European Journal of Soil Science最新文献

In terrestrial ecosystems, resource availability and soil microbial biomass are substantially changed with ecological recovery. However, the shifts in resource stoichiometry and microbial biomass stoichiometry often do not align, leading to stoichiometric imbalance that constrains microbial growth and, consequently, affects plant community succession. The mechanisms by which soil microbes acclimate to these imbalances and how such adjustments influence plant community dynamics remain largely unexplored in alpine grasslands. To address these processes, we examined ecological stoichiometry during the secondary succession of zokor-disturbed grassland on the Qinghai–Tibet Plateau, China, utilizing a space-for-time substitution approach. Carbon (C), nitrogen (N) and phosphorus (P) contents across plant–soil–microbe and soil ecoenzymatic activities involved in soil microbial nutrient acquisition were measured. The results indicated that C:P and N:P imbalances between microbes and their plant resources intensified with the recovery of zokor-disturbed grassland. This led to phosphorus limitation in microbial growth, as indicated by the mean vector angles exceeding 45° and decreased threshold element ratio of C:P. In response, soil microbes increased their production of P-acquiring enzymes to mitigate P limitation. Through structural equation modelling (SEM), we found that the C:N:P ratios within the plant–soil–microbe systems explained 74.5% of the total variance in plant aboveground biomass. We concluded that maintaining balanced C:N:P stoichiometric ratios in plant–soil–microbe systems, facilitated by soil ecoenzymatic activities, enhances plant diversity and net primary productivity during the recovery of zokor-disturbed grassland.

Dispersive soils, characterized by their poor resistance to water erosion and high sodium ion concentrations, pose a significant threat to both engineering and agricultural activities. Thus, the identification and improvement of dispersive soils are of paramount importance. There are several theories regarding the causes of soil dispersion, with the prevailing view attributing it to the expansion of the electrical double layer induced by sodium ions, which subsequently reduces the cohesion between soil particles. As a result, sodium indicators such as exchangeable sodium percentage (ESP), percentage sodium (PS), and sodium adsorption rate (SAR) are commonly employed in the identification of dispersive soils. Currently, in efforts to improve dispersive soils for both engineering and agricultural purposes, chemical and biological agents are being added to enhance the soil's erosion resistance and regulate the concentration of sodium ions. Although numerous reviews have been conducted on the identification and improvement of dispersive soils, they tend to focus on the identification methods and the types of improvers, often overlooking the applicability of identification methods, the economic costs and environmental impacts of improvers. In practical improvement, the accuracy of soil identification must be ensured first and foremost. The selection of improvers should not only prioritise efficacy but also undergo thorough analysis and evaluation from multiple perspectives. This paper, therefore, reviews the advantages and disadvantages of various identification methods and assesses the differences among improvers from economic and environmental standpoints, providing a comprehensive theoretical basis for the improvement of dispersive soils.

Arid and semi-arid lands are exceptionally sensitive to climate change. However, the application of phytolith analysis to these environments is hindered by the potential for lateral migration of phytoliths during wind erosion, which may affect the reliability of phytolith-based paleoenvironmental reconstructions. Moreover, there is a lack of quantitative studies of the dispersion and deposition of phytoliths by wind erosion. Here we apply Sutton's equation and theoretical models from the field of blown sand physics and engineering to quantify the lateral migration of various phytolith morphotypes in the surface soil of sand dunes in the Horqin Sandy Land in China. Phytolith morphotypes and concentrations were determined in addition to sedimentary organic matter content and grain size. Combined with the analysis of plant communities, these measurements were used to quantify the lateral migration of phytolith morphotypes, and the results were compared with theoretical models. We found that phytolith concentrations decreased exponentially under an annual average wind speed with distance from the surface source; specifically, a large proportion of lateral phytolith migration occurred within the distance of ~3–5 m. There were significant linear correlations between the phytolith concentration and other environmental factors. A comprehensive form of Sutton's equation was used to estimate that a relatively large proportion (8.35%) of short-cell phytoliths may migrate laterally on dunes that are vulnerable to wind erosion. However, large phytoliths are deposited almost in situ, and relatively limited lateral migration of wind-transported phytoliths occurs in the Horqin Sandy Land overall. Our results provide a theoretical model and practice template for the application of phytolith analysis to soil and sediments, especially as a proxy of past vegetation and ecological change in the Horqin Sandy Land, and other areas affected by wind erosion. Additionally, short-cell phytoliths in palaeoenvironmental contexts satisfy the criteria necessary to investigate the extent with frequent aeolian activity.

