杉木根系对不同磷斑块浓度与异质分布的阶段性响应

【目的】对杉木根系在异质供磷(P)条件下的觅磷行为进行动态监测,探讨磷斑块的浓度与其异质分布对杉木根系觅磷行为的影响。【方法】以福建漳平五一国有林场的半同胞杉木家系为试验材料,利用垂直异质供磷装置,设置KH2PO4 0 mg/kg(缺磷,P0)、4 mg/kg(低磷,P4)、16 mg/kg(正常供磷,P16)和30 mg/kg(高磷,P30)4个磷浓度斑块,将其按照不同顺序垂直排列构建异质供磷处理。在生长50、100、150 d时,进行3次破坏性取样,测定不同阶段不同异质供磷处理下杉木根系形态、生物量及觅磷效率的变化,进行杉木根系生长及觅磷行为的动态观测。【结果】杉木根系表现出阶段性的觅磷策略: 1)当杉木根系处于表层缺磷或低磷斑块时,通过根系的增生向供磷量更高的斑块觅磷,根系增生促进了缺磷或低磷斑块根系的干物质积累,但其根系含磷量较低; 至处理中期,表层缺磷处理的根系从缺磷斑块生长至低磷斑块后,杉木根系受低磷胁迫持续大量增生; 而当表层低磷处理的根系从低磷斑块生长至高磷斑块后,根系在高磷斑块内大量增生,且促进了根系磷养分的吸收及干物质的积累; 处理末期,当高磷斑块置于最底层时,其斑块内的根系生长量、 干物质积累量及根系含磷量均明显较大。2)当杉木根系处在表层高磷斑块时,根系初期仅在供磷量较高的表层生长,其根系生长量与干物质积累量均低于表层供磷量较低的处理,但其根系含磷量却显著大于表层供磷量较低的处理; 处理中期及末期,表层的根系生长量、 干物质积累量及根系含磷量均显著大于其他层次,且表层充足供磷处理的根系向地生长速度最快。【结论】异质供磷条件下,当杉木根系处在缺磷或低磷斑块时,主要通过根系的大量增生来寻觅磷养分; 当杉木根系处在高磷斑块时,在初期致力于斑块磷养分的吸收之后,表层根系大量增生,且根系的磷养分吸收和干物质积累显著大于其他层次,同时提高根系向地生长速度。

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.