RECENTLY PHOTOSYNTHESIZED CARBON ALLOCATION AND TURNOVER: A MINOR REVIEW OF THE LITERATURE
植物近期光合碳分配及转化

Recently photosynthesized carbon (C) constitutes an important portion of C cycling in plant systems. The quantification of the partitioning of recently photosynthesized C to plant tissues, soils and respirations is essential for understanding the global C cycle. The cycle of recently photosynthesized C is difficult to study due to the rapid turnover of recently metabolized C and that stable organic C compounds are not immediately synthesized. Carbon isotope techniques can be used to study the allocation and turnover of recently photosynthesized C. The following research topics should be addressed in future studies. 1) The fraction of recently photosynthesized C used in respiration of living roots, rhizosphere, and soil organic matter, and photosynthate turnover in the rhizosphere needs to be quantified. 2) The amount of recently photosynthesized C that is lost to atmospheric fluxes of CO_2 and CH_4 should be quantified. 3) Because of significant difference in the physiologies C_3 and C_4 plants, global climate change will produce profound effects on the distribution and productivities of C_3 and C_4 species and further influence the global C cycle pattern. We believe that studies on differences in C allocation and turnover in C_3 and C_4 species are very valuable. 4) The effects of human activities, such as livestock farming and land use, on the cycle patterns of recently photosynthesized C. In order to further understand C partitioning patterns, it is vital that more ecosystem level studies of C cycling are conducted. Little information in photosynthesized C fluxes in China's grasslands is available and this region should be a research priority.