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EN
A warming experiment with two magnitudes was performed in an alpine meadow of Northern Tibet since late June, 2013. Open top chambers (OTCs) with two top diameters (0.60 m and 1.00 m) were used to increase soil temperature. Soil respiration (Rs) was measured during the growing season in 2013–2014. The OTCs with top diameters of 1.00 m and 0.60 m increased soil temperature by 1.30 and 3.10oC, respectively, during the whole study period, but decreased soil moisture by 0.02 and 0.05 m3 m-3, respectively. However, the two patters of OTCs did not affect Rs . These results implied that a higher warming did not result in a higher Rs but a greater soil drying. Therefore, a higher warming may not cause a higher soil respiration, which was most likely due to the fact that a higher warming may result in a greater soil drying.
EN
We use GRACE gravity data released by the Center for Space Research (CSR) and the Groupe de Recherches en Geodesie Spatiale (GRGS) to detect the water storage changes over the Tibetan Plateau (TP). A combined filter strategy is put forward to process CSR RL05 data to remove the effect of striping errors. After the correction for GRACE by GLDAS and ICE-5G, we find that TP has been overall experiencing the water storage increase during 2003-2012. During the same time, the glacier over the Himalayas was sharply retreating. Interms of linear trends, CSR’s results derived by the combined filter are close to GRGS RL03 with the Gaussian filter of 300-km window. The water storage increasing rates determined from CSR’s RL05 products in the interior TP, Karakoram Mountain, Qaidam Basin, Hengduan Mountain, and middle Himalayas are 9.7, 6.2, 9.1, –18.6, and –20.2 mm/yr, respectively. These rates from GRGS’s RL03 products are 8.6, 5.8, 10.5, –19.3 and –21.4 mm/yr, respectively.
EN
The effects of the growing season climatic factors (i.e., temperature, precipitation, vapor pressure and relative humidity) on the growing season maximum normalized difference vegetation index (MNDVI), which can mirror the aboveground net primary production and the vegetation maximum absorbed ability of photosynthetically active radiation, were examined during the period from 2000 to 2012 on the Tibetan Plateau. The effects of climatic factors on the MNDVI changed with vegetation types, which was probably due to the fact that the changes of climatic factors differed with the type of vegetation. There was a significant increasing trend for the spatially averaged MNDVI of the vegetation area over the entire plateau. Approximately 16 and 3% of the vegetation area demonstrated a significant MNDVI increasing and decreasing trend, respectively. The MNDVI was significantly affected by relative humidity and vapor pressure, but not affected by temperature and precipitation over the entire plateau. Our findings suggested that the environmental humidity played a predominant role in affecting the variation of MNDVI over the entire Tibetan Plateau.
EN
Partitioning sources of ecosystem and soil respiration (Reco and Rs) is important for understanding how climate change affects carbon cycling. Plant and microbial biomass analyses and daytime measurements of Reco and Rs were performed for 25 plots in an alpine meadow at elevation 4313 m on the Tibetan Plateau. Plant and microbial biomass were determined by harvesting method and the chloroform fumigation-extraction method, respectively. Respiration fluxes were measured by an automated CO2 flux system (LI-8100, LI-COR Biosciences, Lincoln, NE, USA). Soil respiration can be estimated by a linear or exponential relationship between Reco and aboveground plant biomass (AGB). Microbial respiration (Rm) can be estimated by a linear or exponential relationship between Rs and belowground plant biomass (BGB) or by a multiple relationship between Reco and AGB and BGB. Soil respiration (or Rm) is respiration flux when AGB (or BGB) is extrapolated to zero for the linear and exponential regression methods. Similarly, Rm is respiration flux when both AGB and BGB are zero for the multiple regression method. Our findings suggest that the exponential regression method to partition sources of Reco and Rs may be more appropriate compared to other methods for this alpine meadow of Tibet.
