| 1 | Combining sap flow measurement-based canopy stomatal conductance and ^(13)C discrimination to estimate forest carbon assimilation显示文摘The available methods for studying C uptake of forest and their problems in practices are reviewed, and a new approach to combining sap flow and 13C techniques is proposed in this paper. This approach, obtained through strict mathematic derivation, combines sap flow measure-ment-based canopy stomatal conductance and 13C discrimi-nation to estimate instantaneous carbon assimilation rate of a forest. Namely the mean canopy stomatal conductance (gc) acquired from accurate measurement of sap flux density is integrated with the relationship between 13C discrimination (?) and Ci/Ca (intercellular/ambient CO2 concentrations) and with that between Anet (net photosynthetic rate) and gCO2 (stomatal conductance for CO2) so that a new relation be-tween forest C uptake and ? as well as gc is established. It is a new method of such kind for studying the C exchange be-tween forest and atmosphere based on experimental ecology. | ZHAO Ping LU Ping MA Ling SUN Guchou RAO Xingquan CAI Xi'an ZENG Xiaoping | 2005 | Chinese Science Bulletin2005，50，18： | 9 |
| 2 | High-nitrogen and low-irradiance can restrict energy utilization in photosynthesis of successional tree species in low subtropical forest显示文摘Responses of photosynthesis and the partition of energy utilization to high-nitrogen importation and high-light intensity in leaves of three dominant tree species of subtropical forest,including sun plant or early-successional species Schima superba,mesophyte or intermediate-successional species Canstanopsis hystrix,and shading-tolerant plant or late-successional species Cryptocarya concinna were studied by using the CO2 exchange system and chlorophyll fluorescence method.Our results showed that,regardless of plant species,net photosynthetic rate(Pn)was higher in high-nitrogen supply and high irradiance(HNHL)plants than in low-nitrogen supply and high irradiance(LNHL)plants,implying that low-nitrogen importation would limit Pn of plants grown under high irradiance.However, high-nitrogen supply and low irradiance(HNLL)plants had a lower Pn.Insignificant change of quantum yield(Fv′/Fm′)in opened PS II was found in leaves of HNHL,LNHL or HNLL plants of S.superba and C. hystrix,while a higher Fv′/Fm′occurred in HNHL plants of C.concinna in comparison with LNHL or HNLL plants.The HNHL plants of C.concinna also had a higher photochemical quantum yield(△F/Fm′) than LNHL or HNLL plants,however no similar responses were found in plants of S.superba and C. hystrix(P<0.05).In the irradiance range of 0―2000μmol photon·m -2·s -1,the fraction of energy consumed by photochemistry(φ PSII )was 18.2%in LNHL plants of S.superba which was higher than that in HNHL plants(P>0.05)and it was significantly higher than in HNLL plants(P<0.05).C.hystrix also had a similar response inφ PSII to nitrogen supply and irradiance.Regardless of species HNLL plants had a significantφ PSII and higher heat dissipation in light,and this effect was more severe in C.concinna than in S.superba or C.hystrix.The results may mean that high-nitrogen importation by nitrogen deposit and low irradiance caused by changing climate or air pollution would more severely restrict photosynthetic processes in the late-successional species C.concinna than in the early-successional species S.superba and intermediate-successional species C.hystrix.The continuous high-nitrogen precipitation in the future and the over cast mist or pollution smoke could induce late-successional species to degrade,however,early-successional species would be more adapted to competition for more resources to keep their dominance in ecosystems.In this sense,the zonal vegetation may accelerate degradation caused by high nitrogen precipitation and low irradiance,while the early-successional and mesophytic vegetations can remain longer.Thus,nitrogen precipitation may play an important role in plant community succession. | CAI Xi’An,SUN GuChou,ZHAO Ping &LIU XiaoJing South China Institute of Botany,Chinese Academy of Sciences,Guangzhou 510650,China | 2008 | Science China(Life Sciences)2008，51，7： | 0 |
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