Search Results (57)

Global climate change has intensified the heterogeneity of precipitation regimes in subtropical regions, and the increasing frequency of extreme drought events poses a significant threat to biogeochemical cycling in forest ecosystems. Yet, the pathways by which reduced precipitation regulates deadwood decomposition and thereby influences soil nutrient pools remain poorly resolved. Here, we investigated a Cunninghamia lanceolata (Lamb.) Hook. plantation in subtropical China under ambient precipitation (CK) and precipitation reduction treatments of 30%, 50%, and 80%, systematically examining how reduced precipitation alters the chemical properties of deadwood substrates and, in turn, soil nutrient status. Our findings reveal that (1) as precipitation declined, soil water content decreased significantly (p < 0.01), while deadwood pH declined and total organic carbon (TOC), nonstructural carbohydrates (NSCs), and lignin content markedly accumulated (p < 0.01); (2) these shifts in deadwood chemistry affected feedback mechanisms, leading to the suppression of soil nutrient pools: extreme drought (80% reduction) significantly reduced soil TOC, dissolved organic carbon (DOC), total nitrogen (TN), and total phosphorus (TP) (p < 0.01) and inhibited N and P mineralization, whereas the 30% reduction treatment elicited a transient increase in soil microbial biomass carbon (MBC), indicative of microbial acclimation to mild water stress; and (3) principal component analysis (PCA) showed that the 80% reduction treatment drove lignin accumulation in deadwood, while the 30% reduction treatment exerted the greatest influence on soil DOC, TOC, and MBC; partial least squares path modeling (PLS-PM) further demonstrated that soil water content and deadwood substrate properties (pH, lignin, soluble sugars, TOC, C/N, and lignin/N) were strongly negatively correlated (r = −0.9051, p < 0.01), and that deadwood chemistry was, in turn, negatively correlated with soil nutrient variables (pH, TOC, DOC, MBC, TP, TN, and dissolved organic nitrogen [DON]; r = −0.8056, p < 0.01). Together, these results indicate that precipitation reduction—by drying soils—profoundly modifies deadwood chemical composition (lignin accumulation and NSC retention) and thereby, via slowed organic-matter mineralization, constrains soil nutrient release and accumulation. This work provides a mechanistic framework for understanding forest carbon–nitrogen cycling under climate change. Full article

Carbon (C), nitrogen (N), and phosphorus (P) act as pivotal regulators of biogeochemical cycles, steering organic matter decomposition and carbon sequestration in terrestrial ecosystems through the stoichiometric properties of photosynthetic organs. Deciphering their multi-scale spatiotemporal dynamics is central to unraveling plant nutrient strategies and their coupling mechanisms with global element cycling. In the current study, we modeled biogeochemical parameters (C/N/P contents, stoichiometry, and pools) in plant aboveground parts by using the growing mean temperature, total precipitation, total radiation, and maximum normalized difference vegetation index (NDVImax) across nine models (i.e., random forest model, generalized boosting regression model, multiple linear regression model, artificial neural network model, generalized linear regression model, conditional inference tree model, extreme gradient boosting model, support vector machine model, and recursive regression tree) in Xizang grasslands. The results showed that the random forest model had the highest predictive accuracy for nitrogen content, C:P, and N:P ratios under both grazing and fencing conditions (training R² ≥ 0.61, validation R² ≥ 0.95). Additionally, the random forest model had the highest predictive accuracy for C:N ratios under fencing conditions (training R² = 0.84, validation R² = 1.00), as well as for C pool and P content and pool under grazing conditions (training R² ≥ 0.62, validation R² ≥ 0.90). Therefore, the random forest algorithm based on climate data and/or the NDVImax demonstrated superior predictive performance in modeling these biogeochemical parameters. Full article

