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题名	林下植被对上层乔木影响的生理生态学机理
作者	杜忠
学位类别	博士
答辩日期	2011-05-24
授予单位	中国科学院研究生院
授予地点	北京
导师	李迈和
关键词	植物间交互作用 生理生态 非结构性碳水化合物 乔木-灌木交互作用 去除灌木
其他题名	Understory Effects on Overstory Trees and their Ecophysiological Mechanisms
学位专业	自然地理学
中文摘要	植物间的交互作用一直是生态学研究的中心问题，而且植物的交互作用对整个生态系统的结构和功能方面发挥着重要的作用。当外界的环境（气候变化，养分可获得性）发生变化的时候，植物间的交互作用也会发生相应的变化。森林生态系统植物间的交互作用，多数研究侧重于乔木之间的交互作用对目标乔木树种生长和生理生态的影响，上层乔木对下层植被的影响，以及对土壤和微气候的影响。但是，林下植被对于乔木生长和生理生态的影响，在很长的一段时间内却很少被研究者所关注。在森林经营方面，为了增加森林生产力，去除灌木是最常用的方法，此方法历史比较悠久，尤其在中国和日本。因此，急需了解上层乔木对林下灌木存在的生理适应性和响应研究。为此，在鞍子河自然保护区，以杉木、柳杉、秃杉和水杉为研究对象，采用“自然实验”和“去除实验”相结合的方法，选择自然存在的杉木样地（杉木纯林，杉木-竹子样地，杉木-灌木样地）和去除三种乔木树种（柳杉、秃杉、水杉）的林下灌木样地（长期去灌样地、短期去灌样地），研究了林下灌木对上层乔木（杉木、柳杉、秃杉、水杉）生理生态和生长的影响、对土壤理化性质的影响、对凋落物分解的影响，以探讨林下植被对上层乔木影响的生理生态学机理。通过研究发现如下主要的结论： 1、自然实验中，杉木-竹子、杉木-灌木样地土壤的有机质、全效N、P、K含量、速效N、P、K含量、阳离子交换量、交换性盐基离子总量、土壤酸度都有了显著的改善，而杉木纯林样地的土壤则出现退化状况。究其原因是杉木纯林中的灌木每2-3年被去除一次而且被带出样地作为燃料，导致大量的营养元素被带出样地。而杉木-竹子和杉木-灌木样地内，由于林下灌木竹子和杂灌的存在，给样地提供大量的凋落物，促进了杉木凋落物的分解，改善林地土壤养分状况，提高林地生产力和林分稳定性。而且，林下灌木竹子对土壤的改善作用要大于林下杂灌，主要是因为竹子和杂灌的凋落物的总量、营养元素含量不同。 2、去除实验中，去除灌木样地（长期去灌样地、短期去灌样地）土壤的理化性质要显著优于没有去除灌木的样地。主要因为被去除的灌木放在原样地进行分解，给样地提供了大量的养分。而且，去除林下灌木后，样地内的环境条件改善，促进了凋落物的分解，所以去灌样地中土壤的有机质含量，全效N、P、K含量，速效N、P、K含量，阳离子交换量，交换性盐基离子含量都增大了，而且降低了土壤的酸度。 3、去除林下灌木，使得上层乔木组织的N、NSC（包括可溶性糖和淀粉）及营养元素（P、K、Ca、Mg）含量不同程度的升高，尤其是长期去除林下灌木的样地，这种趋势更加的明显，因为去除灌木后乔木树种对土壤养分和水分的竞争压力减小，而且灌木凋落物分解为乔木提高了大量的养分。去除林下灌木对乔木树种叶、细根的影响更加明显，因为叶是乔木光合作用、呼吸作用、蒸腾作用的场所，而细根是植物吸收水分和养分的部位，所以更容易受到外界干扰的影响，导致其生理指标的变化。 4、长期去灌样地中乔木树种的单叶面积和比叶面积、平均径生长速率和高生长速率都大于没有去除灌木样地。表明林下灌木对上层乔木的影响主要是源于对地下水分和养分的竞争，去除灌木后，乔木的竞争状态被解除，促进了上层乔木树种叶形态的改变。长期去除林下灌木促进了上层乔木的生长，提高了林分的生产力。 5、长期去灌样地的凋落物的分解速率要显著快于没有去灌样地的凋落物分解速率。主要是因为：（1）去灌样地凋落物的基质质量要高，即：N含量高、木质素含量低、C/N比和木质素/N比要低。（2）去除灌木的样地为凋落物分解提供了更加适宜的环境，如：土壤温度高，参与分解的土壤动物区系活性强，土壤中可利用性养分含量高。 6、不同的林下灌木经营措施（去除林下灌木或不去除林下灌木，去除灌木保留在样地或带出样地）对土壤物理化学性质、乔木的生理生态和生长、凋落物的分解都会产生显著的影响。所以，选择合适的林下灌木及经营措施对森林生态系统土壤肥力的改善，以及林地生产力的提高具有非常重要的作用。
英文摘要	Plant-plant interactions are the central issue in ecological research and play a key role in regulating the composition and structure of communities and ecosystems. Plant-plant interactions can be altered themselves by external drivers such as climate changes and nutrient availability. Studies of plant-plant interactions in forest ecosystems have traditionally concentrated on growth (height, diameter, biomass, productivity) and environmental (soils, microclimate) effects, and overstory effects on understory vegetation. The possible effects of understory vegetation on the growth and physiology of overstory trees, on the other hand, have received less attention, due to the smaller biomass fraction and the secondary position of understory in forest stands. Hence, it is highly needed to understand the physiological adaptation and responses of overstory trees to understory vegetation, since understory removal has been applied to improve wood production in plantations worldwide for hundreds of years. Plantations of the common species Cunninghamia lanceolata, Cryptomeria fortunei, Taiwania flousiana, and Metasquoia glyptostroboide grown in the An-Zi-He Nature Reserve (103°07′-103°27′ E；30°42′-30°53′ N) were selected as the study forests. To study the understory effects on the ecophysiology and growth of overstory trees, on the soil physical and chemical properties, as well as on litter decomposition processes, both natural experiment and understory removal experiment were conducted. Our results will deepen our understanding of community-based competition research, and will explore the mechanisms for understory-overstory interactions. Natural experiment (C. lanceolata trees grown with differently dominant understory species): We found that soil organic matter, total N, P, K contents, available N, P, K contents, cation exchange capacity, total exchangeable base cations concentration, soil acidity significantly enhanced in the Cunninghamia–Fargesia stand and Cunninghamia–shrubs stand, compared to the pure Cunninghamia stand (continuously managed stand). The lower levels of those parameters in soils under pure Cunninghamia stand may be caused by reduced nutrients storage due to regularly removing the nutrients contained in the understory plants. The presence of bamboo (Cunninghamia–Fargesia stand) and the mixed shrubs (Cunninghamia–shrubs stand) not only provided lots of litter but also improved the litter quality, and, hence, promoted the decomposition rate of Cunninghamia litter, leading