EN
Microbes remain active and play an important role in soil nitrogen (N) cycle during the winter in soil of the alpine zone. A shift from microbial N immobilization process dominant during summer to prevailing microbial mineralization process during the winter is observed. Warmer soil under deep snow cover may increase the microbial activity and rate of organic matter decomposition over the winter. Furthermore, severe shortages of dissolved carbon (C) in the winter may cause microbial mortality and lyses. Thus, C limitation on microbial growth and activity may have an important effect on winter N mineralization and even on soil N pools. However, the combined effects of additional organic C (litter inputs) and snow cover on soil N biogeochemical processes in the Tibetan Plateau remain unclear. In the current study, the in situ effects of snowpack and litter decomposition on N dynamics in the alpine zone of the Eastern Tibetan Plateau were investigated. Intact soil core incubations in three different snow regimes (0, 30 and 100 cm depth snow) in the winter were used to solve the problem by measure concentrations of mineral form of soil N. In addition, the litter bag method was used to analyze the litter decomposition over the winter. Our results indicate that the snow cover reduced the ammonium (NH4+-N) content, accelerate N mineralization in soil, and did not significantly change the dissolvable organic nitrogen (DON) and microbial biomass nitrogen (MBN). Meanwhile, snowpack increased the litter N content and accelerated litter decomposition in late winter. Litter addition reduced the MBN and NH4+-N contents in soil, but increased the nitrate (NO3--N) content and net N mineralization, suggesting that N availability to plants during the spring thaw period may be enhanced.
EN
The Minjiang River terrace along the Longmen Shan fault zone near Wenchuan, at the eastern margin of the Tibetan Plateau, China, provides archives for tectonic activity and quaternary climate change. However, previous studies were not able to provide ages older than 100 ka due to the limitations of dating material or/and methods applied to date the fluvial sediments. In this study, we used the ESR signal of the Ti-Li center in quartz to obtain the ages of four higher terraces (T3-T6). According to the results, the terraces T3 to T6 were formed at 64±19 ka, 101±15 ka, 153±33 ka, and 423±115 ka, respectively. Combined with previous studies, these results indicate that the formations of all terraces correspond to glacial/interglacial transition periods, such as, T1-T5 being correlated to MIS2/1, MIS4/3, MIS5d/5c, and MIS6/5e respectively, while T6 probably to MIS12/11. According to these data, it is found that the average incision rate was significantly higher over the last 150 ka than that previous 100 ka (250 to 150 ka). As both tectonics and climate have affected the formation of these terraces, in addition to the overall uplifting of Tibetan Plateau, the regional uplift due to isostasy would be an additional tectonic factor in the formation of river terraces in the eastern margin of Ti-betan plateau.
EN
Soil phosphorus (P) availability and fractions are influenced to a large extent by land use and cover changes. Inorganic P (IP) and organic P (OP) fractions in surface soils (0-20 cm) under typical vegetation types, including subalpine coniferous forests, alpine shrubs, and alpine shrub-meadows, near the alpine timberline of the eastern Tibetan Plateau of China, were measured by a modified Hedley fraction method. The results showed that OP is the dominant soil P fraction and the main source of available P in alpine soils near the timberline. Soil organic carbon, total nitrogen, and total P contents were higher in subalpine coniferous forests than in alpine shrubs and alpine shrub-meadows. Concentrations of soil labile P (the sums of Resin-IP, NaHCO3-IP, and NaHCO3-OP) were higher in subalpine coniferous forests than in alpine shrubs and alpine shrub-meadows, an observation that may be partially ascribed to the presence of deep litter layers generated by trees. Concentrations of soil labile and moderately organic P (NaHCO3-OP and NaOH-OP) in subalpine coniferous forests were also greater than in alpine shrubs and alpine shrub-meadows. Greater amounts of soil stable OP (extracted by concentrated HCl and cHCl.OP) were accumulated in alpine shrub-meadows compared to alpine shrubs or subalpine coniferous forests. The reduced availability of OP may be attributed mainly to increasing recalcitrant soil organic matter input in alpine shrub-meadows and alpine shrubs. Concentrations of IP associated with Ca minerals and parent materials (extracted by diluted HCl and HCl-IP, and extracted by concentrated HCl and cHCl-IP, respectively) were lower in subalpine coniferous forests, indicating that coniferous forests are more likely to use recalcitrant IP than alpine shrubs and alpine shrub-meadows. In this alpine region, land cover changes from subalpine coniferous forests to alpine shrubs and alpine shrub-meadows near the alpine timberline could decrease soil P conservation, availability, and supplementation.