Soil viruses, ubiquitous and abundant biological entities that are integral to microbial communities, exert pivotal impacts on ecosystem functionality, particularly within carbon (C) and nitrogen (N) cycles, through intricate interactions with bacteria, archaea, fungi, and other microbial taxa. While their contributions to soil ecosystem dynamics are increasingly elucidated, the specific roles of soil viruses in karst forest soil remain largely underexplored. Karst ecosystems (covering 15% of the global terrestrial surface) are characterized by unique geological formations, thin and patchy soil layers, high pH and Ca²⁺, and rapid hydrological dynamics, collectively fostering unique environmental conditions that may shape viral ecology and modulate C and N cycling. This perspective synthesizes existing knowledge of soil viral functions with the distinctive characteristics of karst forest soil, proposing potential mechanisms by which soil viruses could influence C and N cycling in such fragile ecosystems. Soil viruses regulate C and N cycles both directly and indirectly via their interactions with microbial hosts, mainly including shaping the microbial community structure, mediating horizontal gene transfer and microbial metabolism, increasing C and N availability and alleviating nutrient limitations, promoting C and N sequestration, and mitigating climate change. This work aims to bridge soil viral ecology and karst biogeochemical cycles, providing insights into sustainable forest stewardship and climate resilience. We delineate critical knowledge gaps and propose future perspectives, advocating for targeted metagenomic and long-term experimental studies into viral diversity, virus–host-environment interactions, and temporal dynamics. Specifically, we advocate the following research priorities to advance our understanding of soil viruses in karst forest ecosystems in future studies: (I) soil viral diversity, abundance, and activity: characterizing the diversity, abundance, and activity of soil viruses in karst forests using metagenomics and complementary molecular approaches; (II) virus–host interactions: investigating the dynamics between the viruses and key microbial taxa involved in C and N cycling; (III) biogeochemical impacts: quantifying the contributions of viral lysis and horizontal gene transfer to C and N fluxes within karst forest soil; and (IV) modeling the viral impacts on C and N cycles: developing integrative models that incorporate soil virus-mediated processes into existing karst forest soil biogeochemical frameworks at different temporal and spatial scales. Such efforts are essential to validate the hypothesized viral roles and underlying mechanisms, offering a foundation for nature-based solutions to facilitate C and N cycling and support ecological restoration in vulnerable karst regions amid global climate change. Full article

Biogeochemical cycles are fundamental to the functioning of plant–soil systems, driving the availability and transfer of essential nutrients (like carbon (C), nitrogen (N), phosphorus (P), and sulfur (S)) as well as beneficial elements (like silicon (Si)). These interconnected cycles regulate ecosystem productivity, biodiversity, and resilience, forming the basis of critical ecosystem services. This review explores the mechanisms and dynamics of biogeochemical C, N, P, S, and Si cycles, emphasizing their roles in nutrient/element cycling, plant growth, and soil health, especially in agricultural plant–soil systems. The coupling between these cycles, facilitated mainly by microbial communities, highlights the complexity of nutrient/element interactions and corresponding implications for ecosystem functioning and stability. Human activities including industrial agriculture, deforestation, and pollution disrupt the underlying natural processes leading to nutrient/element imbalances, soil degradation, and susceptibility to climate impacts. Technological advancements such as artificial intelligence, remote sensing, and real-time soil monitoring offer innovative solutions for studying and managing biogeochemical cycles. These tools enable precise nutrient/element management, identification of ecosystem vulnerabilities, and the development of sustainable practices. Despite significant progress, research gaps remain, particularly in understanding the interlinkages between biogeochemical cycles and their responses to global change. This review underscores the need for integrated approaches that combine interdisciplinary research, technological innovation, and sustainable land-use strategies to mitigate human-induced disruptions and enhance ecosystem resilience. By addressing these challenges, biogeochemical processes and corresponding critical ecosystem services can be safeguarded, ensuring the sustainability of plant–soil systems in the face of environmental change. Full article

