scholarly journals Permafrost Degradation Leads to Biomass and Species Richness Decreases on the Northeastern Qinghai-Tibet Plateau

Plants ◽  
2020 ◽  
Vol 9 (11) ◽  
pp. 1453
Author(s):  
Xiaoying Jin ◽  
Huijun Jin ◽  
Xiaodong Wu ◽  
Dongliang Luo ◽  
Sheng Yu ◽  
...  
Keyword(s):  
Species Richness ◽  
Water Content ◽  
Soil Water ◽  
Active Layer ◽  
Plant Cover ◽  
Vegetation Indices ◽  
Tibet Plateau ◽  
Ground Biomass ◽  
Below Ground ◽  
Qinghai Tibet Plateau

Degradation of permafrost with a thin overlying active layer can greatly affect vegetation via changes in the soil water and nutrient regimes within the active layer, while little is known about the presence or absence of such effects in areas with a deep active layer. Here, we selected the northeastern Qinghai-Tibet Plateau as the study area. We examined the vegetation communities and biomass along an active layer thickness (ALT) gradient from 0.6 to 3.5 m. Our results showed that plant cover, below-ground biomass, species richness, and relative sedge cover declined with the deepening active layer, while the evenness, and relative forb cover showed a contrary trend. The vegetation indices and the dissimilarity of vegetation composition exhibited significant changes when the ALT was greater than 2.0 m. The vegetation indices (plant cover, below-ground biomass, evenness index, relative forb cover and relative sedge cover) were closely associated with soil water content, soil pH, texture and nutrient content. Soil water content played a key role in the ALT–vegetation relationship, especially at depths of 30–40 cm. Our results suggest that when the ALT is greater than 2.0 m, the presence of underlying permafrost still benefits vegetation growth via maintaining adequate soil water contents at 30–40 cm depth. Furthermore, the degradation of permafrost may lead to declines of vegetation cover and below-ground biomass with a shift in vegetation species.

scholarly journals Effects of soil water content on carbon sink strength in an alpine swamp meadow of the northeastern Qinghai-Tibet Plateau

2021 ◽  
Author(s):  
Junqi Wei ◽  
Xiaoyan Li ◽  
Lei Liu ◽  
Torben Røjle Christensen ◽  
Zhiyun Jiang ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Climate Warming ◽  
Ecosystem Respiration ◽  
Saturated Soil ◽  
Tibet Plateau ◽  
Sink Strength ◽  
Qinghai Tibet Plateau

Abstract. Predicted intensified climate warming will likely alter the ecosystem net carbon (C) uptake of the Qinghai-Tibet Plateau (QTP). Variations in C sink/source responses to climate warming have been linked to water availability; however, the mechanisms by which net C uptake responds to soil water content in water-saturated swamp meadow ecosystems remain unclear. To explore how soil moisture and other environmental drivers modulate net C uptake in the QTP, field measurements were conducted using the eddy covariance technique in 2014, 2015, 2017, and 2018. The alpine swamp meadow presented in this study was a consistent and strong C sink of CO2 (−168.0 ± −62.5 gC m−2 y−1, average ± standard deviation) across the entire 4-year study period. A random forest machine-learning analysis suggests that the diurnal, seasonal, and annual variations of net ecosystem exchange (NEE) and gross primary productivity (GPP) were controlled by temperature and solar radiation. Ecosystem respiration (Re), however, was found mainly regulated by the variability of soil water content (SWC) at different temporal aggregations followed by temperature, the second contributing driver. We further explored how Re is controlled by nearly saturated soil moisture and temperature comparing two different periods featuring identical temperatures and significantly differences on SWC and vice versa. Our data suggest that, despite the relatively abundant water supply, periods with a substantial decrease of SWC or increase of temperature produced higher Re lowering the C sink strength. Our results reveal that nearly saturated soil conditions during the warm seasons can help to maintain lower ecosystem respiration rates and thus enhance the overall C sequestration capacity in this alpine swamp meadow. We argue that changes in soil hydrological conditions induced by a warming climate near permafrost (or seasonal frozen layers) may affect the C sink magnitude of wet and cold ecosystems through changes in soil hydrology and the subsequent effect on respiration losses.

scholarly journals Effects of Seasonal Snow Cover on Hydrothermal Conditions of the Active Layer in the Northeastern Qinghai-Tibet Plateau

2016 ◽  
Author(s):  
Ji Chen ◽  
Yu Sheng ◽  
Qingbai Wu ◽  
Lin Zhao ◽  
Jing Li ◽  
...  
Keyword(s):  
Moisture Content ◽  
Snow Cover ◽  
Water Content ◽  
Active Layer ◽  
Tibet Plateau ◽  
Thermal Resistivity ◽  
Snow Removal ◽  
Seasonal Snow ◽  
Qinghai Tibet Plateau ◽  
Seasonal Snow Cover

