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雪松年轮里读出南京气候变迁

作者: 南京雪松价格 浏览次数: 时间:2018-10-06 08:34
  南京雪松是很好的树种,南京雪松的价格也是相当公道的。现在南京路边都种了很多,南京路边静静生存的雪松树,不经意间默默地记录着南京的旱涝变迁,形成了一部南京气候的“活”档案,而其中树木的年轮给出了最重要的“表达”。
  中科院南京地理湖泊研究所的副所长沈吉研究员利用2000年从太平门附近砍下的5棵雪松的“树盘”,根据树木年轮里蕴藏的气候学信息破译出过去近20年该地区的气候活动特征,竟和省气象台过去20年的气候记录惊人地吻合。
  树被称为活的档案,年轮就是树木记录的一个最重要的方式。沈吉告诉记者,在南京这样四季分明的城市,树木有非常明显的年轮,每年春回大地的时候,树木进入了快速生长期,新长出来的年轮颜色鲜嫩和前一年冬季里形成的深色年轮之间形成一道比较明显的“分水岭”,这样剖开一棵树,就能看到深浅相间的环,逐年记录着这棵树的生长周期。
雪松价格
  不过树木年轮能说明的可不仅仅是树木本身的年龄,由于树木从一出生就和周围的环境进行着“物质交换”的过程,吸收化学成分,温度、水分的差异都会直接影响着树木的生长,沈吉说,只要我们知道如何揭示树的秘密,就会发现从它出世之日起就非常忠实地记录着周围发生的大量事情,目前利用树木年轮揭示气候变化成为一个热门研究领域。
  沈吉说,雪松这类针叶树由于年轮更为稳定,是研究气候的一个很好的树种,2000年,太平门道路拓宽,他的研究小组及时获取了5棵雪松的树盘。近年来围绕着这些雪松的生长史,他们进行了对于上世纪70年代到90年代的气候学的研究,希望能够找出其中蕴含的气候密码。
  沈吉说,树木对于气候变化非常敏感,比如雨水多、温度高的时候,树木生长就会更快,那么这一年的年轮也会比较粗壮,不过如果仅靠肉眼来判断这个指标会有偏差。因此专家们采用的是碳同位素的测定方法。沈吉解释说,他们对比上世纪70年代至90年代省气象台的气候资料发现,树木中碳同位素的含量的高低起伏和当年5至7月的雨量的多少、7至9月温度的高低保持着惊人的一致。
  一般来说,较高的同位素比值代表着干旱和高温,反之则代表着多雨和低温,沈吉分析说,之所以会出现这样的变化,是因为树木在生长的过程中吸收二氧化碳,比如在干燥、高温的时候,为了防止水分的大量流失,树叶会关闭其部分“呼吸”气孔,吸收空气中的二氧化碳也就比较少,此时碳同位素的比值就会升高。
  树木年轮里不仅藏有关于气候的“密码”,连环境因子的变化信息,也可以通过树轮进行考证。
  沈吉告诉记者,太平门采集的这些雪松生长在道路两侧,而上世纪90年代汽车所使用的还是含铅量极高的汽油,因此排放出来的尾气中含有大量的铅,而这些松树“呼吸”到的铅元素,也成为树轮生长中的“烙印”,含量比较高,与此形成了呼应。
  这个原理听上去很简单:“因为植物需要通过叶片上的气孔与外界环境进行物质交换,在空气污染情况下,有害气体就在交换过程中经气孔进入叶片,扩散到叶肉组织,然后通过疏导组织运输到植物体的其他部位,从而影响到植物的正常生长发育和生理生态特征。”但要从年轮中获得这些烙印,却需要精密的仪器测量。
  展望:利用年轮去猜想未来
  树木年轮里忠实地记录了环境的变迁、气候的改变,沈吉说,我们有气象记录的历史并不长,多不过百年,因此对于规律性的判断还有缺失,而利用树木年轮的这个天然的“气候编年史”,我们能够重新找到第一手资料。通过对于树木年轮和气候环境的关联性研究我们将找出更多的规律性东西,那么通过一棵古树通过古墓里的一片棺木,我们将数千上万年前以及更久远气候记录还原出来。
  沈吉说,在天气异常变动时,树木年轮的反应也会比较明显,因此掌握的规律性的东西也比较多一些,现在国外已经有根据树木年轮来预报洪涝的研究,准确度相当高。我们希望能够通过气候规律的掌握来猜想未来。
  对于树的年轮,大家都不陌生,但作为研究对象的树轮样本,其实与平常印象中的年轮并不一样,因此它制作起来可没那么简单。
  “我们采集到的树轮样本,首先都要进行‘定年’,是用仪器把它所属年代确定下来。”沈吉说,树轮定年以地区不同而方法不同。在西欧,数树轮便能够完成定年工作,因为在该地区生长的树木很少发生缺失轮的现象。但在实际工作中,常常是先量测树轮的宽度,然后再用计算机程序检查定年。拿南京采集的这些树轮来说,树最外面一轮肯定是当年所长出来的,但从外往里推算,由于会“缺轮”,所以同一地区的树要采集20几棵有相同成长时间的才行,且每棵树要采集2个样芯,这样“交叉定年”得到的资料才更接近实际。
  而且,不同气候里树轮成长的痕迹不一样,其深浅也各不相同。比如,在春夏两季,天气温暖,雨水充足,形成层的细胞活动旺盛,这部分木材质地疏松,颜色较浅,称为“早材”或“春材”。夏末至秋季,气温和水分等条件逐渐不适于形成层细胞的活动,这部分木材质地致密,颜色也深,称为“晚材”或“秋材”。因此,在“定年”时,专家还要向行家寻求帮助。“我们都是从外面请来微雕师傅,让他们把轮盘上的每一轮,都用刀子深深雕刻出来,基本上,这些工序都是要在显微镜底下才能进行,一般都要将年轮放大40倍才能进行雕刻。”
  Cedar trees living quietly on the roadside of Nanjing inadvertently silently record the changes of drought and flood in Nanjing, forming a "living" file of Nanjing climate, and the annual rings of the trees give the most important "expression".
