Version classiqueVersion mobile

The Mediterranean region under climate change

 | 
Jean-Paul Moatti
, 
Stéphane Thiébault

Part 3. Adaptation, resilience, conservation of resources and prevention of risk

Sub-chapter 3.2.5. Fodder grass selection in the Mediterranean

The role of summer dormancy

Florence Volaire, Rajae Kallida, Mark Norton, Dariusz Malinowski et Philippe Barre

Texte intégral

The importance and sustainability of grasslands and forage crops in the Mediterranean

1Around the Mediterranean Basin, crop-livestock farming systems contribute significantly to the rural economy. In southern Europe, livestock farming provides high added-value animal products (typically cheese and meat) but the decline in grazing pressure over the last few decades negatively impacts the landscape, since it results in shrub encroachment and greater fire hazards. In Northern Africa, animal production is widespread and mostly extensive, with a strong negative impact because of overgrazing on rangelands. However, an increased production of animal products is required to satisfy the needs of growing populations (Delgado et al. 1999, FAO, 2009). In Morocco for example, public actions (‘Plan Vert’) are implemented to foster livestock farming. In all cases, a key driver for the sustainability of animal production is self-sufficiency in on-farm forage supply to counterbalance the increasing cost of imported feed stuff (Abdelguerfi and El Hassani, 2011, Taher Sraïri, 2011).

2Throughout the Mediterranean Basin, rangelands and grasslands account for 50% of the land surface and about 270 million ha in the arid and semi-arid zones receiving 100-400 mm annual rainfall (CIHEAM, 2009). They provide forage resources as well as many ecosystem services, including carbon storage, limitation of soil erosion, water catchment and biodiversity preservation. However, in the southern Mediterranean countries, the area available for grazing is diminishing due to the expansion of rain-fed annual cereals, to meet increasing demand for human food (Lelièvre and Volaire, 2009). Millions of hectares of fallow land and rangeland have disappeared while stocking rates have increased because of subsidized imported grain and by-products. Grazing at higher stocking rates is thus allocated to dryer and poorer rangelands: the remaining rangeland is drastically degraded due to overgrazing, leading to a dramatic loss of biodiversity, vegetation cover, greater soil erosion and a diminishing ability to provide ecosystem services. Perennial grasses dominate in most natural grasslands and provide the principal nutrition for ruminant livestock.

3However, the genetic diversity of these palatable species is declining due to habitat destruction and overgrazing (CIHEAM, 2009). In the Northern Mediterranean countries, stocking rates tend to decrease along with an increase in extensive permanent pastures that cannot provide sufficient forage resources at all seasons. As a consequence, and around the whole Mediterranean basin, complementary forage crops are crucial to securing farming systems and increasing the productivity and stability of animal production.

4However, the resilience of both native and sown grasslands is threatened by increasing aridity due to climate change (I.P.C.C., 2014). Extreme events and severe heat waves are expected to become more frequent and a decrease in summer precipitation will lead to more frequent and more intense droughts, particularly in Southern Europe (Lehner et al. 2006). In the Mediterranean Basin, the rate of warming may lead to an additional month of summer (Giannakopoulos et al. 2009). This increase in water-shortage also intensifies in winter since ten of the twelve driest winters since 1902 have occurred in just the last 20 years (Hoerling et al. 2012). Therefore, pasture establishment failures and long-term degradation from drought are expected to become more common.

5Under both this greater incidence of drought and increasing population pressure, the amount of water available to agriculture is declining drastically in Mediterranean areas (CIHEAM, 2009). Rainfall use efficiency for forage production must be therefore improved in both native rangelands and rain-fed forage crops. Under these chronic water shortages, perennial forage species have a number of advantages in comparison to the predominantly used annual species including (1) fewer inputs with less field preparation and fertiliser requirement, (2) year-round soil cover reducing the risk of intense soil erosion, (3) optimal use of water throughout all seasons thus enhancing forage production in particular in autumn when cereals are not yet established and (4) greater flexibility because of the multiple uses of these species (grazing, hay, silage). Perennial grasses are therefore an excellent alternative to cereals, contributing to reduce production costs, halt rangeland degradation and confer greater security overall to rain-fed agricultural systems (Lelièvre and Volaire, 2009).

