<?xml version="1.0" encoding="UTF-8"?><xml><records><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>6</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Jarrell, W. M.</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Desertification</style></title><secondary-title><style face="normal" font="default" size="100%">Encyclopedia of Earth Science</style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">JRN</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">1992</style></year></dates><publisher><style face="normal" font="default" size="100%">Academic Press</style></publisher><pub-location><style face="normal" font="default" size="100%">San Diego</style></pub-location><language><style face="normal" font="default" size="100%">eng</style></language><accession-num><style face="normal" font="default" size="100%">LTER.1992-91573</style></accession-num></record><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%">Virginia, R. A.</style></author><author><style face="normal" font="default" size="100%">Jarrell, W. M.</style></author><author><style face="normal" font="default" size="100%">Whitford, W. G.</style></author><author><style face="normal" font="default" size="100%">Freckman, DW</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Soil biota and soil properties associated with surface rooting zone of mesquite (&lt;i&gt;Prosopis glandulosa&lt;/i&gt;) in historical and recently desertified Chihuahuan Desert habitats</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%">1992</style></year></dates><volume><style face="normal" font="default" size="100%">14</style></volume><pages><style face="normal" font="default" size="100%">90-98</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">The woody legume, mesquite (&lt;i&gt;Prosopis glandulosa&lt;/i&gt;), has expanded from its historical habitats (playas and arroyos) to recently occupied grassland and dune habitats during the desertification of perennial grasslands in the Chihuahuan Desert.  We studied historical and recently occupied sites, having hypothesized that the trophic structure and population density of soil microarthropods and nematodes associated with the surface root system of mesquite would differ in sites representing historical and recent habitats, and that the N mineralization potential would be lower in the recent habitats.  Our results showed that net N mineralization potential did not differ significantly among the sites, even though soil nutrient concentrations and texture varied widely.</style></abstract><accession-num><style face="normal" font="default" size="100%">LTER.1992-91598</style></accession-num></record><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%">Schlesinger, W.H.</style></author><author><style face="normal" font="default" size="100%">Reynolds, J. F.</style></author><author><style face="normal" font="default" size="100%">Cunningham, G.L.</style></author><author><style face="normal" font="default" size="100%">Huenneke, L.F.</style></author><author><style face="normal" font="default" size="100%">Jarrell, W. M.</style></author><author><style face="normal" font="default" size="100%">Virginia, R. A.</style></author><author><style face="normal" font="default" size="100%">Whitford, W. G.</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Biological Feedbacks in Global Desertification</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%">1990</style></year></dates><urls><web-urls><url><style face="normal" font="default" size="100%">http:usda-ars.nmsu.edu/biblio/pdf/111.pdf</style></url></web-urls></urls><volume><style face="normal" font="default" size="100%">247</style></volume><pages><style face="normal" font="default" size="100%">1043-1048</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">Studies of ecosystem processes on the Jornada Experimental Range in southern New Mexico suggest that long-term grazing of semiarid grasslands leads to an increase in the spatial and temporal heterogeneity of water, nitrogen, and other soil resources. Heterogeneity of soil resources promotes invasion by desert shrubs, which leads to a further localization of soil resources under shrub canopies. In the barren area between shrubs, soil fertility is lost by erosion and gaseous emissions. This positive feedback leads to the desertification of formerly productive land in southern New Mexico and in other regions, such as the Sahel. Future desertification is likely to be exacerbated by global climate warming and to cause significant changes in global biogeochemical cycles.</style></abstract><accession-num><style face="normal" font="default" size="100%">LTER.1990-91658</style></accession-num></record><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%">Silva, S.</style></author><author><style face="normal" font="default" size="100%">Whitford, W. G.</style></author><author><style face="normal" font="default" size="100%">Jarrell, W. M.</style></author><author><style face="normal" font="default" size="100%">Virginia, R. A.</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">The microarthropod fauna associated with a deep rooted legume, &lt;i&gt;Prosopis glandulosa&lt;/i&gt;, in the Chihuahuan Desert</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%">1989</style></year></dates><volume><style face="normal" font="default" size="100%">7</style></volume><pages><style face="normal" font="default" size="100%">330-335</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">The rhizosphere microarthropod fauna of a woody, deep-rooted legume, &lt;i&gt;Prosopis glandulosa&lt;/i&gt;, was sampled at four sites in the northern Chihuahuan Desert and compared with the rhizosphere microarthropod fauna of a co-dominant shrub, &lt;i&gt;Larrea tridentata&lt;/i&gt;.  