Soil Microbial Diversity, Biomass, and Activity in Two Pine Plantations of Southern Italy Treated with Prescribed Burning

Fire enhances changes in phosphorus (P) dynamics determining potential post-fire soil recovery in Mediterranean woodlands

Soil phosphorus (P), which is essential for ecosystem functioning, undergoes notable changes after fire. However, the extent to which fire characteristics affect P dynamics remains largely unknown. This study investigated the impact of type of fire (prescribed burning and natural wildfires) of different levels of severity on P dynamics in Mediterranean soils. Soil P concentrations in the organic layers were strongly affected by fire severity but not fire type. Low severity fire did not have any observable effect, while moderate fire increased soil P levels by 62% and high severity decreased soil P concentration by 19%. After one year, the soil P concentration remained unchanged in the low severity fires, while rather complex recovery was observed after moderate and high severity fires. In the mineral layers, P concentration was reduced (by 25%) immediately after the fires and maintained for one year (at 42%). 31P-NMR spectroscopy revealed almost complete post-fire mineralization of organic P forms (mono- and diesters), large increases in inorganic orthophosphate and a decrease in the organic:inorganic P ratio (Po:Pi). After one year, di-esters and orthophosphate recovered to pre-fire levels at all sites, except those where parent material composition (high pH and Fe concentration) had an enduring effect on orthophosphate retention, and thus, on the total soil P. We showed that fire severity and soil pH (and hence, soil mineralogy) played an essential role in soil P dynamics. These findings are important for reliable assessment of the effects of fire on soil P conservation and for improving the understanding the impact of prescribed burning.

Contrasting immediate impact of prescribed fires and experimental summer fires on soil organic matter quality and microbial properties in the forest floor and mineral soil in Mediterranean black pine forest

Prescribed fire (PB) is used to achieve ecological objectives and to reduce fuel hazard thus limiting detrimental impacts of wildfire and appropriate selection of prescription window is critical for these goals. Operational use of PB in the Mediterranean forest is scarce and information about its effects on soil remains incomplete. This study for the first time i) compared the immediate impact of spring and autumn PB and experimental summer fire on key properties of forest floor and mineral topsoil in Mediterranean black pine forest, and ii) assessed the capacity of PB to reduce fuel, with limited immediate impacts on soil. PB significantly reduced the 32.5 % of pre-fire forest floor depth, while summer fire consumed 88.5 % and exposed about 30 % of the mineral soil surface. Mean maximum temperature during fire at the mineral soil surface was 23 °C in PB, in contrast to 128 °C in summer fire, while soil heating at 2 cm depth was negligible in both cases. PB did not cause immediate changes in OM quality parameters, and chemical (C and N concentrations, C/N and pH) and microbiological properties (Cmic, Cmic/C, and β-glucosidase, acid phosphatase and alkaline phosphatase activities) in forest floor or mineral topsoil (0-2 cm). By contrast, summer fire greatly increased OM recalcitrance and reduced Cmic, Cmic/C and enzyme activities in forest floor immediately after fire. In the mineral topsoil, only microbial properties were significantly reduced. The maximum temperature reached during fire in forest floor and topsoil was associated with most of the overall changes in properties in both layers. The findings suggest that prescribed fire can significantly reduce fuel with limited initial impacts on soil. Although these findings are encouraging for operational use of prescribed burning in the ecosystem under study, long-term monitoring of repeated application of the technique on soil properties and other ecosystem components is necessary.

