Warming limits daytime but not nighttime activity of epigeic microarthropods in Songnen grasslands

Both climate warming and nitrogen addition have the potential to affect soil fauna. The effect of these changes on the diel variation of soil microarthropods motility remains unknown. In northeastern China, in temperate grasslands with limited moisture and nutrients, epigeic microarthropods were captured by pitfall traps and activity-density and species richness of epigeic Collembola and Oribatida were calculated after four years of simulated environmental change by warming and/or nitrogen addition both in daytime and nighttime. Warming with or without nitrogen addition reduced the total activity-density of epigeic Collembola. However, this effect was pronounced only in daytime, but not nighttime. Epigeic Oribatida was not impacted by warming treatment. Nitrogen addition had no effect on epigeic Oribatida and Collembola. Our results indicate that warming has a pronounced, adverse effect on epigeic Collembola in water-limited temperate grassland and that the effect was microarthropod taxon-specific. We conclude that warming could limit the activity-density of epigeic microarthropods' species that are not resistant to water deficiency and these alterations would not be alleviated by concurrent nitrogen deposition.