Prostigmatid mites (&lt;i&gt;Speleorchestes&lt;/i&gt; sp., &lt;i&gt;Neognathus&lt;/i&gt; sp., &lt;i&gt;Rhagidia&lt;/i&gt; sp., &lt;i&gt;Tydaeolus&lt;/i&gt; sp., &lt;i&gt;Steneotarsonemus&lt;/i&gt; sp., &lt;i&gt;Tarsonemus&lt;/i&gt; sp., &lt;i&gt;Nanorchestes&lt;/i&gt; sp., &lt;i&gt;Gordialycus&lt;/i&gt; sp.), the cryptostigmatid mites (&lt;i&gt;Bankisonoma ovata&lt;/i&gt; and &lt;i&gt;Passalozetes neomexicanus&lt;/i&gt;), the mesostigmatid (&lt;i&gt;Protogamasellus mica&lt;/i&gt;), and the collembolan (&lt;i&gt;Brachystomella arida&lt;/i&gt;) characterized the fauna at depth greater than 1 m.  Microarthropods were recovered from soils at a depth of 13 m at the edge of a dry lake and at depths of 7 m in a dry wash which were pre-European man &lt;i&gt;P. glandulosa&lt;/i&gt; habitats.  In habitats where  &lt;i&gt;P. glandulosa&lt;/i&gt; is a recent invader, root depth and microarthropods were less than 3 m.  In most habitats, population densities of microarthropods at depth &lt;0.5 m were more than 100 times those at depths &gt;0.5 m.  Population densities of microarthropods associated with  &lt;i&gt;P. glandulosa&lt;/i&gt; growing at the edge of a dry wash were not significantly smaller at 0.5-1.0 m depth than at 0-0.5 m.  The deep-rhizosphere microarthropod fauna is a reduced subset of the fauna of surficial soils, suggesting that this fauna plays a role in decomposition and mineralization processes functionally similar to that of microarthropods in surficial soils.</style></abstract><accession-num><style face="normal" font="default" size="100%">LTER.1989-91732</style></accession-num></record><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>6</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Virginia, R. A.</style></author><author><style face="normal" font="default" size="100%">Jarrell, W. M.</style></author><author><style face="normal" font="default" size="100%">P.W. Rundel</style></author><author><style face="normal" font="default" size="100%">Shearer, G.</style></author><author><style face="normal" font="default" size="100%">Kohl, D. H.</style></author></authors><secondary-authors><author><style face="normal" font="default" size="100%">Nagy, K. A.</style></author></secondary-authors></contributors><titles><title><style face="normal" font="default" size="100%">The use of variation in the natural abundance of 15N to assess symbiotic nitrogen fixation by woody plants</style></title><secondary-title><style face="normal" font="default" size="100%">Stable Isotopes in Ecological Research</style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">JRN</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">1989</style></year></dates><publisher><style face="normal" font="default" size="100%">Springer-Verlag</style></publisher><pub-location><style face="normal" font="default" size="100%">New York</style></pub-location><pages><style face="normal" font="default" size="100%">375-395</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">This paper will present selected examples of applications of the natural abundance method to ecological studies.  The emphasis will be on results from ongoing ecosystem level studies examining the role of woody legumes in N cycling in warm deserts... Data from other systems (tropical forest, chaparral) where significant sustained inputs of N fixed by woody plants may affect ecosystem processes are also discussed to demonstrate the utility of the natural abundance method in a diversity of systems.     The natural 15N abundance approach in an important advancement for the study of deeply rooted plants.  Our studies have show that contrary to previous speculation, deeply rooted plants in arid ecosystems can support root symbioses at depths not easily studied using other techniques.</style></abstract><accession-num><style face="normal" font="default" size="100%">LTER.1989-91751</style></accession-num></record><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>6</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Virginia, R. A.</style></author><author><style face="normal" font="default" size="100%">Jarrell, W. M.</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Approaches for studying the function of deep root systems</style></title><secondary-title><style face="normal" font="default" size="100%">Plant Response to Stress</style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">JRN</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">1987</style></year></dates><publisher><style face="normal" font="default" size="100%">Springer-Verlag</style></publisher><pub-location><style face="normal" font="default" size="100%">Berlin Heidelberg</style></pub-location><pages><style face="normal" font="default" size="100%">107-127</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">The potential importance of deep root systems to plant function has long been recognized.  Until recently there have been few attempts to actually quantify the importance of deep roots in securing water and nutrients.  The development of new methods and approaches which allow direct and indirect study of deep root function offers new and exciting possibilities.  Modern drilling equipment can extract deep soil samples with minimal disturbance to roots and the soil biota.  The application of stable isotope techniques using variations in natural abundance is especially exciting since analysis of easily collected aboveground tissues provides information on the function of deep root systems.  Information on symbiotic nitrogen fixation and the identification of water sources used by the plant can be obtained with this approach.  Although poorly described in natural systems, the structure, species composition and population densities of soil rhizosphere biota may proved information on the relative extent of root activity at a particular soil depth.  The application of more than one of these approaches to a single system provides the best opportunity to better understand the functional importance of deep roots to plants.</style></abstract><accession-num><style face="normal" font="default" size="100%">LTER.1987-91815</style></accession-num></record></records></xml>