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Alpine cold ecosystem with permafrost environment is quite sensitive to climatic changes and the changes in permafrost can significantly affect the alpine ecosystem. The vegetation coverage, grassland biomass and soil nutrient and texture are selected to indicate the regime of alpine cold ecosystems in the Qinghai-Tibet Plateau. The interactions between alpine ecosystem and permafrost were investigated with the depth of active layer, permafrost thickness and mean annual ground temperature (MAGTs). Based on the statistics model of GPTR for MAGTs and annual air temperatures, an analysis method was developed to analyze the impacts of permafrost changes on the alpine ecosystems. Under the climate change and human engineering activities, the permafrost change and its impacts on alpine ecosystems in the permafrost region between the Kunlun Mountains and the Tanggula Range of Qinghai-Tibet Plateau are studied in this paper. The results showed that the permafrost changes have a different influence on different alpine ecosystems. With the increase in the thickness of active layer, the vegetation cover and biomass of the alpine cold meadow exhibit a significant conic reduction, the soil organic matter content of the alpine cold meadow ecosystem shows an exponential decrease, and the surface soil materials become coarse and gravelly. The alpine cold steppe ecosystem, however, seems to have a relatively weak relation to the permafrost environment. Those relationships resulted in the fact that the distribution area of alpine cold meadow decreased by 7.98% and alpine cold swamp decreased by 28.11% under the permafrost environment degradation during recent 15 years. In the future 50 years the alpine cold meadow ecosystems in different geomorphologic units may have different responses to the changes of the permafrost under different climate warming conditions, among them the alpine cold meadow and swamp ecosystem located in the low mountain and plateau area will have a relatively serious degradation. Furthermore, from the angles of grassland coverage and biological production the variation characteristics of high-cold ecosystems in different representative regions and different geomorphologic units under different climatic conditions were quantitatively assessed. In the future, adopting effective measures to protect permafrost is of vital importance to maintaining the stability of permafrost engineering and alpine cold ecosystems in the plateau.

Abstract:Seasonal changes over 2 years (2004)(2005)(2006) in soil moisture content ( v ) of frozen alpine frost meadow soils of the QinghaiTibet plateau permafrost region under three different levels of vegetation cover were investigated. Vegetation cover and air temperature changes had significant effects (synergistic effect) on  v and its distribution in the soil profile. During periods of soil freezing or thawing, the less the vegetation cover, the quicker the temperature drop or rise of soil water, and the shorter the duration of the soil water freeze-thaw response in the active soil layer. Under 30% and 65% vegetation cover the amplitude of variation in  v during the freezing period was 20-26% greater than that under 93% cover, while during the thawing period, it was 1Ð5-to 40Ð5-fold greater. The freezing temperature of the surface soil layer, f T s , was 1Ð6°C lower under 30% vegetation cover than under 93% vegetation cover. Changes in vegetation cover of the alpine frost meadow affected  v and its distribution, as well as the relationship between  v and soil temperature (T s ). As vegetation cover decreased, soil water circulation in the active layer increased, and the response to temperature of the water distribution across the soil profile was heightened. The quantity of transitional soil phase water at different depths significantly increased as vegetation cover decreased. The influence of vegetation cover and soil temperature distribution led to a relatively dry soil layer in the middle of the profile (0Ð70-0Ð80 m) under high vegetation cover. Alpine meadow  v and its pattern of distribution in the permafrost region were the result of the synergistic effect of air temperature and vegetation cover.

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CO 2 emission fluxes of two types of ecosystem, swamp meadow and alpine meadow, in the Fenghuoshan region of the Qinghai-Tibet Plateau were studied by the static chamber-portable infrared chromatographic method. The results showed that there was large difference in the CO 2 emission fluxes between the two ecosystems and in the same ecosystem of different degradation degrees. CO 2 emission flux of the swamp meadow gradually decreased with increasing degradation degree, while that of the alpine meadow gradually increased with increasing degradation degree except in May. The CO 2 emission flux of undegraded swamp meadow was 65.1%-80.3% higher than that of undegraded alpine meadow; and the CO 2 emission flux of moderately degraded swamp meadow was 22.1%-67.5% higher than that of alpine meadow; but the CO 2 emission flux of severely degraded alpine meadow was 14.3%-29.5% higher than that of swamp meadow. The soil moisture content and temperature in the upper 5 cm soil layer and above-ground biomass were significantly correlated with the CO 2 emission fluxes and regarded as the main environment factors to control the CO 2 emission.

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Soil organic carbon (OC) and nitrogen (N) associated with particle size fractions can be used as sensitive indicators to evaluate impacts of land use change on soil total OC (TOC) and total N (TN) pools. Aeolian sandy‐soils were collected from seven sites in the Tengger Desert, representing a 56‐year chronosequence of plant restoration at decadal intervals in an arid desert region. Bulk soils were separated into silt + clay (<53 μm), fine sand (53–100 μm), and coarse sand (>100 μm) fractions. TOC and TN concentrations of bulk soil and their levels associated with particle size fractions were analyzed. Results showed that plant restoration promoted C and N sequestration in both topsoil and subsoil layers over time, as indicated by elevated levels of OC and N associated with silt + clay and sand fractions. TOC and TN concentrations of 56‐year restored topsoil respectively increased by 31‐ and 43‐fold than did the control (moving dunes); corresponding levels associated with silt + clay or coarse sand fraction respectively increased by more than 30‐ and 20‐fold, whereas less than 15‐fold increases were found in fine sand fraction. In the early stages of plant restoration, both C and N sequestration primarily resulted from finer particle size fractions. In the later stages, increased C sequestration was principally derived from coarse sand fraction, whereas N sequestration was mainly derived from silt + clay fraction. The results highlight that plant restoration stage and soil textural change are key factors leading to divergent soil C and N sequestration in the arid desert region.

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