【作者】 袁义福；

【导师】 王仁卿；

【作者基本信息】 山东大学 ， 生态学， 2014， 博士

【摘要】 氮(N)和磷(P)是植物生长必需的矿质元素,这两种元素之间的相对关系可以反映土壤中的营养条件,在个体发育、碳同化、新陈代谢和繁育过程中有重要的作用,对植物种间关系和群落结构有重要的影响。自工业革命以来,人类活动对自然生态系统中的营养条件产生了强烈的影响。由于人为氮、磷输入的比例失衡及氮、磷元素在理化性质上的差异,很多生态系统中的氮磷比发生了改变。随着氮磷比营养条件的改变,植物群落中优势种,植物间的种间关系也会随之改变。同时,外来种广泛使用给本地生态系统的影响也受到越来越多的关注,成为当今生态学研究中的热点。营养条件是外来植物定植新栖息地过程中的决定性因素之一,许多外来植物在营养获取、营养利用及营养保持等方面都具有优势,对营养波动具有更好的适应能力,在与本地植物的竞争中处于优势地位。因此,研究不同氮磷比条件下外来植物与本地植物的种间关系可以加深对外来植物生态影响的认识,并为分析气候变化背景下潜在的入侵植物提供依据。为了研究氮磷比营养条件改变对外来植物与本地植物种间关系的影响,我们选取了华北地区植被恢复中常用的外来植物火炬树(Rhus typhina)、本地植物麻栎(Quercus acutissima)和荆条(Vitex negundo var. heterophylla)作为研究物种,通过温室控制实验的方法对该问题进行研究。实验中,根据野外森林土壤的调查数据,由低到高设置了三个氮磷比处理：5,15和45。每种氮磷比处理下以火炬树与麻栎或荆条混种的方式模拟种间竞争,并设置单种的处理作为对照。实验过程中,从植物功能性状入手对植物的生长、生理、生物量积累及分配、叶片化学计量学、种间关系等内容进行了测量和观察,比较了火炬树与麻栎、荆条的差异,并分析了火炬树对这两种本地植物的影响。模拟实验结果表明：氮磷比营养条件的改变对火炬树、麻栎和荆条都产生了显著的影响。三种植物的生物量在氮磷比5或15时最大；而氮磷比45时,三种植物的生物量积累都受到了明显的抑制,主要原因是高氮磷比时,氮磷元素失衡,磷元素成为限制因素,影响了植物的碳同化能力。生物量分配方面,低氮磷比时,三种植物均显著增加了根生物量比,提高对氮元素的获取能力；在高氮磷比时,均没有明显的生物量调整。火炬树生长快,冠幅大,叶生物量比重高,具有较高的净光合速率、低比叶重和高的氮磷元素利用效率,可以积累高生物量并具有较大的根生物量,在氮磷营养和光照的获取方面有很大的优势,对营养条件的改变适应能力很强。本地植物麻栎和荆条均将更多的生物量分配到根,根冠比大,叶生物量比重小,在光合组织中的投入较少,生物量积累能力低,在营养元素和光照获取上均逊于火炬树。混种时,火炬树均具有远高于本地种的相对优势度系数,在种间关系中始终处于绝对的优势地位,并且这种竞争优势没有受到氮磷比条件改变的负面影响。与麻栎相比,火炬树具有更高的净光合速率、更小的比叶重、更高的光合氮利用效率和光合磷利用效率,将较多的氮磷营养分配到与光合作用有关的组织中,具有更强的碳同化能力。虽然荆条在净光合速率、比叶重等性状上与火炬树类似,但由于火炬树生长快,冠幅大,对其产生了遮阴作用,抑制了其光合作用。虽然火炬树并没有对荆条的生理状态造成显著的胁迫作用,但其生物量积累受到严重影响。混种时,由于火炬树的竞争压力,本地种麻栎和荆条均调整了生物量分配,将更多的生物量投入到根,以获取更多的氮磷营养。而火炬树则保持了与单种时基本一致的生物量分配格局,更多的生物量分配到地上部分。这种生物量分配策略上的不同,导致火炬树在地上部分对光照的竞争中占据绝对优势,结合其强的碳同化能力,保证其可以积累明显高于麻栎和荆条的总生物量。虽然火炬树的根生物量比重较麻栎和荆条小,但是其具有很高的生物量,使其在竞争中仍具有较高的根生物量,结合其在根表面积等性状上的优势,保证了其对氮磷营养元素的强竞争能力。在高氮磷处理中,火炬树显著增加了叶生物量比,在磷限制的情景下维持较高的地上部分碳同化能力,进而促进其地下对营养元素的获取,对该条件具有更好的适应性。而本地植物麻栎和荆条的生物量分配格局并没有进行调整,这种适应策略上的内稳性,反映出植物对不利环境较强的耐受性,有利于植物更好的适应营养胁迫的不良条件。但这种策略在营养条件波动时则比较保守,相比于外来植物火炬树,在环境变化下不利于其在竞争中取得优势。总之,与华北地区典型物种麻栎和荆条相比,外来植物火炬树在生长特性、叶片性状、根属性等植物功能性状上具有明显的优势,而且其对不同的氮磷比营养条件表现出了更为积极的生物量和氮磷营养分配策略,保证其具有很高的生物量生产能力。得益于其更强的营养元素吸收能力,在与光合作用相关的组织中更多的生物量和氮磷营养投入,火炬树在竞争中积累了远高于麻栎和荆条的生物量。这种在生物量和叶片营养分配中的权衡,是导致这几种植物在竞争中差异化表现的主要原因,并有助于火炬树在不同的氮磷比营养条件中始终保持绝对竞争优势。另外,在低氮磷比或高氮磷比条件下,即氮限制或磷限制时,火炬树可以产生较麻栎更多的生物量,并能够在人为活动造成的氮磷输入时适应的更快更好。此外,虽然在我们的研究中麻栎幼苗在竞争中生物量没有明显下降,但荆条幼苗因为火炬树的遮阴作用生物量显著下降,因此火炬树对本地植物的影响需要高度关注。在未来的植被恢复过程中,外来植物的引入和管理应重视对外来植物植物功能属性和当地土壤条件的综合分析,并结合当前主要的气候变化因素,分析其可能存在的入侵潜力,以减少外来植物引入所造成的不必要的经济损失和生态风险。更多还原

【Abstract】 Nitrogen (N) and phosphorus (P) are essential mineral nutrient elements in plant and the N:P ratios, as an important indication of soil nutritional conditions, plays vital roles in individual life history, carbon accumulation, metabolism and reproduction, and has important influences on interspecific relationship and community structure. Human activities have exerted a great impact on the original trophic conditions of ecosystems since the beginning of the Industrial Revolution. Due to disproportionately anthropogenic inputs of N and P in fertilization and the differences between element characteristics, the relative importance of nutrient elements (N:P ratios) has been changed in many ecosystems. As a result of those changes, patterns of plant competition would alter and dominated species in plant community may be changed. Biological invasion is also an important aespect of global change and a strong