Do You Get What You Pay for? Evaluating the Reliability of an Inexpensive Portable Photosynthesis System in Measuring Gas Exchange in Rice (Oryza sativa L.) Leaves

Abstract

The availability of commercially available portable photosynthesis systems has facilitated widespread photosynthetic research. Our study aimed to evaluate the reliability of a recently developed inexpensive portable photosynthesis system, Yaxin-1105, in measuring gas exchange in rice (Oryza sativa L.) leaves. Gas exchange parameters, including net photosynthetic rate (A_net), stomatal conductance (g_s), intercellular CO₂ concentration (C_i), and transpiration rate (E), were measured on 88 rice leaves across seven rice cultivars and three growth stages (panicle initiation, heading, and early ripening), using both Yaxin-1105 and LI-6400XT. There were significant difference between each gas exchange parameter at each growth stage measured by Yaxin-1105 and LI-6400XT, except C_i at the heading stage. Mean A_net, g_s, and E measured by Yaxin-1105 were 26–66% lower than those measured by LI-6400XT at panicle initiation, heading, and early ripening stages. Mean C_i measured by Yaxin-1105 was 13–22% higher than that measured by LI-6400XT at panicle initiation and early ripening stages. The coefficients of determination between each gas exchange parameter measured by Yaxin-1105 and by LI-6400XT at panicle initiation, heading, and early ripening stages ranged from only 0.0007 to 0.1889. These results indicate that the Yaxin-1105 is not a reliable tool for measuring gas exchange in rice leaves.

1. Introduction

Photosynthesis is one of the most important biochemical processes on Earth, as the main source of energy, food, and oxygen responsible for the survival and reproduction of almost all life [1]. Although photosynthesis research has been ongoing for more than 350 years and has made great progress [2], it still attracts great interest due to concerns regarding food security, clean and renewable energy, and climate change [3,4].

The measurement of gas exchange is central to photosynthesis research, and commercially available portable photosynthesis systems have facilitated an expansion in the evaluation of photosynthesis performance in plants [5]. The LI-6400XT produced by LI-COR Inc. is the most referenced portable photosynthesis system in peer-reviewed literature worldwide and has helped researchers study photosynthesis for over 20 years.

Recently, the Beijing Yaxin Liyi Technology Co., Ltd. (Beijing, China) has produced a portable photosynthesis system, Yaxin-1105, that sells for less than half the price of an LI-6400XT. The price of Yaxin-1105 is very attractive, but limited information is available on its reliability in measuring gas exchange parameters in photosynthetic research. To bridge this information gap, this study compared gas exchange parameters in rice (Oryza sativa L.) leaves measured by Yaxin-1105 with those measured by LI-6400XT.

2. Materials and Methods

Gas exchange parameters, including net photosynthetic rate (A_net), stomatal conductance (g_s), intercellular CO₂ concentration (C_i), and transpiration rate (E), were measured on 88 fully expanded, uppermost leaves of rice, using both Yaxin-1105 and LI-6400XT. The Yaxin-1105 was operated strictly in accordance with the procedures instructed by the company’s engineer, setting a photosynthetic photon flux density (PPFD) of 1200 μmol m⁻² s⁻¹ and a constant air flow rate (AFR) of 600 μmol s⁻¹. The LI-6400XT was operated according to standard procedures described in the instruction manual, with a PPFD of 1200 μmol m⁻² s⁻¹ and a constant AFR of 500 μmol s⁻¹ [6]. The measured leaves involved 7 rice cultivars (Lingliangyou 268, Zhongjiazao 17, Zhongzao 39, Zhuliangyou 819, Huazheyou 261, Jingliangyou 1468, and Liangyoupeijiu) and 3 growth stages (panicle initiation, heading, and early ripening) (Table 1). All measurements were conducted between 9:00 and 11:00 on days with full sunlight.

Paired-t tests were conducted to determine the significance of differences between each gas exchange parameter measured by Yaxin-1105 and by LI-6400XT for each growth stage. The coefficient of determination (R²) was used to evaluate the similarity between each gas exchange parameter measured by the Yaxin-1105 and LI-6400XT for each growth stage. All statistical analyses were performed by Statistix 8.0 (Analytical Software, Tallahassee, FL, USA).

