Research On Water Characteristics Of Tree Species And Revegetation Mode In Maowusu Desert.

Maowusu desert, as one of the four sandy land in China, lie in multiple ecotone of semiarid region, there are many physical geography factors such as precipitation, sandstorm, soil and weather,which restrict to agriculture, livestock production and ecological environment treatment. The methods of field survey associated with field test have been adopted to study the spatial and space distribution of precipitation, evapotranspiration(ET) and soil moisture. Meanwhile, the water physiological characteristic of shelter forest tree species have been studied, and species of low water consume for all vegetation types have been screened out. The main restoration models and corresponding technology system have been brought forward too. The main conclusions as follows:(1) The precipitation of Maowusu desert is low and its distribution is extremely uneven, and lower the availability greatly. The results showed that the mean precipitation of Wushenqi County is only 340mm with the distribution pattern of the east higher than the west, the relative variability of annual precipitation is between 13% and 26%. The main rainy season is from Jun to Aug, rainstorm is frequently and infiltration rate of sand matrix soil is high, so as little runoff come into being. The mean ET is 252mm and its distribution pattern is similar to precipitation which is characteristiced with single peak normal distribution curve, the highest ET is in Jul and the lowest are in Feb and Dec, which is similar to precipitation too. The uneven precipitation, fragility and ecotone of the sand eco-system together make lower of the availability of water resource.(2) The sap flow of Pinus sylvestris var. mongoLica and Populus alba var. pyramidaLisa Bunge by TDP have been monitored, the results showed that the daily fluctuation of P. sylvestris var. mongoLica present as single-peak curve which have the peak value at 12:00 and 14:00, this time would appear ahead 2 hours while encountering water stress slightly. The water consume of P. sylvestris var. mongoLica increased gradually from Apr to Jul, the total value from Apr to Sep is 1140.0mm, which is 3.56 times of precipitation, namely 6.25mm/day; The daily fluctuation of P. alba var. pyramidaLisa Bunge present as single peak curve, the peak value appear at 12:00 and 14:00, and would appear ahead about 2 hours when meet water stress slightly and the water consume decreased 46.67%. The water consume would decreased when meet middle and serious water stress. The total water consume in main growth season(from Apr to Oct) is 5300.96L, is 4.93 times of precipitation, and is the most in Jun which is 1073.82L,20.26% of the total and is equivalent to 34.64L/day. The water consume of arbor tree species is so high that is not suitable to plant in Maowusu desert.(3) The daily and seasonal fluctuation of transpiration rate(Tr), photosynthesis rate(Pr) and water potential(Wp) of 11 trees such as P. sylvestris var. mongoLica, P. alba var. pyramidaLisa Bunge, P. tabulaeformis, H. rhamnoides L, S. matsudana, S. psammophyila, S. microstachya, A. fruticos, H. fruticosum var mongoLicum, A. ordosica and S. vulgaris have been studied by Li-6400 and portable pressure chamber. It was showed that daily fluctuation curve of Tr of S. matsudana, S. psammophyila and S. microstachya all have a single peak in main growth season(namely from May to Aug) and the highest of Tr is in Aug, Tr of S. microstachya is higher than the others excepted in May. Tr peak time of S. psammophyila from May to Jul is 12:00 and remit to 14:00 in Aug, Tr peak time of S.matsudana from May to Jun is 12:00 and remit to 14:00 in Jul or Aug, but Tr peak time of S. microstachya in May or Jun is 12:00 and ahead of 2 hours in Jul or Aug for its sensitivity to environment.The daily fluctuation curve of Tr of A. fruticos, H. fruticosum var mongoLicum, A. ordosica and S. vulgaris is multi-peak type. The Tr curve of A. fruticos is double peak in Jun and Jul with peak time of 10:00 and 16:00 respectively, and is single peak in Aug and Sep with peak time of 12:00; The Tr curve of A. ordosica is double peak too in Jun and Jul with peak time of 10:00 and 14:00 respectively; The Tr curve of H. fruticosum var mongoLicum have three peak in Jun with peak time of 10:00,14:00 and 18:00, but in Jul, it had two peak with 10:00 and 16:00, and become to single peak in Aug and Sep. The Tr curve of S. vulgaris in Jun is double peak with 12:00 and 16:00 and become to single type in Jul, Aug and Sep.The comparative analysis of transpiration, photosynthesis and water potential of 11 tree species indicated that:H. fruticosum var mongoLicum has high photosynthesis rate(Pr), high Tr and low water utilization effiency(WUE); H. rhamnoides L, S. microstachya and S. psammophyila have low Tr, high Pr and WUE; C. intermedia and A. fruticos have middle Tr, Pr and WUE; S. matsudana has middle Pr, low Tr and high WUE; A. ordosica has high Pr, middle Tr and low WUE; The two coniferous trees, namely P. sylvestris var. mongoLica and P. tabulaeformis, have similar Pr value, but Tr of the first is low than the latter and the WUE is high than the latter; S. vulgaris has low Pr and WUE.(4) Maowusu desert is characteristiced with ecotone and special physical geography hydrology features, and the vegetation restoration in moving and semi-moving dune based on the water balance and hydraulic physiology ecology characteristics would promote accord development of vegetation and economy.