Roots, Shoots, and Sky-High Science and Extension: Our dedicated team has actively engaged in research and extension events this year that offer valuable insights into plant ecology and climate change adaptation.
Field Research: Graduate student Scout Dahms-May led extensive research into how ornamental shrubs respond to drought conditions. Her dedication shone through as she ventured into the field for pre-dawn plant water potential assessments, sharing the experience with hot air balloonists and the local coyotes. Our excellent undergraduate students, along with the new graduate student, Josh Perrault, played a pivotal role in the research by meticulously measuring the leaf area of over 100 plants. Their hard work serves as a testament to the commitment of students pursuing cutting-edge agricultural research.
Extension: Standout events this season included an impressive demonstration of sprayer drones. Visitors had the opportunity to witness these cutting-edge technologies in action, gaining insights into how they can be used in modern agriculture and horticulture.
Another highlight was a grand field day that showcased the spirit of collaboration at NWREC, involving students, staff like Brent Warneke, Dalyn McCauley, and Clint Taylor from the Nackley Lab, as well as guest appearances by experts, including Dr. Rebelo, a visiting scholar from South Africa, and Dr. Wiman, Orchards Program Leader, and Dr. Yang, a Blueberry Extension Specialist. This summer, NWREC demonstrated its position as a hub of research, learning, and community engagement, driven by our shared commitment to advancing the field of plant science.
Kym Pokorny published this fantastic write up on the goings-on for the Climate Ready ornamental plant study we’ve been working on for the last few years – check it out here or click below the image to read more!
Unlocking Nature’s Water Secrets for Greener Futures, Part 1
TL;DR Plant hydraulics unravels the journey of water within plants, aiding tree health, nursery production, urban forest management, and climate resilience. 🌿🌿
Last month, we delved into the fascinating world of soil hydraulics, exploring how water moves beneath our feet. In this post, we’re staying within the realm of water movement but shifting our focus to a different dimension of nature – plants. Prepare to journey through the intricate pathways of plant hydraulic physiology, where we uncover the secrets of how trees and other woody plants manage water, adapt to challenging conditions, and ultimately contribute to a greener, more sustainable world.
Plant hydraulic physiology is all about how water moves through plants. Scientists study this to understand how trees and other woody plants react when they have enough water or not enough. This knowledge helps us figure out how different ways of growing plants in nurseries affects their growth. People have known for a while that this field is important for plants in forests. But now, thanks to recent discoveries by this lab and others, this amazing field of science is being applied to nurseries and other horticultural production systems. In this summary, I will explain the basic ideas about how water moves through plants , how it connects to their structure and how they work. With this knowledge, scientists, nursery workers, and people who care for forests can ensure they grow strong, healthy trees that can handle harsh conditions when planted outside.
UNDERSTANDING WATER MOVEMENT IN PLANTS Let’s start by talking about how water moves in plants. Imagine it’s like water moving through a hose in your garden. We can measure this flow of water using something called “flow rate,” which is just how much water moves in a certain amount of time.
We use units like gallons per minute or liters per minute to measure it. For example, think about a water hose in your garden. If you want to know how much water it sprays out in a minute, that’s its flow rate. Now, here’s something interesting: the size of the pipe or hose matters. A big hose can let a lot more water flow through than a tiny one. In fact if you double the diameter of a hose it can allow 4 times the flow of the smaller diameter hose. Plants have tiny water pipes called “xylem.”
XYLEM CONDUCTANCE Okay, now let’s talk about “conductance.” Think of it as how easy or hard it is for water to move through something. For plants, this refers to how easily water can travel through their pipes. We usually keep the pressure the same, like when you use a hose with a constant water pressure. This helps make sure the plants get water evenly. Lastly, there’s something called “conductivity.” It’s like a fancy version of conductance but scaled to the size of different parts of the plant. It helps us compare how different parts of the plant move water. For example, we might want to know how water moves through the stem compared to the roots.
