LABWORK

The hidden beauty of leaves! After two months of hard work my undergraduate students James, Sam, and Diana and I finally finished preparing 888 microscopical cross-section of leaves. The next step is to use a special microscope to take pictures of those slides, so then we will be able to analyze how the number, size and spatial organization of the xylem vessels (responsible for transporting water through the leaf) varies across angiosperms families.

Everything is ready for us to start staining our more than 800 microscopical slides of leaf cross-sections. Using the traditional safranin-O and fast-green stain protocol we will be able to easily identify the xylem and phloem vessels in more than 120 different species of angiosperms. I am very excited to contemplate the beautiful variety of anatomical features in those leaves!

Microtome is a simple but very useful instrument that allow us to make very thin anatomical sections on leaf samples that were previously embedded in paraffin. Each cut stick to the previous one forming those nice paraffin ribbons that you can see in this image. My ambitious goal is to prepare paraffin sections of 122 plant species collected from the UC Berkeley Botanical Garden, and use those anatomical information to better understand the water transport in angiosperms leaves.

Although they look like candles, these are actually small pieces of leaves embedded in paraffin! This week I have been learning the paraffin embedding technique to prepare samples for microscopic analysis. After embedding the samples in paraffin, we use a microtome to cut very thin pieces of the leaf (< 0.01mm), then we stain those cuts (with safranin and fast green). So, we will be able to visualize the xylem vessels under the optical microscope. Hopefully, I will be sharing some of our leaf cross-sectional images soon!

If you scroll this page all the way down, you will see a post of about 6 years ago, when I first (unsuccessfully) tried to use the optical method to obtain leaf vulnerability curves. Today, I finally learned the method. Thank you very much Roxy to take your time to teach it to us. Roxy you rock!

After suffering an accident with the pressure chamber -where the leaf petiole exploded under -6MPa pressure and the small leaf pieces hit my face causing superficial lacerations - now we are wearing face shields to obtain vulnerability curves. Lab safety!!!

To re-train our LeafVein CNN (see post 27 April 2020) we are hand-tracing some low-resolution leaf images that we downloaded from publicly available databases. It is a very time-consuming activity, but it is also somehow relaxing and therapeutic. A nice task for pandemic times... This pic is a Vauquelinia californica leaf, hand-traced by our summer internship Hailey Park. Nice job Hailey :D

It is time to use our brand new Universal Testing Machine to measure how much force we need to apply to cut, punch, shear, tear and bend leaves of different plant species. Any guess? For the Quercus leaf in the picture beside, we used a maximum force of 1.3N to shear the leaf!

As the whole world entered in quarantine, I had to change my plans for this summer. Instead of conducting fieldwork in Ghana and Peru, I will ... play with electronic circuits!!!

Don't worry! I did not lost my job in the eco-physiology lab and became an electrician. I am just using the electronic–hydraulic analogy, to investigate whether I can estimate the leaf hydraulic conductance, by converting the leaf venation network into an electronic circuit and, then simply applying the well-known Ohm's law.

I finally get started with the Leaf Vein CNN, a MATLAB app developed by the Macrosystem Ecology Lab and collaborators, that uses deep learning algorithms to segment and extract the leaf venation networks. Now, we are getting closer to abandon the time-consuming hand-trancing method...

After many weeks of hard work, we finally assembled four systems to measure leaf hydraulic conductance (Kleaf is a measure of how efficiently the water can be transported through leaves). We will measure Kleaf in several plant species using the evaporative flux method (read more here), which involves evaporating water out of the leaf lamina while determining the flow rate into the petiole (with pressure transucers) and the water potential drop across the leaf (with a pressure chamber).

What a mess! This is my first attempt to build a pressure flowmeter. Basically, the water generate pressure which deformate the diaphragm of the pressure sensor. The physical deformation produces an electrical resistance change which is converted in a voltage difference. The Data Aquisition Board convertes the voltage back in pressure, which can be logged into a computer. All this allow us to obtain the leaf hydraulic conductance, a measure of how efficiently water is transported through the leaf!

Is the leaf hydraulic conductance most affected when herbivores cut the primary or the secondary leaf veins? We are simulating herbivory in leaves with distinct venation patters to answers this and many other interesting questions!

A quick demonstration on how to use this amazing machine (LICOR 6800) to investigate the carbon (leaf-level gas exchange) and light reactions (chlorophyll fluorescence) of photosynthesis.

Why are these leaves on the clothesline (leavesline)? That is one of the steps to measure the leaf mininimum epidermal conductance. Check out all the steps (protocol) here.

I am helping my colleagues of the Plant Ecology Lab (UERJ, RJ, Brazil) to determine the xylem vulnerability to cavitation using the new pneumatic method. If you are curious about how to do it, read more here.

This week I had to literally sleep at work (fortunately I had my sleeping bag there)! I have been working hard to obtain pressure volume (PV) curves for 12 species from the Itatiaia National Park (RJ, Brazil). My main objective is to determine the leaf water potential at the turgor loss point, since it is considered as a good trait to describe plant vulnerability to drought. Learn more about PV curves here.

During the last few months I have been collecting seeds from species of the Itatiaia National Park (RJ, Brazil). I intent to measure both seed size and seed mass; and then, use those and other plant traits to describe the eco-physiological strategies of plant response to droughts!

Foliar water uptake is the water absorption through leaf surfaces. One way we can determine it is by submerging leaves in distilled water (usually for 3h) and then measuring the leaf mass difference after and before the submersion. Read this paper to see more details about this method.

Today I was trying to apply the optical vulnerability technique to determine the leaf xylem vulnerability to cavitation. This new method, described here, would allow me to obtain metrics of xylem vulnerability for both woody and herbaceous species. But, as you can see from the photo aside, I have been having problems with pictures overlapping!

It is a five microliter water droplet resting on flat leaves surfaces. Why am I taking pictures of that? To measure the leaf water repellency. A leaf trait that indicates how much the water can spread on the leaf.... and why am I measuring leaf water repellency? Take a look here, and discover!

Archimedes' principle states that the upward buoyant force that is exerted on a body immersed in a fluid is equal to the weight of the fluid that the body displaces. What this has to do with stem density? Based on that principle, we can easily determine the stem density (the oven-dry mass of a stem divided by its fresh volume) with a oven, a calliper, a scale, and a cup of water. Learn how to do it by reading the water displacement method here.

Spending my day (and night, and dawn...) measuring leaf traits: leaf area, specific leaf area, leaf thickness, leaf dry matter content and leaf sucullence. Learn how to measure all those leaf traits by checking out the manual of plant trait measurements here.

Leaf water retention is the angle of tilt in which the water droplets first begins to roll down the leaf surface. It provides a measurement of water adherence to the leaf. High angular values (>60°) indicate a greater tendency of droplets to be retained on the leaf, while low values (<20°) indicate leaf surfaces that readily shed droplets.