Management of a Globally Imperiled and Fire-Dependent Ecosystem in the Urban Matrix of Miami–Dade County, Florida: A Case Study of the Richmond Tract Pine Rocklands

Pine rockland habitat of South Florida is among the most highly threatened terrestrial ecosystems in the neo-subtropics and is among the rarest worldwide. With only 1.2% of its original extent remaining outside Everglades National Park, fewer than 780 hectares of this ecosystem remains across all of South Florida. This fire-dependent ecosystem—habitat for many rare, endemic species—has experienced substantial deforestation and defaunation due to urbanization, land use change, habitat fragmentation, fire suppression, and exotic plant invasions. Owing to the small size of remaining fragments, and the fact that most are surrounded by urbanization, adequate burning regimes are suppressed. The Richmond Tract, a complex of twelve separate parcels under multiple private and public ownership partially surrounding Zoo Miami, is the largest tract of pine rockland outside the federal protection of Everglades National Park. In this article, we take inventory of the threatened biodiversity at the Richmond Tract and focus on the policy and management landscape. We take a close look at threats to the pine rockland’s persistence here and review approaches that either help maintain the health of this ecosystem or those that may need to be reconsidered. We end by discussing coordination among multiple stakeholder groups, the potential use for incentive-based conservation practices, and suggesting ways to improve management in highly urbanized South Florida.

Fire frequency and type regulate the response of soil carbon cycling and storage to fire across soil depths and ecosystems: A meta-analysis

Fire is a very common disturbance in terrestrial ecosystems and can give rise to significant effects on soil carbon (C) cycling and storage. Here, we conducted a global meta-analysis on the response of soil C cycling and storage across soil profiles (organic layer, 0-5 cm, 0-10 cm, 0-20 cm, and 20-100 cm) to fire reported in 308 studies across 383 sites and examined the role of fire frequency, fire type, soil type, ecosystem type, and post-fire time in regulating the response of soil C dynamics to fire. Overall, we found soil C cycling and storage were more responsive to one fire and wildfire as compared to frequent fire and prescribed fire, respectively. Soil respiration significantly decreased by 22 ± 9% by one fire, but was not significantly affected by frequent fire across ecosystems. One fire significantly reduced soil C content in the organic, 0-10 cm, and 20-100 cm layers by 27 ± 16%, 10 ± 9%, and 33 ± 18%, respectively, while frequent fire significantly reduced soil C content at a depth of 0-5 cm and 0-20 cm by 29 ± 8% and 16 ± 12%, respectively. Soil C cycling and storage showed little response to frequent prescribed fire. In addition, the response of soil C cycling and storage varied among different soil and ecosystem types, with a stronger response being observed in forest than in grassland. Within 20 years post-fire, soil C cycling and storage tended to recover only after one fire but not after frequent fire. We also found that soil physicochemical properties and microbial communities were more responsive to one fire than frequent fire, which could indirectly affect the effects of fire on soil C cycling and storage. The results of our study have filled some critical gaps in previous meta-analyses in fire ecology.

Multifarious Responses of Forest Soil Microbial Community Toward Climate Change

Forest soils are a pressing subject of worldwide research owing to the several roles of forests such as carbon sinks. Currently, the living soil ecosystem has become dreadful as a consequence of several anthropogenic activities including climate change. Climate change continues to transform the living soil ecosystem as well as the soil microbiome of planet Earth. The majority of studies have aimed to decipher the role of forest soil bacteria and fungi to understand and predict the impact of climate change on soil microbiome community structure and their ecosystem in the environment. In forest soils, microorganisms live in diverse habitats with specific behavior, comprising bulk soil, rhizosphere, litter, and deadwood habitats, where their communities are influenced by biotic interactions and nutrient accessibility. Soil microbiome also drives multiple crucial steps in the nutrient biogeochemical cycles (carbon, nitrogen, phosphorous, and sulfur cycles). Soil microbes help in the nitrogen cycle through nitrogen fixation during the nitrogen cycle and maintain the concentration of nitrogen in the atmosphere. Soil microorganisms in forest soils respond to various effects of climate change, for instance, global warming, elevated level of CO₂, drought, anthropogenic nitrogen deposition, increased precipitation, and flood. As the major burning issue of the globe, researchers are facing the major challenges to study soil microbiome. This review sheds light on the current scenario of knowledge about the effect of climate change on living soil ecosystems in various climate-sensitive soil ecosystems and the consequences for vegetation-soil-climate feedbacks.

