Interdune Lowlands Research Articles

High ecostoichiometric stability and accumulating SiO2 and NO3− as main physiological adaptive mechanisms for reed to adverse environments

Previous studies have shown that nutrients accumulation played important roles in resisting to stress resistance of plants. Our study examined the ecostoichiometric internal stability (EIS) of nutrients accumulation and, concomitantly identified the main resistant regulating substances and their contributions to stress resistance of reed (Gramineae) in arid desert areas. Plants (digging method) and soil samples (quartering method)) obtained from sand dune (SD), desert steppe (DP), interdune lowland (IL), saline meadow (SM) and wetland (W) habitats were brought back to the lab for nutrients analysis. Results indicated that soil nutrients differed obviously, while reed maintained relatively stable ratios of SiO2: N, N: K, and P: K when the eco-environments changed in different habitats. Furthermore, reed exhibits common adaptive characteristics by mainly accumulating large amounts of SiO2 (122.6–174.0 g/kg) and NO3− (166.1–216.6 g/kg), as well as moderate levels of soluble sugar (SS: 24.0–55.0 g/kg), which are mainly stored in leaves for stress resistance. The contribution of ions to stress resistance was 80.03%–91.15% (with SiO2 and NO3− accounting for 54.91%–63.10%), whereas the contribution of solutes was only 8.85%–19.97% (with SS contributing to 5.14%–10.91%) in different habitats. These findings suggest that maintaining relatively high EIS, while still accumulating SiO2 and NO3− as main physiological regulators might be an effective strategy for reed to positively respond to adverse habitats, which provide a strong theoretical basis and technical reference for searching useful methods for restoration and reconstruction of the degraded ecosystems in desert oasis regions.

Biomass Allocation and Allometric Relationship of Salix gordejevii Branches in Sandy Habitats Heterogeneity in Northern China

The patterns of biomass allocation are crucial for understanding the growth, reproduction, and community functions of plant individuals. We investigated the allometric growth characteristics and biomass allocation patterns of Salix gordejevii fascicular branches in various habitats of the Hunshandake Sandy Land to delve into their adaptability to environmental changes and role in the carbon cycle. We discovered the following: (1) The base diameter-to-branch length of S. gordejevii fascicular branches exhibited allometric growth relationships in mobile dunes and interdune lowlands, whereas it showed isometric growth relationships in semifixed and fixed dunes. As the soil moisture gradient increased, the length growth rate of S. gordejevii fascicular branches became faster than the base diameter growth rate in mobile dunes, demonstrated isometric growth in semifixed and fixed dunes, and was slow in interdune lowlands. (2) The biomasses of S. gordejevii fascicular branches significantly varied across different habitats, with the biomass of each component showing an increasing trend as habitat conditions improved. This study revealed the resource utilization strategies and adaptability of S. gordejevii fascicular branches in different habitats, providing new insights into the carbon sink function of desert ecosystems in semiarid regions.

Middle-Late Holocene climate change in an East Asian sandy land: Perspectives from the phytolith record of different geomorphic units