Now, here’s where it gets cool: in plants, water doesn’t get pushed like in your garden hose. It gets pulled up by something called “tension.” This happens because plants lose water from their leaves when it evaporates. Imagine a plant sipping water through a straw from the soil. When the water evaporates from the leaves, it creates tension, like a vacuum pulling water up the plant. This is how water can move up the tallest trees. So, we measure something called “water potential” to understand this tension. It tells us how much “pull” the plant has on the water. When there’s a difference in water potential between different parts of the plant, it’s like a driving force that makes water move from where there’s less pull to where there’s more. This helps water move up from the roots to the leaves, even against gravity. We call this whole process the “Soil-Plant-Atmosphere Continuum,” but you can just think of it as how plants drink water.
And that’s the basics of how water moves in plants!
Nursery science researchers have embarked on a journey to harness the principles of soil hydraulics to reshape container production practices. In the past couple of years, Dr. Chris Criscione and Dr. Jeb Fields and others released a series of articles that showed that stratifying pine bark can serve as a substitute for peat-based media in floriculture and bark-based woody plant production. Through layering premium floriculture media over cost-effective pine bark within containers, they reduced reliance on peat. In their study focused on Petunia hybrid ‘Supertunia Honey’, the stratified substrates yielded crops of comparable size and quality, along with enhanced root productivity. Their work also showed superior performance of bark:coir substrates in a stratified setup, even when subjected to reduced irrigation when producing Loropetalum chinense ‘Ruby’ liners. Positive microbial communities in stratified systems further aided in mitigating water stress. Furthermore, Red Drift® rose plants grown in stratified substrates exhibited equal or superior crop growth despite receiving less controlled-release fertilizer. This suggests potential for reducing fertilizer and irrigation rates while upholding crop quality, offering a sustainable avenue for containerized crops. This blog post aims to shed light on stratified substrates and also provide insights into ongoing projects at the Nackley Lab that are delving into this innovative frontier of nursery science.
Image: mixing coarse and fine substrates in containers to address soil stratification
Soil hydraulics delves into the intricate world of water movement within soils—how water traverses the soil matrix, its distribution, and its intricate interactions with soil particles and structure. It’s a field dedicated to understanding the physics governing water’s journey through soils, and this knowledge carries significance for agriculture, environmental science, hydrology, and civil engineering. Soil hydraulics guides irrigation strategies, shapes drainage designs, and fuels sustainable land management practices.
Image: water in saturated and unsaturated soils
Central to soil hydraulics is the concept of matric potential, a critical factor in irrigation management and plant-available water. Matric potential captures the degree to which soil particles retain water due to molecular attractions—it’s essentially the “stickiness” of water to soil particles. When soil isn’t completely saturated, minuscule air-filled spaces exist between particles. Water molecules adhere to these particles, creating capillary forces that coax water upwards. The strength of the bond between water and soil particles determines the matric potential, effectively influencing water availability to plants.
Image: the gaseous, liquid and solid phases of soils
Two other essential players in the realm of soil hydraulics are soil texture and structure. Envision soil as an intricate mosaic, with particles coming together to form aggregates, shaping distinct pathways and chambers. This arrangement, referred to as soil structure, creates macropores— akin to express highways—through which water can flow rapidly. At the same time, micropores, reminiscent of narrow alleyways, gently retain water against gravity’s pull, acting as reservoirs for plant roots during dry spells. Additionally, soil structure influences permeability, determining how efficiently water infiltrates and the risk of surface runoff.
Soil texture, on the other hand, hinges on the proportions of sand, silt, and clay particles in the soil. Each particle type comes with distinct traits that shape water dynamics. Coarser-textured soils with more sand have ample space between particles, allowing water to move quickly with less retention. Finer-textured soils, rich in silt and clay, boast smaller gaps between particles, leading to slower water movement and higher water-holding capacity.
Image: The Soil Texture Triangle
However, when soil is confined to pots or containers, it undergoes transformations in its natural structure due to various container-related factors. The restricted space of a pot, contrasting with the expanse of natural soil, can lead to the erosion of soil structure. Aggregates—clusters of particles forming pores and pathways—can deteriorate over time due to limited expansion room. This confined space often results in compaction, where soil particles compress closely, reducing essential air-filled pores needed for root growth and water movement. The watering practices specific to potted plants can contribute further by compacting soil particles as water occupies gaps. The absence of natural soil organisms and plant roots within containers hampers the maintenance of soil structure. Repeated disturbances, like transplanting or repotting, can exacerbate these structural changes. To counter these effects, selecting appropriate potting mixes that retain structure, incorporating organic matter for improved aeration and water retention, and being mindful of compaction during planting and watering are recommended.
