Verification of a Leaf Litter Decomposition Model Based on Long-term Field Trials in Gongga Mountain, Qinghai-Tibetan Plateau, China

Background and aimsAlthough litter decomposition is a vital soil ecosystem process in forest ecosystems, most decomposition models are based on short-term decomposition experiments. Prediction of long-term decomposition dynamics using short-term decomposition models may lead to unreliable results. A leaf-litter decomposition model was evaluated and verified using a long-term field trial in Gongga Mountain, on the eastern flank of the Qinghai-Tibetan Plateau, China. Methods A 90-month experiment employing 360 broad-leaf litter (five species) samples were conducted using the litterbag method at three elevations (2250 m, 2780 m and 3000 m a.s.l.) in Gongga Mountain. The remaining litter mass was measured to fit a mathematical decomposition model by different exponential functions (two-, three-, four- and six-parameters) and akaike information criterion (AIC). ResultsThe four-parameter model (B) employed for each litter type among the four functions showed the highest R2 and lowest AIC value. The fast and slow decomposition rate constant (kf and ks) for a given litter at 2250 m was higher than that observed at 3000 m. ConclusionsThese results indicated that the four-parameter exponential function (two-pool model) was recommended as a suitable decomposition model of long-term broadleaf litter decomposition at different elevations on Gongga Mountain.

Distribution Trends of Cadmium and Lead in Timberline Coniferous Forests in the Eastern Tibetan Plateau

The concentrations of Pb and Cd in the needles and twigs of fir and spruce collected from 26 sites in the Eastern Tibetan Plateau were measured and analyzed in this study. The mean concentrations of Cd and Pb were 0.034 and 1.291 mg/kg, respectively, in the needles and 0.101 and 2.511 mg/kg, respectively, in the twigs. These concentrations increased significantly with needle and twig age and peaked at 5 years. The twigs were significantly enriched in Pb and Cd compared with the needles. The spatial distributions of Pb and Cd were determined using the inverse-distance-weighted spatial interpolation method on the basis of the mean concentration of the elements in the needles and twigs from each site. The highest concentrations of Pb and Cd in twigs and needles were found in Yunnan Province and Gongga Mountain. They showed a tendency to decline from Yunnan Province to the northern direction, as well as from Gongga Mountain to the western area. Principal component analysis showed that Pb and Cd originated from the anthropogenic activities in this area. The mining activities and climatic factors may be the main sources of Pb and Cd in this area. Combining the HYSPLIT (The Hybrid Single-Particle Lagrangian Integrated Trajectory) model and PCA, the results implied that exterior Pb and Cd sources from Southeast Asia and the eastern developed cities in China can infiltrate the ecosystem through long-range transportation and accumulate in timberline forests, with atmospheric deposition in the Eastern Tibetan Plateau. This plateau suffers from severe Pb pollution but slight Cd contamination.

Vertebrate prey composition analysis of the Pallas’s cat (Otocolobus manul) in the Gongga Mountain Nature Reserve, based on fecal DNA

Diet analysis is essential to fully understanding the biology of a species and its function within the ecosystem, and is also key in identifying food web interactions and the population dynamics of predators and prey. There is currently little information on the diet of small to mid-sized carnivores due to their elusive behavior. We used a DNA-based method to analyze the vertebrate prey of the Pallas’s cat (Otocolobus manul) in the Gongga Mountain Nature Reserve of southwestern China, a global biodiversity hotspot region. We confirmed 14 scat samples containing the Pallas’s cat DNA from 100 small carnivore scats collected at altitudes between 3200 and 4900 m, and then performed polymerase chain reaction (PCR) amplifications using primers targeting the vertebrate mitochondrial 12S rRNA gene with a blocking oligonucleotide specific to the predator sequence. We identified a total of 18 prey taxa, including nine mammals, eight birds and one fish. Our results show that pikas (in 79% of the scats) and birds (in 50% of the scats) are the predominant prey consumed by the Pallas’s cat in our investigation area. The most important finding in our study is that Cypriniformes species were found in the Pallas’s cat’s diet, exhibiting dietary diversification consistent with the accessible fauna of the surrounding environment. In order to increase the detectability of both typical and rare vertebrate prey items, we constructed a blocking primer to inhibit the amplification of the Pallas’s cat DNA.