The accuracy of the regional palaeoclimate reconstruction is vital for ecological restoration and future climate predictions. Clarifying the regional climate signal on different geomorphological units within the same region plays a key role in regional climate researches. Here, we select the Horqin Sandy Land as the research area, and collect sedimentary from two typical geomorphological units (interdune lowlands: ML profile, DBS profile; dunes: CS profile, FX profile) as the research objects. The regional averaging method is employed to isolate distinct climate signals originating from interdune lowlands (IC-Score (Peat)) and dunes (IC-Score (Dune)), alongside an amalgamated climate signal (IC-Score (Peat&Dune)) synthesized from these two geomorphological units. This methodological approach facilitates the identification of variations in climate signals that collectively encapsulate the broader regional context. Meanwhile, local microclimate signals from dunes (IC-D-Value (Dune)) and interdune lowlands (IC-D-Value (Peat)) were separately analyzed to examine microclimate changes on different geomorphological units. The results indicate that different sedimentary carriers on various geomorphological units capture the local climate characteristics of their own units while recording regional climate changes. IC-D-Value (Peat) reflects ‘warm-humid’ climate, and IC-D-Value (Dune) represents ‘cold-dry’ climate. Climate signals derived from diverse geomorphological units exhibit the capacity to portray overarching regional climate patterns, yet they manifest variations concerning both semi-quantitative and quantitative climate parameters, notably temperature and precipitation. A regional average method is used to synthesize climate signals from different geomorphological units, which is more advantageous in documenting regional climate change. Regional climate signal reveals a change from warm-humid (9300 ∼ 4000 cal yr BP) to cold-dry (4000 ∼ 2000 cal yr BP) and then to slightly warm-humid (2000 ∼ 560 cal yr BP). Furthermore, regional climate signal shows the significant ∼ 2000-yr，∼1000-yr, ∼500-yr periodicities since 7300 cal yr BP, and solar activities are identified as one of the important driving factors.

Artificial Vegetation for Sand Stabilization May Impact Sand Lake Dynamics in Dune Regions.

Vegetation on dunes regulates the water supply from the dunes to the inter-dune lowland, which is a crucial factor affecting lake water dynamics in the inter-dune lowland. Previous researchers have paid insufficient attention to the water regulation function of dunes on a landscape- and regional scale. To fill this gap, both remote sensing technology and field observations were used to analyze the variations in the lake area and their influence factors, such as vegetation coverage and precipitation in the lake watershed, on a multi-year scale (2000-2020) and one-year scale (2021), respectively. The results showed that precipitation is the main factor influencing the changes in lake water, and artificial sand vegetation can regulate the changes in lake water. On the multi-year scale, with the coverage of artificial sand-fixing vegetation increasing on sand dunes in the lake watershed, the areas of the lakes were gradually decreasing. On the one-year scale, with dune vegetation coverage increased, the water supply from dunes to lakes showed a decreasing trend. This model can provide a possibility for estimating and predicting the influence of water supply from dunes to lakes that is affected by sand-fixing vegetation. The findings have significant theoretical and practical utility for the rational utilization of water resources in sandy land, as well as for assisting in the selection of an optimized construction mode for desert control projects.

Soil microbial community shifts explain habitat heterogeneity in two Haloxylon species from a nutrient perspective.

Haloxylon ammodendron and Haloxylon persicum (as sister taxa) are dominant shrubs in the Gurbantunggut Desert. The former grows in inter-dune lowlands while the latter in sand dunes. However, little information is available regarding the possible role of soil microorganisms in the habitat heterogeneity in the two Haloxylon species from a nutrient perspective. Rhizosphere is the interface of plant-microbe-soil interactions and fertile islands usually occur around the roots of desert shrubs. Given this, we applied quantitative real-time PCR combined with MiSeq amplicon sequencing to compare their rhizosphere effects on microbial abundance and community structures at three soil depths (0-20, 20-40, and 40-60 cm). The rhizosphere effects on microbial activity (respiration) and soil properties had also been estimated. The rhizospheres of both shrubs exerted significant positive effects on microbial activity and abundance (e.g., eukarya, bacteria, and nitrogen-fixing microbes). The rhizosphere effect of H.ammodendron on microbial activity and abundance of bacteria and nitrogen-fixing microbes was greater than that of H.persicum. However, the fertile island effect of H.ammodendron was weaker than that of H.persicum. Moreover, there existed distinct differences in microbial community structure between the two rhizosphere soils. Soil available nitrogen, especially nitrate nitrogen, was shown to be a driver of microbial community differentiation among rhizosphere and non-rhizosphere soils in the desert. In general, the rhizosphere of H.ammodendron recruited more copiotrophs (e.g., Firmicutes, Bacteroidetes, and Proteobacteria), nitrogen-fixing microbes and ammonia-oxidizing bacteria, and with stronger microbial activities. This helps it maintain a competitive advantage in relatively nutrient-rich lowlands. Haloxylon persicum relied more on fungi, actinomycetes, archaea (including ammonia-oxidizing archaea), and eukarya, with higher nutrient use efficiency, which help it adapt to the harsher dune crests. This study provides insights into the microbial mechanisms of habitat heterogeneity in two Haloxylon species in the poor desert soil.