Nitrogen deposition can significantly impact soil biogeochemical cycling; however, its effects on the decomposition processes and nutrient release from leaf and twig litter in subtropical plantations remain inadequately understood. In this study, we focused on the Pinus yunnanensis Franch. forest in the central Yunnan Plateau, southwestern China, and explored how nitrogen addition influences litter decomposition nutrient release over two years, under four levels: control (CK, 0 g·m⁻²·a⁻¹), low nitrogen (LN, 10 g·m⁻²·a⁻¹), medium nitrogen (MN, 20 g·m⁻²·a⁻¹), and high nitrogen (HN, 25 g·m⁻²·a⁻¹). The results indicate that after 24 nitrogen application treatments, the rates of remaining mass in both leaf and twig litters followed the pattern: LN < CK = MN < HN. Under all nitrogen application treatments, the rate of remaining mass in leaf litters was significantly lower than that of twig litters (p < 0.05). Under LN, the mass retention in leaf and twig litters decreased by 3.96% and 8.41%, respectively, compared to CK. In contrast, under HN treatments, the rates of remaining mass in leaf and twig litters increased by 8.57% and 5.35%, respectively. This demonstrates that low nitrogen accelerates decomposition, whereas high nitrogen inhibits it. Significant differences in the remaining amounts of lignin and cellulose in both leaf and twig litters were observed when compared to CK (p < 0.05). Additionally, decomposition time and nitrogen deposition had significant effects on the remaining rates of nutrients (C, N, P) and their C/N, C/P, and N/P in litters (p < 0.05). Following nitrogen application, the C/N of the litters significantly reduced, while the N/P increased. The results suggest that nitrogen addition alleviates the nitrogen limitation on the litters while intensifying the phosphorus limitation. Full article

Silicon (Si) is one of the biogenic elements in lake aquatic ecosystems. Sediments are both sinks and sources of Si, but little is known about its influence on the biogeochemical cycle of Si in lakes and its relationship to other biogenic factors such as carbon and nitrogen. Examining Caohai Lake, a typical macrophytic lake in China, this study systematically examined the different Si forms and biogenic silica (BSi) distribution characteristics and their coupling relationships with total organic carbon (TOC) and total nitrogen (TN) in surface sediments. Iron–manganese-oxide-bonded silicon (IMOF-Si) and organic sulfide-bonded silicon (OSF-Si) jointly accounted for 95.9% of Valid-Si in the sediments, indicating that the fixation of Si by organic matter and iron–manganese oxides was the main mechanism underlying the formation of the different forms of Valid-Si in sediments. The release and recycling of Si in sediments may be mainly driven by mineralized degradation of organic matter and anoxic reduction conditions at the sediment–water interface. The content of biogenic Si (BSi) in the sediments was relatively higher in the southern and eastern areas, which could be explained by the intensification of eutrophication and the increased abundance of diatomaceous siliceous organisms in these areas seen in recent years. The TOC and TN contents in the sediments were generally high, and the sources of organic matter in the sediments included both the residues of endophytes (main contributors) and the input of terrigenous organic matter. TOC and TN both had highly significant correlations with OSF-Si and Valid-Si, which demonstrated that Valid-Si had excellent coupling relationships with C and N in the sediments. The good correlation between BSi, TOC and TN (p < 0.01), as well as the high C/Si, N/Si mole ratio of TOC and TN to BSi, respectivelny, indicating that the dissolution and release rate of BSi may be much higher than the degradation rate of organic matter from the sediments, especially in the areas with a higher abundance of siliceous organisms. Full article