Image: Hydrangea in pot with drip emitter irrigation
Traditionally, the nursery field has focused on creating homogeneous potting mixes that maintain structure while offering suitable hydraulic properties. Classic blends often comprise bark, coir, peat, perlite, vermiculite, and pumice. However, a recent shift in focus has led scientists to explore how layering media can simulate natural soil hydraulics—an approach known as stratified substrates.
Coarse substrate
Fine substrate
Stratified substrates involve arranging potting media of varying textures in layers within a single container. This structured layering entails placing coarser-textured substrates at the bottom and finer-textured ones on top, mimicking natural soil layers. This technique aims to influence water movement, nutrient distribution, and hydraulic behavior within the confined environment of a container. By borrowing from the stratification seen in the ground, stratified substrates strive to optimize resource efficiency, plant growth, and root development in controlled settings like potted plants.
Some may draw parallels between stratified substrates and the practice of placing rocks or gravel at the bottom of larger plant pots. While both concepts involve layering materials, there are distinctions. The practice of adding gravel or rocks to enhance drainage in larger pots shares a kinship with stratified substrates. However, it doesn’t replicate the comprehensive layering dynamics seen in stratified substrates. Adding gravel mainly addresses drainage concerns without fully incorporating the layered hydraulic principles inherent to stratified substrates.
Image: fine (l) and coarse (r) substrate, side by side
Dr. Chris Criscione, in collaboration with the Dr. Jeb Fields group at Louisiana State University, has been at the forefront of investigating stratified substrates in containerized plant growth. Their research delves into how layering different potting media textures can enhance water retention, nutrient availability, and overall plant performance. The studies highlight promising outcomes, such as heightened root productivity, improved growth, and enhanced quality under stratified conditions compared to conventional substrates. This technique holds potential for bolstering sustainable crop cultivation within controlled environments.
Image: potted hydrangeas on the gravel pad at NWREC
Nevertheless, it’s crucial to acknowledge that findings from studies conducted in one geographic region—such as the Southeastern USA—may not seamlessly extrapolate to other areas with distinct climates and environmental conditions, like the Pacific Northwest. Climate, temperature, humidity, and other factors can significantly influence plant growth and water dynamics. Given this variation, research in regions like the Pacific Northwest, such as Oregon, is crucial. The unique environmental factors there, including cooler temperatures and higher rainfall, can impact water movement, nutrient availability, and plant response to stratified substrates. Bark-based substrates, common in some areas, may behave differently in terms of water retention and drainage in regions with distinct soil compositions. To address this, the Nackley Lab initiated a collaboration with Dr. Fields and others in 2022, planning to explore the impacts and benefits of stratifying substrates in Nursery production. The first stratified substrate experiment was launched in 2023 at Oregon State University North Willamette Research and Extension Center (NWREC), aiming to reduce resource demand and provide insights into the effectiveness of stratified substrates in that context, contributing to more informed decision-making for nursery production and horticulture practices in the region.
The Gravel Pad update you’ve been waiting for, and more!
There’s so much going on in the season of plenty around NWREC! Enjoy this virtual tour of a few projects around the nursery.
Dalyn has been continuing her work with mini-lysimeters that control irrigation in shade trees – these tiny scales weigh the potted plants and use the change in weight as they dry to determine when to turn on the water. The lysimeters are gathering data on plant weight along with an on-site weather station to better understand the relationship between heat and irrigation in gravel pad production. Read more about this project here.
Young red maple trees on the gravel pad are using lysimeters to monitor water loss in conjunction with a dedicated weather station (left).
