Reforestation regulated soil bacterial community structure along vertical profiles in the Loess Plateau

IntroductionReforestation is a widely used strategy for ecological restoration in areas facing ecological degradation. Soil bacteria regulate many functional processes in terrestrial ecosystems; however, how they respond to reforestation processes in surface and deep soils remains unclear.MethodsArtificial Robinia pseudoacacia plantation with different stand ages (8, 22, and 32 years) in a typical fallow forest on the Loess Plateau was selected to explore the differential response of soil bacterial community to reforestation in different soil depths (surface 0–200 cm, middle 200–500 cm, and deep 500-100 cm). Soil bacterial diversity, community composition and the co-occurrence patterns, as well as the functions were analyzed.Results and discussionThe results showed that alpha diversity and the presence of biomarkers (keynote species) decreased with the increasing soil depth, with a sharp reduction in family-level biomarker numbers in 500–1,000 cm depth, while reforestation had a positive impact on bacterial alpha diversity and biomarkers. Reforestation induced a more loosely connected bacterial community, as evidenced by an increase of 9.38, 22.87, and 37.26% in the average path length of the co-occurrence network in all three soil layers, compared to farmland. In addition, reforestation reduced the hierarchy and complexity but increased the modularity of the co-occurrence network in top and deep soil layers. Reforestation also led to enrichment in the relative abundance of functional pathways in all soil layers. This study sheds light on the strategies employed by deep soil bacteria in response to reforestation and underscores the significant potential of deep soil bacteria in terrestrial ecosystems, particularly in the context of human-induced environmental changes

Deciphering microbiomes dozens of meters under our feet and their edaphoclimatic and spatial drivers

24 páginas.- 7 figuras.- referenciasMicrobes inhabiting deep soil layers are known to be different from their counterpart in topsoil yet remain under investigation in terms of their structure, function, and how their diversity is shaped. The microbiome of deep soils (>1 m) is expected to be relatively stable and highly independent from climatic conditions. Much less is known, however, on how these microbial communities vary along climate gradients. Here, we used amplicon sequencing to investigate bacteria, archaea, and fungi along fifteen 18-m depth profiles at 20-50-cm intervals across contrasting aridity conditions in semi-arid forest ecosystems of China's Loess Plateau. Our results showed that bacterial and fungal α diversity and bacterial and archaeal community similarity declined dramatically in topsoil and remained relatively stable in deep soil. Nevertheless, deep soil microbiome still showed the functional potential of N cycling, plant-derived organic matter degradation, resource exchange, and water coordination. The deep soil microbiome had closer taxa-taxa and bacteria-fungi associations and more influence of dispersal limitation than topsoil microbiome. Geographic distance was more influential in deep soil bacteria and archaea than in topsoil. We further showed that aridity was negatively correlated with deep-soil archaeal and fungal richness, archaeal community similarity, relative abundance of plant saprotroph, and bacteria-fungi associations, but increased the relative abundance of aerobic ammonia oxidation, manganese oxidation, and arbuscular mycorrhizal in the deep soils. Root depth, complexity, soil volumetric moisture, and clay play bridging roles in the indirect effects of aridity on microbes in deep soils. Our work indicates that, even microbial communities and nutrient cycling in deep soil are susceptible to changes in water availability, with consequences for understanding the sustainability of dryland ecosystems and the whole-soil in response to aridification. Moreover, we propose that neglecting soil depth may underestimate the role of soil moisture in dryland ecosystems under future climate scenarios.This project was supported by the Joint Key Funds of the National Natural Science Foundation of China (U21A20237), the Strategic Priority Research Program of Chinese Academy of Sciences (XDB40020202). M.D.-B. acknowledges support from TED2021-130908B-C41/AEI/10.13039/501100011033/Unión Europea NextGenerationEU/PRTR and from the Spanish Ministry of Science and Innovation for the I + D + i project PID2020-115813RA-I00 funded by MCIN/AEI/10.13039/501100011033. R.O.H. was funded by the Ramón y Cajal program of the MICINN (RYC-2017 22032), by the R&D Project of the Ministry of Science and Innovation PID2019-106004RA-I00 funded by MCIN/AEI/10.13039/501100011033, and by the European Agricultural Fund for Rural Development (EAFRD) through the “Aid to operational groups of the European Association of Innovation (AEI) in terms of agricultural productivity and sustainability,” Reference: GOPC-CA-20-0001Peer reviewe

