• Energy Research
• 2016-2025close

ABSTRACTThe interaction of biochar with mineral fertilization has attracted attention as a strategy to reduce N losses and enhance nitrogen use efficiency. In this study, we investigated the coapplication of biochar with two optimized fertilization strategies based on split urea and a microbial inoculant (Azospirillum brasilense) in a commercial pointed white cabbage crop. Additionally, we evaluated a third optimized N fertilization alternative, a biochar‐based fertilizer (BBF) enriched in plant‐available N, which was developed from the same biochar. We assessed environmental impacts such as greenhouse gasses (GHG) and NH3 emissions, yield‐scaled N2O emissions, and global warming potential (GWP). Additionally, we evaluated agronomical outcomes such as crop yield, plant N, and chlorophyll concentration. Moreover, we examined the N‐fixing gene's total and relative abundance (nifH and nifH/16S). Biochar and BBF exhibited similar crop yield, GHG, and NH3 emissions compared to split applications of the synthetic fertilizer. The main difference was associated with the higher soil C sequestration in biochar and BBF treatments that reduced the associated GWP of these fertilization strategies. Finally, biochar favored the activity of the N‐fixing bacteria spread, compared to the sole application of bacteria and BBF demonstrated a promoting effect in the soil's total abundance of natural N‐fixing bacteria.

AbstractLand use is a key factor driving changes in soil carbon (C) cycle and contents worldwide. The priming effect (PE)—CO2 emissions from changed soil organic matter decomposition in response to fresh C inputs—is one of the most unpredictable phenomena associated with C cycling and related nutrient mobilization. Yet, we know very little about the influence of land use on soil PE across contrasting environments. Here, we conducted a continental‐scale study to (i) determine the PE induced by 13C‐glucose additions to 126 cropland and seminatural (forests and grasslands) soils from 22 European countries; (ii) compare PE magnitude in soils under various crop types (i.e., cereals, nonpermanent industrial crops, and orchards); and (iii) model the environmental factors influencing PE. On average, PEs were negative in seminatural (with values ranging between −60 and 26 µg C g−1 soil after 35 days of incubation; median = −11) and cropland (from −55 to 27 µC g−1 soil; median = −4.3) soils, meaning that microbial communities preferentially switched from soil organic C decomposition to glucose mineralization. PE was significantly less negative in croplands compared with seminatural ecosystems and not influenced by the crop type. PE was driven by soil basal respiration (reflecting microbial activity), microbial biomass C, and soil organic C, which were all higher in seminatural ecosystems compared with croplands. This cross European experimental and modeling study elucidated that PE intensity is dependent on land use and allowed to clarify the factors regulating this important C cycling process.

Shifts in soil microbial communities over altitudinal gradients and the driving factors are poorly studied. Their elucidation is indispensable to gain a comprehensive understanding of the response of ecosystems to global climate change. Here, we investigated soil archaeal, bacterial, and fungal communities at four Alpine forest sites representing a climosequence, over an altitudinal gradient from 545 to 2000 m above sea level (asl), regarding abundance and diversity by using qPCR and Illumina sequencing, respectively. Archaeal community was dominated by Thaumarchaeota, and no significant shifts were detected in abundance or community composition with altitude. The relative bacterial abundance increased at higher altitudes, which was related to increasing levels of soil organic matter and nutrients with altitude. Shifts in bacterial richness and diversity as well as community structure (comprised basically of Proteobacteria, Acidobacteria, Actinobacteria, and Bacteroidetes) significantly correlated with several environmental and soil chemical factors, especially soil pH. The site at the lowest altitude harbored the highest bacterial richness and diversity, although richness/diversity community properties did not show a monotonic decrease along the gradient. The relative size of fungal community also increased with altitude and its composition comprised Ascomycota, Basidiomycota, and Zygomycota. Changes in fungal richness/diversity and community structure were mainly governed by pH and C/N, respectively. The variation of the predominant bacterial and fungal classes over the altitudinal gradient was the result of the environmental and soil chemical factors prevailing at each site.

Water shortage and low organic carbon content in soil limit soil fertility and crop productivity. The use of desalinated seawater is increasing as an alternative source of irrigation water. However, it has a high boron (B) content that could cause toxicity in the plant-soil microbial system. Here, we evaluated the responses of the soil microbiota and lemon trees to 3 irrigation B doses (0.3, 1, and 15 mg L-1) under two types of soil management (conventional, CS; and organic, OS) in a 180-days pot experiment. High B doses promoted B accumulation in soil, reaching harmful concentrations that affected soil biodiversity. Our results suggest a close interaction between B and organic labile fractions that increased B availability in soil solution. Besides, B addition to soil impacted on microbial biomass. The bacterial community showed sensitivity to the B dose. Organic amendment did not increase B soil adsorption but it favored B plant uptake. The highest B dose had a detrimental impact on plant physiology, finally resulting lethal for the plants. Our study provides a comprehensive assessment of the microbes-plant interactions in soils irrigated with water with high B content. This will be fundamental in the design of future fertirrigation strategies.

In the current context of climate change, the study of microbial communities along altitudinal gradients is especially useful. Only few studies considered altitude and season at the same time. We characterized four forest sites located in the Italian Alps, along an altitude gradient (545-2000 m a.s.l.), to evaluate the effect of altitude in spring and autumn on soil microbial properties. Each site in each season was characterized with regard to soil temperature, physicochemical properties, microbial activities (respiration, enzymes), community level physiological profiles (CLPP), microbial abundance and community structure (PLFA). Increased levels of soil organic matter (SOM) and nutrients were found at higher altitudes and in autumn, resulting in a significant increase of (soil dry-mass related) microbial activities and abundance at higher altitudes. Significant site- and season-specific effects were found for enzyme production. The significant interaction of the factors site and incubation temperature for soil microbial activities indicated differences in microbial communities and their responses to temperature among sites. CLPP revealed site-specific effects. Microbial community structure was influenced by altitudinal, seasonal and/or site-specific effects. Correlations demonstrated that altitude, and not season, was the main factor determining the changes in abiotic and biotic characteristics at the sites investigated.

AbstractThe study of soil microbial responses to environmental changes is useful to improve simulation models and mitigation strategies for climate change. We here investigated two Alpine forest sites (deciduous forest vs. coniferous forest) situated at different altitudes (altitudinal effect) in spring and autumn (seasonal effect) regarding: (i) bacterial and fungal abundances (qPCR); (ii) diversity and structure of bacterial and fungal communities (amplicon sequencing); and (iii) diversity and composition of microbial functional gene community (Geochip 5.0). Significant altitudinal changes were detected in microbial abundances as well as in diversity and composition of taxonomic and functional communities as a consequence of the differences in pH, soil organic matter (SOM) and nutrient contents and soil temperatures measured between both sites. A network analysis revealed that deciduous forest site (at lower altitude) presented a lower resistance to environmental changes than that of coniferous forest site (at higher altitude). Significant seasonal effects were detected only for the diversity (higher values in autumn) and composition of microbial functional gene community, which was related to the non-significant increased SOM and nutrient contents detected in autumn respect to spring and the presumable high capacity of soil microbial communities to respond in functional terms to discreet environmental changes.