An in-depth look into the effects of nitrogen availability on soil organic matter mineralisation

The alteration of soil organic matter (SOM) decomposition by plant carbon (C) input, known as the priming effect, is a key biogeochemical process that influences soil carbon dynamics and soli condition for crop growth. Yet, the patterns and factors driving this priming effect are not well understood, particularly between different soil types.

The addition of nitrogen (N) to increase crop productivity in agricultural soils can also an affect on the priming effect. However, our understanding of this affect in current literature varies drastically between studies. One proposed explanation to this variation is the additional effects of soil carbon stability: the tendency of organic carbon in soil to resist change and/or loss.

To address this knowledge gap, Zheng et al. (2023) investigated the contribution of soil carbon stability to the priming effect and the responses of the priming effect to nitrogen addition by comparing different carbon fractions: particulate organic matter (POM) and mineral-associated organic matter (MAOM). The effects of these relationships were studied on two soils, one from a woodland area and the other from a cropland.

The researchers found the priming effect was higher in the MAOM than in POM, possibly due to stronger carbon limitation for greater microbial activation in MAOM. Furthermore, nitrogen addition increased the priming effect in the POM of particularly the woodland soil with low nitrogen availability because Nnitrogen addition stimulated fungal growth and microbial functions on the decomposition of soil organic matter.

Interestingly, nitrogen addition stimulated the priming effect in the POM but not in the MAOM, likely due to the already-high nitrogen status for microbial metabolism in MAOM.

These results indicate that soils with higher MAOM portions could be more susceptible to the priming effect, while nitrogen fertilisation could stimulate a higher priming effect in soils with more POM. These findings highlight the importance of soil carbon fractionation in predicting soil carbon dynamics through the priming effect, to generate informed farm practices guided by knowledge on its effects and relationships.

 

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