Improving perennial forage grasses in the Mediterranean

6Attempts to improve productivity of rain-fed and natural pastures in semi-arid Mediterranean regions by the introduction of cultivars bred in more favourable temperate areas have repeatedly proven unsuccessful (Lelièvre and Volaire, 2009). At present, most cultivars of grass species including cocksfoot (Dactylis glomerata L.) and tall fescue (Festuca arundinacea Schreb.), are bred in and for higher rainfall temperate climates with several hundred cultivars already registered (OECD, 2010). Unfortunately, these temperate cultivars are poorly suited and do not survive the severe summer water deficits of Mediterranean summers (Lelièvre et al. 2011). Due to very limited breeding work carried out in Mediterranean areas, the number of cultivars adapted to summer drought and available to farmers is extremely small: five cultivars of tall fescue and cocksfoot (Lelièvre and Volaire, 2009), all originating from North African germplasm. The development of new innovative perennial grass cultivars produced from Mediterranean selected germplasm is fundamental (Abdelguerfi and El Hassani, 2011) both for the restoration of rangelands and the development of forage crops with enhanced summer drought adaptation and high productivity during the cooler rainy seasons.

7In Mediterranean areas, the adaptation of perennial herbaceous plants depends on their long-term persistence mediated by the ability of plants to survive successive summer droughts (Norton et al. 2016). Grasses have developed different adaptive strategies, such as dehydration avoidance/delay and dehydration tolerance to persist through successive summer droughts. However, genotypes with the highest survival rate of the most arid conditions exhibit responses associated with summer dormancy (Volaire and Norton, 2006). This adaptive trait has been developed specifically by perennial herbaceous species subjected to the predictably long and intensely dry summers characteristic of southern Mediterranean environments. It ensures plant survival by maintaining the viability of meristems during the hostile summer. There is a growing interest in this trait since, in cocksfoot and tall fescue, summer dormancy improved survival by up to 30% during long intense summer droughts (Norton et al. 2006). In Mediterranean environments, perennial grasses with summer dormancy have a longer grazing season than annual species. They provide earlier and more sustainable herbage due to fast re-growth at the onset of autumn rains, and make better use of residual moisture at the end of the cooler growing season. However, the environmental factors associated with the induction and the relaxation of this trait remain unclear (Ofir and Kigel, 2006, Volaire et al. 2009) and need to be clarified to design ideotypes and crop management suited to local environments. Unravelling the relationships between plant stage and dormancy induction will also provide key knowledge to understand drought resistance in autumn-winter (establishment stage) when summer dormancy is not expressed. While the winter dormancy of plants growing in temperate climates is well understood, the summer dormancy trait occurring in plant species from Mediterranean-type areas has been little studied even though it has the potential to greatly improve forage crops.

8Moreover, it is recognized that highly efficient forage crops are mixtures combining grasses and legumes in order to maximise nitrogen acquisition from legume fixation, reduce fertilization inputs and produce high protein forage. The very low water use of dormant grasses in summer has been shown to reduce competition and enhance the functional complementarity of resource use between associated components (Volaire et al. 2014). Lucerne (Medicago sativa L.) is the main perennial legume crop of the Mediterranean basin. Although mainly cultivated under irrigation in the region, recent efforts have been made to develop better drought-adapted cultivars (Annicchiarico et al. 2011). Moreover, new lines of Portuguese subterranean clover (Trifolium subterraneum L.), a self-reseeding annual species, are available. Either lucerne or subterranean clover and perennial grasses are associated in traditional forage mixtures grown over large areas in temperate regions, particularly in southern Australia. Indeed, in the Southern Great Plains of the USA where severe summer drought is common, mixing summer-dormant tall fescue either (1) with lucerne under the right sowing design or (2) with annual medics (Medicago sp.), enabled the maintenance of adequate stand density and persistence of both species (Malinowski et al. 2011, Malinowski and Pinchak, 2015). Complementarity between grasses and legumes under rain-fed conditions requires further investigation to provide innovative mixtures for a range of environmental conditions.

