Data to accompany: Seedling responses to soil moisture amount versus pulse frequency in a dominant semi-arid shrub

The timing, frequency and quantity of rainfall is rapidly changing in
dryland regions, leading to profound alterations to dryland plant
communities. Understanding dryland plant responses to future rainfall
scenarios is crucial for implementing proactive management strategies,
particularly in light of intensive changes to land cover concurrent with
climate change. One such change is woody plant encroachment, an increasing
abundance of woody plant species in areas formerly dominated by grasslands
or savannas. The continued encroachment of P. velutina will depend, in
part, on seedling capacity to establish and thrive under future climate
conditions. Seedling performance is primarily impacted by soil moisture
conditions that are governed by precipitation amount (quantity) and
frequency. We hypothesized that H1) seedling performance would be enhanced
by both greater soil moisture and greater pulse frequency, such that
seedlings with similar mean soil moisture would perform best under high
moisture pulse frequency. Alternatively, H2) mean soil moisture would have
greater influence than pulse frequency, such that at a given pulse
frequency would have little influence on seedling performance. The
hypotheses were tested by growing 256 P. velutina seedlings under two
distinct soil moisture treatments, each of which was maintained by two
different pulse frequency treatments. Contrary to H1, mean soil moisture
had far greater impact than pulse frequency on seedling growth,
photosynthetic gas exchange, leaf chemistry and biomass allocation. These
results indicate that P. velutina seedling establishment may be more
responsive to rainfall amount than rainfall frequency.