Scale dependence of plant species richness and vegetation-environment relationship along a gradient of dune stabilization in Horqin Sandy Land, Northern China

Ecological patterns and processes in dune ecosystems have been a research focus in recent years, however the information on how dune stabilization influences the spatial scale dependence of plant diversity is still lacking. In this study, we measured the plant species richness, soil properties and altitude across four spatial scales （1, 10, 100 and 1,000 m2） at three different dune stabilization stages （mobile dune, semi-fixed dune and fixed dune） in Horqin Sandy Land, Northern China. We also examined the relationships between plant species richness, community composition and environmental factors along the gradient of dune stabilization. Our results showed that plant species richness increased with the increase of spatial scales in each dune stabilization stage, as well as with the increase of dune stabilization degrees. Canonical correspondence analysis （CCA） showed that plant distribu- tions in the processes of dune stabilization were determined by the combined environmental gradient in relation to soil organic carbon （SOC）, total nitrogen （TN）, carbon/nitrogen （C/N）, pH, electrical conductivity （EC）, soil water content （SWC）, fine sand （FS）, very fine sand （VFS）, silt and clay （SC）, and altitude. Plant species richness was significantly and positively correlated to SOC and TN in mobile dune, and significantly and positively correlated to SOC, TN, C/N, VFS and SC in semi-fixed dune. However, no significant correlation between plant species richness and environmental factors was observed in fixed dune. In addition, plant species richness in different dune stabili- zation stages was also determined by the combined gradient of soil properties and altitude. These results suggest that plant species richness has obvious scale dependence along the gradient of dune stabilization. Soil resources depending on dune habitats and environmental gradients caused by dune stabilization are important factors to de- termine the scale dependence of species diversity in sand dune ecosystems.

Effect of spatial scale and topography on spatial heterogeneity of soil seed banks under grazing disturbance in a sandy grassland of Horqin Sand Land, Northern China

Soil seed banks play an important role in the distribution and composition of plant communities in semiarid grassland ecosystems. However, information on how spatial scale influences the spatial heterogeneity of soil seed banks in a grassland under grazing disturbance is still lacking. Based on field sampling and greenhouse germination, we measured the species composition and seed density of soil seed banks at different spatial scales （30 mx30 m, 30 mx60 m and 30 mx90 m） along a topographical gradient in a sandy grassland in Horqin Sand Land, Northern China. By applying geostatistical methods, we examined how spatial scale and topography affected the spatial distribution of soil seed banks in the study area. Our results showed that the total number of species in soil seed banks, as well as the number of dominant annuals, increased with the increase of spatial scales. Seed density in soil seed banks decreased with the increase of spatial scales due to an increase in the slopes and relative heights of the sampling points. Geostatistical analysis showed that the relative structural variance （C/（C0＋C）） of seed density and species richness were over 65% for all spatial scales, indicating that these variables had an ob- vious spatial autocorrelation and the spatial structured variance accounted for the largest proportion of the total sample variance. Spatial autocorrelation of seed density in soil seed banks increased with the increase of measured scales, while that of species richness showed a reverse trend. These results suggest that the total number of spe- cies in soil seed banks is spatial scale dependent and lower topography may accommodate more seeds. Spatial distribution of seed density in soil seed banks is also scale dependent due to topographic variation. Grassland management, therefore, needs to consider local grazing disturbance regime, spatial scale and topography.

Land cover changes and the effects of cultivation on soil properties in Shelihu wetland,Horqin Sandy Land,Northern China

Land cover change plays an essential role in the alternation of soils properties. By field investigation and applying satellite images, land cover information in the Shelihu wetland was carried out in an area of 2,819 hm2 in 1985, 1995, 2000, 2005, 2010 and 2011, respectively, in Horqin Sandy Land. A total of 57 soil sampling sites across Shelihu were chosen in wet meadow （CL0）, cropland （CL） and sandy land （SL） according to the spatial characteristics of water body change. Soil texture, organic carbon （SOC）, total nitrogen （TN） and total phosphorus （TP） contents, electrical conductivity （EC） and pH were measured at the soil depths of 0-10, 10-20 and 20-40 cm to examine the influence of agricultural conversion and continuous cultivation on soil properties. The results showed that the study area was covered by water body in 1985, which gradually declined afterwards and then reclaimed rapidly at a mean annual rate of 132.1 hm2/a from wet meadow to cropland since 1995. In 2011, water body was drained and the area was occupied by 10.8% of CL0, 76.9% of CL and 12.3% of SL. Large amounts of SOC, TN and TP were accumulated in the above depths in CL0. Soil in CL0 also had higher EC and silt and clay fractions, lower pH than in SL and CL. Soil in SL was seriously degraded with lower contents of SOC, TN and TP than in CL and CL0. SOC, TN content and EC in CL decreased with the increase of cultivation age, while pH showed a reverse trend with significance at plough horizon. The agricultural conversion in Shelihu was driven by the comprehensive factors of precipitation reduction, economic development and intense competitions for irrigation water. Continuous cultivation in this process is not sustainable because of SOC degradation and nutrient content reduction. The key point is that conventional tillage and removal of residuals induced further land degradation. Wetland reclamation for immediate economic interests led to greater costs in the long-term environmental restoration in Horqin Sandy Land.

