A low-cost automated growth chamber system for continuous measurements of gas exchange at canopy scale in dynamic conditions

Abstract

Background Obtaining instantaneous gas exchanges data is fundamental to gain information on photosynthesis. Leaf level data are reliable, but their scaling up to canopy scale is difficult as they are acquired in standard and/or controlled conditions, while natural environments are extremely dynamic. Responses to dynamic environmental conditions need to be considered, as measurements at steady state and their related models may overestimate total carbon (C) plant uptake. Results In this paper, we describe an automatic, low-cost measuring system composed of 12 open chambers (60 × 60 × 150 cm; around 400 euros per chamber) able to measure instantaneous CO2 and H2O gas exchanges, as well as environmental parameters, at canopy level. We tested the system’s performance by simulating different CO2 uptake and respiration levels using a tube filled with soda lime or pure CO2, respectively, and quantified its response time and measurement accuracy. We have been also able to evaluate the delayed response due to the dimension of the chambers, proposing a method to correct the data by taking into account the response time ($${t}_{0}$$ t 0 ) and the residence time (τ). Finally, we tested the system by growing a commercial soybean variety in fluctuating and non-fluctuating light, showing the system to be fast enough to capture fast dynamic conditions. At the end of the experiment, we compared cumulative fluxes with total plant dry biomass. Conclusions The system slightly over-estimated (+ 7.6%) the total C uptake, even though not significantly, confirming its ability in measuring the overall CO2 fluxes at canopy scale. Furthermore, the system resulted to be accurate and stable, allowing to estimate the response time and to determine steady state fluxes from unsteady state measured values. Thanks to the flexibility in the software and to the dimensions of the chambers, even if only tested in dynamic light conditions, the system is thought to be used for several applications and with different plant canopies by mimicking different environmental conditions.

Does Fluctuating Light Affect Crop Yield? A Focus on the Dynamic Photosynthesis of Two Soybean Varieties

“…We grew a commercial green soybean variety (Eiko, Asgrow, United States) and the chlorophyll deficient mutant MinnGold ( Campbell et al, 2015 ) in a growth chamber system (DYNAMISM; Salvatori et al, 2021 ). MinnGold is the result of a non-synonymous substitution in a magnesium chelatase ChlI subunit leading to plants with a “yellow” or “golden” phenotype with approximately 80% less chlorophyll than the green varieties ( Campbell et al, 2015 ; Sakowska et al, 2018 ).…”

“…Transmitted light (tPPFD) was continuously measured within each chamber using a solar bar placed horizontally at the bottom of the canopy. Each bar was made of eight photodiodes in parallel (model S1087-01, Hamamatsu Photonics, Japan) with a 100 Ω resistance and was calibrated against a reference quantum sensor (Li-190R, Licor, United States) before setting up the system ( Salvatori et al, 2021 ). Albedo (i.e., the ratio between reflected and incident radiation) was weekly measured.…”

“…Canopy net CO 2 flux (A) and evapotranspiration (E) were continuously monitored ( Salvatori et al, 2021 ): each chamber was sampled once per hour for 290 s and A was calculated as an average between 110 and 290 s, thus to not consider the tube’s purging after chamber switch (110 s). At the end of every hour, a matching procedure was applied to compute the difference in CO 2 and H 2 O concentration between cell A and B of the LI-7000 gas analyzer and correct the measured data.…”

“…As we used an inert substrate, the measured A correspond to NPP (i.e., heterotrophic respiration was cancelled). Air temperature and transmitted light across the canopy were monitored every second within each chamber using thermistors and a solar bar ( Salvatori et al, 2021 ).…”

“…We hypothesized that in fluctuating light conditions leaves with less chlorophyll would undergo smaller changes in incident light intensities (simply by absorbing less light) and consequently would stress less the photoprotective machinery, which is thought to interfere with the velocity of photochemical quenching induction/relaxation dynamics in fluctuating conditions ( Kromdijk et al, 2016 ). To test this hypothesis, we assessed the response of two soybean cultivars grown in controlled conditions ( Salvatori et al, 2021 ) and exposed to different light conditions (constant and fluctuating light): a green cultivar (Eiko) and a chlorophyll deficient mutant (MinnGold). In particular, we tested if MinnGold and Eiko showed the same net primary production (NPP) at canopy scale under non-fluctuating light and if Eiko showed a more pronounced decrease in NPP under fluctuating light.…”