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Keywords:

  • competition;
  • drought;
  • facilitation;
  • nitrogen pulses;
  • trade-offs

Summary

1 A 3-year field study examined the physiological and demographic consequences of resource pulse use by an herbaceous, aridland perennial, Cryptantha flava, as well as potential competitive and facilitative interactions with larger shrubs.

2 We applied a pulse of urea and faecal pellets, simulating Mule deer excretions, to plants growing between and under Sagebrush and Rabbitbrush canopies.

3 We hypothesized that C. flava would show strong positive responses to N pulses in open microhabitats, and such plants had approximately 50% increases in leaf N concentrations within days of pulse application, accompanied by increased photosynthetic rates. Over the next year, higher rates of growth and reproduction were found in the plants receiving supplemental N.

4 We predicted that due to shading, plants would not respond to N pulses when growing under shrubs but supplemental N caused increases in leaf N similar to that in open growing plants. However, the response of both growth and reproduction was less than in the open, suggesting at least partial light limitation.

5 In 2000, a year of below average precipitation, all plants decreased in size, but survival was facilitated under shrubs (93%) relative to that of open plants (84%).

6 In the open, there was a trade-off between rapid growth in favourable years and survival in dry years. Supplemental N in years of average precipitation increased RGR from 0.42 to 1.16 rosettes rosette−1 year−1, but reduced from −0.02 to −0.2 in dry years.

7 Plant performance in aridlands thus results from complex interactions between microhabitat, nutrient pulses and yearly precipitation patterns.