Toward sustainable desertification reversion:A case study in Horqin Sandy Land of northern China

Desertification reversion is an interactive process involving climate, land use change, and water processes. In order to reveal the relationship between desertification reversion and these factors, we analyzed historical data on precipitation, air temperature, desertified land changes, underground water tables, and water body changes in Naiman County in the central part of Horqin Sandy Land. Our analysis showed that during 1961-2010 the annual precipitation fluctuated dramatically and has decreased fairly consistently in recent years. The air temperature increased by 0.50-1.25℃, and the minimum temperature increased more obviously. The desertified land area increased from 42,300 km^2 in 1959 to 62,000 km^2 in 1985, and then declined to about 50,000 km^2 in 2010. The underground water tables have been lowered by about 10 m in the past 30 years, and declined more rapidly in recent years. Desertified land is significantly related to the amount of total cropland, and underground water tables are signifcantly correlated with annual precipitation and the amount of irrigated cropland. Therefore, it is necessary to pursue sustainable desertification reversion without compromising the capacity for local development and restoration of degraded land, through application of appropriate management measures for improving water availability in this region.

Afforestation effects on soil microbial abundance, microbial biomass carbon and enzyme activity in dunes of Horqin Sandy Land, northeastern China

In order to investigate the effects of afforestation on soil microbial abundance, microbial biomass carbon and enzyme activity in sandy dunes, 20-year-old Pinus sylvestris var. mongolica Litv. （PSM） and Populus simonii Carri6re （PSC） mature forests were se- lected in Horqin Sandy Land, and mobile dunes was set as a control （CK）. Results show that PSM and PSC plantations can im- prove soil physicochemical properties and significantly increase microbiological activity in mobile dunes. Soil microbial abun- dance, microbial biomass carbon and enzyme activity show an order of PS〉PSM〉CK. Total soil microbial abundance in PSM and PSC was respectively 50.16 and 72.48 times more than that in CK, and the differences were significant among PSM, PSC and CK Soil microbial biomass carbon in PSM and PSC was respectively 23.67 and 33.34 times more than that in CK, and the difference was insignificant between PSM and PSC. Soil enzyme activity, including dehydrogenase （DEH）, peroxidase （PER）, protease （PRO）, urease （URE） and cellobiohydrolase （CEL） in PSM and PSC were respectively 19.00 and 27.54, 4.78 and 9.89, 4.05 and 8.67, 29.93 and 37.46, and 9.66 and 13.42 times of that in CK. R sylvestris and P. simonii can effectively improve soil physico- chemical and microbiological properties in sandy dunes and fix mobile dunes in Horqin Sandy Land. The Cmic：C ratio is an appli- cable indicator to estimate soil stability and soil water availability, and based on an overall consideration of plantation stability and sustainability, R sylvestris is better than R simonii in fixing mobile dunes in sandy land.

Accumulation of soil organic carbon during natural restoration of desertified grassland in China's Horqin Sandy Land

China＇s Horqin Sandy Land,a formerly lush grassland,has experienced extensive desertification that caused considerable carbon（C） losses from the plant-soil system.Natural restoration through grazing exclusion is a widely suggested option to sequester C and to restore degraded land.In a desertified grassland,we investigated the C accumulation in the total and light fractions of the soil organic matter from 2005 to 2013 during natural restoration.To a depth of 20 cm,the light fraction organic carbon（LFOC） storage increased by 221 g C/m2（84%） and the total soil organic carbon（SOC） storage increased by 435 g C/m2（55%）.The light fraction dry matter content represented a small proportion of the total soil mass（ranging from 0.74% in 2005 to 1.39% in 2013）,but the proportion of total SOC storage accounted for by LFOC was remarkable（ranging from 33% to 40%）.The C sequestration averaged 28 g C/（m2·a） for LFOC and 54 g C/（m2·a） for total SOC.The total SOC was strongly and significantly positively linearly related to the light fraction dry matter content and the proportions of fine sand and silt＋clay.The light fraction organic matter played a major role in total SOC sequestration.Our results suggest that grazing exclusion can restore desertified grassland and has a high potential for sequestering SOC in the semiarid Horqin Sandy Land.

