Duckweed Lab Report

Duckweed Geometric Growth

Phosphate Depletion

Lab Report

Max Duron

ID# 80491771

Introduction:

            For Lab 7, the duckweed lab, the purpose is to test what factors might affect the growth of duckweed. In this case phosphate was taken away from the nourishment given to the plant; this was to see how it might affect the plants growth rate after a few weeks. As the weeks went by a significant difference between the duckweed samples without phosphate and the samples with phosphate was noticeable, the duckweed without phosphate had a lower growth rate. This goes to show that in a case where growth rate of plants is important phosphate must be present to raise the growth rate significantly for the first few weeks.

            This is important in a case where duckweed might be being used as a nutrition source of a certain organism, knowing that phosphate is crucial for healthy duckweed growth comes in handy to be able to have the maximum growth rate available and have the duckweed be a reliable nutrition source for the specific organism being fed the duckweed. Since this plant is high in protein it is a good nutrition source, so it is a good idea to grow a supply of the plant at home in case of a drastic emergency, were the only sources of protein have become scarce and perhaps being able to grow this plant rapidly help a person get the source of protein they need to survive and live a healthy life. Or in other cases where duckweed is used as a novel feedstock for bioethanol production by Saccharomyces cerevisiae (energies), whatever the use is for, there is high interest on what conditions the plant grows the best in, and in this experiment the point is to find out how phosphate will affect the plant.

Method:

            To begin this experiment three plastic cups are needed. These cups will be the place where the duckweed will be grown for a period of three weeks. Fill three cups with 175ml of MLB water which will be the control groups for the experiment; these cups will start off with 15 plants each. Then repeat the process for the other three cups but fill them with 175ml of phosphate lacking water as the experiment group. Count the number of thalli (leaves) in each cup and record that number (this will be used to determine the growth rate later in the experiment). Record all the information of the number of thalli in a graph labeled control and phosphate groups to keep track of which is which and to be able to determine growth rates; start off with day zero and initial number of thalli, followed by day 7^th, 14^th, and 21^st.

            After gathering all the information about the growth of the number of thalli as the weeks go by, estimate the average growth rate of the control group and the group lacking phosphate. Graph out the results for geometric growth rate and even the class average to better calculate the results. After all this is done measure the length and with of the thalli to estimate the average of the growth of the duckweed itself to understand not only the reproductive growth rate of the thalli but the size of the plant as well. Record all the data gathered in the experiment and all steps have been completed evaluate whether the hypothesis was correct and record all results to conclude how phosphate depletion has affected the growth rate.

Results:

            As the lab concluded the results were both evident and significant. It is very clear that by eliminating phosphate in the water the duckweeds growth rate is slowed down significantly, the control group which had a good amount of phosphate to provide nourishment for the duckweed reproduced not only fast but efficiently as well, the number of thalli in each control group doubled the first week, and kept a steady growth rate through the following weeks of the experiment, while the lacking  phosphate group hardly even doubled by the time the experiment was over, the growth rate was slow, but steady, and very clearly demonstrated that without phosphate as a nutrient the duckweed cannot grow to its full potential.

This graph demonstrates the growth rate for both groups:

Control Group:

CONTROL TREATMENT
REPLICATE					NUMBER OF THALLI										RELATIVE GROWTH RATE
					DAY 0				DAY 7				DAY 14		WEEK 1		WEEK 2
#1					35				67				108		1.91		1.61
#2					25				43				89		1.72		2.07
#3					27				65				100		2.41		1.54
AVERAGE					29				58.3333333				99		2.01333333		1.74
STANDARD DEVIATION					5.29150262				13.3166562				9.53939201		0.35641736		0.2879236
	CONTROL
	POPULATION SIZE					LAMBDA
			29			2.01
			58.33			1.74
	EXPERIMENTAL
	PHOSPHATE DEPLETED
	POPULATION SIZE					LAMBDA
			32.66			1.5
			49			1.58

FIGURE 1: POPULATION SIZE VS. TIME
TIME	#THALLI	#THALLI
DAYS	CONTROL	PHOSPHATE DEPLETED
0	29	32.66
7	58.33	49
14	99	77.33

