Growth and gas exchange of different ponderosa pine stock types on dry sites


Pinto, Jeremiah Ray.. (2009). Growth and gas exchange of different ponderosa pine stock types on dry sites. Theses and Dissertations Collection, University of Idaho Library Digital Collections.

Growth and gas exchange of different ponderosa pine stock types on dry sites
Pinto, Jeremiah Ray.
Ponderosa pine--Growth
Natural Resources
Successful seedling establishment following outplanting relies heavily on a seedling's ability to access soil moisture. In the Inland Northwest USA, the summer season brings drought conditions causing low soil moisture in the upper soil profile--a potentially large barrier to seedling establishment. During the 2007 growing season, three studies examined the survival, growth, and gas exchange attributes of several ponderosa pine (Pinus ponderosa Dougl. ex Laws.) stock types on two forest sites and on a drought stress experimental plot. These studies examined the advantages of seedling container type and their relationship to overcoming site limiting factors, such as soil moisture. The studies were unique in that they used seedlings cultured specifically to their container types to achieve uniformity in nutrition and water use efficiency, something previous studies failed to address.;The first study evaluated the performance of six different stock types on two sites (mesic and xeric) that varied in volumetric soil moisture content ([straight theta]), average temperature, and total precipitation. After two growing seasons, seedlings planted at the mesic site showed high survival (> 99%) and large growth gains; container types exhibited differences in total height, root-collar diameter (RCD), and stem volume with larger containers generally yielding the largest seedlings. Seedlings planted at the xeric site experienced 83% survival and had small growth gains; container types also exhibited differences in height, RCD, and stem volume but the largest containers did not consistently yield the largest seedlings.;N the second study, seedlings from three stock types were planted in a field and subjected to three levels of imposed seasonal drought using winter wheat (Triticum aestivum L. em.) as a model soil moisture competitor. Winter wheat was sown in three densities (0, 150, and 300 plants m{esc}p-2{esc}s; D{esc}b0{esc}s, D{esc}b150{esc}s, and D{esc}b300{esc}s, respectively) and was successful at reducing soil moisture 17 cm below the soil surface. High rates of net photosynthesis (A) indicated that seedlings with adequate soil moisture and without vegetative competition were established within three weeks. Conversely, low A, low soil moisture, and low pre-dawn water potential ([Psi]nwp) measurements indicated that seedlings planted with vegetative competition were moisture stressed ([Psi]nwp <-2.1 MPa) and not established. As a consequence, mortality rates were severe in both D{esc}b150{esc}s and D{esc}b300{esc}s with smaller containers reaching 100% mortality, while the largest container experienced 63-75% mortality; seedlings in D{esc}b0{esc}s suffered no mortality.;Using three stock types, the third study examined temporal and spatial variability in soil moisture and the resultant effects on growth and gas exchange. Soil moisture reached minimum volumetric soil moisture contents ([straight theta]) of 0.08 m{esc}p3{esc}s m{esc}p-3{esc}s at a 15 cm depth and 0.15 m{esc}p3{esc}s m{esc}p-3{esc}s at 90 cm by late September. Predicted soil water potential ([Psi]soil) reached minima of -1.55 and -0.27 MPa for 15 and 90 cm depths respectively. Seedling net photosynthetic assimilation (A) and transpiration (E) rates followed soil moisture trends, also reaching seasonal lows in September. In early October, gas exchange rates nearly doubled following a replenishment of upper-profile soil moisture by precipitation. Stock types did not differ in gas exchange rates (P [equal to or greater than] 0.15), biomass (P [equal to or greater than] 0.45), or root penetration depth (P = 0.60). Regardless of container size, data suggests upper-profile soil moisture is critical to seedling establishment and growth, and can be drastically compromised by competing vegetation and subsequent rapid changes in soil moisture availability. Essential to successful seedling establishment is to coincide planting with sufficient moisture in the upper soil profile, incorporate practices that enhance soil moisture such as vegetation management, and plant seedlings with sufficient root length to allow root systems ample time to access moisture. These studies enhance our understanding of the tolerance of ponderosa pine seedlings to drought under various reforestation scenarios, thereby providing guidance in the best management practices to improve outplanting performance.
Thesis (Ph. D., Natural Resources)--University of Idaho, August 2009.
Major Professor:
John D. Marshall.
Defense Date:
August 2009.
Format Original:
xvii, 78 leaves :ill. ;29 cm.

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