EN
In the present study, we selected a total of 26 Salix sphaeronymphe Gorz shrubs of various sizes on a cutover in the eastern Tibetan Plateau to evaluate the effects of shrub size on richness, cover and biomass of the understorey herbaceous community, grasses and forbs, as well as litter cover and biomass. Results indicated that the richness of herbaceous community, grasses and forbs significantly increased with the increased area of both undershrub canopies and open field. However, the cover and biomass of the herbaceous community beneath the shrub canopies decreased with increasing shrub size. Grasses and forbs, as different functional groups, responded differently to the increasing area of shrubs: the cover and biomass of grasses decreased while those of forbs increased. The cover and biomass of herbaceous community, grasses and forbs in the open field did not obviously vary with area. Under the shrub canopies, the cover and mass of litter positively correlated to area, but this was not the case in the open field. Our results suggest that shrubs have a positive effect on diversity and a negative effect on the cover and productivity of the herbaceous community in forest secondary succession on the alpine cutovers, and that these effects are size.dependent. Moreover, different functional groups of herbaceous plants can respond differently to the presence of shrubs.
EN
We studied the effects of roads on presence of Plateau brown frogs (Rana kukunoris Nikolsky, 1918) and Tibetan frogs (Nanorana pleskei Gunther, 1896) in temporary pools of Sedges dominated wetland area in eastern Qinghai-Tibetan Plateau. The road is seven meter-wide, asphalt-paved with daily traffic rate about 400 vehicles. The temporary pools hold water only in summer with surface area of about 2 m2. We used logistic regression models, a theoretic information approach, and model averaging to test the effects of distance from road and depth, area and pH of pools on distribution of frogs in terms of presence/absence in 180 small pools located at 10 to 150 m from the road edge. Observed data showed that presence probabilities of both species declined in the vicinity of roads, starting at approximately 100 m away from the road edge. Model averaging based on AICc ([Sigma Omega i] = 95% confidence) indicated that both distance from road edge and its quadratic term were important predictors for explaining presence of both amphibians. Model-averaged prediction based on 95% confidence model set also revealed non-monotonic increasing curve relationships between presence probability of both amphibians and distance from road edge, even when other habitat variables were held constant. These results indicated that the road-effect zone for both amphibians extended 100 m on side of the wetland roads along which we sampled. Additionally, the results showed that water depth and water pH of pools positively influenced presence of Tibetan frogs and had highest contribution to the models. In contrast, water depth influenced presence of Plateau brown frogs negatively. It was indicated that environmental variables influence the presence of the two species of amphibians in different ways.
