Journal Article

Aboveground Rather Than Belowground Productivity Drives Variability in Miscanthus × giganteus Net Primary Productivity

Howe, Adina, Masters, Michael D., VanLoocke, Andy, Hartman, Theodore, Heaton, Emily A., Studt, Jacob E., Mitchell, Corey A., DeLucia, Evan H., McDaniel, Marshall D.

2025

Overview

Quantifying the carbon (C) uptake of Miscanthus × giganteus (M × g) in both aboveground and belowground structures (e.g., net primary productivity (NPP)) and differences among methodological approaches is crucial. Our objectives were to directly measure Mxg NPP and evaluate the effects of nitrogen application, location, and belowground biomass sampling methods. We hypothesize that increased nitrogen application increases the overall NPP of M × g and that quantifying rhizome biomass using excavations will produce the lowest variability between replicates. We collected biomass from mature M × g stands from three locations in Iowa with three nitrogen application rates and one site in Illinois. We destructively sampled at two time points, when rhizome mass is anticipated to be at a minimum (initial) and anticipated to be at its maximum (peak). Biomass was collected from 1 × 1 m quadrats in which one in‐clump and one beside‐clump cores were collected and then excavated to 30 cm depth to extract all rhizomes. We found that aboveground M × g NPP ranged from 15.4 Mg Da ha–1 year–1 to 36.4 Mg Da ha–1 year–1 and belowground M × g NPP ranged from 4.4 Mg Da ha–1 year–1 to 19.6 Mg Da ha–1 year–1. M × g NPP varied across sites, fertilization, and calculation assumptions. Aboveground NPP (yield) was on average 68.7% of the total NPP. Root‐to‐shoot ratios at peak biomass decreased with nitrogen application rate, from an average of 1.9 for 0 N plots to 0.89 for 224 N fertilized plots. There was more variation in core data than from excavations; however, when in‐clump and beside‐clump cores were averaged together, core and excavation averages were not different. Overall, these results show that the range of mature M × g NPP is driven by aboveground productivity, influenced by nitrogen application and site. Our results provide useful data to constrain agro‐ecosystem models and provide crucial insights for future perennial belowground sampling. Many estimates of Miscanthus × giganteus (M × g) productivity focus on aboveground harvestable yields and do not directly address belowground biomass in this perennial crop. To more accurately constrain the amount of carbon taken up by M × g in both aboveground and belowground plant parts, we calculated the net primary productivity (NPP) of mature M × g at three sites with three nitrogen application rates using collections of aboveground and belowground biomass at two time points during the growing season. These estimates help improve our understanding of M × g carbon sequestration potential and will improve the representation of M × g in agro‐ecosystem models.

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Agricultural ecosystems / belowground biomass / Biomass / carbon / Carbon sequestration / Cores / Crops / Ecosystem models / Ecosystems / Excavation / Fertilization / Influence / Miscanthus / Net Primary Productivity / Nitrogen / nitrogen fertilization / Productivity / Rhizomes / Sampling / Sampling methods / translocation / Variability