The Parque Nacional La Campana (PNLC) was recently recognized for its high soil surface microbial richness. Here, we explored the microbial community structure in soil profiles from contrasting facing slopes where sclerophyllous forest (SF) and xerophytic shrubland (XS) develop. Soil physicochemical conditions (dry density, pH, and organic matter C and N isotopic soil signatures) were determined at three depths (5, 10, and 15 cm depths). Amplicon sequencing (16S rRNA and ITS1-5F) and specific quantification (qPCR bacteria, archaea and ammonia-oxidizing archaea, fungi) were used to profile the microbial community. Our results indicate that opposite slopes, with different vegetation types and soil conditions studied potentially explained the spatial variability of the microbial community composition, especially between sites than through soil depth. Discriminative taxa were observed to vary between sites, such as, C. nitrososphaera (ammonia-oxidizing archaea) and Sphingomonas, and bacteria associated with Actinobacteria and Bacteroidetes were predominant in SF and XS, respectively. Fungi affiliated with Humicola and Preussia were more abundant in SF, while Cladosporium and Alternaria were in XS. Higher ASV richness was observed in SF compared to XS, for both prokaryotes and fungi. Furthermore, SF showed a higher number of shared ASVs, while XS showed a decrease in unique ASVs in deeper soil layers. In XS, the genus DA101 (Verrucomicrobia) increases with soil depth, reaching higher levels in SF, while Kaistobacter shows the opposite trend. PNLC soils were a reservoir of redundant microbial functions related to biogeochemical cycles, including symbiotic and phytopathogenic fungi. In conclusion, as with the predominant vegetation, the structure and potential function of microbial life in soil profiles were associated with the contrasting the effect of facing slopes as toposequence effects. Full article

Conventional cropping systems (CCSs) rely heavily on large-scale and intensive crop production, using mechanical tillage and synthetic inputs such as chemical fertilizers and pesticides. While these methods can be economically beneficial, they can also be environmentally destructive. Organic cropping systems (OCSs), on the other hand, offer a more sustainable approach with less harmful effects on the environment. CCSs exhibit higher prevalence rates compared to OCSs. This means that there is less research on soil processes in organic fields and the impact of these processes on soil quality. In this study, we aim to assess the functional potential of soils by analyzing their ability to transform carbon, nitrogen, phosphorus, and sulfur. We use shotgun sequencing data to predict the activities of enzymes involved in these cycles. These predictions are then compared to the actual enzyme activity measured in the soil. The objects of study are samples of Chernozem soil from fields cultivated for 11 years using the OCS method and 20 years using the CCS method. It was found that the chemical properties of the studied soils differed significantly in terms of total carbon and total and available nitrogen and phosphorus. Except for phosphorus, the concentration of these elements was significantly higher in the CCS than in the OCS. We assessed the quality of the soils by measuring their enzymatic activities. A comparison of the two cropping systems showed that the activities of the enzymes involved in the C, N, P, and S cycles were, on average, 2.91, 1.89, 1.74, and 1.86 times higher in the CCS than in the OCS, respectively. A two-way PERMANOVA showed that the cropping system was the main variable (F = 14.978, p < 0.01) determining the enzymatic activity of soils, followed by soil depth (F = 9.6079, p < 0.01). We used shotgun sequencing to identify functional genes involved in C, N, P, and S metabolism, as well as genes encoding the measured soil enzymes. Compared to the OCS, the CCS soils had a higher relative abundance of genes involved in N-conversion (log2(FC) +0.22), C-conversion (log2(FC) +0.14), P-conversion (log2(FC) +0.47), and S-conversion (log2(FC) +0.24). At the same time, we found no significant differences between the systems in the relative abundance of genes encoding the measured soil enzymes. Thus, the comparison of the two cropping systems studied showed that the soil microbiome in the CCS has a greater functional potential to support biogeochemical cycles of the key biogenic elements than in the OCS. In addition, this study links the data on the representation of functional genes with the actual activity of enzymes. Based on the results, it would be helpful to focus more specifically on actual enzyme activity or to combine several indicators to obtain a more accurate understanding of soil quality. Full article