threat to native community biodiversity and ecosystem functioning. As a hot spot in ecology research, plant invasion is attracting more and more attention. Resource is a main environmental factor that determines invasion success of invasive species. Invasive plants with traits related to resource acquisition, resource conservation, or high resource-use efficiency could outperform the other native species, profiting from capability of responding quickly to nutrient fluctuation. Therefore, studying the effects of different N:P ratios on the interaction between exotic and native species will favor the understanding of occurrence of plant invasions and prediction of future invaders under the global change background.We conducted a greenhouse experiment to study the effects of different N:P ratios on the performance of alien R. typhina and native Q. acutissima, Vitex negundo var. heterophylla, and the interaction between them. All species are widely used in vegetation restoration in Northern China. The seedlings of Q. acutissima, V. negundo and R. typhina were grown in monoculture or mixture, with three different N:P ratios, to simulate different interspecific relationship. In this study, plant functional traits related to plant growth, physiology, leaf stoichiometry, biomass allocation, and nutrient absorption were determined, to evaluate impacts of R. typhina on native species.Results indicated that N:P supply ratio had significant effects on all species. The biomass of these species was highest under the N-limited condition (N:P=5) or the basic N and P supply condition (N:P=15). As a result of high N:P ratios, there was an unbalance between N and P, showing a P-limited condition, which inhibited the biomass production, they has lowest biomass under the high N:P ratio (N:P=45). Under N-limitation, plants had the highest RMR for obtaining nitrogen, while no significant adjustment of biomass allocation under high N:P ratio condition. With high performance, such as high plant growth, high crown area, high leaf mass ratio, high net photosynthesitic rate, low leaf mass per area, high net photosynthetic rate, R. typhina could product high biomass and root biomass, which help it in competition for nutrients and light, giving it strong capability of responding quickly to nutrient fluctuation. Compared with R. typhina, native species Q. acutissima and V. negundo invested more biomass in root and less biomass and nutrients in photosynthesis apparatus, with high root:shoot ratio and low leaf mass ratio, causing their lower competiveness for nutrients and light.In mixture, R. typhina was the superior competitor and had higher relative dominance index than native species Q. acutissima and V. negundo. RDI of R. typhina was not affected disadvantageously by N:P ratios and its dominance did not change. Compared with Q. acutissima, R. typhina has higher net photosynthetic rate, lower LMA and higher photosynthetic nitrogen-use efficiency and photosynthetic phosphorus-use efficiency, indicating its higher investment of nutrients in photosynthesis apparatus, to maintain higher biomass productivity. Similar to R. typhina, V. negundo had high net photosynthesitic rate and low LMA. However, photosynthesis of it was inhibited by shade effect, casuing