Abstract:
Paired 30-day trials were conducted to evaluate
Agropyron spicatum germination when treated with two
concentrations of throughfall leachates from western
juniper slash in two stages of decomposition. Data from
a second pair of 49-day greenhouse trials were analyzed
to evaluate emergence and growth of Aqropyron spicatum,
Oryzopsis hymenoides, and Poa ampla when watered with
throughfall leachates from fresh green slash and year-old
red slash from western juniper. The objectives of
these studies were to assess plant responses to the
addition of chemicals derived from the leachates.
Few differences in ion concentrations were evident
between the two slash sources. No detectable quantities
of nitrogen were leached from either source. Losses of
Al, B, P, S, and Sr appeared greater from the red slash
than from the green slash. Real additions of nutrients
from slash relative to controls appeared greatest for
Al, B, Ca, K, Mg, Na, P, S, and Sr.
Leachates did not affect Agropyron spicatum
germination, and final total emergence of the 3 test
species was unaffected by either leachate. Leachates
generally inhibited growth, but effects varied among
species depending upon the parameter measured. Red
slash leachates most often inhibited growth
significantly, while effects of green slash leachates
were intermediate and seldom significantly reduced
growth. Growth of Oryzopsis hymenoides was the least
inhibited by leachates, while Poa ampla growth was very
much inhibited by leachates.
A further objective of the study was to explore
allelopathic inhibition of ion uptake as a possible
explanation for the observed general pattern of reduced
growth associated with the leachates. A sample of the
red slash leachate contained 5x more volatile compounds
than a paired sample from the green slash leachate, and
contained 4 phenolic compounds while the green slash
leachate contained no detectable phenolics. The lack
of phenolics may explain the relatively more moderate
inhibition of growth caused by the leachates from the
green slash. Morphological responses did not indicate
reduced availability or uptake of nitrogen due to
allelopathic inhibition, but may implicate interference with uptake of other ions or inhibition of growth
hormone functions. Implications are discussed for slash
management on sites converted to improve productivity.
