Morphological traits variability and effect of osmotic water stress on germination of Tunisian populations of Quercus ilex acorns

Transcription

1 UNIVERSITY OF CARTHAGE Morphological traits variability and effect of osmotic water stress on germination of Tunisian populations of Quercus ilex acorns Nabil AMIMI 1,2, Hana GHOUIL 1,2, Mejda ABBASSI 1, Youssef AMMARI 1 1 : Laboratory of forest ecology, INRGREF National Research Institute for Rural Engineering, Water and Forestry, Rue Hedi Karray B.P.N 10 Ariana Tunisia 2: Faculty of Sciences Bizerte, Jarzouna University of Carthage Tunisia

2 In the Mediterranean environment, characterized by important seasonal and episodic droughts, water availability is a limiting factor of prime importance in the regeneration of oaks and other woody species. This may aggravate in the future. According to most climate change scenarios for the region, the severity of the summer drought may increase as well as the frequency of severe droughts

3 In Tunisia, the forest area, especially of oak, experienced significant reductions following the fires, shifting cultivation, overgrazing and the increasing human pressure. Quercus genus is represented by five species of which two are deciduous : Oak afares (Quercus afares), Oak zeen (Quercus canariensis) and three evergreens (cork oak (Quercus suber), Oak Kermes (Quercus coccifera) and Holm oak Quercus ilex )

4 Quercus ilex is an element of maquis vegetation that can play an important role in the rehabilitation and restoration of Mediterranean countries. Among the Mediterranean evergreen species, Quercus ilex is considered to represent the prototype of the Mediterranean sclerophyllous species.

5 It plays a vital role in soil and water conservation. The Holm oak acorns represent a major component in the feeding systems of many Mediterranean wild and livestock species.

6 Regenerative seed traits play an important, yet overlooked, role because they largely determine the ability of plants to disperse and re-establish In addition, the consequences of drought depending on its start-up period compared to the cultural stage (e.g. germination stage) and its action duration

7 Questions?: The aims of this study are: The prospection and identification of different Holm Oak populations in Tunisia (Iliçaie) To study the diversity of morphological traits in acorns from these populations Also, This work is carried out to evaluate the bihaviour of 5 populations within those used for morphological traits, with regards to evaluate intraspecific response to an osmotic stress at the germination stage

8 MATERIALS AND METHODS

9 1/ Prospection and population's identification

10

11 Prospecting Holm oak has allowed us to establish a phyto -ecological map of presence Holm oak in Tunisia (using the ARCGIS software) and define sources of acorns used in this work.

12 2/ Morphological traits of acorns Acorns of different populations were collected in December 2015 from the sites listed in table 1. At each site the acorns are harvested from 3 to 10 trees according to the site. Healthy and full ripen were selected and used for the measurement of morphological features namely: * Acorn size (length and maximum diameter ) * Fresh and dry of the acorn * Water content The measurements of the morphological features and the water content are performed on 100 randomly collected acorns for each population.

13 3/ Effect of osmotic water stress on germination of Holm oak (Quercus ilex) acorns from 5 provenances of Tunisia Acorns from 5 populations of Quercus ilex were subjected to germination test who it has been carried out in a growth chamber under a temperature of 25 C. and humidity of 70%. The applied water stress was simulated using the polyethylene glycol 6000 (PEG 6000) at different levels of water potential ( 0, 0.25, 0.5 and 1MPa). The germination potential was evaluated by determination of the percentage of germination and the average time of germination, time to 50% of germination. Aridity + P1 P15 P4 P10 P13 Sub-Humid Semi-Arid

14 RESULTS

15

16 Table 1: Geographical details of 16 populations of Quercus ilex at the Tunisian dorsal Populations Locality GPS coordinates Altitude Forest name Bioclimate P 1 Siliana (Kesra) 32S UTM m Mansoura (Glands doux) Sub humid P 2 Siliana (Kesra) 32S UTM m Mansoura (Glands amères) Sub humid P 3 Kef (El Ksour) 32S UTM m Aïn Fdhil Semi arid P 4 Makthar 32S UTM m Djebel ballouta Semi-arid P 5 Bargou (Aïn Bousaadia) 32S UTM m Ballouta Sub humid P 6 Bargou (Aïn Bousaadia) 32S UTM m Ballouta Sub humid P 7 Bargou (Aïn Bousaadia) 32S UTM m Ballouta Sub humid

17 Populations Locality GPS coordinates Altitude Forest name Bioclimate P 8 Bargou (Aïn Bousaadia) 32S UTM m Ballouta Sub humid P 9 Bargou (Djebel Esserj) 32S m Parc national Sub humid UTM Djebel esserj P 10 Zaghouan (Sidi Aouidet) 32S UTM P 11 Siliana 32S UTM P 12 Zaghouan 32S UTM P 13 El Krib 32S UTM m Djebel Mansour Semi arid 1074m Plateau Kesra Sub- humid 332m Sidi Médian Sub-humid 635m Djebel Boukhil Semi -arid P 14 Kef 32S m Jradou (Sakiet Sidi Sub- humid UTM Youssef) P 15 Kef 32S m Jradou Sakiet Sidi Sub -humid UTM Youssef) P 16 Gaafour 32S UTM m Ramlia, Sidi Ayed Semi-arid