Abstract. Snow cover significantly influences the moisture and thermal properties of the active layer in permafrost regions. Seasonal snow cover, soil temperature, and moisture were monitored in the northeastern Qinghai-Tibet Plateau (QTP) from December 2012 to February 2015. According to field data, the following conclusions were drawn. (1) The snow season in this region is predominantly during spring (March to May) and autumn (September to November), the thickness of individual snowfall events is usually less than 5 cm, and the duration of land surface snow cover is generally no longer than 5 days. (2) Removal of seasonal snow cover is beneficial for cooling the active layer in a whole year and in other seasons with the exception of summer. Further analysis on the ground temperature in the active layer shows that the cooling effect of the snow removal maybe results from the high thermal resistivity of snow, the delay of snowfall time in autumn, and the drastic decrease of moisture content in the active layer. (3) Seasonal snow cover maintains the high water content of the active layer. Snow removal can therefore lead to a rapid decrease of soil moisture content. A small decrease in water content of the active layer at the natural snow site (NSS) is related with less rainfall during the monitoring period. Significant differences between the NSS and the snow removal site (SRS) may depend predominantly on the inhibitory action of snow cover on the evaporation capacity of surface soil because of its cooling and shading effects during the daytime and in summer.

scholarly journals Small-Baseline Approach for Monitoring the Freezing and Thawing Deformation of Permafrost on the Beiluhe Basin, Tibetan Plateau Using TerraSAR-X and Sentinel-1 Data

Sensors ◽  
2020 ◽  
Vol 20 (16) ◽  
pp. 4464
Author(s):  
Jing Wang ◽  
Chao Wang ◽  
Hong Zhang ◽  
Yixian Tang ◽  
Xuefei Zhang ◽  
...  
Keyword(s):  
Active Layer ◽  
Surface Deformation ◽  
Residual Deformation ◽  
Dynamic Monitoring ◽  
Tibet Plateau ◽  
Time Lags ◽  
Freezing And Thawing ◽  
Linear Deformation ◽  
Small Baseline ◽  
Qinghai Tibet Plateau

The dynamic changes of the thawing and freezing processes of the active layer cause seasonal subsidence and uplift over a large area on the Qinghai–Tibet Plateau due to ongoing climate warming. To analyze and investigate the seasonal freeze–thaw process of the active layer, we employ the new small baseline subset (NSBAS) technique based on a piecewise displacement model, including seasonal deformation, as well as linear and residual deformation trends, to retrieve the surface deformation of the Beiluhe basin. We collect 35 Sentinel-1 images with a 12 days revisit time and 9 TerraSAR-X images with less-than two month revisit time from 2018 to 2019 to analyze the type of the amplitude of seasonal oscillation of different ground targets on the Beiluhe basin in detail. The Sentinel-1 results show that the amplitude of seasonal deformation is between −62.50 mm and 11.50 mm, and the linear deformation rate ranges from −24.50 mm/yr to 5.00 mm/yr (2018–2019) in the study area. The deformation trends in the Qinghai–Tibet Railway (QTR) and Qinghai–Tibet Highway (QTH) regions are stable, ranging from −18.00 mm to 6 mm. The InSAR results of Sentinel-1 and TerraSAR-X data show that seasonal deformation trends are consistent, exhibiting good correlations 0.78 and 0.84, and the seasonal and linear deformation rates of different ground targets are clearly different on the Beiluhe basin. Additionally, there are different time lags between the maximum freezing uplift or thawing subsidence and the maximum or minimum temperature for the different ground target areas. The deformation values of the alpine meadow and floodplain areas are higher compared with the alpine desert and barren areas, and the time lags of the freezing and thawing periods based on the Sentinel-1 results are longest in the alpine desert area, that is, 86 days and 65 days, respectively. Our research has important reference significance for the seasonal dynamic monitoring of different types of seasonal deformation and the extensive investigations of permafrost in Qinghai Tibet Plateau.

scholarly journals Linking floral biodiversity with nitrogen and carbon translocations in semi-natural grasslands in Lithuani

2015 ◽  
Vol 34 (2) ◽  
pp. 137-146
Author(s):  
Saulius Marcinkonis ◽  
Birutė Karpavičienė ◽  
Michael A. Fullen
Keyword(s):  
Plant Cover ◽  
Chemical Properties ◽  
Above Ground Biomass ◽  
Long Term Effects ◽  
Specific System ◽  
Ground Biomass ◽  
Natural Grasslands ◽  
Below Ground ◽  
Grassland Communities

AbstractThe aim of the present study is to evaluate the long-term effects of long-term piggery effluent application on semi-natural grassland ecotop-phytotop changes (above- and below-ground phytomass production, and carbon and nitrogen allocation in grassland communities) in relation to changes (or variability) in topsoil properties. Analysis of phytomass distribution in piggery effluent irrigated grassland communities showed that dry biomass yield varied from 1.7−5.3 t ha-1. Variability in soil and plant cover created a unique and highly unpredictable site specific system, where long-term anthropogenic influences established successor communities with specific characteristics of above- and below-ground biomass distribution. These characteristics depend more on grassland communities than on soil chemical properties. Families of grasses (Poaceae) dominated the surveyed communities and accumulated most carbon and least nitrogen, while legumes accumulated most nitrogen and lignin and least carbon. Carbon concentrations in above-ground biomass had minor variations, while accumulation of nitrogen was strongly influenced by species diversity (r = 0.94, n = 10, p <0.001) and production of above-ground biomass

Effect of increasing rainfall on the thermal—moisture dynamics of permafrost active layer in the central Qinghai—Tibet Plateau

2021 ◽  
Vol 18 (11) ◽  
pp. 2929-2945
Author(s):  
Zhi-xiong Zhou ◽  
Feng-xi Zhou ◽  
Ming-li Zhang ◽  
Bing-bing Lei ◽  
Zhao Ma
Keyword(s):  
Active Layer ◽  
Tibet Plateau ◽  
Qinghai Tibet Plateau ◽  
Moisture Dynamics
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