Effects of Short-Term Nitrogen Addition on Soil Fungal Community Increase with Nitrogen Addition Rate in an Alpine Steppe at the Source of Brahmaputra.

The soil fungal community plays a crucial role in terrestrial decomposition and biogeochemical cycles. However, the responses of the soil fungal community to short-term nitrogen addition and its related dominant drivers still remain unclear. To address this gap, we conducted an experiment to explore how different levels of nitrogen addition (five levels: 0, 2.5, 5, 10, and 20 g N m-2 y-1) affected the soil fungal community in an alpine steppe at the source of Brahmaputra. Results showed that the reduced magnitudes of soil fungal species and phylogenetic α-diversity increased with the increasing nitrogen addition rate. Nitrogen addition significantly changed the community composition of species, and the dissimilarity of the soil fungal community increased with the increasing nitrogen addition rate, with a greater dissimilarity observed in the superficial soil (0-10 cm) compared to the subsurface soil (10-20 cm). Increases in the soil nitrogen availability were found to be the predominant factor in controlling the changes in the soil fungal community with the nitrogen addition gradient. Therefore, short-term nitrogen addition can still cause obvious changes in the soil fungal community in the alpine grassland at the source of Brahmaputra. We should not underestimate the potential influence of future nitrogen deposition on the soil fungal community in the high-altitude grassland of the Qinghai-Tibet Plateau. Adverse effects on the soil fungal community should be carefully considered when nitrogen fertilizer is used for ecosystem restoration of the alpine grassland of the Qinghai-Tibet Plateau.

Affecting Factors of Plant Phyllosphere Microbial Community and Their Responses to Climatic Warming-A Review.

Phyllosphere microorganisms are not only an important part of plants, but also an important part of microorganisms. In this review, the function of phyllosphere microorganisms, the assembly mechanism of phyllosphere microorganisms, the driving factors of phyllosphere microbial community structure, and the effects of climate warming on phyllosphere microbial community structure were reviewed. Generally, phyllosphere microorganisms have a variety of functions (e.g., fixing nitrogen, promoting plant growth). Although selection and dispersal processes together regulate the assembly of phyllospheric microbial communities, which one of the ecological processes is dominant and how external disturbances alter the relative contributions of each ecological process remains controversial. Abiotic factors (e.g., climatic conditions, geographical location and physical and chemical properties of soil) and biological factors (e.g., phyllosphere morphological structure, physiological and biochemical characteristics, and plant species and varieties) can affect phyllosphere microbial community structure. However, the predominant factors affecting phyllosphere microbial community structure are controversial. Moreover, how climate warming affects the phyllosphere microbial community structure and its driving mechanism have not been fully resolved, and further relevant studies are needed.

[A Comparative Study on the Calibration Accuracy of Landsat 8 Thermal Infrared Sensor Data].

The satellite thermal infrared image has been an important data source for the acquisition of the earth's surface temperature. The thermal infrared sensor (TIRS) Landsat 8 satellite newly launched onboard has added valuable data for this mission. However, the calibration parameters for the two bands of the TIRS, i.e., TIRS Bands 10 and 11, had been modified several times since its launch. This finally led the United States Geological Survey (USGS) to reprocess all achieved Landsat 8 data starting from February 2014. In order to examine the calibration accuracy of the reprocessed TIRS data, this paper crossly compares Landsat 8 TIRS data with synchronized, well-calibrated Landsat 7 ETM+thermal infrared data. A total of three date-coincident image pairs of western United States, downloaded from USGS Earth Explorer website, were used for the cross comparison. Three test sites were selected respectively from the three image pairs for the comparison, which representing moderate vegetation-cover area (test site 1), low vegetation-cover area (test site 2), and bare soil area (test site 3). The thermal infrared data of the three image pairs of both sensors had been firstly converted to at-sensor temperature. A band-by-band comparison and a regression analysis were then carried out to investigate the relationship and difference between the two sensor thermal data. The results show a very high degree of agreement between the three compared Landsat 8 TIRS and Landsat 7 ETM+thermal infrared image pairs because the correlation coefficients between the retrieved at-sensor temperature of the two sensors are generally greater than 0.95. Nevertheless, the cross comparison also reveals differences between the thermal infrared data of the two sensors. Compared with retrieved at-sensor temperature of Landsat 7 ETM+Band 6, TIRS Band 10 shows an overestimation, which can be up to 1.37 K, whereas TIRS Band 11 underestimates the temperature, with a difference reaching to -3 K. This suggests that in spite of the reprocessing of Landsat 8 thermal infrared data, the calibration parameters for the satellite's TIRS data are still unstable, especially for TIRS Band 11. It was found that the at-sensor temperature difference between ETM+Band 6 and TIRS Band 10 was enhanced with the decrease in vegetation coverage from test site 1 to test site 3. The at-sensor temperature difference of test site 1 is 0.07 K and increased to 1.37 K in test site 3, a net increase by 1.3 K. While the at-sensor temperature difference between ETM+Band 6 and TIRS Band 11 had an inverse performance. With the decrease in vegetation coverage from test site 1 to test site 3, the at-sensor temperature difference was reduced from ~-3.0 to -0.4 K. Therefore, in bare soil dominated test site 3, the temperature difference was 1.37 K for TIRS Band 10 and -0.4 K for TIRS Band 11. The RMSE of TIRS Band 11 is also much lower than that of TIRS Band 10. This suggests that TIRS Band 11 can perform batter in bare soil area than TIRS Band 10 though the latter shows an overall batter performance than TIRS Band 11. The study also found that in low vegetation cover areas like in test sites 2 and 3, taking an averaged at-sensor temperature of TIRS Bands 10 and 11, the difference between the two sensors' at-sensor temperature can be reduced to less than -0.5 K.