| Mu Us sandy land is an important ecological barrier in Northern China. Artemisiaordosica is the dominant species in Mu Us sandy land, which covers31.2%of the total area.With tolerance to drought, sand buried, resistance to barren and wind erosion, and easybreeding, A. ordosica plays an important role in maintaining the local ecosystem stability. Thesuccession of A. ordosica community in Mu Us sandy land experiences the following stages:pioneer stage in shifting sand dunes--sparse stage in semi-fixed sand dunes--build phase infixed sand dunes--degradation stage in old fixed sand dunes--shifting sand dunes. Previousstudies considered that soil moisture was an important factor which driving the cyclesuccession of A. ordosica community. However, at present, most of the researches on soilmoisture in Mu Us sandy land were timing, fixed-point sampling, the dates were little and lackof continuity, which couldn’t reflect the dynamic of soil moisture. In this experiment weobserved the soil moisture of A. ordosica community of pioneer stage in shifting sand dunes,sparse stage in semi-fixed sand dunes and build stage in fixed sand dunes with a long-termcontinuous monitoring, analyzed the characteristics of soil moisture of different successionstages of A.ordosica community, supplied conditions of precipitation to soil moisture and theredistribution of biological soil crust (BSC) to precipitation; At the same time combined thephysiological and ecological characteristics of A. ordosica, in order to better understand therole of soil moisture in the succession process of A. ordosica community in Mu Us sandy land,which could provide a scientific and reasonable way for local government to rebuild vegetationin Mu Us sandy land. The main conclusions can be drawn as follows:1. There were horizontal and vertical difference of soil moisture with all of the three kindsof samples, soil moisture of shifting sand dunes in every layer were significantly higher thanthe fixed and semi-fixed sand dunes; soil moisture was mainly influenced by rainfall, the depthof infiltration was determined by the amount of rainfall, most of less than10mm rainfalls wereabsorbed by top soil while10-20mm rainfall could infiltration deeper than30cm, the rainfall more than30mm and less than40mm could reach depth more than60cm but less than100cm;soil moisture less than30cm was dramatically, but soil moisture at60cm was less dramaticallywhich was mainly affected by rainfall events more than30mm, soil moisture at100cm and160cm were stability which almost not affected by rainfall; the heterogeneity of soil moisturebetween fixed, semi-fixed and shifting sand dunes was mainly caused by the differences ofinfiltration depth of rainfall and roots distribution of vegetation.2. Water is the most important limited factor in the arid and semi-arid ecosystems, whileroots are the important organs for plant to uptake soil moisture. In the three kinds ofsand-dunes, the most A. ordosica roots were all coarse roots, followed by medium-coarse rootsand fine roots, and the three kinds of roots biomass were all exponential-like decreased withthe increase of soil depth. The proportion of fine roots range of0~40cm in the fixed,semi-fixed and drifting sand-dunes were79.11%,74.71%and53.23%, respectively. A.ordosicain the fixed, semi-fixed sand-dunes mainly uses the0~40cm soil moisture while A. ordosica inthe drifting sand-dunes could use more soil moisture below40cm. The leaf water potential ofA. ordosica in all of the three kinds of samples had the peak value at5:00, then decreasing withthe augmentation of the of the solar radiation intensity, reaching the lowest value around13:00,after that, the leaf water potential gradually began to rise again with the decreasing of the angleof the sun; the correlation analysis showed that the leaf water potential of A. ordosica had anegative correlation to the air temperature and the photosynthetic available radiation, but therewere no significant correlation with atmospheric relative humidity and soil moisture; the basictrend of leaf water potential of A. ordosica in the three kind of sample were in the followingorder: shifting sand dune> semi-fixed sand dune> fixed sand dune, but the trend wereopposite between15:00-17:00, which were mainly caused by age difference of A.ordosica andthe shallow soil moisture.3. The BSC coverage was83.74%on average in fixed sand dunes, and in semi-fixed sanddunes the BSC cover was23.54%on average. The distribution proportion of mosses, lichensand alga dominated BSC were28%,21%and51%in fixed sand dunes, and6.3%,2.5%and91.2%in semi-fixed sand dunes, respectively. Most of the BSC in semi-fixed sand dunes was alga crust which belongs to the initial developmental stage. The development of BSC inA.ordosica communities could significantly improve the soil physicochemical properties andaffect the redistribution process of precipitation. Regardless of precipitation size, the responsetimes of BSC were significantly greater than NBSC at the same depth, the initial infiltrationcoefficient and the mean infiltration coefficient of BSC were all significantly lower than NBSCat the same precipitation, which means the presence of BSC hindered the infiltration ofprecipitation, this situation was more obviously in small precipitations; most of the absorbingroots of A. ordosica were within the40cm soil, primarily take advantage of soil water in thislevel, but the development of biological soil crust seriously impediment the less than20mmprecipitations, which is the most common precipitation events, that would resulting in thedeterioration of soil moisture within40cm, and led to the recession of A.ordosica in the fixedsand dunes in a long time; at the same time, the change of precipitation pattern could have animportant impact on soil moisture and vegetation succession. |
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