Water and nitrogen dynamics in an arid woodland

  • Evans R
  • Ehleringer J
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Arid environments are characterized by spa-tial and temporal variation in water and nitrogen avail-ability. Differences in 815N and 8D of four co-occurring species reveal contrasting patterns of plant resource acquisition in response to this variation. Mineraliz-ation potential and nitrogen concentration of surface soils associated with plant canopies were greater than inter-canopy locations, and values decreased with in-creasing depth in both locations. Mineralization poten-tial and nitrogen concentration were both negatively correlated with soil 815N. The spatial variation in soil 15 N caused corresponding changes in plant 815 N such that plant 8~SN values were negatively correlated with nitrogen concentration of surface soils. Plants occur-ring on soils with relatively high nitrogen concen-trations had lower ~lSN, and higher leaf nitrogen concentrations, than plants occurring on soils with relatively low nitrogen concentrations. Two general temporal patterns of water and nitrogen use were apparent. Three species (Yuniperus, Pinus and Arternisia) relied on the episodic availability of water and nitrogen at the soil surface. 8~5N values did not vary through the year, while xylem pressure potentials and stem-water 8D values fluctuated with changes in soil moisture at the soil surface. In contrast, Chrysothamnus switched to a more stable water and nitrogen source during drought. 815N values of Chrysothamnus increased throughout the year, while xylem pressure potentials and stem-water 8D values remained constant. The contrasting patterns of re-source acquisition have important implications for community stability following disturbance. Distur-bance can cause a decrease in nitrogen concentration at the soil surface, and so plants that rely on surface water and nitrogen may be more susceptible than those that switch to more stable water and nitrogen sources at depth during drought.

Author-supplied keywords

  • Cryptobiotic crust
  • Desert ecology
  • Nitrogen cycle
  • Stable isotopes
  • Water source

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