The Willamette Valley has had a few HOT summers in a row, even though lately this one has been pretty mild. Nevertheless, we haven’t given up on finding solutions for heat mitigation – including growing ornamentals under drought conditions to see which are the most “climate-ready” to meet changing needs. We’ll be asking the public to evaluate those plants in the upcoming Climate-Ready Field Day, come along and see how the plants are progressing (click the link above for more info).
In addition, we’re evaluating different means of mitigating the heat and the resultant high rates of evapotranspiration (basically ways to reduce plant sweat), from misting the young plants to covering tissues with kaolin, introducing fungicides that may be beneficial in managing water loss, using white pots instead of the traditional black, and even growth inhibitors – it’s been a pretty amazing feat to monitor the effects as you can see- check out this monitoring station!
Dalyn, Lloyd and summer hire Jaiden show off the monitoring station in the heat stress/evapotranspiration mitigation study.
Does the color of the pot change the heat stress for these water-loving shrubs on the gravel pad?
A small project growing marigolds for festivals and holidays – like Dia de los Muertos – is also underway. Growing the marigolds has certainly brightened up the Nursery Zone at NWREC, and we’ve progressed into evaluating passive means to dry the flowers, saving energy and resources while preserving the gorgeous summer color.
Marigold blooms
There’s even more in the works – stay tuned for information about fall workshops and PACE courses created specifically for nursery and greenhouse production for topics covering drone sprays, integrated pest management, and more.
Photos: UC Davis Plant Trial Field Day 2020 Credit: Karrie Reid
About this Event
The ever-changing climate iputs pressure on the industry to develop more sustainable plants. As part of a six-university study, OSU seeks to improve urban water-use efficiency by evaluating landscape plant performance on three irrigation treatments corresponding to the Water Use Classification of Landscape Species (WUCOLS): High, Moderate, and Low categories of water need. The plants are irrigated regularly during their first summer after planting. Treatments are imposed during the second growing season where researchers collect growth and quality ratings.
The Field Day allows landscape, nursery, and horticultural industry professionals and educators the opportunity to see new plants in their 2nd year and share your opinions and preferences by rating a representative sample of the plants in the field undergoing irrigation treatments. One plant from each of the 3 water levels, for 15 different species (some released to the public and some not yet) will be surveyed. Along with this field of 360 plants, you will be able to get a sneak peek at the next year’s field, currently in an establishment phase.
Important Details: The fields are packed dirt/uneven mulch, sturdy comfortable shoes, sunscreen and/or a hat are suggested. At the trial site, you will be provided a ratings sheet, clipboard, pen, and given general instructions when you arrive. It is a self-guided tour among our 720 landscape plants. Lots to look at but only a small sub set to evaluate. Hot Coffee and cold water will be provided. We value your feedback and hope to see you there!
Unmanned Aerial Systems applications in agriculture have interested me from the time I saw some trial flights at the World Ag Expo in Tulare, California in 2020. The possibilities of crop mapping, using multispectral imagery to create NDVI data, and optimizing resources seemed endless. And while all of this is still true, I have learned over the last couple years that there is a lot more to it than just getting out the drone and flying it over a field.
Dalyn McCauley, captured in a 2022 drone image
In the Fall quarter of 2022, I was able to take a class on campus from Dr. Michael Wing called “Unmanned Aerial Systems Remote Sensing. In this course I was able to get some hands-on experience flying a DJI Phantom 4, a DJI Matrice 200, and a DJI Matrice 300. We also were able to take aerial imagery with a MicaSense Altum multispectral and thermal camera attached to the DJI Matrice 300 and analyze that data during the course of the class. To analyze the data we learned how to use AgiSoft Metashape photogrammetry software to make orthomosaics of our area of interest. With the orthomosaics, we were able to perform different sorts of analysis using ArcGIS Pro software and R. This class really gave me a solid introduction to the collection and analysis of aerial imagery.
The DJI matrice 210 with a zen muse xt2 camera flying over red maples
With some knowledge under my belt after taking that course, I decided to look into taking the Part 107 Certification exam to obtain my FAA administered Remote Pilot License. The purpose of this certification is to be able to fly a drone for commercial, government, or any other non- recreational purposes. In the Nackley Lab, we have access to a DJI Matrice 210 quadcopter and a MicaSense Red-Edge M camera so I wanted to be able to open up some more avenues for research by being able to pilot this drone for our lab!
