Jianyuan Cui

Specific Leaf Area and Leaf Dry Matter Content of Plants Growing in Sand Dunes

We investigated the variations in specific leaf area (SLA) and leaf dry matter content (LDMC) of 20 species (10 annuals and 10 perennials) that have different distributional patterns in the Kerqin Sandy Land in northern China. The main purpose of our study was to determine if SLA and/or LDMC could be used as indicators of plant resource-use strategy in sand dune environments. The selected species were mainly distributed in three types of sand dunes: mobile sand dune, semi-fixed sand dune, and fixed sand dune. The three differed in their soil nutrient content and vegetation productivity. Both SLA and LDMC varied substantially among species in the different dunes. Maximum SLA (28.2 m^2 kg^(-1)) was observed in the annual grass Setaria viridis in a fixed sand dune, and the lowest SLA (8.6 m^2 kg^(-1)) was found in the perennial grass Pennisetum centrasiatum in a semi-fixed sand dune. LDMC varied from 0.10 g g^(-1) for the annual forb Chenopodium glaucum in a fixed sand dune to 0.41 g g^(-1) for the perennial grass Phragmitis australis in a fixed sand dune. For species common to two or three sites, their SLA and LDMC were significantly different between sites (P＜0.05), except for two species for SLA and six species for LDMC. SLA and LDMC were negatively correlated both in the three types of sand dunes and for each functional type (annual versus perennial species). However, SLA and LDMC were significantly correlated only for the species in fixed sand dune, perennial species as well as all species. The results of our study showed that the SLA of annual plant species was generally higher than that of perennial species and that LDMC was significantly different between annual compared to perennial plants (P＜0.05).

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.

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.