Quantifying Nutrient Trade in the Arbuscular Mycorrhizal Symbiosis Under Extreme Weather Events Using Quantum-Dot Tagged Phosphorus

Abstract

Given the current trends in climate change, extreme weather events are expected to increase in strength and frequency. Such events can impact species survival and species interactions. One of the most ubiquitous symbioses on earth is the nutrient exchange partnership between arbuscular mycorrhizal fungi and their host plants. While past work has shown that mycorrhizal fungi can help alleviate stress, it is unknown how phosphorus uptake by plants to fungi is affected by extreme weather events, such as flooding and heat waves. To test this response, we grew Medicago truncatula host plants with or without mycorrhizal fungi and then exposed them to extreme weather treatments: increasing soil temperature by 12°C, or by flooding the plant roots for 7 days. We measured plant and fungal performance, and quantified phosphorus (P) uptake before and after extreme weather treatments using a technique in which we tagged apatite, a form of rock phosphorus, with fluorescing quantum-dots (QDs) nanoparticles. We then measured fluorescence in root and shoot tissue at harvest. We found that plants and arbuscular mycorrhizal fungi were affected by soil flooding, with plant survival, fungal colonization and QD-apatite uptake decreasing under flooded conditions. We did not see these negative effects in the heat treatment. While the presence of arbuscular mycorrhizal fungi affected plant biomass allocation, leading to an increase in shoot biomass, the symbiosis did not increase plant survival, total biomass or QD uptake in either treatment. More generally, we found host tissue contained roughly 80% more QD-apatite from the pre-treatment compared to the post-treatment nutrient injection. Future studies should focus on various plant-fungal combinations to create databases on which predictive models to extreme weather events can be constructed.

Decreasing relatedness among mycorrhizal fungi in a shared plant network increases fungal network size but not plant benefit

“…We added quantum‐dot‐apatite as a phosphorus source to the partner root compartment and determined how much was transferred from the fungal network into the focal root. This approached allowed us to compare cumulative patterns of phosphorus transfer from the network to the host root using visual florescence in the roots (van 't Padje, Oyarte Galvez, et al, 2020 ; van 't Padje, Werner 2020 ; van 't Padje et al, 2021 ; Whiteside et al, 2019 ). We found that roots contained more phosphorus (Figure S7 ), and that more quantum‐dot‐apatite was transferred to focal roots per mg focal extraradical fungal biomass when the roots were colonised by A5‐A5 networks (Figure 5c ).…”

“…Past work has shown that quantum‐dot‐apatite can be taken up by fungal hyphae (van 't Padje, Oyarte Galvez, et al ( 2020 ), video S1 ), and while the precise mechanisms are unknown, uptake likely relies on dissolution, followed by endocytic processes, commonly observed in fungi (Alloush & Clark, 2001 ; Pel et al, 2018 ; Powell & Daniel, 1978 ). In addition, quantum‐dot‐apatite has been shown to accumulate in growing root and leaf tissue, as is expected with nutrients allocated to building new tissue (van 't Padje et al, 2021 ; Whiteside et al, 2019 ). While more work is needed in determining how florescence measurements relate to absolute values of phosphorus accumulation in host tissue (Färkkilä et al, 2021 ), the technique gives a useful proxy to compare relative rates of transfer from fungal networks to host roots across treatments (Supporting Information).…”

“…Our aim was to understand how fungal relatedness affects the physical formation and nutrient transfer in a fungal network formed between hosts. To study phosphorus distribution and transfer, we employed a technique in which we tag phosphorus rock (apatite) with fluorescent quantum‐dot nanoparticles (van 't Padje, Oyarte Galvez, et al, 2020 ; van 't Padje, Werner 2020 ; van 't Padje et al, 2021 ; Whiteside et al, 2019 ) Quantum‐dots fluoresce in bright and pure colours when excited with UV‐light (Färkkilä et al, 2021 ). We used a class of quantum‐dots that were highly fluorescent, and stable (Gustafsson et al, 2015 ; Whiteside et al, 2009 ).…”

How to reconnect mycorrhizal research with natural environments

“…In addition, increased CO 2 concentration did not seem to affect plant growth responses. A direct measurement of plant and fungal performance, and quantification of P uptake before and after extreme weather treatments revealed that plants and AM fungi were affected by soil flooding, but not upon heat treatment ( Van 't Padje et al, 2021). Interestingly, nitrogen fixation in legume trees strongly increases upon temperature increase, suggesting that plant carbon and N gain are decoupled with respect to temperature (Bytnerowicz et al, 2022).…”

Comparison of Toxicity and Cellular Uptake of CdSe/ZnS and Carbon Quantum Dots for Molecular Tracking Using Saccharomyces cerevisiae as a Fungal Model

“…In this respect, conjugating the nutrients to intrinsically fluorescent quantum dots (QDs) for nutrient tracking in mycorrhiza-plant systems could be a viable option to exclude the alternative pathways and determine whether such transfer is taking place [ 5 ]. Unlike isotopically labelled nutrients, QDs conjugated with nutrients (such as an amino acid or apatite) can be visually followed to determine transfer pathways in real-time instead of just measuring total isotope concentrations in the final target after exposure [ 6 , 7 ]. It has even been reported that CdSe/ZnS semiconductor QDs conjugated to a nitrogen source could be tracked from the soil through mycorrhizal fungi to plants, even in field conditions [ 8 , 9 ].…”