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The influence of elevated atmospheric CO2 concentrations ([CO2]) on the decomposition of spring wheat (Triticum aestivum L. cv. Triso) residues remaining in the soil after harvest was simulated in a microcosm incubation experiment in the lab. Undisturbed soil cores with and without visible wheat residues were taken in the third year after establishment from a Mini-free-air carbon dioxide enrichment (FACE) system, in which we used 13C-depleted CO2 to determine the contribution of plant-derived carbon to overall carbon mineralization. The Mini-FACE system is located on a Gleyic Cambisol near Hohenheim (Baden-Württemberg, Germany). Carbon dioxide production and leaching of nitrogen and inorganic and organic carbon were measured during 191 days of incubation. Rates of CO2 production were generally highest in all treatments during the first two weeks of the incubation and this was followed by a steady decrease until day 58. After this day mineralization rates declined only weakly until the end of the incubation. Cumulative carbon mineralization was similar in the two treatments without visible wheat residues, but significantly lower in the elevated (−19.0%) versus ambient [CO2] treatment with visible plant residues (significant [CO2]×residue interaction; F 1,13 =7.17; P =0.019). This result demonstrated reduced decomposition of wheat residues grown under elevated [CO2]. The contribution of plant-derived carbon to soil respiration was highest in the beginning, followed by a steady decrease until the end of the incubation. Irrespective of incubation time, the amount of mineralized, plant-derived carbon was higher in the treatment with visible wheat residues. Leaching of inorganic carbon (DIC) tended to be affected by [CO2] (F 6,8 =4.50; P =0.057), with more DIC leached in the elevated [CO2] treatment without (+47.2%) and with visible plant residues (+29.5%) than in the respective ambient CO2 treatments. The amount of carbon potentially sequestered as DIC in the wheat cropping system was small compared to the effects of elevated [CO2] on the amounts and decomposition of plant residues. Increased input of plant residues and reduced decomposition of plant-derived carbon are discussed as possible mechanisms for enhanced carbon sequestration under elevated atmospheric CO2 concentration.
No abstract is provided for this article.
No abstract is provided for this article.
This letter explains the processes and mechanisms involved in the nitrogen-induced soil acidification causing substantial carbonate losses and subsequent CO
Soil zymography represents a non-invasive methodology facilitating the in situ visualization and localization of potential enzyme activities in soil. Due to universality and simplicity of zymography method, it has been widely used to visualize the hidden microbial and root life in soil, which is a very heterogeneous and “dark” environment. Following the pioneering use of fluorogenic substrates for enzyme activity visualization in soil, a significant methodological advancement occurred within the subsequent decade. Our primary focus is to highlight the progress in the last 10 years, with respect to the spectrum of enzyme activity imaging, zymography resolution, standardization and hotspot identification. Specifically, we emphasize the integration of zymography with the visualization of soil acidification, root exudation, pore distribution, nutrient and water movements. Although the majority of applications so far have centered on enzyme activities in the rhizosphere to reveal plant-soil-microbial interactions, we present the case studies to identify soil heterogeneity and microbial activity also in biopores, detritusphere and other hotspots. We present not only the advancements made but also the current possibilities, challenges, and the potential directions of soil zymography. This technique finds applications across natural and agricultural ecosystems, both in field settings and laboratory studies, capable of scaling from the entire root system (dm) down to microbial communities (μm). In the decade ahead, the future of enzyme research, particularly zymography imaging, will continue to broaden the scope of microbial studies and hotspot localization. This expansion will involve integrating with disciplines such as (bio)chemical, physico-chemical, microbial cell imaging, and isotope applications, facilitating a deeper understanding of soil processes and microbial interactions.
Carbon isotopic composition of soils subjected to C3–C4 vegetation change is a suitable tool for the estimation of C turnover in soil organic matter (SOM) pools. We hypothesized that the biological availability of SOM pools is inversely proportional to their thermal stability. Soil samples from a field plot with 10.5 years of cultivation of the C4 plant Miscanthus×gigantheus and from a reference plot under C3 grassland vegetation were analysed by thermogravimetry coupled with differential scanning calorimetry (TG-DSC). According to differential weight losses (dTG) and energy release or consumption (DSC), five SOM pools with increasing thermal stability were distinguished: (I) 20–190°C, (II) 190–310°C, (III) 310–390°C, (IV) 390–480°C, and (V) 480–1000°C. Their δ 13C values were analysed by EA-IRMS. The weight losses in pool I were connected with water evaporation, since no significant C losses were measured and δ 13C values remained unchanged. The δ 13C of pools II and III in soil samples under Miscanthus were closer to the δ 13C of the Miscanthus plant tissues (−11.8‰) compared to the thermally stable SOM pool V (−19.5‰). The portion of the Miscanthus-derived C4-C in total SOM in 0–5cm reached 55.4% in the 10.5 years. The C4-C contribution in pool II was 60% and decreased down to 6% in pool V. The mean residence times (MRT) of SOM pools II, III, and IV were similar (11.6, 12.2, and 15.4 years, respectively), while pool V had a MRT of 163 years. Therefore, we concluded that the biological availability of thermal labile SOM pools (<480°C) was higher, than that of the thermal stable pool decomposed above 480°C. However, the increase of SOM stability with rising temperature was not gradual. Therefore, the applicability of the TG-DSC for the separation of SOM pools with different biological availability is limited.
No abstract is provided for this article.
No abstract is provided for this article.
Mineral and organic fertilizers are the important factors for maintenance and improvement of soil fertility and aggregation. Despite aggregation and aggregate stability are proxy of soil fertility, the connection between fertilization and aggregation is not direct, as short and long-term processes may affect the aggregate formation in different directions. In this study, the long-term effects of a 20-year application of mineral and organic fertilizers were studied in an intensive horticultural crop rotation with the following treatments: i) without fertilization (control soil), ii) nitrogen applied by mineral fertilizer, and iii) farmyard manure application with low (30 t ha−1 y−1) or iv) high (60 t ha−1 y−1) rates. In case of short-term aggregation process, K-polyacrylate was added to the soil to change aggregate composition and then the aggregated soils were incubated for 2 weeks. Long-term fertilization increased the soil organic C (SOC) content by 42–73% and the portion of small macroaggregates (1–0.25 mm) compared to control soil. In contrast, soil aggregation induced by K-polyacrylate showed an increase of the large macroaggregate (2–1 mm) portion independent of fertilization. Polyacrylate had no effect on soil microbial biomass C. According to the increased SOC content, the fertilization increased CO2 efflux from soil (4.2–5.2% of SOC after 80 days of incubation). Short-term aggregation by K-polyacrylate decreased the SOC mineralization rate mainly of the labile C-pools. In conclusion the data of this study suggest that long-term fertilization mainly contributes to the formation of small macroaggregates. In contrast, the formation of large macroaggregates is mediated mainly by short-term processes and contributes to the decrease of SOC mineralization.
