Recipient Organization
UNIVERSITY OF CALIFORNIA, DAVIS
410 MRAK HALL
DAVIS,CA 95616-8671
Performing Department
Land, Air and Water Resources
Non Technical Summary
This project will provide key information on growth characteristics and limitations for seedlings of Fremont cottonwood (Populus fremontii) the primary colonizer and foundation species of riparian forests in California. Detailed parameterization of models that describe establishment of cottonwood seedlings is needed so that the models can be reliably used by Bureau of Reclamation and other management agencies to plan flows and other actions needed to protect and regenerate sustainable riparian forests along the Sacramento and San Joaquin Rivers. The experiments in this project will determine relationships between root growth rates of cottonwood seedlings and the seasonal decline in the water table in point bars during recession phases of the river hydrograph, which coincide with the natural establishment period of Fremont cottonwood. Interactions with variable hydrographs can lead to seedling inundation as well as drought. These two factors, drought and inundation, are major documented causes of cottonwood seedling mortality. Since flow control by dams and diversions, establishment of viable new cohorts of cottonwoods has been minimal along rivers in California and other western states. Multiple experiments that simulate both drought and inundation causes of mortality will be conducted to provide values for parameters needed to model the survival and growth responses of 10-90 day old cottonwood seedlings. Much previous research has used older cottonwood seedlings or even cuttings; both of these types of plant materials have much greater resistance to stresses than the young seedlings we will use. Plant growth responses will be quantified in great detail, including measurement of: maximum root depth growth rate, partitioning of biomass to roots, stems and leaves, limits of water stress tolerance, heat damage thresholds with and without drought stress, excess light damage thresholds with and without drought stress, mortality rates per day with partial and complete inundation, and effects of water temperature on inundation-induced mortality. This approach will not only provide detailed inputs for the established models being used by the Bureau and others, but will generate new knowledge of responses not currently included in the models. For successful simulation of cottonwood seedling establishment interactions of drought, heat, and light stresses as well as water characteristic effects on inundation may need to be added to the models. These interactions become even more relevant as attempts are made to model riparian forest establishment and growth under variable conditions expected with climate changes and future water developments.
Animal Health Component
(N/A)
Research Effort Categories
Basic
100%
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
The overriding goal of the proposed research is to provide realistic parameters for models of riparian cottonwood seedling establishment along the Sacramento River. The multiple research objectives will allow meeting the needs for the current model formulation as well as providing new information that will facilitate model modification to better simulate responses to under variable conditions expected with climate changes and future water developments. These results will be fully documented in peer-reviewed publications and results will be used in modeling efforts by the U.S. Bureau of Reclamation related to river flow planning in California. Objectives: 1. Determine maximal root and shoot growth rates for Sacramento River populations of Fremont cottonwood seedlings in typical point bar sediments and parameterize the components of growth rate responses to water table declines that vary from 0-4 cm / day. 2. Quantify the interactions of heat stress, excess light stress, and drought stress on cottonwood seedlings to determine which factors are most responsible for seedling damage and mortality. 3. Investigate effects of inundation depth, duration, and seedling age on survival and growth of Fremont cottonwood seedlings. 4. Make measurements of cottonwood seedlings along the Sacramento River to define the range of realistic field values for plant water stress, transpiration and photosynthesis rates, root/shoot allocation, and other parameters that affect seedling growth. These measurements will provide confirmation of realistic ranges and reactions that will be compared with parameter values determined in the mesocosm experiments needed for Objectives 1-3.
Project Methods
Fremont cottonwood seeds from several dozen mother trees will be collected along the Sacramento River, near Grimes, California. All experiments will include a random sampling of seedlings derived from this population of trees. All seedlings will be irrigated with a nutrient solution to assure that nutrient limitations do not occur. Objectives 1 & 2-Experiments will be conducted in mesocosms (rhizopods; modified after Mahoney and Rood 1991) that simulate the point bar environment where Fremont cottonwood seedlings naturally germinate in spring. Replicated experiments will be conducted in two growing seasons with harvests 1, 7, 14, 28, 56 and 90 days after germination. In addition to an optimal (control) treatment that will be well drained but irrigated twice daily, there will be four treatments with different rates of water table decline (1, 2, 3, 4 cm/d). Parameters affecting seedling growth rate will be measured before harvest or on harvested seedlings. Measurements through a diurnal cycle include: transpiration, photosynthesis; leaf, stem and soil water potentials; leaf conductance; leaf and air temperatures; chlorophyll fluorescence of leaves. Harvests will quantify seedling biomass and leaf area, leaf area index, root/stem/leaf biomass allocation, specific leaf area, penetration velocity of the rooting front, root branching patterns, specific root length and root depth distribution, and organ C and N content. Seedling in each rhizopod will be recorded twice weekly. These parameters provide all the inputs needed for the current version of the riparian habitat establishment model and provide data for calibration and validation of the model. To study heat, light, and water stress interactions (Objective 2), multiple dry-down experiments will be conducted. Measurements include: predawn and midday leaf petiole water potentials; leaf photosynthesis, transpiration, and conductance; and chlorophyll fluorescence. Objective 3-Seedlings will be grown in pots to different sizes. Galvanized steel stock tanks will be used to allow inundation of the potted plants to different depths. Cool inundation water will approximate Sacramento River water temperature (11 and 18 C night & day) and warm water will be 18 to 24 C (night & day). Treatments will be: A) age of plant: six or ten weeks old; B) temperature: cool or warm; C) duration: one, two, or four weeks; D) depth of inundation: soil surface, complete submergence of shoot, or no inundation. At the end of each inundation period, subsample plants will be harvested and other subsamples will be allowed to recover (like controls) for four weeks prior to final harvest. Measurements at harvest will include: leaf area and stem length, root length and average diameter, and root, stem and leaf biomass. Mortality will be recorded twice weekly. Objective 4-Cottonwood seedlings along the Sacramento River near Grimes will be marked and measured several times during two-three growing season to provide comparative field data for validation of the mesocosm measurements of plant water stress, transpiration and photosynthesis rates, root/stem/leaf biomass allocation, and root depth.