High T3 Induces β-Cell Insulin Resistance via Endoplasmic Reticulum Stress

Hyperthyroidism can cause glucose metabolism disorders and insulin resistance. Insulin resistance in muscle and adipose tissues has been extensively studied, whereas investigations on β-cell insulin resistance are limited. This study preliminarily explored the effects of high T3 levels on β-cell line (MIN6) insulin resistance, as well as the roles of endoplasmic reticulum stress (ERS). In this study, we treated β-cell line with T3, with or without an inhibitor of phosphotyrosine phosphatases (PTPs, sodium vanadate) or ERS inhibitor (4-PBA). The results indicated that high levels of T3 significantly inhibited insulin secretion in β-cell line. In addition, we observed an upregulation of p-IRS-1ser307 and downregulation of Akt. These results can be corrected by sodium vanadate. Moreover, high T3 levels upregulate the ERS-related proteins PERK, IRE1, ATF6, and GRP78, as well as ERS-related apoptosis CHOP and caspase-12. Similarly, this change can be corrected by 4-PBA. These results suggest that high T3 levels can induce insulin resistance in β-cell line by activating ERS and the apoptotic pathway

Factors controlling spatial variation in soil aggregate stability in a semi-humid watershed

Soil aggregate stability (SAS) is a key soil property that affects soil erosion and soil ability to support ecosystem functions. The effects of different environmental factors on SAS are extensively documented. However, the relative importance of the factors that drive variation in SAS at watershed scale is not entirely clear. To investigate the effects of the interactions of environmental variables on spatial variation in SAS, 88 sampling sites were selected across an entire watershed (1.1 km2) on the Chinese Loess Plateau (CLP), from where undisturbed soil samples were collected at the 0-10 and 10-20 cm soil depths. Three indices were used to evaluate the SAS - water-stable aggregates greater than 0.25 mm (WSA>0.25, %), mean weight diameter (MWD, mm) and mean geometric diameter (MGD, mm). The results showed that variation of SAS across the watershed was moderate, with coefficient of variation (CV) of 23.5-38.9 %. From combined Spearman's correlation analysis (r), redundancy analysis (RDA) and structural equation modelling (SEM), it was found that soil intrinsic properties, mainly soil texture and organic carbon content (SOC), were the primary control on SAS variation. Topographic attributes, primarily wetness index (TWI) and altitude, were also important controls on SAS. These controls were either the direct or indirect effect through SOC dynamics, spatial distribution of land use (LUT) or vegetation cover (NDVI). The effect of LUT on SAS was mainly driven by SOC and TWI at the 0-10 cm depth but by NDVI and TWI at the 10-20 cm depth. SAS was positively correlated with sand content and SOC, but negatively correlated with silt content, altitude, TWI and NDVI. For LUT, SAS in the apple orchard was significantly lower than in shrubland and grassland, however, it was comparable with that in forest. Considering the effects of improving soil structure and the related economic cost, natural restoration of grassland was a good choice for preventing soil erosion in the study area. The results of this study could deepen our understanding of the controls on SAS variation and therefore become useful in soil management and vegetation restoration decisions on CLP and other regions with similar conditions

Factors controlling the spatial variability of soil aggregates and associated organic carbon across a semi-humid watershed

Y Soil aggregates (SA) play crucial roles in soil organic carbon (SOC) sequestration. Different SA fractions contribute differently to the sequestration of SOC. However, few studies have examined the factors controlling SA fractions and associated SOC contents across a watershed. Soil samples were collected at 0-10 cm (surface layer) and 10-20 cm (subsurface layer) from 88 sites across a semi-humid watershed (1.1 km(2)) on the Loess Plateau, China. These samples were separated into macroaggregates (MA), microaggregates (MI), and silt + clay fractions (SC) by wet-sieving, and SOC content of each fraction was determined. The objectives were to: 1) investigate the spatial variability of SA fractions and associated SOC contents as well as their main controls across an entire watershed, and 2) explore the linkages between soil aggregation and SOC sequestration. The bulk and aggregate SOC contents of all SA fractions showed moderate variability, with coefficient of variations of 23.3-31.9%. Geostatistical analysis indicated that the spatial patterns of SA fractions and SOC content varied with aggregate size. From combined Spearman's correlation analysis and structural equation modelling, we found that soil texture was an important control on the spatial variability of all SA fractions and associated SOC contents. Vegetation dynamics and management practices associated with land use were also important controls on MA and MI and their associated SOC contents, especially in the surface layer. However, SC and its associated SOC content were more sensitive to ecohydrological processes related to topography. Among the land uses, grassland had the greatest SOC sequestration potential. The fine roots of herbs can wrap MI in MA and increase SOC content within MA, which is the primary mechanism responsible for SOC sequestration in grasslands. These results indicate that using vegetation with fine root systems for restoration is a good strategy to increase SOC sequestration in this region. (C) 2021 Elsevier B.V. All rights reserved

Watershed spatial heterogeneity of soil saturated hydraulic conductivity as affected by landscape unit in the critical zone

