RAPID RESPONSE CURVES AND SURVEY MEASUREMENTS
Systems and methods for measuring plant leaf gas exchange based on instantaneous mass balance in the sample chamber. The response of leaf net assimilation rate (A net ) to computed leaf internal CO 2 concentration (C 1 ) is measured by continuously varying the input CO 2 concentration and measuring the continuous difference between chamber input (reference) and output (sample) concentrations to compute a continuous series of A net values, which can then be plotted against computed C i . When combined with a similar response test using an empty chamber test to allow for sample chamber mixing and/or gas analyzer match dynamics and/or small flow-related residual time delays, such method provides accurate and rapid A C i response (RAC i R) curves in a much shorter time than conventional methods.
1 . A method for determining a rapid net assimilation rate (A net ) to computed sample internal CO 2 concentration (C i ) response (RAC i R) curve for a photosynthesis capable sample in a gas exchange analysis system having an enclosed sample chamber defining a measurement volume, V, for analysis of the photosynthesis capable sample, the sample chamber having an inlet port and an outlet port, the method comprising:
with a photosynthesis capable sample in the sample chamber, continuously varying one or more of a) a concentration of CO 2 introduced into a gas flow line connected with the inlet port of the sample chamber from a first concentration to a second concentration, b) an intensity of light illuminating the photosynthesis capable sample in the sample chamber, and c) a temperature of the measurement volume of the sample chamber, during the continuously varying:
i) measuring, at each of a first plurality of measurement times, a first concentration of CO 2 in a gas exiting the sample chamber using the first gas analyzer;
ii) measuring, at each of the first plurality of measurement times, a second concentration of CO 2 in the gas entering the sample chamber using the second gas analyzer; and
iii) determining, for each of the first plurality of measurement times, an apparent assimilation rate value A app , wherein the determining the apparent assimilation rate value A app includes subtracting the measured first concentration value from the measured second concentration value;
determining a net assimilation rate value of the photosynthesis capable sample by solving a chamber mass balance equation for the sample chamber; and
providing the net assimilation rate value as an output.
2 . The method of claim 23 , wherein i) and ii) are performed simultaneously.
3 . The method of claim 23 , wherein the chamber mass balance equation solved for assimilation is given by
A
=
u
s
(
C
e
-
C
o
)
-
V
ρ
s
d
C
o
d
t
where C e and C o are dry CO 2 mole fractions entering and leaving the sample chamber, respectively, where ρ is the density of the air in the sample chamber, u is the air mass flow rate, and s is an area of the sample in the sample chamber.
4 . An open-path gas exchange analysis system for determining a rapid net assimilation rate (A net ) to computed sample internal CO 2 concentration (C i ) response (RAC i R) curve for a photosynthesis capable sample, the system comprising:
a CO 2 source coupled to a gas flow line, wherein responsive to a received control signal, the CO 2 source adjusts a concentration of CO 2 provided to the gas flow line in a continuous manner from a first concentration to a second concentration;
an enclosed sample chamber having an inlet port and an outlet port, the inlet port coupled with the gas flow line;
a first gas analyzer coupled to the outlet port of the enclosed sample chamber and configured to measure a first concentration of CO 2 exiting the enclosed sample chamber;
a second gas analyzer coupled to the second output port of the flow splitting device and configured to measure a second concentration of CO 2 entering the enclosed sample chamber; and
a control circuit, the control circuit adapted to:
a) in response to an indication that a photosynthesis capable sample has been placed in the enclosed sample chamber:
with the photosynthesis capable sample in the enclosed sample chamber, send a second control signal to the CO 2 source to control the CO 2 source to continuously vary the concentration of CO 2 introduced into the gas flow line from the first concentration to the second concentration, and during the continuously varying:
i) control the first gas analyzer to measure, at each of a first plurality of measurement times, a first concentration of CO 2 in a gas exiting the enclosed sample chamber;
ii) control the second gas analyzer to measure, at each of the first plurality of measurement times, a second concentration of CO 2 in the gas entering the enclosed sample chamber;
iii) determine, for each of the plurality of the first measurement times, an apparent assimilation rate value A app , wherein the determining the apparent assimilation rate value A app includes subtracting the first concentration value from the second concentration value; and
c) determine a net assimilation rate value of the photosynthesis capable sample by solving a chamber mass balance equation for the sample chamber.
5 . The system of claim 26 , wherein the control circuit is adapted to perform i) and ii) simultaneously.
6 . The system of claim 26 , wherein the chamber mass balance equation solved for assimilation is given by
A
=
u
s
(
C
e
-
C
o
)
-
V
ρ
s
d
C
o
d
t
,
where C e and C o are dry CO 2 mole fractions entering and leaving the sample chamber, respectively, ρ is the density of the air in the sample chamber and s is an area of the sample in the sample chamber.
7 . A method for determining a rapid net water vapor transpiration rate (E t ) for a photosynthesis capable sample in a gas exchange analysis system having an enclosed sample chamber defining a measurement volume, V, for analysis of the photosynthesis capable sample, the sample chamber having an inlet port and an outlet port, the method comprising:
with a photosynthesis capable sample in the sample chamber, continuously varying one or more of a) a concentration of CO 2 introduced into a gas flow line connected with the inlet port of the sample chamber from a first concentration to a second concentration, b) an intensity of light illuminating the photosynthesis capable sample in the sample chamber, and c) a temperature of the measurement volume of the sample chamber, during the continuously varying:
i) measuring, at each of a first plurality of measurement times, a first concentration of H 2 O in a gas exiting the sample chamber using the first gas analyzer;
ii) measuring, at each of the first plurality of measurement times, a second concentration of H 2 O in the gas entering the sample chamber using the second gas analyzer; and
iii) determining, for each of the first plurality of measurement times, an apparent transpiration rate value E app , wherein the determining the apparent transpiration rate value E app includes subtracting the measured second concentration value from the measured first concentration value;
determining a net water vapor transpiration rate value E of the photosynthesis capable sample by solving a chamber mass balance equation for the sample chamber; and
providing the net transpiration rate value as an output.
8 . A method for determining an average net assimilation rate (A net ) for a photosynthesis capable sample in a gas exchange analysis system having an enclosed sample chamber defining a measurement volume for analysis of the photosynthesis capable sample, the sample chamber having an inlet port and an outlet port, the method comprising:
with a photosynthesis capable sample in the sample chamber:
i) measuring, at each of a first plurality of measurement times, a first concentration of CO 2 in a gas exiting the sample chamber using the first gas analyzer;
ii) measuring, at each of the first plurality of measurement times, a second concentration of CO 2 in the gas entering the sample chamber using the first gas analyzer or a second gas analyzer; and
iii) determining, for each of the first plurality of measurement times, an apparent assimilation rate value A app , wherein the determining the apparent assimilation rate value A app includes subtracting the measured first concentration value from the measured second concentration value;
determining an average net assimilation rate value of the photosynthesis capable sample by solving a chamber mass balance equation for the sample chamber; and
providing the average net assimilation rate value as an output.
9 . The method of claim 8 , further including, with the photosynthesis capable sample in the sample chamber, varying one or more of a) a concentration of CO 2 introduced into a gas flow line connected with the inlet port of the sample chamber from a first concentration to a second concentration, b) an intensity of light illuminating the photosynthesis capable sample in the sample chamber, and c) a temperature of the measurement volume of the sample chamber, during the varying.