【作者】 张鹏；

【导师】 金光泽；

【作者基本信息】 东北林业大学 ， 生态学， 2023， 博士

【摘要】 植物对养分的获取以及元素间的计量关系是维持生态系统初级生产力的重要途径。尽管植物多样性和初级生产力之间的正相关关系已经被充分认识,但是多样性如何通过影响植物的养分利用策略促进生产力仍然不清楚。本文基于东北阔叶红松林不同演替阶段(白桦林、阔叶混交林、针阔混交林和阔叶红松林)形成的多样性差异,以演替序列上12个森林样地为研究对象,测定样方内所有木本植物器官和生态系统组分的碳、氮和磷含量,旨在探明演替过程中植物受养分限制状态的变化规律,以及在此条件下多样性如何通过调控养分循环和化学计量特征维持生产力,研究结果有助于深化我们对森林生态系统多样性和生态系统功能的关系的认知。(1)在个体尺度上,叶片氮、磷含量在演替末期显著增加,而叶片氮磷比无显著变化;氮重吸收效率随进展演替显著增加,然而磷重吸收效率先增加后减少;氮重吸收效率与磷重吸收效率的比值仅在演替末期显著增加;植物氮循环对土壤养分的响应比磷循环更弱。在群落尺度上,随着进展演替,叶片氮、磷含量呈现先降低后升高的趋势,主要受香农-维纳多样性指数(Shannon-Wiener index,H’)和物种丰富度的影响;叶片氮磷比随演替而显著变化,主要由胸径的群落加权平均值决定;氮重吸收效率从37%±6%增加至57%±5%,主要受物种丰富度和胸径的影响,而磷重吸收效率相对稳定。因此,氮重吸收效率与磷重吸收效率的比值从1.01±0.19显著增加至1.33±0.19,表明随着温带森林的进展演替,氮限制加剧。这些结果可能反映了较高生物多样性群落中物种间对有限资源的激烈竞争,体现了生物因子在驱动森林生态系统养分循环中的重要性,为中国温带和北方森林可持续经营的施肥管理提供了参考。(2)演替过程中植物主要受到氮的限制,氮重吸收效率(NRE)随演替显著提高,然而从根部吸收的氮(NRSAF)从0.0197显著降低至0.0137,这表明氮缺乏可能随着进展演替而加剧。因此,演替晚期植物的氮利用策略比演替早期植物更为保守。相比之下,磷循环(PRE和PRSAF)保持相对稳定。随着演替的进行,叶片氮和磷的浓度分别从14.75 mg g-1和1.69 mg g-1显著增加至20.98 mg g-1和2.50 mg g-1,叶片氮磷比相对稳定,这主要是受养分重吸收途径的控制。然而,树木的绝对生长速率和相对生长速率随演替分别从2.45 mm year-1和0.15 mm mm-1 year1显著下降至1.19 mm year-1和0.05 mm mm-1 year-1,与叶片氮磷比无显著相关关系,但与叶片氮、磷浓度呈负相关关系。这些结果表明,植物为了更好地应对自然生态系统中各种不利于生存的干扰因子,将大多数的氮和磷分配到防御组织而不是光合组织,导致植物养分状态与生长速率解耦,这一推测需要在将来的研究中进一步证实。(3)植物群落水平的叶片氮重吸收效率随着进展演替显著增加,而凋落物的氮矿化速率则从0.65±0.11显著减少至0.31±0.07。相较于氮的矿化,氮的重吸收对于驱动多样性和生产力的正相关关系更为重要。然而,随着演替的进行,氮的重吸收效率增加导致氮的矿化速率减少。研究结果表明森林演替过程中重吸收是森林氮获取的主要途径,并从机理上揭示了多样性如何通过调控养分循环促进生产力。在将来的森林管理实践中,建议适当施用氮肥,以减轻演替末期土壤氮限制对幼苗更新的负面影响,从而有利于温带森林生态系统的可持续发展。(4)植物器官和植物群落的C:N:P化学计量特征随演替发生了显著变化,这些变化主要受树木大小和植物多样性变化的影响,然而凋落物和土壤中的C:N:P化学计量特征没有随着演替发生显著变化。此外,生态系统中C-N-P计量关系中的异速生长指数大多无显著差异,数值等于1,这表明所研究的生态系统中的C-N-P异速生长关系具有很强的保守性。研究结果阐明了森林演替过程中植物器官和生态系统组分的元素之间等速的变化规律,这些发现还有助于我们更好地理解从植物器官水平到生态系统水平的C:N:P化学计量变化的内在机制。更多还原