  Shen Ji, deputy director of Nanjing Institute of Geography and Lakes, Chinese Academy of Sciences, used the "tree discs" of five cedars cut down near Taipingmen in 2000 to decipher the climatic characteristics of the region in the past 20 years based on climatic information contained in tree rings, which was surprisingly consistent with the climatic records of the provincial meteorological observatory in the past 20 years.
  Trees are known as living files, and ring is one of the most important ways to record trees. Shen Ji told reporters that in a city with four distinct seasons like Nanjing, trees have very distinct rings. Every year when they return to the earth in spring, trees enter a rapid growth period. The newly-grown rings form a clear "watershed" between the bright colors of the rings and the dark rings formed in the winter of the previous year. A tree can see deep and shallow rings, and record the growth cycle of this tree year after year.
  But tree rings may not only indicate the age of the tree itself, because the tree is born with the surrounding environment for "material exchange" process, absorption of chemical composition, temperature, water differences will directly affect the growth of trees, Shen Ji said, as long as we know how to reveal the secret of the tree, on It has been faithfully documented since its birth, and the use of tree rings to reveal climate change has become a hot area of research.
  Shen Ji said that conifers such as cedars are a good species for climate research because of their more stable rings. In 2000, Taipingmen Road was widened and his research team acquired five cedar trees in time. In recent years, around the growth history of these cedars, they have conducted climatological studies from the 1970s to the 1990s, hoping to find out the climatic codes contained in them.
  Shen Ji says trees are very sensitive to climate change, for example, when there is more rain and temperature, trees grow faster, and the annual rings will be thicker, but there will be deviations if the naked eye is used to judge the index. So experts use carbon isotope measurement. Shen Ji explained that they compared climate data from the provincial meteorological observatory in the 1970s and 1990s and found that the fluctuations in carbon isotope content in trees were surprisingly consistent with the amount of rain from May to July and the temperature from July to September.
  Generally speaking, higher isotope ratios represent drought and high temperatures, and vice versa, rain and low temperatures. Shen Ji says the reason for this change is that trees absorb carbon dioxide during their growth, such as when they are dry and hot, to prevent a large loss of moisture, leaves close. Close some of the "breathing" pores, absorb less carbon dioxide in the air, when the carbon isotope ratio will rise.
  Tree rings contain not only the "code" of climate, but also information about changes in environmental factors, which can be verified by tree rings.
  Shen Ji told reporters that the cedars collected at Taipingmen grew on both sides of the road, and the cars in the 1990s still used high-lead gasoline, so the exhaust gas contains a lot of lead, and the lead that these pine trees "breathe" to become a "brand" in the growth of tree rings, the content is relatively high. And echoed with this.
  This principle sounds simple: "Because plants need to exchange material with the environment through the stomata on the leaves, in the case of air pollution, harmful gases enter the leaves through the stomata during the exchange process, diffuse to mesophyll tissue, and then transport to other parts of the plant through the drainage tissue, thereby affecting The normal growth and development of plants and their physiological and ecological characteristics. But to get these marks from the rings, we need sophisticated instruments to measure them.
  Prospect: use the ring to guess the future.
  The tree rings faithfully record changes in the environment and climate. Shen Ji said that we have not had a long history of meteorological records, more than a hundred years, so there is still a lack of judgment on the regularity. Using this natural "climate chronicle" of tree rings, we can rediscover first-hand data. By studying the relationship between tree rings and climate, we will find more regularities, and by passing an ancient tree through a coffin in the tomb, we will restore climate records tens of thousands of years ago and beyond.
  Shen Ji said that when the weather changes abnormally, the tree ring response will be more obvious, so grasp the regularity of things more, now foreign countries have based on tree ring to predict flooding research, the accuracy is quite high. We hope that we can guess the future through the mastery of the laws of climate.
  For tree rings, everyone is familiar with, but as the study of tree ring samples, in fact, and the usual impression of the ring is not the same, so it is not so simple to make.
  "The tree-ring samples we collected were first'dated'by instruments." Shen Ji said tree ring dating varies from region to region. In Western Europe, several tree rings can be used to complete the dating work, because there are few missing rings in trees growing in the region. But in practical work.
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