Changes and determinants of belowground bud banks along an interdune lowland sequence

Understanding the changes and determinants of the belowground bud bank density of different plant functional groups along an interdune lowland sequence is essential for the exploration of community structure and vegetation restoration in sand dune ecosystems. However, how bud banks of different plant groups change and what are the regulating factors are still not clear, especially for the degraded ecosystems such as sand dune fields in desertified grasslands. In Horqin Sandy Land, Northeastern Inner Mongolia, China, we measured the bud bank densities of different plant functional groups (grasses, sedges and forbs) and biotic and abiotic parameters relevant to bud banks in five interdune lowlands differing in area and shape. Belowground bud bank densities of different plant functional groups varied with increasing interdune lowland area. Plant density had direct positive effects, but the area and shape of interdune lowlands had an indirect effect on bud bank density. The bud bank density was significantly smaller for the graminoid plants but increased for non-sedge forbs in the large interdune lowland compared to the smaller ones. Water stress and interdune lowland features exerted strong indirect effects on bud bank density. These findings suggest that plant conservation programs in active dune ecosystems should consider the joint effects of plant density, water regime, and interdune lowland area and shape on bud bank density for different plant functional groups.

Effects of long-term grazing exclusion on plant and soil properties vary with position in dune systems in the Horqin Sandy Land

Grazing exclusion is an important policy currently being employed by the Chinese government to recover degraded grasslands. Despite many field experiments, controversy still exists concerning the effects of grazing exclusion on the restoration of sand dune ecosystems. In order to examine the response of plant and soil parameters to grazing exclusion, a 32-year field experiment was conducted in active dune systems in the Horqin Sandy Land. The results showed that the dominant species changed significantly at the windward and leeward sides of dunes, and at interdune lowlands after long-term grazing exclusion. Plant density, cover, species richness, and soil organic carbon and total nitrogen (N) significantly increased across all topographic locations in areas with grazing exclusion. The effects of grazing exclusion on plant and soil parameters varied as a function of position in the dune system. In general, the recovery of plant and soil parameters occurred more rapidly at the windward side than at the leeward side when grazers were excluded. Soil organic carbon and total N were positively correlated with plant community density, cover, and species richness in active and stabilized sand dune systems. In addition, grazing exclusion strengthened the relationship between soil and plant parameters. The results showed that the effects of grazing exclusion on plant and soil properties were strongly dependent on dune position. These findings should prompt those responsible to assess the recovery of sand dune systems by synthesizing the effects of multiple positions within a dune system.

Silicon accumulation by Phragmites australis positively responds to rise in groundwater depth in the desert oasis areas of the HeXi Corridor, China

AbstractOur study investigated the characteristics of Phragmites australis (Gramineae) silicon (Si) accumulation, and the response relationship between P. australis Si accumulation and groundwater depth changes. Plants were dug out and taken back to the laboratory for Si accumulation analysis, and a supplementary survey of P. australis Si accumulation was conducted among different groundwater depths. Result showed that Si absorbed and accumulated by P. australis mainly came from the soil and the Si accumulation differed significantly in tissues and growth stages, and the total Si accumulations (withering stage) of P. australis in sand dune (SD), desert steppe (DT), interdune lowland (IL), saline meadow (SM), and wetland (W) habitats were 7.09%, 6.77%, 5.72%, 7.73%, and 8.12%, respectively. More importantly, P. australis Si accumulation was almost equal to the total accumulation of nitrogen, phosphorus, and potassium, and even higher than of the total accumulation of calcium, magnesium, and sulfur. P. australis Si accumulation (withering stage) reduced first from SD to DT habitat, and then increased remarkably from DT to W habitat with a significant increase of −23.95% and 41.96%, respectively. P. australis Si accumulation positively responds to the groundwater depths, and the relationship was an increasing linear function of one variable. Our findings suggested that accumulating Si might be one of the effective strategies for P. australis to adapt to adverse habitats, and the Si‐rich characteristic of P. australis was likely to lay a solid theoretical foundation for exploring effective measures to restore and reconstruct the degraded ecosystems in desert oasis areas.

