AUTHOR=Lori Martina , Symanczik Sarah , Mäder Paul , Efosa Norah , Jaenicke Sebastian , Buegger Franz , Tresch Simon , Goesmann Alexander , Gattinger Andreas 

TITLE=Distinct Nitrogen Provisioning From Organic Amendments in Soil as Influenced by Farming System and Water Regime

JOURNAL=Frontiers in Environmental Science

VOLUME=6

YEAR=2018

URL=https://www.frontiersin.org/journals/environmental-science/articles/10.3389/fenvs.2018.00040

DOI=10.3389/fenvs.2018.00040

ISSN=2296-665X

ABSTRACT=<p>The majority of soil organic nitrogen (N) is bound in protein-like compounds and therefore its proteolysis in peptides and amino acids is considered the initial and rate limiting step of N mineralization. Proteolysis of N bound in organic fertilizer and subsequent provisioning for crops is a central element in agro-ecological intensification. Long-term farming system effects on N provisioning from organic fertilizer to crops and its underlying functional microbial communities were analyzed in experiments conducted in soils from the “DOK” system comparison trial (bio-Dynamic, bio-Organic, and “Konventionell”) subjected to optimal and future projected drought scenarios. A plant nutrition experiment using <sup>15</sup>N labeled lupine as a fertilizer (green manure) identified 30% higher amounts of N derived from fertilizer in ryegrass grown on organically compared to conventionally managed soil, but only when subjected to dry conditions. A second experiment, also amended with lupine green manure, assessed the effect of farming system and drought stress on N cycling microbes with a focus on <italic>alkaline</italic> (<italic>apr</italic>) and <italic>neutral</italic> (<italic>npr</italic>) <italic>metallopeptidase</italic> encoding microbial communities. <italic>apr</italic> encoding microbial communities were more strongly affected by farming system and water treatment than <italic>npr</italic> encoding communities. Differences in structure and diversity of <italic>apr</italic> encoding microbial communities showed concomitant patterns with distinct N provisioning from organic fertilizer in the plant nutrition experiment. It is suggested that conventionally managed systems are less capable in maintaining diversity and initial structure of <italic>apr</italic> encoding microbial communities when subjected to drought scenarios. Overall, we demonstrated organically managed soils to provide a more stable N provisioning potential from organic fertilizer under future drought scenarios, likely facilitated by a distinct and more adaptive proteolytic microbial community. This work contributes to an in-depth comprehension of yet poorly studied fundamental soil processes and helps developing strategies to maintain a versatile and functioning microbial community in a rapidly changing environment.</p>