EXPERIMENTAL TREATMENT			PHOSPHATE DEPLETED
REPLICATE		NUMBER OF THALLI			RELATIVE GROWTH RATE
		DAY 0	DAY 7	DAY 14	WEEK 1	WEEK 2
#1		33	52	74	1.58	1.42
#2		32	48	86	1.5	1.79
#3		33	47	72	1.42	1.53
AVERAGE		32.6666667	49	77.3333333	1.5	1.58
STANDARD DEVIATION		0.57735027	2.64575131	7.57187779	0.08	0.19

           

            As the graphs demonstrated the results show a significant difference between both groups, the duckweed need phosphate in order to have an ideal source of nutrients for successful reproduction. Granted the duckweed will keep growing without the phosphate being in the water, it won’t cause the plant to die from the depletion of the nutrient, in other words the containers will eventually be filled with the plant, the process will just be significantly slower that in the control group containing the phosphate, if growing duckweed is urgent than the water must contain phosphate to nourish the plant for a “pristine” growth rate.

Discussion:

              This experiment has reviled one very significant result, and that is that in order for duckweed to grow not only fast but efficiently as well, the plant needs a high source of phosphate from where to get nourishment from, without the phosphate the geometric growth of the plant is noticeably slower. As other scientists such as Appenroth have researched, lowering the phosphate concentration in the water has significant results to where the growth rate is always slower (Plant, Cell & Environment). Yet another interesting study done by scientist Akira Haste showed that the plant does better with a slow amount of phosphate, that yes indeed the plant does need phosphate to have a pristine growing conditions, however the amount of phosphate had to be low, too much and the plant does not benefit from the phosphate in the water (Physiologia Plantarum ).

            All these countless experiments, including our own and the data we gathered, have all pointed to the same direction; duckweed does in fact need phosphate to reproduce more efficiently, however the plant will still reproduce without the nutrient present in the water. Other more detailed results illustrated that the plant only needs a small quantity of phosphate to prosper, if too much is added to the water source the plant stops to benefit from the nutrient and again the growth rate is slowed down caused by algae blooms from the high phosphate levels, which can even eventually kill the plant. Phosphate is not necessarily crucial for duckweed growth however it does enhance significantly in the right amounts.

Conclusion/Abstract:

            Duckweed in fact does not need phosphate to reproduce and live. The water source, or experimental group of the experiment kept reproducing and growing through the full time of the experiment, indicating that without phosphate the plant still has a chance to prosper, however having phosphate in the water, like the control groups did, does have benefits to the plants geometric growth rate. Having phosphate in the water such as the control group did, did in fact made the reproduction of the plant’s thalli twice as fast as the experimental group without phosphate, this significant results means that phosphate is not crucial to the plants survival however it is beneficial to the plants growth rate, so it is better to have a small amount of phosphate to provide nutrients to the plant.

References:

http://encore.utep.edu/iii/encore/home?lang=eng

http://researchpro.utep.edu/iii/mfrpro-utep/loadSearchPage.do?searchpage=simple&searchtype=simple&accountid=utep&accountpassword=utep

Appenroth K. Co-action of temperature and phosphate in inducing turion formation in Spirodela polyrhiza      (Great duckweed)*. Plant, Cell & Environment [serial online]. September 2002;25(9):1079-1085.   Available from: Academic Search Complete, Ipswich, MA. Accessed October 29, 2012.

Hase A, Nishikoori M, Okuyama H. Induction of high affinity phosphate transporter in the duckweed             Spirodela oligorrhiza. Physiologia Plantarum [serial online]. February 2004;120(2):271-279.   Available from: Academic Search Complete, Ipswich, MA. Accessed October 29, 2012.

Qian C, Yanling J, Guohua Z, Yang F, Yao X, Hai Z. Improving Production of Bioethanol from Duckweed        (Landoltia punctata) by Pectinase Pretreatment. Energies (19961073) [serial online]. August      2012;5(8):3019-3032. Available from: Academic Search Complete, Ipswich, MA. Accessed             October 29, 2012.