| Ultraviolet (UV) radiation has strong biological, chemical effects. UV radiation enhancement caused by ozone thinning has produced or will produce the serious ecology effect, and it will take significant effects on people, animals, plants and even terrestrial and aquatic ecosystems. Research on enhanced UV radiation biological effects becomes a hot topic after the global atmospheric carbon dioxide concentration enrichment. UV radiation ecology emphasises on the relationship between biology and UV radiation, which is a new cross discipline for ecology and environmental science based on the thinning of atmospheric ozone layer and enhancement of UV radiation.In this study, a semi physical and semi empirical model for surface UV radiation estimation was proposed by combining a simplified mode of UV radiation transfer equation and climatologically estimation model. A regional surface UV radiation estimation scheme was put out for the subtropical climate ozone based on geographical information technology. Temporal and spatial evolutions of UV radiation in China were studied by using meteorological data. A model that describing the response of net photosynthetic rate to UV radiation changes was put forward by using data from literature and experiment. Furthermore, an improvement for IBIS model was made to simulate the effect of the UV spatiao-temporal variation on the carbon budget in subtropical areas of China. The paper composes of four parts:(1) A new model for estimating surface UV radiation was put forwarded to solve the problem of the observational data series limitation in China, and to be a basis for long term research of surface UV radiation.(2) A surface UV radiation estimation scheme in Chinese subtropical areas was put forwarded by combining with the geographic information system technology; and by using climate observation data, a dataset for Chinese subtropical surface UV radiation evolution during last50a was obtained.(3) According to the dataset of recent50a surface UV radiation evolution in Chinese subtropical areas, the trends and variation of UV radiation were analyzed to support the research on global change of UV radiation.(4) A model was made to describe the response of net photosynthetic rate to UV radiation changes; and then the model was integrated into the IBIS ecological model to simulate the effects of UV radiation on carbon budget in Chinese subtropical areas. The results include:1) A novel surface UV radiation model suitable for UV radiation estimation in hourly and daily scale was presented in this paper. The UV radiation transmissivity and integrated impact factor for UV radiation in hourly (daily) scale were the dependent and independent variables, separately in this model. The integrated impact factor was composed with two constituents:the resultant effects of all the attenuation factors assumed cloud free sky and the cloud effect in hourly (daily) scale. Spatially and temporally evolutional dataset of hourly surface UV radiation is urgently needed to reconstruct by model with daily scale since it is difficult to obtain hourly observed data. Suitability assessment analysis was conducted by utilizing the in-situ observed UV radiation and solar radiation data from14subtropical zone located observatories of Chinese Ecosystem Research Network (CERN). Sub-data sets accounting for25%of all data were made for the purpose of the model accuracy assessment on each observatory at first and the results showed that RMSE values were lower than11%indicating that the novel model presented here had a relative satisfying accuracy and can be deployed to estimate the surface UV radiation at these14observatories. Cross validation was also conducted for all these14observatories with quite different locations to evaluate the zonal application potential of this model and the results showed that RMSE values on most observatories were below15%with few RMSE exceptions greater than20%indicating that the novel model had the application potential for UV radiation distribution estimation on a zonal scale.2) An approach for zonal distributed surface UV radiation estimation was suggested to reconstruct the daily UV radiation from1961to2010and further investigations on the spatially and temporally evolutional pattern of monthly, seasonal and annual mean UV radiation were achieved in this paper. The results showed that:①An insignificant decrease trend was obtained for the annual mean UV radiation in the whole subtropical region and the spatial distribution pattern for multiyear averaged UV radiation implied a significant relationship between UV radiation and altitude and consequently, latitudinal zonality varied significantly with the topography. The maximum and minimum values of averaged UV radiation were found on Yunnan-Guizhou plateaus and Sichuan basins, separately. The UV radiation in coastal zones was much higher than that of inland areas.②A decrease trend was also obtained for the seasonal mean UV radiation in the last50years and the change in summer and winter was much more significant than that in spring and autumn. Summer season had the highest UV radiation, followed by spring and autumn, while winter season had the lowest UV radiation in the multi-yearly averaged version. The spatial distribution pattern for multi-yearly averaged UV radiation showed a peak value on Yunnan-Guizhou plateaus while a minimum value in Sichuan basins and the seasonally averaged UV radiation in coastal region, such as Guangzhou and Fujian, was much higher than that of inland areas.