To analyze the effects of elevated carbon dioxide concentration （PCO2） on the mass flow of reduced nitro- gen （N） in the phloem and xylem of trees, juvenile beech （Fagus sylvatica L.） and spruce （Picea abies ...To analyze the effects of elevated carbon dioxide concentration （PCO2） on the mass flow of reduced nitro- gen （N） in the phloem and xylem of trees, juvenile beech （Fagus sylvatica L.） and spruce （Picea abies （L.） Karst.） were grown in phytotrons and exposed to ambient and elevated PCO2 （plus 687.5 mg/m^3 CO2） for three growing seasons. Elevated PCO2 significantly decreased the mass flow of N from the shoot to roots of beech by significantly reducing the concentration of soluble amino compounds in the phloem, even if the area of conductive phloem of cross-sectional bark tissue was significantly increased, because of less callus deposition in the sieve elements. In spruce, the downward mass flow of reduced N also tended to be decreased, similar to that in beech. Resembling findings in the phloem, N mass flow from roots to shoot in both tree species was significantly diminished owing to significantly reduced concentrations of amino compounds in the xylem and a lower transpiration rate. Therefore, the mass flow of reduced N between shoots and roots of trees was mainly governed by the concentrations of soluble amino compounds in the phloem and xylem in relation to the loading of reduced N in both long-distance transport pathways.展开更多
We studied the effects of expected end-of-the-century p CO_2(1000 ppm)on the photosynthetic performance of a coastal marine cyanobacterium Synechococcus sp.PCC7002 during the lag,exponential,and stationary growth phas...We studied the effects of expected end-of-the-century p CO_2(1000 ppm)on the photosynthetic performance of a coastal marine cyanobacterium Synechococcus sp.PCC7002 during the lag,exponential,and stationary growth phases.Elevated p CO_2significantly stimulated growth,and enhanced the maximum cell density during the stationary phase.Under ambient p CO_2conditions,the lag phase lasted for 6 days,while elevated p CO_2shortened the lag phase to two days and extended the exponential phase by four days.The elevated p CO_2increased photosynthesis levels during the lag and exponential phases,but reduced them during the stationary phase.Moreover,the elevated p CO_2reduced the saturated growth light(Ik)and increased the light utilization efficiency(α)during the exponential and stationary phases,and elevated the phycobilisome:chlorophyll a(Chl a)ratio.Furthermore,the elevated p CO_2reduced the particulate organic carbon(POC):Chl a and particulate organic nitrogen(PON):Chl a ratios during the lag and stationary phases,but enhanced them during the exponential phase.Overall,Synechococcus showed differential physiological responses to elevated p CO_2during different growth phases,thus providing insight into previous studies that focused on only the exponential phase,which may have biased the results relative to the effects of elevated p CO_2in ecology or aquaculture.展开更多
文摘To analyze the effects of elevated carbon dioxide concentration （PCO2） on the mass flow of reduced nitro- gen （N） in the phloem and xylem of trees, juvenile beech （Fagus sylvatica L.） and spruce （Picea abies （L.） Karst.） were grown in phytotrons and exposed to ambient and elevated PCO2 （plus 687.5 mg/m^3 CO2） for three growing seasons. Elevated PCO2 significantly decreased the mass flow of N from the shoot to roots of beech by significantly reducing the concentration of soluble amino compounds in the phloem, even if the area of conductive phloem of cross-sectional bark tissue was significantly increased, because of less callus deposition in the sieve elements. In spruce, the downward mass flow of reduced N also tended to be decreased, similar to that in beech. Resembling findings in the phloem, N mass flow from roots to shoot in both tree species was significantly diminished owing to significantly reduced concentrations of amino compounds in the xylem and a lower transpiration rate. Therefore, the mass flow of reduced N between shoots and roots of trees was mainly governed by the concentrations of soluble amino compounds in the phloem and xylem in relation to the loading of reduced N in both long-distance transport pathways.
基金supported by the National Key Research and Development Program of China (Grant No. 2016YFA0601402)the China SOA Grant Associated with Task (Grant No. GASI-03-01-02-05)+1 种基金the CNOOC Zhanjiang Branch (Grant No. CNOOC-KJ 125 FZDXM 00 ZJ 001-2014)the National Natural Science Foundation of China (Grant Nos. 41606092 & 41676156)
文摘We studied the effects of expected end-of-the-century p CO_2(1000 ppm)on the photosynthetic performance of a coastal marine cyanobacterium Synechococcus sp.PCC7002 during the lag,exponential,and stationary growth phases.Elevated p CO_2significantly stimulated growth,and enhanced the maximum cell density during the stationary phase.Under ambient p CO_2conditions,the lag phase lasted for 6 days,while elevated p CO_2shortened the lag phase to two days and extended the exponential phase by four days.The elevated p CO_2increased photosynthesis levels during the lag and exponential phases,but reduced them during the stationary phase.Moreover,the elevated p CO_2reduced the saturated growth light(Ik)and increased the light utilization efficiency(α)during the exponential and stationary phases,and elevated the phycobilisome:chlorophyll a(Chl a)ratio.Furthermore,the elevated p CO_2reduced the particulate organic carbon(POC):Chl a and particulate organic nitrogen(PON):Chl a ratios during the lag and stationary phases,but enhanced them during the exponential phase.Overall,Synechococcus showed differential physiological responses to elevated p CO_2during different growth phases,thus providing insight into previous studies that focused on only the exponential phase,which may have biased the results relative to the effects of elevated p CO_2in ecology or aquaculture.
