Seasonal variations in carbon dioxide exchange in an alpine wetland meadow on the Qinghai-Tibetan Plateau

Alpine wetland meadow could functions as a carbon sink due to it high soil organic content and low decomposition. However, the magnitude and dynamics of carbon stock in alpine wetland ecosystems are not well quantified. Therefore, understanding how environmental variables affect the processes that regulate carbon fluxes in alpine wetland meadow on the Qinghai-Tibetan Plateau is critical. To address this issue, Gross Primary Production (GPP), Ecosystem Respiration (<i>R</i><sub>eco</sub>), and Net Ecosystem Exchange (NEE) were examined in an alpine wetland meadow using the eddy covariance method from October 2003 to December 2006 at the Haibei Research Station of the Chinese Academy of Sciences. Seasonal patterns of GPP and <i>R</i><sub>eco</sub> were closely associated with leaf area index (LAI). The <i>R</i><sub>eco</sub> showed a positive exponential to soil temperature and relatively low <i>R</i><sub>eco</sub> occurred during the non-growing season after a rain event. This result is inconsistent with the result observed in alpine shrubland meadow. In total, annual GPP were estimated at 575.7, 682.9, and 630.97 g C m<sup>−2</sup> in 2004, 2005, and 2006, respectively. Meanwhile, the <i>R</i><sub>eco</sub> were equal to 676.8, 726.4, 808.2 g C m<sup>−2</sup>, and thus the NEE were 101.1, 44.0 and 173.2 g C m<sup>−2</sup>. These results indicated that the alpine wetland meadow was a moderately source of carbon dioxide (CO<sub>2</sub>). The observed carbon dioxide fluxes in the alpine wetland meadow were higher than other alpine meadow such as <i>Kobresia humilis</i> meadow and shrubland meadow

Seasonal variations in carbon dioxide exchange in an alpine wetland meadow on the Qinghai-Tibetan Plateau

Alpine wetland meadow could functions as a carbon sink due to it high soil organic content and low decomposition. However, the magnitude and dynamics of carbon stock in alpine wetland ecosystems are not well quantified. Therefore, understanding how environmental variables affect the processes that regulate carbon fluxes in alpine wetland meadow on the Qinghai-Tibetan Plateau is critical. To address this issue, Gross Primary Production (GPP), Ecosystem Respiration (<i>R</i><sub>eco</sub>), and Net Ecosystem Exchange (NEE) were examined in an alpine wetland meadow using the eddy covariance method from October 2003 to December 2006 at the Haibei Research Station of the Chinese Academy of Sciences. Seasonal patterns of GPP and <i>R</i><sub>eco</sub> were closely associated with leaf area index (LAI). The <i>R</i><sub>eco</sub> showed a positive exponential to soil temperature and relatively low <i>R</i><sub>eco</sub> occurred during the non-growing season after a rain event. This result is inconsistent with the result observed in alpine shrubland meadow. In total, annual GPP were estimated at 575.7, 682.9, and 630.97 g C m<sup>−2</sup> in 2004, 2005, and 2006, respectively. Meanwhile, the <i>R</i><sub>eco</sub> were equal to 676.8, 726.4, 808.2 g C m<sup>−2</sup>, and thus the NEE were 101.1, 44.0 and 173.2 g C m<sup>−2</sup>. These results indicated that the alpine wetland meadow was a moderately source of carbon dioxide (CO<sub>2</sub>). The observed carbon dioxide fluxes in the alpine wetland meadow were higher than other alpine meadow such as <i>Kobresia humilis</i> meadow and shrubland meadow

Effect of Plateau Pika (\u3cem\u3eOchotonacurzionae\u3c/em\u3e) Disturbance on Soil Microelements Content in Alpine Meadow

The plateau pika (Ochotonacurzoniae) creates the extensive disturbance on alpine meadow ecosystem in the QinghaiTibetan Plateau (Smith and Foggin, 1999, Delibes-Mateos et al., 2011), especially on soil nutrient (Davidson et al., 2012). Previous studies show that intermediate active burrows of plateau pika improved soil macro-element (organic matter, total nitrogen and total phosphorus) in alpine meadow (Guo et al., 2012). However, there is little knowledge about the underlying contribution of plateau pika disturbance in determining soil microelement in alpine meadow. The density of active burrow entrances is used to divide the disturbances levels of plateau pika to determine the effect of various disturbance levels of plateau pika on soil microelement content of alpine meadow in the Qinghai-Tibetan Plateau in this study

