Combining the time-lapse amino-mapping and zymography to co-localize spatial distribution of organic N with enzymatic activity in the rhizosphere

As N limitation strongly influences ecosystem functioning, numerous studies explored the transformation process of mineral nitrogen. In contrast, the importance of organic nitrogen, which can short-circuit the mineralization step, for plant nutrition in different ecosystems often overlooked. A spatial link between the sources of organic N and N-acquiring enzymatic activity in soil is still missing due to the lack of suitable techniques. Here we developed a novel approach: in situ amino-mapping and coupled it with time-lapse zymography to quantify distribution of organic nitrogen in the rhizosphere of Zea mays L and tested spatial association of enzymatic activity with organic nitrogen abundance at the root-soil interface. Coupling the two approaches enabled identification the hotspots of amino-N, and revealed their co-occurrence with N-related enzymatic activity in seminal roots and root tips: intensive enzymatic activity was accompanied by large amino-N content, especially in the rhizosphere of seminal root tips. This work was conducted within the framework of the Priority program 2089 “Rhizosphere spatiotemporal organization – a key to rhizosphere functions”, funded by German Research Foundation (DFG – Project number: 403664478). Seeds of the maize were provided by Caroline Marcon and Frank Hochholdinger (University of Bonn).