Seasonal changes in the relationship between species richness and community biomass in grassland under grazing and exclosure, Horqin Sandy Land, northern China

How species diversityroductivity relationships respond to temporal dynamics and land use is still not clear in semi-arid grassland ecosystems. We analyzed seasonal changes of the relationships between vegetation cover, plant density, species richness, and above- ground biomass in grasslands under grazing and exclosure in the Horqin Sandy Land of northem China. Our results showed that in grazed and fenced grassland, vegetation cover, richness, and biomass were lower in April than in August, whereas plant density showed a reverse trend. Vegetation cover during the growing season and biomass in June and August were higher in fenced grassland than in grazed grassland, whereas plant density in April and June was lower in fenced grassland than in grazed grassland. A negative relationship between species richness and biomass was found in August in fenced grassland, and in grazed grassland the relationship between plant density and biomass changed from positive in April to negative in August. The relationship between the density of the dominant plant species and the total biomass also varied with seasonal changes and land use （grazing and exclosure）. These results suggest that long-term grazing, seasonal changes, and their interaction significantly influence vegetation cover, plant density, and bio- mass in grasslands. Plant species competition in fenced grassland results in seasonal changes of the relationship between species rich- ness and biomass. Long-term grazing also affects seasonal changes of the density and biomass of dominant plant species, which fur- tiler affects the seasonal relationship between plant density and biomass in grasslands. Our study demonstrates the importance of tem- poral dynamics and land use in understanding the relationship between species richness and ecosystem fianction.

Litter decomposition in fragile ecosystems:A review

As a linkage between plants and soil,litter decomposition and its effect on nutrient recirculation have an important ecolog‐ical significance as they contribute to soil structure improvement and the restoration of degraded ecosystems.Fragile eco‐systems in arid regions(both hot and cold)are depleted in soil organic matter,and as a result of various factors their circu‐lation of material and energy is slower.Here we discuss how litter decomposition is necessary to maintain the stability of fragile ecosystems.We reviewed research on litter decomposition carried out in arid regions.Our objective in this review is to outline how litter decomposition,and the subsequent buildup of organic matter in soil,is a key process determining the stability of fragile ecosystems.Our review shows that existing studies have focused on the influence of single ecologi‐cal factors on litter decomposition and nutrient cycling,and highlights how the exploration of interactions among factors determining litter decomposition is still lacking.This interaction is a key aspect,since in the real world,decomposition and nutrient return to soil of litter products is affected by multiple factors.We propose a network setup on a cross-regional scale using standardized methods(e.g.,the tea bag method)to understand litter decomposition and nutrient return in frag‐ile ecosystems.Such a unique network could contribute to establish predictive models suitable for litter decomposition and nutrient return in these areas,and thus could provide theoretical and practical support for regional ecological protec‐tion and high-quality development.

Diversity and composition of culturable fungi in Horqin Sandy Land

Soil fungi play a key role in soil functional performance and ecological restoration.To understand the diversity and composition of culturable fungi in soils of Horqin Sandy Land,China,mobile dune,semi-fixed dune,fixed dune and sandy grassland were selected to investigate the soil fungal diversity using a traditional culture-dependent approach.ITS sequencing was applied to identify the fungal strains.The counts of culturable fungi increased significantly from mobile dune to sandy grassland along the gradient of sandy land restoration.The Shannon-Wiener,Simpson and Evenness indices of culturable fungi ranged from 1.26-1.71,0.22-0.37 and 0.83-0.87,respectively.A total of 27 fungal strains were isolated using dilution plate cultural technique.The 27 fungal isolates were clustered into three groups:Ascomycota,Basidiomycota and Mucoromycota at phylum level,indicating that Ascomycota was the dominant fungal phylum(88.9%of the total).The isolated fungi were grouped into 3 phyla,5 classes,6 orders,11 families and 13 genera.The results show that culturable fungi were diverse in sandy land soils and fungal isolates have potential function in lipid turnover,cellulose degradation and ethanol,glucose and fatty acid production.Future studies should be carried out to explore their ecological and biological function for degraded sandy land restoration.

