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University of Adelaide (2018)

Clonal integration in Ochthochloa compressa under extreme environmental conditions

Al Mosallam, Mobarak S

Titre : Clonal integration in Ochthochloa compressa under extreme environmental conditions

Auteur : Al Mosallam, Mobarak S

Université de soutenance : University of Adelaide

Grade : Doctor of Philosophy (PhD) 2018

Résumé
While multiple studies have indicated the benefit of clonal integration and its role in resisting harsh environmental conditions, many researchers have indicated the need for further studies to understand fully the role of clonal integration and what determines the optimal strategies in various environments. In this project a series of studies were carried out in an extremely arid area (Al Thumam area in the Arabian Peninsula) to contribute to the knowledge of the benefits of clonal integration and understanding the behaviour of the clonal grass Ochthochloa compressa. This study is unique because it has investigated the benefits of clonality in one of the harshest environments where clonal plants are found. Experiment 1. I aimed to understand the patterns of spread and expansion of stolons, particularly whether stolons grew in random directions or are directed to better patches by the mother ramets to establish new daughter ramets maximizing their chances of success. I measured nutrient contents (N, P and K) in patches where mother plants grew, and where daughter ramets had established. In addition, I sampled nearby unoccupied patches. Mother plants were found in patches with higher N concentrations than where the daughter ramets were found. There were no differences in concentration of P ; while K was the lowest where not fully rooted daughters were found. The results suggest that daughter ramets did not establish in the best areas, indicating that the spread and expansion of stolons in the O. compressa occurs randomly. Experiment 2. I investigated the effects of the addition of fertilizer to mother and daughter ramets, including addition of nutrients to daughters disconnected from the mother ramets. Cutting the stolons caused to death of the daughter because these ramets were still dependent on the mother ramets. When connected, mothers that received nutrients affected some transference nutrients to daughter ramets. In contrast, the daughters accumulated the nutrients in above ground tissue when receiving added fertilizer, and there was no sign of transference to the mother ramet. Nutrient addition did not affect in any case the efficiency photosynthetic in both mother and daughter ramets. Experiment 3. In this experiment, I focused on the effect of the distance between mother and daughter ramets on the performance of daughter ramets. Daughters located close to the mother ramets could suffer competition by the mother if they are within the area of the root system. The results showed no significant differences between mother and daughter ramets in the concentration of nitrogen, phosphorus, and potassium nor in photosynthetic activity. This indicates that the daughters have the ability to resist competition through continued support from their mothers despite the scarcity of resources and the harsh environmental conditions in the study area. Experiment 4. In this experiment, I studied the effect of simulated grazing on both mother and daughter ramets when one of them was clipped and 50-60% of the leaves were removed, while remaining connected. Clipping did not affect the N content of mother ramets, but the concentration of phosphorus was decreased by clipping. K was lower in mother ramets connected to clipped daughters. Daughters connected to clipped mothers had higher N concentration but K and P did not change. Clipping of daughters did not have any effect on mother ramets concentration of nutrients. Photosynthetic efficiency did not record any significant differences when ramets were clipped. The results indicate that O. compressa strategy to resist grazing consists mainly in continuing to support daughter ramets. As far as I know, this is the first study of the phenomenon of clonal integration for O. compressa. This study revealed the importance of clonal integration for O. compressa to resistance of the harsh environmental conditions. Under the harsh conditions these plants live, the preferred strategy seems to be for the mother ramets to expand by producing ramets in random sites and heavily subsidize their growth with nutrient, and almost certainly water. Indeed, I documented strong evidence of transfer of nutrients through the stolons from mother ramets to daughter ramets but no evidence of transfer in the other direction even when nutrients were supplied to daughters. Further, seemingly surplus N available to the mother when clipping limited their foliar tissues was directed to daughters rather than to re-sprouting (which was probably limited by water availability). The insights obtained on the biology of O. compressa are critical as it is a native plant in a harsh environment, and it is suitable for fodder for pastoral animals, as well as having potential for restoration of degraded areas. Further, it provides new insights into the phenomenon of clonal integration in harsh habitats, and area which still needs further study and research.

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Page publiée le 9 novembre 2018