Abstract. The on-going global warming is causing rapid changes in the carbon cycle of the Arctic. Yet the response of the Arctic to these environmental changes are not fully understood. In this study, we investigate bulk organic parameters (TOC, TN, δ13Corg, δ15N, C/N) and terrestrial n-alkanes (TERR-alkanes) from 19 surface sediments and 5 210Pb-dated sediment cores covering up to the last three centuries from the Chukchi Sea. Downcore profiles indicate increasing OC since the beginning of the Industrial Era in all cores. They also show higher TOC and TN values in southern Chukchi Sea cores coincident with decreasing δ13Corg indicating an increasing contribution of terrestrial OC that is confirmed by TERR-alkanes. Comparison with regional paleo-records and instrumental data emphasize the key role of air temperature and sea ice cover on the OC cycle and vegetation of the surrounding landmasses.
Abstract In this study, we reconstruct three-century of sea ice cover history in the Chukchi Sea from the downcore profile of total organic carbon (TOC) and biomarker proxies, namely the Ice Proxy with 25 carbon atoms (IP25), the di- and tri-unsaturated highly branched isoprenoid (HBI II and HBI III) and two phytosterols (brassicasterol and dinosterol) in three sediment cores from the northern, eastern and southern Chukchi Sea reflecting different sea ice conditions. Our data indicate higher IP25 values in the eastern site and lowest ones in the northern Chukchi Sea site that are consistent with the modern sea ice distribution. They also underline the predominance of sympagic over pelagic production except at the southern site where pelagic production depicts a sharp increased over the last decades. We present a new approach improving the linear relationship between PIIIIP25 (PBIP25) and satellite-derived spring (summer) sea ice concentrations (SIC) to advance sea ice reconstructions across the Arctic Ocean. This method results in better assessment of PIP25 derived SIC and reconstruction of past seasonal sea ice conditions. They indicate marginal sea ice conditions at the three sites until 1950s-1960s followed by a reduction of seasonal sea ice as captured by PBIP25 index.
Abstract The integration of thermal and electromagnetic interference (EMI) insulation is of great significance for fields such as aerospace that face extreme environments. The challenge lies in ensuring that the protective layer is lightweight while simultaneously possessing the ability to suppress heat conduction, heat convection, thermal radiation, and electromagnetic radiation. To address these challenges, we propose a novel ultralight all‐fiber‐structure composite sponge, yttria‐stabilized zirconia/polyvinyl butyral‐supported silver (YAP) nanofiber sponge, with ultralight mass (∼65 mg/cm 3 ), exceptionally low thermal conductivity (21 mW/m K at 25°C, and 329 mW/m K at 500°C), and remarkable EMI shielding effectiveness (∼62.6 dB). Moreover, benefiting from its all‐fiber‐structure, the YAP nanofiber sponge can endure 100 cycles of compression up to 50% of its original volume while retaining its mechanical properties with minimal degradation. These characteristics render YAP nanofiber sponge an ideal material for integrated thermal and EMI insulation, offering a promising solution to the rigorous demands of extreme environment protection such as space exploration.
Excessive fertilization is often applied to produce rice. To reduce nitrogen loss and improve nitrogen use efficiency (NUE), we studied the effects of application depth (surface application, 5 and 10 cm) and shape of nitrogen fertilizers (row application and deep application of large granular fertilizer) on rice growth, soil N distribution and ammonia volatilization. The results showed that grain yield, shoot biomass and total dry biomass of the treatment with N in large granular fertilizer applied at 10 cm depth were significantly higher than those of all other treatments. Moreover, compared with the surface application, the N recovery efficiency and the N agronomic efficiency of deep application treatments were enhanced by 18.1–52.3% and 35.6–95.6%, respectively. Deep application significantly increased NH4+-N concentration at their fertilization points. During the growth season, N in large granular fertilizer treatments (mixed with clay to form an unusually large pellet of 1.0–1.5 cm in diameter) distributed closer to the roots, while N in other treatments, including row application treatments, was more widely distributed. Compared with the surface application, deep application significantly reduced NH3 volatilization and NH4+-N concentration in surface water by 58.7–64.8% and 26.0–72.5%, respectively. Furthermore, the NH3 volatilization from large granular treatment was 7.6–11.0% lower than that in the row application. In conclusion, applying N in large granular fertilizer at 10 cm depth reduces ammonia volatilization, and improves rice growth and grain yield, indicating improved NUE and lowered environmental risks.