Effects of dune stabilization on vegetation characteristics and soil properties at multiple scales in Horqin Sandy Land,Northern China

Ecological patterns and processes in dune ecosystems have been a research focus in recent years, however information on how dune stabilization influences vegetation and soil at different spatial scales is still lacking. In this study, we measured vegetation characteristics and soil properties across three spatial scales （10, 100 and 1,000 m^2） along gradient dune stabilization stages （mobile dune, semi-fixed dune and fixed dune） in Horqin Sandy Land, Northern China. Vegetation cover over all scales significantly increased with degree of dune stabilization, as well as species richness and C/N ratio at 10 m^2 scale. Species richness significantly increased with the increase in measured scales at each stage of dune stabilization and was higher in fixed dune than that in mobile dune and semi-fixed dune at 100 and 1,000 m^2 scales. Over all scales, aboveground biomass was lower in mobile dune than that in semi-fixed dune and fixed dune, and soil organic C, total N, EC, very fine sand and silt ＋ clay contents were higher in fixed dune than those in mobile dune and semi-fixed dune. These results suggest that along the gradient dune stabilization, species richness has strong spatial scale-dependence, but vegetation cover, aboveground biomass and soil properties is generally scale independent （i.e., the pattern of response is consistent across all scales）. Effect of dune stabilization on vegetation and soil over all spatial scales results in the positive correlation among vegetation cover, species richness, biomass, soil organic C, total N, C/N, EC, very fine sand and silt ＋ clay along the gradient dune stabilization. In addition, species response to dune stabilization. Thus, the monitoring strategies diversity in semiarid dune ecosystems. richness at the smallest scale （10 m^2） has more sensitive at small scales are essential to detect changes of species

Screening of cellulose decomposing fungi in sandy dune soil of Horqin Sandy Land

Cellulose decomposing fungi play an important role in litter decomposition and are decisive in nutrient cycling in sandy land ecosystems. Thirty-one strains were isolated to select efficient cellulose decomposers, and four efficient cellulose decomposing fungi （NM3-1, NM3-2, NM3-3, and NM3-4） were screened using a CMC （carboxymethyl cellulose） carbon source in dune soil of Horqin Sandy Land. They were identified as Asperigillus calidoustus, Fusarium oxysporum, Fusarium solani, and Hypocrea lixii by rDNA-ITS molecular biological methods. Cloth decomposition rates were 15.71%, 15.89%, 17.29%, and 17.89% by the four efficient decomposers incubated for 30 days, respectively. Screening of efficient cellulose decomposers can not only increase the dune soil functional microbe bank, but can also accelerate litter decom- position and available nutrient input in the Horqin Sandy Land.

Effects of land-use changes on organic carbon in bulk soil and associated physical fractions in China's Horqin Sandy Grassland

The Horqin Sandy Grassland is one of the most seriously desertified areas in China＇s agro-pastoral ecotone due to its fragile ecology, combined with improper and unsustainable land management. We investigated organic carbon changes in bulk soil （0 to 5 cm）, light fraction of soil organic matter, and soil particle-size fractions induced by land-use and cover type changes. The results indicated that total soil organic carbon （SOC） storage decreased by 121 g/m^2 with the conversion of grassland into farmland for 30 years, and increased by 261 g/m^2 with the conversion of grassland into plantation for 30 years. Total SOC storage decreased by 157 g/m^2 as a result of severe grassland desertification due to long-term continuous livestock grazing, whereas total SOC increased by 111 g/m^2 following the practice of grazing exclusion （16 years） in desertified areas. Changes in land-use and cover type also show great effects on carbon storage in soil physical fractions.

