261. 题目: Changes in soil C–N–P stoichiometry after 20 years of typical artificial vegetation restoration in semiarid continental climate zones
Vegetation restoration is one of the principal strategies for ecosystem recovery in degraded land of fragile regions, which is an important driving factor for soil fertility and elemental circulation. While the relationship between revegetation and soil C–N–P stoichiometry remains unclear. To evaluate the relationships between vegetation restoration and soil C–N–P stoichiometry, the distribution of soil C, N, and P within 0–30 cm soil depth under five typical artificial restored vegetation types on the Loess Plateau was analyzed and the influencing factors were evaluated. The results showed that soil C, N, and P contents were relatively lower at the study site than the mean values for topsoil in China. Compared with other vegetation types (Populus simonii Carr., Pinus tabuliformis Carr., and Caragana korshinskii Kom.), Medicago Sativa L. and Stipa bungeana Trin. helped improve soil fertility better; the soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) contents within the 0–30 cm soil layer respectively maximized under Stipa bungeana Trin. (3.30 g kg−1), Medicago Sativa L. (0.34 g kg−1), and Medicago Sativa L. (0.41 g kg−1). The values of soil C/N, C/P, and N/P for the five vegetation types were 9.50–11.85, 15.36–21.47, and 1.29–1.90, respectively. The contents of SOC and TN under the five vegetation types were significantly (P < 0.001) affected by soil depth and vegetation type (P < 0.001) and decreased with increasing soil depth. However, the TP content was significantly (P < 0.001) affected by vegetation type and not by soil depth. Considering the better adaptability of native species, native herb vegetation types should be considered first for ecological restoration in semiarid continental climate zones.
262. 题目: Root response and phosphorus uptake with enhancement in available phosphorus level in soil in the presence of water-soluble organic matter deriving from organic material
Understanding the available phosphorus (P) levels in the presence of water-soluble organic matter (WSOM) deriving from organic materials can be important for the improvement of the P use efficiency. This study aimed to: (i) determine which types of WSOM (deriving from the organic material) can suppress P immobilization, and (ii) understand whether plants can uptake P that the immobilization is suppressed by the presence of WSOM, as well as how the plant roots response depending on the available P levels. The P sorption test revealed that the presence of WSOM deriving from cattle manure compost (CM), sewage sludge compost (SSC), and hydrothermal decomposed liquid fertilizer (HDLF) can suppress the P sorption by 44, 44, and 24%, respectively, as compared to single P. In the incubation test, the percentage of the available P to that added as P fertilizer was found to be >21% higher in the presence of a CM- or a SSC-derived WSOM than those of single P, but the effect of the HDLF-derived WSOM was not. In the cultivation test, P uptake was found to be improved in the CM-, the SSC-, and the HDLF-deriving WSOM by 17, 13, and 11%, respectively, as compared to single P. Moreover, the root weight was found to decrease along with an increase in the amount of P uptaken by the plant. These findings provide the first experimental evidence that the presence of the WSOM deriving from CM, SSC, and HDLF simultaneously enhance the available P level in the soil and P uptake by the plant at the lab-scale test. In addition, the higher the available P levels in the presence of WSOM, the lower the root developments. The presence of WSOM, particularly of one of high maturity, can suppress the P sorption by 24–44%; as a result, >20% of the P added remains as the available P depending on the type of organic material used.
