Evans R D, Ehleringer J R
Stable Isotope Ratio Facility for Environmental Research, Department of Biology, University of Utah, 84112, Salt Lake City, UT, USA.
Oecologia. 1994 Sep;99(3-4):233-242. doi: 10.1007/BF00627735.
Arid environments are characterized by spatial and temporal variation in water and nitrogen availability. differences in δN and δD of four co-occurring species reveal contrasting patterns of plant resource acquisition in response to this variation. Mineralization potential and nitrogen concentration of surface soils associated with plant canopies were greater than inter-canopy locations, and values decreased with increasing depth in both locations. Mineralization potential and nitrogen concentration were both negatively correlated with soil δN. The spatial variation in soil δN caused corresponding changes in plant δN such that plant δN values were negatively correlated with nitrogen concentration of surface soils. Plants occurring on soils with relatively high nitrogen concentrations had lower δN, 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 (Juniperus, Pinus andArtemisia) relied on the episodic availability of water and nitrogen at the soil surface. δN values did not vary through the year, while xylem pressure potentials and stem-water δD 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. δN values ofChrysothamnus increased throughout the year, while xylem pressure potentials and stem-water δD values remained constant. The contrasting patterns of resource acquisition have important implications for community stability following disturbance. Disturbance 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 drougnt.
干旱环境的特点是水和氮的可利用性存在时空变化。四种共生植物的δN和δD差异揭示了植物对这种变化的资源获取模式的对比。与植物冠层相关的表层土壤的矿化潜力和氮浓度高于冠层间区域，且两个区域的值均随深度增加而降低。矿化潜力和氮浓度均与土壤δN呈负相关。土壤δN的空间变化导致植物δN相应变化，使得植物δN值与表层土壤的氮浓度呈负相关。生长在氮浓度相对较高土壤上的植物比生长在氮浓度相对较低土壤上的植物具有更低的δN和更高的叶片氮浓度。水和氮利用呈现出两种一般的时间模式。三种植物（杜松、松树和蒿属植物）依赖于土壤表层水和氮的间歇性可利用性。δN值全年不变，而木质部压力势和茎水δD值随土壤表层土壤湿度变化而波动。相比之下，金色鼠尾草在干旱期间转向更稳定的水和氮源。金色鼠尾草的δN值全年增加，而木质部压力势和茎水δD值保持不变。资源获取的对比模式对干扰后的群落稳定性具有重要意义。干扰会导致土壤表层氮浓度降低，因此依赖表层水和氮的植物可能比在干旱期间转向更深层更稳定水和氮源的植物更易受影响。
