Compounded Disturbance Chronology Modulates the Resilience of Soil Microbial Communities and N-Cycle Related Functions.

Kadiya Calderón,Marie-Christine Breuil,Laurent Philippot,David Bru,Florian Bizouard,Aymé Spor

doi:10.3389/fmicb.2018.02721

Abstract

There is a growing interest of overcoming the uncertainty related to the cumulative impacts of multiple disturbances of different nature in all ecosystems. With global change leading to acute environmental disturbances, recent studies demonstrated a significant increase in the possible number of interactions between disturbances that can generate complex, non-additive effects on ecosystems functioning. However, how the chronology of disturbances can affect ecosystems functioning is unknown even though there is increasing evidence that community assembly history dictates ecosystems functioning. Here, we experimentally examined the importance of the disturbances chronology in modulating the resilience of soil microbial communities and N-cycle related functions. We studied the impact of 3-way combinations of global change related disturbances on total bacterial diversity and composition, on the abundance of N-cycle related guilds and on N-cycle related activities in soil microcosms. The model pulse disturbances, i.e., short-term ceasing disturbances studied were heat, freeze-thaw and anaerobic cycles. We determined that repeated disturbances of the same nature can either lead to the resilience or to shifts in N-cycle related functions concomitant with diversity loss. When considering disturbances of different nature, we demonstrated that the chronology of compounded disturbances impacting an ecosystem determines the aggregated impact on ecosystem properties and functions. Thus, after 3 weeks the impact of the ‘anoxia/heat/freeze-thaw’ sequence was almost two times stronger than that of the ‘heat/anoxia/freeze-thaw’ sequence. Finally, we showed that about 29% of the observed variance in ecosystem aggregated impact caused by series of disturbances could be attributed to changes in the microbial community composition measured by weighted UniFrac distances. This indicates that surveying changes in bacterial community composition can help predict the strength of the impact of compounded disturbances on N-related functions and properties.

Highlights

All ecosystems are exposed to increasing natural and human disturbances and understanding the effects of disturbances is fundamental
We calculated an index describing the aggregated measures of the impact of disturbances on ecosystem functions and properties (EAI)
We detected a significant and transient NO3− accumulation in disturbed microcosms compared to control ones (Figure 1A). These shifts in NO3− pools were significantly positively related to shifts in the abundance of ammonia oxidizing archaea and to the relative proportion of ammonia oxidizing bacteria, but negatively related to shifts in Potential Denitrification Activity (PDA) (Supplementary Table S1)

Summary

Introduction

All ecosystems are exposed to increasing natural and human disturbances and understanding the effects of disturbances is fundamental. The responses of ecosystems, plants and soil microbial communities to elevated CO2 or to changes in precipitation patterns have been the subject of major research efforts (Easterling et al, 2000). While there is some generality in our understanding of the effects of single or simultaneous disturbances, the consequences of temporal series of disturbances for ecosystem functioning and stability are unclear. As the research front on the effects of human-driven environmental changes on ecosystems advances, it is a timely challenge to anticipate the dynamics of the ecosystems response to multiple sequential disturbances (O’Gorman et al, 2012)

Objectives

Methods

Results