Phosphorus assimilation of Chinese fir from two provenances during acclimation to changing phosphorus availability

To identify the differences in phosphorus (P) assimilation of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) from provenances Y and G displaying slow and fast growth, respectively, and to elucidate the physiological acclimation mechanisms of these conifers to changes in P availability, Chinese fir seedlings were treated with 0 (P starvation), 2 (normal P) or 4 (high P) mM P. The conifer from provenance Y had a greater specific root surface area, and higher activities of APs and PEPC in the roots, resulting in higher P concentrations and lower PUEs in the roots than those from provenance G. Notably, higher activities of APs, PEPC and MDH, and a greater PUE were observed in the needles from provenance G compared to those from provenance Y supplied with high P level. The transcriptional regulation responsiveness of several genes involved in P acquisition and transport was stronger in conifers from provenance Y than those from provenance G treated with P starvation, but the opposite was true under high P condition. These results suggest that Chinese fir from provenance Y possesses a greater capacity for P acquisition and transport compared to that from provenance G under low P availability, whereas conifers from provenance G can more efficiently utilize available P to produce biomass than those from provenance Y under high P conditions. P starvation resulted in increased specific root surface area, higher activities of APs, PEPC and MDH, lower P concentrations, and higher PUEs in Chinese fir, while high P supply caused the opposite changes. Consistently, P starvation led to transcriptional overexpression of genes involved in P acquisition and transport including PHT1.4 and PHO1, AP, and MDH in Chinese fir, and high P availability suppressed PHT1.4 transcript levels and increased PHT2.1 mRNA levels. These results suggest that Chinese fir can activate P-solubilizing enzymes, and upregulate transcript levels of key genes involved in P acquisition and transport under P deficiency conditions, whereas the conifers can enhance P translocation from the roots to the shoots to promote the growth of aerial parts under high P conditions.