Sensitivity of groundwater levels and chemistry to partial removal of vegetation in Prosopis woodlands of the Monte Desert, Argentina

Land use changes affecting ecological and hydrological processes often shape the biogeochemistry of deserts. As highly productive hotspots, Prosopis flexuosa woodlands located in interdune lowlands of the Monte Desert are subject to intense transformations by humans and livestock, and offer a unique opportunity to understand how phreatophyte vegetation, groundwater, rainfall variability, and vertical solute fluxes connect with each other. In this ecosystem, we evaluated the consequences of heavy disturbance by livestock settlements (partial tree removal, intense grazing) on shallow (7–15 m deep) groundwater recharge/discharge dynamics and vertical solute (nutrients and salts) transport. We compared three relatively undisturbed woodlands with three paired livestock stations in the Telteca Reserve (Mendoza, Argentina). At these locations we monitored groundwater levels and chemical and isotopic compositions during six years (2011–2017). Seasonal groundwater level fluctuations reflected shifts in water demand (lower in the cold season) rather than rainfall (high in the warm season), as shown by fall-winter rises and spring-summer declines. These seasonal fluctuations were more intense in undisturbed woodlands than in livestock stations. At a shorter time scale, intense rainfall events were associated to groundwater level raises, suggesting a partial decoupling of phreatophyte vegetation from the free aquifer and, less likely, recharge episodes. Livestock stations also affected groundwater chemistry by locally increasing chloride and nitrate concentrations, and salinity, suggesting higher water percolation and nitrate leaching to the aquifer in livestock stations than in control woodlands. This study addressed ecohydrological processes, which are necessary to understand the coupling between phreatophyte vegetation and groundwater, and its relationships with human and livestock activities.

Temporal–spatial changes in the belowground bud bank in interdune lowlands of an active sand dune ecosystem in northeastern China

Abstract Aims The belowground bud bank plays an important role in vegetation restoration of sand dune ecosystems in semi-arid regions. However, few studies have focused on the temporal–spatial changes of belowground bud banks in interdune lowlands. Methods The size and composition of belowground bud bank in five interdune lowlands with different sizes were investigated for one growing season to determine the temporal and spatial changes in belowground bud bank. Important Findings Total bud bank density was the highest in the medium-sized interdune lowland as was tiller bud density. The density of stem-base buds exhibited an opposite trend while rhizome bud density did not change with interdune lowland size. There was a significant seasonal change in the bud bank size. The total bud density peaked in August and was the lowest in October. A similar trend was found for rhizome bud density, whereas the density of stem-base buds showed an opposite trend, and tiller bud density did not change significantly during the growing season. We conclude that the belowground bud bank density is changed with interdune lowland size and season. These results contribute to the understanding of adaptive strategies of plants growing in active dune ecosystems and provide pointers for adopting effective measures to restore and conserve dune vegetation in semi-arid regions.

The spatial pattern of the belowground bud bank and its responses to soil water status in the interdune lowlands of active sand dunes of Inner Mongolia, China