263. 题目: Proportional allocation with soil depth improved mapping soil organic carbon stocks
Soil organic carbon (SOC) is vital to the assessment of land quality, management of farmland and ecological environment, and carbon cycle. A more accurate spatial prediction of multilayer soil organic carbon density (SOCD) can contribute to a better interpretation of the changes in multilayer SOC stocks and carbon dynamics. However, previous mapping techniques still have limitations, such as ignoring the relationship of profile depths, not further taking advantage of vertical distribution and surface categorical information. In addition, it is unclear whether it is better to model each depth interval of SOC separately or to model the total layer and then allocate it. Here, we propose two new methods based on the proportional allocation of soil depth for multilayer mapping: vertical log-ratio method (VLR) of SOCD by applying the percentage of SOCD data and isometric log-ratio (ILR) transformation, and vertical distribution method (VD) of SOCD by considering different land-use types. We compared five methods, including the two new methods, the exponential and equal-area spline functions, and independent modeling without depth information. We combined these five methods with the generalized linear model (GLM) and random forest (RF) to produce predictions of the Sanjiang Plain, northeastern China. The results demonstrated that SOCD did not always decrease with increasing soil depth, and classification of SOCD vertical distribution features needs to be considered by combining with soil depths. For accuracy assessment, the exponential mode with both GLM and RF over-calculated the predicted values and performed poorly, indicating that the blind use of depth information increased the prediction error. The spline function prediction was scarcely better than that of independent modeling. The proportional allocation methods performed better than other separate modeling methods for accuracy and interpretability with GLM or RF, especially for the middle and surface layers. The GLM generated more aggregated predictions than the RF, losing the distribution pattern of the original data. Therefore, we recommend RF combined with proportional allocation methods for spatial SOCD prediction in large-scale study areas. We calculated the SOC stocks in the Sanjiang Plain using our new methods, which were more reasonable compared with those of previous studies and had the advantages of in-depth information, environmental variable selection, and model optimization. Our findings provide not only other perspectives for SOCD mapping, with more fully integrated depth information and more accurate assessment of multilayer SOC stocks, but also provide guidance for the evaluation of land quality, farmland, and ecological environmental management.
264. 题目: Combined effect of humic acid and vetiver grass on remediation of cadmium-polluted water
Effective treatment of water pollution is an economic and social requirement globally. Humic acid (HA) is a popular mitigator for such waters. However, the combined effect of HA and restorative plants on cadmium (Cd) remediation is not well understood. Therefore, we experimented on Cd remediation using HA along with vetiver grass and HA-vetiver grass. We observed that vetiver grass effectively removed Cd at 15～30 mg/L. The accumulation capacity of the root was significantly higher than the shoots (P < 0.05), and Cd distribution followed the trend: cell wall > organelle > soluble substance (F1 > F2 > F3). The plant’s accumulation capacity against 25 mg/L Cd was higher than for other treatments. The root accumulation capacity was much higher (702.3 mg/L) than those without added HA. However, upon adding 200 and 250 mg/L HA, the phytoremediation of Cd in the root and shoot significantly reduced (P < 0.05). Conversely, HA improved the Cd removal efficiency of the plants, notably at a lower HA concentration (150 mg/L). In addition, HA (especially at 150 mg/L) influences Cd distribution in vetiver cells (P < 0.05) and can significantly increase the proportion of Cd in the root cytoplasm. Consequently, a low HA concentration can significantly improve Cd accumulation in the vetiver, shorten the metal’s bioremediation cycle, and improve the biological absorption efficiency.
265. 题目: Optical properties and potential sources of water-soluble and methanol-soluble organic aerosols in Taipei, Taiwan
The optical properties and sources of brown carbon (BrC) have been poorly constrained in climate models due to the variability of spatiotemporal characteristics, impeding the accurate understanding of its impact on air quality and climate. In this study, daily PM2.5 samples, which were collected from January to November 2021 in urban Taipei, Taiwan, and seasonal variations of optical properties of water-soluble and methanol-soluble organic carbon (WSOC and MSOC) were evaluated. The light absorption coefficients at 365 nm (Abs365) of both extracts, which strongly correlated with WSOC and MSOC mass concentrations, displayed distinct seasonal variations with the highest in winter and the lowest in summer. The Absorption Ångström Exponent of WSOC and MSOC ranged from 4.16 to 7.75 and 4.03–6.83, with averages of 6.05 ± 0.56 and 5.29 ± 0.61, respectively. The mass absorption efficiency (MAE365), which normalizes the Abs365 of both extracts to the mass of WSOC and MSOC, showed significant seasonal difference with the high MAE365, WSOC of 0.96 ± 0.29 m2 g−1 in winter and the lowest in summer of 0.49 ± 0.07 m2 g−1, whereas contrasting with the largest MAE365, MSOC of 0.99 ± 0.46 m2 g−1 in summer and the lowest in winter of 0.66 ± 0.28 m2 g−1, respectively. Fossil fuel combustion, such as traffic emission, and biomass burning, such as crematorium, were identified to be important contributors to light-absorbing substances. The estimated fractional radiative forcing by WSOC and MSOC to elemental carbon was most significant during winter (8.15 ± 3.77%) and spring (13.90 ± 4.38%), respectively, which may greatly affect the atmospheric photochemistry and climate. This study suggests that the impact of BrC in Taiwan on the local and regional air quality and climate is non-negligible.
