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• Spatiotemporal DSL variation and associated forcings were explored at a semi-humid catchment. • Land use type was the dominant control on DSL variation at a catchment scale. • DSL response to meteorological factors differed between the semiarid and semi-humid catchments. • The mixed "forest/shrubland + grass" plantation type is recommended for the semi-humid catchment. The formation of dried soil layers (DSLs) is a broad consequence of climate change (i.e., through temperature increases and/or precipitation decreases) and poor land management practices, where these layers exist has severe negative effects (i.e., retardation of vegetation, negative water cycle balance) on the sustainability of restored ecosystems and health of agriculture. Because of the effort and time required, only sporadic in situ measurements on spatial and temporal DSL variation have been reported, particularly at a catchment scale. However, this information is essential for understanding mechanisms associated with evolutionary DSL processes as well as developing effective land management techniques. Accordingly, this study monitored soil water content to a 5 m depth over a 5-year period in a semi-humid catchment on the Loess Plateau while also investigating temporal DSL dynamics and dominant controls. In the semi-humid catchment, DSLs occurred at 90.7 % of all sampling sites. Spatially and temporally averaged DSL formation depth (DSLFD), DSL thickness (DSLT), and DSL soil water content (DSL-SWC) within the 0–5 m profile were 170 cm, 262 cm, and 9.52 %, respectively. Forest and shrubland DSL regimes were drier than those of grassland. These three DSL indices exhibited significant correlation with temperature variables, while only DSLFD variables significantly correlated to precipitation. Land use type was the predominant control of DSL variation at a catchment scale. A spatial DSLT variation comparison under different land use treatment positions determined the feasibility of planting grass at an upslope position and mixed forest/shrubland + grass at mid-slope and downslope positions in the semi-humid catchment, which provides a good case study for afforestation practices at a catchment scale. Findings from this study are intended to aid in catchment soil and water conservation, soil drought mitigation, and sustainable vegetation management practices on the Loess Plateau as well as other water-limited regions worldwide. [ABSTRACT FROM AUTHOR]

• Land-use types, seasons, slope position significantly affected SOC and SWC. • Revegetation increased SWS consumption and SOC accumulation. • There was a positive linear relationship between SOC and SWC. • Planting grass and shrubs is recommended in the semi-arid hilly and gully regions. Understanding the response of soil organic carbon (SOC) and moisture to different land-use types, slope positions, seasonal variations, and their interactions has great significance for land use and management. However, the coupling effects of SOC and soil moisture in typical hilly and gully regions are still elusive. Therefore, in this study, five different land-use types, including cropland, abandoned land, grassland, shrubland, and forestland were selected in a typical Chinese loess hilly-gully region, and soil samples were collected from 0 to 200 cm profiles at the upper, middle, and lower slope positions in four seasons. The results demonstrated that the distributions of SOC and soil moisture were jointly significantly affected by land-use types, seasons, and slope positions (P < 0.01). Average SOC content was found to be highest in the shrubland, followed by grassland, abandoned land, forestland, and cropland. SOC storage at the lower slope position was 10.97% higher than that at the upper slope position. SOC storage in winter was 45.47% higher than that in summer. SOC storages of abandoned land, grassland, shrubland, and forestland were 17.38%, 33.08%, 52.52% and 1.26% more than that of cropland, respectively. Soil moisture fluctuated greatly in 0–100 cm layers and was stable beneath the 100 cm layers, which was highest in autumn, and lowest in summer. Whereas, under different land-use types, the soil moisture of cropland was the highest, especially significantly higher than all revegetated treatments in the 60–200 cm soil layers. Compared with cropland, soil water storage at other land-use types was averagely 36.45 % lower in the entire 200 cm soil profile. SOC was positively correlated with soil moisture under different factors. Thus, we recommend planting shrub and grass in watersheds with serious soil erosion in the semi-arid hilly and gully region, because they can sequestrate more SOC and retain more soil water. [ABSTRACT FROM AUTHOR]