The ecological stoichiometric characterization of plant and soil elements is essential for understanding the biogeochemical cycles of ecosystems. Based on three forest ages of Pinus taiwanensis Hayata (P. taiwanensis) plantations in the Gujingyuan National Nature Reserve (i.e., young (16 years), middle-aged (32 years), and mature forests (50 years)), we conducted a field experiment to analyzed C, N, and P stoichiometry and the relationships between needles, litter, soil, and micro-organisms in P. taiwanensis plantations. We intended to elucidate the nutritional characteristics and stability mechanisms of the artificial P. taiwanensis forest ecosystem. The results showed that the C contents of live needles, leaf litter, soil, and micro-organisms in P. taiwanensis plantation forests of the three forest ages were 504.17–547.05, 527.25–548.84, 23.40–35.85, and 0.33–0.54 g/kg, respectively; the respective N contents were 11.02–13.35, 10.71–11.76, 1.42–2.56, and 0.08–0.12 g/kg; and the respective P contents were 0.82–0.91, 0.60–0.74, 0.19–0.36, and 0.03–0.06 g/kg. Forest age significantly influenced both the C, N, and P contents in live needles, leaf litter, soil, and micro-organisms as well as stoichiometric characteristics (p < 0.05). Furthermore, although the litter N:P content was comparable to that of needles, the ratios of C:N and C:P in the litter were notably higher compared to those in needles. Soil C:P and N:P ratios were the highest in mature forests while microbial C:P and N:P ratios continuously decreased. Stoichiometric analyses of our findings suggest that forest stand age can influence divergent changes in element cycling among plants, soil, and micro-organisms. The presented results can aid in further understanding nutrient utilization strategies and regulatory mechanisms for P. taiwanensis plantation forest systems. Full article

Forest gaps alter the environmental conditions of forest microclimates and significantly affect the biogeochemical cycle of forest ecosystems. This study examined how forest gaps and non-gap areas affect soil’s physical properties and eco-stoichiometric characteristics. Relevant theories and methods were employed to analyze the impact of forest gaps on nutrient cycling in Pinus densiflora Sieb. (PDS) and Robinia pseudoacacia L. (RPL) forests located in the Taishan Mountains. The results revealed that (1) forest gaps significantly enhanced the soil physical properties of PDS and RPL forests compared to non-gap areas (NPs). Notably, the bulk density of the soil decreased by 53%–12%, particularly in the surface layer (0–20 cm). Additionally, its non-capillary porosity increased by 44%–65%, while the clay and silt content rose by 39%–152% and 24%–130%, respectively. Conversely, the sand content decreased significantly, by 24%–32% (p < 0.05). (2) The contents of C, N, and P in the gap soil of PDS forests showed a significant increase compared to those in non-gap soil, with increases of 56%–131% for carbon, 107%–1523% for nitrogen, and 100%–155% for phosphorus. There was a significant drop of 10%–33% and 39%–41% in their C:N and C:P ratios, respectively (p < 0.05). The contents of C and P in the gap soil of the Robinia pseudo acacia L. Forest increased significantly, by 14%–22% and 34.4%–71%, respectively. Its C:P and N:P ratios significantly increased, by 14% to 404% and 11% to 41%, respectively (p < 0.05). (3) Compared with NPs, the forest gap significantly reduced the soil electrical conductivity and increased the soil pH. Additionally, compared to the soil at the gap’s edge, the surface soil in the gap’s center had noticeably higher concentrations of C, N, and P. (4) Key variables affecting the soil pH, silt content, bulk density, and overall porosity in forest gaps include the concentrations of carbon (C), nitrogen (N), and phosphorus (P) present and their ecological stoichiometric ratios. The findings showed that forest gaps had a considerable impact on the soil’s physical characteristics and ecological stoichiometry. They also had a high potential for providing nutrients, which might aid in the establishment of plantation plants. Full article

Rhizosphere microorganisms play a pivotal role in biogeochemical cycles, particularly in relation to carbon (C) and nitrogen (N) cycles. However, the impact of stand age on the composition of rhizosphere microbial communities and the abundance involved in C and N cycling remains largely unexplored in restoration ecosystems dominated by shrubs of temperate deserts. This study focuses on revealing changes in microbial composition and functional genes in the rhizosphere soil of Caragana korshinskii after revegetation, as well as their response mechanisms to changes in environmental factors. The alpha diversity of bacteria tended to increase with stand age, whereas that of fungi decreased. The abundance of denitrification; dissimilatory nitrate reduction to ammonium, nitrification, and ammonium assimilation; and C fixation-related gene levels increased with stand age, whereas those related to the degradation of starch, pectin, hemicellulose, cellulose, and aromatics decreased. The parameters MBC, MBN, and TC were the key factors affecting the bacterial community, whereas the fungal community was regulated by TN, EC, pH, and MBC. Stand age indirectly regulated C and N cycling functions of genes through altered soil properties and microbial community structures. This study presents a novel approach to accurately evaluate the C and N cycling dynamics within ecosystems at various stages of restoration. Full article

