干旱区生态环境知识资源中心

We compared intra- and interspecific competitive responses of wild barley, Hordeum spontaneum, from four populations originating in distinct environments in Israel. The environments ranged along two parallel gradients of rainfall amount and predictability, from low (desert) to moderate (semi-steppe batha) to high (Mediterranean grassland and mountain, the latter also experiencing frost stress). The target barley plants grew under one of five densities (0, 4, 8, 16, and 32 surrounding plants per bucket) of either barley from the same population or oats (A vena sterilis) from a neutral population. The traits examined included estimates of fitness, reproductive traits, and resource allocation.

The effect of intraspecific competition was stronger than interspecific competition at a high increment of neighbor density (from 4 to 32 neighbors). There was no difference in interspecific competitive responses of plants originating in the four environments at any neighbor density increments, but intraspecific competitive responses of the four ecotypes consistently differed at low competitive intensity (4 neighbors). The superior competitors were the plants originating from Mediterranean grassland, the most favorable with respect to rainfall and abiotic stress (i.e., drought or frost) environment. The plants from the mountain environment, which is highly productive and predictable with respect to rainfall but experiences severe frost stress, were the poorest competitors. Our results are inconsistent with the hypothesis that there is no relationship between competitive ability and environmental favorability. High competitive ability appears to be a distinct property of plants living in favorable environments (i.e., productive, predictable, and without abiotic stress) corresponding to the "competitive" strategy of the C-S-R model. However, in less productive and/or predictable environments, or under conditions of severe abiotic stress, plant features other than ability to tolerate low water or nutrient levels may be more important, with reduced competitive ability as a trade-off.