266. 题目: Dissolved organic matter tracers reveal contrasting characteristics in the concentrated flow zone and matrix-with-fractures zone of a sulfate-contaminated karst aquifer in South China
Dissolved organic matter (DOM) is of great importance in biogeochemical processes, such as sulfate reduction, in groundwater. H2S is generated from microbial-mediated sulfate reduction fueled by DOM and erodes carbonate. However, understanding the transformation and fate of DOM in sulfated-contaminated karst aquifers is still poor. Here, fluorescence spectroscopy was used to characterize the DOM pool in the sulfate-contaminated (from human activities) karst aquifer of the Zengpiyan Site, South China, by investigating the groundwater flow system. A comparison of fluorescence DOM (FDOM) characteristics between the concentrated flow zone (CFZ) composed of highly permeable small conduits and fracture networks and the matrix-with-fractures zone (MFZ) made of low permeable fractures and matrix rock aquifers was done. The relative groundwater residence times for all sample sites were estimated using , which are consistent with those of the groundwater tracer test. The FDOM in groundwater in the CFZ was composed mainly of terrestrial-derived fulvic acid (FA)- and humic acid (HA)-like components, with relatively small contributions of microbially derived tryptophan (TPH)-like components. Compared with CFZ groundwater, the MFZ groundwater showed a longer residence time and reducing conditions, more bioavailable DOM, dominant TPH-like components with relatively small contributions of FA-like components, and fewer humus and hydrophobic structures. Hydrogeological conditions indirectly altered DOM composition by altering the biotic and abiotic activity conditions. The coexistence of relatively strong reducibility conditions and the higher proportion of bioavailable DOM in the MFZ would promote sulfate reduction to H2S gas, possibly amplifying carbonate dissolution, leading to the erosion of cultural relics. It is hoped that this study will contribute to knowledge on DOM behavior in karst aquifers and provide a scientific basis for cave site protection.
267. 题目: Clarifying the evidence for microbial- and plant-derived soil organic matter, and the path towards a more quantitative understanding
268. 题目: The emerging role of drought as a regulator of dissolved organic carbon in boreal landscapes
One likely consequence of global climate change is an increased frequency and intensity of droughts at high latitudes. Here we use a 17-year record from 13 nested boreal streams to examine direct and lagged effects of summer drought on the quantity and quality of dissolved organic carbon (DOC) inputs from catchment soils. Protracted periods of drought reduced DOC concentrations in all catchments but also led to large stream DOC pulses upon rewetting. Concurrent changes in DOC optical properties and chemical character suggest that seasonal drying and rewetting trigger soil processes that alter the forms of carbon supplied to streams. Contrary to expectations, clearest drought effects were observed in larger watersheds, whereas responses were most muted in smaller, peatland-dominated catchments. Collectively, our results indicate that summer drought causes a fundamental shift in the seasonal distribution of DOC concentrations and character, which together operate as primary controls over the ecological and biogeochemical functioning of northern aquatic ecosystems.