Bud bank composition in interdune lowlands plays a key role in population colonization and vegetation restoration in active sand dune ecosystems. However, no studies have explicitly explored the spatial pattern of belowground bud banks in the interdune lowlands of active sand dune ecosystems and their response to soil moisture conditions. Therefore, this study investigated belowground bud banks and measured soil moisture contents in four interdune lowlands in the Horqin Sandy Land of northeastern Inner Mongolia. The density of total buds, rhizome buds, and tiller buds decreased significantly at the windward slope‐interdune and leeward slope‐interdune transitional zones (p < 0.05), while the densities of both root‐collar buds and root‐sprouting buds were the highest at the edge of the interdune lowland. Rhizome buds (60–100%) were predominant over tiller buds in the windward slope transitional zone, while root‐collar buds (57–62%) and tiller buds (60–79%) were prominent in the leeward slope transitional zone. Furthermore, all bud types except the root‐collar bud had obvious water dependence. It was concluded that there is a significant difference in bud density between the different interdune lowland positions, and root‐collar buds were more resistant to water stress than the other bud banks. These survival strategies and responses may be important in the recovery of both artificial and sand‐fixing vegetation in semiarid regions of China.

Roles of aboveground vegetation, soil properties, and disturbance in determining belowground bud bank in sand dune ecosystems

The processes whereby vegetation characteristics, soil properties, and disturbance events interact to determine the characteristics of plant bud bank are of considerable significance with respect to population recruitment and vegetation restoration in sand dune ecosystems. However, gaining an understanding of these processes represents a major challenge. In this study, we examined variations in the bud bank demographics of dune vegetation and the role of vegetation, soil properties, and disturbance in determining the size and composition of bud bank during the stabilization processes from active to fixed sand dunes. We investigated bud bank size and composition, vegetation characteristics, and soil properties in the interdune lowlands of active and fixed sand dunes in Inner Mongolia, China. We found that sand dune fixation increased bud bank density. Soil properties were determined to be the primary factors affecting bud bank in the interdune lowlands of an active dune, whereas vegetation density was the most important factor affecting bud bank in the interdune lowlands of a fixed sand dune. Among the different bud types, we found that rhizome and root-sprouting buds were dependent to a greater extent on soil moisture content in the interdune lowlands of active dunes, while in the interdune lowlands of fixed dunes, rhizome and root-sprouting buds had a greater dependence on soil total carbon. In contrast, tiller buds tended to be more related to vegetation density, whereas no evidence showed there was a prominent influence of any factor on collar buds. The mechanisms (vegetation, stress, and disturbance) affecting bud bank demographics are modified by sand dune fixation. The responses of different bud types to environmental factors differ in the interdune lowlands of both active and fixed sand dunes.

Variation in depth of water uptake for Pinus sylvestris var. mongolica along a precipitation gradient in sandy regions

Mongolian pine (Pinus sylvestris var. mongolica) has been widely used in vegetation restoration and for windbreaks in sandy regions of northern China where water is the principal factor limiting tree survival and growth. An understanding of water use in Mongolian pine plantations is critical for effective vegetation restoration. To determine water sources in a Mongolian pine plantation, we investigated the stable isotopic ratios of δ18O and δD in precipitation, groundwater, in soil water in different soil layers, and in tree xylem at different tree ages along a precipitation gradient and in different micro-landforms. The results indicated that the main water sources for Mongolian pine were precipitation-derived shallow soil water in semi-humid regions and that the contribution proportion decreased with an increase in tree age. With reduced precipitation in semi-arid and arid regions, contribution of deep soil water to Mongolian pine water use gradually increased, and differences in soil water contribution among trees due to tree age also significantly increased. Water use patterns in trees planted in different micro-landforms (e.g. sand dune crest or inter-dune lowland) became more distinct as precipitation gradually decreased across humid to semiarid and arid regions. Moreover, Mongolian pine, including 15-, 20-, 25-, and 45-year-old trees, similar height and DBH without groundwater in semi-arid climate (in Ejin Horo banner), while trees planted in extremely arid climate (Linze) relied on irrigation for survival despite abundant and available groundwater at that study site. These results indicated that groundwater may be beyond reach to be a main water source for Mongolian pine trees. Soil water conditions determined the survival and sustainable growth of planted trees, especially at depths less than 1 m where soil layers were recharged mainly by precipitation. Although Mongolian pine exhibits strong ecological adaptability, a trait that makes it ideally-suited for controlling desertification in sandy regions of northern China, water stress, crown dieback, or even tree mortality are likely to occur under conditions of extremely low precipitation.