18 2/ Morphological traits of acorns

19 ( lenght/diameter) ratio 2,7 a a a a ab a a a a a a a f 2,2 b e 1,7 c 1,2 P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 P15 P16 Populations Figure 1 Acorn lenght /diameter ratio of 16 tunisian populations of Quercus ilex. Values are presented as the means ± CI. Different letters denote statistically significant differences at the 5% level. Each bar represents a mean value from 100 acorns

20 Acorn dry weight (g) 6 d 5 d 4 abc abc abc c bc bc a ab f e 3 af af ac af 2 e 1 P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 P15 P16 Populations Figure 2: Acorn dry weight of 16 Tunisian populations of Quercus ilex. Values are presented as the means ± CI. Different letters denote statistically significant differences at the 5% level. Each bar represents a mean value from 100 acorns

21 Acorn Water content (%) 0,45 0,4 a ac 0,35 abc a ab bc a bcd bcd bcd b b bd 0,3 dbc bcd db 0,25 P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 P15 P16 Populations Figure 3 Acorn water content expressed on a fresh weight basis of 16 tunisian populations of Quercus ilex. Values are presented as the means ± CI. Different letters denote statistically significant differences at the 5% level. Each bar represents a mean value from 100 acorns

22 Conclusion 1 This study deals with the acorns morphology (Lenght, diameter and mass), analysed in 16 Tunisian populations of Quercus ilex from la DORSAL. Analysis of variance of morphological traits shows significant differences within populations. The highest values of dry weights were measured in populations P7 and P10, however P5 had the lowest acorn dry weight. In Conclusion, About the acorn Studied lenght/diameter Tunisian populations ratio, P16 of Quercus had the highest ilex, differ ratiofrom and the each lowest other ratioin belongs their acorn to P8. morphometry. Analyse of variance shows that acorn dimensions and weight are significantly different within populations. P1 and P15 (climate sub-humid) had the highest acorn water content but P10 (semi- arid) had the lowest acorn water content.

23 3/ Effect of osmotic water stress on germination of Holm oak

24 Germination P1 (%) P1 Germination P4 (%) P Germination P10 (%) P10 Germination P13 (%) P Germination P15 (%) P15 Figure 2. Germination Percentage (Gc) of the five populations (P1, P4, P10, P13 and P15) in response to different levels of water potential during 20 days Time (hours)

25 Figure 4: Time required to 50% germination of the 5 populations depending on the variation of the water potential. T50 was estimated by linear regression according to a logistic function.

26 Figure 5: Relationship between 1/T50 and water potential. The figure shows linear regression equation for each population.

27 Following water potentials are obtained for the 5 populations, by calculating the intercept after linear regression. Coefficient R2 of the linear regression is mentioned. Table 2: Water potential corresponding to loss of the germination for each population with correlation coefficient R2. Population Predawn Water potentiel (Mpa) R2 P P P P P

28 This work is carried out to test the behaviour of different populations of Quercus ilex, with regards to evaluate the effects of water stress at the germination stage. The germination potential was evaluated by determination of the percentage of germination, the average time of germination, time to 50% of germination. Without water stress, the germination behavior of the five populations is different according to the recorded results. Under water stress, the cumulative percentage of germination for 20 days for each population varies depending on the water potential. Decreasing of the water potential causes a decrease in the percentage of germination. The time of 50% of germination (T50%) varies with intensity of water stress for the five populations. The T 50% was 3 days for both populations P10 and P15, four days for P13 and 5 days for P4 at a water potential of 0 MPa. However, at a low level water potential (-1 MPa) the T 50% reached 4,6,8,9 and 10 days for populations P1,P15,P10,P13 and P4 respectively.

29 Conclusion Seed germination is one of the multiple criteria for populations selection regarding tolerance to water stress. The study of the effect of water stress shows that the five populations of Quercus ilex germinate at very low water potentials. Nevertheless, behavior variability to water stress was observed among the five populations. Indeed, populations P13 and P15 seemed to be more tolerant to water stress than other population(p1, P4 and P10). This study is a test. We must relate our results with climatic data. This work has to be repeated during at least 3 years to confirm this variability. This work should serve as guidelines for the selection of trees yielding fruits possessing the morphological characteristics. But we needs other studies to determinate how the morphological and physiological caracteristics of acorns are affected by biotic and abiotic factors.

30 Conclusion Seed germination is one of the multiple criteria for populations selection regarding tolerance to water stress. The study of the effect of water stress shows that the five populations of Quercus ilex germinate at very low water potentials. Nevertheless, behavior variability to water stress was observed among the five populations. Indeed, populations P13 and P15 seemed to be more tolerant to water stress than other population(p1, P4 and P10). This study is a test. We must relate our results with climatic data. This work has to be repeated during at least 3 years to confirm this variability. This work should serve as guidelines for the selection of trees yielding fruits possessing the morphological characteristics. But we needs other studies to determinate how the morphological and physiological caracteristics of acorns are affected by biotic and abiotic factors.

31