Effects of temperature and water stresses on germination of some varieties of chickpea (Cicer arietinum)

Chickpea production did not progress, in spite, of intensification of agricultural practices. Drought and thermal stresses were the major factors that decreased yield when the crop is generally sown in spring. Nevertheless, winter sowing has opened new opportunities for increasing chickpea production in arid areas. This culture is based on two essential factors: (i) preclude rainfall during the flowering and fruiting period (April/May) after a beneficial one in January and February for a good crop development and (ii) reducing the risk of infection by Ascochyta rabiei (considered as the main pathogen of chickpea) whose development is limited in arid area. The influence of temperature on seeds germination of the four varieties (Ghab4, Neyra, Kasseb and Chetoui) has been evaluated with seven temperatures (5, 10, 15, 20, 25, 30 and 35°C) and the effect of drought stress has been determined with seven water stresses induced by different solution of PEG 4000 (0, 1, 2, 3, 4, 5 and 10 g/L). During germination, the tested varieties presented differential sensitivity to thermal stress. The Chetoui and Ghab4 varieties were more tolerant, to cold temperature, than the other varieties. Osmotic potential induced by PEG 4000 had significant effects on seeds germination. Chetoui and Ghab4 were the best tolerant to drought stress. Therefore, we opted for the Chetoui variety that better meets the conditions of stresses induced by low temperatures and water deficit. This best performing variety must have, throughout their development cycle, been tolerant to environmental stresses; which allows us to obtain early tools for discriminative selection between chickpea genotypes.Keywords: Chickpea, thermal stress, drought stress, germinationAfrican Journal of Biotechnology Vol. 12(17), pp. 2201-220

Process based model sheds light on climate sensitivity of Mediterranean tree-ring width

We use the process-based VS (Vaganov-Shashkin) model to investigate whether a regional <i>Pinus halepensis</i> tree-ring chronology from Tunisia can be simulated as a function of climate alone by employing a biological model linking day length and daily temperature and precipitation (AD 1959–2004) from a climate station to ring-width variations. We check performance of the model on independent data by a validation exercise in which the model's parameters are tuned using data for 1982–2004 and the model is applied to generate tree-ring indices for 1959–1981. The validation exercise yields a highly significant positive correlation between the residual chronology and estimated growth curve (<i>r</i>=0.76 <i>p</i><0.0001, <i>n</i>=23). The model shows that the average duration of the growing season is 191 days, with considerable variation from year to year. On average, soil moisture limits tree-ring growth for 128 days and temperature for 63 days. Model results depend on chosen values of parameters, in particular a parameter specifying a balance ratio between soil moisture and precipitation. Future work in the Mediterranean region should include multi-year natural experiments to verify patterns of cambial-growth variation suggested by the VS model

Biogeographic, Atmospheric, and Climatic Factors Influencing Tree Growth in Mediterranean Aleppo Pine Forests

There is a lack of knowledge on how tree species respond to climatic constraints like water shortages and related atmospheric patterns across broad spatial and temporal scales. These assessments are needed to project which populations will better tolerate or respond to global warming across the tree species distribution range. Warmer and drier conditions have been forecasted for the Mediterranean Basin, where Aleppo pine (Pinus halepensisMill.) is the most widely distributed conifer in dry sites. This species shows plastic growth responses to climate, being particularly sensitive to drought. We evaluated how 32 Aleppo pine forests responded to climate during the second half of the 20th century by using dendrochronology. Climatic constraints of radial growth were inferred by fitting the Vaganov-Shashkin (VS-Lite) growth model to ring-width data from our Aleppo pine forest network. Our findings reported that Aleppo pine growth decreased and showed the highest common coherence among trees in dry, continental sites located in southeastern and eastern inland Spain and Algeria. In contrast, growth increased in wetter sites located in northeastern Spain. Overall, across the Aleppo pine network tree growth was enhanced by prior wet winters and cool and wet springs, whilst warm summers were associated with less growth. The relationships between site ring-width chronologies were higher in nearby forests. This explains why Aleppo pine growth was distinctly linked to indices of atmospheric circulation patterns depending on the geographical location of the forests. The western forests were more influenced by moisture and temperature conditions driven by the Western Mediterranean Oscillation (WeMO) and the Northern Atlantic Oscillation (NAO), the southern forests by the East Atlantic (EA) and the august NAO, while the Balearic, Tunisian and northeastern sites by the Arctic Oscillation (AO) and the Scandinavian pattern (SCA). The climatic constraints for Aleppo pine tree growth and its biogeographical variability were well captured by the VS-Lite model. The model performed better in dry and continental sites, showing strong growth coherence between trees and climatic limitations of growth. Further research using similar broad-scale approaches to climate-growth relationships in drought-prone regions deserves more attention

Palaeolimnological evidence for an east-west climate see-saw in the Mediterranean since AD 900

