Nitrogen dynamics in arctic tundra soils of varying age: differential responses to fertilization and warming

In the foothills of the Brooks Range, Alaska, different glaciation histories have created landscapes with varying soil age. Productivity of most of these landscapes is generally N limited, but varies widely, as do plant species composition and soil properties (e.g., pH). We hypothesized that the projected changes in productivity and vegetation composition under a warmer climate might be mediated through differential changes in N availability across soil age. We compared readily available [water-soluble NH₄ ⁺, NO₃ ^?, and amino acids (AA)], moderately available (soluble proteins), hydrolyzable, and total N pools across three tussock-tundra landscapes with soil ages ranging from 11.5k to 300k years. The effects of fertilization and warming on these N pools were also compared for the two younger sites. Readily available N was highest at the oldest site, and AA accounted for 80–89 % of this N. At the youngest site, inorganic N constituted the majority (80–97 %) of total readily available N. This variation reflected the large differences in plant functional group composition and soil chemical properties. Long-term (8–16 years) fertilization increased the soluble inorganic N by 20- to 100-fold at the intermediate-age site, but only by twofold to threefold at the youngest site. Warming caused small and inconsistent changes in the soil C:N ratio and AA, but only in soils beneath Eriophorum vaginatum, the dominant tussock-forming sedge. These differential responses suggest that the ecological consequences of warmer climates on these tundra ecosystems are more complex than simply elevated N-mineralization rates, and that the responses of landscapes might be impacted by soil age, or time since deglaciation.     

Seasonal dynamics of the fish parasite Neoplagioporus ayu (Digenea) in its definitive host, Plecoglossus altivelis, in the Chikugo River, Kyushu, Japan

Seasonal dynamics of the fish parasite Neoplagioporus ayu (Digenea; Opecoelidae; Plagioporinae) in its definitive host, the ayu Plecoglossus altivelis, in the Chikugo River, Kyushu, Japan, was examined. Natural ayu are amphidromous. In the upper Chikugo River, ayu fry raised in hatcheries are released into the river every spring because the migration of ayu is completely blocked by a dam that has no fish-pass channel. Ayu collected in April 2003 (within 1 month after release) harbored no N. ayu, but the prevalence of N. ayu rose to about 80% in May. The prevalence, abundance, and maturity of N. ayu were maintained at high levels from June to September. These finding indicate that the life cycle of N. ayu is completed in a freshwater area, although its intermediate hosts have not yet been identified despite the intense examination of invertebrates.     

Factors influencing body composition in persons with spinal cord injury: a cross-sectional study.

To determine the body composition differences across age, 133 men with chronic spinal cord injury (SCI) (66 with tetraplegia, 67 with paraplegia) were compared with an age-, height-, and ethnicity-matched able-bodied male reference population (n = 100) using two different dual-energy X-ray absorptiometry densitometers. The effects of duration of injury, level, and completeness of lesion were analyzed in the SCI population. Independent of age, total body and regional lean mass were lower and fat mass was higher in persons with SCI compared with controls. The SCI group was 13 +/- 1% (means +/- SE) fatter per unit of body mass index (kg/m2) compared with the control group (P < 0.0001). Advancing age was strongly associated with less lean mass and greater adiposity in those with SCI, whereas it was mildly related in the controls. Total body and regional arm and trunk, but not leg, lean tissues were lower in subjects with SCI, across all ages, than in the controls. In summary, persons with SCI were fatter for any body mass index and demonstrated significantly less lean and more adipose tissues for any given age compared with controls.