269. 题目: Contribution of components in natural soil to Cd and Pb competitive adsorption: Semi-quantitative to quantitative analysis
Cadmium (Cd) and lead (Pb) are two of the most common elements found in contaminated sites. The behavior of specific metals in the soil may be affected by other metals because of the competition for adsorption sites. In this study, adsorption experiments after chemical extraction, multi-surface models, and advanced spectroscopy technology were jointly used to explain the adsorption mechanism of Cd and Pb and to determine the contribution of each component in the competitive system. The results show that pH is the key factor in determining the contribution of soil components to metal adsorption. Soil organic matter (SOM) is the dominant adsorbent for both Cd and Pb. Clay minerals play an adsorption role at low pH, whereas Fe/Al oxides adsorb metals primarily in the high pH range. Further, the competitive effect of Pb on Cd occurred primarily on SOM rather than on clay minerals. When the Pb concentration increased from 0 to 500 mg/L, the adsorption of Cd on SOM decreased by 132.0 mg/kg, whereas it decreased only by 1.9 mg/kg on clay minerals. Therefore, the competitive effect of Pb on Cd cannot be ignored in soils with high organic matter content.
270. 题目: Bioremediation pretreatment of waste-activated sludge using microalgae Spirulina platensis derived biochar coupled with sodium sulfite: Performance and microbial community dynamics
4-Nonylphenol is a typical endocrine-disrupting compound found in waste-activated sludge. This study evaluates the feasibility of blue-green algae (Spirulina platensis)-based biochar as a carbon-neutral material to improve sodium sulfite (S(IV))-mediated sludge purification. Blue-green algae-based biochar is an effective activator (at 500 °C and 3 × 10−6 M) of sodium sulfite and removed 75% of 4-nonylphenol at pH 6 using at 1.7 g L−1 of dosage. Possible synergistic relationships among the coexisting oxidizing species (SO3•−, SO4•−, HO•, and 1O2), obvious defect structure, and abundant carbonyl oxygen groups on the surface of the biochar together dived advanced oxidation process. The bacterial consortia promoted the decomposition of biologically available substrates in the biosolid mixture, which led to the enrichment of Denitratisoma, and boosted 4-nonylphenol biodegradation. This study outlines a potential carbon-neutral, cost-effective, and sustainable sludge treatment strategy using renewable blue-green algae-based biochar, aiding 4-nonylphenol biodegradation in waste-activated sludge.
271. 题目: Nitrogen wet deposition stoichiometry: the role of organic nitrogen, seasonality, and snow
Wet deposition of dissolved inorganic nitrogen (N) is declining nationally, accompanied by a shift in stoichiometry from predominantly oxidized to reduced forms of N. Stoichiometric trends that include the organic fraction of N wet deposition have yet to be assessed in light of anthropogenic pressures and global change, including shifting seasonality. Here we use 17 years of weekly, year-round wet deposition data from a temperate watershed in New Hampshire (USA) to assess long-term and seasonal trends in NO3−, NH4+, and dissolved organic nitrogen (DON), and quantify the dependence of N stoichiometry on precipitation type (rain or snow). Concentration, load, and relative abundance of DON are increasing, a pattern previously unreported in the U.S. Deposition of total dissolved nitrogen at this site is declining, but is increasingly depleted in NH4+, contrary to national trends. The stoichiometry of inorganic N is highly sensitive to precipitation type with snow containing significantly more NO3− than rain, which was relatively enriched in NH4+. The effects of climate change on seasonality such as warmer winters could result in a greater proportion of precipitation entering the biosphere as rain that is relatively enriched in reduced N, with significant implications for watershed biogeochemical cycles at the regional scale. This study demonstrates variability in contemporary N deposition inputs including trends in stoichiometry and explores the role of organic N and seasonality in regulating inter- and intra- variability in N deposition stoichiometry.
272. 题目: Divergent changes in particulate and mineral-associated organic carbon upon permafrost thaw
Permafrost thaw can stimulate microbial decomposition and induce soil carbon (C) loss, potentially triggering a positive C-climate feedback. However, earlier observations have concentrated on bulk soil C dynamics upon permafrost thaw, with limited evidence involving soil C fractions. Here, we explore how the functionally distinct fractions, including particulate and mineral-associated organic C (POC and MAOC) as well as iron-bound organic C (OC-Fe), respond to permafrost thaw using systematic measurements derived from one permafrost thaw sequence and five additional thermokarst-impacted sites on the Tibetan Plateau. We find that topsoil POC content substantially decreases, while MAOC content remains stable and OC-Fe accumulates due to the enriched Fe oxides after permafrost thaw. Moreover, the proportion of MAOC and OC-Fe increases along the thaw sequence and at most of the thermokarst-impacted sites. The relatively enriched stable soil C fractions would alleviate microbial decomposition and weaken its feedback to climate warming over long-term thermokarst development.