③Quite different zonal variation tendency was demonstrated for different months in the last50years. A significant decrease trend was obtained for January, July, and August with a Regional Mann-Kendall computation results of-2.23,-2.18and-2.07, separately, all of which were of95%significance. Parcels with decrease trend in February, March and December were also relative integrated; but few regions were of95%significance. Several regions conjunction with Yunnan-Guizhou plateaus and Sichuan basins had an increase tendency in each month and some other regions outside Yunnan-Guizhou plateau also had an increase trend in April, May, June, July, September and October. July and August had the maximum monthly averaged UV radiation while that in January, February and November was the lowest. The spatial pattern for monthly averaged UV radiation displayed that the peak value for all12months was obtained on Yunnan-Guizhou plateau while the minimum value was located in Sichuan basin and was extended to the middle reaches of Yangtze River in March and April. The monthly averaged UV radiation in coaster regions, such as Guangdong and Fujian, was much higher than that of inland areas in each month.3) UV radiation stress would suppress or enhance the plant’s photosynthesis. It would be a great improvement for IBIS model to take account of the plant’s response mechanism of net photosynthetic rate, which is a significant factor for photosynthesis, to varied radiation stress. The response mechanism was defined in IBIS as follows: The variation of net photosynthetic rate can be computed from the above formula once the variation of UV is input into the model. The net photosynthetic rate inside the canopy is computed based on the Absorbed Photosynthetic Active Radiation (APAR) of the canopy in the canopy physiology module of IBIS model. Response of net photosynthetic rate to variation of UV radiation can be obtained by taking off the previous net photosynthetic rate with controlled UV radiation.There was much difficulty to accurately assess the impact of variation of UV-B radiation to carbon cycle in subtropical region of China due to lack of quantitative research reports about the impact of UV-B radiation variation to subtropical plants. Most studies on this topic concentrated on herbaceous crops and followed by evergreen broadleaf trees in all subtropical plants and previous research showed significant variation of the sensitivity to UV-B for different spices and subspecies. Statistical regression relationships between UV-B intensity and net photosynthetic rate were constructed for herbaceous crops and evergreen broadleaf trees, separately, which were displayed as follows: y=-0.2051x-0.1424and.y=-0.2161x-0.1614.The effects of temporal and spatial patterns of UV radiation on carbon budget at subtropical ecosystems were studied based on the improved IBIS model. The results showed that:①Multi-annual averaged NPP during1961-2006showed significant latitudinal zonality of Chinese subtropical regions because of UV stress. Multi-annual averaged NPP of north subtropical regions was the lowest with the value of670g/m2/year. NPP of mid-subtopic regions followed, which was780g/m2/year. And multi-annual averaged NPP of southern subtropical regions was the highest that was910g/m2/year. The difference was related to the different land cover types and climatic characteristics in the three regions. The maximum multi-annual averaged NPP of Chinese subtropical regions was1679.43g/m2/year.②Compared with other subtropical regions of China, Yungui Plateau had higher elevations, where affected greater by UV radiation. Therefore, multi-annual averaged NPP of Yungui Plateau was lower than other subtropical regions of China. insignificant decrease trend was obtained for the annual mean UV radiation in the whole subtropical region and the spatial distribution pattern for multiyear averaged UV radiation implied a significant relationship between UV radiation and altitude and consequently, latitudinal zonality varied significantly with the topography. The maximum and minimum values of averaged UV radiation were found on Yunnan-Guizhou plateaus and Sichuan basins, separately. The UV radiation in coastal zones was much higher than that of inland areas.②A decrease trend was also obtained for the seasonal mean UV radiation in the last50years and the change in summer and winter was much more significant than that in spring and autumn. Summer season had the highest UV radiation, followed by spring and autumn, while winter season had the lowest UV radiation in the multi-yearly averaged version. The spatial distribution pattern for multi-yearly averaged UV radiation showed a peak value on Yunnan-Guizhou plateaus while a minimum value in Sichuan basins and the seasonally averaged UV radiation in coastal region, such as Guangzhou and Fujian, was much higher than that of inland areas.