Sand dune stabilization changes the vegetation characteristics and soil seed bank and their correlations with environmental factors

Currently the amount of data available on the effect of sand dune stabilization on species conservation in inter-dune lowland is very limited, especially for the sand dune systems in semi-arid regions. In this study, we determined whether the characteristics of above-ground vegetation, soil seed bank and their relationships with environmental factors changed with sand dune stabilization in the inter-dune lowlands in Horqin Sandy Land, China. Species composition, abundance and coverage of aboveground vegetation as well as soil seed bank composition and density were surveyed and their correlations with environmental factors (pH, organic matter content, total nitrogen and total phosphorus) were determined. The results showed that changes in the relationship between aboveground vegetation, soil seed bank and soil quality followed the changes in aboveground vegetation and soil seed banks. Aboveground vegetation species richness increased with sand dune stabilization, but soil seed bank species richness declined. The inter-dune lowland of active sand dunes could provide specific habitats for some endemic species and pioneer psammophyte species as indicated by data on aboveground vegetation and soil seed bank. Our results suggested that both active and stabilized sand dunes should be maintained since active sand dunes are essential for the survival of endemic or pioneer species and stabilized sand dunes are important for sustaining species richness.

Spatial distribution characteristics of soil moisture in different types of sand dune in the Mu Us Sandy Land, adjacent to north of Chinese Loess Plateau

The distribution of soil moisture in arid and semiarid regions is a major environmental factor and is regulated by regional topography, vegetation and soil texture. Here, we present the results of a study of the spatial distribution characteristics of soil moisture in the Mu Us Sandy Land, which is the transitional area between the northwestern deserts and the Chinese Loess Plateau, in North China. Samples were taken from holes drilled to a depth of 4 m in 52 different microtopographic positions on different types of dune (bare dunes, shrub-covered dunes and tree-covered dunes). The sites were located in the northwestern margin, the central region and the southeastern margin. All samples were analyzed for moisture content and grain size distribution. The results show that: (1) for the same type of dune, the soil moisture content varies in different microtopographic positions. The soil moisture content on windward slopes is greater than on leeward slopes in the shrub-covered dunes and the tree-covered dunes, while this is the case in only some of the bare migratory sand dunes. In addition, the soil moisture content on leeward slopes is greater than on the corresponding windward slope. (2) The vegetation type and density have a large influence on the moisture content of sandy soils; specifically, the presence of shrubs and trees significantly affects the soil moisture content of windward and leeward slopes and the inter-dune lowland. (3) Soil moisture content is positively correlated with the clay and silt content of sandy soils. From northwest to southeast across the Mu Us Sandy Land, the silt and clay content increases gradually; however, in the case of dunes covered with planted trees, a peak in the content of fine-grained material occurs in the central region, while for shrub-covered sand dunes, the peak occurs in the southeastern margin. In addition, the correlation between soil moisture and soil grain size distribution of the three types of dunes varies from northwest to southeast. (4) The proportion of fine-grained material and the correlation between the content of fine-grained material and soil moisture are the two main factors influencing the soil moisture distribution of the different types of dune. A soil moisture concentration index can be used as a rough indicator of the distribution characteristics of soil moisture.

Effects of Soil Moisture on Vegetation Invasion into Transition Zones between Windword Slopes of Active Dunes and Interdune Lowlands

During the vegetation natural regenerations in semi-arid sand areas, seed germination and seedling emergence are critical phases of maintaining plant population and realizing natural regeneration. It is generally accepted that soil moisture and soil seed bank are primary dependent factors in the phases. But the binary correlation analysis between seedling density and soil seed bank density as well soil moisture in transition zones between windword slopes of active dunes and interdune lowlands indicated that the correlation between seedling density and soil seed bank density was not significant (P > 0.05) in the plant growing season; but the one between seedling density and soil moisture was significant and positive (P < 0.05); moreover, seedling density increased logarithmically with the increasing of soil moisture. The conclusions reveal that soil moisture is a primary dependent factor during seedling emergence and establishment in the transition zones between the windword slopes of active dunes and interdune lowlands, but soil seed bank is not; and plant natural regeneration depends more on those propagating seeds from plant communities in neighbouring sand dunes.