This study focused on four vegetation restoration stages of grasslands, shrublands, secondary forests and primary forests in the typical karst peak-cluster depression. The soil core method was used to collect fine roots with 2 mm or less in diameter in three layers (0-10, 10-20, 20-30 cm). The biomass, morphological characteristics of fine roots and their relationship with soil properties were analyzed. The results showed that fine root biomass ranged between 194.63 and 255.19 g·cm-2 in different vegetation restoration stages. Most of fine roots distributed in the surface soil of 0-10 cm, which accounted for more than 60% of the total biomass in the soil layer of 0-30 cm. No significant difference was found among different stages in fine root biomass. There was significant difference among different stages in the specific root length and specific surface area of fine roots. Both parameters were gradually decreased with vegetation forward restoration from grassland to primary forest. More than 66% root length and 64% root area were distributed in the surface soil of 0-10 cm. The length and area of most of the fine root were in the diameter class of 0-0.5 mm and 0.5-1mm, respectively. These two levels of the root length and root area accounted for more than 87% and 72% of the total amount, respectively. Results from the redundancy analysis showed that there were different correlations between karst peak-cluster depression vegetation community characteristics and soil properties, with soil organic carbon, available potassium, and total nitrogen having a great influence on the characteristics of fine roots. It is an effective strategy for plants to better adapt to the habitats.以喀斯特峰丛洼地不同植被恢复阶段的草丛、灌丛、次生林和原生林为研究对象,采用土芯法,分 0～10、10～20、20～30 cm等3层获取群落活细根(直径≤2 mm),分析其生物量、形态特征及其与土壤性状的关系.结果表明: 各恢复阶段细根生物量为194.63～255.19 g·m-2,集中分布在0～10 cm表层土壤中,占0～30 cm土层总生物量60%以上,不同恢复阶段群落生物量的差异不显著;细根比根长和比表面积在不同恢复阶段差异显著,随着植被由草丛向原生林正向恢复而逐渐降低;超过66%的根长和64%的根面积分布在0～10 cm表层土壤中,多数细根根长和根面积均在0～0.5 mm和0.5～1 mm径级,这两级根长和根面积占其总量的87%和72%以上.冗余分析表明,喀斯特峰丛洼地植物群落细根特征与土壤性状之间存在着不同的相关性,其中土壤有机碳、速效钾和全氮对细根特征影响较大.这是植物长期适应生境条件形成的有效策略.
The stoichiometric characteristics of C, N, and P in plants result from long-term adaptation to environmental conditions. In this study, we analyzed leaf, branch, and soil C, N, and P stoichiometry in a karst primary forest plant community in China. The results showed that N and P content in leaves was higher than that in branches, while C content in the latter was higher than in leaves. Moreover, the coefficient of the variation in C, N, and P content in branches was greater than that in leaves but there was no significant difference in said coefficients in soil. The values of the C:N and C:P ratios were both branch > leaf > soil, whereas the value of the N:P ratio was leaf > branch > soil. There was also a significant positive correlation between leaf nitrogen (LN), leaf phosphorus (LP), branch nitrogen (BN), and branch phosphorus (BP) concentrations but no significant correlation between leaf carbon (LC), branch carbon (BC), and other element concentrations. We found that leaf stoichiometry was strongly influenced by species diversity, whereas branch stoichiometry was mainly influenced by leaf and species diversity; the environmental factors influencing the stoichiometric characteristics of leaves and branches were mainly altitude, soil pH, and total soil P. Finally, these results are relevant as they are helpful to understand the adaptation mechanisms and eco-geochemical processes in karst forest plants and they can also provide a scientific basis for vegetation restoration and reconstruction in these degraded ecosystems.
In karst ecosystems, plants absorbing smaller amounts of nutrients, owing to shallow soil, show limited growth. In addition, fine roots (diameter < 2 mm) contribute to the regulation of nutrient cycles in terrestrial ecosystems. However, the spatial and temporal variations of fine root biomass in different vegetation types of the karst region remains poorly understood. In this study, we investigated the seasonal and vertical variation in biomass, necromass, and total mass of fine roots using sequential soil coring under different stages of vegetation restoration (grassland, shrubland, secondary forest, and primary forest) in Southwest China. The results showed that the fine root biomass and necromass ranged from 136.99 to 216.18 g m-2 and 47.34 to 86.94 g m-2, respectively. The total mass of fine roots and their production ranged from 187.00 to 303.11 g m-2 and 55.74 to 100.84 g m-2 year-1, respectively. They showed a single peak across the vegetation restoration gradient. The fine root biomass and total fine root mass also showed a single peak with seasonal change. In autumn, the fine root biomass was high, whereas the necromass was low. Most of the fine roots were concentrated in the surface soil layer (0-10 cm), which accounted more than 57% root biomass, and decreased with increasing soil depth. In addition, fine root production showed a similar vertical pattern of variation with biomass. Overall, our results suggested that fine roots show clear seasonal and vertical changes with vegetation succession. Moreover, there was a higher seasonal fluctuation and a greater vertical decreasing trend in late-successional stages than in the early-successional stages. The conversion of degraded land to forest could improve the productivity of underground ecosystems and vegetation restoration projects in the fragile karst region should, therefore, continue.
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