Modelled hydraulic redistribution by sunflower (Helianthus annuus L.) matches observed data only after including night-time transpiration

Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of John Wiley & Sons for personal use, not for redistribution. The definitive version was published in Plant, Cell & Environment 37 (2014): 899-910, doi:10.1111/pce.12206.The movement of water from moist to dry soil layers through the root systems of plants, referred to as hydraulic redistribution (HR), occurs throughout the world and is thought to influence carbon and water budgets and ecosystem functioning. The realized hydrologic, biogeochemical, and ecological consequences of HR depend on the amount of redistributed water, while the ability to assess these impacts requires models that correctly capture HR magnitude and timing. Using several soil types and two eco-types of sunflower (Helianthus annuus L.) in split-pot experiments, we examined how well the widely used HR modeling formulation developed by Ryel et al. (2002) matched experimental determination of HR across a range of water potential driving gradients. H. annuus carries out extensive nighttime transpiration, and though over the last decade it has become more widely recognized that nighttime transpiration occurs in multiple species and many ecosystems, the original Ryel et al. (2002) formulation does not include the effect of nighttime transpiration on HR. We developed and added a representation of nighttime transpiration into the formulation, and only then was the model able to capture the dynamics and magnitude of HR we observed as soils dried and nighttime stomatal behavior changed, both influencing HR.This work was supported by a NOAA Climate and Global Change Postdoctoral Fellowship to RBN, administered by the University Corporation for Atmospheric Research, by a grant from the Andrew W. Mellon Foundation to NMH, and by DOE Terrestrial Ecosystem Science grant ER65389 to ZGC and RBN.2014-10-2

Ecological and physiological implications of vascular structure and function in oaks

University of Minnesota Ph.D. dissertation. December 2019. Major: Ecology, Evolution and Behavior. Advisor: Jeannine Cavender-Bares. 1 computer file (PDF); vi, 82 pages.A plant's ability to transport water is one of its most critical physiological functions. Indeed, plant vasculature has been described as the ”backbone” supporting the productivity of terrestrial ecosystems. In my dissertation research I have investigated connections between plant hydraulics and ecological function at at two scales: first, the role that whole-plant water movement plays in how three oak species partition a hydrologic gradient, and second, the ways leaf level vascular structure can offer insights into overall plant function when studied through a framework informed by network theory. I will discuss results from a study testing how differences in water-use traits might permit three oak species to co-exist in a small geographic area, where we have shown that whole-plant hydraulic conductance is one of several characteristics that explains their local distribution. I will then introduce "LeafGrapher," a software tool I have developed to apply a network analysis approach to leaf venation architecture. Finally I demonstrate the validity of these metrics by looking at the relationships between these network-derived venation traits and known plant functional traits measured on North American and European oaks in a common garden. This work gives us some novel insights into the role plant vascular biology plays in a broader eco-physiological framework

Drivers of habitat partitioning among three Quercus species along a hydrologic gradient

A critical process that allows multiple, similar species to coexist in an ecological community is their ability to partition local habitat gradients. The mechanisms that underlie this separation at local scales may include niche differences associated with their biogeographic history, differences in ecological function associated with the degree of shared ancestry and trait-based performance differences, which may be related to spatial or temporal variation in habitat. In this study we measured traits related to water-use, growth and stress tolerance in mature trees and seedlings of three oak species (Quercus alba L., Quercus falcata Michx. and Quercus palustris Münchh). which co-occur in temperate forests across the eastern USA but tend to be found in contrasting hydrologic environments. The three species showed significant differences in their local distributions along a hydrologic gradient. We tested three possible mechanisms that influence their contrasting local environmental distributions and promote their long-term co-existence: (i) differences in their climatic distributions across a broad geographic range, (ii) differences in functional traits related to water use, drought tolerance and growth and (iii) contrasting responses to temporal variation in water availability. We identified key differences between the species in both their range-wide climatic distributions (especially aridity index and mean annual temperature) and physiological traits in mature trees and seedlings, including daily water loss, hydraulic conductance, stress responses, growth rate and biomass allocation. Taken together, these differences explain the habitat partitioning that allows three closely related species to co-occur locally

Using an Observation Protocol To Evaluate Student Argumentation Skills in Introductory Biology Laboratories

ABSTRACT Argumentation is vital in the development of scientific knowledge, and students who can argue from evidence and support their claims develop a deeper understanding of science. In this study, the Argument-Driven Inquiry instruction model was implemented in a two-semester sequence of introductory biology laboratories. Student’s scientific argumentation sessions were video recorded and analyzed using the Assessment of Scientific Argumentation in the Classroom observation protocol. This protocol separates argumentation into three subcategories: cognitive (how the group develops understanding), epistemic (how consistent the group’s process is with the culture of science), and social (how the group members interact with each other). We asked whether students are equally skilled in all subcategories of argumentation and how students’ argumentation skills differ based on lab exercise and course. Students scored significantly higher on the social than the cognitive and epistemic subcategories of argumentation. Total argumentation scores were significantly different between the two focal investigations in Biology Laboratory I but not between the two focal investigations in Biology Laboratory II. Therefore, student argumentation skills were not consistent across content; the design of the lab exercises and their implementation impacted the level of argumentation that occurred. These results will ultimately aid in the development and expansion of Argument-Driven Inquiry instructional models, with the goal of further enhancing students’ scientific argumentation skills and understanding of science