Belowground Bud Banks and Land Use Change: Roles of Vegetation and Soil Properties in Mediating the Composition of Bud Banks in Different Ecosystems

Introduction: Belowground bud banks play integral roles in vegetation regeneration and ecological succession of plant communities; however, human-caused changes in land use severely threaten their resilience and regrowth. Although vegetation attributes and soil properties mediate such anthropogenic effects, their influence on bud bank size and composition and its regulatory mechanisms under land use change have not been explored.Methods: We conducted a field investigation to examine impacts of land use change on bud bank size and composition, vegetation attributes, and soil properties in wetlands (WL), farmlands (FL), and alpine meadow (AM) ecosystems in Zhejiang Province, China.Results: Overall, 63 soil samples in close proximity to the vegetation quadrats were excavated using a shovel, and samples of the excavated soil were placed in plastic bags for onward laboratory soil analysis. The total bud density (1514.727 ± 296.666) and tiller bud density (1229.090 ± 279.002) in wetland ecosystems were significantly higher than in farmland and alpine meadow ecosystems [i.e., total (149.333 ± 21.490 and 573.647 ± 91.518) and tiller bud density (24.666 ± 8.504 and 204.235 ± 50.550), respectively]. While vegetation attributes critically affected bud banks in WL ecosystems, soil properties strongly influenced bud banks in farmland and alpine meadow ecosystems. In wetland ecosystems, total and tiller buds were predominantly dependent on soil properties, but vegetation density played a significant role in farmlands and alpine meadow ecosystems. Root sprouting and rhizome buds significantly correlated with total C in the top 0 – 10 cm layer of farmland and alpine meadow ecosystems, respectively, and depended mainly on soil properties.Discussion: Our results demonstrate that land use change alters bud bank size and composition; however, such responses differed among bud types in wetland, farmland, and alpine meadow ecosystems

Relationship between Live Weight Gain of Tibetan Sheep and Available Pasture in Qinhai-Tibetan Plateau

Overgrazing is a universal phenomenon on the Qinghai-Tibetan Plateau, which results in 90% of the alpine meadow grassland being degraded (Gao and Hou 2011). As well, animal productivity of the grassland is becoming lower because of the yearly continuous grazing. Improved grazing management will play a key role in the sustainable use of alpine meadow grasslands

Short-Term Effects of Phosphorus Application on Phosphorus Content in Soil and Dominant Species under Ungrazed and Grazed Conditions in the Tibetan Plateau

Phosphorus (P) availability in soils is an important indicator for health and growth in plants. The available phosphorus (AP) content of alpine meadow soil in northern China is low. Previous studies of alpine meadow have reported that soil nutrient levels have been significantly improved after a 9-year enclosure (Wu et al. 2010b) whereas continuous grazing over 19 years reduced total P (TP) by 25% in a Leymus chinensis steppe (Li 2001). Many studies have shown that the application of P fertilizer can improve dry matter production and forage quality in cultivated grasslands (Shi et al. 2007). However, the benefits of applying P fertiliser to alpine meadow in terms of increases in soil AP content and P concentrations in plants in both grazed and ungrazed meadows are less well known. The objective of this study was to investigate the short-term effects of P application on the AP content in top soil and total P content in the foliage of dominant meadow plant species

Symbiotic nitrogen fixation by legumes in two Chinese grasslands estimated with the (15)N dilution technique

Symbiotic nitrogen (N) fixation by legumes was investigated using the (15)N dilution technique in two Chinese grasslands: one in the north-eastern Tibetan Plateau and the other in Inner Mongolia in China. A small amount (0.03 g N m(-2)) of (15)N labelled (NH(4))(2)SO(4) fertilizer was evenly distributed in two soils. One month after the (15)N addition, four legumes (Astragalus sp., Gueldenstaedtia diversifolia, Oxytropis ochrocephala and Trigonella ruthenica) in the alpine meadow and two legumes (Thermopsis lanceolata and Melissitus ruthenica) in the temperate steppe were collected. Several non-legume plant species were harvested as the reference. Above-ground biomass of legumes ranged from 8 to 24 g m(-2) in the alpine meadow and from 11 to 35 g m(-2) in the temperate steppe. The reference plants showed distinctly higher (15)N atom% excess than legumes (0.08% vs. 0.02% in the alpine meadow, 0.10% vs. 0.02% in the temperate steppe). The N derived from atmosphere (%Ndfa) ranged from 50 to 90% N in the alpine meadow, while it ranged from 85 to 92% in the temperate steppe. Based on the legume above-ground biomass, total symbiotic N(2)-fixation rate was estimated to be 1.00 g N m(-2) year(-1) in the alpine meadow and 1.15 g N m(-2) year(-1) in the temperate steppe. These N inputs by legumes can account for 9% of the gap between the N demand and the seasonal N release by mineralization in the alpine Kobresia grassland and 20% in the temperate Leymus grassland, respectively. Considering additional contribution of the root biomass, we suggest that biological N(2)-fixation by legumes plays an important role in the cycling of N in both Kobresia and Leymus grasslands on an annual scale