DJI matrice 300 with a micasense altum camera
In our lab, a lot of our work centers around major challenges to the nursery production industry in Oregon. Working with a drone can allow you to survey a large area for early signs of drought stress, nutrient deficiencies, or pests to minimize a loss in yield. Now that I have the Remote Pilot Certification, my goal is to help our lab create more aerial imagery (data) that ties into our work which addresses major challenges to nursery production in Oregon like irrigation application, pest management, plant nutrition, and climate adaptations.
For the past few years we’ve limited gatherings on the farm due to COVID-19 restrictions. In the summer of 2022, however, we were finally able to welcome the public back for Nursery Program Field Days. We’d like to take this opportunity to boast about a few of our highlights from the last several months.
Sadie Keller discusses shade tree physiology
For the first time, the Nackley Nursery Production team was an official stop on the Oregon Association of Nurseries Farwest Innovative Production Grower Tour. Our portion of the tour at NWREC showcased sensor-controlled irrigation, heat-stress mitigation techniques, LiDAR smart-sprayer systems, and practices that can reduce boxwood blight spread, and methods of scouting and monitoring insects in nurseries and greenhouses. These projects offer a wide range of savings for growers.: up to 80% improvement in irrigation efficiency, up to 70% reduction in sprayed pesticides, and a significant reduction in boxwood blight infection.
Stakeholders evaluating climate-readiness of various landscape ornamentals
The second big event was an open house for our Climate Ready Landscape Plant trial, the largest coordinated landscape plant irrigation trial in the Western US. Plant professionals from around the region came to rate plants and discuss how we, as a society, are going to maintain healthy landscapes while faced with increasing extreme weather.
Ongoing projects that will continue this year include, research by our graduate student Sadie Keller, who is investigating Oak and Maple drought tolerance. This summer, Sadie shared her preliminary findings with scientists at the American Society for Horticultural Science, in Chicago.
Sadie Keller and Lloyd Nackley at the ASHS Meeting in Chicago.
In addition, Dr. Melissa Scherr continues our research on the Pacific Flatheaded beetle, with the anticipation of a grower event hosted at NWREC discussing current research on Flathead Borer biology and control this coming April – 2023.
Shade tree growers need to be prepared for the effects of climate change in Oregon.
In order to equip growers with the tools necessary for production success, we aim to determine critical shade tree stress thresholds, characterize plant responses to drought conditions, and correlate remotely collected spectral images with ground based plant water stress measurements.
Previous studies have sought drought response measurements for Acer rubrum (Red Maple) and Quercus rubra (Red Oak), but never in a nursery production setting.
We aim to disseminate this information to Oregon shade tree growers at the completion of this experiment with the hope to aid growers in making data driven irrigation decisions and demonstrate the use of these technologies in nursery production settings.
Sadie Keller in the shade trees equipped with soil moisture sensors and a weather station.
The Problem:
In Oregon’s Willamette Valley, the heart of the nursery country, rainfall is scarce during the summer and humidity is low. Oregon’s dry summer conditions can lead to low moisture stress conditions for maples and oaks in normal years. Plant stress resulting from low soil moisture, high heat, and low relative humidity have been exacerbated in recent years with the increasing frequency of heatwaves and drought. Drought and heat stress scorch the maple and oak canopies, which can lead to decreased plant quality and economic losses for shade tree growers. Sensor-based technologies can be used to model plant responses to environmental gradients to develop warning systems to help growers prevent stress and bridge a knowledge gap in the nursery production industry regarding drought responses.
How are we studying plant stress responses?
Starting late June 2022, we will implement two irrigation treatments (well-watered and drought) in our shade tree planting with each row having independent irrigation control. The well-watered rows will be maintained at a soil water potential of >-1.0 mPa. The drought treatment rows will be allowed to naturally dry down to a soil water potential of -4 mPa. If during the experiment, our metrics (stomatal conductance and stem water potential) do not show considerable responses at -4 mPa tension, we will allow the drought treatment to continue to dry down progressively (-1 mPa) until stress is evident.
