Nitrapyrin has far reaching effects on the soil microbial community structure, composition, diversity and functions

Abstract

Nitrapyrin is one of the most common nitrification inhibitors that are used to retain N in the ammonia form in soil to improve crop yields and quality. Whereas the inhibitory effect of nitrapyrin is supposedly specific to ammonia oxidizers, in view of the keystone role of this group in soils, nitrapyrin could have far-reaching impacts. Here, we tested the hypothesis that nitrapyrin leads to large shifts in soil microbial community structure, composition, diversity and functions, beyond its effect on ammonia-oxidizers. To test this hypothesis, we set-up a field experiment where wheat (Triticum aestivum cv. AC Walton) was fertilized with ammonium nitrate (NH4NO3) and supplemented or not with nitrapyrin. Rhizosphere and bulk soils were sampled twice, DNA was extracted, the 16S rRNA gene and ITS region were amplified and sequenced to follow shifts in archaeal, bacterial and fungal community structure, composition and diversity. To assess microbial functions, several genes involved in the nitrogen cycle were quantified by real-time qPCR and volatile organic compounds (VOCs) were trapped in the rhizosphere at the moment of sampling. As expected, sampling date and plant compartment had overwhelming effects on the microbial communities. However, within these strong effects, we found statistically significant effects of nitrapyrin on the relative abundance of Thaumarchaeota, Proteobacteria, Nitrospirae and Basidiomycota, and on several genera. Nitrapyrin also significantly affected bacterial and fungal community structure, and the abundance of all the N-cycle gene tested, but always in interaction with sampling date. In contrast, nitrapyrin had no significant effect on the emission of VOCs, where only sampling date significantly influenced the profiles observed. Our results point out far-reaching effects of nitrapyrin on soil and plant associated microbial communities, well beyond its predicted direct effect on ammonia-oxidizers. In the longer term, these shifts might counteract the positive effect of nitrapyrin on crop nutrition and greenhouse gas emissions.

The Effects of Quinone Imine, a New Potent Nitrification Inhibitor, Dicyandiamide, and Nitrapyrin on Target and Off-Target Soil Microbiota

“…Previous studies ( 43 , 47 ) suggested a selective effect of DCD on the diversity of AOB, while AOA were not affected, in line with our findings. Recently Schmidt et al ( 23 ) showed that NP, when applied at rates similar to our high dose rate, induced a significant shift on the AOA soil community, in accord with our results. Our study provides first evidence for the effects of NP and QI on the diversity of AOB and AOA, indicating a greater impact of both compounds on AOB compared to AOA, even in soils numerically and functionally dominated by AOA.…”

“…The studies available have explored the effects of DCD- (or DMPP-) fortified fertilizers on the abundance of bacteria or fungi or on microbial community structure determined by low-resolution methods (e.g., PLFAs and DGGE), with contradictory results ( 21 , 22 ). On the other hand, the potential effects of NP on nontarget soil microorganisms are less studied, with recent reports suggesting possible effects on the overall soil microbial community within and beyond N cycling ( 23 , 24 ). Careful evaluation of the off-target effects of NIs on the soil microbiota is essential to define potential risks associated with their use in agricultural settings that might compromise soil ecosystem diversity and functioning, beyond nitrification and N cycling.…”