The comparative ecology of plant responses to nutrient availability

Although soil mineral availability is among the most important factors controlling plant distributions, we have far more speculation than reliable knowledge about what traits adapt plants to different levels of nutrients. The studies which comprise this dissertation address a variety of hypotheses concerning the adaptation of plants to environments differing in soil resource availability.; Chapter two presents data which support the hypothesis that the topology of root system branching differs in species from high and low soil resource sites. Grass species from two sites in Israel (one a poor soil desert site, the other a richer coastal site) have uniform and invariant branching patterns. Dicot species show a plastic response to soil resource availability, and species from the resource poor desert site had more "herringbone" topologies than those from the coastal site.; Chapter three presents the results of an experiment designed to test for hypothesized differences in the leaf nitrogen-photosynthesis relationship between species which utilize the NAD-ME and NADP-ME variants of C{dollar}sb4{dollar} photosynthesis. No differences were found.; Chapter four examines the mechanistic underpinnings of intraspecific differences in growth response to nitrogen supply. There was no correlation between the RGR of 17 grass species grown in high and low nitrogen conditions, and the plant characteristics associated with RGR were different in the two treatments. At high nitrogen availability high growth rate was associated with high leaf area on either a plant weight (LAR) or leaf weight (SLA) basis. In low nutrient conditions high RGR was associated instead with a high leaf nitrogen content.; Chapter five presents a test of the hypothesis that species from fertile environments have a lower RWR than those from infertile environments, when grown under optimal nutrient conditions. No relationship was found. Chapter five also presents evidence for a positive relationship between the RGR{dollar}rmsb{lcub}max{rcub}{dollar} of a plant species and the fertility of the habitats in which it is typically found. An analysis of the hypothesis that interspecific hierarchies of plant growth rate are consistent across nutrient gradients shows equivocal results, pointing out what may be a general shortcoming in the design of experiments which address this question.