Halin Zhao

Influencing Mechanisms of Several Shrubs on Soil Chemical Properties in Semiarid Horqin Sandy Land, China

Horqin Sandy Land is one of the serious desertification areas in the semiarid zone of north China. Shrubs are the dominant plant species in this region and they play an important role in the wind erosion-prone fragile ecosystem. This study deals with the differences of some chemical properties in the soils under shrub canopies and from adjacent open spaces and analyses their characteristics in the shrub rhizospheric soils and bulk soils. The results showed that: (1) the concentrations of organic C, total N, and total P, and the value of electrolytic conductivity (EC) in the soils under the canopy of shrubs increased by 56%, 51%, 37%, and 51%, respectively, compared with those of the soils in open spaces, but there was no significant difference in pH between the soils under shrub canopies and open spaces; (2) shrub rhizosphere soils exhibited significantly higher contents of organic C, total N, and values of EC as well as a lower value of pH compared to the bulk soils, but there was no significant difference in total P between rhizosphere and bulk soils; (3) there were close relationships between the properties in soils under shrub canopies and the rhizosphere soils, indicating that the development of “fertile islands” are favorable to root growth and induce greater amount of rhizodeposition, and vice versa; and (4) soils under Artemisia frigida and Caraganda microphylla canopies and rhizospheres had significantly higher organic C and total N contents than those of Artemisia halodendron and Salix gordejevii. The results suggested that shrubs were of vital importance for the sequestration and accumulation of nutrients and maintenance of soil fertility in the Horqin Sandy Land ecosystem.

Sheep gain and species diversity: in sandy grassland, Inner Mongolia

Abstract A grazing experiment was conducted from 1992 to 1996 at a sandy grassland in the Horqin sandy land, located in the northeastern part of China. The grassland had been grazed by sheep for many years before the experiment at an intensity of 4.5 sheep ha−1. The experiment consisted of 4 grazing treatments: no grazing (0 sheep ha−1), light grazing (2 sheep ha−1), moderate grazing (4 sheep ha−1) and overgrazing (6 sheep ha−1). Plant species diversity, plant biomass, soil properties, and sheep liveweight under various grazing treatments were examined. Overgrazing resulted in considerable decreases in both species diversity and plant biomass. As a result, sheep liveweight gain decreased significantly in the last 3 years of the experiment in the overgrazing treatment. No grazing and light grazing treatments had higher species diversity as well as higher biomass production than moderate grazing and overgrazing treatments. The results indicate that light sheep grazing is sufficient for the recovery of overgrazed grassland in this region and for the maintenance of plant species diversity. The proper grazing intensity should be 2–3 sheep or sheep equivalents per hectare for the sandy grassland in Inner Mongolia.

Grassland changes under grazing stress in Horqin sandy grassland in Inner Mongolia, China

Abstract A grazing trial was conducted from 1992 to 1996 in the Horqin sandy grassland area, located in north‐eastern China. The trial had four grazing intensity treatments: no grazing (0 sheep ha−1), light grazing (2 sheep ha−1), moderate grazing (4 sheep ha−1) and overgrazing (6 sheep ha−1) plots. The overgrazing reduced plant diversity by 87%, vegetation cover by 82%, canopy height by 94%, standing crop biomass by 98%, and root biomass by 92% compared with ungrazed grassland in the fifth year. The proportion of poor quality herbages increased to 86%. Non‐grazing assisted recovery of deteriorated vegetation. Though moderate and light grazing also reduced biomass, these treatments did not lead to serious damage to the community species structure. The plant diversity, vegetation cover, and standing biomass in the lightly grazed plots increased over grazing time. The trial showed that a grazing intensity of 2–3 sheep equivalents per hectare was sustainable in the Horqin sandy grassland in Inner Mongolia, China.

