RESUMEN
To manage eutrophication of reservoirs, it is important to consider the potential for unexpected releases of organic phosphorus (OP) from areas around the reservoir where the water level fluctuates. In this study, we investigated the absorption and release of OP from a riparian soil/sediment from the Miyun Reservoir under fluctuating water levels using laboratory simulations. The total organic phosphorus (TOP) content in the soils/sediments ranged from 250.76 to 298.62 mg/kg, which accounted for between 5.6 and 38.5% of the total phosphorus (TP) content. We measured three OP fractions and found that the concentration of moderately labile OP (MLOP) was the highest, followed by labile OP (LOP), and the concentration of non-labile OP (NLOP) was the lowest. As the soils and sediments dried, they adsorbed phosphorus (P). The inorganic phosphorus (IP) contents were significantly and negatively correlated with the LOP and MLOP contents, indicating exchange between IP with these two fractions when the concentrations of bioavailable phosphorus in the soil are low. During flooding, the physicochemical properties varied at the sediment-water interface, inducing the release of Fe/Al-P. Some of the LOP and MLOP in the sediments were mineralized to IP. Our results suggest that when there are external P inputs, P may be released when sediments around a reservoir are subjected to wetting and drying as water levels fluctuate, which may cause P enrichment in reservoirs, especially in areas with poor water exchange.
Asunto(s)
Suelo , Contaminantes Químicos del Agua , Monitoreo del Ambiente , Sedimentos Geológicos , Agua , Contaminantes Químicos del Agua/análisisRESUMEN
Biogeochemical hotspots of nitrogen cycling such as ammonia oxidation commonly occur in riparian ecosystems. However, the responses of ammonia-oxidizing archaea (AOA) and bacteria (AOB) to water-level fluctuations (WLF) in riparian zones remain unclear. In this study, two patterns of WLF (gradual waterlogging and drying) were investigated in a 9-month column experiment, and the abundances and activities of AOA and AOB were investigated. The recovery evaluation revealed AOB abundance had not returned to the initial level at the end of the experiment, while AOA abundance had recovered nearly completely. AOA outnumbered AOB at almost all depths, and AOA showed higher resistance and adaptation to WLF than AOB. However, higher microbial abundance was not always linked to the larger contribution to nitrification. Changes in environmental parameters such as moisture and dissolved oxygen caused by WLF instead of ammonia-oxidizing microorganism (AOM) abundance might play a key role in regulating the expression of amoA gene and thus the activity of ammonia oxidizers. In addition, the community structure of AOM evolved over the incubation period. The composition of AOA species in sediment changed in the same way as that in soil, and the Nitrosopumilus cluster showed strong resistance to WLF. Conversely, waterlogging changed the community structure of AOB in soil while drying had no significant effect on the AOB community structure in sediment. This study suggests that the ammonia oxidizers will respond to WLF and eventually affect N fate in riparian ecosystems considering the coupling with other N transformation processes.
Asunto(s)
Amoníaco , Ecosistema , Amoníaco/análisis , Archaea/genética , Nitrificación , Oxidación-Reducción , Filogenia , Suelo , Microbiología del Suelo , AguaRESUMEN
By using eddy covariance technique, this paper quantitatively analyzed the photosynthetic characteristics of tropical seasonal rainforest ecosystem and related environmental controlling factors in Xishuangbanna in 2003-2006. In the study period, less interannual difference was observed in the net photosynthesis of the ecosystem, with the maximum photosynthesis rate (P(eco,opt)), respiration at daytime (R(eco,d)), and apparent quantum yield (alpha) averaged by 0.813 mg x m(-2) x s(-1), 0.238 mg x m(-2) x s(-1), and 0.0023 mg x micromol(-1), respectively. As affected by the interaction of air temperature (Ta) and vapor pressure deficit (VPD), the photosynthetic characteristics had some seasonal differences. In rainy season, the ecosystem had the strongest photosynthetic capacity because of the higher precipitation and warmer air temperature; in foggy and cool season, fog drip played an important role in the water relations of plants, and thereby, the ecosystem photosynthetic capacity was still higher; in dry and hot season, due to the limited precipitation and high temperature, the Ta and VPD increased, inducing a decrease of ecosystem alpha and P(eco,opt). The net CO2 exchange of the ecosystem strongly depended on the Ta above 20 degrees C and the VPD above 1 kPa.
Asunto(s)
Ecosistema , Fotosíntesis/fisiología , Árboles/fisiología , China , Humedad , Estaciones del Año , Temperatura , Clima TropicalRESUMEN
By the methods of chamber-based and eddy covariance measurements, the CO2 exchange of dominant tree species Pometia tomentosa and Gironniera subaequalis at leaf and canopy levels in the tropical seasonal rain forest of Xishuangbanna was measured in different seasons of 2004. The results showed that for the two tree species, the maximum net photosynthesis (P(max A)) of canopy based on chamber-based measurement ranked in the order of rainy season (RS) > end of rainy season (ERS) > foggy-cool season (FS) > dry-hot season (DS), and the dark respiration rate (Rd) of leaf was RS > ERS > DS > FS. The P(max B) based on eddy covariance measurement was in the same order as that based on chamber-based measurement, while the canopy respiration rate (Re) was RS > DS > FS > ERS. The maximum net photosynthetic rate of canopy in different seasons measured by the two methods had a comparatively small difference, ranging from 0.9 to 2.0 micromol m(-2) s(-1).
Asunto(s)
Dióxido de Carbono/metabolismo , Fotosíntesis/fisiología , Hojas de la Planta/metabolismo , Árboles/metabolismo , China , Modelos Teóricos , Hojas de la Planta/fisiología , Transpiración de Plantas/fisiología , Estaciones del Año , Árboles/fisiología , Clima TropicalRESUMEN
In this paper, various correction methods were compared, based on the observation data of the CO2 and water fluxes above the canopy of a tropical seasonal rainforest in Xishuangbanna during 1-9 March, 2003. The results showed that it was necessary to correct the observation data when calculating the carbon flux, though various correction methods contributed differently to the results. For daytime data, WPL made the most important contribution, while sonic temperature correction did the least. t test indicated that no significant difference was found between the carbon fluxes corrected by WPL and the standard values. Cluster analysis showed that triple-rotation correction was helpful to improve the precision of the data. For nighttime data, it was the triple-rotation correction that made the most important contribution, and sonic temperature correction also did the least. There existed significant differences between the carbon fluxes corrected by WPL, planar-fit correction and their combination and the standard values, while the differences between the carbon fluxes corrected by double-or triple-rotation and the standard values were not significant. Cluster analysis showed that the data corrected orderly by coordinate axes-rotated correction and WPL would be propitious to improve the precision. The results would provide a basis for calculating the fluxes within tropical rainforest in the future, and supply reference to the fluxes calculation for other areas.