273. 题目: Sedimentary organic carbon and nitrogen stocks of intertidal seagrass meadows in a dynamic and impacted wetland: Effects of coastal infrastructure constructions and meadow establishment time
Seagrass meadows, through their large capacity to sequester and store organic carbon in their sediments, contribute to mitigate climatic change. However, these ecosystems have experienced large losses and degradation worldwide due to anthropogenic and natural impacts and they are among the most threatened ecosystems on Earth. When a meadow is impacted, the vegetation is partial- or completely lost, and the sediment is exposed to the atmosphere or water column, resulting in the erosion and remineralisation of the carbon stored. This paper addresses the effects of the construction of coastal infrastructures on sediment properties, organic carbon, and total nitrogen stocks of intertidal seagrass meadows, as well as the size of such stocks in relation to meadow establishing time (recently and old established meadows). Three intertidal seagrass meadows impacted by coastal constructions (with 0% seagrass cover at present) and three adjacent non-impacted old-established meadows (with 100% seagrass cover at present) were studied along with an area of bare sediment and two recent-established seagrass meadows. We observed that the non-impacted areas presented 3-fold higher percentage of mud and 1.5 times higher sedimentary organic carbon stock than impacted areas. Although the impacted area was relatively small (0.05–0.07 ha), coastal infrastructures caused a significant reduction of the sedimentary carbon stock, between 1.1 and 2.2 Mg OC, and a total loss of the carbon sequestration capacity of the impacted meadow. We also found that the organic carbon stock and total nitrogen stock of the recent-established meadow were 30% lower than those of the old-established ones, indicating that OC and TN accumulation within the meadows is a continuous process, which has important consequences for conservation and restoration actions. These results contribute to understanding the spatial variability of blue carbon and nitrogen stocks in coastal systems highly impacted by urban development.
274. 题目: Determining patterns in the composition of dissolved organic matter in fresh waters according to land use and management
In fresh waters, the origins of dissolved organic matter (DOM) have been found to exert a fundamental control on its reactivity, and ultimately, its ecosystem functional role. A detailed understanding of landscape scale factors that control the export of DOM to aquatic ecosystems is, therefore, pivotal if the effects of DOM flux to fresh waters are to be fully understood. In this study we present data from a national sampling campaign across the United Kingdom in which we explore the variability in DOM composition in three broad landscape types defined by similar precipitation, geology, land use and management, hydrology, and nutrient enrichment status. We characterised samples from fifty-one sites, grouping them into one of three major underlying classifications: circumneutral streams underlain by clay and mudstone (referred to as ‘clay’), alkaline streams underlain by Cretaceous Chalk or by Carboniferous or Jurassic Limestone (‘limestone’), and acidic streams in peatland catchments underlain by a range of low permeability lithologies (‘peat’). DOM composition was assessed through organic matter stoichiometry (organic carbon: organic nitrogen; organic carbon: organic phosphorus; C/N(P)DOM) and metrics derived from ultra-violet (UV)/visible spectroscopic analysis of DOM such as specific UV absorption (a254 nm; SUVA254). We found similar SUVA254, C/NDOM and DOM/a254 relationships within classifications, demonstrating that despite a large degree of heterogeneity within environments, catchments with shared environmental character and anthropogenic disturbance export DOM with a similar composition and character. Improving our understanding of DOM characterisation is important to help predict shifts in stream ecosystem function, and ecological responses to enrichment or mitigation efforts and how these may result in species composition shifts and biodiversity loss in freshwater ecosystems.