Fixed dunes are indicators of successful recovery of desertified land after several years of vegetation restoration. Land use profoundly influences soil properties; however, the effects of changes in land use, after the dunes are fixed, on soil physical, chemical and microbial biomass properties are still unclear. This study investigates the soil physical and chemical properties and soil microbial biomass in a desertified land located in the Xiaojihan desertification control station in northern Shaanxi province, where land use changed from shrub land to arboreal land, arable land and nursery garden. No significant changes in soil properties were found when shrubland was changed to arboreal land. However, changing the fixed desertified land from shrub land to arable land and nursery garden decreased soil porosity, but significantly increased soil bulk density (BD), soil organic matter (SOM), cation exchange capacity (CEC), total nitrogen (TN) and available nutrients (N, P, K). Soil microbial biomass carbon (MBC), nitrogen (MBN) and phosphorus (MBP), as well as microbial quotient (MBC/SOC, MBN/TN, MBP/TP), decreased significantly. No significant changes were detected in soil texture, total phosphorus (TP) and total potassium (TK). Results of this study indicated that agricultural land use can improve the fertility of fixed desertified land; however, soil microbial biomass could decrease. Therefore, conversion of fixed dunes to agricultural usage is full of risks. [ABSTRACT FROM AUTHOR]

• Multiple runoff components in a soil-epikarst system were directly monitored. • Critical zone structure exerted more evident influence on carbon loss than land uses. • Thicker soils with less undulating soil-epikarst contact facilitated carbon loss. • Artificial forage grasslands reduced carbon loss. In karst hillslopes, the soil-epikarst system is not only the main reservoir of soluble carbon, but also the hot spots of hydrological and biogeochemical processes. However, the soluble carbon loss mechanism through various runoff components occurring in the soil-epikarst system is not clear. We hypothesize that the karst critical zone structure determines the runoff and soluble carbon loss, and that these response processes can be regulated by land use. 12 experimental plots on a typical karst hillslope (each with 5 × 20 m projected area) of four land uses (naturally recovered shrubland, forage grassland, economic forest land, and cropland) were intensively instrumented for separately monitoring surface, subsurface, and epikarst seepage runoffs and their dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) concentration. Results show that economic forest land had the highest total runoff and soluble carbon loss, followed by cropland, naturally recovered shrubland, and forage grassland. Generally, karst critical zone structure was the most important factors for controlling DOC and DIC loss through surface, subsurface, and epikarst seepage runoffs. Critical zones with thicker soil and less undulating soil-epikarst contact were more susceptible to runoff and soluble carbon loss. Although not as important as critical zone structures, land use can effectively regulate runoff and prevent soluble carbon loss by affecting rainfall partitioning in karst hillslopes. Planting forage grassland is an effective method of reducing carbon loss, due to its remarkable ability of reducing runoff in the soil-epikarst systems. Our results provide useful insights for determining appropriate land uses and optimizing soil and water conservation strategies in karst hillslopes. [ABSTRACT FROM AUTHOR]

Abstract: Land use change is one of the major factors that affect soil organic carbon (SOC) variation and global carbon balance. Since the late 1970s, a significant area of the hilly Loess Plateau has undergone major land use changes during several revegetation programs, especially in the Grain for Green Project. However, so far there has not been a comprehensive study to determine temporal and spatial variations in SOC due to revegetation in this region, which hampers accurate predictions of the SOC sequestration potential and the land use change impacts. In this study, slope cropland and five typical revegetation types in the hilly Loess Plateau were selected, and then classified into 36 groups according to different revegetation years and landforms to investigate temporal and spatial variations of SOC and the impacts of relevant factors following revegetation. The results showed that the SOC concentration in the top soil horizon (0–5cm) increased most significantly with revegetation and that increases in SOC slowed with increasing soil depth, but coefficient of variations in different soil horizons indicated that revegetation could cause SOC concentration differences at up to a 30cm depth. Temporal variation in SOC occurred in two main phases in replanted cropland: in the first 10 or 15yr, the profile mass of SOC (SOC density, SOCD) increased slightly; after this phase, SOCD increased significantly, with sequestration rates of 0.69, 0.55 and 0.24t·ha−1·yr−1 (revegetation 10 to 35yr) for planted woodland, planted shrubland and abandoned cropland, respectively. The SOC sequestration rate in wild grassland was 0.23t·ha−1·yr−1 (revegetation 10 to 35yr), which was similar to that in abandoned cropland. In contrast, the SOCD in wild shrubland increased rapidly in the first 10yr, with a rate of 0.93t·ha−1·yr−1, and then by 0.56t·ha−1·yr−1 over the next 25years. SOCD spatial differences in different landforms had reached several times the annual SOCD increment and followed a new trend after revegetation: SOC sequestration in shady slope areas was significantly higher than in sunny slope areas, but no significant difference was found between gentle slopes and steep slopes after revegetation. A general linear model was used to identify the factors that were most relevant to SOC variation. Revegetation years accounted for nearly half of the total contribution to SOC variation (42%), and land use type was responsible for 33% of SOC variation. SOCD distribution in a watershed confirmed that variables of land use and years after revegetation dominated SOC variation. Landforms had a small influence on SOC variation at the regional scale, but the influence of the slope aspect was still large. The SOC sequestration rate was about 0.21 to 0.64t·ha−1·yr−1 with revegetation in the hilly Loess Plateau, which was highest in wild shrubland, followed by planted woodland, planted shrubland, abandoned cropland and wild grassland. Considering the large area of revegetation and relatively high SOC sequestration rate, SOC sequestration in this region should contribute significantly to decreasing the carbon concentration in atmosphere. [Copyright &y& Elsevier]