3. Results and Discussion

There were significant differences between A_net measured by Yaxin-1105 and LI-6400XT at panicle initiation, heading, and early ripening stages (Figure 1a). Mean A_net measured by Yaxin-1105 was lower than that measured by LI-6400XT by 26% at the panicle initiation and heading stages and by 31% at the early ripening stage. The differences between g_s measured by Yaxin-1105 and by LI-6400XT at panicle initiation, heading, and early ripening stages were significant (Figure 1b). Mean g_s measured by Yaxin-1105 was lower than that measured by LI-6400XT by 46% at the panicle initiation stage, 48% lower at the heading stage, and 45% lower at the early ripening stage. The differences between C_i measured by Yaxin-1105 and by LI-6400XT at panicle initiation and early ripening stages were significant, while the difference between C_i measured by Yaxin-1105 and by LI-6400XT at heading stage was not significant (Figure 1c). Mean C_i measured by Yaxin-1105 was higher than that measured by LI-6400XT by 13% at the panicle initiation stage and 22% higher at the early ripening stage. There were significant differences between E measured by Yaxin-1105 and by LI-6400XT at panicle initiation, heading, and early ripening stages (Figure 1d). Mean E measured by Yaxin-1105 was 55% lower at the panicle initiation stage, 66% lower at the heading stage, and 60% lower at the early ripening stage than measured by LI-6400XT. Moreover, the results of this study showed that the coefficients of determination (R²) between each gas exchange parameter measured by Yaxin-1105 and by LI-6400XT at panicle initiation, heading, and early ripening stages were very low, ranging from 0.0007 to 0.1889 (Figure 2a–d).

The above results indicate that the Yaxin-1105 is not a reliable portable photosynthesis system for measuring gas exchange in rice leaves. According to our observations during measurement, we found that Yaxin-1105 has the following issues: (1) the leaf chamber is poorly sealed and (2) the CO₂ concentration in the leaf chamber is unstable. Although we do not have experience in developing a photosynthesis system and do not have a comprehensive understanding of the problems of Yaxin-1105, we still recommend that researchers should be careful in purchasing the inexpensive portable photosynthesis system Yaxin-1105 for measuring leaf gas exchange.

In our present study, we only evaluated the reliability of Yaxin-1105 in measuring gas exchange parameters in rice leaves. However, in addition to the leaf gas exchange parameters, light-response curve parameters are also important in photosynthesis research [7]. If the trend of light-response curves measured by Yaxin-1105 and LI-6400XT is similar, the Yaxin-1105 can be used for estimating light-response curve parameters throughout an entire experiment. Therefore, further investigations are required to assess the light-response curve measured by Yaxin-1105 to obtain a better understanding of its performance.

Author Contributions

Conceptualization, M.H.; investigation, X.L., J.X., Z.X., C.Z. (Chunrong Zhao), Y.K., C.Z. (Chuanming Zhou), F.C., and J.C.; funding acquisition, M.H.; writing—original draft preparation, X.Y. and M.H. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflict of interest.

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Figures and Table

Figure 1. (a) Net photosynthetic rate (Anet), (b) stomatal conductance (gs), (c) intercellular CO2 concentration (Ci), and (d) transpiration rate (E) in rice leaves measured by both Yaxin-1105 and LI-6400XT. The box-and-whisker plot shows the minimum (end of the lower whisker), 25th percentile (lower edge of the box), median (horizontal line within the box), mean (cross within the box), 75th percentile (upper edge of the box), and maximum (end of the upper whisker) values of the data.

Figure 2. Coefficients of determination (R2) between (a) net photosynthetic rate (Anet), (b) stomatal conductance (gs), (c) intercellular CO2 concentration (Ci), or (d) transpiration rate (E) measured by Yaxin-1105 and LI-6400XT. The dashed line is 1:1 line.

Table 1

Descriptions of leaf samples.

Growth Stage	Cultivar	Type	Site	Sample Size
Panicle initiation	Lingliangyou 268	Hybrid	Liuyang	7
	Zhongjiazao 17	Inbred	Liuyang	3
	Zhongzao 39	Inbred	Liuyang	6
	Zhuliangyou 819	Hybrid	Liuyang	6
Heading	Huazheyou 261	Hybrid	Hengyang	21
	Jingliangyou 1468	Hybrid	Liuyang	9
	Liangyoupeijiu	Hybrid	Liuyang	12
Early ripening	Jingliangyou 1468	Hybrid	Liuyang	12
	Liangyoupeijiu	Hybrid	Liuyang	12

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