A Study On The Occurrence Regulation Of Suspended Dust And The Effects Of Suspended Dust In Tarim Basin On Winter Wheat

Suspended dust is a kind of weather phenomena, in which dusts float in air equably and the horizontal visibility is less than10km. Suspended dust usually occurs in spring and summer, the vigorous growth seasons for crops, and has an important role on crop growth and development. Tarim basin in southern Xinjiang, China, is the most serious area occurring suspended dust, and winter wheat is one of main food crops here. The studies on suspended dust occurrence regulations and the effects of suspended dust on growth of winter wheat in tarim basin are of important theoretical and practical significance.The studied areas in this project included Hotan, Yuli, and Tieganlike in Tarim basin. Through references summarizing, field investigations, suspended dust observation and winter wheat planting in field stations, simulation tests, physical and chemical analysis, and other means, this study summarized the occurrence regulation of suspended dust oversees and domestics, especially in Tarim basin, including the sources of suspended dust, distribution, occurrence time, characteristics, composition, dust amount, etc. The occurrence and mechanisms of suspended dust in Tarim basin were discussed, and the Local Atmospheric Circulation was contributed as one of the occurrence mechanisms. Finally, the effects of suspended dust on the growth and development of winter wheat were studied. The main results are as follows:1. Occurrence regulations of suspended dust1.1Distribution of suspended dustUnder the condition of specific climates, soils, and special combination of environment and landform (or specific dust mode), suspended dust happens. In the world, suspended dust occurs mostly in the areas located in the mainland of10-50degree at both north and south latitudes. The factors of the form of suspended dust are as follows:(1) Arid, semiarid and continental climate; less than400mm annual rainfall to be unevenly distributed; higher than2for the ratio of evaporation to precipitation; great difference in temperature; windy and wind speed surpassing4.5m/s.(2) Dry, loose soil lack of structure and vegetation including desert soils, aridisols and steppe soils.(3) The inland remote from sea.(4) Continental environment with the terrain conditions of the combination of "high mountain-steppe desert or desert". The moisture from the ocean is blocked by the high mountain. The terrain structure is of obvious difference between high mountains and low flats. resulting in formation of the Local Atmospheric Circulation. In the areas of above terrain conditions, suspended dust easily happens. According to our references summarizing, there are14sensitive areas in the world in which occurrence of suspended dust is frequent. They are locating at the north of Chile, Argentina, the middle and west of America, the north of Africa and Sahel, the middle of Australia, the Arabian Peninsula, central Asia and the west of China.1.2Origins and formation mechanisms of suspended dustThe origins of suspended dust can be divided into two groups:one is spontaneous (from itself), and is caused by the local region dust emission. The characters of this suspended dust are small range, strong regularity, and floating a long time, produced in the region or nearby, the same areas of dust emission and dust fall, ranging a short distance. The material composition of suspended duct is the same in source as the local soil, and this kind of suspended dust is usually caused by Local Atmospheric Circulation.The other suspended dust was introduced cases, also named extraneous. The characters of this suspended dust are big range, short time, coming from distant dust emission area, emission dust area far away from landing area, the material composition of suspended duct different from the local soil. This kind of suspended dust is often caused by atmospheric circulation, polar cold snap, ocean currents sport, and they often changes with monsoon. This kind of suspended dust often accompanies with dust storm, and has some relationships with occurring winds and sandstorms. It generally occurs on the outskirts of the sandstorm area at the end of dust storms.The occurrence of suspended dust in Tarim basin behaves a certain periodicity. It happens more frequently in spring, the peak usually in May-June, and less in winter.There are two kinds of mechanisms for the suspended dust occurrence in Tarim basin. One is the climate produced by cold air current across Tianshan from north to south in eastern and western Xinjiang. The other is weather caused by local atmospheric circulation. Due to the huge contrast caused by terrain elevation, when the mountain elevation over3000m, a regional temperature difference between mountain and plains can cause directional air flow and produce "Local Atmospheric Circulation", resulting winds. When the temperature difference is higher than18℃and the near-ground surface wind speed over4.5m/s, suspended dust is produced. Because the geothermal in spring heating up too fast, suspended dust is produced easily.This is called "effect of pot bottom". Local Atmospheric Circulation is a global common phenomenon, and it has a close relationship with the occurrence of suspended dust.2. Composition and properties of suspended dustThe most serious period of suspended dust happens basically the same with the growth of winter wheat period. The quantities of suspended dust are different in different regions, time and heights. At70cm height, the fall dust quantity of the whole year is18913.71kg/hm2in Hetian area, where the suspended dust contains more salt, and total salt is56.8g/kg. This suspended dust can influence indirectly on the growth and development of winter wheat through soil. The suspended dust contains many kinds of microelements and heavy metals, also contains a certain amount of nutrients, especially the organic matter and nitrogen. It also contains a variety of pristine, easy weathering minerals, especially low weathered lime and plaster. The pH values in suspended dust are alkaline, and the main machinery contents are thick powder sand (0.02-0.05mm).3. Effects of suspended dust on winter wheat3.1Yield and quality of winter wheatThe effects of suspended dust on the weight of thousand seeds of winter wheat are not significantly, but suspended dust reduces the yield of winter wheat by17%mainly through reducing spikelet number per spike and grain number per main spike of winter wheat. Suspended dust decreases the absorption of winter wheat for N, P. and K. and reduces the contents of amino acids in winter wheat and the grain protein and starch contents in wheat seeds. However, suspended dust increases winter wheat to absorb trace elements, heavy metal elements, and salts, especially for Cl-and SO42-ions. Cl-and SO42-ion in winter wheat reaches27.65g/kg and27.55g/kg, respectively. The cellulose and lignin contents in the stems of winter wheat decrease, tannin content and total carbon increase, and the transfer of starch is affected, when winter wheat is under the conditions of suspended dust environment.3.2Physiological and biochemical process of winter wheatFrom the tillering stage to the flowering period, suspended dust enhances obviously malondialdehyde (MDA) contents, resulting in the damage in winter wheat. Meanwhile, the activity of catalase (CAT) and superoxide dismutase (SOD) diminishes in the leaves of winter wheat at the jointing stage, thus increasing proline contents and relative electrical conductivities and showing real damage in winter wheat. In the conditions of suspended dust, light quantum flux decreases, temperature of leaf surface rises, stomatal conductance significantly decreases, and stomatal resistance significantly increases. Otherwise, suspended dust reduces the area of photosynthesis, jams porosity, inhibits gas exchange, and produces adverse effects on winter wheat photosynthesis and respiration.3.3Morphological structure of winter wheatEther the jointing stage or the fullbloom stage, winter wheat blade structure is subject to the influences of suspended dust, including closer arrangement of mesophyll cells, smaller space of intercellulars, thus affecting blade gas exchange water transpiration. At the jointing stage, the mechanical tissues in winter wheat leaves with suspended dust more develop than those without suspended dsut. At the fullbloom stage, the mechanical tissues are inhibited for a certain extent. The most sensitive period that suspended dust influences winter wheat is the period from March to April, developmental phase from late tillering stage to booting stage, panicle primordium differentiation stage from ear axis to tetrad formation stage. After the flowering stage, suspended dust has no obvious influences on the winter wheat at the grain filling stage.