| Sumario: | In deserts, seedling emergence occurs only
after precipitation threshold has been exceeded,
however, the presence of trees modifies microenvironmental
conditions that might affect the
effectiveness of a water pulse. In the Monte
desert, Prosopis flexuosa trees generate
different micro-environmental conditions that
might influence grass seedlings establishment.
The objective of this work was: a) to know
the effective minimum water input event that
triggers the emergence of native perennial
grass seedlings; b) to relate this fact with the
effect of the shade of P. flexuosa canopy and
the seasonal temperatures. Three important
forage species of the Monte were studied:
Pappophorum caespitosum and Trichloris crinita,
with C4, and Jarava ichu, with C3 metabolism.
Each season, seeds of these species were sown
in pots placed at two light conditions: shade
(similar to P. flexuosa cover) and open area, and
with seven irrigation treatments (0, 10, 20, 30,
40, 2*10 and 3*10 mm). J. ichu did not emerge
in any of the treatments. Significant seedling
emergence was registered for P. caespitosum
and T. crinita in shade conditions with 40 mm
irrigation treatment in summer. Since 40 mm
precipitation events are infrequent in the Monte,
seedling emergence for these species would
be restricted to exceptional rainy years. The
facilitating effect of P. flexuosa shade would be
important during the hot season.
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