Dynamics and Drivers of the Alpine Timberline on Gongga Mountain of Tibetan Plateau-Adopted from the Otsu Method on Google Earth Engine

The alpine timberline, an ecosystem ecotone, indicates climatic change and is tending to shift toward higher altitudes because of an increase in global warming. However, spatiotemporal variations of the alpine timberline are not consistent on a global scale. The abundant and highest alpine timberline, located on the Tibetan Plateau, is less subject to human activity and disturbance. Although many studies have investigated the alpine timberline on the Tibetan Plateau, large-scale monitoring of spatial-temporal dynamics and driving mechanisms of the alpine timberline remain uncertain and inaccurate. Hence, the Gongga Mountain on the southeastern Tibetan Plateau was chosen as the study area because of the most complete natural altitudinal zonation. We used the Otsu method on Google Earth Engine to extract the alpine timberline from 1987–2019 based on the normalized difference vegetation index (NDVI). Then, the alpine timberline spatiotemporal patterns and the effect of topography on alpine timberline distribution were explored. Four hillsides on the western Gongga Mountain were selected to examine the hillside differences and drivers of the alpine timberline based on principal component analysis (PCA) and multiple linear regression (MLR). The results indicated that the elevation range of alpine timberline was 3203–4889 m, and the vegetation coverage increased significantly (p < 0.01) near the alpine timberline ecotone on Gongga Mountain. Moreover, there was spatial heterogeneity in dynamics of alpine timberline, and some regions showed no regular trend in variations. The spatial pattern of the alpine timberline was generally high in the west, low in the east, and primarily distributed on 15–55° slopes. Besides, the drivers of the alpine timberline have the hillside differences, and the sunny and shady slopes possessed different driving factors. Thus, our results highlight the effects of topography and climate on the alpine timberline on different hillsides. These findings could provide a better approach to study the dynamics and formation of alpine timberlines.

Distribution of preferential flow pathways and solute transfer along the Hailuogou Glacier Chronosequence on the Eastern Tibetan Plateau

&lt;p&gt;Preferential flow pathways (PFPs) are key contributors for the ecological status of the hydrosphere in high mountain environments, as the precipitation will transfer to PFPs with rapid solute transport from soil to groundwater. This particularly refers to nutrient allocation from soils to groundwater and surface waters.&lt;/p&gt;&lt;p&gt;To understand the effects of the pedogenesis and forest types on the soil PFPs, the soil preferential flow was studied by &lt;em&gt;in situ&lt;/em&gt; dye tracing image analysis and elemental chemical analysis at the Hailuogou glacier chronosequence, Gongga Mountain on the eastern Tibetan Plateau. A soil chronosequence and a vegetation primary succession following the retreat of the Hailuogou glacier has been forming since ~1890. Three sites representing different exposure age (45, 85 and 125 years) in the Hailuogou glacier retreat area chronosequence and two sites typical forest lands (deciduous broadleaf forest and coniferous forest) were selected to carry out a brilliant blue dyeing experiment to visualize the distribution of water infiltration in soil.&lt;/p&gt;&lt;p&gt;The tracer-infiltration patterns were parameterized by dye coverage (DC), preferential flow fraction (PF), length index (L&lt;sub&gt;i&lt;/sub&gt;) and the variation coefficient of DC in the PFPs (C&lt;sub&gt;V&lt;/sub&gt;). Furthermore, the distribution of PFPs, transported solute of soil PFPs was analyzed including Hailuogou glacier chronosequence and vegetation succession.&lt;/p&gt;&lt;p&gt;According to the comparison of PFPs parameters, soil PFPs at the 125-year-old site extremely more developed than that at the younger site due to the fracture development between rock and soil on the process of soil development. The soil PFPs under broadleaf forest is more pronounced than that in coniferous forest soils, largely depending on the different root system.&lt;/p&gt;&lt;p&gt;In general, PFPs in Gongga Mountain were important contributors to the potential translocation of bioavailable inorganic P (PBPi) and organic P translocation to the hydrosphere. The elements transported with PFPs could be divided into three categories, reactive, conservative, and both reacted and conservative elements for the concentration of the elements remain in the PFPs. The results indicated that Mg and Al are the reactive elements, while Na, K, Ca and Mn are the conservative elements in the PFPs. Iron is both reacted and conservative element in the PFPs.&amp;#160;Zn, Na, K, Mg, PBPi, had a significant correlation with the variation coefficient of DC in the PFPs (C&lt;sub&gt;V&lt;/sub&gt;).&lt;/p&gt;&lt;p&gt;The results highlight the effects of the pedogenesis and forest types on the distribution of PFPs and solute transfer. Preferential flow contributes largely to elements flow at the Hailuogou glacier chronosequence and vegetation succession, Gongga Mountain.&lt;/p&gt;&lt;p&gt;The financial support of this work was obtained from National Natural Science Foundation of China (Grant No. 41272220) and Natural Scientifc Foundation for Young Scientists of Guangxi Zhuang Autonomous Region of China (Grant No. 2017GXNSFBA198162). The first author was financially supported by the Sino-German (CSC-DAAD) Postdoc Scholarship Program funded by China Scholarship Council (CSC) and Deutscher Akademischer Austausch Dienst (DAAD).&lt;/p&gt;