Design and experimental investigation of potential low-thermalconductivity high-entropy rare-earth zirconates

Developing new high-entropy rare-earth zirconate(HE-RE_(2)Zr_(2)O_(7))ceramics with low thermal conductivity is essential for thermal barrier coating materials.In this work,the average atomic spacings,interatomic forces,and average atomic masses of 16 rare-earth elements occupying the A site of the cubic A_(2)B_(2)O_(7) crystal structure were calculated by density functional theory.These three physical qualities,as vectors,characterize the corresponding rare-earth elements.The distance between two vectors quantitatively describes the difference between two rare-earth elements.For greater differences between two rare-earth elements,the disorder degree of HE-RE_(2)Zr_(2)O_(7)is greater,and therefore,the thermal conductivity is lower.According to the theoretical calculations,the thermal conductivity of the ceramics gradually increases in the order of(SC_(0.2)Y_(0.2)La_(0.2)Ho_(0.2)Yb_(0.2))_(2)Zr_(2)0_(7),(SC_(0.2)Ce_(0.2)Nd_(0.2)Eu_(0.2)Gd_(0.2))_(2)Zr_(2)0_(7),(SC_(0.2)Y_(0.2)Tm_(0.2)Yb_(0.2)Lu_(0.2))_(2)Zr_(2)0_(7),and(Sc_(0.2)Er_(0.2)Tm_(0.2)Yb_(0.2)Lu_(0.2))_(2)Zr_(2)O_(7).Using the solution precursor plasma spray method and pressureless sintering method,four types of HE-RE2Zr2Oz powder and bulk samples were prepared.The samples all showed a single defective fluorite structure with a uniform distribution of the elements and a stable phase structure.The thermal conductivities of the sintered HE-RE_(2)Zr_(2)0_(7) bulk samples ranged from 1.30 to 1.45 Wm^(-1).K^(-1) at 1400℃,and their differences were consistent with the theoretical calculation results.Among the ceramics,(Sc_(0.2)Y_(0.2)La_(0.2)Ho_(0.2)Yb_(0.2))_(2)Zr_(2)O_(7) had the lowest thermal conductivity(1.30 W·m^(-1)·K^(-1),1400℃),highest thermal expansion coefficient(10.19×10^(-6) K^(-1),200-1400℃),highest fracture toughness(1.69±0.28 MPa·m^(1/2)),and smallest brttleness index(3.03μm^(1/2)).Therefore,(Sc_(0.2)Y_(0.2)La_(0.2)Ho_(0.2)Yb_(0.2))_(2)Zr_(2)0_(7)is considered to be an ideal candidate material for next-generation thermal barrier coating applications.

Slippery quartz surfaces for anti‐fouling optical windows

The surface of camera‐based medical devices is easily smeared by blood and fog during the surgical procedure,causing visual field loss and bringing great distress to both doctors and patients.In this article,a slippery liquid‐infused porous surface(SLIPS)on a quartz window surface that can repel various liquids,especially blood droplets is reported.A femtosecond laser pulse train was used to create periodic microhole structures on the silica surface.The subsequent low surface energy treatment and lubricant infusion led to the successful preparation of a slippery surface.Such blood‐repellent windows exhibited high transparency,great antifogging,and antibacterial properties.In addition,the slippery ability of the as‐prepared surface exhibited outstanding stability since the surface could withstand harsh treatments/environments,such as repeated pipette scratches and immersion in different pH solutions.The as‐prepared millimeter‐sized quartz samples with SLIPS were attached to the endoscope lens as a protective coating and could maintain high visibility after repeated immersion in blood.We believe that the coating developed in this study will provide inspiration for the design of next‐generation endoscopes or other camera‐guided devices that will resist fouling,keep clear vision,and reduce operation time,thus offering great potential applications in lesion diagnosis and therapy.

Changes in the phytoplankton community structure of the Backshore Wetland of Expo Garden, Shanghai from 2009 to 2010

Phytoplankton community structure,abundance,and species'spatial and temporal distributions were examined for the Backshore Wetland of Expo Garden in Shanghai from September 2009 to August 2010.A total of 371 phytoplankton species were identified from 109 genera 8 phyla.There were 18 dominant species in total,and Phormidium tenue was dominant during four seasons.The mean annual abundance and biomass were 711.11×10^(4) cells/L and 5.70 mg/L,respectively.The seasonal changing trend of existing stocks was bimodal,with main peaks of density and biomass occurring in the winter and a secondary peaks occurring in the summer.The Shannon–Wiener diversity index(H′),the Margalef species richness index(D),and Pielou's species evenness index(J)showed a clear seasonal trend.All of the indices showed a changing pattern,with the highest recorded values from the summer to autumn and the lowest recorded values from the winter to spring.The canonical correspondence analysis(CCA)showed that environmental factors,including water temperature,nitrate nitrogen,and pH were the main influencing factors to the change of phytoplankton community structure in the Backshore Wetland of Expo Garden in Shanghai.