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Graduate assistantship available in the Tree Ecophysiology Lab to study source-sink relationships in fruit trees

Published on July 29, 2021 by scruffpalmerLeave a comment

We are looking for a graduate student to help us develop a systematic understanding of the relationship between canopy area and fruit load. This will be addressed in the context of water and carbon supply and demand. This project will produce knowledge that is directly relevant to producers while addressing fundamental hypotheses of water and carbon.

Fruit production depends on the development and maintenance of fruit sinks, supported by interactions with carbon and water supply and allocation. Citrus growers need guidelines to help them manage crop load in high-value citrus varieties. Although carbon supply plays a major role in crop set, subsequent development can strain carbon or water supply capacity. The chosen candidate will have the opportunity to address both food production and fundamental hypotheses related to this dynamic. The overall aim is to develop a quantitative framework of the relationship between canopy area and fruit growth.

The selected candidates will develop a variety experiments to quantify the tradeoffs involved in these underlying relationships. The candidate will have the opportunity to use unique methodologies at the UF Tree Ecophysiology Lab, including a range of methods to assess photosynthesis, water relations, and carbohydrate translocation and allocation. The work involves combinations of field, greenhouse, and laboratory work, including direct collaboration with the citrus producers who need this knowledge.

The work environment is highly collaborative, and demonstration of the ability to work in diverse teams will be valued in the selection process. Critical thinking, independent judgment, and interest in the subject matter are essential. Other valued skills include:

Quantitative analysis
Written communication
Knowledge of plant carbohydrate allocation and transport processes or of plant hydraulics

The tree ecophysiology lab (website here) at the Citrus Research and Education Center in Lake Alfred, Florida, uses whole-plant physiological approaches to address challenges in horticultural productivity in perennial plants. The Citrus Research and Education Center offers ample opportunities for collaboration with 25 labs working in areas as varied as genetics, plant pathology, and entomology. The PI of the Tree Ecophysiology lab places a high importance on mentorship and the development of skills of and opportunities for students. If you are interested, please send your questions or a resume to Christopher Vincent at civince@ufl.edu. We will accept application until 9/1/2021.

Sugar movement in long leaf pines: accepting their limitations to keep moving

Published on July 16, 2021 by scruffpalmerLeave a comment

Plants face many hurdles to keep water moving up and sugars moving down, while keeping photosynthesis churning. Add to these challenges the fact that some plants may create their own limitations with constricted phloem. Recent work by a number of labs, in which we played a small part, shows that some trees may have restrictions in phloem movement.

Long leaf pines are rare in nature. Only a handful of conifer species worldwide have leaves longer than about 4″ (10 cm). Longleaf pines, though, native to the southeastern U.S. have needles up to about 1 foot (30 cm)! Why are long leaf species so rare, and why are our pine’s needles so long?

Longleaf pine (Pinus palustris) native to the Southeastern U.S.

The challenge of narrow pipes

It turns out that most conifers, including longleaf pine (Pinus palustris), have narrow sets of phloem tubes that all the sugars from photosynthesis along the whole length have to move into in order to make it out of the leaf. This means that the leaf closer to the base is loading into the same narrow “pipes” that the tip is loading. Imagine if you took a bunch of bottles, lined them up and connected them with only small holes between them so that the each bottle drained into the next. Then you poured a liquid – imagine, say, pink lemonade, because that’s more fun – into all the bottles at the same time. The end bottle would drain the slowest, while the base bottle would drain fastest. The result is that, without some adaptation, the base and the tip compete for loading and the tip may be unable to add enough sugar to make the phloem flow. This may help explain why most species don’t have long needles. But that begs the question, how do longleaf pines do it?

A “bottle model” of how export is limited in long needles.

Longleaf pines accept their limitations

Longleaf pines have anatomical adaptations that help reduce the loading limitation in their needles. They have specific files of phloem tubes that load mostly from certain leaf segments, which helps reduce the competitive effect, but not eliminate it. Because of this, they accumulate starch in their tips during the day, while the base regions run the sugar export show. But at night the tips rev up, and begin to export as the base begins to run out of reserves. In this way the various regions alternate in export over time, and keep export going.

Are long needles the only place where phloem constricts transport?

This is the clearest case of phloem transport limitation so far, but there may be other species that have similar challenges. Which we will discuss in the near future.

Fasih Khalid

Published on June 18, 2020 by scruffpalmerLeave a comment

Fasih Khalid came to CREC from Pakistan for a six-month program to work as a horticulturist focused on stress physiology. He also wanted to learn about physiological techniques and how to use different instruments. In Pakistan, he spent time working on abiotic stresses like water deficits and salinity. In our lab, he worked on experiments dealing with sap flow and hydraulic conductance. He said with the results the lab can determine whether “the sap flow movement is OK in relation to the regular irrigation.” Because of rising prevalence of water deficit problems in the world, it is important to see how irrigation levels in plants can be adjusted to save water and lead to more efficient water practices in the future.

