How neighbor canopy architecture affects target plant performance

Plant competition is a process that occurs through the negative effects that individual plants have on resource availability to neighboring individuals. Therefore com- petition experiments need to examine how different species change resource availability to their neighbors, and how different species respond to these changes-allocationally, ar- chitecturally, and physiologically-through time. In a greenhouse study we used a model system of annuals to examine how canopies of species having differing morphologies differed in their architectures and light-interception abilities, and how different species performed when grown in these canopies. Abutilon theophrasti, Datura stramonium, and Polygonum pensylvanicum were grown as "targets," surrounded by neighbors of a single species. Neigh- bors could be any one of the target species or Setaria faberii. Plants were grown in pots, with one target plant and four neighbor plants. Detailed measurements of neighbor canopy structure and target plant canopy architecture were made at five harvests. Species with different morphologies showed large differences in canopy structure, par- ticularly when grass and forb species were compared. Setaria, a grass, had a more open canopy than the other species (all forbs), and was a consistently weak competitor. Overall, however, the relative effects of different neighbors on target biomass varied with target species. Target biomass was poorly correlated with neighbor biomass and leaf area, but was highly correlated with a measure of target light-interception ability that took into account both target leaf deployment and neighbor light interception. Despite clear differ- ences among neighbor species in canopy structure and effect on light penetration, the results suggest no broad generalizations about the effects of different species as neighbors. Knowl- edge of morphological, physiological, and life history characteristics of both the target and neighbor species may be necessary to explain the results of their competition.

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