SITE FERTILITY AND LEAF NUTRIENTS OF SYMPATRIC EVERGREEN AND DECIDUOUS SPECIES OF QUERCUS IN CENTRAL COASTAL CALIFORNIA

Leaf and soil nutrient levels interact with and may each influence the other. We hypothesize that to the extent soil fertility influences th e nutritional state of trees, soil fertility should correlate with sum mer leaf nutrient levels, whereas to the extent that trees influence s oil nutrient levels, the quality of leaf litterfall should correlate w ith soil fertility. We examined these correlations for five sympatric oak species (genus Quercus) in central coastal California. Soil fertil ity, including both nitrogen and especially phosphorus, correlated sig nificantly with summer leaf nutrient levels. In contrast, phosphorus, but not nitrogen, in the leaf litterfall correlated positively with so il nutrients. These results suggest that soil nitrogen and phosphorus influence tree nutrient levels and that leaf phosphorus, but not leaf nitrogen, influence soil fertility under the trees. Feedback between t he soil and the tree for phosphorus, but not nitrogen, is apparently s ignificant and caused by species-specific differences in leaf quality and not by litterfall quality differences within a species. We also co mpared functional differences between the evergreen and deciduous oak species at our study site. There were no differences in soil nitrogen and only small differences for soil phosphorus between the phenologica l types. Differences in leaf nutrient concentration were much more pro nounced, with the evergreen species having substantially lower levels of both nitrogen and phosphorus. Evergreen species conserved more phos phorus, but not more nitrogen, than the deciduous species, but there w as no consistent relationship between retranslocation and either soil nitrogen or phosphorus. These results do not support the hypothesis th at evergreenness is an adaptation to low soil fertility in this system .