③Quite different zonal variation tendency was demonstrated for different months in the last50years. A significant decrease trend was obtained for January, July, and August with a Regional Mann-Kendall computation results of-2.23,-2.18and-2.07, separately, all of which were of95%significance. Parcels with decrease trend in February, March and December were also relative integrated; but few regions were of95%significance. Several regions conjunction with Yunnan-Guizhou plateaus and Sichuan basins had an increase tendency in each month and some other regions outside Yunnan-Guizhou plateau also had an increase trend in April, May, June, July, September and October. July and August had the maximum monthly averaged UV radiation while that in January, February and November was the lowest. The spatial pattern for monthly averaged UV radiation displayed that the peak value for all12months was obtained on Yunnan-Guizhou plateau while the minimum value was located in Sichuan basin and was extended to the middle reaches of Yangtze River in March and April. The monthly averaged UV radiation in coaster regions, such as Guangdong and Fujian, was much higher than that of inland areas in each month.3) UV radiation stress would suppress or enhance the plant’s photosynthesis. It would be a great improvement for IBIS model to take account of the plant’s response mechanism of net photosynthetic rate, which is a significant factor for photosynthesis, to varied radiation stress. The response mechanism was defined in IBIS as follows: The variation of net photosynthetic rate can be computed from the above formula once the variation of UV is input into the model. The net photosynthetic rate inside the canopy is computed based on the Absorbed Photosynthetic Active Radiation (APAR) of the canopy in the canopy physiology module of IBIS model. Response of net photosynthetic rate to variation of UV radiation can be obtained by taking off the previous net photosynthetic rate with controlled UV radiation.There was much difficulty to accurately assess the impact of variation of UV-B radiation to carbon cycle in subtropical region of China due to lack of quantitative research reports about the impact of UV-B radiation variation to subtropical plants. Most studies on this topic concentrated on herbaceous crops and followed by evergreen broadleaf trees in all subtropical plants and previous research showed significant variation of the sensitivity to UV-B for different spices and subspecies. Statistical regression relationships between UV-B intensity and net photosynthetic rate were constructed for herbaceous crops and evergreen broadleaf trees, separately, which were displayed as follows: y=-0.2051x-0.1424and.y=-0.2161x-0.1614.The effects of temporal and spatial patterns of UV radiation on carbon budget at subtropical ecosystems were studied based on the improved IBIS model. The results showed that:①Multi-annual averaged NPP during1961-2006showed significant latitudinal zonality of Chinese subtropical regions because of UV stress. Multi-annual averaged NPP of north subtropical regions was the lowest with the value of670g/m2/year. NPP of mid-subtopic regions followed, which was780g/m2/year. And multi-annual averaged NPP of southern subtropical regions was the highest that was910g/m2/year. The difference was related to the different land cover types and climatic characteristics in the three regions. The maximum multi-annual averaged NPP of Chinese subtropical regions was1679.43g/m2/year.②Compared with other subtropical regions of China, Yungui Plateau had higher elevations, where affected greater by UV radiation. Therefore, multi-annual averaged NPP of Yungui Plateau was lower than other subtropical regions of China. ③The NPP was underestimated based on IBIS model by considering UV radiation disturbance, which indicated that UV stress affected the photosynthetic rate, thus affected the NPP. NPP difference sequence appeared slightly increasing trend, which resulted from the general decrease of the long time series of UV. In1985NPP performed different from other years. The reason was that there were mutations of UV in the period between1970and1980, and the effects lagged for NPP. UV stress made the NPP decrease and ecosystem heterotrophic respiration weaken, which might be the reason for the increase of△NEP. In1985, the trend was different from other years, which caused by the mutations of UV sequence.④In sutropical regions of China, the decrement of total carbon budget during the stress of UV was0.5%in the whole year. UV stress decreased photosynthesis rate, but the effects on carbon budget was small. The possible reason was that UV stress had obvious effects on photosynthesis rate of seedling while weak effects on mature forests. Annual carbon budget of subtropical regions of China showed a declining trend, which was not related to the average time series of UV, but may be closely associated with climatic factors such as temperature and precipitation.The paper had two innovations:(1) A model for zonal distributed surface UV radiation estimation was proposed out. The model had high precision by using cross validation method. Based on the model, UV radiation was estimated and its monthly averages, seasonal averages, and annual averages during1961-2010were analyzed for the first time in the subtropical climate region of China.(2) Another model for the response of photosynthetic rate to UV stress was established by using experimental data. And IBIS model was improved based on the response model. It was the first time to adopt distributed model to analyze effects the variation of UV on the NPP and NEP of vegetaion in subtropical regions of China. Then, the ability of storage carbon of the ecosystem under UV stress was investigated, which was the basis of ecosystem carbon cycle under the variation of UV. |
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