warm as a result of climate change, maintenance costs of roots and nutrient availability may increase and

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contribute to higher rates of root turnover, which is a strong nutrient sink for most plants, except the annual crops where root turnover is not an important issue even in a CO2 enriched atmosphere (Gill and Jackson, 2000; Norby and Jackson, 2000).

Across Europe, average wheat (Triticum aestivum L.) yields have markedly increased since the early 1960s, but rates of increase have been slower in southern countries (e.g. Portugal and Spain) when compared with the United Kingdom and France reflecting the impact of the warming and drought since the 1990s (Schär et al., 2004; Brouder and Volenec, 2008).

IPPC (2007) identified the Mediterranean region and south Europe in particular, as one of the most vulnerable regions to climatic change, with high temperatures, water deficit, lower crop productivity, higher forest fires frequency, and higher incidence of human diseases caused by the heat waves. Such changes will have marked effects on soil biology including plant growth and physiological characteristics (shoots and roots).

Droughts are increasingly being observed in many regions of Europe, requiring innovative science-based approaches to evaluate the complexity of environmental and socio-economic impacts and people's vulnerability. In the European context, it is essential to improve the understanding of drought processes and occurrences, develop innovative drought indicators and methodologies for reducing and monitoring the vulnerability of drought-related risks and their impacts to society and the environment, in particular in water stressed areas, and modeling, forecasting and monitoring, taking into considerations different European geo-climatic regions.

The first objective of EU policy for climate change is, through research, to provide integrated solutions for action on mitigation of, and adaptation to climate change in order to respond to global challenges and the EU's ambitious commitment to combating climate change. Research will improve the estimation of impacts and provide scientific and policy advice on mitigation and adaptation options. Land-use and forestry changes, as well as urban areas and coastal zones will be studied for adaptation needs.

The second EU’s objective, again through research, is to support eco-innovation for eco-efficiency in society. The transformation to sustainable societies implies the development and availability of technologies, products and services that help to minimize the environmental "footprint" of all human activities through energy and resource efficiency.

The third EU’s objective, still through research, is to provide a systemic approach for governance in a changing environment. A transition towards economic and environmental sustainability

must involve the whole society and requires a coordinated strategy in Europe.

2 The contribution of Portuguese

agriculture to mitigation Mitigation is the process to reduce or eliminate the causes of climate change. The Portuguese Program for Climatic Changes (PNAC) established a 52% reduction of CO2 emission of anthropogenic origin (1.1 Mt CO2) by 2010 comparing to 1990, but this objective was not fulfilled. The new challenge is to reduce anthropogenic CO2 emission by 40% in 2020 (Carranca, 2010).

The Portuguese agriculture is conditioned by European Common Agriculture Policy (CAP), which integrates environmental protection, potential areas for agriculture, and farmers’ income and economic welfare. It contributes for less than 10% of total GHGs emissions (2% by excluding the agro-industry), where 34% comes from CH4 in animal husbandry, and 64% from N oxides (NOx and N2O) by the intensive use of mineral fertilizers, the incomplete nitrification and denitrification processes, the waterlogged rice fields, the addition of organic compounds to the soil, the drip fertigation, the N2 fixation by legumes, particularly the pastures, animal husbandry, and the sediments, by the alternate wetting and drying processes and the presence of soil organisms such as worms (Carranca, 2010).

Animal husbandry is the main responsible (71%) of total emissions coming from agriculture, mainly as CH4, particularly from the dairy cows housed, but also by direct grazing. Methane emission from the animal housing is mainly caused by enteric fermentation. Feed additives can alter rumen environment, potentially changing the end products of fermentation. During storage and after spreading of farmyard manure in the soil, substantial differences concerning CH4 and NO+N2O emissions occur with composted and anaerobically stacked farmyard manure.

Studies on GHGs (NOx, CH4, VOCs) fluxes from paddy rice fields in Portugal have been run for mitigation and to establish good agricultural practices.

