Resistance and Resilience of Soil Nitrogen Cycling to Environmental Stresses.

Soil degradation and climate change are increasing the occurrence of environmental stresses that can deteriorate soil functions such as nitrogen (N) cycling. Sustaining soil function and quality is becoming an urgent challenge, with new indices required to explore not only the capacity to tolerate the immediate stress (resistance), but also subsequent recovery over time (resilience).

In this study, resistance and resilience of nitrification and denitrification, and the underpinning microbial community dynamics were determined. Our study found that although the effects from a transient heat increase (40 ℃ for 16 h) were rapid and severe, nitrification and denitrification recovered by 28 days after perturbation. In contrast, after a persistent Cu stress (1 mg Cu/g soil) nitrification and denitrification decreased by 62-92%, and did not recover. Bacterial community structure was less resistant but more resilient to heat than Cu.

To determine the key drivers of resistance and resilience, the impacts of soil water content, organic matter and pH were studied in more detail because of their unique effects on soil functioning. We found that an increase in water content towards 80% WFPS could alleviate the negative impacts from heat on soil denitrification, thereby enhancing its resilience. Increasing organic matter by incorporation of crop residue could double the resistance and resilience of nitrification to both Cu and heat. Soil nitrification was more resistant and resilient to Cu in soils of high pH than low pH condition. However, higher pH did not lead to more resistance and resilience to heat.

We concluded that soil water, organic matter, and pH play a vital role in regulating N cycling, through interactions with the microbial community structure to determine N resistance and resilience. This study investigated the mechanisms driving N cycling response to environmental stress and the key determinants of its resistance and resilience, which contributes to improved soil health and ecosystem sustainability.