Quantifying citrate-enhanced phosphate root uptake using microdialysis

Fletcher, Daniel McKay; Shaw, Rory; Sánchez‐Rodríguez, Antonio Rafael; Daly, Keith R.; Veelen, Arjen van; Jones, Davey L.; Roose, Tiina

doi:10.1007/s11104-019-04376-4

Cited by 22 publications

(31 citation statements)

References 47 publications

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“…Three possible reasons are proposed to explain this discrepancy. First, singular time point bulk‐scale solubilization experiments, such as those cited above, may not be able to simultaneously capture diffusion, uptake, adsorption and desorption, which occur at different timescales (McKay Fletcher et al , 2019b). Second, bulk‐scale measurements (even when analyzing rhizosphere soil) do not measure local pore scale concentrations.…”

Section: Discussionmentioning

confidence: 99%

Linking root structure to functionality: the impact of root system architecture on citrate‐enhanced phosphate uptake

et al. 2020

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Summary Root citrate exudation is thought to be important for phosphate solubilization. Previous research has concluded that cluster‐like roots benefit most from this exudation in terms of increased phosphate uptake, suggesting that root structure plays an important role in citrate‐enhanced uptake (additional phosphate uptake due to citrate exudation). Time‐resolved computed tomography images of wheat root systems were used as the geometry for 3D citrate‐phosphate solubilization models. Citrate‐enhanced uptake was correlated with morphological measures of the root systems to determine which had the most benefit. A large variation of citrate‐enhanced uptake over 11 root structures was observed. Root surface area dominated absolute phosphate uptake, but did not explain citrate‐enhanced uptake. Number of exuding root tips correlated well with citrate‐enhanced uptake. Root tips in close proximity could collectively exude high amounts of citrate, resulting in a delayed spike in citrate‐enhanced uptake. Root system architecture plays an important role in citrate‐enhanced uptake. Singular morphological measurements of the root systems cannot entirely explain variations in citrate‐enhanced uptake. Root systems with many tips would benefit greatly from citrate exudation. Quantifying citrate‐enhanced uptake experimentally is difficult as variations in root surface area would overwhelm citrate benefits.

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Section: Discussionmentioning

confidence: 99%

Linking root structure to functionality: the impact of root system architecture on citrate‐enhanced phosphate uptake

et al. 2020

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“…This would not cause increasing efflux rates into the MD environment as long as the microbial citrate sink is controlled by constant concentration-dependent kinetics. Several models of citrate concentration around exuding roots are based on decay constants (Geelhoed et al, 1999;Schnepf et al, 2012;McKay Fletcher et al, 2019). When parametrized with literaturebased decay constants these models yield a radius of 0.1 and 0.4 cm around the exuding surface where citrate concentrations approach zero.…”

Section: Citrate Effluxmentioning

confidence: 99%

“…As mentioned above, a comprehensive process description of the interaction between carboxylate exudation and P absorption is challenging. However, MD experiments simulate P mobilization by exudating fine root better than other infinite-sink extraction methods (Brackin et al, 2017;Demand et al, 2017;McKay Fletcher et al, 2019).…”

Section: Introductionmentioning

confidence: 98%

“…Various MD applications in soil science are listed in the comprehensive review of Buckley et al (2020). The applicability of this dynamic extraction technique for soil phosphate including the effect of citric acid has been shown first by Demand et al (2017). McKay Fletcher et al (2019 measured the short-time dynamic of citrate release on P absorption to parameterize a rhizosphere model.…”

Section: Introductionmentioning

confidence: 99%

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The Cumulative Amount of Exuded Citrate Controls Its Efficiency to Mobilize Soil Phosphorus

