Overview of the article selection process. N = the number of published literatures. See Supplemental File 1 for data and metadata.
Single-leaf photosynthetic rates (Pn) of northern highbush blueberry (NHB) and southern highbush blueberry (SHB) cultivars. No study of highbush blueberry Pn was published between 2000 and 2010.
Infrared gas analyzer setpoints used for blueberry research during 1986 to 2025. A Kruskal-Wallis nonparametric analysis of variance was performed to compare infrared gas analyzer setpoints between northern highbush blueberry (NHB) and southern highbush blueberry (SHB).
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This comprehensive review examined leaf photosynthetic rates, research methodologies, and existing knowledge gaps in highbush blueberry (Vaccinium corymbosum interspecific hybrids) research through a systematic and quantitative analysis of scientific literature spanning the past six decades. Studies of photosynthesis in northern and southern highbush blueberry were reviewed, revealing a lack of consensus on environmental set points for studying blueberry photosynthesis. Research of northern highbush blueberry has been more prevalent than that of its southern counterpart. According to the literature, northern highbush blueberry exhibits higher leaf photosynthetic rates than that of southern highbush blueberry, but both blueberry types exhibit lower photosynthetic rates than those of other fruit crops. Additionally, there is no evidence that selective breeding has increased blueberry leaf photosynthetic rates. Additional research is needed to understand and optimize highbush blueberry photosynthesis in agricultural settings.
Photosynthesis is the source of all carbon available for plant growth, defense, and productivity. Thus, photosynthesis measurements represent an invaluable source of information for horticulturists, plant biologists, and plant breeders. Nevertheless, photosynthesis research is costly both in terms of time and resources. Therefore, little is known about the photosynthetic activity of several important crops. Highbush blueberry (Vaccinium corymbosum interspecific hybrids) is one of those crops. Despite the popularity of this fruit crop and its cosmopolitan cultivation (Fang et al. 2020), our understanding of the factors that affect blueberry photosynthesis is limited. This review aimed to explore photosynthesis research of highbush blueberry plants over the past six decades by drawing upon a systematic and quantitative analysis of literature.
Most blueberry Pn research focuses on plant responses to environmental factors or agronomic practices. For example, nitrogen nutrition (Cárdenas-Navarro et al. 2024), light intensity, carbon dioxide (CO2) concentration (Reyes-Díaz et al. 2016; Wen et al. 2022), temperature (Hao et al. 2019), soil pH (Jiang et al. 2019), pathogen attacks (Hilário et al. 2023), growing substrates (Viencz et al. 2021; Yang and Lin 2025), and water stress (Rho et al. 2012) affect blueberry Pn. Nevertheless, there is no consensus about instrumentation set points used for this research. Therefore, this review also aimed to provide a set of recommendations to standardize blueberry photosynthesis research and allow aggregation and meta-analyses in the future.
We surveyed peer-reviewed articles available in Clarivate’s Web of Science. Two sets of keywords were used: [“blueberry” AND “photosynthesis”] and [“blueberry” AND “photosynthetic”]. Literature data were collected from Aug 1965 to Dec 2024. This review focused on the primary literature of studies of highbush blueberry. Both northern highbush blueberry (NHB) and southern highbush blueberry (SHB) were included. Publications that focused on lowbush, rabbiteye, and wild blueberry were excluded. This search returned 243 publications; of these, 56 duplicate articles were removed (Fig. 1). A total of 68 relevant peer-reviewed articles were selected to be discussed in this review. When comparisons were made, the Kruskal-Wallis nonparametric analysis of variance (α = 0.05) was used. Analyses and illustrations were performed in R (version 4.4.2; R Cor Development Team 2021).
Citation: HortScience 60, 8; 10.21273/HORTSCI18630-25
Blueberry Pn measurements between 1986 to 2000 were available (Fig. 2). Notably, no published literature between 2000 and 2010 was found. However, from 2010 to 2023, a substantial increase in reports of blueberry Pn occurred (Fig. 2). From 1986 to 2016, research of blueberry photosynthesis focused on NHB cultivars, but few studies reported SHB (Fig. 2). After 2017, however, research of SHB photosynthesis became more prevalent, likely because of the increasing cultivation of this blueberry type in tropical and subtropical regions (Fang et al. 2020).
