<?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%">SILLA, F.</style></author><author><style face="normal" font="default" size="100%">Escudero, A.</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Nitrogen-use efficiency: trade-offs between N productivity and mean residence time at organ, plant and population levels</style></title><secondary-title><style face="normal" font="default" size="100%">Functional Ecology</style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">Drought stress</style></keyword><keyword><style  face="normal" font="default" size="100%">herbivory</style></keyword><keyword><style  face="normal" font="default" size="100%">nitrogen loss</style></keyword><keyword><style  face="normal" font="default" size="100%">nitrogen uptake</style></keyword><keyword><style  face="normal" font="default" size="100%">plant strategies</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">2004</style></year><pub-dates><date><style  face="normal" font="default" size="100%">2004///</style></date></pub-dates></dates><urls><web-urls><url><style face="normal" font="default" size="100%">http://dx.doi.org/10.1111/j.0269-8463.2004.00872.x</style></url></web-urls></urls><volume><style face="normal" font="default" size="100%">18</style></volume><pages><style face="normal" font="default" size="100%">511 - 521</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">* 1Nitrogen-use efficiency (NUEN) is often decomposed into the product of N productivity (AN) and the mean residence time of N (MRTN). Theory suggests a trade-off between both components, but direct experimental evidence is still scarce. A field study with young trees of the evergreen Quercus ilex and the marcescent-evergreen Quercus faginea was carried out to test this trade-off through analysis of plant traits at organ, whole-plant and population levels. * 2Specific leaf area (SLA) was the main trait positively related to AN in Q. faginea. By contrast, greater litter production and consumption by caterpillars resulted in larger N losses and shorter MRTN in Q. faginea. Early leaf senescence in Q. faginea produced leaf litter with high N concentration that contributed significantly to N loss. Moreover, Q. ilex had higher plant survivorship. The inverse relationship between leaf longevity and SLA is probably a key component of the trade-off between N losses and plant N productivity. * 3Quercus faginea had greater N uptake from soil, linked to its longer specific root length of fine roots and greater biomass allocation to underground tissues. Smaller N losses in Q. ilex compensated for its smaller N uptake and allowed a similar N balance at whole-plant level. * 4Our results support the hypothesis of a trade-off between AN and MRTN. Quercus ilex had a long MRTN, while Q. faginea has a high AN, and vice versa. The long MRTN in Q. ilex involves not only reduced N loss through long intrinsic leaf life span, but also resistance to harsh environmental factors and defence against herbivores. This suggests that a long MRTN is a potentially successful strategy in nutrient-poor environments.</style></abstract><issue><style face="normal" font="default" size="100%">4</style></issue><notes><style face="normal" font="default" size="100%">The following values have no corresponding Zotero field:&lt;br/&gt;publisher: Blackwell Science Ltd</style></notes></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%">SILLA, F</style></author><author><style face="normal" font="default" size="100%">Escudero, a</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Nitrogen-use efficiency: trade-offs between N productivity and mean residence time at organ, plant and population levels</style></title><secondary-title><style face="normal" font="default" size="100%">Functional Ecology</style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">Drought stress</style></keyword><keyword><style  face="normal" font="default" size="100%">herbivory</style></keyword><keyword><style  face="normal" font="default" size="100%">nitrogen loss</style></keyword><keyword><style  face="normal" font="default" size="100%">nitrogen uptake</style></keyword><keyword><style  face="normal" font="default" size="100%">plant strategies</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">2004</style></year></dates><publisher><style face="normal" font="default" size="100%">Blackwell Science Ltd</style></publisher><volume><style face="normal" font="default" size="100%">18</style></volume><pages><style face="normal" font="default" size="100%">511-521</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">* 1Nitrogen-use efficiency (NUEN) is often decomposed into the product of N productivity (AN) and the mean residence time of N (MRTN). Theory suggests a trade-off between both components, but direct experimental evidence is still scarce. A field study with young trees of the evergreen Quercus ilex and the marcescent-evergreen Quercus faginea was carried out to test this trade-off through analysis of plant traits at organ, whole-plant and population levels. * 2Specific leaf area (SLA) was the main trait positively related to AN in Q. faginea. By contrast, greater litter production and consumption by caterpillars resulted in larger N losses and shorter MRTN in Q. faginea. Early leaf senescence in Q. faginea produced leaf litter with high N concentration that contributed significantly to N loss. Moreover, Q. ilex had higher plant survivorship. The inverse relationship between leaf longevity and SLA is probably a key component of the trade-off between N losses and plant N productivity. * 3Quercus faginea had greater N uptake from soil, linked to its longer specific root length of fine roots and greater biomass allocation to underground tissues. Smaller N losses in Q. ilex compensated for its smaller N uptake and allowed a similar N balance at whole-plant level. * 4Our results support the hypothesis of a trade-off between AN and MRTN. Quercus ilex had a long MRTN, while Q. faginea has a high AN, and vice versa. The long MRTN in Q. ilex involves not only reduced N loss through long intrinsic leaf life span, but also resistance to harsh environmental factors and defence against herbivores. This suggests that a long MRTN is a potentially successful strategy in nutrient-poor environments.</style></abstract></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%">Joffre, R</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Plant and soil nitrogen dynamics in mediterranean grasslands: a comparison of annual and perennial grasses</style></title><secondary-title><style face="normal" font="default" size="100%">Oecologia</style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">Annual</style></keyword><keyword><style  face="normal" font="default" size="100%">grassland</style></keyword><keyword><style  face="normal" font="default" size="100%">Nitrogen mineralization</style></keyword><keyword><style  face="normal" font="default" size="100%">nitrogen uptake</style></keyword><keyword><style  face="normal" font="default" size="100%">Perennial</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">1990</style></year></dates><volume><style face="normal" font="default" size="100%">85</style></volume><pages><style face="normal" font="default" size="100%">142-149</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">The predominance of annual species in the rangelands of southwestern Spain is not due only to climatic factors but is also strongly influenced by grazing management. Manipulating the grazing system in an experimental plot gave a vegetation structure with patches of annual grasses (mainly Vulpia ssp. and Bromus hordeaceus) and patches of perennial grasses (mainly Phalaris aquatica). This vegetation change allowed us to test the hypothesis that life-cycle differences between annual and perennial grasses affect soil nitrogen availability and plant uptake. Nitrogen availability, measured by in situ incubation, and nitrogen uptake were measured through the growing period (October to June). Amounts of in situ mineralized nitrogen over the whole growth phase were more important for soils supporting perennials (37 ppm) than for soils supporting annuals (27 ppm). The difference between the mineral nitrogen produced in situ and the mineral nitrogen accumulated during the same time in the soil allowed an estimation of the maximum mineral nitrogen quantity which can be taken up by the vegetation during each incubation period. The quantities accumulated over the year were 47 and 38 ppm (or 103 and 83 kg/ha) for soils supporting perennials and annuals respectively. For the same period, amounts of nitrogen immobilized in biomass production were 90 and 70 kg/ha for perennials and annuals respectively. During the autumn, a large proportion of mineral nitrogen was leached from soils supporting annual plants which had only just commenced germination. By contrast, the ability to use mineral nitrogen as soon as autumn rains occurred gave a competitive advantage to the perennial species, but only if they were protected from grazing during this period. The higher mineralization and use of this nitrogen reserve by perennials indicates that they made more efficient use of nitrogen resources than annuals, and validate the initial hypothesis.</style></abstract></record></records></xml>