Abstract
The endophytic fungus Phomopsis liquidambari performs an important ecosystem service by assisting its host with acquiring soil nitrogen (N), but little is known regarding how this fungus influences soil N nutrient properties and microbial communities. In this study, we investigated the impact of P. liquidambari on N dynamics, the abundance and composition of N cycling genes in rhizosphere soil treated with three levels of N (urea). Ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB) and diazotrophs were assayed using quantitative real-time polymerase chain reaction and denaturing gradient gel electrophoresis at four rice growing stages (S0: before planting, S1: tillering stage, S2: grain filling stage, and S3: ripening stage). A significant increase in the available nitrate and ammonium contents was found in the rhizosphere soil of endophyte-infected rice under low N conditions. Moreover, P. liquidambari significantly increased the potential nitrification rates, affected the abundance and community structure of AOA, AOB, and diazotrophs under low N conditions in the S1 and S2 stages. The root exudates were determined due to their important role in rhizosphere interactions. P. liquidambari colonization altered the exudation of organic compounds by rice roots and P. liquidambari increased the concentration of soluble saccharides, total free amino acids and organic acids in root exudates. Plant-soil feedback mechanisms may be mediated by the rice-endophyte interaction, especially in nutrient-limited soil.
Highlights
Biotic processes, such as symbioses, can improve agricultural sustainability with less reliance on non-renewable inputs such as synthetic fertilizers (Cardoso and Kuyper, 2006)
The NH4+ concentrations were significantly increased by P. liquidambari infection in rhizosphere soil under the low N condition and maintained concentrations 21.2–28.8% higher than that of the control, during the S1–S2 stages
Soil NO3− concentrations were increased by P. liquidambari infection in rhizosphere soil, being 41.1–41.9% higher in the E+ treatments than in E− treatments under low N conditions during the S1–S3 stages and 17.3–19.3% higher in the E+ treatments than in E− treatments under medium N conditions during the S1–S2 stages
Summary
Biotic processes, such as symbioses, can improve agricultural sustainability with less reliance on non-renewable inputs such as synthetic fertilizers (Cardoso and Kuyper, 2006). Cross-host species inoculation of rice with P. liquidambari revealed that this endophyte forms a mutualistic symbiotic relationship with rice (Yang et al, 2014a), promotes the growth and yield of rice (Yuan et al, 2007), improves the N accumulation and N use efficiency of rice (Yang et al, 2014b), and significantly reduces the required amount of soil N fertilizer (Li et al, 2009). Previous work reported that P. liquidambari stimulates the expression of several genes involved in N-uptake and the metabolism of rice seedlings (Yang et al, 2014a). These results indicate the beneficial effects of P. liquidambari on N use in rice plants, but the mechanisms involved are largely unknown
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