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    Author(s): Jeremy Pinto; John D. Marshall; Kas Dumroese; Anthony S. Davis; Douglas R. Cobos
    Date: 2016
    Source: New Forests. 47(2): 223-241.
    Publication Series: Scientific Journal (JRNL)
    Station: Rocky Mountain Research Station
    PDF: View PDF  (1.0 MB)

    Description

    In many forests of the world, the summer season (temporal element) brings drought conditions causing low soil moisture in the upper soil profile (spatial element) - a potentially large barrier to seedling establishment. We evaluated the relationship between initial seedling root depth, temporal and spatial changes in soil moisture during drought after outplanting, and subsequent seedling performance using seedlings of Pinus ponderosa Laws. var. ponderosa grown in three containers similar in dimension except for depth (i.e. three stocktypes). Soil moisture patterns were quantified and growth, gas exchange, and carbon isotope analysis were used as metrics for stocktype evaluation. Soil moisture reached minimum volumetric soil moisture contents (θ) of 0.078 m3 m-3 at a 15 cm depth and 0.15 m3 m-3 at 90 cm by late summer, which also translated to estimated soil water potential values of -2.29 and -0.02 MPa, respectively. Seedling photosynthesis (A) and transpiration (E) rates followed soil moisture trends, also reaching seasonal lows in late summer. In early fall, gas exchange rates nearly doubled following a replenishment of upper-profile soil moisture by precipitation. Over the course of the growing season, stocktypes did not differ in gas exchange rates (P ≥ 0.15), biomass (P ≥ 0.45), root penetration depth (P = 0.60), or carbon isotope signature (P ≥ 0.60). For all seedlings, current-year needles showed greater capacity for A than previous-year needles (P ≤ 0.01), and A was only significantly correlated with soil moisture in the upper soil profile (15 cm; P ≤ 0.03). In this study, stocktype was not a significant factor, suggesting that seedling access to soil moisture was not different among them. The temporal and spatial variation observed in soil moisture availability, however, provides critical biophysical information on outplanting timing as it relates to subsequent seedling establishment and potential root growth. As well, needle formation, carbon gain, and the relationship to soil water depth further indicate the importance for managing soil water or seedling stocktype for successful seedling survival and growth.

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    Citation

    Pinto, Jeremiah R.; Marshall, John D.; Dumroese, R. Kasten; Davis, Anthony S.; Cobos, Douglas R. 2016. Seedling establishment and physiological responses to temporal and spatial soil moisture changes. New Forests. 47(2): 223-241.

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    Keywords

    ponderosa pine, soil water potential, container seedlings, stocktype, volumetric water content

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