In agriculture, forests are the main responsible for CO2 emission (4 Mt CO2 equivalent year-1) by the respiration process. The double amount can be reached in presence of fires.

Portuguese forests occupy 38% of total area (Fig. 1), where most part (85%) is private, 3% is public and 12% belongs to the local communities. Eucalyptus stands (E. globulus L.) represent 21% of the total forest area and CO2 emission can amount to 67 kt CO2 year-1 (Dias et al., 2007). Portugal made the commitment of reducing total CO2 emission by 7.6-8.8 Mt by 2012.

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However, forests have an important role on CO2 capture during the photosynthetic process and C accumulation in the plant biomass and soil OM (mitigation). The Portuguese forest can sequester about 80 t CO2 ha-1 year-1 and contributed to about 18% of C sequestration by 2010 (Carranca, 2010).

Fig. 1. Evolution of Portuguese forest in the mainland (103 ha) (Source: MADRP, 2007).

The eucalyptus has a very efficient capacity to use water and nutrients and can accumulate C in the biomass and soil more efficiently than other plant species in temperate climate (Alves et al., 2007; Carranca, 2010). In the soil, the C content is higher than in oak (Quercus sp.) soils, although the degree of humification is similar (Madeira, 1986; Madeira et al., 1989; Carranca, 2010). However, the presence of humic and fulvic acids is higher in eucalyptus soils (42%) comparing to other tree species (29-32%).

Eucalyptus forms endo- and ectomycorrhiza. A few plant genera are able to support both mycorrhizal types and give the tree the high efficiency for water and nutrient absorption. Arbuscular mycorrhizal (endo-) produces glomalin (a heat-stable hydrophobic glycoprotein which prevents the fungi hyphae from desiccating) that gives a better soil structure and enriches the soil C pool (glomalin contains 30-40% C). This protein lasts for years in the soil and may be in the slow or recalcitrant soil C fraction (Rillig et al., 2003). Pools of glomalin are responsive, even in the short-term, to ecosystem perturbation, such as elevated atmospheric CO2 concentrations, warming, and various agricultural management practices and can be used as a soil quality indicator (Rillig et al., 2003). Ectomycorrhiza also probably influences the soil aggregate stability by their ability to produce hydrophobin (cystein enriched proteins expressed only by filamentous fungi). They form a hydrophobic coating on a surface.

“Montado” is an extensive agro-forest farming system at south Portugal consisting of cork and holms-oak trees, several shrubs and natural or improved pastures (Fig. 2). This is a very sustainable agricultural system where the improved pastures may consist of biodiverse pastures with

more than twenty crop species, including several legumes.

Fig. 2. A partial view of the extensive agricultural system “montado” (oak and pasture), in Portugal.

This system can sequester more than 4 t C ha-1 year-1, particularly in the soil, since pastures are used for animal feeding (-4.5 t C km−2 year-1, indicating the crop removal) (Schulp et al., 2008; Carranca, 2010; Carranca et al., 2010). Supposing an increase from 10 to 30 g OM kg-1 soil by converting the natural pasture into improved pasture, an accumulation of 33 t C ha-1 in a 15 cm layer is expected, corresponding to a sequestration of 128 t CO2 ha-1 (Carranca, 2010). These data show that 200,000 ha of permanent improved pastures would largely meet the Kyoto Protocol Commitment (1997) in Portugal.

Microbial activity in soil is responsible for CO2 emission by respiration, particularly under soil disturbance. This is particularly relevant in the case of conversion of forests to pastures or croplands, or pastures conversion to arable land. The increase of winter temperature in south Europe will also increase soil microbial respiration thus reducing sequestered C and increasing the CO2 emission. Soil conservation practices used, for instance, for permanent pastures, will sequester appreciable amounts of C in soil (mitigation practice).