Ecological stoichiometry is essential for investigating biogeochemical cycling in an ecosystem. Thinning, a management practice that closely mimics natural processes, significantly influences stand structure and microclimate, thereby affecting nutrient cycling. Nonetheless, seasonal variations in ecological stoichiometry across the leaf-litter-soil continuum under different thinning regimes remain inadequately understood. In this study, we evaluated three thinning methods (strip filling (SF), ecological thinning (ET), and forest gap (FG)) to investigate the stoichiometric characteristics of Cupressus funebris Endl (C. funebris). within the leaf-litter-soil system in Southwest China. The samples were collected during four distinct seasonal periods: early dry season (January–March, EDS), late dry season (April–June, LDS), early wet season (July–September, EWS), and late wet season (October–December, LWS). The results indicated that the (1) carbon (C), nitrogen (N), and phosphorus (P) contents and C:N:P ratio in leaves, litter, and soils varied widely and were strongly influenced by thinning method and season. (2) In the EDS, the soil TP content significantly decreased by 36.9% (p < 0.05), 41.67% (p < 0.05), and 17.9% (p < 0.05) under ET, FG, and SF treatments compared to the pure C. funebris forest (PC). (3) Compared to the PC, the leaf organic C content under ET significantly increased by 6.6% (EDS, p < 0.05), 8.4% (EWS, p < 0.05), 24.8% (LDS, p < 0.05), and 11.5% (EWS, p < 0.05). (4) Under identical thinning methods, the contents of litter C, litter N, litter P, leaf N, and leaf P (excluding litter C in SF) were found to be highest in the LWS. Conversely, the ratios of litter C:N, litter C:P, litter N:P, leaf C:N, leaf C:P, leaf N:P, soil N:P, and soil C:P (except for the ratios of litter N:P in ET and FG) were observed to be lowest in the LWS. (5) Season and thinning method significantly affected the internal stability of P stoichiometric homeostasis, and litter P under ET (EWS) was categorized as “plastic” (p < 0.1, 0.75 < H). (6) The results of the structural equation model show that the thinning method has a direct positive impact on leaf C, N, and P contents and a direct negative impact on the chemical stoichiometry of leaves and soil. Season has a direct positive impact on soil C, N, and P contents, as well as on the chemical stoichiometry of litter and leaves; however, they have a direct negative impact on leaf C, N, and P contents. This study contributes to C. funebris plantation management and provides basic information for global stoichiometric analysis. Full article

Shrub invasion affects plant growth and soil physicochemical properties, resulting in soil microbiota metabolic pathway changes. However, little is known about the shrub expansion intensity of microbial metabolic pathway processes. In this study, we used metagenome sequencing technology to investigate changes in soil microbial C and N metabolic pathways and community structures, along with different shrub invasion intensities, in the Sanjiang Plain wetlands. Different shrub invasion intensities significantly affected the soil microbial composition (β diversity), with no significant effect on the α diversity compared to CK. AN, pH, and TP were the major factors influencing the microbial community’s structures. Compared to CK, the shrub expansion intensity did not significantly affect C fixation and central metabolism but significantly reduced methanogenesis, which involves the CO₂-to-methane transition that occurs in methane metabolism, and denitrification, the nitrite to nitric oxide (nirK or nirS) transition that occurs in N metabolism. This study provides an in-depth understanding of the biogeochemical cycles of wetland ecosystems in cold northern regions undergoing shrub invasion. Full article