Carbon Mineralization Potential in Soils of Different Habitats in the Semiarid Horqin Sandy Land: A Laboratory Experiment

Soil organic carbon mineralization potential in four different sandy habitats (shifting, semi-fixed, fixed sand dune, and interdunal lowland) and the effects of litter addition from shrubs and annual plants on soil microbial respiration were measured using a laboratory soil incubation experiment. Soil samples were collected from beneath and outside the canopies of shrubs in all habitats. Soils were incubated for 33 days with and without litter addition. It was concluded that the differences in C mineralization of soils among habitats correlated with the vegetation cover, litter accumulation, and soil structure, organic C, and N contents. Very poor organic C and N as well as very weak microbial respiration were found in soils of the shifting sand dune, suggesting that sandy desertification strongly depleted both bulk of soil organic C and soil labile C pool. Caragana microphylla litter amended soils and annual plant litter amended soils had the greatest and the lowest microbial respiration, respectively, which might in part be attributed to the N contents and C/N ratios in litters. Shrubs accumulated more organic material and created fertile islands with larger organic C and nutrients and microbial activity under their canopies, and therefore, significantly contributed to C sequestration.

Spatial pattern and heterogeneity of soil organic carbon and nitrogen in sand dunes related to vegetation change and geomorphic position in Horqin Sandy Land, Northern China

To assesses the effect of geomorphology, topography, and vegetation changes on spatial pattern of soil organic carbon (C) and total nitrogen (N) in sand dunes, we used the quantitative methods to examine the spatial heterogeneity of vegetation cover, soil organic C, and total N in an 11-year naturally restored mobile dune (RMD11) and a 20-year naturally restored mobile dune (RMD20) that had been fenced to exclude grazing in Horqin Sandy Land, northern China. Our results showed that the vegetation cover, plant density, species number and diversity, soil organic C, and total N increased from RMD11 to RMD20 and increased from the 50 × 50-m plot (crest) to the 100 × 100-m plot (slope) in each dune. Geostatistical analysis showed that the spatial structural variance accounted for the largest proportion of the total sample variance in vegetation cover, soil organic C, and total N in each dune plot. Calculated spatial autocorrelation ranges of vegetation cover, soil organic C, and total N increased from RMD11 to RMD20, indicating that longer time since vegetation restoration results in a more homogeneous distribution of vegetation cover, soil organic C, and total N in sand dunes. In addition, the spatial continuity of vegetation cover, soil organic C, and total N decreased from the 50 × 50-m plot (crest) to the 100 × 100-m plot (slope) in each dune. These results suggest that the spatial distribution of soil organic C and total N in sand dunes is associated closely with geomorphic position related to the dune crest and slope, relative elevation of sampling site, and vegetation cover. Understanding the principles of this relationship between them may guide strategies for the conservation and management of semiarid dune ecosystems.

Floristic Composition of Vegetation and the Soil Seed Bank in Different Types of Dunes of Kerqin Steppe

The floristic composition of the vegetation and the soil seed bank in different types of dunes of Kerqin steppe were compared. The aim of this study was to examine the influence of desertification on the floristic composition of the vegetation and soil seed bank. An indirect germination method was used to study the seed bank. Thirty species of the vegetation and 25 of the seed bank were identified, 23 species being common to both. Differences between four types of dunes (mobile sand dune, MSD; semifixed sand dune, SSD; fixed sand dune, FSD; interdunal lowland, ILD) in floristic composition of the vegetation and the soil seed bank were examined using nonparametric methods. In the four types of dune, species composition varied significantly except between site MSD and site SSD as well as between site FSD and site ILD in aboveground vegetation. As for soil seed bank, the number of species and seeds differed significantly only between site FSD and site ILD. Species diversity revealed that species numbers increased in the sequence of MSD, SSD, FSD and ILD. The dominant species of aboveground vegetation in site MSD and site SSD were Agriophyllum squarrosum and Setaria viridis, respectively. While in both site FSD and site ILD, the dominant was Eragrostis pilosa. Of total germinated seed, the most abundant species in site MSD were Agriophyllum squarrosum, but the dominant species was Eragrostis pilosa in the other three sites. In each site, more than half of the species recorded in aboveground vegetation were found in the seed bank, even more in the seed bank of site FSD and site ILD. In site FSD and site ILD, high correspondence was observed between the species composition of the aboveground vegetation and of the associated soil seed bank. Spearmans rank correlation coefficients were 0.295, 0.046, 0.704, and 0.612 for site MSD, site SSD, site FSD and site ILD, respectively. These results indicated that desertification development decreased correlation between the seed bank and vegetation in Kerqin Steppe.

