Fruit removal increases root-zone respiration in cucumber.

H-P Kläring,A Heißner,I Hauschild

doi:10.1093/aob/mcu192

H-P Kläring, A Heißner + Show 1 more

Open Access

https://doi.org/10.1093/aob/mcu192

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Abstract

Background and AimsMany attempts have been made to avoid the commonly observed fluctuations in fruit initiation and fruit growth in crop plants, particularly in cucumber (Cucumis sativus). Weak sinks of the fruit have been assumed to result in low sink/source ratios for carbohydrates, which may inhibit photosynthesis. This study focuses on the effects of low sink–source ratios on photosynthesis and respiration, and in particular root-zone respiration.MethodsMature fruit-bearing cucumber plants were grown in an aerated nutrient solution. The root containers were designed as open chambers to allow measurement of CO2 gas exchange in the root zone. A similar arrangement in a gas-exchange cuvette enabled simultaneous measurements of CO2 exchange in the shoot and root zones.Key ResultsReducing the sinks for carbohydrates by removing all fruit from the plants always resulted in a doubling of CO2 exchange in the root zone within a few hours. However, respiration of the shoot remained unaffected and photosynthesis was only marginally reduced, if at all.ConclusionsThe results suggest that the increased level of CO2 gas exchange in the root zone after removing the carbon sinks in the shoot is due primarily to the exudation of organic compounds by the roots and their decomposition by micro-organisms. This hypothesis must be tested in further experiments, but if proved correct it would make sense to include carbon leakage by root exudation in cucumber production models. In contrast, inhibition of photosynthesis was measurable only at zero fruit load, a situation that does not occur in cucumber production systems, and models that estimate production can therefore ignore (end-product) inhibition of photosynthesis.

Highlights

Many endeavours have been made to avoid the commonly observed fluctuations in fruit initiation and fruit growth, in cucumber (Cucumis sativus), where the fruit is the main sink organ for carbohydrates (Marcelis, 1992)
The fruit load of investigated plants usually increased over the course of the experiments
In experiment C1 (12 plants), fruits were removed from the plants at the harvest stage, which meant that only two of the 12 plants had no fruit when they were transferred to the cuvette

Summary

Introduction

Many endeavours have been made to avoid the commonly observed fluctuations in fruit initiation and fruit growth, in cucumber (Cucumis sativus), where the fruit is the main sink organ for carbohydrates (Marcelis, 1992) For this reason, weak sinks of the fruit were assumed to result in low sink/ source ratios for carbohydrates, which may inhibit photosynthesis. Inhibition of photosynthesis was measurable only at zero fruit load, a situation that does not occur in cucumber production systems, and models that estimate production can ignore (end-product) inhibition of photosynthesis

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