Abstract: Spatial patterns of soil properties are linked to patchy vegetation in arid and semi-arid landscapes. The patterns of soil properties are generally assumed to be linked to the ecohydrological functioning of patchy dryland vegetation ecosystems. We studied the effects of vegetation canopy, its spatial pattern, and landforms on soil properties affecting overland flow and infiltration in shrublands at the Sevilleta National Wildlife Refuge/LTER in central New Mexico, USA. We studied the patterns of microtopography and saturated conductivity (Ksat), and generally found it to be affected by vegetation canopy and pattern, as well as landform type. On gently sloping alluvial fans, both microtopography and Ksat are high under vegetation canopy and decay with distance from plant center. On steeper hillslope landforms, only microtopography was significantly higher under vegetation canopy, while there was no significant difference in Ksat between vegetation and interspaces. Using geostatistics, we found that the spatial pattern of soil properties was determined by the spatial pattern of vegetation. Most importantly, the effects of vegetation were present in the unvegetated interspaces 2–4 times the extent of vegetation canopy, on the order of 2–3 m. Our results have implications for the understanding the ecohydrologic function of semi-arid ecosystems as well as the parameterization of hydrologic models. [Copyright &y& Elsevier]

• Soil respiration including winter CO 2 efflux was studied in the desert-oasis region. • Annual soil CO 2 emissions varied from 176 to 918 g C m−2 across the study ecosystems. • The ratio of cold season CO 2 emissions to the annual was 6–15% across ecosystems. • Land use conversion influenced soil respiration across the desert-oasis ecoregion. Quantifying annual soil CO 2 emissions and the effects of physical and geochemical factors on soil CO 2 efflux will improve the carbon budget estimates, as well as enhance predictions of how soil CO 2 emission will response to climate change in arid areas. To data, variability in soil respiration rates caused by land use conversion in the desert-oasis ecoregion of Northwest China remains poorly characterized, especially the contribution of cold season (November-February) CO 2 emission. Soil respiration was measured in a Haloxylon ammodendron desert shrubland, a Zea mays cropland, a Populus gansuensis forest, and a Tamarix chinensis Lour wetland using a LI-COR 8100 Soil Respiration Observation System from April 2016 to March 2019. Annual soil CO 2 emissions totaled 176, 778, 918, and 397 g C m−2 in the desert shrubland, cropland, forest, and wetland, respectively. The ratio of cold season CO 2 emissions to the annual varied from 6 to 15% across ecosystems. Therefore, ignoring cold season CO 2 emissions would lead to underestimates of carbon losses in the desert-oasis ecoregion. The soil respiration rate at 10 °C was influenced by soil organic carbon content in all four ecosystems. In the cropland and forest, soil respiration rate was affected by the interaction of soil moisture and soil temperature, while in the wetland and desert shrubland, soil respiration was sensitive to a single factor, soil temperature. Land use conversion induced differences in organic matter accumulation, soil temperature, and soil moisture, and as a consequence, produced variability in soil respiration rates across the desert-oasis ecoregion. [ABSTRACT FROM AUTHOR]