title: Sensitivity of growth and biomass allocation patterns to increasing nitrogen: a comparison between ephemerals and annuals in the Gurbantunggut Desert, north-western China.
abstract: OBJECTIVE
  Biomass accumulation and allocation patterns are critical to quantifying ecosystem dynamics. However, these patterns differ among species, and they can change in response to nutrient availability even among genetically related individuals. In order to understand this complexity further, this study examined three ephemeral species (with very short vegetative growth periods) and three annual species (with significantly longer vegetative growth periods) in the Gurbantunggut Desert, north-western China, to determine their responses to different nitrogen (N) supplements under natural conditions.
  
  
  METHODS
  Nitrogen was added to the soil at rates of 0, 0.5, 1.0, 3.0, 6.0 and 24.0 g N m(-2) year(-1). Plants were sampled at various intervals to measure relative growth rate and shoot and root dry mass.
  
  
  RESULTS
  Compared with annuals, ephemerals grew more rapidly, increased shoot and root biomass with increasing N application rates and significantly decreased root/shoot ratios. Nevertheless, changes in the biomass allocation of some species (i.e. Erodium oxyrrhynchum) in response to the N treatment were largely a consequence of changes in overall plant size, which was inconsistent with an optimal partitioning model. An isometric log shoot vs. log root scaling relationship for the final biomass harvest was observed for each species and all annuals, while pooled data of three ephemerals showed an allometric scaling relationship.
  
  
  CONCLUSIONS
  These results indicate that ephemerals and annuals differ observably in their biomass allocation patterns in response to soil N supplements, although an isometric log shoot vs. log root scaling relationship was maintained across all species. These findings highlight that different life history strategies behave differently in response to N application even when interspecific scaling relationships remain nearly isometric.
authors.affiliation: Xinjiang Institute of Ecology and Geography, Key Laboratory of Biogeography and Bioresource in Arid Land, Chinese Academy of Sciences, Urumqi 830011, China.
authors.forename: Xiaobing
authors.initials: X
authors.lastname: Zhou
authors.forename: Yuanming
authors.initials: Y
authors.lastname: Zhang
authors.forename: Karl J
authors.initials: KJ
authors.lastname: Niklas
mesh_terms: D027703:Amaranthaceae / Q000187:drug effects* / Q000254:growth & development; D019659:Asteraceae / Q000187:drug effects* / Q000254:growth & development; D018533:Biomass; D002681:China; D003889:Desert Climate; D031314:Geraniaceae / Q000187:drug effects* / Q000254:growth & development; D008018:Life Cycle Stages; D009584:Nitrogen / Q000494:pharmacology*; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development; D018520:Plant Shoots / Q000187:drug effects / Q000254:growth & development; D011891:Rain; D012621:Seasons; D012987:Soil / Q000737:chemistry; D013045:Species Specificity; D013696:Temperature; D013997:Time Factors
chemical_list: D012987:Soil; D009584:Nitrogen
keywords: Alyssum linifolium; Biomass allocation; Ceratocarpus arenarius; Erodium oxyrrhynchum; Horaninowia ulicina; Hyalea pulchella; Salsola ruthenica; allometric relationship; annuals; ephemerals; nitrogen availability; optimal partitioning