Impact of Intercropping on the Diazotrophic Community in the Soils of Continuous Cucumber Cropping Systems

Diazotrophs are important soil components that help replenish biologically available nitrogen (N) in the soil and contribute to minimizing the use of inorganic N fertilizers in agricultural ecosystems. However, there is little understanding of how diazotrophs respond to intercropping and soil physicochemical properties in cucumber continuous cropping systems. In this study, using the nifH gene as a marker, we have examined the impacts of seven intercropping plants on diazotrophic community diversity and composition compared to a cucumber continuous cropping system during two cropping seasons. The results showed that intercropping increased the abundance of the nifH gene, which was negatively correlated with available phosphorous in the fall. Diazotrophic diversity and richness were higher in the rape-cucumber system than in the monoculture. Multivariate regression tree analysis revealed that the diversity of the diazotrophic communties was shaped mainly by soil moisture and available phosphorous. Skermanella were the dominant genera in all of the samples, which increased significantly in the mustard-cucumber system in the fall. There was no effect of intercropping on the structure of the diazotrophic community in this case. Non-metric multidimensional scaling analysis showed that cropping season had a greater effect than intercropping on the community structure of the diazotrophs. Overall, our results suggest that intercropping altered the abundance and diversity rather than the structure of the diazotrophic community, which may potentially affect the N fixation ability of continuous cropping systems.

Changes in Multi-Level Biodiversity and Soil Features in a Burned Beech Forest in the Southern Italian Coastal Mountain

In the context of global warming and increasing wildfire occurrence, this study aims to examine, for the first time, the changes in multi-level biodiversity and key soil features related to soil functioning in a burned Mediterranean beech forest. Two years after the 2017 wildfire, changes between burned and unburned plots of beech forest were analyzed for plant communities (vascular plant and cover, bryophytes diversity, structural, chorological, and ecological variables) and soil features (main chemical properties, microbial biomass and activity, bacterial community composition, and diversity), through a synchronic study. Fire-induced changes in the micro-environmental conditions triggered a secondary succession process with colonization by many native pioneer plant species. Indeed, higher frequency (e.g., Scrophularia vernalis L., Rubus hirtus Waldst. and Kit. group, and Funaria hygrometrica Hedw.) or coverage (e.g., Verbascum thapsus L. subsp. thapsus and Digitalis micrantha Roth ex Schweigg.) of the species was observed in the burned plots, whereas the typical forest species showed a reduction in frequency, but not in cover, except for Fagus sylvatica subsp. sylvatica. Overall, an increase in plant species and family richness was found in the burned plots, mainly in the herbaceous and bryophyte layers, compared to the unburned plots. Burned plots showed an increase in therophytes, chamaephytes, cosmopolites, steno-Mediterranean and Atlantic species, and a decrease in geophytes and Eurasiatic plants. Significant differences were found in burned vs. control soils for 10 phyla, 40 classes, 79 orders, 145 families, 342 genera, and 499 species of bacteria, with about 50% of each taxon over-represented and 50% under-represented in burned than in control. Changes in bacterial richness within several families (reduction in Acidobacteriaceae, Solibacteraceae, Rhodospirillaceae, and Sinobacteraceae; increase in Micrococcaceae, Comamonadaceae, Oxalobacteraceae, Pseudomonadaceae, Hymenobacteraceae, Sphingomonadaceae, Cytophagaceae, Nocardioidaceae, Opitutaceae, Solirubrobacteraceae, and Bacillaceae) in burned soil were related to fire-induced chemical changes of soil (pH, electrical conductivity, and cation exchange capacity). No evident effect of the wildfire was found on organic C content, microbial biomass (total microbial carbon and fungal mycelium) and activity, and microbial indexes (fungal percentage of microbial C, metabolic quotient, and quotient of mineralization), suggesting that soil functions remained unchanged in the burned area. Therefore, we hypothesize that, without an additional disturbance event, a re-establishment of beech forest can be expected but with an unpredictable time of post-fire succession.