| || MARIE SKŁODOWSKA-CURIE ACTIONS|
|Start date 06/2017|
End date 05/2019
Plant roots are a vital part of the carbon (C) cycle. C stored in roots increases and decreases over time as roots grow and die. Root activity also releases CO2 as plants metabolize and use energy for root functions such as nutrient uptake and maintenance of root tissues.
Methods to measure ecosystems over time at high resolution are now well established in ecology. System such as Eddy Covariance systems and phenocams (specialist digital cameras for standardized ecosystem photography) are fairly commonplace (for example, see our MANIP site). From these devices we can get information about whole-system above-ground plant growth (from greenness indices calculated from phenocams) and carbon budgets (from C fluxes calculated from Eddy Covariance measurements). However our understanding of root growth and phenology is more limited as soils are opaque and directly sampling soil and measuring root biomass is destructive, non-repeatable, and high effort.
Above-ground growth should be linked to below-ground growth as this creates demand for nutrient and water uptake by roots. This is likely especially true in annual plants with little capacity to store nutrients. However, root phenology is also potentially more complicated than leaf phenology, as leaves have a single purpose (photosynthesis), but roots’ functions are water and nutrient uptake (and physical stability), while water and nutrient uptake can also be achieved by other means (e.g. mycorrhizal fungal symbionts or root exudates) by plants without growing roots.
Minirhizotrons (camera systems placed within specially installed belowground observatories) offer a method for non-destructive and repeatable observation of the soil system surrounding the tube, including viewing roots in undisturbed soil. The technique is limited by both the need to visit sites to make manual measurements and the need to process images for which there are few satisfactory automatic approaches. This can involve identifying root biomass, as well as root traits, such as colour and morphology, which may relate to root functions (e.g. nutrient uptake potential) and vitality.
Work is needed to develop systems and interpret gathered images to understand the link between below- and above-ground phenology and whole-system carbon fluxes. With better tools to observe root growth, we can consider the drivers of root phenology. Varying nutrient and/or water availability is commonly observed to affect harvested root biomass, but such relationships are not so clear in the field where multiple other factors (e.g. seasonal drought, grazing pressure, canopy type) may affect both how much of plant biomass is roots, and how the relationships between nutrient availability and root biomass differs. By deploying newly developed systems in both a custom-built mesocosm and the MANIP experimental site, we will be able to investigate how root phenology varies given different N and P stoichiometry and environmental conditions, comparing these to other metrics of performance such as above-ground phenology and C fluxes.
• Develop a new minirhizotron system capable of automatically collecting images up to a daily timescale
• Develop methods of image interpretation suitable for use alongside conventional human markup for high time resolution images collected from an automatic system
• Deploy these automatic systems in both a highly controlled and instrumented greenhouse mesocosm, and in the field as part of the MANIP experiment
• How is root growth linked to nutrient status? Does root phenology change with different availability of N and P?
• How is root growth linked to water availability? Does this interact with nutrient status?
• How is does root phenology related to above-ground phenology? How does root phenology relate to ecosystem C fluxes and GPP?
• Is root growth/phenology representative of below-ground C assignment? Does nutrient status affect C used belowground in ways not measurable using minirhizotrons?
• Mesocosm Experiment: 9 Mesocosms with facilities for available for measurement of CO2 fluxes, above-ground ‘phenocam’ style camera measurements, soil moisture and root growth measurements by other methods (ingrowth cores), as well as one horizontally-deployed minirhizotron per mesocosm.
• Field Minirhizotron Experiment: (minirhizotrons): Custom built remote-operating minirhizotrons will be installed for > 1 year in our group’s main field site, Majadas del Tietar, Spain. This is a heavily seasonal system with a dry summer, a wet winter, and two main growing seasons, in autumn and spring. Data collected from the minirhizotrons will be compared to above-ground phenology from phenocams and eddy-covariance measured CO2 fluxes.
• 13C Tracer Experiment: Stable (non-radioactive) isotopes can be used to trace elements in biogeochemical experiments. We will use the stable isotope carbon-13 to label photosynthates at Majadas and trace the fate of this carbon below-ground. By analyzing 13C recovery in different pools (e.g. roots, soil microbes), we will be able to examine if minirhizotron root growth is representative of total plant C use belowground.