During the period of instrumental records, the North Atlantic Oscillation (NAO) has strongly influenced inter-annual precipitation variations in the western Mediterranean, while some eastern parts of the basin have shown an anti-phase relationship in precipitation and atmospheric pressure. Here we explore how the NAO and other atmospheric circulation modes operated over the longer timescales of the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA). High-resolution palaeolimnological evidence from opposite ends of the Mediterranean basin, supplemented by other palaeoclimate data, is used to track shifts in regional hydro-climatic conditions. Multiple geochemical, sedimentological, isotopic and palaeoecological proxies from Estanya and Montcortés lakes in northeast Spain and Nar lake in central Turkey have been cross-correlated at decadal time intervals since AD 900. These dryland lakes capture sensitively changes in precipitation/evaporation (P/E) balance by adjustments in water level and salinity, and are especially valuable for reconstructing variability over decadal-centennial timescales. Iberian lakes show lower water levels and higher salinities during the 11th to 13th centuries synchronous with the MCA and generally more humid conditions during the 'LIA' (15th-19th centuries). This pattern is also clearly evident in tree-ring records from Morocco and from marine cores in the western Mediterranean Sea. In the eastern Mediterranean, palaeoclimatic records from Turkey, Greece and the Levant show generally drier hydro-climatic conditions during the LIA and a wetter phase during the MCA. This implies that a bipolar climate see-saw has operated in the Mediterranean for the last 1100. years. However, while western Mediterranean aridity appears consistent with persistent positive NAO state during the MCA, the pattern is less clear in the eastern Mediterranean. Here the strongest evidence for higher winter season precipitation during the MCA comes from central Turkey in the northeastern sector of the Mediterranean basin. This in turn implies that the LIA/MCA hydro-climatic pattern in the Mediterranean was determined by a combination of different climate modes along with major physical geographical controls, and not by NAO forcing alone, or that the character of the NAO and its teleconnections have been non-stationary. © 2011 Elsevier B.V

Biogeographic, atmospheric, and climatic factors influencing tree growth in Mediterranean Aleppo pine forests

There is a lack of knowledge on how tree species respond to climatic constraintslike water shortages and related atmospheric patterns across broad spatial and temporal scales.These assessments are needed to project which populations will better tolerate or respond to globalwarming across the tree species distribution range. Warmer and drier conditions have been forecastedfor the Mediterranean Basin, where Aleppo pine (Pinus halepensisMill.) is the most widely distributedconifer in dry sites. This species shows plastic growth responses to climate, being particularly sensitiveto drought. We evaluated how 32 Aleppo pine forests responded to climate during the second half ofthe 20th century by using dendrochronology. Climatic constraints of radial growth were inferred byfitting the Vaganov-Shashkin (VS-Lite) growth model to ring-width data from our Aleppo pine forestnetwork. Our findings reported that Aleppo pine growth decreased and showed the highest commoncoherence among trees in dry, continental sites located in southeastern and eastern inland Spain andAlgeria. In contrast, growth increased in wetter sites located in northeastern Spain. Overall, across theAleppo pine network tree growth was enhanced by prior wet winters and cool and wet springs,whilst warm summers were associated with less growth. The relationships between site ring-widthchronologies were higher in nearby forests. This explains why Aleppo pine growth was distinctlylinked to indices of atmospheric circulation patterns depending on the geographical location of theforests. The western forests were more influenced by moisture and temperature conditions drivenby the Western Mediterranean Oscillation (WeMO) and the Northern Atlantic Oscillation (NAO),the southern forests by the East Atlantic (EA) and the august NAO, while the Balearic, Tunisian andnortheastern sites by the Arctic Oscillation (AO) and the Scandinavian pattern (SCA). The climaticconstraints for Aleppo pine tree growth and its biogeographical variability were well captured by theVS-Lite model. The model performed better in dry and continental sites, showing strong growthcoherence between trees and climatic limitations of growth. Further research using similar broad-scaleapproaches to climate-growth relationships in drought-prone regions deserves more attention

Old World megadroughts and pluvials during the Common Era

Climate model projections suggest widespread drying in the Mediterranean Basin and wetting in Fennoscandia in the coming decades largely as a consequence of greenhouse gas forcing of climate. To place these and other “Old World” climate projections into historical perspective based on more complete estimates of natural hydroclimatic variability, we have developed the “Old World Drought Atlas” (OWDA), a set of year-to-year maps of tree-ring reconstructed summer wetness and dryness over Europe and the Mediterranean Basin during the Common Era. The OWDA matches historical accounts of severe drought and wetness with a spatial completeness not previously available. In addition, megadroughts reconstructed over north-central Europe in the 11th and mid-15th centuries reinforce other evidence from North America and Asia that droughts were more severe, extensive, and prolonged over Northern Hemisphere land areas before the 20th century, with an inadequate understanding of their causes. The OWDA provides new data to determine the causes of Old World drought and wetness and attribute past climate variability to forced and/or internal variability

Multidecadal variability in Atlas cedar growth in northwest Africa during the last 850 years: implications for dieback and conservation of an endangered species

Widespread forest dieback is a phenomenon of global concern that requires an improved understanding of the relationship between tree growth and climate to support conservation efforts. One priority for conservation is the Atlas cedar (Cedrus atlantica), an endangered species exhibiting dieback throughout its North African range. In this study, we evaluate the long-term context for recent dieback and develop a projection of future C. atlantica growth by exploring the periodic variability of its growth through time. First, we present a new C. atlantica tree- ring chronology (1150–2013 CE) from the Middle Atlas mountains, Morocco. We then compare the new chronology to existing C. atlantica chronologies in Morocco and use principal components analysis (PCA) to isolate the common periodic signal from the seven longest available records (PCA7, 1271–1984 CE) in the Middle and High Atlas portions of the C. atlantica range. PCA7 captures 55.7% of the variance and contains significant multidecadal ( ̃95yr, ̃57yr, ̃21yr) periodic components, revealed through spectral and wavelet analyses. Parallel analyses of historical climate data (1901–2016 CE) suggests that the multidecadal growth signal ori- ginates primarily in growing season (spring and summer) precipitation variability, compounded by slow- changing components of summer and winter temperatures. Finally, we model the long-term growth patterns between 1271–1984 CE using a small number (three to four) of harmonic components, illustrating that sup- pressed growth since the 1970s – a factor implicated in the dieback of this species – is consistent with recurrent climatically-driven growth declines. Forward projection of this model suggests two climatically-favourable periods for growth in the 21st century that may enhance current conservation actions for the long-term survival of the C. atlantica in the Middle and High Atlas mountains