Organic fertilization is considered an effective approach in promoting agricultural green development, dramatically affecting soil phosphorus (P) availability. Nonetheless, limited information is available on the comprehensive impact of full substitution of organic fertilizer for chemical fertilizer on P speciation, phytoavailability, and apparent balance throughout different rice-growth stages. To address this gap, a 5-year field experiment was conducted, implementing five organic P gradients ranging from 0 (P₀), 70 (P₇₀), 140 (P₁₄₀), 210 (P₂₁₀) to 280 (P₂₈₀) kg P₂O₅ ha⁻¹ of organic fertilizer. To assess P phytoavailability in the root zone with submillimetre spatial resolutions, this study employed techniques such as the one- and two-dimensional diffusive gradients in thin films (DGT) technique and the high-resolution soil solution sampling technology (HR-Peeper). The findings revealed that increasing P rates enhanced soil Olsen-P and biological-based P fractions across rice-growth stages, primarily driven by variation in mineral-associated P. Notably, the P₁₄₀ treatment demonstrated the highest P uptake efficiency among the different rice-growth stages, with a significant increase in soil DGT-P, particularly in the 0–60 mm soil layer (p <0.05), providing tangible evidence for enhanced P uptake. Moreover, compared with higher P treatments (P₂₁₀ and P₂₈₀), the P₁₄₀ treatment markedly increased P use efficiency by 31.7% and 99.0%, respectively (p <0.05). Further, with a high ratio of DGT-P to Peeper-P and a low apparent balance of P, organic fertilization at the rate of 140 kg P₂O₅ ha⁻¹ effectively struck a balance between ensuring adequate P supply for yield stability and mitigating potential P loss risks. These results underscore the significance of optimal organic fertilization in enhancing agronomic benefits while reducing environmental risks. They offer valuable insights to support field P management strategies and government decision-making processes.

The water potential in drying soils, comprising both matric potential and osmotic potential components, can be measured using the dew point method (DPM). By combining DPM data with retention curve data acquired from techniques such as the suction plate method or the simplified evaporation method (SEM), it becomes possible to determine the soil water retention curve across the entire moisture spectrum. However, as the latter methods only determine the matric potential, the osmotic potential component in DPM data must either be negligible or known so that osmotic and matric potential components can be separated. This study aims to critically analyse common approaches for calculating the osmotic potential. To achieve this, we measured the water retention properties of a silt loam, a sandy loam and a sand across the entire moisture range by combining SEM and DPM. By using almost salt-free soil material, we characterized reference water retention curves with negligible osmotic potential components. The impact of salt on water potential was analysed by conditioning soils with MgCl₂ solutions of different concentrations, drying them, and measuring the water potential at different water contents using the DPM. The resulting water potentials were compared to the reference potentials and differences were interpreted as the osmotic potential component. The DPM-measured water potentials in drying soils can be significantly affected by osmotic potential, especially at higher matric potentials (low suctions). Two models accounting for ideal and one model accounting for non-ideal electrolyte behaviour were used to compare osmotic potential predictions with measurements. At low to medium salt concentrations, all models performed fairly well. At high concentrations, only the model accounting for non-ideal behaviour predicted the osmotic potential satisfactorily, whereas at very high concentrations, all models underestimated the impact of osmotic potential on water potential. This suggests that the surface properties of the soil matrix, such as the specific surface area and surface charges, may lead to a decrease in osmotic potential beyond what is expected in pure solutions.