EN
In alpine zones, cold season processes, particularly those associated with snow accumulation and ablation, have a central role in ecosystem functioning. However, we know very little about soil carbon and nitrogen processes under the snowpack in these ecosystems, including the Tibetan Plateau. We conducted an experiment comparing three snow regimes (11 m x 1 m plots) of different snow depths and durations at an altitude of 4,100 m in the Minshan Range on the eastern Tibetan Plateau. The three snow regimes included a shallow and short duration snowpack (SS; depth <10 cm), a moderate snow depth and medium duration snowpack (MS; depth <20 cm), as well as a deep and long duration snowpack (DS; depth > 30 cm). This study explores the effects of different snow conditions on soil temperature, and further describes the sequence and timing of dissolved nutrients and microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) in soils under different snow regimes during the autumn-winter transition (i.e. November 7, 2008 - March 7, 2009). Three successive phases of temperature change were distinguished: I - initial decline - soil temperatures dropped steadily from 4[degrees]C to about 0[degrees]C at the same rate for all three snow regimes; II - moderate freezing - soil temperatures fluctuated between 0[degrees]C and -7[degrees]C under all three snow regimes; III - multiple freeze-thaw cycles took place in the SS and MS regimes, but permanent freezing occurred in the DS regime. Under moderate freezing, we found that soil temperature fluctuation was an essential factor for the transformation of soil C and N. Our results indicate that larger temperature fluctuations correlate with a greater increase in dissolved organic nitrogen (DON) content. Dissolved organic carbon (DOC) content increased markedly only under the most drastic temperature fluctuations. In contrast, MBC content increased significantly only when soil temperatures were relatively steady. Under the permanent freezing, only a large number of freeze-thaw cycles caused a significant decline of NO[^][3] -N and DOC concentrations. DON content declined markedly under permanent freezing and multiple freeze-thaw cycles. However, MBC content declined significantly only under permanent freezing. Ultimately, multiple freeze-thaw cycles resulted in the export of dissolved nutrients (organic and inorganic nitrogen) from the alpine ecosystem which had previously accumulated in the moderate freezing phase of the soil.
EN
Nutrients may be mobilized from senescing leaves and transported to other plant tissues, enabling plants to conserve them and reuse. Nitrogen and phosphorus are two dominant nutrients related to photosynthetic capacity and limiting plant growth. In this study, we examined the effect of canopy height on nutrient use by analyzing N and P concentrations of green and senescent leaves collected from different canopy heights of Abies georgei var. smithii (Viguie et Gaussen) Cheng growing at the alpine timberline in Sergyemla Mt.(4 350 m a.s.l), southeastern Tibetan Plateau. The results showed that N and P concentrations per unit needle mass decreased significantly with needle age, but no significant difference was found among upper, middle and lower canopy. However, area-based N and P concentrations increased with the height of canopy. The leaf level nutrient resorption and use efficiency varied in the order: upper canopy> middle canopy >lower canopy for both N and P. The higher nutrient resorption efficiency had significant relationship with leaf level nutrient use efficiency, that is, higher leaf level nutrient use efficiency was partly due to the high resorption from senescent needles. Additionally, the higher nutrient resorption was related to high current nutrient concentration. Vertical variations of leaf level nutrient use efficiency in this study reflected the strategy of alpine trees to respond to imbalance between light availability and soil nutrients.
EN
This study was conducted to examine the seasonal dynamics of biomass and plant nitrogen (N) content under three grazing intensities (light grazing - LG: 1.2, moderate grazing - MG: 2.0, and heavy grazing - HG: 2.9 yaks ha[^-1]) in representative alpine meadow on the eastern Tibetan Plateau. Differentiation in grazing intensity in the study area started since 1997 and has continued to the present time. Plant samples were collected in the middle of June, August and September. The highest aboveground biomass occurred at the MG site for both August and September. Over the growing season, belowground biomass (0.30 cm) increased as grazing intensity increased. The total belowground biomass averaged over all sampling dates was 1226, 1908 and 2244 g m[^-2] for LG site, MG site and HG site, which accounted for 75, 81 and 88% of total biomass, respectively. The results suggested that grazing intensity changed biomass allocation pattern between aboveground and belowground parts of plants. Higher grazing intensity resulted in higher N concentration in both live and dead aboveground biomass over the study period. Increased grazing intensity tended to increase plant N content averaged over all sampling dates, which were 17.9 g m[^-2], 23.8 g m[^-2] and 27.6 g m[^-2] in LG site, MG site and HG site. The results indicated that higher grazing intensity had a potential to increase the ecosystem pool of plant N.
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