Fasih loves research and learning. After his Master’s he spent about a month working in a farmer’s co-op in Pakistan, which he didn’t enjoy. As soon as an opportunity presented itself, he entered his PhD. He had done research on lychee in his Master’s and had published it, so he decided to go back to school and into the research field. After a couple of months in his PhD, he decided “…there is nothing in the world for me except research. I have to be researching.” He initially was interested in horticulture after going through his required two years of studying it in Pakistan. He thought he wanted to work in floriculture and landscaping but ultimately found pomology to be the most engaging because there are many different opportunities in that field. Plus, “The good thing of fruit is you can research or if you don’t want to research you can eat.”

During his time at CREC, he was also able to participate in several competitions, most of which were academic, though one was a t-shirt design contest for CREC, which he won! The academic competitions allowed Fasih to share the work he did at CREC, as well as help him improve his English. He liked to share that his work is important because it helps growers understand how to adapt to a world with climate change. He believes it is important for all people, not just growers, to care about changing water conditions and how this affects plants because “…we have to save water for the world and for the plants, for the next [plants].” If growers are unable to find solutions for their plants in water scarce conditions, this will cause further problems for the world as demand for fresh water reserves increases, eventually affecting our food supply, which would affect us all. He wants to take the things he’s learned during his time here back to Pakistan. His two big takeaways were time efficiency and the benefits of using hydraulics instrumentation for research. He hopes to apply these lessons as he continues horticulture research in the future.

Mark Keeley

Published on February 20, 2020April 4, 2020 by scruffpalmerLeave a comment

Mark Keeley turned a lifelong passion for plants into work that hopefully will help us better understand the way HLB affects Florida citrus trees. He worked in citrus research before starting his Master’s, but said he’s always been interested in plants and has been playing around with them for as long as he can remember. He made his way to plant research after trying out several undergrad degrees that didn’t fit quite right. Eventually, to no one’s surprise he told me, he joined the UF Horticultural Sciences Department. From there he had several jobs before landing one at a private agricultural research station. He likes his job because he said it’s, “Me and orange groves 4 or 5 days a week. Me and the plants, it’s quiet. Calming.” Through this job he decided to pursue a Masters in Agronomy. When asked why he’s pursuing his masters and working full-time for the private lab he laughed and said it was mostly for selfish, personal reasons. As a part of his master’s program he’s working with the tree physiology lab on a project that’s attempting to show a relationship between photosynthesis and citrus greening.

At the tree physiology lab, we hope to improve citrus growth based on understanding its environmental physiology. This particular experiment’s goal to describe the effects of HLB on photosynthesis. Part of this experiment also includes looking at the difference between shoot photosynthesis and leaf photosynthesis. This photosynthetic activity can’t be translated between leaf and tree, so we are trying to determine why. Studying photosynthesis on the leaf level can help garner understanding for the effects of photosynthesis on the whole canopy, but we need to understand what causes differences, too. Mark explained, “[We are] specifically looking at impacts of greening on photosynthesis as well as the amount of photosynthesis acquired from the leaf material and the stem material and what those impacts are over time on maturation.” In terms of the importance of this work for management, “It’s no longer preventing the bacteria from being there; it’s more how do we support the tree in [spite] of the bacteria,” he explained. This would be helpful because Mark believes the current approach to managing HLB isn’t working, so this could open the door to try other approaches.

The project uses an infared gas analyzer (affectionately called “IRGA”) called Li-Cor 6800. The machine cycles a known amount of CO₂ and water over the leaf and measures how the concentrations change after they pass over to determine how much CO₂ is being taken in and how much water is being released by the plant. This allows us to measure photosynthetic activity. Doing this in the lab with a known amount of light allows us to see the direct impacts of disease or other treatments over time without having to contend with clouds, different radiation intensities, etc. Eventually Mark would like to do work like this in the field, but while he’s still developing the methods, inside the lab is the best opt

The project uses an infared gas analyzer (affectionately called “IRGA”) called Li-Cor [RV1] 6800. The machine cycles a known amount of CO₂ and water over the leaf and measures how the concentrations change after they pass over to determine how much CO₂ is being taken in and how much water is being released by the plant. This allows us to measure photosynthetic activity. Doing this in the lab with a known amount of light allows us to see the direct impacts of disease or other treatments over time without having to contend with clouds, different radiation intensities, etc. Eventually Mark would like to do work like this in the field, but while he’s still developing the methods, inside the lab is the best option.

When I asked why he believes this work is important he said, “Fascination for me. I keep going down the rabbit hole more than anything. I think it will be important if we find some of these relationships with the infection level and the tree. Like I said, it’ll change the way we culturally try to manage the disease [HLB]. Other than that, it’s more of a curiosity.”