<?xml version="1.0" encoding="UTF-8"?><xml><records><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Ludwig, J. A.</style></author><author><style face="normal" font="default" size="100%">Cunningham, G.L.</style></author><author><style face="normal" font="default" size="100%">Whitson, P. D.</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Distribution of annual plants in North American deserts</style></title></titles><keywords><keyword><style  face="normal" font="default" size="100%">JRN</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">1988</style></year></dates><volume><style face="normal" font="default" size="100%">15</style></volume><pages><style face="normal" font="default" size="100%">221-227</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">Early researchers concluded that the winter-annual flora was richest in the California deserts and became relatively poorer towards the east, whereas summer-annuals were richest in the deserts of western Texas and their richness progressively declined in to eastern California.  US/IBP Desert Biome and subsequent studies support these trends and add much relevant information.  Winter-annuals have the C3 photosynthetic pathway, whereas most summer-annuals have the C4 pathway.  While the Sonoran and Chihuahuan deserts have a few C3 'summer' annuals (actually 'winter' annuals which can persist into the summer), the Mojave Desert lacks C3 summer-annuals.  The Great Basin Desert has only a few prevalent winter or summer-annuals (mostly introduced species).     Studies of the micro-distribution of desert-annuals have shown their close association with perennial shrubs.  Some shrubs produce substances that are reportedly toxic to some annuals; the role of such toxins in structuring annual plant communities is unclear.  The importance of nutrients associated with shrub canopies on the micro-distribution of many desert-annuals is becoming evident through LTER and other studies.</style></abstract><accession-num><style face="normal" font="default" size="100%">LTER.1988-91769</style></accession-num></record></records></xml>