Knowledge Resource Center for Ecological Environment in Arid Area
| 青藏高原东北部树木径向生长对气候变化响应研究 | |
| 其他题名 | Tree radial growth trends response to the climatic change in the northeastern of Qinghai-Tibetan Plateau |
| 王文志 | |
| 出版年 | 2015 |
| 学位类型 | 博士 |
| 导师 | 秦大河 ; 刘晓宏 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 森林具有保持水土、涵养水源、防风固沙、净化空气等功能，在生态文明建设中发挥着重要作用。同时，森林作为陆地生态系统的重要组成部分，储存着整个陆地生态系统中45%的碳，是一个重要的碳库。随着全球气候变暖、干旱加剧和大气CO2浓度升高，势必会对森林的动态变化和演替造成重要影响。IPCC第五次评估报告中，对气候环境如何影响树木生长及其动态演化进行详细评估。评估结果认为世界范围内已经出现了大量树木死亡的现象，高信度的证据表明气候变化，尤其是快速升温导致的干旱胁迫加剧是树木大面积死亡的重要原因。同时也有相关报道指出，快速升温和大气CO2浓度升高促进了树木加速生长。另外，随着大气CO2浓度不断升高，导致叶片气孔导度降低，从而使得树木长期水分利用效率(intrinsic water-use efficiency, iWUE)提高。然而，水分利用效率的提高在一些地区并没有促进树木的加速生长。青藏高原东北部，作为全球平均气温升高最为剧烈的地区之一，其树木径向生长和长期水分利用效率如何变化及其相互作用还不得而知。为此，本论文利用研究区的16条树轮宽度序列和6条树轮稳定碳同位素比率(δ13C)序列开展青海云杉和祁连圆柏树木径向生长变化及长期水分利用效率变化方面的相关研究。 通过本研究，得出以下主要结论： 1) 祁连山中部祁连圆柏与青海云杉在三个样点高低海拔1800-2012年期间BAI变化序列表明，祁连圆柏在1950-2012年期间高低海拔均显著加速生长，高海拔加速生长速率高于低海拔地区，但是高低海拔祁连圆柏树木生长年际间差异不显著。通过综合祁连山中部祁连圆柏BAI序列与区域气象资料响应分析，发现上一年冬季平均温度的升高是促进祁连圆柏加速生长的主要因素，而降水量的变化对祁连圆柏影响较弱。祁连山中部青海云杉在1950-2012年期间不同样点树木生长变化差异较大；扎麻什高低海拔样点树木生长显著下降，青羊沟和寺大隆两个样点高低海拔生长均显著上升。青海云杉BAI序列与气象资料响应分析，表明青海云杉生长变化对平均温度和降水量响应均不敏感。综上所述，祁连山中部气候变暖对祁连圆柏与青海云杉两树种树木径向生长影响不同。 2) 通过对比祁连山中部6条祁连圆柏BAI序列和柴达木盆地东北部4条祁连圆柏BAI序列自1800年以来生长变化趋势，发现两个区域祁连圆柏生长变化较为一致，特别是自1950年以来都存在加速生长的趋势，并且两个区域祁连圆柏加速生长速率基本相同。利用两个区域树轮BAI综合序列与对应区域气象资料响应分析发现，驱动两个区域祁连圆柏加速生长的气候因素不同。冬季的快速升温主要促进半干旱区祁连山中部祁连圆柏的加速生长，而干旱区柴达木盆地东北部祁连圆柏的加速生长主要受惠于生长季初期降水量的增加，生长季初期的快速升温主要抑制祁连圆柏的生长。滑动相关分析表明，随着区域温度的逐渐升高，平均气温、平均最低气温和平均最高气温对祁连山中部和柴达木盆地东北部祁连圆柏树木径向生长的促进和抑制作用都将逐渐增强。 3) 祁连山中部4条青海云杉树轮δ13C序列和柴达木盆地2条祁连圆柏树轮δ13C序列，自1900年以来都表现出显著下降趋势，反映了大气CO2浓度升高导致大气δ13C下降的事实。比较祁连山中部青海云杉高低海拔树轮δ13C序列与对应样点BAI序列，发现海拔差异对于树轮δ13C序列影响小于对BAI序列的影响；祁连山中部寺大隆和扎麻什两个样点树轮δ13C序列显著正相关，而两个样点BAI序列则具有相反生长趋势，说明树轮δ13C受到大范围因素的控制要大于BAI序列。通过祁连山中部青海云杉树轮δ13C序列与区域气象资料响应分析，表明全年SPEI干旱指数是影响树轮δ13C分馏的最主要气候因素。柴达木盆地2条祁连圆柏树轮δ13C序列与气象资料相关分析，也表明SPEI干旱指数主要控制该地区树轮δ13C分馏。 4) 祁连山中部和柴达木盆地东北部长期水分利用效率变化表明，两个区域在过去的150多年中，由于大气CO2浓度升高和气候变化导致的青海云杉和祁连圆柏两树种水分利用效率均显著提高。祁连山中部高海拔地区水分利用效率提高幅度要略低于低海拔地区，两个区域两树种之间水分利用效率提高幅度差别不大。长期水分利用效率提高显著促进了寺大隆青海云杉树木径向生长和祁连圆柏树木径向生长，但是并没有促进扎麻什青海云杉径向生长。两个树种在整个分析时段内，叶片内外CO2浓度之比(Ci/Ca)基本不变，即树木生长对于大气CO2浓度升高保持主动响应模式。在典型干旱时期，青海云杉和祁连圆柏通过提高水分利用效率的方式适应干旱胁迫，然而这种适应主要是通过气孔关闭的方式来调整，因此，在干旱时期长期水分利用效率提高并不能增加树木径向生长。 |
| 英文摘要 | Forests cover 30% of the world’s land surface and have an important role in the global carbon cycle and are valued globally for the services that they provide to society. Around the globe societies rely on forests for essential services such as timber, watershed protection and less tangible but equally important recreational, aesthetic, and spiritual bene?ts. Consequences of global warming, reduced water availability and increasing atmospheric CO2 concentration on forest ecosystems are already visible worldwide. In the latest IPCC 5th report, forest dynamics and tree mortality became the focus of the attention. The tree mortality observed over the past few decades has been attributed to the effects of high temperatures and drought, or to changes in the distribution and abundance of insect pests and pathogens related, in part, to warming. In addition, the effects of climate change on forests also include positive effects (e.g. increases in forest vigor and growth from CO2 fertilization, increased water use ef?ciency, and longer growing seasons). Changes in intrinsic water-use ef?ciency (iWUE), which represents the ratio of photosynthetic assimilation (A) to stomatal conductance (gw), are important for ecosystems, since higher iWUE can result from reducing gw, increasing A, or a combination of the two responses. However, some results indicated that trees did not signi?cantly increase their growth despite increasing atmospheric CO2 and increasing iWUE. In the northeastern of Qinghai-Tibetan Plateau, forests play an important role in preventing the development of deserti?cation. It is therefore important to evaluate the future severity of the effects of rising CO2 and climate change on forest growth and studying past variations in the growth of trees can provide important clues to support this evaluation. In the present study, we developed 16 basal area increment (BAI) series and 6 tree ring δ13C series from the Qilian juniper and Qinghai spruce to evaluate their radial growth and iWUE variations respond to the rapid warming and atmospheric