Novel digital assessment technique used to describe peanut nodulation life history

Biological nitrogen fixation (BNF) in legume root nodules is an important source of N globally. Typically, the quantification of BNF is an estimate of N fixation through techniques such as an acetylene reduction assay or isotopic signatures. However, these methods have large logistical limitations, and do not allow for assessments of the nodule morphology or the nodulation process itself, knowledge that is important to fully understand the BNF process. To provide an updated method of nodulation assessments, peanut (Arachis hypogaea L.) nodules were sampled from a two-year field trial and quantified using scanned images of excised nodules, allowing digital assessment of nodule number and size. Further, a digital color analysis method was developed to assess internal nodule color (a known proxy for nodule BNF activity and senescence). To apply and evaluate the new method, peanut nodulation trait data was used for an exploration of the relationship between nodulation traits, plant physiological processes, and nitrogen status in the plant, followed by a nodulation life history analysis. The nodulation assessment method was confirmed by strong correlation with measures of peanut tissue N, biomass, photosynthetic function, and yield. Nodulation life history data suggest novel findings regarding differences in the development of nodules between taproots and lateral roots, contrary to the previous understanding of peanut nodulation life history. This new nodulation assessment method can provide further insight into the BNF process by allowing the collection of detailed data in a relatively simplified manner in field conditions.