【Abstract】 Plant access to nutrients and the stoichiometric relationships among elements are important ways to maintain ecosystem primary productivity.Although the positive correlation between plant diversity and primary productivity is well understood,how diversity contributes to productivity by influencing stoichiometry remains unclear.Based on the differences in diversity at different succession stages(white birch forest,broadleaved mixed forest.coniferous broadleaved mixed forest and primary mixed broadleaved-Korean pine(Pinus koraiensis)forest),we determined the concentrations of carbon,nitrogen and phosphorus in all woody plant organs and ecosystem components in 12 forest plots of Liangshui mixed broadleaved-Korean pine forest.We want to investigate how the type of nutrient limitation of plant community changes during succession and resolve the response mechanism of nutrient cycling to nutrient limitation patterns.We investigate the important role of nutrient cycling in maintaining the relationship between diversity and productivity,and investigate the variation patterns of diversity-driven stoichiometric characteristics at the ecosystem level and the underlying influencing mechanisms.This scientific research project aims to investigate how diversity maintains productivity by regulating nutrient cycling and stoichiometric characteristics under nutrient-limited conditions during succession,and the results of this study will help deepen our knowledge of the relationship between diversity and ecosystem function in forest ecosystems.(1)At the individual scale,leaf N and P concentrations had a significant increase at the end of the succession,and leaf N:P ratio showed no change.NRE increased significantly with succession,but PRE first increased and then decreased.Significant increase in NRE:PRE ratios only occurred at the end of the succession.Moreover.Plant N cycling was less responsive to soil nutrient than P.At the community scale,we found that leaf N and P concentrations first decreased and then increased along forest succession,were mainly affected by ShannonWiener index and species richness.Leaf N:P ratio significantly varied with succession,was mainly determined by community weighted mean diameter at breast height(DBH).Nitrogen resorption efficiency(NRE)increased from 37%±6%to 57%±5%,which was significantly influenced by species richness and DBH.while P resorption efficiency(PRE)was relatively stable.Thus.the NRE:PRE ratios significantly increased from 1.01±0.19 to 1.33=0.19.indicating that N limitation was exacerbated with the temperate forest succession.These results might reflect the intense interspecific competition for limiting resource in a higher biodiversity community.In conclusion,our findings highlight the importance of biotic factors in driving forest ecosystem nutrient cycling and provide valuable information for sustainable fertilizer management practices in China’s temperate and boreal forests.(2)The successional chronosequence was mainly limited by N,and nitrogen resorption efficiency(NRE)significantly increased while the N root-soil accumulation factor(NRSAF)significantly decreased from 0.0197 to 0.0137 over succession,indicating that N deficiency may be exacerbated with succession.Thus,later successional plants have a more conservative N use strategy than those of early succession.By contrast.P cycling(PRE and PRSAF)remained relatively stable.Leaf N and P concentrations significantly increased from 14.75 mg g-1 and 1.69 mg g-1 to 20.98 mg g-1 and 2.50 mg g-1,respectively,and leaf N:P ratio was relatively constant with succession,which was mainly controlled by nutrient resorption pathway.Nevertheless,absolute and relative tree growth rate significantly decreased from 2.45 mm year-1 and 0.15 mm mm-1 year-1 to 1.19 mm year-1 and 0.05 mm mm-1 year-1 along succession,respectively,showing a poor correlation to leaf N:P ratio but negative correlation to leaf N and P concentrations.These results suggested that a substantial amount of N and P may be allocated to the defense tissues rather than the photosynthetic tissues in order to better cope with the long-term adverse environment in the natural forest ecosystem,leading to the decoupling of plant nutrient status from growth rate.In future studies,the allocation of nutrient to different functions should be considered when using the GRH in natural forest ecosystems.(3)Leaf N resorption efficiency(NRE)at the community level increased significantly along the successional chronosequence.whereas litter N mineralization rate significantly decreased from 0.65±0.11 to 0.31±0.07.Leaf NRE was more important than litter N mineralization rate in driving the diversity-productivity relationship.However,higher leaf NRE led to less N mineralization as succession progressed along the chronosequence.Our results highlight the importance of the N resorption pathway rather than the N mineralization pathway for forest N acquisition with community succession,and they provide mechanistic insights into the positive effects of biodiversity on ecosystem functioning.In future forest management practices,we recommend appropriate application of N fertilizer to mitigate the adverse effects of N-poor soil on seedling regeneration during late succession and thus maintain the sustainable development of temperate forest ecosystems.(4)The C:N:P stoichiometry of plant organs and the plant community varied significantly along the succession chronosequence,with variation mainly driven by changes in tree size and plant diversity.The C:N:P stoichiometry in litter and soil did not change with succession.Furthermore,most allometric exponents of C-N-P scaling relationships did not differ among plant organs and ecosystem components and were equal to 1.indicating strong conservatism of the C-N-P stoichiometry scaling relationship in this ecosystem.Our findings highlight the conservative isometric allocation strategies of elements among different organs and ecosystem components during forest succession.Further,they help improve our understanding of the underlying mechanisms for variations in C:N:P stoichiometry from the plant organ level to the ecosystem level.更多还原