The Automated Root Exudate System (ARES): a method to apply solutes at regular intervals to soils in the field.

Root exudation is a key component of nutrient and carbon dynamics in terrestrial ecosystems. Exudation rates vary widely by plant species and environmental conditions, but our understanding of how root exudates affect soil functioning is incomplete, in part because there are few viable methods to manipulate root exudates in situ. To address this, we devised the Automated Root Exudate System (ARES), which simulates increased root exudation by applying small amounts of labile solutes at regular intervals in the field. The ARES is a gravity-fed drip irrigation system comprising a reservoir bottle connected via a timer to a micro-hose irrigation grid covering c. 1 m2; 24 drip-tips are inserted into the soil to 4-cm depth to apply solutions into the rooting zone. We installed two ARES subplots within existing litter removal and control plots in a temperate deciduous woodland. We applied either an artificial root exudate solution (RE) or a procedural control solution (CP) to each subplot for 1 min day-1 during two growing seasons. To investigate the influence of root exudation on soil carbon dynamics, we measured soil respiration monthly and soil microbial biomass at the end of each growing season. The ARES applied the solutions at a rate of c. 2 L m-2 week-1 without significantly increasing soil water content. The application of RE solution had a clear effect on soil carbon dynamics, but the response varied by litter treatment. Across two growing seasons, soil respiration was 25% higher in RE compared to CP subplots in the litter removal treatment, but not in the control plots. By contrast, we observed a significant increase in microbial biomass carbon (33%) and nitrogen (26%) in RE subplots in the control litter treatment. The ARES is an effective, low-cost method to apply experimental solutions directly into the rooting zone in the field. The installation of the systems entails minimal disturbance to the soil and little maintenance is required. Although we used ARES to apply root exudate solution, the method can be used to apply many other treatments involving solute inputs at regular intervals in a wide range of ecosystems

Data from: The Automated Root Exudate System (ARES): a method to apply solutes at regular intervals to soils in the field

1) Root exudation is a key component of nutrient and carbon dynamics in terrestrial ecosystems. Exudation rates vary widely by plant species and environmental conditions but our understanding of how root exudates affect soil functioning is incomplete, in part because there are few viable methods to manipulate root exudates in situ. To address this, we devised the Automated Root Exudate System (ARES), which simulates increased root exudation by applying small amounts of labile solutes at regular intervals in the field. 2) The ARES is a gravity-fed drip irrigation system comprising a reservoir bottle connected via a timer to a micro-hose irrigation grid covering c. 1 m2; 24 drip-tips are inserted into the soil to 4-cm depth to apply solutions into the rooting zone. We installed two ARES subplots within existing litter removal and control plots in a temperate deciduous woodland. We applied either an artificial root exudate solution (RE) or a procedural control solution (CP) to each subplot for 1 min d-1 during two growing seasons. To investigate the influence of root exudation on soil carbon dynamics, we measured soil respiration monthly and soil microbial biomass at the end of each growing season. 3) The ARES applied the solutions at a rate of c. 2 L m-2 wk-1 without significantly increasing soil water content. The application of RE solution had a clear effect on soil carbon dynamics but the response varied by litter treatment. Across two growing seasons, soil respiration was 25% higher in RE compared to CP subplots in the litter removal treatment, but not in the control plots. By contrast, we observed a significant increase in microbial biomass carbon (33%) and nitrogen (26%) in RE subplots in the control litter treatment. 4) The ARES is an effective, low-cost method to apply experimental solutions directly into the rooting zone in the field. The installation of the systems entails minimal disturbance to the soil and little maintenance is required. Although we used ARES to apply root exudate solution, the method can be used to apply many other treatments involving solute inputs at regular intervals in a wide range of ecosystems

ARES soil variables

This dataset describes soil variables (0-10-cm depth) measured in subplots with daily applications of root exudate solution (RE) or a procedural control solution (CP), applied using the Automated Root Exudate System (ARES) within experimental litter removal (0L) and control plots (1L) in an old-growth deciduous woodland in Wytham, Oxfordshire, UK. Full descriptions of the study site and experimental design are given in the paper and appendices. Data included in this file are: soil water content, soil pH and microbial biomass carbon and nitrogen measured in the subplots at the end of the growing season in the first and second year of treatments (September 2015 and 2016) as well as fine root biomass in the second year of the study (July 2016). Column headings and abbreviations are as follows: block = replicate block A-E; Plot = unique experimental plot identifier P1-P15; treatm = litter manipulation treatment, where 0L is litter removal and 1L is control; ARES = subplot treatment, where RE is root exudate solution and CP is procedural control; year = year of study; swc = gravimetric soil water content in %; pH = soil pH; MBC and MBN = microbial biomass carbon and nitrogen, respectively, in ug g-1; fine.roots = fine root biomass in g m-2

ARES soil respiration data

This dataset describes monthly measurements of soil CO2 efflux, soil water content, and soil temperature in subplots with daily applications of root exudate solution (RE) or a procedural control solution (CP), applied using the Automated Root Exudate System (ARES) within experimental litter removal (0L) and control plots (1L) in an old-growth deciduous woodland in Wytham, Oxfordshire UK. Full descriptions of the study site and experimental design are given in the paper and appendices. Column headings and abbreviations are as follows: block = replicate block A-E; Plot = unique experimental plot identifier P1-P15; treatm = litter manipulation treatment, where 0L is litter removal and CT is control; ARES = subplot treatment, where RE is root exudate solution, CP is procedural control and 'plot' is the main litter manipulation plot; year = year of study; month = month of measurement; nom.date = nominal date of measurement (set at 1st of the month); time = consecutive time point during the study; swc = soil water content at 0-6 cm depth in %; temp10 = soil temperature at 0-10 cm depth; Rsoil = soil CO2 efflux in mg C m2-1 h-1; Flux = soil CO2 efflux in umol m-2 s-1; Comments = reasons for outliers and missing values; ObsDateTime = actual date and time of each measurement