Grasslands and agro-ecosystems occupy one-third of the global terrestrial area. However, great uncertainty still exists about their contributions to the global carbon cycle. This study used various combinations of a s...Grasslands and agro-ecosystems occupy one-third of the global terrestrial area. However, great uncertainty still exists about their contributions to the global carbon cycle. This study used various combinations of a simple ecosystem respiration model and a photosynthesis model to simulate the influence of different climate factors, specifically radiation, temperature, and moisture, on the ecosystem carbon exchange at two dissimilar study sites. Using a typical alpine meadow site in a cold region and a typical cropland site in an arid region as cases, we investigated the response char- acteristics of productivity of grasslands and croplands to different environmental factors, and analyzed the seasonal change patterns of different model parameters. Parameter estimations and uncertainty analyses were performed based on a Bayesian approach. Our results indicated that： （1） the net ecosystem exchange （NEE） of alpine meadow and seeded maize during the growing season presented obvious diurnal and seasonal variation patterns. On the whole, the alpine meadow and seeded maize ecosystems were both apparent sinks for atmospheric CO2; （2） in the daytime, the mean NEE of the two ecosystems had the largest values in July and the lowest values in October. However, overall carbon uptake in the cropland was greater than in the alpine meadow from June to September; （3） at the alpine meadow site, temperature was the main limiting factor influencing the ecosystem carbon exchange variations during the growing season, while the sensitivity to water limitation was relatively small since there is abundant of rainfall in this region; （4） at the cropland site, both temperature and moisture were the most important limiting factors for the variations of ecosystem carbon exchanges during the growing season; and （5） some parameters had an obvious characteristic of seasonal patterns, while others had only small seasonal variations.展开更多
Quantification of soil macropores is important to enhance our understanding of preferential pathways for water, air, and chemical movement in soils. However, the soil architecture of different land uses is not well un...Quantification of soil macropores is important to enhance our understanding of preferential pathways for water, air, and chemical movement in soils. However, the soil architecture of different land uses is not well understood in elusive alpine regions. The objective of this study was to quantify the architecture of soil macropores in a Kobresia meadow, farmland, and sand in the Qinghai Lake watershed of northeastern Qinghai-Tibet Plateau, China using X-ray computed tomography. Nine soil cores at 0–50 cm depth were collected at three sites with three replicates. At each site, the three collected cores were scanned using a GE Hi Speed FX/i medical scanner(General Electric, USA). To analyze soil architecture, the number of macropores, macroporosity, and mean macropore equivalent diameter within the 50 cm soil profile were determined from the X-ray computed tomography. Analysis of variance indicated that land use significantly influenced macroporosity, mean macropore equivalent diameter, and number of macropores. The soils of the Kobresia meadow and farmland had greater macroporosity and developed deeper and longer macropores than that of sand. For the Kobresia meadow, macropores were distributed mainly in the 0–10 cm soil layer, while they were distributed in the 0–20 cm soil layer for the farmland. The large number of macropores observed in the soils of the Kobresia meadow and farmland could be attributed to greater root development. The results of this study provided improved quantitative evaluation of a suite of soil macropore features with significant implications for non-equilibrium flow prediction and chemical transport modeling in soils.展开更多
基金funded by the National Natural Science Foundation of China(Nos.41401412,91125004)the Foundation for Excellent Youth Scholars of CAREERI,CAS(No.51Y451271)the Open Fund of the Key Laboratory of Desert and Desertification,CAS(No.KLDD-2014-007)
文摘Grasslands and agro-ecosystems occupy one-third of the global terrestrial area. However, great uncertainty still exists about their contributions to the global carbon cycle. This study used various combinations of a simple ecosystem respiration model and a photosynthesis model to simulate the influence of different climate factors, specifically radiation, temperature, and moisture, on the ecosystem carbon exchange at two dissimilar study sites. Using a typical alpine meadow site in a cold region and a typical cropland site in an arid region as cases, we investigated the response char- acteristics of productivity of grasslands and croplands to different environmental factors, and analyzed the seasonal change patterns of different model parameters. Parameter estimations and uncertainty analyses were performed based on a Bayesian approach. Our results indicated that： （1） the net ecosystem exchange （NEE） of alpine meadow and seeded maize during the growing season presented obvious diurnal and seasonal variation patterns. On the whole, the alpine meadow and seeded maize ecosystems were both apparent sinks for atmospheric CO2; （2） in the daytime, the mean NEE of the two ecosystems had the largest values in July and the lowest values in October. However, overall carbon uptake in the cropland was greater than in the alpine meadow from June to September; （3） at the alpine meadow site, temperature was the main limiting factor influencing the ecosystem carbon exchange variations during the growing season, while the sensitivity to water limitation was relatively small since there is abundant of rainfall in this region; （4） at the cropland site, both temperature and moisture were the most important limiting factors for the variations of ecosystem carbon exchanges during the growing season; and （5） some parameters had an obvious characteristic of seasonal patterns, while others had only small seasonal variations.
基金supported by the National Natural Science Foundation of China (Nos. 41471018 and 41730854)
文摘Quantification of soil macropores is important to enhance our understanding of preferential pathways for water, air, and chemical movement in soils. However, the soil architecture of different land uses is not well understood in elusive alpine regions. The objective of this study was to quantify the architecture of soil macropores in a Kobresia meadow, farmland, and sand in the Qinghai Lake watershed of northeastern Qinghai-Tibet Plateau, China using X-ray computed tomography. Nine soil cores at 0–50 cm depth were collected at three sites with three replicates. At each site, the three collected cores were scanned using a GE Hi Speed FX/i medical scanner(General Electric, USA). To analyze soil architecture, the number of macropores, macroporosity, and mean macropore equivalent diameter within the 50 cm soil profile were determined from the X-ray computed tomography. Analysis of variance indicated that land use significantly influenced macroporosity, mean macropore equivalent diameter, and number of macropores. The soils of the Kobresia meadow and farmland had greater macroporosity and developed deeper and longer macropores than that of sand. For the Kobresia meadow, macropores were distributed mainly in the 0–10 cm soil layer, while they were distributed in the 0–20 cm soil layer for the farmland. The large number of macropores observed in the soils of the Kobresia meadow and farmland could be attributed to greater root development. The results of this study provided improved quantitative evaluation of a suite of soil macropore features with significant implications for non-equilibrium flow prediction and chemical transport modeling in soils.
