Variation In Organic Carbon Isotope Composition Values Of Plant And Surface Soil Along An Altitude Gradient In The Tianshan Mountains

Mountains provide sites where climate (including temperature, precipitation, atmospheric CO2 concentration and mineral nutrients in soil, etc) change rapidly over short distances. Changing environmental conditions of alpine plants may result in morphological and physiological responses. All the environmental factors and biological factors can influence leafδ13C in alpine plants directly or indirectly. Thus, changes ofδ13C in alpine plants along with altitude provide ideal indications for understanding the effects of environmental and biological factors on plantδ13C, and may predict that to what degree environmental differences caused by climate changes will influence plants in the future. The spatial variation ofδ13C in alpine plants is influenced by alpine climate diversity and regional difference, but the explanation of mechanism has not reached the same conclusions. Moreover, when the higher plants litter is decomposed to soil organic matter, carbon isotopic fractionation is likely to occur. This will induce the discrepancies ofδ13C values between in surface soil organic matter and standing vegetation. However, regional climatic diversity and different plant types can make the different range of fractionation inδ3C between in alpine plants leaf and in surface soil organic matter. Study the relationships betweenδ13C values in surface soil organic matter and in modern standing vegetation can provide the scientific basis for obtaining the valuable information of paleo-vegetation and reconstructing the paleo-climate and paleo-environment fromδ13C values in sediments of interior mountainous areas and surrounding areas (such as inland lake sediment).Tianshan Mountains lie in the inland arid area of Asia, have the typical vertical vegetation distribution. And the distribution of vegetation is controlled by the precipitation brought by westerly zone. The thesis analyzed the variation trends of theδ13C value in alpine plants leaf and in surface soil organic matter along an altitudinal gradient (from 617 m to 3660m) in Tianshan Mountains, to reveal the influence mechanism of environmental factors (including meteorological factors and edaphic factors) and biological factors in the variation trends in leafδ13C value of alpine plants along an altitudinal gradient in the northern and southern slopes, and contrasted them among the vegetation types (dividing into herbs, shrubs and trees). Moreover, adaptive strategies to environmental conditions of different type of plants in the northern and southern slopes were analyzed from the water use efficiency (WUE) viewpoint. At last, the fractionation ofδ13C between alpine plants leaf and surface soil organic matter and the relationships betweenδ13C values in surface soil organic matter under different vegetation types against elevations also were discussed and contrasted in the northern and southern slopes. At the mean time, the characteristics of variation trends of theδ13C value in alpine plants leaf and in surface soil organic matter along an altitudinal gradient were contrasted between Tianshan Mountains where influenced by westerly zone and the mountains in monsoon region of our country. Main conclusions of this dissertation are outlined as follows: 1 Variation and influencing factors in leafδ13C values of C3 plants along an altitude gradient in the northern and southern slopes of the Tianshan MountainsLeafδ13C values in C3 plants in the Tianshan Mountains ranged from-31.65%o to-23.39%o, with a mean of-27.99%o, more negative than that of global C3 alpine plants, and that of C3 alpine plants in monsoon region of our country. Leafδ13C values of C3 alpine plants in the northern slopes of Tianshan Mountains showed variable trends with respect to altitudes. It decreased with increasing altitude below 2240 m, and increased with increasing altitude above 2240 m. Therefore, the variation in leafδ13C values of C3 alpine plants along an altitude gradient would be controlled mainly by two different climatic factors: precipitation at low distribution altitude, and temperature at high altitude. Overall, temperature had great influence on plants. Among the influencing factors controlling the variation trends in leafδ13C value of alpine plants along an altitudinal gradient in the northern slopes, soil total phosphorus(TP) was the primary edaphic factor; The chlorophyll content was the primary biological factor. Leafδ13C values of C3 alpine plants in the southern slopes increased