不同生态型硬叶兜兰的氮素利用效率差异比较及其碳氮分配策略

Comparison of nitrogen use efficiency among different ecotypes of Paphiopedilum micranthum and their carbon-nitrogen allocation strategies

关键词:  硬叶兜兰, 喀斯特生态型, 氮利用效率, 生态适应性, 碳氮分配

Key words:  Paphiopedilum micranthum, karst ecotype, nitrogen use efficiency(NUE), ecological adaptation, carbon-nitrogen allocation

摘要:

为揭示喀斯特生境中硬叶兜兰(Paphiopedilum micranthum)不同生态型对氮素的适应机制,该研究以滇东南同一石灰岩区域分布的3种生态型(岩生型、灌丛地生型、林下地生型)硬叶兜兰为对象,旨在比较其氮素吸收与利用效率的差异,并从碳氮分配角度阐明其生态适应策略。通过测定定居地土壤有效氮含量、分析植株氮表型及关键氮代谢酶活性,比较不同生态型在氮积累与利用效率方面的差异,并进行关联因素分析。结果表明:(1)不同生态型硬叶兜兰氮吸收效率(NUpE)无显著性差异,而氮利用效率(NUE)存在显著分化(P<0.05),岩生型[(2.83±0.14)g·mg^-1]和林下地生型[(2.83±0.05)g·mg^-1]的NUE显著高于灌丛地生型[(2.64±0.22)g·mg^-1]。(2)不同生态型间形成了差异化的适应策略:林下地生型的总根长[(64.80±9.86)cm]与根冠比(0.95±0.22)显著高于岩生型[总根长(50.26±17.50)cm,根冠比0.72±0.17]; 岩生型则具有最高的单位根长吸氮量,显著高于林下地生型(P<0.05); 灌丛地生型表现为强硝态氮同化能力,其硝酸还原酶活性[(49.37±1.08)μg NO₂^-·g^-1 FW·h^-1]及叶氮浓度均为三者最高。(3)碳氮分配策略迥异:岩生型全株碳氮比(C/N)最高; 灌丛地生型碳氮积累量最大但C/N最低; 林下地生型各项指标多居中。(4)关联分析显示,氮利用效率与总根长、根部碳积累量及叶片C/N呈显著正相关,而与土壤铵态氮含量呈显著负相关。综上,不同生态型的硬叶兜兰通过调控根系构型、碳氮分配,形成了互补的氮适应机制。岩生型凭借更高的单位根长吸氮效量和较高的C/N所体现的资源分配策略,实现了最高的氮素利用效率。该研究通过对比生态型在氮吸收利用效率及氮代谢生理特性的差异,从碳氮分配的角度揭示了硬叶兜兰的生态适应机制,为该物种的科学保护与人工栽培提供了理论依据。

Abstract:

To reveal the nitrogen adaptation mechanisms of different Paphiopedilum micranthum ecotypes in karst habitats, this study focused on three ecotypes(lithophytic type, scrub terrestrial type, and understory terrestrial type)co-occurring in a limestone area in southeastern Yunnan. We aimed to compare their nitrogen uptake and utilization efficiencies and elucidate their ecological adaptation strategies from the perspective of carbon-nitrogen allocation. By measuring soil available nitrogen content, and analyzing plant N phenotypes along with the activities of key N metabolism enzymes. We compared inter-ecotype differences in N accumulation and utilization efficiency, followed by correlation analysis of influencing factors. The results were as follows:(1)While no significant difference was observed in nitrogen uptake efficiency(NUpE), nitrogen use efficiency(NUE)differed significantly among ecotypes(P<0.05). The lithophytic type [(2.83±0.14)g·mg^-1] and the understory terrestrial type [(2.83±0.05)g·mg^-1)exhibited significantly higher NUE than the scrub terrestrial type [(2.64±0.22)g·mg^-1).(2)Divergent adaptive characteristics were formed: the understory terrestrial type had significantly greater total root length [(64.80±9.86)cm)and root-to-shoot ratio(0.95±0.22)than the lithophytic type [total root length:(50.26±17.50)cm; root-to-shoot ratio: 0.72±0.17]. In contrast, the lithophytic type displayed the highest nitrogen uptake per unit root length, significantly surpassing the understory terrestrial type(P<0.05). The scrub terrestrial type demonstrated a strong nitrate assimilation capacity, possessing the highest nitrate reductase activity [(49.37±1.08)μg NO₂^-·g^-1 FW·h^-1] and leaf N concentration.(3)Carbon-nitrogen allocation strategies differed markedly: the lithophytic type had the highest whole-plant carbon-to-nitrogen ratio(C/N), whereas the scrub terrestrial type exhibited the greatest C and N accumulations but the lowest C/N. The understory terrestrial type generally displayed intermediate values for these traits.(4)The correlation analysis showed that, nitrogen use efficiency was significantly positively correlated with total root length, root carbon accumulation, and leaf C/N, and significantly negatively correlated with soil ammonium nitrogen content. In conclusion, the different ecotypes develop complementary nitrogen adaptation mechanisms by regulating root architecture and carbon-nitrogen allocation. The lithophytic type achieved the highest nitrogen use efficiency through more nitrogen uptake per unit root length and a resource allocation strategy characterized by a higher C/N. By comparing the differences in nitrogen uptake/use efficiency and N metabolism physiology among ecotypes, this study elucidates their ecological adaptation mechanisms from the perspective of carbon-nitrogen allocation, and provides a theoretical basis for the scientific conservation and cultivation of this species.