Symbiotic fungal endophyte Phomopsis liquidambari‐ rice system promotes nitrogen transformation by influencing below‐ground straw decomposition in paddy soil

Aims To explore if and how symbiotic Phomopsis liquidambari ‐rice system influences below‐ground straw decomposition and then nitrogen(N) transformation in response to environmental N levels. Methods and Results Litter bag experiments were utilized to trace the decay process during rice growth phases (seedling (T1), tillering (T2), heading (T3) and maturing (T4) stage), with (E+) and without endophyte (E−), under low ( LN ), medium ( MN ) and high nitrogen ( HN ) supply. Litter, soil and plant samples were collected to evaluate the decay process, N transformations, plant quality and relative abundance of soil ammonia‐oxidizing archaea ( AOA ), ammonia‐oxidizing bacteria ( AOB ) and P. liquidambari . The results showed that straw decomposition increased by 19·76% ( LN , T2 stage), 14·05% ( MN , T3 stage) and 16·88% ( MN , T4 stage) in E+ pots when compared with E− pots. Further analysis revealed that no significant endophyte × N interaction was found for straw decay rate and that the decay rate was reduced by a higher N supply ( LN , 37·16 ± 0·65%; MN , 32·27 ± 1·72%; HN , 29·44 ± 1·22%) at the T1 stage, whereas straw decay rate and N release increased by 9·38 and 11·16%, respectively, mainly by endophyte colonization at the T4 stage. The abundance of AOA and AOB were altered, corresponding with the decay rate. Soil mineral N, straw mineral N and plant quality were shown to increase in E+ pots, depending on environmental N conditions and growth phase. The yield increased by 2·98% for E+ plants under MN level. Conclusions Symbiotic P. liquidambari ‐rice system promoted below‐ground straw decomposition and N transformation, depending on environmental N levels and plant growth phase. Significance and Impact of the Study This study provides evidence that fungal endophyte–plant systems are able to promote N transformation by increasing straw decomposition. A reasonable combination of N inputs could enhance its advantage in agriculture ecosystems.