After a 2 month growing and censusing period, followed by a harvesting, drying, and biomass census I have concluded my 200 pot competition series.
During this period, I had obtained a photometer to measure light levels and did two light census for both the overall pot as well as below canopy. I am hoping that these light measures will provide quantifiable insight on the effect light has on growth. I hypothesize that plants receiving ambient light will yield greater mean biomass per species, while those in shade conditions (to mimic shrub presence) will have a greater mean height due to leggy growth.
I wanted to quantify the growth of my plants through several metrics, and therefore chose to obtain both height and leaf measurements for each species from each pot. In order to acquire these measurements, I implemented a new censusing technique for my second and final census. In this census I counted the number of individuals of each separate species there were per pot. Following this, I took the tallest individual of each species, and recorded its height along with the number of leaves. This way, following the harvest and mechanical oven drying period I would be able to compare the biomass of the plant with its height and leaf count. This would allow me to evaluate plant growth using two separate dimensions; plant height along and number of leaves vs. plant biomass.
After using a mechanical drying oven set to 62 degrees Fahrenheit for 48 hours, I used a precision scale to obtain the biomass of each plant.
The experiment planning, seed counting, pot filling, plant censusing, harvesting, and biomass analysis processing were extensive processes. I am extraordinarily grateful to Dr. Christopher Lortie, Dr. Jacob Lucero, Masters graduate Jenna Braun, research practicum student Anuja, and Economics and Finance student Denis Karasik for their time, efforts, and immense assistance with running this experiment.
Statistical analyses for all of the results are still in work, and I am eager to see the conclusion my experiment comes to.
Belowground harvest: need to harvest entire plant at once by removing plants and roots from pot experiments (for instance) and gently washing to remove all soil but keeping roots and shoots intact. Then, snip aboveground growth from below.
Depending on level of replication and lowest possible independent sample unit, harvest one individual, one species, or all individuals of one species per pot into independent paper bags.
Place in ovens at 68F for at least 2 days.
Leave all plants in paper bags in oven until the moment you are ready to weigh.
Remove from paper bags to weigh for small plants. Typically, I weigh to 3-4 decimal grams for small desert annual plants.
Return plants to bag, do not return to oven, store in a paper box for a few weeks or until all data entered and checked.
I want my final paper to be useful for and applicable to restoration ecology. This led me to inquire what data I should collect for my second census. My germination rates are up, and all four species are present, so would relying on number of individuals and biomass of each species per pot be enough data? I decided that since I am using light as a limiting factor I must include height in my data; the plants may have somewhat similar biomass, but if it is due to leggy growth in the shaded pots then it will be important to note that although biomass was similar resource allocation was not equal. Are great amounts of leggy, weak, and nutrient deficient plants with few leaves better for ecosystems then having fewer shorter but thicker, more leafy plants? I measured the number of individuals per species per pot, alongside with the height and number of leaves the tallest member of each species had per pot. I have yet to analyze these numbers, but did notice trends when doing the census!
Side note: I conducted a germination experiment in the greenhouse prior to using these seeds, and have let them grow out. My Phacelia tanacetifolia is growing a beautiful flower!
Salvia columbariae, Phacelia tanacetifolia, and Plantago insularis are key phytometers (plants that indicate ecosystem conditions) in the San Joaquin Desert of California. As the highly invasive exotic Bromusmadritensis colonizes in this non-native environment it lacks the environmental suppressors and competitors it faces in its native habitat. This leads to native Californian desert ecosystems to shift to a new model where native plants are excluded due to competitive disadvantages. decreases in native biodiversity are directly correlated to the health of an ecosystem, ecosystem services, resiliency to climate change, as well as the resources and for these reasons, identifying methods of restoration ecology is crucial.
Using my 3 factor (ambient light vs shaded conditions, low vs high B.madritensis density, native seeds at 6 levels of density (0,3,6,9,15, or 30 natives)) greenhouse competition trials I aim to identify what density of native species must present in a pot with a surface area of 153cm2 to outcompete an exotic one.I have previously run an experiment to identify optimal density in pots of the same surface area using each of the native species in monoculture, implementing the same light versus shade conditions with a total of 365 replicates. I will assess if I am able to compare these differences in optimal monoculture mix density to a polyculture mix with invader presence. If my data finds an optimal density using these methods, I hope to further my research and apply my findings to population ecology by estimating necessary population metrics required to apply this to ecosystem for large scale restoration and contribute it towards field work.
My experiment currently contains 200 pots, 100 of which are shaded by a bamboo structure I suspended. Germination has begun, yet it is still difficult to differentiate among species this early on. As predicted, the shaded individuals have demonstrated leggy growth as they reach towards the light source, yet there seems to be leaf production in possibly higher concentrations in the shaded pots than the ones experiencing ambient light. It appears that the shaded pots have a higher germination and growth rate (measured by number of individuals and number of leaves per pot). Is it possible that the shade-preferring B.madritensis is facilitating growth through positive density dependence? Am I witnessing an Allee effect in the form of environmental conditioning? Or is the answer as simple as light levels in the shaded conditions being sufficient for the natives as well as B.madritensis? Using the metrics of germination of species per pot as well as leaves per species and finally above ground biomass at the end of my experiment I will continually assess success through the different factors and levels I have designed and implemented in my experiment and hope to achieve a successful conclusion.
I am currently running an experiment to observe how an invasion of red brome impacts the growth and success of 3 native Californian plants (Plantago insularis, Phacelia tancetifolia, Salvia columbariae) across 5 different watering regimes. These watering regimes simulate conditions from extreme drought to very wet years. The experiment utilizes a total of 300 pots with 10 replicates per treatment; 100 pots are being used for each species, with 50 of those pots containing brome and 50 lacking brome.
As the experiment progresses 4 measurements will be obtained:
Establishment by 5 weeks
Total Biomass production at the conclusion of the experiment
My native versus exotic competition experiment is all set up in the greenhouse, so just waiting on germination now. Have planted additive densities of 0,3,6,9,15 and 25 natives with brome at high (10 seeds) and low (5 seeds) densities, 10 reps per treatment at ambient light versus shaded conditions for a total of 200 pots. I hung up a wooden bamboo structure to provide shade and imitate shrub presence to half of the pots, and hung it in a way that it is easy to suspend for pot censusing. Here are photos of what it all looks like.