significantly with increasing altitude. Among the influencing factors controlling the variation trends in leafδ13C value of alpine plants along an altitudinal gradient in the southern slopes, temperature was the primary meteorological factor; soil water content (SWC) was the primary edaphic factor; the leaf thickness was the primary biological factor. The variation trends in leafδ13C value of alpine plants along an altitudinal gradient in the Tianshan Mountains were influenced by environmental factors and biological factors together, but temperature was the most important factor among the environmental factors. So the variation trends in leafδ13C value of alpine plants along an altitudinal gradient in the Tianshan Mountains could reflect changes of temperature. It was because the disparity of the natural environment between the northern slopes and southern slopes that made different influences in leafδ13C value of alpine plants caused by different environmental factors and different biological factors.2 Variation and influencing factors in leafδ13C values of C3 herbs along an altitude gradient in the northern and southern slopes of the Tianshan MountainsLeafδ13C values in C3 herbs in the Tianshan Mountains ranged from-28.82%o to-23.39‰, with a mean of-27.73%o, more negative than that of global alpine C3 herbs, and that of alpine C3 herbs in monsoon region of our country, but more positive than that of alpine C3 herbs in East Tianshan Mountains. Leafδ13C values of alpine C3 herbs in the northern slopes decreased with increasing altitude below 2240 m, and increased with increasing altitude above 2240 m. Leafδ13C values of alpine C3 herbs increased linearly with altitude in the southern slopes, and was in accordance with the altitudinal trends of global alpine C3 herbs, alpine C3 herbs in monsoon region of our country and alpine C3 herbs in East Tianshan Mountains. Among the influencing factors controlling the variation trends in leafδ13C value of alpine herbs along an altitudinal gradient, precipitation was the primary meteorological factor at low distribution altitude, and temperature was the primary meteorological factor at high altitude in the northern slopes, while temperature was the primary meteorological factor in the southern slopes; TP was the primary edaphic factor in the northern slopes, soil organic matter content (O.M.) was the primary edaphic factor in the southern slopes; the chlorophyll content was the primary biological factor in the northern slopes, leaf nitrogen concentration per unit mass(Nm) was the primary biological factor in the southern slopes.3 Variation and influencing factors in leafδ13C values of shrubs along an altitude gradient in the northern and southern slopes of the Tianshan MountainsLeafδ13C values in alpine shrubs in the Tianshan Mountains ranged from-30.03‰to-23.85%o, with a mean of-27.81%o, more negative than that of alpine shrubs in monsoon region of our country. Leafδ13C values of alpine shrubs in the northern slopes showed no obviously trend with increasing altitude, while that of alpine shrubs in the southern slopes increased with increasing altitude. Among the influencing factors controlling the variation trends in leafδ13C value of alpine shrubs along an altitudinal gradient, influence of meteorological factors were small in the northern slopes, while temperature was the primary meteorological factor in the southern slopes; O.M. was the primary edaphic factor in the northern slopes, TP was the primary edaphic factor in the southern slopes; leaf water content (LWC) was the primary biological factor in the northern slopes, the leaf thickness was the primary biological factor in the southern slopes.4 Variation and influencing factors in leafδ13C values of alpine trees along an altitude gradient in the northern and southern slopes of the Tianshan MountainsLeafδ13C values in alpine trees in the Tianshan Mountains ranged from-31.52%o to-24.69%o, with a mean of-28.72%o, more negative than that of global alpine trees, and that of alpine trees in monsoon region of our country. Leafδ13C values of alpine trees in the northern slopes showed no obviously trend with increasing altitude, while that of alpine trees in the southern slopes showed variable trends with increasing altitudes. Among the influencing factors controlling the variation trends in leafδ13C value of alpine trees along an altitudinal gradient, temperature was the primary meteorological factor in the northern and southern slopes; O.M. was the primary edaphic factor in the northern slopes, TP was the primary edaphic factor in the southern