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Differential responses of UK upland plants to nitrogen deposition   总被引:5,自引:0,他引:5  
Native upland species, Nardus stricta , Eriophorum vaginatum , Erica cinerea and Vaccinium vitis-idaea were given 3 or 60 kg N ha−1 yr−1, over 2 yr, applied as a mist (NH4NO3). The high N treatment increased above-ground biomass in all four species, but only significantly in E. cinerea , E. vaginatum and N. stricta . Biomass increases in E. vaginatum and N. stricta resulted from enhanced tiller production rather than shoot elongation. Root growth increased in N. stricta , so that root:shoot ratio in this species was unchanged by N. Root growth in E. vaginatum , E. cinerea and V. vitis-idaea did not respond to N and their root:shoot ratios decreased. Tissue N concentrations increased in both shoots and roots of all species in response to N. The accumulated foliar N did not increase the proportion of N allocated to Rubisco and the photosynthetic capacities of N. stricta , E. vaginatum and V. vitis-idaea were unchanged. Thus growth responses to N were due to altered allocation rather than increased rate of photosynthesis per unit leaf area. The high N treatment increased flower production significantly in E. cinerea but not in the other species. Although in this experiment dwarf shrubs were more responsive than graminoids to N, in the field at current N inputs the enhanced tillering of the graminoids may be more competitively advantageous, especially where gaps develop in the canopy. Thus increasing N deposition may lead to increased grassiness of upland heath, and in particular, a spread of N. stricta .  相似文献   
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Recruitment of Infauna: Positive or Negative Cues?   总被引:3,自引:0,他引:3  
The current paradigm for recruitment invokes passive transportof the larva in the water column followed by larval choice ofhabitat after deposition of the larva on or near the bottom.Larval choice is typically considered to be based on positivecues. I argue herein that the evidence for emphasizing rejectionof substrata by negative cues is at least as compelling as thatfor acceptance by positive cues. Data from the literature oncosts of rejection of settlement sites, types of emigrationby larvae and/or juveniles, and criteria by which infaunal larvaeand/or juveniles reject habitats are used to support this thes.  相似文献   
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Interphyletic Competition Among Marine Benthos   总被引:1,自引:0,他引:1  
Marine benthic environments are of two basic types: hard substrataand sediments. Organisms living in these habitats are morphologicallyand taxonomically diverse. Nevertheless, they can be subdividedinto a limited number of functional groups according to thedifferent ways they use and alter the substratum. Each functionalgroup is polyphyletic and includes many trophic modes. Two groups,tube builders in sediments and sheet-like animals on hard substrata,are examined in detail. Factors most important in competitionbetween members of different functional groups are often notthe same as for competition between members of the same functionalgroup. In both situations there is more evidence for competitionbetween distantly related taxa than between closely relatedforms.  相似文献   
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Structure and composition of soluble feather keratin   总被引:3,自引:0,他引:3       下载免费PDF全文
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