The permafrost carbon inventory on the Tibetan Plateau : a new evaluation using deep sediment cores

Acknowledgements We are grateful for Dr. Jens Strauss and the other two anonymous reviewers for their insightful comments on an earlier version of this MS, and appreciate members of the IBCAS Sampling Campaign Teams for their assistance in field investigation. This work was supported by the National Basic Research Program of China on Global Change (2014CB954001 and 2015CB954201), National Natural Science Foundation of China (31322011 and 41371213), and the Thousand Young Talents Program.Peer reviewedPostprin

No Consistent Evidence for Advancing or Delaying Trends in Spring Phenology on the Tibetan Plateau

Vegetation phenology is a sensitive indicator of climate change and has significant effects on the exchange of carbon, water, and energy between the terrestrial biosphere and the atmosphere. The Tibetan Plateau, the Earth\u27s “third pole,” is a unique region for studying the long‐term trends in vegetation phenology in response to climate change because of the sensitivity of its alpine ecosystems to climate and its low‐level human disturbance. There has been a debate whether the trends in spring phenology over the Tibetan Plateau have been continuously advancing over the last two to three decades. In this study, we examine the trends in the start of growing season (SOS) for alpine meadow and steppe using the Global Inventory Modeling and Mapping Studies (GIMMS)3g normalized difference vegetation index (NDVI) data set (1982–2014), the GIMMS NDVI data set (1982–2006), the Moderate Resolution Imaging Spectroradiometer (MODIS) NDVI data set (2001–2014), the Satellite Pour l\u27Observation de la Terre Vegetation (SPOT‐VEG) NDVI data set (1999–2013), and the Sea‐viewing Wide Field‐of‐View Sensor (SeaWiFS) NDVI data set (1998–2007). Both logistic and polynomial fitting methods are used to retrieve the SOS dates from the NDVI data sets. Our results show that the trends in spring phenology over the Tibetan Plateau depend on both the NDVI data set used and the method for retrieving the SOS date. There are large discrepancies in the SOS trends among the different NDVI data sets and between the two different retrieval methods. There is no consistent evidence that spring phenology (“green‐up” dates) has been advancing or delaying over the Tibetan Plateau during the last two to three decades. Ground‐based budburst data also indicate no consistent trends in spring phenology. The responses of SOS to environmental factors (air temperature, precipitation, soil temperature, and snow depth) also vary among NDVI data sets and phenology retrieval methods. The increases in winter and spring temperature had offsetting effects on spring phenology

Effect of Nitrogen Addition on Selection of Germination Trait in an Alpine Meadow on the Tibet Plateau

Seed germination requirements may determine the kinds of habitat in which plants can survive. We tested the hypothesis that nitrogen (N) addition can change seed germination trait-environmental filter interactions and ultimately redistribute seed germination traits in alpine meadows. We determined the role of N addition on germination trait selection in an alpine meadow after N addition by combining a 3-year N addition experiment in an alpine meadow and laboratory germination experiments. At the species level, germination percentage, germination rate (speed) and breadth of temperature niche for germination (BTN) were positively related to survival of a species in the fertilized community. In addition, community-weighted means of germination percentage, germination rate, germination response to alternating temperature and BTN increased. However, germination response to wet-cold storage (cold stratification) and functional richness of germination traits was lower in alpine meadows with high-nitrogen addition than in those with no, low and medium N addition. Thus, N addition had a significant influence on environmental filter-germination trait interactions and generated a different set of germination traits in the alpine meadow. Further, the effect of N addition on germination trait selection by environmental filters was amount-dependent. Low and medium levels of N addition had less effect on redistribution of germination traits than the high level