Why and how do we measure stem water potential?
Plant water status is commonly defined in terms of water potential or the ability of the water to do work. In most cases, well watered plants have “high” water status and drought conditions lead to a “low” water status (Levin and Nackley 2021). Using the pressure chamber, we will take midday stem water potential measurements twice weekly from 12pm-3pm. This time frame is important because it represents the time of day where leaf transpiration is at its maximum.
First, we will cover the leaf and stems to be measured with an opaque bag for at least 10 minutes before pressurization to allow the plant to stop transpiring. Once we excise the sample from the tree it should be placed into the pressure chamber or “pressure bomb” within 30 seconds (Levin 2019). Once the stem is placed into the chamber and pressure is applied, the amount of pressure that it takes to cause water to appear at the cut surface tells us how much tension the stem is experiencing.
We measure stomatal conductance using a porometer that measures the degree of stomatal openness and the number of stomata (Licor.com). This indicates the plant’s physiological response to its current environment. If a plant is stressed, it will tend to close its stomata and lower the stomatal conductance rate. We will be using a combination of the LI-6800 Portable Photosynthesis System and the LI-600 Porometer/Fluorometer to make our measurements twice a week from 12pm-3pm.
For more information:
Please stay tuned in the coming months for more blog posts about how we will find plant stress thresholds by measuring the hydraulic conductivity of these shade trees. We will also correlate remotely collected spectral and thermal images with our ground based plant stress measurements to demonstrate how implementing a UAS equipped with a multispectral and thermal camera can be used to detect water stress in nursery production.
How we are using low-cost and open-source weather stations for decision support
Dalyn McCauley
On-farm weather data can provide valuable information to growers including informing irrigation scheduling, tracking plant growth indices, and mitigating damaging events like frost, heat waves or disease. Weather can vary widely across landscapes, even across a single field, and we have found that there is value in having multiple distributed weather stations on-farm to capture variability across small spatial scales. To do this cost effectively, I developed a low-cost open-source weather station (LOCOS) for my M.S. thesis at the University of Idaho that uses low-cost sensors and an Arduino microcontroller for data logging. By distributing multiple LOCOS across a vineyard, we found that there were distinct micro-climates that had varying susceptibility to grape powdery mildew disease. From calculating a Powdery Mildew Risk Index at each station, we saw that some vineyard blocks could benefit from unique fungicide application schedules. You can read more about this project here.
Figure 1: The first iteration of the LOCOS design installed at a vineyard in 2019 (Julieatta, Idaho).
Since then, the LOCOS have been adapted to study crop water stress. In the summer of 2021, we used LOCOS equipped with infrared thermometers to develop a crop water stress index (CWSI) for hazelnuts. The CWSI is based on leaf temperature and weather data (air temperature, relative humidity, wind speed, and solar radiation). Leaf temperature is a known indicator of plant stress. When a plant is actively transpiring the leaves will be cooler than the surrounding air because of the evaporative cooling effect of transpiration. Whereas a plant that is stressed and not transpiring will have a warmer canopy that is closer to the ambient air temperature. The CWSI varies from 0 to 1, where 1 indicates a stressed, non-transpiring plant, and 0 indicates a well-watered plant transpiring at max potential.
We used the LOCOS to collect canopy temperature of the hazelnut trees from June to September, 2021. The trees were subject to three different irrigation treatments, over watered, moderate water, and no water (dryland) so we could get a range of canopy temperatures to incorporate into our model. We also collected data on leaf water potential, leaf transpiration and leaf conductance to validate the index against. We found that the CWSI we developed was closely correlated with leaf water potential (r2 = 0.84), leaf conductance (r2 = 0.75) and leaf transpiration (r2 = 0.72). These are exciting results because it shows that the LOCOS could provide continuous data on crop water stress that can be used to inform irrigation decision in near real-time. This summer, we will use the LOCOS in another study to develop a CWSI for red maples.
Figure 2: LOCOS installed in a hazelnut orchard for CWSI study in 2021 (Aurora, OR).