275. 题目: Combined management of olive mill wastewater and compost in olive grove: Effects on soil chemical properties at different layers depth
The effects of combined agronomic application of olive mill wastewater (OMW) with compost were evaluated in an olive field (Tunisia). Four treatments were used. The first plot was spread by 50 m3 ha−1 of OMW, the second treated with 5 T ha−1 of compost, the third amended by both (50 m3 ha−1 + 5 T ha−1), and the fourth, used as a control. After ten days of organic amendment, the soil upper layers presented the highest organic matter (OM), total nitrogen, available phosphorus, exchangeable potassium and sodium contents, with the highest values noted for the mixed treatment. Also, this treatment exhibited the most important soil phenolic concentrations accumulation. All organic fertilizing treatments produced significant increase in the total alkali-extractable humic carbon (HEC), humic acid carbon (HAC) and fulvic acid carbon (FAC) concentrations, especially with OMW and compost applied simultaneously.
276. 题目: Permafrost Landscape History Shapes Fluvial Chemistry, Ecosystem Carbon Balance, and Potential Trajectories of Future Change
277. 题目: The use of stable carbon isotopes to decipher global change effects on soil organic carbon: present status, limitations, and future prospects
Major global change factors, including carbon dioxide (CO2) fertilization, warming, change in precipitation, nitrogen deposition, and land-use change have the potential to significantly affect future stocks of soil organic carbon (SOC). These factors, individually or by interacting with each other, can also trigger positive or negative feedback to the processes affecting the rate of SOC formation or loss. Despite rapid progress in the understanding of carbon (C) cycling processes in the last few decades, much uncertainty remains in our ability to precisely forecast potential changes in SOC stocks in the rapidly changing future world. Stable C isotopes have been extensively used in natural observational studies as well as in laboratory and field experiments that manipulate CO2 concentration, temperature, moisture, nitrogen fertilization, and vegetation type to understand the complex interactions and feedbacks that result from changing climate, plants and their herbivores, as well as soil microorganisms. Newly developed tools such as compound-specific isotope analysis, nano-SIMS (secondary ion mass spectroscopy), and stable isotope probing (SIP) permit isotope tracing in a specific ecosystem pool into specific C compounds and processes, thus providing in-depth insights into many processes affecting C biogeochemistry. The recent availability of affordable and reliable field-deployable optical isotope monitoring devices has provided researchers with a new set of tools for continuously tracking the 13C-CO2 fluxes at the ecosystem level, enabling deeper insights into C biogeochemistry under changing environmental conditions. Despite these great strides, there is a scarcity of review studies that have comprehensively examined the use of C isotopes in studying SOC responses under global change factors. This review highlights recent progress in understanding the effect of major global change factors on SOC fluxes and stocks using selected examples covering scales from plant rhizospheres to geographic regions. Moreover, we discuss the strengths and limitations of current approaches and recent scientific advancements to highlight the new prospects evolving from the exceptional temporal and spatial resolution of stable isotope analysis in studying how global change affects SOC. Finally, we suggest that studies using stable C isotopes are well-poised to focus on identifying how dominant SOC cycling processes respond to environment-specific limiting factors and any thresholds and tipping points that define those relationships.
278. 题目: Priming of soil organic carbon mineralization and its temperature sensitivity in response to vegetation restoration in a karst area of Southwest China
Plant residue input alters native soil organic carbon (SOC) mineralization through the priming effect, which strongly controls C sequestration during vegetation restoration. However, the effects of different vegetation types on SOC priming and the underlying microbial mechanisms due to global warming are poorly understood. To elucidate these unknowns, the current study quantified soil priming effects using 13C-labeled maize residue amendments and analyzed the community structure and abundances in the soils of a vegetation succession gradient (maize field (MF), grassland (GL), and secondary forest (SF)) from a karst region under two incubation temperatures (15 °C and 25 °C). Results revealed that after 120 d of incubation, vegetation restoration increased the soil priming effects. Compared to MF, the priming effects of SF at 15 °C and 25 °C increased by 142.36 % and 161.09 %, respectively. This may be attributed to a high C/N ratio and low-N availability (NO3−), which supports the “microbial nitrogen mining” theory. Variations in soil priming were linked to changes in microbial properties. Moreover, with vegetation restoration, the relative abundance of Actinobacteria (copiotrophs) increased, while Ascomycota (oligotrophs) decreased, which accelerated native SOC decomposition. Co-occurrence network analysis indicated that the cooperative interactions of co-existing keystone taxa may facilitate SOC priming. Furthermore, structural equation modeling (SEM) indicated that changes in the priming effects were directly related to the fungal Shannon index and microbial biomass C (MBC), which were affected by soil C/N and NO3−. Warming significantly decreased soil priming, which may be attributed to the increase in microbial respiration (qCO2) and decreased MBC. The temperature sensitivity (Q10) of SOC mineralization was higher after residue amendment, but significant differences were not detected among the vegetation types. Collectively, our results indicated that the intensity of priming effects was dependent on vegetation type and temperature. Microbial community alterations and physicochemical interactions played important roles in SOC decomposition and sequestration.