Citation: HortScience 60, 8; 10.21273/HORTSCI18630-25
With the exception of one report, all highbush blueberry Pn was less than 20 µmol·m−2·s−1 (Supplemental File 1), which is lower than that of other fruit crops like apple (Fu et al. 2015), pear (Zhao et al. 2022), peach (Jiménez et al. 2020), strawberry (Lalk et al. 2023), and citrus (Nebauer et al. 2013) (Supplemental Fig. 1). In general, NHB exhibited higher leaf Pn than that of SHB, with maximum and minimum Pn values of 27.0 µmol·m−2·s−1 (‘Brigitta’) and 0.9 µmol·m−2·s−1 (‘Gulfcoast’) for NHB and 16.0 µmol·m−2·s−1 (‘Jewel’) and 2.0 µmol·m−2·s−1 (‘Camellia’) for SHB (Fig. 2). Blueberry leaf Pn measurements were typically conducted at 400 µmol·mol−1 CO2, photosynthetic photon flux density (PPFD) of 800 to 1000 µmol·m−2·s−1, air temperature of 25 to 30 °C, and 60% to 70% relative humidity (Hao et al. 2019; Smrke et al. 2023).
Blueberry Pn in the literature is almost exclusively obtained from single-leaf measurements of young, fully expanded, and healthy leaves (usually in the second to fifth node) that are fully exposed to solar radiation (Petridis et al. 2020). This practice is consistent with research that suggested blueberry leaf age affects Pn. Older leaves exhibit Pn that is lower than that of recently matured ones (Forsyth and Hall 1965; Long et al. 2024).
Photosynthetic measurements of branches or groups of leaves are still rare in this crop (Retana-Cordero and Nunez 2025). Research of low bush blueberry (V. angustifolium) identified chamber size effects that can lead to underestimation of leaf Pn when large cuvettes are used for these measurements (Tasnim and Zhang 2021). It is unknown if this issue is also present in highbush blueberry branches.
Highbush blueberry Pn measurements usually were performed in the morning or at mid-day. Daily Pn curves for several SHB cultivars suggest that steady-state mid-day measurements can be performed between 12:00 and 2:00 PM (Li et al. 2009; Salazar-Gutiérrez et al. 2023) when PPFD is highest. However, mid-day Pn rates might not be the highest daily rate of blueberry (Osorio et al. 2020; Salazar-Gutiérrez et al. 2023). For example, ‘Bluecrop’ NHB exhibited mid-day photosynthesis depression, which is a phenomenon primarily attributed to stomatal limitations caused by high temperatures and high vapor pressure deficits (Kim et al. 2011; Li et al. 2009). Therefore, researchers should conduct daily response curves before settling on a time of day for survey Pn measurements. The time of the year when Pn measurements are made also appears to be relevant because changes in the timing of seasonal peak photosynthetic activity have been previously reported (Park et al. 2019).
Despite the well-known challenges encountered when performing Pn measurements when cuvette conditions are different from ambient (Haworth et al. 2018), there are no reports of blueberry leaf acclimation times. Therefore, currently, the duration of the necessary leaf acclimation to cuvette conditions in blueberry is unknown. Petridis et al. (2018) and da Silva Benevenute et al. (2025) reported slow stomatal conductance (gs) responses to a step change in PPFD in several NHB and SHB cultivars. Thus, it is possible that some of the reported instantaneous measurements represent leaves that are not fully acclimated to cuvette conditions, especially if stomata are closed at the start of the measurement. This may explain the wide range of Pn reported for some cultivars (for example, Brigitta NHB). This knowledge gap should be addressed to ensure that accurate Pn measurements are made.
Blueberry leaf Pn varies depending on genotype and environmental factors. Some cultivars exhibited higher Pnmax than that of others (Salazar-Gutiérrez et al. 2023), but high leaf Pn rates are not directly reflected in agronomic performance. Additionally, environmental factors like high temperature (Hancock et al. 1992; Lobos and Hancock 2015), water deficit (Ribera-Fonseca et al. 2019), and plant-to-plant competition for light (Strik and Buller 2005) can lead to lower Pn. However, optimal nitrogen fertilization (Swain and Darnell 2001), reflective plastic mulches (Muneer et al. 2019; Petridis et al. 2021), and selective pruning (Lee et al. 2015) can increase Pn. Understanding these dynamics is crucial to optimizing blueberry production and enhancing overall photosynthetic efficiency.
Blueberry steady-state Pn measurements are usually conducted with infrared gas analyzers set at CO2 concentrations of 400 μmol·mol−1 (Fig. 3A). The Pn correlates linearly with the ambient CO2 concentration in the range of 150 to 400 μmol·mol−1 (Davies and Flore 1986). Whenever measurements were made at higher CO2 concentrations, Pn rates were inflated; therefore, they are not comparable with the literature. High ambient CO2 concentrations lead to high Pn, especially in crops that perform C3 photosynthesis such as blueberries. Studies that related cuvette CO2 concentrations to leaf Pn responses indicated that blueberry plants could benefit from cultivation in controlled environments with CO2 enrichment. In several NHB cultivars, Pn increased rapidly as the intercellular CO2 concentration increased. However, the rate of Pn increase tapered at intercellular CO2 concentrations above 250 μmol·mol−1, presumably because of limitations in the maximum carboxylation (Vcmax) efficiency of ribulose 1,5-bisphosphate carboxylase oxygenase (RuBisCO) (Moon et al. 1987; Petridis et al. 2018). The Vcmax of blueberry is lower than that of other fruit crops (P = 0.06), including apple (Hassan and Ito 2023; Yang et al. 2021), citrus (Hussain et al. 2024; Ribeiro et al. 2009), raspberry (Fernandez 1994), peach (Walcroft et al. 2002), and strawberry (Yu et al. 2023). The Vcmax is an important indicator used to determine the photosynthetic capacity and overall productivity of the plant (Lu et al. 2020), including blueberry (Rho et al. 2012; Wu et al. 2022).
