The Characteristics And Variations Of Organic Stable Carbon Isotope Composition Among 18 Typical Shrubs And Their Related Site Soils In Xinjiang

As the main component of desert vegetation in Xinjiang, shrub has a wide distribution area and a large number of species, and plays an important role in maintaining the stability of the ecological system in arid and semi-arid areas. Grasp the stable carbon isotope composition characteristics of shrubs and soil organic matter can not only to evaluate the drought resistance among different shrub species, and to explore the effects of environment factor on shrub ?13C, but also can determine the range of fractionation in ?13C between shrubs leaf and surface soil organic matter, which has important significance to the desert ecological conservation, damaged ecosystem restoration and shrub- soil carbon cycle process. Based on this, 18 common shrubs in Xinjiang were chosen as the research object in this study, and the ?13C value, C content,N content in the leaf(C3) / assimilation branch(C4) and the ?13C value and SOC content of the site soil were measured according to its distribution area and habitat characteristics(34 samples),and the composition and variation characteristics of carbon isotopic composition and its relationship with environmental factors were analyzed. The main results are as follows:(1)?13C in the assimilating branch of H. ammodendron averaged 14.15‰ with a range from-13.14 to-15.38‰ at a 95% confidence interval, and different from the ?13C value distribution range of C3 photosynthetic pathway plant(-23.00‰ ~-38.00‰), which indicated that H.ammodendron was characterized by a C4 photosynthetic pathway. Along an environmental gradient, ?13C values of H. ammodendron was negatively and significantly correlated with mean annual precipitation and mean annual temperature, but positively correlated with altitude, duration of sunshine, and evaporation.?13C values of H. ammodendron varied significantly among different habitats, and the highest ?13C values appeared when H. ammodendron was found with Nitraria tangutorum and Reaumuria Linn. in grey and grey-brown desert soils, and distributed in plain,mountainous and hill habitats, whereas the lowest ?13C values were observed when H.ammodendron was found with Ceratoides arborescens and Calligonum mongolicum located in aeolian sandy and chisley soils, and distributed in Junggar Basin. Together, our results demonstrated that water use efficiency of H. ammodendron varied significantly along environmental gradients and habitats, indicating a divergent adaptation strategy for water use efficiency.(2) Leaf ?13C values in 18 kinds of typical shrubs in Xinjiang ranged from-12.95‰ to-29.40‰. Among them, leaf ?13C values in C3 plants ranged from-22.89‰ to-29.40‰,with the mean of-26.63‰, more positive than that of global C3 plants; the ?13C values of assimilating branche in C4 plants ranged from-12.95‰ to-15.00‰,with the mean of-13.96‰. The long-term water use efficiency was different in different shrub species, and the long-term water use efficiency of Halostachyscaspica, Suaedacrassifolia, Reaumuriasoongarica, Tamarixchinensis,Ephedra, Kalidium were higher than Alhagisparsifolia, Atraphaxisfrutescens, Nitrariatangutorum.In our study area, the leaf ?13C values of C3, C4 plants were decreased significantly with theincreasing of carbon content and C/N. The ?13C values, C and N content and C/N are difference significant in different organs of C3 shrub, and the?13C values of leaves, branches and stems were gradually positive. The ?13C values of assimilating branches in C4 plants ranged from-12.95‰ to-15.00‰, with the mean of-13.96‰, and the ?13C values of stem in C4 plants ranged from-12.51‰ to-14.87‰, with the mean of-13.64‰, thus, the ?13C values of stems was more positive than assimilating branches in C4 plants.(3)SOC content of surface soil(0~5 cm) in 33 plots of our study area ranged from 0.14 g·kg-1to 102.91g·kg-1, including 24 plots(all of them is desertifieation grassland) less than 10 g·kg-1,accounting for more than 70% of the total plots, suggesting that surface soil organic matter is relatively poor in desert area of Xinjiang. The vertical direction, SOC content with soil depth was generally characterized by the following changes: the SOC content was decreased dramatically from the maximum value in surface soil, and then fell to a certain depth in slowly decreasing stage and remained stable in the deep soil layer; but the SOC reduce speed and depth of soil layer are different in different sites. In contrast with the SOC, the ?13C values of soil organic matter were increased with the increasing of soil depth at first, and decreased with the increasing of soil depth after reached the maximum value in mostly shrub site. However, because the different vegetation development status and developmental history, the ?13C values of soil organic matter were decreased with the increasing of soil depth in several sites. There was significant positive correlation between leaf ?13C values of shrubs(?13C values of assimilating branch in C4 plants) and?13C values of surface soil organic matter.