Are Wild Blueberries a Crop with Low Photosynthetic Capacity? Chamber-Size Effects in Measuring Photosynthesis

Rafa Tasnim,Yong-Jiang Zhang

doi:10.3390/agronomy11081572

Abstract

Wild lowbush blueberries, an important fruit crop native to North America, contribute significantly to the economy of Maine, USA, Atlantic Canada, and Quebec. However, its photosynthetic capacity has not been well-quantified, with only a few studies showing its low photosynthetic rates. Its small leaves make accurate leaf-level photosynthetic measurements difficult and introduce potential uncertainties in using large leaf chambers. Here, we determined the photosynthetic rate for five different wild blueberry genotypes using a big leaf chamber enclosing multiple leaves and a small leaf chamber with a single leaf to test whether using big leaf chambers (branch-level measurements) underestimates the photosynthetic capacity. Photosynthetic rates of wild blueberries were significantly (35–47%) lower when using the big leaf chamber, and they are not a crop with low photosynthetic capacity, which can be as high as 16 μmol m−2 s−1. Additionally, wild blueberry leaves enclosed in the big chamber at different positions of a branch did not differ in chlorophyll content and photosynthetic rate, suggesting that the difference was not caused by variation among leaves but probably due to leaf orientations and self-shading in the big chamber. A significant linear relationship between the photosynthetic rate measured by the small and big leaf chambers suggests that the underestimation in leaf photosynthetic capacity could be corrected. Therefore, chamber-size effects need to be considered in quantifying photosynthetic capacity for small-leaf crops, and our study provided important guidelines for future photosynthesis research. We also established the relationship between the Electron Transport Rate (ETR) and photosynthetic CO2 assimilation for wild blueberries. ETR provides an alternative to quantify photosynthesis, but the correlation coefficient of the relationship (R2 = 0.65) suggests that caution is needed in this case.

Highlights

An improved understanding of crop physiology has contributed to the advancement of agricultural production over the past few decades [1,2,3,4,5]
Using the big leaf chamber with multiple leaves significantly underestimated the leaf photosynthetic capacity, and our results suggest that V. angustifolium is not a crop species with low leaf photosynthetic capacity
The leaf photosynthetic rate measured with the small leaf chamber was significantly higher (p < 0.001) compared to that with the big leaf chamber (Figure 3a,b) for all five studied wild blueberry genotypes under 1000 μmol m−2 s−1; PAR

Summary

Introduction

An improved understanding of crop physiology has contributed to the advancement of agricultural production over the past few decades [1,2,3,4,5]. Wild blueberries naturally grow in the field (not human-planted) and have been managed to form a unique semi-natural agricultural system, which has different genotypes with considerable genetic variation [20,21,22]. This unique crop is managed on a two-year cycle. Growers prune the field either by mowing or burning This small fruit crop may have low photosynthetic capacity compared to cultivated crops that are selected to maximize productivity. Precise measurements of photosynthesis of this crop are necessary for studying its physiological response to climate change, which is important because wild blueberry fields experienced higher rates of climate warming compared to the entire region [23]

Objectives

Methods

Results