Abiotic contribution to total soil CO2 flux across a broad range of land-cover types in a desert region

As an important component of ecosystem carbon (C) budgets, soil carbon dioxide (CO2) flux is determined by a combination of a series of biotic and abiotic processes. Although there is evidence showing that the abiotic component can be important in total soil CO2 flux (Rtotal), its relative importance has never been systematically assessed. In this study, after comparative measurements of CO2 fluxes on sterilized and natural soils, the Rtotal was partitioned into biotic flux (Rbiotic) and abiotic flux (Rabiotic) across a broad range of land-cover types (including eight sampling sites: cotton field, hops field, halophyte garden, alkaline land, reservoir edge, native saline desert, dune crest and interdune lowland) in Gurbantunggut Desert, Xinjiang, China. The relative contribution of Rabiotic to Rtotal, as well as the temperature dependency and predominant factors for Rtotal, Rbiotic and Rabiotic, were analyzed. Results showed that Rabiotic always contributed to Rtotal for all of the eight sampling sites, but the degree or magnitude of contribution varied greatly. Specifically, the ratio of Rabiotic to Rtotal was very low in cotton field and hops field and very high in alkaline land and dune crest. Statistically, the ratio of Rabiotic to Rtotal logarithmically increased with decreasing Rbiotic, suggesting that Rabiotic strongly affected Rtotal when Rbiotic was low. This pattern confirms that soil CO2 flux is predominated by biotic processes in most soils, but abiotic processes can also be dominant when biotic processes are weak. On a diurnal basis, Rabiotic cannot result in net gain or net loss of CO2, but its effect on transient CO2 flux was significant. Temperature dependency of Rtotal varied among the eight sampling sites and was determined by the predominant processes (abiotic or biotic) of CO2 flux. Specifically, Rbiotic was driven by soil temperature while Rabiotic was regulated by the change in soil temperature (ΔT). Namely, declining temperature (ΔT 0) resulted in positive Rabiotic (i.e., CO2 released from soil). Without recognition of Rabiotic, Rbiotic would be overestimated for the daytime and underestimated for the nighttime. Although Rabiotic may not change the sum or the net value of daily soil CO2 exchange and may not directly constitute a C sink, it can significantly alter the transient apparent soil CO2 flux, either in magnitude or in temperature dependency. Thus, recognizing the fact that abiotic component in Rtotal exists widely in soils has widespread consequences for the understanding of C cycling.

The role of sexual vs. asexual recruitment of &amp;lt;i&amp;gt;Artemisia wudanica&amp;lt;/i&amp;gt; in transition zone habitats between inter-dune lowlands and active dunes in Inner Mongolia, China

Abstract. Artemisia wudanica is an endemic, perennial, pioneering psammophyte species in the sand dune ecosystems of western Horqin Sand Land in northern China. However, no studies have addressed how sexual and asexual reproduction modes of A. wudanica perform at the transitional zones between active dune inter-dune lowlands and active dunes. In early spring, quadrats were randomly set up in the study area to monitor surviving seedling and/or ramet density and frequency coming from sexual/asexual reproduction of A. wudanica. Iron sticks were inserted near each quadrat to determine wind erosion intensity (WE). Additionally, soil samples were collected nearby each quadrat to test for soil moisture (SM), organic matter (OM) and pH. Surviving seedlings of A. wudanica showed an inverse response in comparison with ramets to SM, OM and WE. Soil moisture showed the most positive effect, and WE the negative effect, on surviving, sexual reproduction seedlings. Contrarily, WE had the most positive effect, and SM the negative effect, on asexual reproduction ramets. This suggests that increases in SM and decreases in WE should benefit recruitment of A. wudanica seedlings. On the contrary, ramets coming from asexual reproduction showed a different response to environmental factors in transition zone habitats. While SM was not a key constraint for the survival of seedlings, they showed a better, positive response to wind erosion environments. Overall, various study environmental parameters could be improved to foster A. wudanica invasion and settlement in the plant community through different reproductive modes, thereby promoting vegetation restoration and rehabilitation.

