外源施N对干旱河谷白刺花(Sophora davidii)幼苗生长，生物量及C、N、P积累与分配的影响

Growth,accumulation and partitioning of biomass,C,N and P of Sophora davidii seedlings in response to N supply in dry valley of upper Minjiang River

干旱气候条件下改善土壤养分能否提高植物抗旱能力,促进植物生长一直是一个争论性的问题。为了解外源施N是否可提高岷江上游干旱河谷优势灌木白刺花(Sophora davidii)幼苗适应干旱贫瘠环境的能力,研究了不同施N(0、92 mg N.kg-1土和184 mg N.kg-1土)处理下一个生长季节内白刺花幼苗生长、生物生产量、C、N和P的积累与分配特性,以及N和P利用效率。研究结果表明:轻度施N(92 mg N.kg-1土)处理促进了植物生长,增加了生物生产量,强化了C的固定和N、P等资源的吸收和积累,提高了其它受限资源的利用效率(如P),降低了N利用效率;但并不显著改变幼苗生物生产量及C、N和P等资源的分配格局,从而维持了资源的吸收、分配与利用的相对平衡,可能改善白刺花幼苗适应干旱贫瘠环境能力。而重度施N(184 mgN.kg-1土)处理虽然也相对于对照增加了叶片数目、生物生产量和C、N、P的积累量,但显著降低了幼苗根系的长度,抑制了根系的生长,并导致生物量及资源(生物量、C、N、P)较多地分配给地上部分(主要是叶片),不利于干旱环境下水分的吸收和利用,因而可能会加重幼苗受胁迫伤害的程度。综合分析表明,适当施加N肥可以促进白刺花幼苗的生长,一定程度上提高幼苗抗旱能力,改善幼苗定居,但也应避免过度施N。

The dry valley of upper Minjiang River is generally noted for their low primary productivity which is due to a combination of low, unpredictable water supply and nutrient deficiency. How to improve the efficiency in using limited resources and restore vegetation is always the problem which troubled ecosystem managers. Sophora davidii is a native perennial shrub of arid valleys, which is often predominant on eroded slopes and plays a vital role in retaining ecological stability in this region. It has been found that S. davidii was better adapted to dry environment than other shrubs, prompting its use for reclamation of arid degraded lands. But the shrub exhibits weak regeneration with poor seedling emergence and early growth in the field. In order to explore whether or not N supply could enhance the adaptation ability of S. davidii seedlings to dry and infertile environment, we investigated the growth, accumulation and partitioning of biomass, C, N, and P, and nutrient （N and P） use efficiency of S. davidii seedlings under three different N supply regimes （0, 92, and 184 mg N·kg^-1 soil）over one growing period. N supply dramatically influenced the growth, biomass and resources （ C, N, and P） accumulation and partitioning, and nutrient use efficiency of S. davidii seedlings. The seedlings exhibited stronger responses to low N supply （92 mg N·kg^ -1 soil） than to high N supply treatment （184 mg N·kg^ -1 soil） in this study. Low N supply facilitated seedlings growth by increasing leaf number, basal diameter, root length, biomass production, C, N and P accumulation and absorption, and enhancing the use efficiency of other limited resources as P. Compared to control, however, low N supply did little effect on altering biomass, C, N and P portioning in seedlings components. On the contrary, high N supply treatment also increased leaf number, biomass and C, N and P accumulation relative to control, but significantly decreased root length, and altered more biomass and resources to above-ground, which strongly reduced the ability of absorbing water under drought condition, and thus which might deep the drought stress. The results suggested that appropriate N supply was seemed to enhance the ability that S. davidii seedlings adapted to the xeric and infertile environment by stimulating plant growth, increasing recourses accumulation, enhancing use efficiency of other limited resources, and balancing biomass and resources partitioning. Appropriate, Nsupply, therefore, would be recommended to improve S. davidii seedling establishment in this region, but excess N supply should be avoided.