Microbial dynamics and carbon and nitrogen cycling following re-wetting of soils beneath two semi-arid plant species

• Published in: Oecologia Vol. 142; no. 2; pp. 247 - 260
• Main Authors: Saetre, P, Stark, J.M
• Format: Journal Article
• Language: English
• Published: Berlin Springer 01-01-2005; Springer Nature B.V
• Subjects: Agricultural soils; Animal and plant ecology; Animal, plant and microbial ecology; Animals; Arid soils; Artemisia; Artemisia tridentata; Bacteria - growth & development; Biologi; Biological and medical sciences; Biology; Bromus; Bromus tectorum; carbon; Carbon - metabolism; carbon dioxide; Cell and molecular biology; Cell- och molekylärbiologi; Comparative Study; Desert soils; Ecosystem; Ecosystem Ecology; Eukaryota - growth & development; Feeding Behavior - physiology; food webs; Fundamental and applied biological sciences. Psychology; Fungi - growth & development; gas production (biological); Genetics; Genetik; Grassland soils; grazing; immobilization in soil; mathematical models; microbial activity; Microbial biomass; Microbial degradation; Mineralization; Models, Biological; NATURAL SCIENCES; NATURVETENSKAP; Nematoda; Nematoda - physiology; Nitrification; Nitrogen; Nitrogen - metabolism; Nitrogen cycle; Organic matter; Organic soils; Plant species; Population Dynamics; Protozoa; Protozoa/growth & development; rain; semiarid soils; shrublands; Soil biochemistry; soil fauna; Soil Microbiology; Soil microorganisms; Soil moisture; soil nematodes; soil respiration; Soil types; Soil water; soil water content; Soils; Synecology; Terrestrial ecosystems; Utah; Water; Wetting; Utah; USA, Utah; Microbial food webs; Microbial model; Immobilization; Biogeochemical cycle; N mineralization; Climatic zone; Carbon; Substrate; Trophic chain; Soils; Plant; N immobilization; Nitrogen cycle; Food web; Mineralization; Semi arid zone; Substrate-use efficiency; Models; U.S. Gov't; Research Support; Biological; Non-U.S. Gov't; Non-P.H.S
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/s00442-004-1718-9

Sporadic summer rainfall in semi-arid ecosystems can provide enough soil moisture to drastically increase CO₂ efflux and rates of soil N cycling. The magnitudes of C and N pulses are highly variable, however, and the factors regulating these pulses are poorly understood. We examined changes in soil respiration, bacterial, fungal and microfaunal populations, and gross rates of N mineralization, nitrification, and NH₄⁺ and NO₃⁻ immobilization during the 10 days following wetting of dry soils collected from stands of big sagebrush (Artemisia tridentata) and cheatgrass (Bromus tectorum) in central Utah. Soil CO₂ production increased more than tenfold during the 17 h immediately following wetting. The labile organic C pool released by wetting was almost completely respired within 2-3 days, and was nearly three times as large in sagebrush soil as in cheatgrass. In spite of larger labile C pools beneath sagebrush, microbial and microfaunal populations were nearly equal in the two soils. Bacterial and fungal growth coincided with depletion of labile C, and populations peaked in both soils 2 days after wetting. Protozoan populations, whose biomass was nearly 3,000-fold lower than bacteria and fungi, peaked after 2-4 days. Gross N mineralization and nitrification rates were both faster in cheatgrass soil than in sagebrush, and caused greater nitrate accumulation in cheatgrass soil. Grazing of bacteria and fungi by protozoans and nematodes could explain neither temporal trends in N mineralization rates nor differences between soil types. However, a mass balance model indicated that the initial N pulse was associated with degradation of microbial substrates that were rich in N (C:N &lt 8.3), and that microbes had shifted to substrates with lower N contents (C:N = 15-25) by day 7 of the incubation. The model also suggested that the labile organic matter in cheatgrass soil had a lower C:N ratio than in sagebrush, and this promoted faster N cycling rates and greater N availability. This study provides evidence that the high N availability often associated with wetting of cheatgrass soils is a result of cheatgrass supplying substrates to microbes that are of high decomposability and N content.