Mined rock phosphate is expected to become a scarce resource within the next few decades as global phosphorus (P) deposits are declining. As a result, mineral P fertilizer will be less available and more expensive. Therefore, improved knowledge is needed on other P resources, for example, apatite fertilizers derived from the by-products of iron mining. Forestry is a potential future consumer of apatite-rich products with the aim of obtaining more wood per hectare. The actual P availability in apatite to plants has so far been barely quantified. We therefore examined tree P uptake using ³³P apatite under chamber-grown and outdoor conditions. We examined the P uptake for the two main conifer species spruce (Picea abies) and pine (Pinus sylvestris) used in Fenno-Scandinavian forestry. We synthesized ³³P-enriched apatite and applied it to mesocosms with growing seedlings of spruce and pine. The P uptake from ³³P-labelled hydroxylapatite was subsequently traced by (bio)imaging of radioactivity in the plants and by liquid scintillation counting (LSC) upon destructive harvest in all plant fractions (leaves, stem and roots) and rhizosphere soil. Two climatic conditions were compared, one at natural outdoor conditions and one set as 5°C warmer than the climate record from the previous years. Plant P uptake from ³³P-labelled hydroxylapatite was enhanced in chamber-grown compared with outdoor seedlings for both tree species. This uptake was manifested in the clear radioactive images obtained over ca. 1 month after soil apatite application. Furthermore, all aboveground plant fractions of both spruce and pine seedlings showed a higher P uptake in warmer than colder daytime environments. The observed quantities and rates of P uptake from ³³P-labelled hydroxylapatite by spruce (18 Bq g⁻¹ hour⁻¹) and pine (83 Bq g⁻¹ hour⁻¹; averages in chamber condition) are as to our knowledge unique observations. Natural forest soils in Sweden are often P-poor. Our research suggests that apatite-based P fertilization of spruce and pine forests can increase wood production by overcoming any existing P limitation.

Municipally sourced biosolids are commonly used as cost-effective fertilizers, diverting material from landfills and contributing to the circular economy. However, biosolids contain high concentrations of microplastics (MPs), which are emerging contaminants of concern due to their ubiquity in the environment. Despite this, there is a lack of environmentally relevant field studies. In 2022, composite topsoil samples (0–15 cm depth) were collected from seven agricultural fields in Southern Ontario, Canada, representing a chronosequence of biosolid applications ranging from 1 to 9 years since amendment and a control (untreated) field. MP particles down to 20 μm in size were extracted by density separation, enumerated, characterized by stereomicroscope and polymers identified using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Here, we report on the characteristics, abundance and polymer type of MP particles in the study area to assess their fate in biosolid-amended soils. The average MP concentration among fields was 6.87 ± 1.47 MP g⁻¹ (3.43 ± 0.74 mg MP kg⁻¹). Additionally, the MP soil pool increased with repeated applications of biosolids. The dewatered biosolid plastic content of 8816 ± 1809 MP g⁻¹ dry weight (11.6 ± 17.5 g MP kg⁻¹ dry weight) was used to estimate a mean MP loading of 94.5 ± 10.9 kg ha⁻¹ to each field per application, suggesting that 7% of the MP soil pool persisted over time. Quantifying the MP pool in biosolid-amended agricultural soil will inform evidence-based plastic policy changes in our global effort to understand and reduce plastic pollution.

The words we choose to describe our research ultimately directs its course. A dominant term in soil science now, is ‘sequestration’, referring to the removal of carbon (C) from air and its irreversible seclusion in soil, ideally as stable soil organic carbon (SOC). An emerging view, however, now sees SOC as an inherently dynamic assemblage of forms, all potentially vulnerable to decay, with no discrete, measurable fraction holding C in ‘sequestered’ form. Rather than speaking of C ‘sequestration’, then, we might refer instead to SOC ‘stewardship’. This word, now, enfolds the entire spectrum of SOC, not merely some elusive ‘persistent’ or ‘stable’ fraction, perhaps redirecting inquiry; for example, does C need to be ‘sequestered’ in stable form for SOC to serve as effective repository of excess atmospheric CO₂? ‘Stewardship’ explicitly accepts the relentless turnover of SOC, emphasizing the need to manage not only fixed stocks of C, but also the cyclical flows of C through ecosystems that drive their functions. Among other benefits, ‘stewardship’ might motivate us to consider all functions of SOC (not only climate mitigation), consider the entire C cycle (not only enhancing soil C), and preserve existing troves of SOC (not only augmenting them in selected places.) Perhaps most fundamentally, by its etymology, ‘stewardship’ poses a compelling, timeless question: for whom do we steward SOC? Asking why look after SOC, not only reflects our own underlying quest for resilience, but also expands our potential audience and entices the more creative minds that must succeed us. Although ‘stewardship’ may elicit new and fruitful inquiry, we may need to look for words even more evocative, more alluring, more true to our mandate of living well within the circling C that must always sustain us.

