Tian Changyan

Suitable scale of Weigan River plain oasis

Desert coexists with oasis in long time, and the existence and development of oasis system demand better oasis vegetation ecological system. Oasis scale of arid zone plain encircling water should be determined in case of desertification caused by land over-reclamation under the circumstance of water resources shortage. Steady oasis with virtuous circle must have appropriate land use structure for agriculture, forestry and graziery. The study on the suitable scale and developmental space of oasis will provide theoretical and applicable foundation for effective construction of oases. By analyzing the hydrothermal, water and soil balance, an optimal mathematical model has been established. Based on hydrometeorology data collected for years in Weigan River plain, and by the principle of water balance, a calculation has been made of the water resources for evapotranspiration and the optimal acreage of oasis and cultivated land, which shows that the water resources for evapotranspiration in the Weigan River plain oasis is 22.32×108 m3 and the optimal oasis acreage under the condition of conventional irrigation mode is 3716.06 km2, in which the suitable cultivated land acreage is 1564.79 km2. Under the condition of water-saving irrigation, the suitable oasis acreage is 5515.49 km2, in which the suitable cultivated land acreage is 2322.31 km2. The oasis area had reached 4123 km2, and the cultivated land acreage had reached 1507 km2 after the Agriculture Irrigation Drainage Water Project of World Bank Loan in Weigan River basin was finished in 1997. The oasis and cultivated land acreage will be more suitable, and the oasis scale can be enlarged moderately by means of water saving irrigation.

Arbuscular mycorrhizal associations in the Gurbantunggut Desert

The plants in the Gurbantunggut Desert located in Xinjiang, China are drought adapted species and grow in generally nutrient-poor soils. A survey was conducted in the desert to determine the arbuscular mycorrhizal (AM) status associated with the desert plants which belong to 23 species from 11 families of annuals and perennials. Roots from all plants were examined for the presence of internal and external hyphae, vesicles and coils/arbuscules to determine the status and extent of mycorrhizal colonization. Of the plant species surveyed, 14 (61%) were found to form AM associations, 5 (22%) were possible AM colonized species, and 4 were non-mycorrhizal plants. The proportions of annuals and shrubs forming AM were significantly lower than those of perennials and herbs, respectively. Spore density varied from 5 to 21 per 20 g in soil of root zone. 14 AM fungal taxa in 3 genera were isolated and identified, 10 of which belonged to Glomus, 3 to Acaulospora, and 1 to Archaeospora. Glomus was the dominant genus in all genera identified. G. deserticola and G. etunicatum were the most common taxa isolated, with occurrence frequencies of 77.4% and 74.8%, and relative abundances of 14.4% and 15.5%, respectively.

Characteristics and dynamics of the soil seed bank at the north edge of Taklimakan Desert

In order to understand the potential of revegetation of halophytic community at the north edge of Taklimakan Desert, the species structure, storage capacity, the vertical distribution pattern and seasonal dynamics of soil seed bank and their interrelationship with community structure of above-ground plants were investigated. The results show that (i) 9 species were identified from seed bank in different seasons indicating that plant composition in this area was simple. (ii) The seed density in soil was 222±10.79 grain/m2 on average, and showed a seasonal variation range from 132±8.16 grain/m2 in summer to 303±12.70 grain/m2 in autumn. (iii) The similarity coefficient between soil seed bank and above-ground vegetation was 0.778. (iv) Vertically, seed densities declined with soil depth. 82.4% of total seeds were found in the top 3 cm of soil profile. No active seeds were found in soil profile below 6 cm. It is concluded that the seed bank at the north edge of Taklimakan Desert contains active seeds of all plant species observed on above ground, and is able to supply potential contribution to reconstruction of vegetation.

Models for calculating phreatic water evaporation on bare and Tamarix-vegetated lands

Groundwater is the main source of water consumption of natural vegetation in arid regions. It is an effective approach to study ecological water demand of natural vegetation by phreatic evaporation. In order to study the ecological water demand of Tarim river basin, based on the observation data of phreatic evaporation on bare lands at the Aksu Water Balance Experimental station from 1989 to 1996, by analyzing the relationship of phreatic evaporation, depth of phreatic surface and evaporation of water, taking the limit rate of phreatic evaporation as the control condition, and based on the objective law that the relation between phreatic evaporation and evaporation of water is nonlinear, we establish models for calculating phreatic evaporation on bare land, which can fully reflect the law of phreatic evaporation in the Tarim river basin. According to the data of depth of phreatic surface and soil moisture when pheratic level decline is caused just by evapotranspiration on Tamarix-vegetated land from 2003 to 2004, we calculate the amount of phreatic evapora-tion and set up models for calculating phreatic evaporation on Tamarix-vegetated land. Phreatic evaporation on bare land and Tamarix-vegetated land could be transformed each other by a Tamarix vegetation conversion coefficient. The test results show that the calculation accuracy of the models is high and the models are suitable for Tarim river basin.

Diversity and zonal distribution of arbuscular mycorrhizal fungi on the northern slopes of the Tianshan Mountains

The arbuscular mycorrhizal (AM) fungal status of the 20 most common plant species distributed in 4 vegetation types (meadow steppe, desert steppe, steppe desert and typical desert) on the northern slopes of the Tianshan Mountains was investigated. Samples of the plant species and their rhizosphere soils were collected from the 4 vegetation zones and examined to compare their mycorrhizal status, AM fungal spore densities, biovolumes, and community structures. 28 AM fungal species were isolated from the rhizosphere soils: of these, 5 belonged to Acaulospora, 1 to Archaeospora and 22 to Glomus. 5 AM fungi, Glomus aggregatum, G. claroideum, G. deserticola, G. etunicatum and G. sinuosum, were observed in all 4 zonal types. No significant differences were observed in mean proportion of root length colonized by AM fungi among the plant species within each zonal type. Comparing the 4 zonal types, Plantago minuta (84.5%) in steppe desert and Eremopyrum orientale (83.1%) in typical desert showed the highest root colonizatsion rates. AM fungal spore densities and biovolumes were significantly different in the different zonal types. AM fungal spore densities and biovolumes, species richness and diversity were highest in meadow steppe and lowest in typical desert.