Phosphorus distribution inside Chinese fir seedlings under different P supplies based on 32P tracer

Aim The objective of this study was to determine the amount and distribution of exogenous phosphorus (P) in different organs, as well as their changes in Chinese fir (Cunninghamia lanceolata) under different P supply levels. The results could be used as scientific base for selecting P-efficient genotypes.Methods Seedlings of two Chinese fir genotypes (M1 and M4), both with high P use efficiency, were treated with different P supply levels and quantified by using 32P isotope tracer for P distributions in different organs. The seedlings used in this study were selected by our team through previous research as the experimental materials.Important findings We found that the distribution of exogenous P in M1 and M4 was the highest in the roots and the lowest in the stems, and at an intermedia level in the needles. The ³²P content of each organ under the same treatment was ranked as root > stem > needle on the horizontal projection plane. The exogenous P content by the roots, stems and needles of M1 and M4 under low-P treatment appeared lower than that under the high-P treatment. The blackening degree of low-P image of roots, stems and needles under the same treatment was also lower than that under high-P treatment. The content of exogenous P in these organs under the low-P treatment increased slowly, indicating that the low-P stress significantly affected the absorption and accumulation of P in the seedlings. P allocation rates in the roots of M1 and M4 showed an initial decreasing and increasing later under low-P stress, while under the high-P treatment, the root P level increased first and stabilizing later. These findings indicate that M1 and M4 could adapt to external low-P stress through redistribution of P within the plants by transferring P from roots to above-ground parts at the early stage under low P stress. With the extension of stressing time, P from above-ground parts was shifted to roots. However, the distribution of exogenous P in M1 and M4 was significantly different under the low P treatment. The distribution of exogenous P from the beginning to the end of M1 was greater in the roots than that in above-ground parts, while M4 showed a similar pattern in early stages but a higher rate toward the above-ground parts later. This indicates that M1 has a higher degree of strengthening P circulation in vivo than M4 with low P stress, i.e. the tendency of P transfer from above-ground parts to roots is stronger in M1 than in M4.