Interactions between neighbouring plants

Eve, Chrisopher (1998). Interactions between neighbouring plants. PhD thesis The Open University.



This thesis addresses the issue of interactions between neighbouring plants by looking at theory and models used in the study of wild plants with a view to applying them in the design of agroforests. In Part I difficulties of designing mixed crop stands are considered. Grime's model of the ecological strategies pursued by wild plants is described and its potential usefulness pointed out. Experimental results are presented suggesting that stress tolerant trees may interfere less with an understorey component than do competitive trees through the different patterns of spatial occupation manifested by their roots.

Part II describes a statistical method to determine how any measurable attribute of one plant depends on the proximity and/or other characters of neighbouring plants. The method overcomes the need for unfeasibly large numbers of treatments encountered by conventional field trial methods.

The method has the potential to offer a firm basis for the design of optimized plant production systems; and will also allow ecologists to detect and quantify interactions between wild plants in the field.

Part III, using concepts of Evolutionary Game Theory, examines the question of cooperation in plants: both between the green plant and its associated vesicular-arbuscular mycorrhizal (VAM) fungi; and between neighbouring green plants connected by common VAM fungal hyphae. Exploring the implications for plants of Axelrod and Hamilton's (1981) Game Theoretic approach to the evolution of cooperative behaviour, it examines a logical problem in the view that the relationship between a green plant and associated VAM fungus is mutually beneficial. That the association is of mutual benefit would be insufficient to explain its persistence, and the fact that it does persist tells us something about its structure.

It is shown that no logical paradox exists in postulating the simultaneous existence of competition for resources and of resource-sharing cooperation between a given pair of neighbouring green plants; and that at least a certain minimal type of cooperation may be deemed to exist between connected plant neighbours. Putting together findings from two fields - direct nutrient transfers and biotic specialisation - solves problems for both, and provides evidence for inter-plant cooperation. Possible evolutionary stages through which cooperation could have passed are discussed. Given this theory it can no longer safely be assumed that plants do not cooperate, and experimental results are presented suggesting that they may be able to.

Scientific and economic implications are indicated for all three areas covered. Fertile ground exists for further research and suggestions are made for directions and methods.

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