Periodical response of Chinese fir root to the phosphorus concentrations in patches and heterogeneous distribution in different growing stages

【Objectives】This study aimed to dynamic investigation of the effect of inhomogeneous P supply on the P foraging behavior of Chinese fir roots.【Methods】 The tested materials in the pot experiment was Chinese fir clone belongs to half-sib family, which were cultivated in Wuyi state-owned forest in Zhangping County, Fujian Province. Phosphorous patches with KH2PO4 of 0, 4, 16 and 30 mg/kg were prepared, and the patches were loaded in four different orders inside a column to make four treatments of heterogeneous P supply. The fir seedlings were destructively samples at the 50, 100 and 150 d after transplanted into the treatment pots. The root morphology, biomass and P acquisition efficiency were measured.【Results】 It exhibits different adaptive strategies of Chinese fir roots in response to different P concentrations and patches distribution in stages. 1)The roots grew in patches with P deficiency or low P supply proliferate for foraging P in other patches with higher P supply at the initial. The root proliferation contributes to the dry matter accumulation but not the P content of roots in P deficiency or low P patches. Roots continue to proliferate in the patch with no P supply due to low P stress when roots grew from the P deficiency patch to the P-poor patch. However, the increase was slowed down when roots grew from the P-poor patch to the P-rich patch, resulting proliferation in the P-rich patch, and the proliferation results in the increase of P absorption and dry matter accumulation. At the last stage, the P-rich patches have higher roots increment, dry matter accumulation and P content when they are at the bottom-most layers. 2)Roots of the treatments with P-rich supply in the first layer only grow in the P-rich patches at the initial stage. The roots increment and dry matter accumulation of these patches are all higher than those of the treatments with P deficiency or low P supply in the first layer, while the roots’ P content shows an opposite result. At the second and last stages, the roots increment, dry matter accumulation and P contents in the surface layers are all higher than those in the other layers. In addition, the treatment with the most P supply in the surface layer has the fastest speed to downward grow. 【Conclusions】 P deficiency or low P supply result in root proliferation which contributes to foraging P. Roots in the surface layer with P-rich supply are committed to P absorption at the initial stage. Then roots proliferate in the surface layer, and the P absorption, dry matter accumulation and downward growth of roots are higher than those in the other layers.