slopes; Nm was the primary biological factor in the northern slopes, the leaf thickness was the primary biological factor in the southern slopes.5 Differences of water use efficiency (WUE) and adaptive strategies to environmental conditions of different type of plants in the northern and southern slopes of the Tianshan MountainsLeafδ13C values of C3 plants (including herbs, shrubs and trees) in the southern slopes were more positive than that in the northern slopes, this revealed that C3 plants in the southern slopes have higher water use efficiency (WUE) than that in the northern slopes. Precipitation in the southern slopes is obviously less than that in the northern slopes, so changes of water in habitats cause changes of WUE in plants. C3 plants in the southern slopes enhanced its water use pattern to adapt to habitats with deficient water level, and this will increase its competitive ability and ecological adaptability across a wide range of habitats than that in the northern slopes. Regardless of it was in the northern slopes or in the southern slopes, leafδ13C values of perennial herbs were more positive than that of annual herbs, and leafδ13C values of evergreen shrubs were more positive than that of deciduous shrubs, and leafδ13C values of evergreen trees were more positive than that of deciduous trees (except that leafδ13C values of deciduous trees were more positive than that of evergreen trees in the northern slopes). All of these indicated that plants with long life cycle enhanced its water use pattern and increased its ecological adaptability than that with short life cycle.6 Variation inδ13C values of surface soil organic matter along an altitude gradient and fractionation ofδ13C between plants leaf and surface soil organic matter in the northern and southern slopes of the Tianshan Mountains(1) Theδ13C values in surface soil organic matter in the Tianshan Mountains ranged from-28.99%o to -19.62‰, with a mean of-25.09‰, more negative than that of surface soil organic matter in monsoon region of our country. Theδ13C values of surface soil organic matter in the southern slopes were more positive than that in the northern slopes, were in accordance with the result that leafδ13C values of C3 plants in the southern slopes were more positive than that in northern the slopes. Theδ13C values of surface soil organic matter decreased with increasing altitude at low altitude, and increased with increasing altitude at high altitude in the northern and southern slopes, were consistent with the altitudinal trends ofδ13C values in surface soil organic matter in the Qinghai-Tibetan Plateau. The altitudinal trend ofδ13C values in surface soil organic matter in the northern slopes was in accordance with that of leafδ13C values in C3 plants in the northern slopes, but the altitudinal trend ofδ13C values in surface soil organic matter in the southern slopes was inconsistent with that of leafδ13C values in C3 plants in the southern slopes, perhaps it was influenced more by local topography and local environment than by meteorological factors.(2) Under the vegetation types in the northern slopes, the averageδ13C values of surface soil organic matter showed an increase trend with a sequence of trees< shrubs<herbs. When herbs were subdivided, the averageδ13C values of surface soil organic matter showed an increase trend with a sequence of alpine meadow< trees< shrubs< subalpine meadow< desert grassland. Under the vegetation types in the southern slopes, the averageδ13C values of surface soil organic matter showed an increase trend with a sequence of shrubs≈herbs< trees. When herbs were subdivided, the average<δ13C values of surface soil organic showed an increase trend with a sequence of subalpine meadow< desert grassland< shrubs< trees < alpine meadow. The sequences of increase trend in averageδ13C values of surface soil organic matter under the vegetation types in Tianshan Mountains were inconsistent with that in the Qinghai-Tibetan Plateau.(3) The fractionations ofδ13C between alpine plants leaf and surface soil organic matter in Tianshan Mountains were large than that in some other place. The fractionations ofδ13C in the northern slopes ranged from 0.23‰to 4.39‰, with a mean of 2.75‰, while the fractionations ofδ13C in the southern slopes ranged from 0.21‰to 4.20‰, with a mean of 2.32‰. We could see that the fractionations ofδ13C in the northern slopes were large than that in the southern slopes. And the sequence of fractionations ofδ13C were unity among different plants types in the southern and northern slopes, trees> shrubs> C3 herbs.