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The ghost of disturbance past: long-term effects of pulse disturbances on community biomass and composition.

ABSTRACT: Current global change is associated with an increase in disturbance frequency and intensity, with the potential to trigger population collapses and to cause permanent transitions to new ecosystem states. However, our understanding of ecosystem responses to disturbances is still incomplete. Specifically, there is a mismatch between the diversity of disturbance regimes experienced by ecosystems and the one-dimensional description of disturbances used in most studies on ecological stability. To fill this gap, we conducted a full factorial experiment on microbial communities, where we varied the frequency and intensity of disturbances affecting species mortality, resulting in 20 different disturbance regimes. We explored the direct and long-term effects of these disturbance regimes on community biomass. While most communities were able to recover biomass and composition states similar to undisturbed controls after a halt of the disturbances, we identified some disturbance thresholds that had long-lasting legacies on communities. Using a model based on logistic growth, we identified qualitatively the sets of disturbance frequency and intensity that had equivalent long-term negative impacts on experimental communities. Our results show that an increase in disturbance intensity is a bigger threat for biodiversity and biomass recovery than the occurrence of more frequent but less intense disturbances.

SUBMITTER: Jacquet C

PROVIDER: S-EPMC7423489 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Disturbance regimes have a major influence on the baseline carbon that characterizes any particular ecosystem. Often regimes result in lower average regional baseline C (compared to those same systems if the disturbance processes were lessened/removed). However, in infrequently disturbed systems the role of disturbance as a "background" process that influences broad-scale, baseline C levels is often neglected. Long-term chronosequences suggest disturbances in these systems may serve to increase regional biomass C stocks by maintaining productivity. However, that inference has not been tested spatially. Here, the large forested system of southeast Alaska, USA, is utilized to 1) estimate baseline regional C stocks, 2) test the fundamental disturbance-ecosystem C relationship, 3) estimate the cumulative impact of disturbances on baseline C. Using 1491 ground points with carbon measurements and a novel way of mapping disturbance regimes, the relationship between total biomass C, disturbance exposure, and climate was analyzed statistically. A spatial model was created to determine regional C and compare different disturbance scenarios. In this infrequently disturbed ecosystem, higher disturbance exposure is correlated with higher biomass C, supporting the hypothesis that disturbances maintain productivity at broad scales. The region is estimated to potentially contain a baseline 1.21-1.52 Pg biomass C (when unmanaged). Removal of wind and landslides from the model resulted in lower net C stocks (-2 to -19% reduction), though the effect was heterogeneous on finer scales. There removal of landslides alone had a larger effect then landslide and wind combined removal. The relationship between higher disturbance exposure and higher biomass within the broad ecosystem (which, on average, has a very low disturbance frequency) suggest that disturbances can serve maintain higher levels of productivity in infrequently disturbed but very C dense ecosystems. Carbon research in other systems, especially those where disturbances are infrequent relative to successional processes, should consider the role of disturbances in maintaining baseline ecosystem productivity.

Project description:The objective of this study was to explore the long-term effects of different organic and inorganic fertilizers on activity and composition of the denitrifying and total bacterial communities in arable soil. Soil from the following six treatments was analyzed in an experimental field site established in 1956: cattle manure, sewage sludge, Ca(NO3)2, (NH4)2SO4, and unfertilized and unfertilized bare fallow. All plots but the fallow were planted with corn. The activity was measured in terms of potential denitrification rate and basal soil respiration. The nosZ and narG genes were used as functional markers of the denitrifying community, and the composition was analyzed using denaturing gradient gel electrophoresis of nosZ and restriction fragment length polymorphism of narG, together with cloning and sequencing. A fingerprint of the total bacterial community was assessed by ribosomal intergenic spacer region analysis (RISA). The potential denitrification rates were higher in plots treated with organic fertilizer than in those with only mineral fertilizer. The basal soil respiration rates were positively correlated to soil carbon content, and the highest rates were found in the plots with the addition of sewage sludge. Fingerprints of the nosZ and narG genes, as well as the RISA, showed significant differences in the corresponding communities in the plots treated with (NH4)2SO4 and sewage sludge, which exhibited the lowest pH. In contrast, similar patterns were observed among the other four treatments, unfertilized plots with and without crops and the plots treated with Ca(NO3)2 or with manure. This study shows that the addition of different fertilizers affects both the activity and the composition of the denitrifying communities in arable soil on a long-term basis. However, the treatments in which the denitrifying and bacterial community composition differed the most did not correspond to treatments with the most different activities, showing that potential activity was uncoupled to community composition.

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The ghost of disturbance past: long-term effects of pulse disturbances on community biomass and composition.

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