Citation: HortScience 60, 8; 10.21273/HORTSCI18630-25
Blueberries, like many crops, are experiencing the impacts of a changing planet. Human activity is increasing ambient CO2 concentrations, especially in urban and peri-urban settings. Single leaf Pn of blueberry plants is likely to increase under CO2 concentrations higher than 400 μmol·mol−1. Nevertheless, CO2 enrichment will likely lead to different higher-order constraints that will hinder productivity, like water or mineral nutrient limitations. Research that examined whole plant responses to CO2 enrichment is necessary to predict impacts and devise mitigation strategies for sustainable blueberry production in the future.
Light plays a crucial role in affecting Pn, plant growth, and survival. The infrared gas analyzer settings ranged between 0 and 2000 µmol·m−2·s−1 (Fig. 3B). The relationship between light intensity and Pn (light response curves) of only a few blueberry cultivars has been studied. ‘Bluecrop’ NHB, ‘Liberty’ NHB, ‘Darrow’ NHB, ‘Duke’ NHB, and ‘Misty’ SHB reach single-leaf light saturation points between 500 µmol·m−2·s−1 and 600 µmol·m−2·s−1 (Kim et al. 2011; Petridis et al. 2018, 2020; Rho et al. 2012). Leaf light saturation points of ‘Bluecrop’ NHB and ‘O’Neal’ SHB were higher and lower than this range, respectively (Li et al. 2012; Long et al. 2024). Blueberry light saturation points are lower than those of other cultivated soft fruits (P < 0.001) such as apple (Yang et al. 2021), peach (Quilot et al. 2004), strawberry (Choi et al. 2016), raspberry (Qiu et al. 2017), and citrus (Wang et al. 2020). The low light saturation points of blueberry invite close examination of infrared gas analyzer settings for instantaneous Pn measurements because settings far above 600 µmol·m−2·s−1 might cause photoinhibition.
While single leaves reach light saturation at relatively low photosynthetically active radiation intensities, research of other fruit crops suggested that whole plant photosynthesis benefits from light intensities above the light saturation point. Polyethylene and Mylar film chambers have been previously used to measure whole canopy gas exchange in apple (Corelli-Grappadelli and Magnanini 1993; Lakso et al. 1996) and grapevine (Miller et al. 1996). Modeling tools have also been used to estimate canopy gas exchange (Kaneko et al. 2022; Luo et al. 2018). Neither approach has been applied to highbush blueberry research. However, research suggested that light is a yield-limiting factor in blueberry production in some locations (Petridis et al. 2018). As a result, reflective plastic mulch has been used to increase irradiance within the plant canopy, positively impacting blueberry crop production (Muneer et al. 2019; Petridis et al. 2018).
Rapid fluctuations in light intensity caused by changes in cloud cover, the angle of the sun, and shading by neighboring plants affect blueberry and other crops (Assmann and Wang 2001; McAusland et al. 2016; Pearcy 1990; Petridis et al. 2021). However, the fluctuations might be particularly detrimental for highbush blueberry plants because of their slow stomatal responses (da Silva Benevenute et al. 2025; Petridis et al. 2018). Thus, NHB and SHB plants might be better suited for locations with constant diffuse light. Understanding these light interactions is crucial for optimizing growing conditions and improving the productivity of both NHB and SHB cultivars.
The chamber flow rate is a critical parameter in leaf gas exchange measurements because it significantly influences the accuracy of photosynthesis estimates. In other fruit crops and model plants, high flow rates (>400 mL·min−1) can lead to rapid removal of CO2 from the chamber, potentially underestimating photosynthetic rates. Low flow rates (<200 mL·min−1) lead to CO2 accumulation within the chamber, potentially overestimating photosynthetic rates. Low flow rates can also result in condensation in the chamber as water vapor from transpiration accumulates. The Pn measurements are stable and consistent between 200 to 300 mL·min−1 (Adnew et al. 2021; Busch et al. 2024; Keeley et al. 2022; Le et al. 2021). Crop-specific research of chamber flow rates is not available for highbush blueberry. In the surveyed literature, chamber flow rates in the blueberry literature range from 200 mL·min−1 to 395 mL·min−1 (Fig. 3C).