to enhanced soil nutrient availability, tree growth and forest productivity. Moreover, soil quality in Cunninghamia–Fargesia stand was better than that in Cunninghamia–shrubs stand, may be a result of biological properties of understories because bamboo could provide more litters and nutrient contents than the mixed shrubs. Understory removal experiments (understory intact vs. long-term and newly understory removal in C. fortunei, T. flousiana, and M. glyptostroboide stands): Unlike the results gained from the natural experiment, we found that the soil physical and chemical quality in the continuously-managed and newly-managed stand was significantly better than in unmanaged stand. This result may mainly resulted from the understory management practice because the aboveground biomass of understory did not remove from the stands but was left in situ on the forest floor for decomposition. Moreover, removal of understory shrubs improved the environmental conditions with enhanced soil temperature and water availability, leading to increased litter decomposition rate. Hence, soil organic matter content, total N, P, K contents, available N, P, K contents, cation exchange capacity, total exchangeable base cations concentrations increased and soil acidity decreased in the managed stands. Overstory trees grown in the absence of understories (removal) had higher levels of N, NSC (non-structural carbohydrate) and its components (soluble sugars and starch), and nutrients (P, K, Ca, Mg) concentration in tissues compared to trees grown in the presence of understories. These enrichments may be the consequence of reduced competition for environment resource and enhanced soil quality mentioned above. Effects of understory removal were found to be more pronounced in needles and fine roots, because they are very sensitive and more vulnerable to outside environmental variations, for example, the needles are the place for carbon gain (photosynthesis) and fine roots for water and nutrients uptake. Overstory trees grown in the continuously-managed stands had greater specific leaf area (= smaller leaf mass per unit leaf area) compared to trees grown in the presence of understories. The mean diameter growth rate and height growth rate have also been improved in the continuously-managed stands, indicating that understroy shrubs had significant effects on overstory growth. Such understory effect on overstory growth may be mainly resulted from the underground competition for water and nutrients. Long-term understory removal reduced the understory competition for resource, and thus, increased the overstroy growth and forest productivity. The decomposition rate of litter in the continuously-managed stands was significantly faster compared to litters decomposed in the stands with understories. This result may be mainly resulted from: (1) increased litter quantity because the aboveground biomass of understory shrubs was regularly cut but left on the forest floor, (2) increased litter quality because the litter of broad-leaved shrubs had higher substrate quality with higher N content, lower lignin content, and lower C/N ratio and lignin/N ratio, and (3) suitable decomposition environment because understroy removal resulted in enrichment of soil temperature, soil fauna activity, and soil nutrients availability. The present study indicated that understory vegetation significantly affected the growth and physiology of overstory trees. The positive effect of understory removal on overstory growth was a result of increased availability of nutrients and NSC availability in overstory trees. Understory removal reduced the belowground competition and significantly increased soil physical and chemical quality and litter decomposition rate, leading to significant increase in soil resource availability and increase in physiological activity in overstory trees. This study will help us to improve our understanding of community-based competition research, and will have important implications for developing ecophysiology-based management strategies for dealing with understory vegetation in forest ecosystems, to improve the productivity and protect the species diversity.
语种	中文
公开日期	2013-01-31
内容类型	学位论文
源URL	[http://192.168.143.20:8080/handle/131551/4870]
专题	成都山地灾害与环境研究所_山地表生过程与生态调控重点实验室
推荐引用方式 GB/T 7714	杜忠. 林下植被对上层乔木影响的生理生态学机理[D]. 北京. 中国科学院研究生院. 2011.

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