Towards new drought-tolerant cultivars of perennial grasses

9Current research programs aim to develop a range of innovative, highly drought-resilient and water efficient cultivars of perennial grasses from Mediterranean germplasm and from crosses with temperate elite material by incorporating the summer dormancy trait. These new cultivars should provide rain-fed forage crops for Mediterranean areas subjected to increasing aridity and desertification risk and therefore will reduce the vulnerability of farming systems to climate change. Based on the remaining rich biodiversity in perennial grasses already collected in Mediterranean areas, it will add value to the summer dormancy trait that is endemic in this region. The aim is to select plant material adapted to severe summer drought but productive during the cooler rainy season thus enhancing the resilience of farming systems to climate change. In addition, seed productivity should also be improved in order to meet the demands of the seed market. Opportunities to use these cultivars also extend to temperate areas, in particular in Europe, where they can be used in breeding programs for improving adaptation to moderate drought.

10Cocksfoot is the fourth most widely used grass genera of forage crops in the world (Bondesen, 2007) and thus appears to be a “model perennial grass”. Moreover, this species is very widespread with ecotypes found from Northern Africa expressing complete summer dormancy to temperate northern Europe (Fig. 1).

Figure 1
The perennial grass Dactylis glomerata L. has a large intra-specific variability including Mediterranean ecotypes with complete summer dormancy conferring an exceptional survival under severe drought

11The three main current research objectives are as follows: first, to create and select innovative plant material based on the analysis of linkages among the key traits, including summer dormancy, phenology, biomass production, and seed production. This will define the best trade-offs between traits across a range of ideotypes through the analysis of the genetic basis of these traits (Kallida et al. 2016). Second, to identify the environmental control of induction of summer dormancy since a clearer understanding of the role of photoperiod, temperature and water deficit is needed to predict the ideotypes best suited to local environments and to provide key knowledge for improving pasture management (sowing and defoliation stage, etc.). Third, to test the most promising lines/cultivars of cocksfoot in association with companion legumes since under increasing drought, species mixtures combining both Mediterranean grasses and legumes should improve multi-annual productivity of forage crops through greater water and nitrogen use efficiency as well as long term drought resilience.

Bibliographie

References

Abdelguerfi A, El Hassani T, A. 2011
Interactions between cereal cropping systems and pastoral areas as the basis for sustainable agriculture development in Mediterranean countries. In: Lemaire G, Hodgson J, Chabbi A eds. Grassland productivity and Ecosystem services. CAB International.

Annicchiarico P, Pecetti L, Abdelguerfi A, Bouizgaren A, Carroni AM, Hayek T, Bouzina MM, Mezni M. 2011
Adaptation of landrace and variety germplasm and selection strategies for lucerne in the Mediterranean basin. Field Crops Research, 120: 283-291.

Bondesen O. 2007
Seed production and seed trade in a globalised world. In: TS Aamlid LH, B Boelt ed. 6th International Herbage Seed Conference. Bioforsk: Ås, Norway.

CIHEAM. 2009
Mediterra - Repenser le développement rural en Méditerranée (Centre International de Hautes Etudes Agronomiques Méditerranéennes). In: Bertrand Hervieu HLT ed. Paris, Presses de Sciences Po.

Delgado C, Rosegrant M, Steinfeld H, Ehui S, Courbois C. 1999
Livestock to 2020: the next food revolution. Washington, IFPRI.

FAO. 2009
The state of food and agriculture. Livestock in the balance. Rome.

Giannakopoulos C, Le Sager P, Bindi M, Moriondo M, Kostopoulou E, Goodess CM. 2009
Climatic changes and associated impacts in the Mediterranean resulting from a 2 degrees C global warming. Global and Planetary Change, 68: 209-224.

Hoerling M, Eischeid J, Perlwitz J, Quan XW, Zhang T, Pegion P. 2012
On the Increased Frequency of Mediterranean Drought. Journal of Climate, 25: 2146-2161.