Legumes are important crops in Mediterranean regions and can fix most plant N from the atmosphere through the symbiotic process with the generically called Rhizobium bacteria. Atmospheric N2 is a renewable resource and its use in the symbiosis for bacteria to obtain energy acts as an indirect clean energy source, reducing the use of mineral N fertilizer on legume nutrition and the use of fossil energy for processing mineral fertilizers. Legumes are recommended crops for intercropping with non-legumes such as grasses, fruit and olive trees, vineyards, pastures and forests since they transfer nutrients to the non-legumes.

Symbiosis efficiency is improved in mycorrhized host plants. If both legume and non-legume plants show mycorrhizal hyphae, a strong contribution to C sequestration in the soil can occur. About 80% of cultivated plants are colonized by mycorrhizal soil fungi [micorrhizal =

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myke (soil fungi) + rhiza (fine symbiosis is ubiquitous and allows a better performance and health for most plants, particularly under biotic and abiotic stresses such as drought, high temperature, saline and contaminantsand Carranca, 2010). Mycorrhized more CO2 from the atmosphere photosynthetic process (mitigation)higher levels of photo assimilates which are exuded by the roots to the soil enriching the mycorrhizosphere and contributing toC sequestration (mitigation) (Carranca, 2010)

Fig. 3. Root nutrient uptake in response to COconcentration and soil temperature BrassiriRad, 2000).

(larger picture can be found at the end of the article)

Fig. 3 shows the root nutrient uptake kinetics in function of CO2 concentration and soil temperature. BrassiriRad (2000) reported that plant N uptake response to elevated CO2 was more closely correlated with root physiology capacity under low N availability (mycorrhizal effect), but correlated more strongly with root biomass under relatively high N contMycorrhized plants are more efficient to absorb water and nutrients (Cruz and Carranca, 2010).

It is commonly accepted that an important determinant of plant and ecosystem responses to elevated CO2 concentrations is plant nutrientTherefore, knowledge on root characteristics that influence nutrient uptake and their response to the high CO2 concentrations is critical in accurately predicting the long-term plant and ecosystems responses to CO2 enrichment (BrassiriRad, 2000). Temperate grasslands allocate between 24% and 87% of net primary production belowground. In forests, belowground net primary productivity typically accounts for 30-50% of total net primary production (Gill and Jackson, 2000).the contribution of roots and mycorrhizal hiphae to soil OM and C sequestration. Mycorrhizal tissue

fine roots)]. This allows a better

performance and health for most plants, particularly such as drought,

high temperature, saline and contaminants (Cruz plants capture

from the atmosphere through the (mitigation), producing

higher levels of photo assimilates which are exuded enriching the to atmospheric

(Carranca, 2010).

in response to CO2 and soil temperature (Source:

(larger picture can be found at the end of the

oot nutrient uptake kinetics concentration and soil (2000) reported that plant

concentration was more closely correlated with root physiology capacity under low N availability (mycorrhizal effect), but correlated more strongly with root biomass under relatively high N content. Mycorrhized plants are more efficient to absorb water and nutrients (Cruz and Carranca, 2010).

It is commonly accepted that an important determinant of plant and ecosystem responses to

concentrations is plant nutrient status. root characteristics that

influence nutrient uptake and their response to the concentrations is critical in accurately

term plant and ecosystems enrichment (BrassiriRad, 2000).

Temperate grasslands allocate between 24% and 87% of net primary production belowground. In forests, belowground net primary productivity

total net primary production (Gill and Jackson, 2000). This shows

roots and mycorrhizal hiphae to Mycorrhizal tissue

comprises a substantial fraction of soil OM in many systems, and aspects of the biology and chemistry of mycorrhized hyphae can influence the C cycling in soil (Norby and Jackson, 2000; Carranca, 2010).