CO2 concentration raising. The main conclusions are followed: (1) Tree radial growth (BAI) of two species in the high- and low-elevation of three sites during the period 1800-2012 showed that Qilian juniper growth consistent along the altitude gradient, and they are both speedup in recent six decades. Response analysis showed that the previous winter temperature strongly positive correlated to the tree radial growth, but the precipitation has little effect on tree growth. The Qinghai Spruce showed divergent growth trends in the three sites, but the tree growth significantly coherent in the high and low elevations. The temperature and precipitation both not significant correlated with the Qinghai Spruce growth. It showed sites and species specific response to the climate change in the Qilian Mountains. (2) Results indicated that consistent patterns of tree growth have occurred at high and low elevations in the middle of the Qilian Mountains, and that tree growth in the semi-arid and arid regions of the northeastern of Qinghai-Tibetan Plateau showed highly consistent trends (increased growth since 1950), but with different driving factors. The details of the response and the moving-window correlation analysis for the relationship of BAI growth and regional climate factors demonstrated that increasing temperatures (particularly in the winter) accelerated tree growth in the semi-arid middle of the Qilian Mountains, but decreased tree growth in the arid northeastern Qaidam Basin. Conversely, increasing precipitation during the growing season stimulated growth in the Qaidam Basin. These results suggest that growth of Qilian juniper in semi-arid areas should increase steadily in the future, whereas growth may remain stable or even decrease in the arid regions of the northeastern Qinghai-Tibetan Plateau. These contrasting responses to temperatures provide valuable information on forest dynamics in the critical mid-latitude regions that should be incorporated into predictions of future forest carbon cycling under global warming. (3) All the tree-ring δ13C series of Qinghai spruce and Qilian juniper showed strong decreasing trends in the 20th century. After correct the decreasing trend, uniform year-to-year variations in δ13C were found across sites, but distinct differences in BAI according to habitat. The Qinghai spruce δ13C from both the high and low elevations showed high climate sensitivities independent of site, and much stronger than radial growth. The Qilian juniper δ13C also showed significant negative correlations with SPEI during two sites. High correlations with SPEI demonstrate the potential of regional tree-ring δ13C for reconstructing past drought conditions in the Northeastern of Qinghai-Tibetan Plateau. (4) To understand how tree growth responds to rising atmospheric CO2 concentration and climate change in arid and semi-arid regions, it is important to determine how trees in natural forests adjust physiologically to the changing atmospheric environment. Results showed that trees responded strongly to the increase in atmospheric CO2 over the last 150 years, iWUE increased dramatically in both the Qinghai spruce and Qilian juniper. The increased rate of the iWUE in the low-elevation was higher than the high-elevation, and there are no significant differences among the stands. The iWUE strongly stimulated the Qinghai spruce BAI speedup in the Sidalong site and the Qilian juniper trees, but it did not improve the Qinghai spruce radial growth in the Zhamashi site. During the most periods, the Ci/Ca of the two species remained mostly constant, it meas the trees kept an active response to elevated atmospheric CO2. The increased iWUE was mainly caused by a reduction in stomatal conductance during the drought periods, and thus the drought-induced stomatal closure has reduced transpiration at the cost of reduced carbon uptake and growth. |
| 中文关键词 | 青藏高原东北部 ; 树木径向生长 ; 气候变化 ; 长期水分利用效率 |
| 英文关键词 | Northeastern of Qinghai-Tibetan Plateau Tree radial growth Climate change intrinsic water-use ef?ciency (iWUE) |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 自然地理学 |
| 来源机构 | 中国科学院西北生态环境资源研究院 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287545 |
| 推荐引用方式 GB/T 7714 | 王文志. 青藏高原东北部树木径向生长对气候变化响应研究[D]. 中国科学院大学,2015. |
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