Abstract:

Objective: To investigate the exogenous carbon fixation and photosynthetic carbon transport and allocation in different organs of seedlings of two Chinese fir families under different CO₂ concentrations, and to provide a theoretical basis for revealing the response mechanism of carbon fixation and photosynthetic carbon allocation strategy to the increase of CO₂ concentration. Method: Three CO₂ concentration gradients were established: a control concentration of (400±50) μmol·mol^?1 (C400) and two elevated concentrations of (800±50) μmol·mol^?1 (C800) and (1 000±50) μmol·mol^?1(C1 000) were established in the seedlings of No.020 and No.061 Chinese fir, which are extensively cultivated in the southern forest region, with the objective of quantifying the flow and distribution of fixed photosynthetic carbon in diverse tissues and organs at varying stages following tracer labeling, employing the ¹³C labeling method. The ¹³C labeling method was employed to label varying concentrations of CO₂, quantify the flow and distribution of fixed photosynthetic carbon in each tissue and organ at different stages of the tracer labelling process, and analyse the net photosynthetic rate. The objective is to ascertain the proportion of biomass distributed to each organ and to elucidate the growth differences. Furthermore, the aim is to determine the differences in carbon fixation capacity and the in vivo distribution of photosynthetic carbon in seedlings of each Chinese fir family under different CO₂ concentration conditions. Result: The ¹³C allocation and biomass allocation ratios of all tissue organs in seedlings of each Chinese fir family exhibited a pattern of leaf > stem > root under different CO₂ concentration treatments. As the CO₂ labelling concentration increased, the net photosynthetic rate and δ¹³C value of each organ in seedlings of each Chinese fir family generally increased subsequently. No.020 facilitated the transfer of ¹³C to the roots, as evidenced by an increase in the latter. Following a 1 d treatment, the C800 and C1 000 treatments resulted in 50.40% and 109.63% of the ¹³C allocation to the roots, respectively, in comparison to the C400 treatment. Following 30 d, the ¹³C allocation ratio of No.020 aboveground exhibited an increase of 6.23% and 6.03% in comparison to the C400 treatment, while the ¹³C allocation ratio of stems demonstrated a rise of 39.50% and 50.31%, respectively. The C800 and C1 000 treatments yielded statistically significant results (P<0.05) with the ¹³C allocation ratio of No.061 root system increasing by 22.40% and 70.26%, respectively. Additionally, the ¹³C allocation proportion of stems decreased by 2.45% and 15.10%(P<0.05), respectively, while the biomass allocation proportion of No.061 stems decreased by 12.44%. Conversely, the biomass allocation proportion of roots increased by 5.22% under the C1 000 treatment. Conclusion: In conditions of normal atmospheric CO₂ concentration, No.020 fir seedlings demonstrate a greater capacity for metabolic translocation. The elevated CO₂ concentrations promoted higher net photosynthetic rates and increased photosynthetic carbon synthesis in the seedlings of the two Chinese fir. Furthermore, the accelerated downward transport of photosynthetic carbon in the No.020 fir seedlings was observed, as well as the impact of elevated CO₂ on the photosynthetic carbon allocation strategies in the two genotypes of the species. The fir, with No.020 tending to store photosynthetic carbon in the aboveground parts, particularly in the stems, and No.061 tending to allocate photosynthetic carbon at the expense of the stems in order to increase root photosynthetic carbon supply.

Key words: ¹³C marker, Chinese fir, different families, elevated CO₂ concentration, photosynthetic carbon allocation