Schack‐Kirchner

Loew

Lang

2020

Front. For. Glob. Change

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Root exudation of citrate is discussed as mechanism to mobilize P from the soils' solid phase. Microbial processes can mitigate the mobilization efficiency of citrate. Due to higher microbial activity in topsoils compared to subsoils, we hypothesized a lower mobilization efficiency of exuded citrate in topsoils than in the subsoils. As a model system we used microdialysis (MD) probes and we followed diffusive fluxes of citrate from the perfusate into the soil and of phosphate from the soil into the dialysate in three soil horizons (Oa, Ah, Bw) of a Fagus sylvatica L. stand Cambisol. Three different MD perfusates with a KCl background concentration have been used: control, 1, and 3 mmol L−1 citric acid. Fluxes have been measured after 24, 48, and 144 h. The high-citrate perfusate increased the cumulative 144 h P-influx by a factor of 8, 13, and 113 in the Oa, Ah, and Bw horizon, respectively. With the high-citrate treatment, P mobilization efficiency decreased over time, whereas for the low citrate, P mobilization efficiency had a maximum at day 2. Minimum P mobilization efficiency of citrate was 1:25,000 mol phosphate per mol citrate in the Oa horizon between days 2 and 6, and maximum was 1:286 in the Bw-horizon during day 2. An increasing citrate efflux over time indicated an increasing sink term for citrate in the soil due to microbial decay or immobilization processes. Cumulative phosphate influx could be fitted to cumulative citrate efflux and soil horizon in a logarithmic model explaining 87% of the variability. For the first time, we could follow the localized P-uptake with citrate exudation over several days. Cumulative citrate efflux as the main control of P-mobilization has been barely discussed yet, however, it could explain some gaps in the role of carboxylates in the rhizosphere. Batch experiments are not capable to elucidate microscale dynamic competition for phosphate and carboxylates. MD is a promising tool for spatially explicit investigation of phosphate–citrate exchange, since such detailed insights in are not possible with batch experiments. In combination with the analysis of microbial properties, this technique has a huge potential to identify mobilization processes in soils as induced by citrate.

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“…Chemical sampling techniques, such as suction cups or microdialysis, can be used to capture time-resolved fluid flow through plant and soil systems. However, these approaches can only provide a coarse spatial resolution (Fletcher et al 2019;Gottlein et al 1996;Miro and Frenzel 2004;Petroselli et al 2020;Vetterlein and Jahn 2004). In using XCT it is possible to capture 3D spatial information for timeresolved fluid flow and transport of iodinated contrast media in live plant roots intact within soil.…”

Section: Introductionmentioning

confidence: 99%

Developing a system for in vivo imaging of maize roots containing iodinated contrast media in soil using synchrotron XCT and XRF

et al. 2020

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Aims We sought to develop a novel experimental system which enabled application of iodinated contrast media to in vivo plant roots intact in soil and was compatible with time-resolved synchrotron X-ray computed tomography imaging. The system was developed to overcome issues of low contrast to noise within X-ray computed tomography images of plant roots and soil environments, the latter of which can complicate image processing and result in the loss of anatomical information. Methods To demonstrate the efficacy of the system we employ the novel use of both synchrotron X-ray computed tomography and synchrotron X-ray fluorescence mapping to capture the translocation of the contrast media through root vasculature into the leaves. Results With the application of contrast media we identify fluid flow in root vasculature and visualise anatomical features, which are otherwise often only observable in ex vivo microscopy, including: the xylem, metaxylem, pith, fibres in aerenchyma and leaf venation. We are also able to observe interactions between aerenchyma cross sectional area and solute transport in the root vasculature with depth. Conclusions Our novel system was capable of successfully delivering sufficient contrast media into root and leaf tissues such that anatomical features could be visualised and internal fluid transport observed. We propose that our system could be used in future to study internal plant transport mechanisms and parameterise models for fluid flow in plants.

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Quantifying citrate-enhanced phosphate root uptake using microdialysis

Cited by 22 publications

References 47 publications

Linking root structure to functionality: the impact of root system architecture on citrate‐enhanced phosphate uptake

Linking root structure to functionality: the impact of root system architecture on citrate‐enhanced phosphate uptake

The Cumulative Amount of Exuded Citrate Controls Its Efficiency to Mobilize Soil Phosphorus

Developing a system for in vivo imaging of maize roots containing iodinated contrast media in soil using synchrotron XCT and XRF

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