by R. typhina with higher growth rate, height and crown area. In our study, there was no significant stress on physiology of V. negundo casued by R. typhina, but its biomass accumulation was significantly inhibited. In mixtures, under competitive pressure from R. typhina, Q. acutissima and V. negundo partitioned more biomass to roots and less to leaves than those in monocultures, to acquire more nutrients. Whereas, no significant difference in biomass allocation was observed for R. typhina, maintaining high shoot biomass ratio. This difference in biomass allocation strategies lead to an absolute advantage in light competition for R. typhina. And with high carbon accumulation capability, it can product much higher biomass than native Q. acutissima and V. negundo. Root mass raio of R. typhina was lower than native species, but owing to a high carbon assimilation capacity, R. typhina was able to maintain much higher root biomass in all treatments. Besides, with high performance root characteristics, high root surface area, R. typhina also has an absolute advantage in nutrients competition. Under high N:P ratio condition, Q. acutissima and V. negundo maintained similar biomass alloction to those under the medium N and P supply condition, whereas R. typhina significantly increased LMR and decreased RMR. This adjustment maintained its high biomass production and root mass, to keep its advantage in nutrients absorption, showing more adaptive to increasing N:P ratios. Biomass allocation of Q. acutissima and V. negundo indicated that they have greater tolerance to stressful environments. However, this strategy may be conservative for environmental changes that lead to fluctuating resource availability and cause the disadvantage in competition.Generally, compared to the native species Q. acutissima and V. negundo, the exotic species R. typhina, with higher growth performance in leaf and root traits, adopts more positive strategies for biomass and nutrient allocation to better acclimate to different nutrient conditions and maintain high biomass productivity. Given its higher nutrient absorption capacity and higher investment of biomass and nutrients in photosynthetic tissues, R. typhina shows greater biomass production under competition with Q. acutissima and V. negundo. The different trade-offs in biomass and nutrient allocation of the two species is the main reason for their distinct performances under competition and helps R. typhina to maintain absolute dominance under different N:P supply ratios. Furthermore, in low N:P ratio or high N:P ratio sites, exotic R. typhina might have higher biomass production and benefit more strongly from increasing anthropogenic nitrogen and phosphorus input. In our study, there was no significant difference between biomass of Q. acutissima in monocultures and mixtures, but a seriously reduce for V. negundo, caused by shade effect. Thus, the potential invasiveness of R. typhina and its effects on native plants needs further study in a long time scale. In future plant introduction and management programs, plant traits and local nutrient conditions should receive greater attention under the main factors of climate change, to evaluate their invisibility and avoid economic and ecological risk.更多还原