Characteristics of soil freeze–thaw cycles and their effects on water enrichment in the rhizosphere

The freeze–thaw process can lead to water enrichment in freezing layers of soil, and may have beneficial effects on vegetation restoration efforts in sandy land habitats. This study determined the characteristics of soil water migration in dunes and interdune areas during freeze–thaw process, and discussed its potential application to the restoration and recovery of sandy land plant communities. In this research, the mobile sand dunes and interdune lowlands were chosen as the study objects in Horqin Sandy Land, north China. We investigated the soil temperature and moisture content on depths of 20cm, 50cm, 100cm and 150cm during soil freeze–thaw period (from September 20, 2010 to April 9, 2011), and determined the migrated water during freezing–thawing processes on soil of sand dunes and interdune lowlands, and discussed its potential application on plant recovery processes. Results showed that the soil freeze–thaw process occurred mostly at a depth of 0–100cm, and the longest period of soil that remained frozen is 104days at a depth of 20cm and the shortest period is 39days at a depth of 100cm in sand dunes. The number of freeze–thaw cycles was not different between sand dune and interdune area over winter. Most freeze–thaw cycles occurred in the thawing process, and mostly at a depth of 0–50cm. The freeze–thaw cycles of interdune areas only occurred in the thawing process, but the freeze–thaw cycles of sand dunes occurred both in the process of freezing and thawing. More water of the interdune areas apparently migrated than did in the sand dunes. The range of soil water storage content at depths of 0 to 100cm increased to 92.4mm on interdune, and 10.8mm on sand dunes during the freeze–thaw process. A negative correlation was found between soil temperature and moisture at depths of 100cm and 150cm, and while a positive correlation existed at depths of 20cm and 50cm. The freeze–thaw process can lead to water enrichment in freezing layer of soil on sand dunes and interdune. Soil texture affected the quantity of soil water migrating during the freeze/thaw process, and more water migrated in interdune areas than in sand dune habitat.

Species shifts in above-ground vegetation and the soil seed bank in the inter-dune lowlands of an active dune field in Inner Mongolia, China

Degradation of semi-arid ecosystems leading to desertification presents a global environmental challenge. However, few studies have investigated seed bank and above-ground species composition in degraded semi-arid dune systems, particularly in relation to their potential to contribute to stabilisation and revegetation. We determined whether soil seed bank and above-ground species composition differed along a chronosequence in the inter-dune lowlands of an active dune field in Inner Mongolia, China. Soil cores were collected in early April 2011 and soil seed bank composition determined using a combination of the seedling emergence and seed extraction methods. Established vegetation, including species composition and abundance, was also surveyed. Relative importance values for all above-ground species and similarities in species composition of vegetation and soil seed bank along the chronosequence were analysed. A clear successional trend was shown for established vegetation along the first three stages identified, followed by a final stage reverting to more mobile substrate due to disturbance by dune movement. This trend was not reflected in the seed bank. Plant and seed bank density increased over time, however, species composition of the seed bank reflected earlier stages rather than the corresponding established vegetation. There was a relationship between established vegetation and the soil seed bank at the earliest stage, driven mainly by the persistence of seeds of the pioneer species Agriophyllum squarrosum and Corispermum candelabrum. A relatively close relationship was also found at the final stage, where frequent disturbance occurred as a result of increasing sand burial, caused by constant directional sand dune movement. While a clear relationship between the seed bank and associated vegetation was not found along the whole chronosequence, the seed bank displayed potential for restoration of pioneer psammophytes and annual herb species, suggesting that it would contribute to regeneration, as well as support latter-stage annuals and several rare and endemic species.