苗圃氮加载及水分胁迫对栓皮栎苗木叶片光合氮分配及生物量积累的影响

The combined effects of nitrogen loading and spring drought on photosynthetic machinery nitrogen distribution and accumulation of biomass of Quercus variabilis seedlings

苗圃科学施氮(N)作为提高苗木N贮存水平与质量的核心手段,能否提高干旱立地苗木造林效果仍存在争议;N贮存水平与干旱如何协同作用影响叶片光合N分配及苗木生物量积累尚不明确。阐明上述问题,能够为干旱立地下的森林植被恢复以及造林苗木科学精准施N提供科学依据。选择栓皮栎(Quercus variabilis Blume)为研究对象,对一年生苗木设置2个苗圃木质化期N加载水平(0、24 mg N/株),翌年春苗木移栽后设置2个灌溉水平(85%、40%田间持水量),取样测定苗木生物量、叶片N、叶绿素与脯氨酸水平、以及气体交换参数,计算光合N分配及光合N利用效率(PNUE)。结果表明,叶片发育完成后,干旱抑制N向光合系统分配,但N加载处理提高了干旱下的光合N含量,从而在一定程度上抵消干旱对生物量积累的抑制;无N加载苗木则向光合系统投入更少的N,而提高脯氨酸水平,生物量积累受抑制更为显著。无N加载苗木在遭受干旱后将N向羧化组分分配,而N加载苗木遭遇干旱后则显著抑制叶片将N向羧化系统以及电子传递系统分配,捕光组分N的分配则不受植物体内N贮存或外部水分状况的影响,栓皮栎苗木通过调整不同功能组分光合N含量和分配以维持干旱下较高的PNUE。

As one of the most important ways to improve seedling stored nitrogen(N)levels and quality,whether manipulating N fertilization could improve the field performance in dry areas was still under discussion.It was also not clear that the combined effects of stored N levels and drought on the partitioning of total leaf N among the different pools of the photosynthetic machinery and the accumulation of biomass.Clarifying above problems could provide a scientific basis for forest vegetation restoration and nursery N fertilization regimes for seedlings in dry areas,as well as the improvement of seedling quality under the difficult sites.During the first growing season,we produced Quercus variabilis Blume seedlings with distinct N content by applying two hardening phase N fertilization rates(0,24 mg N per seedling).At the beginning of the second growing season,the seedlings were transplanted into larger pots and subjected to two watering levels(85%,40%of field capacity).The seedling biomass,leaf N,chlorophyll,proline,and gas exchange parameters were measured.N distribution of functional components of leaf photosynthetic system and photosynthetic N-use efficiency(PNUE)were calculated.The results showed that water stress during spring reduced N allocation of leaf photosynthetic system.Nevertheless,high N storage could partially counteract the effect of drought on the accumulation of seedlings biomass due to increased N allocation to photosynthetic machinery.However,low N storage allocated less N to photosynthetic machinery,but increased the proline level,and the biomass inhibition of low N storage seedlings was more significant.The proportion of N allocated leaf Rubisco enzyme in low N storage seedlings increased under drought,while the proportion of N allocated leaf Rubisco enzyme and electron transport component in high N storage seedlings decreased under drought.Light-harvesting component was not affected by N storage levels or drought.Q.variabilis seedlings maintained higher PNUE under drought by adjusting photosynthetic N allocation content and distribution of different functional components.