Farrar and Jones (2000) reported that the presence of higher COtemperature will produce bigger plants, with bigger root systems as a consequence of their size, but with little or no change in C partitioning t(Table 1). However, as these large plants have more demand for water and nutrients, and the soil is relatively depleted in these resources as a consequence, there will be more growth of (mycorrhized) roots relative to shoots directed by mechanisms as yet unknown, and if soil nutrients are low there might also be more exudation from roots and C transfer to mycorrhiza and the soil, but these effects of elevated CO Table 1. Growth and root metabolism of barley 14-days after germination under(Source: Farrar and Jones, 2000)

Variables

Dry weight (mg) Root weight ratio Rate of elongation of seminal axis (cm h−1) Number of nodal roots Rate of lateral root production (h−1) Carbohydrate content of seminal axes (mg g−1

FW) Respiration of seminal axes (nmol g−1 s−1) Carbohydrate content of root tips (mg g−1

FW) Respiration of root tips (pmol per tip s−1) FW=fresh weight.

Trees with reduced absorbing a great potential for efficientfungi. This is the case of ‘Rangpur’ rootstockcitrus, which is the most used its great potential to support drought stress.

The main factors that affect mycorrefficiency are plant type and abundance and diversity of soil fungi, which in turn depend on: soil disturbance, which destroyspores and disturbs microbialduration of water scarcityabundance and diversity; contaminants or inhibitors, such as heavy metals, which reduce the abundance of fungi; iv) crop rotation, which increases soil fungi abundance and diversity; and irrigation, which reduce colonizamycorrhizal efficiency.

The evaluation of impacts on Portuguese agriculture was primarily based onsimulating models such as

comprises a substantial fraction of soil OM in many systems, and aspects of the biology and chemistry of mycorrhized hyphae can influence the C cycling

son, 2000; Carranca, 2010). Farrar and Jones (2000) reported that the

presence of higher CO2 concentration and temperature will produce bigger plants, with bigger root systems as a consequence of their size, but with little or no change in C partitioning to them (Table 1). However, as these large plants have more demand for water and nutrients, and the soil is relatively depleted in these resources as a consequence, there will be more growth of (mycorrhized) roots relative to shoots directed by

s yet unknown, and if soil nutrients are low there might also be more exudation from roots and C transfer to mycorrhiza and the soil, but these effects of elevated CO2 will be indirect.

Growth and root metabolism of barley at germination under two CO2 levels

(Source: Farrar and Jones, 2000) CO2 concentration (ppm)

350 700 154 222 0.31 0.31 0.12 0.18

3.4 5.8 1.1 1.8

3.2 4.0

2.7 3.9

17.3 37.9

22 33

Trees with reduced absorbing fine roots have efficient colonization by soil

. This is the case of ‘Rangpur’ rootstock for citrus, which is the most used rootstock in Brazil by

potential to support drought stress. The main factors that affect mycorrhizal

efficiency are plant type and abundance and , which in turn depend on: i)

destroys the plant roots and microbial activity; ii) long

water scarcity, which reduces fungi abundance and diversity; iii) the presence of

inants or inhibitors, such as pesticides and , which reduce the abundance of

crop rotation, which increases soil fungi abundance and diversity; v) intensive fertilization and irrigation, which reduce colonization or

The evaluation of impacts of climate change agriculture was primarily based on

simulating models such as DSSAT (Decision

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Support Systems for Agro-technology Transfer) and CERES WHEAT (wheat) and CERES MAIZE (maize) (Santos et al., 2001). It was shown that higher CO2 concentration may increase crop productivity and water use efficiency, but higher temperature will induce faster growth rate and higher water requirement (Santos et al., 2001). There is a general agreement that both single-leaf and canopy photosynthesis by C3 plants will increase more than that of C4 plants as atmospheric CO2 concentration increases, partly due to an inhibition of photorespiration by CO2 in C3 plants, a process that does not impact photosynthesis of C4 plants (Brouder and Volenec, 2008). These plants have higher photosynthetic rates than C3 plants and prefer high temperatures. Frequently, they are referred as “warm-season” plants [e.g. maize (Zea mayz L.), sorghum (Sorghum bicolor L. Moench), sugarcane (Saccharum officinarum L.), bermudagrass (Cynodon dactlylon L.)]. This shows that C3 plants are more responsive to the CO2 increase than C4 plants. Water use efficiency of C4 plants is often twice that of C3 plants, sometimes by stomata closure (Brouder and Volenec, 2008). The elevated CO2 concentration reduces stomata conductance in many plant species.