Biophysical properties as determinants for soil organic carbon and total nitrogen in grassland salinization.

Grassland salinization causes considerable changes to soil and vegetation, which can lead to changes in soil organic carbon (C) and total nitrogen (N). These changes have complex causal relationships. A significant correlation between soil organic C and total N and any soil or vegetation property does not necessarily imply a significant direct effect of the property on soil organic C and total N. In this study, a field survey was conducted to investigate the changes in soil organic C and total N in grassland along a salinity gradient in Hexi corridor, China, and the direct and indirect effects of soil and vegetation properties on both stocks were quantified using a path analysis approach. Significant decrease in soil organic C and total N contents were observed with increasing salinity. Both had significant positive correlations with the Normalized Difference Vegetation Index (NDVI), soil water, and fine particles (silt+clay) content (p<0.01) and significant negative correlations with soil EC, and sand content (p<0.01). NDVI, fine particles content and soil water content had positive direct effects on soil organic C and total N stocks. Soil EC affected soil organic C and total N stocks mainly through its indirect negative effect on NDVI, soil texture, and water content. NDVI, soil texture, and moisture also indirectly affected soil organic C and total N stocks via changes in each other. These indirect effects augmented each other, although in some cases indirect effects worked in opposing directions.

Comparison of Seed Germination of Agriophyllum squarrosum (L.) Moq. and Artemisia halodendron Turcz. Ex Bess, Two Dominant Species of Horqin Desert, China

Both Agriophyllum squarrosum and Artemisia halodendron play essential roles in the vegetation rehabilitation process in Horqin desert. Responses of germination to temperature, water potential, and burial depth in the two species were studied experimentally. The results showed that: (1) seeds of the two species could germinate with high final percentages (> 67%) at prevailing surface soil (0–5 cm) temperatures from April to July. However, Agriophyllum squarrosum had more efficient mechanisms to ensure that seeds germinate quickly at prevailing May temperatures but slowly at the temperatures of April and July, in comparison to Artemisia halodendron; (2) Artemisia halodendron had higher final germination percentages than Agriophyllum squarrosum when water potential was low (p < .0.01); and (3) seedlings of Artemisia halodendron emerged well only at a depth less than 1 cm and did not emerge at all when the burial depth reached 4 cm, while those of Agriophyllum squarrosum emerged with a final percentage of 21.6% even at the depth of 4 cm. These different characteristics of seed germination and seedling emergence could partially explain the phenomenon that Agriophyllum squarrosum always precedes Artemisia halodendron in establishing on moving sand dunes in Horqin desert.

Biomass Energy, Carbon and Nitrogen Stores in Different Habitats along a Desertification Gradient in the Semiarid Horqin Sandy Land

ABSTRACT The Horqin Sandy Land is one of the most seriously desertified regions of China. We sampled total aboveground and belowground biomass, biomass energy, and the C and N stores in five different habitats along a desertification gradient in the Horqin Sandy Land: interdunal lowland, fixed sand dune, semifixed sand dune, semimobile sand dune, and mobile sand dune habitats. These habitats correspond to the potential, light, moderate, severe, and most-severe levels of desertification. We also sampled soil organic C and N stores at all sites. Along the spectrum from potential desertification to most-severe desertification, total aboveground and belowground biomass decreased by 89 and 91%, respectively, versus decreases of 90 and 91% for the aboveground and belowground biomass energy stores, 91 and 87% for the total aboveground biomass C and N stores, 91 and 96% for the belowground biomass C and N stores, and 90 and 83% for the soil organic C and N stores.

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.