We have pleasure in introducing the latest EJSS Russell Review ‘Soil Carbon Stewardship: Thinking in Circles’ by Professor H. Henry Janzen (2024). The article forms the first of a series of our most prestigious invited reviews commissioned to celebrate the EJSS' 75th Anniversary (for further information see Dungait et al., 2024).

The author of this Russell Review, Prof H. Henry Janzen, is one of the world's foremost and respected experts on both the science and the philosophy of soil carbon and its integral place in sustaining our future on Earth. In this review, Prof Janzen eloquently makes the case for a new term, ‘carbon stewardship’, that emphasizes the essential relationship between society and soil carbon, and the urgent need to nurture it in all its forms. He presents a compelling argument for a radical change in the way we think and talk about the value that soils have for us.

The term ‘carbon sequestration’ was coined ~40 years ago. Both within and beyond academia, excitement about ‘carbon sequestration’ in soils as a nature-based solution to climate change continues to grow as the impacts of global warming manifest. Measuring, modelling and mapping soil carbon remain active areas of research, and considerable efforts have been expended to define ‘stable carbon’ and the underlying mechanisms leading to its stabilization, in order that this can be targeted to accrue soil carbon¹.

In this Russell Review, Prof Janzen argues that the benefits of soil carbon to human society go far beyond just locking it away. Rather than referring to ‘carbon sequestration’, he suggests that we replace the term with ‘carbon stewardship’ that ‘denotes recognizing and valuing the benefits that SOC [soil organic carbon] offers to land and all its inhabitants, and then caring for this treasured entity on behalf of other current and future beneficiaries of its goodness’.

The ability to communicate one's scientific research in a way that captures hearts as well as minds is an enviable skill. It takes expertise, integrity and passion, and Prof Janzen has all of these ‘in spades’ (no soil science pun intended!). Anyone who has had the privilege of witnessing in person his presentations on the importance of the soil, and soil carbon in particular, cannot help but be inspired by his depth of knowledge of soil science and the power of his mesmeric storytelling. This ability extends to the written word, and the Invited Review published in the EJSS a decade ago, ‘Beyond carbon sequestration: soil as conduit of solar energy’ (Janzen, 2015), stimulated new ways of thinking about the carbon cycle, within and beyond academia. We are sure that this Russell Review will continue Prof Janzen's legacy of inspiration and commend it to EJSS' readers.

Rapid urbanization has increased the areas of urban forests that store considerable soil carbon (C). Different soil C fractions may show distinctive contents and spatial patterns in view of their contrasting sensitivities to various drivers. However, current studies on soil C fractions are mostly limited to natural ecosystems and little is known about the large-scale patterns and drivers of soil C fractions in urban forests. Based on a field survey of urban forests across a north–south transect in eastern China, we analysed the spatial variations and main drivers of topsoil (surface layer, 0–10 cm; subsurface layer, 10–20 cm) C fractions (i.e., soil organic C, SOC; soil inorganic C, SIC; particulate organic C, POC; mineral-associated organic C, MAOC). Our results showed that topsoil contents of POC, MAOC and SOC changed non-linearly with latitude, with lowest values occurring in the cities in the warm temperate region. In contrast, SIC content showed the highest values in the warm temperate region. POC instead of MAOC was found to be a major fraction of SOC in urban forests. The spatial variation in topsoil POC content was mainly explained by mean annual temperature, soil clay and silt content, and park age. The spatial variation in MAOC content was mainly explained by soil clay and silt content, mean annual precipitation, mean annual temperature and park age. In contrast, the spatial variation in SIC content was mainly explained by mean annual precipitation and soil pH. These findings demonstrate distinct features of different soil C fractions in urban forests and provide useful implications for urban soil carbon management.