The spatial heterogeneity and related driving factors of the saturated hydraulic conductivity (K-s) in the Earth's critical zones (CZs) have been documented widely in the literature. However, information regarding the effect of distinct landscape units (i.e., Slope-land, Gully-land, and Tableland) on such heterogeneity at the watershed scale in CZs characterized by complex topographic conditions remains scant. In the current study, we collected undisturbed and disturbed soil samples from the surface soil layer (0-5 cm) at 1195 sampling sites across the ShuangChaGou watershed (0.22 km(2)) in the Chinese Loess Plateau (CLP). According to classical and geostatistical analyses combined with the structural equation model (SEM), the mean K-s followed the sequence Slope-land (0.25 cm.min(-1)) > Gully-land (0.187 cm.min(-1)) > All samples (0.186 cm.min(-1)) > Tableland (0.14 cm.min(-1)) (p < 0.05), with the K-s values exhibiting moderate variations except for the Gully-land (strong variation). The LogK(s) spatial variation characteristics (i.e., the anisotropy ratio, effective range, and C/(C-0 + C)) considering the influence of topography varied among the landscape units and the entire watershed. The SEM identified that soil bulk density, saturated soil water content, silt content, plan curvature, NDVI, and slope gradient were the controlling factors in sequence affecting the K-s variation for All samples (AS). In contrast, factors controlling K-s variations were different under the Tableland, Gully-land, Slope-land, and AS. The magnitudes, spatial variations and controlling factors of the surface K-s were greatly affected by the landscape units. Our study provided a robust assessment of the spatial variation of K-s in CZs involving complicated topographic features, highlighting the utility of dividing distinct landscape units when evaluating the K-s variation. A good understanding of this information is helpful for developing distributed hydrological models and for evaluating water and solute transportation in CZs of the CLP and similar regions around the world

Transference of Robinia pseudoacacia water-use patterns from deep to shallow soil layers during the transition period between the dry and rainy seasons in a water-limited region

Soil water plays a critical role in determining plant survival and growth globally, especially in water-limited regions. This study explores water-use characteristics of Robinia pseudoacacia during the transition period between the dry and rainy seasons in the Chinese Loess Plateau (CLP). A stable isotope technique (delta O-18 and delta D) and two complementary approaches (i.e., the direct inference method and the MixSIAR model) were used to distinguish water source changes during this transition period. Based on delta O-18 and delta D distribution patterns, we subdivided a 500 cm soil profile into four potential water sources: shallow (0-40 cm), intermediate-shallow (40-120 cm), intermediate (120-200 cm) and deep (200-500 cm). During the transition period, R. pseudoacacia exhibited different water uptake patterns. In April 26.2% and 48.4% of water uptake derived from the 40 to 120 and 200 to 500 cm soil profile layers; in May, 21.5%, 24.5% and 37.4% of water was absorbed from the 0 to 40, 40 to 120 and 200 to 500 cm soil profile layers. In June and July, 51.6% and 53.6% of the water mainly derived from the 0 to 120 cm soil profile layer, respectively. During the dry season (April), the trend in water uptake shifted to the deep soil layer, potentially a key period for the onset of soil desiccation in this soil layer. As precipitation increased, the proportion of water uptake from the shallow and intermediate-shallow soil layers increased. Because water-use pattern characteristics could provide important information on the development of the dried soil layer (DSL), the stable isotope technique could help reveal the water sources used by trees while also offering insight into water movement mechanisms of local ecosystems. Given its usefulness, the application of the stable isotope technique should be expanded in analyzing practical ecohydrological issues that occur in deep soils in the future

Assessing the value of electrical resistivity derived soil water content: Insights from a case study in the Critical Zone of the Chinese Loess Plateau

Acquiring data for the soil water content (theta) is important for assessing vegetation growth, drought, and climate change. However, it is a time-consuming and labor-intensive task that is especially challenging in deep soils. Therefore, we introduce the noninvasive technique of electrical resistivity tomography (ERT) for indirectly determining theta through the development of prediction models for loessial regions under different site conditions (i.e., soil texture, land use, soil depth, and dry/wet conditions). We obtained 2769 pairs of electrical resistivity (rho) and theta datasets using ERT (53 sites) and a neutron probe (69 access tubes) on the Chinese Loess Plateau. We built linear and nonlinear models correlating rho and theta and selected the best model according to the coefficient of determination (R-2) and root-mean-square error (RMSE). The uncertainty and sensitivity of ERT-derived theta were further evaluated and acceptable results were obtained. The new models correlating rho and theta under different site conditions are the first set of models based on field data from a loessial region, and their acceptable performance makes them applicable for measuring different soil parameters in the Loess Plateau and possibly other loessial regions around the world