Crop productivity is also a function of soil quality. A good soil is an important sink for C sequestration (1.5 Gt C year-1), equivalent to two/three times the atmospheric CO2 level (Gallego, 2001; Carranca, 2010). Portuguese agricultural soils can accumulate 47 t C ha-1 in a 30 cm layer. This natural resource is subject to degradation (erosion, loss of OM and biodiversity, acidification, contamination, salinization, flooding, sealing, landslides, fires), and is not renewable in a human scale [1000-10000 years to completely form a 30 cm soil (Haberli et al., 1997; Carranca, 2010)]. Most Portuguese soils (90%) are poor in OM, showing a high to moderate erosion risk (69%), with an erosion rate of 4.5 t ha-1 year-1 (Carranca, 2010). Erosion and loss of OM are due to extreme rainfall events, high mineralization rates influenced by the high air temperature, soil type and slope, and wrong agricultural practices, such as tillage, fallow, intensive grazing, reduced crop rotations.

Good agricultural practices to increase soil OM content (e.g. cultivation of permanent or annual pastures, soil conservation practices, biological production, maintenance of soil cover, efficient mycorrhization, introduction of legumes in crop rotations with long duration, and as intercropping) should be encouraged. Bare soils can be more than 5 ºC warmer with much higher surface evapotranspiration than residue covered soils, resulting in altered rates of mineralization and nutrient diffusion (Brouder and Volenec, 2008).

3 Adaptation of Portuguese

agriculture to climatic changes Adaptation is a process to reduce the negative impacts of climate change in different socio-economic sectors (e.g. agriculture) and biophysics systems. Previous to adaptation strategies, the impacts of climate change should be identified. Adaptation to climate change is planned by local or national government, or spontaneous, i.e., done privately without government. In Portugal, adaptation strategies include: i) information and research; ii) vulnerability reduction and responsiveness; iii) participation, awareness and dissemination; iv) international cooperation.

Climate will change but details regarding impact on agriculture remain vague and it is not easy to predict future food supply. A first requirement is mapping the land-use and climate change. Crop models are also major tools for studying climate change scenarios in agriculture. Developing dynamic models is recommended for annual and perennial crops to evaluate physiological rates (stomata conductance and photosynthetic processes, water and nutrient use efficiency, etc.), root response to global change (e.g. root biomass, morphological characteristics, hydraulic conductivity kinetics, mycorrhizal), new pests and diseases, and adaptation strategies for fruit and olive trees, vineyards, forest trees. Ver Sofo et al (2005) nas micorrizas

There are a few models that can simulate climate data for the future. One of those is HadRM3, a regional model from Hadley Centre, which generates temperature data, from emission scenarios data (Santos et al., 2001; Almeida, 2009). The results of this model showed an increase of temperature in Portugal for the years to come. To estimate ecological fitness, in the present and in a future scenario, a system named SISAP (System for Crop Adaptation) was developed in Portugal. This program crossed soil and weather requirements of crops with other environmental data. Results showed that crops can grow in the Alqueva irrigation area at south Portugal with reduced to medium productivity. When comparing the results for the present and the future scenario, it is easy to understand that in the future all crops will achieve higher productions, due to the higher temperatures and CO2 concentrations. The only exception from tested crops was kenaf (Hibiscus cannabinus sp.), where future will bring the worst results. A large perennial C4 grass (Miscanthus sp.), which can be used as a biodiesel crop, was the most interesting plant from an ecological standpoint for this area.