Silicon (Si) is one of the main biogenic elements in the aquatic ecosystem of lakes, significantly affecting the primary productivity of lakes. Lake sediment is an important sink of Si, which exists in different Si forms and will be released and participate in the recycling of Si when the sediment environment changes. Compared to carbon (C), nitrogen (N) and phosphorus (P), the understanding of different Si forms in sediments and their biogeochemical cycling is currently insufficient. Dianchi Lake, a typical eutrophic lake in southwest China, was selected as an example, and the contents of different Si forms and biogenic silicon (BSi), as well as their correlations with total organic carbon (TOC), total nitrogen (TN), and chlorophyll a in the surface sediments, were systematically investigated to explore Si’s recycling characteristics. The results showed that the coupling relationship of the four different Si forms in the surface sediments of Dianchi Lake was poor (p > 0.05), indicating that their sources were relatively independent. Moreover, their formation may be greatly influenced by the adsorption, fixation and redistribution of dissolved silicon by different lake substances. The contents of different Si forms in the surface sediments of Dianchi Lake were ranked as iron-manganese-oxide-bonded silicon (IMOF-Si) > organic sulfide-bonded silicon (OSF-Si) > ion-exchangeable silicon (IEF-Si) > carbonate-bound silicon (CF-Si). In particular, the contents of IMOF-Si and OSF-Si reached 2983.7~3434.7 mg/kg and 1067.6~1324.3 mg/kg, respectively, suggesting that the release and recycling of Si in surface sediments may be more sensitive to changes in redox conditions at the sediment–water interface, which become the main pathway for Si recycling, and the slow degradation of organic matter rich in OSF-Si may lead to long-term and continuous endogenous Si recycling. The low proportion (0.3~0.6%) and spatial differences of biogenic silicon (BSi) in the surface sediments of Dianchi Lake, as well as the poor correlation between BSi and TOC, TN, and chlorophyll a, indicated that the primary productivity of Dianchi Lake was still dominated by cyanobacteria and other algal blooms, while the relative abundance of siliceous organisms such as diatoms was low and closer to the central area of Dianchi Lake. Additionally, BSi may have a faster release capability relative to TOC and may participate in Si recycling. Full article

Soil nitrite (NO₂⁻) is an important reactive intermediate in many nitrogen transformation processes, but it is unstable under acidic conditions and may be lost as gaseous N. The canonical extraction method of soil NO₂⁻ using a potassium chloride (KCl) solution greatly underestimates its concentration. To reflect the concentration more accurately, we optimized the extraction method of soil NO₂⁻ for three agricultural soils differing in soil texture and pH, an alkalic fluvo-aquic soil and acidic Mollisol and Ultisol soils, respectively. Both extractable soil ammonium (NH₄⁺) and nitrate (NO₃⁻) were systematically investigated to optimize the simultaneous extraction of soil inorganic nitrogen. The effects of different extractants (deionized water (DIW), un-buffered 2 mol L⁻¹ KCl, and pH-buffered 2 mol L⁻¹ KCl), shaking time (10 and 30 min), and storage duration of the extracts (stored at −20 °C for 1 day, and at 4 °C for 1, 3, and 6 days) on the determination of soil inorganic nitrogen were investigated. The results showed that the un-buffered KCl extractant significantly underestimated soil NO₂⁻ concentration compared to DIW. The highest recovery of NO₂⁻ was obtained by extracting with DIW at 10 min of shaking for all three soils. Compared with DIW, the concentration of NH₄⁺ and NO₃⁻ in soil extracted from the KCl solution increased significantly. Furthermore, the soil inorganic nitrogen content of extracts stored at 4 °C for one day was closer to the direct measurements of fresh samples than with the other storage methods. Overall, the recommended analysis method for soil NO₂⁻ was extraction by DIW, shaking for 10 min, and filtering with a 0.45 µm filter, while soil NH₄⁺ and NO₃⁻ were extracted with a KCl solution and shaken for 30 min. The extract should be stored at 4 °C and analyzed within 24 h. Our study provides an efficient extraction method for soil NO₂⁻ and supports studies on the biogeochemical nitrogen cycle, e.g., in the investigation of soil nitrous acid (HONO) and nitric oxide (NO) emissions. Full article