Carbon and nitrogen dynamics in the rhizosphere of Pinus ponderosa seedlings
The rhizosphere is a dynamic soil region characterized by dense microbial populations and enhanced rates of microbial processes. The rhizosphere may be especially important in determinign the spatial distribution of carbon and nitrogen cycling in forest soils. The author has investigated the flow of carbon from roots to the soil, the quantity and metabolic status of bacteria and fungi, and the production and consumption of inorganic nitrogen in the rhizosphere of Pinus ponderosa seedlings. The role of plant/microbial competition for inorganic nitrogen in determining the availability of nitrogen to plant assimilation was assessed. The author examined the flow of recently fixed photosynthate from roots to the soil using a [sup 14]C pulse-labelling technique. The highest concentration of recently fixed photosynthate carbon in the soil was adjacent to the young root tip region. Fine mycorrhizal roots had the highest rate of carbon loss to the soil per unit carbon assimilated by the root. Mycorrhizal hyphae played an important role in the redistribution of recently fixed photosynthate throughout the soil. The input of plant carbon to the soil by rhizodeposition was an important energy source for the microbial community even in soil not directly adjacent to the root. In short-term [sup 15]N experiments, the author observed that rates of mineralization and NH[sub 4][sup +] immobilization were higher in soils harvested from adjacent to roots than in soils harvested from greater than 5 mm from any root. Results from intact microcosms suggest that NH[sub 4][sup +] supply and competition between roots, heterotrophs and nitrifiers for NH[sub 4][sup +] were the direct controls on NH[sub 4][sup +] immobilization rates rather than the supply of, recently fixed carbon by rhizodeposition. Plants were more successful competitors for NH[sub 3][sup [minus]] than for NH[sub 4][sup +].
- Research Organization:
- California Univ., Berkeley, CA (United States)
- OSTI ID:
- 6914222
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
PINES
PHOTOSYNTHESIS
SOILS
MINERAL CYCLING
BIOLOGICAL AVAILABILITY
CARBON 14
CARBON CYCLE
MYCORRHIZAS
NITROGEN 15
NITROGEN CYCLE
NUTRIENTS
ORGANIC COMPOUNDS
ROOTS
SEEDLINGS
SOIL CHEMISTRY
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CARBON ISOTOPES
CHEMICAL REACTIONS
CHEMISTRY
CONIFERS
EVEN-EVEN NUCLEI
ISOTOPES
LIGHT NUCLEI
NITROGEN ISOTOPES
NUCLEI
ODD-EVEN NUCLEI
PHOTOCHEMICAL REACTIONS
PINOPHYTA
PLANTS
RADIOISOTOPES
STABLE ISOTOPES
SYNTHESIS
TREES
YEARS LIVING RADIOISOTOPES
540220* - Environment
Terrestrial- Chemicals Monitoring & Transport- (1990-)
560300 - Chemicals Metabolism & Toxicology