279. 题目: Effects of nitrogen-enriched biochar on subtropical paddy soil organic carbon pool dynamics
Agronomic management practices present an opportunity to improve the sustainability of crop production, including reductions of greenhouse gas emissions through impacts on soil organic carbon (SOC) dynamics. We investigated the impacts of contrasting application rates of nitrogen (N)-enriched biochar (4 and 8 t ha−1) on the concentrations of total and active SOC, microbial biomass carbon (MBC), soil aggregates, and the carbon (C) pool management index (CPMI) as an indicator of soil quality in tillering and mature subtropical early and late rice in China. Soil salinity and soil bulk density increased, and soil water content generally decreased under the application of N-enriched biochar at 4 t ha−1. Following the application of the biochar, there were greater soil concentrations of SOC and lower concentrations of dissolved organic-C and active labile organic‑carbon, indicating reduced mineralization and enhanced stocks of stable-C. Biochar application (4 and 8 t ha−1) led to lower soil Ca-SOC concentrations and greater soil Fe(Al)-SOC concentrations. Concentrations of Fe(Al)-SOC were greater under the application of N-enriched biochar at 4 t ha−1, indicating the bonding capacity of iron‑aluminum oxide and organic carbon provided by biochar improved levels of SOC fixation. The composition of soil aggregates under each treatment was mainly micro-aggregates (<0.25 mm). The greater soil content of macro-aggregates (>0.25 mm) increased under amendment with 4 t of biochar ha −1 and the greater SOC content led to greater soil aggregate stability. Levels of C pool activity, C pool index, and CPMI reduced following application of the biochar, while C pool activity index increased slightly, indicating an increase in soil quality. These results indicate that the application of N-enriched biochar during rice cultivation may lead to reductions in SOC mineralization and C emissions and increases in soil C sink capacity, due to greater SOC pool stability, thus improving the sustainability of paddy rice production.
280. 题目: Multiple drying aspects shape dissolved organic matter composition in intermittent streams
Water availability is a fundamental driver of biogeochemical processing in highly dynamic ecosystems such as intermittent rivers and ephemeral streams (IRES), which are recognized as the most common fluvial ecosystem globally. Because of their global extent, IRES have a remarkable contribution to organic matter processing, which is expected to intensify as climate change and water extraction expand IRES extension. Nevertheless, the effect of the complexity of the drying process on river biogeochemistry remains unclear. This study investigated how drying aspects affect the dissolved organic carbon (DOC) concentration and composition in 35 streams along a wide flow-intermittence gradient in the NE Iberian Peninsula. To do that, four drying aspects: annual drying duration, annual frequency, duration of the last drying event, and time since the last drying event were characterized. Results showed that DOC concentration and the contribution of humic-like compounds were positively associated with intensifying drying conditions. In addition, protein-like compounds decreased over the drying gradient. More specifically, changes in DOC concentration were driven mainly by annual drying duration, whereas annual drying frequency and the duration of the last drying event jointly explained dissolved organic matter composition. These results suggest that the quantity and composition of dissolved organic matter in streams respond differently to the temporal aspects of the drying process. Our study can help to better anticipate changes in organic matter in the context of climate change.