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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]

Changes in land use type can lead to variations in soil water characteristics. The objective of this study was to identify the responses of soil water holding capacity (SWHC) and soil water availability (SWA) to land use type (grassland, shrubland and forestland). The soil water characteristic curve describes the relationship between gravimetric water content and soil suction. We measured the soil water characteristic parameters representing SWHC and SWA, which we derived from soil water characteristic curves, in the 0–50 cm soil layer at sites representing three land use types in the Ziwuling forest region, located in the central part of the Loess Plateau, China. Our results showed that the SWHC was higher at the woodland site than the grassland and shrubland, and there was no significant difference between the latter two sites, the trend of SWA was similar to the SWHC. From grassland to woodland, the soil physical properties in the 0–50 cm soil layer partially improved, BD was significantly higher at the grassland site than at the shrubland and woodland sites, the clay and silt contents decreased significantly from grassland to shrubland to woodland and sand content showed the opposite pattern, the soil porosity was higher in the shrubland and woodland than that in the grassland, the soil physical properties across the 0–50 cm soil layer improved. Soil texture, porosity and bulk density were the key factors affecting SWHC and SWA. The results of this study provide insight into the effects of vegetation restoration on local hydrological resources and can inform soil water management and land use planning on the Chinese Loess Plateau. [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]

We aimed to test the effect of soil drought conditions projected by general circulation models and eco-physiological models for the next few decades on emission rates of isoprenoids by Mediterranean shrublands. We conducted a field experiment in which we generated soil drought (ca. 12%-20% decreased soil moisture) using automatically sliding curtains, and we measured foliar isoprenoid emissions in the three dominant species of the studied shrubland (Erica multiflora L., Globularia alypum L., and Pinus halepensis L.) in two different annual periods. Monoterpene emissions were detected in the three studied species, but isoprene emissions were significantly detected only in E. multiflora. Main volatile terpenes emitted by the three species were α-pinene, β-myrcene, limonene, and Δ³-carene. In general, maximum isoprenoid emission rates were found in the hottest periods, and minimum emission rates were found in winter. Isoprene emissions in E. multiflora ranged between practically 0 μg g-1 (dry matter) h-1 in winter 2005 and 57 μg g-1 (dry matter) h-1 in summer 2003. Isoprene emissions were 75% lower during the dry second annual period, 2004-2005, than during the first year, 2003-2004. In E. multiflora, there was an overall decrease of 19% in isoprene emissions in response to soil drought. Conversely, monoterpene emissions increased by 26.4% in drought treatment. In G. alypum, there was an overall increase of 75% in terpene emissions in response to soil drought. In P. halepensis, drought treatment increased terpene emission rates by 156%. Drought treatment affected the emissions mainly in the hottest seasons, spring and summer. There were strong compound-specific, species-specific, interannual, and seasonal changes in the emission rates and in their response to the treatments. These data might help to improve prediction algorithms, inventories, and modeling of isoprenoid emissions and of their response to climate change (decreased isoprene emissions and increased monoterpene emissions under moderate or short-term drought and decreased emissions under severe or long-term drought), but the great variability highlights the difficulty of the task. [ABSTRACT FROM AUTHOR]

• A novel method quantifies Q 10 -soil moisture relationships. • Rs suppressed in cropland and orchard at higher soil water content, but not in grassland and shrubland. • Q 10 in shrubland showed least sensitivity to soil moisture variation. • Mean growing season Rs is more sensitive to soil moisture variation in grassland and shrubland. Soil respiration (Rs) in drylands is strongly influenced by precipitation. However, there is a lack of long-term studies on how land-use conversion impact the Rs's responds to precipitation variations. In situ Rs, soil moisture and soil temperature were monitored in cropland, and cropland converted jujube orchard, grassland and shrubland in the semiarid Loess Plateau, China for four years with significant interannual precipitation variation. Q 10 -soil moisture relationships were quantified by selecting observations within limited range of soil moisture. As soil moisture increased, Rs was found to be markedly suppressed in cropland and jujube orchard with great disturbance, with volumetric water content exceeding 0.15 and 0.16, respectively, but increased in grassland and shrubland with few disturbances. Q 10 became saturated as soil moisture increased in cropland, and was linearly correlated with soil moisture in jujube orchard, grassland and shrubland. Q 10 was least sensitive to soil moisture variation in shrubland, which was characterized by a nitrogen-fixing shrub. The interannual variation in mean growing season Rs (MGR) was positively correlated with mean soil moisture. The difference in MGR between land-use types was significant except during the extreme drought year: converting cropland to jujube orchard saw a reduction in MGR by 5–18%, while converting cropland to grassland and shrubland saw an increase in MGR by 16–53% and 67–126%, respectively. This corresponded with a greater sensitivity of MGR to soil moisture in grassland and shrubland. These results suggest a greater response of soil carbon emission in the land-use applied with afforestation or restoration to the enhanced soil moisture as precipitation intensify, compared to agricultural land-use. [Display omitted] [ABSTRACT FROM AUTHOR]

• 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]

• Watershed scale soil water to a depth of 500 cm was investigated from 2013 to 2016. • Half of the 500-cm profiles were drying out below 125 cm, and dried soil layers responded strongly to rainfall in wet years. • DSLT and DSLFD were controlled by climatic variables in time, and DSL-SWC was controlled by land use and topography in space. • Plan curvature, slope gradient, clay and silt content were the dominant factors of DSLs both in space and time. • Grassland may be the optimum land use type to minimize DSL occurrences. Soil drought caused by climatic change and/or poor land management in arid and semi-arid regions are seldom recognised due to a lack of comparative data on soil moisture (SM) in soil profiles. This lack of information endangers the sustainability of these fragile ecosystems. The current study assessed spatial-temporal variations of soil drought, as indicated by dried soil layers (DSL), at a watershed scale, and tested the hypothesis that soil drought in deep profiles is controlled by the combined effects of meteorological processes, land use, and topography. We measured SM to a depth of 500 cm on 20 occasions at 73 locations from 2013 to 2016 at a small watershed on the Chinese Loess Plateau (CLP). We also collected data on possible environmental factors including meteorological variables, land use, topographical elements, and soil properties. The DSLs occurred at > 90% of the sampling sites within the watershed, and the spatially and temporally averaged DSL formation depth (DSLFD), DSL thickness (DSLT) and soil water content within the DSL (DSL-SWC) were 125 cm, 257 cm, and 10.4%, respectively. This suggests that 51.4% of the 500-cm-profile is drying out below 125 cm. The DSLFD, DSLT and DSL-SWC demonstrated a moderate degree of variability (20% < CV < 84%) in space, and showed a moderate, moderate and weak temporal variability, in time, respectively. The temporal series of the mean spatial DSLT and DSLFD were significantly correlated with climatic variables. The spatial variation of the mean temporal DSL-SWC differed significantly among the land uses and between shaded and sunlit aspects. We found that plan curvature, slope gradient, clay and silt content regulated DSLs in both space and time. This result verified our hypothesis that meteorological processes, land use, and topography play an essential role in shaping DSL variation and distribution pattern. Taking DSL reclamation into account in the study area, grassland would be the optimum land use type. Understanding this information is helpful for watershed soil and water conservation, and soil drought meditation via the best management practices in the CLP and other water-limited regions with deep soils. [ABSTRACT FROM AUTHOR]