I.P.C.C. 2014
International Panel of Climatic changes. Fifth assessment report (AR4).

Kallida R, Zhouri L, Volaire F, Guérin A, Julier B, Shaimi N, Fakiri M, Barre P. 2016.
Combining drought survival via summer dormancy and annual biomass productivity in Dactylis glomerata L. Frontiers in Plant Science, doi: 10.3389/fpls.2016.00082.

Lehner B, Doll P, Alcamo J, Henrichs T, Kaspar F. 2006
Estimating the impact of global change on flood and drought risks in europe: A continental, integrated analysis. Climatic Change, 75: 273-299.

Lelièvre F, Seddaiu G, Ledda L, Porqueddu C, Volaire F. 2011
Water use efficiency and drought survival in Mediterranean perennial forage grasses. Field Crops Research, 121: 333-342.

Lelièvre F, Volaire F. 2009
Current and potential development of perennial grasses in rainfed Mediterranean farming systems. Crop Science, 49: 2371-2378.

Malinowski DP, Butler TJ, Belesky DP. 2011
Competitive Ability of Tall Fescue against Alfalfa as a Function of Summer Dormancy, Endophyte Infection, and Soil Moisture Availability. Crop Science, 51: 1282-1290.

Malinowski DP, Pinchak WE. 2015
Summer dormancy trait as a strategy to provide perennial cool-season grass forage alternatives in southern latitude environments affected by climate change. Agronomy Journal, 107: 1227-1234.

Norton M, Malinowski D, Volaire F. 2016
Plant drought survival under climate change and strategies to improve perennial grasses. A review. Agronomy for Sustainable development: 36:29-DOI 10.1007/s13593-016-0362-1.

Norton M, Malinowski D, Volaire F. 2016
Summer dormancy in Dactylis glomerata L., the influence of season of sowing and a simulated mid-summer storm on two contrasting cultivars. Australian Journal of Agricultural Research, 57: 565-575.

OECD. 2010
Varieties of grasses and legumes eligible for certification within OECD http://www.oecd.org/dataoecd/52/16/41920785.pdf

Ofir M, Kigel J. 2006
Opposite effects of daylength and temperature on flowering and summer dormancy of Poa bulbosa. Annals of Botany, 97: 659-666.

Taher Sraïri M. 2011
Le développement de l’élevage au Maroc: succès relatifs et dépendance alimentaire. Courrier de l’Environnement de l’inra, 60: 91-101.

Volaire F, Barkaoui K, Norton M. 2014
Designing resilient and sustainable grasslands for a drier future: Adaptive strategies, functional traits and biotic interactions. European Journal of Agronomy, 52: 81-89.

Volaire F, Norton M. 2006
Summer dormancy in perennial temperate grasses. Annals of Botany, 98: 927-933.

Volaire F, Seddaiu G, Ledda L, Lelièvre F. 2009
Water deficit and induction of summer dormancy in perennial Mediterranean grasses. Annals of Botany, 103: 1337-1346.

Auteurs

INRA, CEFE-CNRS, France
Ecophysiologist, Institut national de la recherche agronomique (INRA), CEFE (CNRS) Montpellier, France
florence.volaire@cefe.cnrs.fr

INRA, CRRA, Morocco
Ecophysiologist, Institut national de la recherche agronomique (INRA), Centre régional de la recherche agronomique, Rabat, Morocco
rkallida@yahoo.fr

Agricultural Institute, Graham Centre for Agricultural Innovation, Australia
Agronomist, Agricultural Institute, Graham Centre for Agricultural Innovation, Wagga Wagga, Australia
mark.norton@dpi.nsw.gov.au

Texas AgriLife Research, USA
Agronomist, plant breeder, Texas AgriLife Research, Vernon, USA
dmalinow@ag.tamu.edu

INRA, URP3F, France
Geneticist, Institut national de la recherche agronomique (Inra), URP3 Lusignan, France
philippe.barre@lusignan.inra.fr

© IRD Éditions, 2016

Conditions d’utilisation : http://www.openedition.org/6540

Rechercher dans OpenEdition Search

Vous allez être redirigé vers OpenEdition Search