Temperature plays a crucial role in the photosynthetic efficiency of blueberry plants. Blueberry Pn is influenced by temperature through its effects on enzymatic activities and physiological processes. Chamber temperature setpoints in the blueberry literature range between 20 and 40 °C (Fig. 3D). In NHB, the optimal temperature range for photosynthesis is 20 to 25 °C (Hancock et al. 2008; Lobos et al. 2018). Exposure to temperatures exceeding 30 °C can lead to photosynthetic decline caused by enzyme deactivation (e.g., RuBisCO) and increased photorespiration (Hancock et al. 1992; Lobos et al. 2018). Increased leaf temperature can decrease stomatal conductance and intercellular CO2 concentrations, inducing photorespiration in highbush blueberry (Ru et al. 2024). Additionally, extremely high temperatures can increase transpiration rates, leading to water deficit stress and further inhibiting photosynthesis (Long et al. 2024).
In SHB, the optimal temperature for photosynthetic activity has not been established because most research has focused on the research conditions established for NHB (Long et al. 2024). Based on the distribution range of SHB (Fang et al. 2020), it is possible that SHB exhibits a higher optimum temperature range for Pn. Future research should address this knowledge gap.
Several factors beyond CO2, light, chamber flow rate, and temperature influence blueberry Pn. Fungal infections like septoria leaf spot (caused by Septoria albopunctata) can severely reduce photosynthetic rates. Studies have shown that as the severity of septoria leaf spot increases, Pn decreases exponentially (Roloff et al. 2004). This reduction is primarily caused by damaged leaf tissues and disrupted chlorophyll production. Fertilization also impacts the blueberry Pn by influencing nutrient availability and overall plant health. Nitrogen is a key component of chlorophyll, which is the pigment responsible for capturing light energy. Studies have shown that nitrogen fertilization can enhance Pn by increasing the chlorophyll content and augmenting the leaf area (Viencz et al. 2021). Larger leaf areas generally lead to increased photosynthetic capacity because of more light being absorbed and more sites for gas exchange, but there are also tradeoffs with transpiration and the efficiency of photosynthesis (Funnell et al. 2002; Hao et al. 2019; Wang et al. 2019). Phosphorus is vital for energy transfer within the plant (Guo et al. 2021). Phosphorus deficiency reduced SHB photosynthetic rates (Retana-Cordero and Nunez 2025). The specific effects of other nutritional deficiencies of blueberry Pn are unknown at this time.
This review explored photosynthesis research of highbush blueberry (Supplemental File 1). Blueberry eco-physiology is inherently heterogenous because of the recent and frequent interspecific crosses used for highbush blueberry breeding (Lobos and Hancock 2015; Lyrene and Olmstead 2012). Thus, large-scale studies that use multiple genotypes and environments are necessary to build a thorough and nuanced understanding of the photosynthetic diversity in this crop. While some authors have claimed that blueberry breeding programs improved photosynthesis efficiency (Lobos and Hancock 2015), our bibliographic research suggested that this goal has not been accomplished or reported yet. Our overarching impression at the conclusion of this review is that more research is necessary to understand blueberry photosynthesis and optimize blueberry cultivation. Additional research is also necessary to integrate blueberry single-leaf Pn measurements, which comprise the majority of what is known of this crop, into canopy modeling, carbon budgeting, and the future of controlled environment agriculture. In this context, this review offers a baseline of existing research and a list of potential research avenues for the future.
Overview of the article selection process. N = the number of published literatures. See Supplemental File 1 for data and metadata.
Single-leaf photosynthetic rates (Pn) of northern highbush blueberry (NHB) and southern highbush blueberry (SHB) cultivars. No study of highbush blueberry Pn was published between 2000 and 2010.
Infrared gas analyzer setpoints used for blueberry research during 1986 to 2025. A Kruskal-Wallis nonparametric analysis of variance was performed to compare infrared gas analyzer setpoints between northern highbush blueberry (NHB) and southern highbush blueberry (SHB).
Contributor Notes
The authors declare no conflict of interest.
The authors are not aware of any affiliations, memberships, funding, or financial holdings that might be perceived as affecting the objectivity of this review.
Overview of the article selection process. N = the number of published literatures. See Supplemental File 1 for data and metadata.
Single-leaf photosynthetic rates (Pn) of northern highbush blueberry (NHB) and southern highbush blueberry (SHB) cultivars. No study of highbush blueberry Pn was published between 2000 and 2010.
Infrared gas analyzer setpoints used for blueberry research during 1986 to 2025. A Kruskal-Wallis nonparametric analysis of variance was performed to compare infrared gas analyzer setpoints between northern highbush blueberry (NHB) and southern highbush blueberry (SHB).