The expected lower amount of rainfall in spring and summer in Portugal will increase irrigation water requirements and may increase the water stress by rainfed crops, although the anticipation of sowing time may reduce this effect. SIAM II and HadCM3 models advised that sowing date should be altered for a better productivity.

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Sowing date should be anticipated from 1 November to 15 October for wheat (rainfed crop) and from 1 April to 15 March for maize (irrigated crop) (Santos et al., 2001). Tuber crops (sugarbeet, potatoes) will beneficiate from higher temperatures and CO2 levels. Irrigated crops will be less responsive to climate variability comparing to rainfed crops. It is supposed that most crops will move to the north part of the country, but possibly the slow-growing plant species like oak trees will move very slowly. Northern European countries will show better conditions for agriculture production in future.

Carbon dioxide emission increases by increasing temperature through the respiration process. This emission should be reduced but avoiding the inhibition of cell respiration (Correia, 2010). The reduction of CO2 must happen for hundred years since the gas resilience in the atmosphere is about a hundred years (Carranca, 2010). C3 plants may accrue a direct benefit from an atmospheric CO2 enrichment. According to Brouder and Volenec (2008), if plants produced under elevated CO2 are simply bigger, but otherwise the same in their gross nutrient content per unit biomass, then present-day nutrient balance calculations for fertilizer recommendations will remain applicable. In crop species that have been extensively improved for agriculture, nutrient concentrations, especially in grain, can be relatively constant when yields are not limited by other factors.

A general model was developed in Visual Basic for fruit trees (Melo e Abreu, 2010). This model has been used to study changes in flowering dates and yield based on Portuguese climate change scenarios. Some models indicated a possible extension for vineyard areas, but there are some CAP restrictions.

Plant breeding is also an important tool for better adapted new varieties and cultivars, and regional cultivars to drought stress and high temperature, namely by shortening or enlarging the growth cycles, and for a better nutrient and water use efficiency. At south Portugal, where water availability is scarce, crops should be replaced by others with a better capacity for water use.

New pests, diseases and weeds will probably appear under the climate change, but the occurrence of fungi diseases such as oidium and mildew may be reduced by the lower spring rainfall. Tropical diseases and pests may increase.

Desertification process will tend to be intensified by climate change. According to the Portuguese Commission for Climatic Changes (2002), robust models should be developed to include C sequestration by forest and changes in land-use, including the fires. In Europe, data basis on C sequestration in forests are mostly empirical.

Models such as ANIMO, CANDY, CENTURY,

DAISY, GEFSOC, HERMES, NCSOIL, NTRM, RothC, SOILN, SUNDIAL, etc. have been tested for OM dynamics in several agro-ecosystems, but only in a local scale. Very few have been used in a regional, national or continental scale (Carranca, 2010). Several problems occur with these models in a broad scale, namely the historical land-use, the OM dynamics in deep layers, etc. The CENTURY and RothC simulation models were calibrated and validated for different ecosystems, including different soil types in temperate climate. The LUC model to evaluate C sequestration in a global scale combines the global economic model (GTAP), the land-use and environmental variability model (IMAGE), and the Dyna-Clue model for spatial variability. Using this LUC model, Schulp et al. (2008) evaluated four scenarios for EU-27 and concluded that climate change by 2030 will not be significant. They stated that intensive cropping will reduce C sequestration up to 2%, but moving from cultivation to abandonment or permanent pastures it will increase by 9-16%. They recommended that only young forests should be replaced, not the old ones with high biomass and accumulated C.

The promotion of extensive livestock, particularly ruminants, taking into account the persistence of pastures and the use of biodiverse and irrigated pastures are also recommended options for the present climatic conditions.

4 Acknowledgements The author thanks Dr. Pedro Reis (INIA) and

Prof. J. beltrão (Univ. Algarve) for their contribution on manuscript revision.

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