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PubMed2006

Dynamics of soil inorganic nitrogen and their responses to nitrogen additions in three subtropical forests, south China.

Three forests with different historical land-use, forest age, and species assemblages in subtropical China were selected to evaluate current soil N status and investigate the responses of soil inorganic N dynamics to monthly ammonium nitrate additions. Results showed that the mature monsoon evergreen broadleaved forest that has been protected for more than 400 years exhibited an advanced soil N status than the pine (Pinus massoniana) and pine-broadleaf mixed forests, both originated from the 1930's clear-cut and pine plantation. Mature forests had greater extractable inorganic N pool, lower N retention capacity, higher inorganic N leaching, and higher soil C/N ratios. Mineral soil extractable NH4(+)-N and NO3(-)-N concentrations were significantly increased by experimental N additions on several sampling dates, but repeated ANOVA showed that the effect was not significant over the whole year except NH4(+)-N in the mature forest. In contrast, inorganic N (both NH4(+)-N and NO3(-)-N) in soil 20-cm below the surface was significantly elevated by the N additions. From 42% to 74% of N added was retained by the upper 20 cm soils in the pine and mixed forests, while 0%-70% was retained in the mature forest. Our results suggest that land-use history, forest age and species composition were likely to be some of the important factors that determine differing forest N retention responses to elevated N deposition in the study region.

Analysis of Variance↗
PubMed1986

The effects of varying energy and nitrogen intake on nitrogen balance, body composition, and metabolic rate.

Body protein content (as measured by N balance) is normally regulated at a constant level, but is influenced by the level of both energy and N intake. Energy and N act synergistically on N balance. Not all forms of energy are equally effective in maintaining zero N balance; approximately 500 kcal of carbohydrate are required daily by the brain, and this minimum amount of dietary carbohydrate cannot be replaced by fat without loss of body N. Acute illness is accompanied by a catabolic state and an increase in the minimum N intake required for zero N balance. Nutritional depletion induces a metabolic state similar to that typical of growing organisms, in that N can be retained at zero energy balance. BMR includes essential thermogenesis and facultative thermogenesis. In addition, food has a specific dynamic action; it increases metabolic rate. Nutrient-induced increases in metabolic rate are exaggerated in acutely ill patients, such that large amounts of IV glucose may constitute a metabolic stress when given to patients. Equivalent N sparing can be obtained when as much as half of the glucose calories are replaced by fat calories. N balance is an incomplete index of nutritional status, and important information may be gained from measurements of body composition of acutely ill patients; in particular, the degree of expansion of ECW may predict outcome.

Acute Disease↗