陕北沙地小叶杨“小老树”的水力适应性

以黄土高原"小老树"发生面积最大的树种-小叶杨为例,研究了不同水分生境下(水分相对好的沟道和干旱的梁坡片沙地,分别标记为生境A和生境B)小叶杨的生长、光合、水力学特性等,试图探讨小叶杨"小老树"对干旱生境的适应机制。结果表明:生境B小叶杨树高、地径、1 m树高处直径明显小于生境A,同时其主茎顶端枯枝长度大于生境A;生境B小叶杨叶净光合速率和气孔导度明显低于生境A。两种生境下小叶杨黎明前和正午叶水势无显著差异,生境B小叶杨正午时小枝枝干的比导水率明显低于生境A,但两种生境的比叶导水率则无显著差异,生境B小叶杨的Huber值明显大于生境A。生境B小叶杨枝干的P50(导水率损失50%时所对应的木质部水势)比生境A低约0.76 MPa左右,其气孔关闭的水势比生境A晚0.2 MPa左右,生境B小叶杨水分传输安全距离明显大于生境A。表明干旱生境下小叶杨高Huber值和低气孔导度有助于其叶水分关系维持相对稳定,低光合速率和维持大的水分传输安全距离所需的木质部碳投资增加是小叶杨形成"小老树"的重要原因。     

施肥对小老树光合速率及水分利用率的影响

不同施肥对小时杨小老树光合速率、蒸腾速度、单叶面积均有明显的提高作用,水分利用率则表现出明显差异,随施磷肥量增加,光合作用增加明显而蒸腾作用基本一致,水分利用率则上升明显,Ｎ肥处理则水分利用率下降。Ｎ、Ｐ混施叶面积增加明显。     

如何履行“保护第一”的承诺

<正>在长白山加速发展的过程中,生态保护与开发建设之间的矛盾日益凸显,新一届管委会负责人提出要把保护好长白山的原生态作为首要任务,"切实做到保护面前再大的利益不动摇,再小的生态不破坏"。但能否落实"保护第一"的承诺,不取决于良好的愿望,而取决于在工作实践中遵循的理念和准则是否正确,采取的措施是否得当。     

鹦鹉宝贝教“爸爸”学说话

鹦鹉学舌并不稀罕,蹊跷的是鹦鹉竟然反过来教主人说话,到底是怎么回事?还是跟着杰米一起去"鹦鹉爸爸"布赖恩先生的家一探究竟吧!     

“寻利型保护”,自然保护区的歧途

<正>借助作者清晰的记忆,我们得以严肃地审视一个国家自然保护区的"三大案例"——三次有组织的人为干扰是怎样摧残美丽、神圣、充满生物多样性的长白山的?我们看到了"风倒木案"中装傻充愣、浑水摸鱼的洗劫者,"红松籽案"中将野生动物的食物卖给外界者,"保护区宾馆案"中将保护区推向人工化建设的"大手笔"。我们看到了20     

“风灾”变为人祸

1986年,发生在长白山自然保护区的一场风干扰,虽造成了大面积的林木倒伏,但并未改变原始生态的性质,更未造成森林生态系统的毁灭,仍属正常的森林演替和生态过程。然而有人以"救灾"为名进行的长达7年之久的风倒木生产和更新人工林的双重人为干扰,才真正酿成了森林生态系统无可挽回的破坏,使风倒区全部丧失了自然特性,一部分林地恢复推迟百年,另一部分发生逆向演替,退化为次生草甸。     

从北大荒到“中华大粮仓”

<正>"北大荒"一词,最早见于我国最古老的地理学典籍之一—《山海经》。《山海经·大荒北经》中记载:"大荒之中,有山曰不咸山(即长白山),有肃慎氏之国。"这里的"大荒北",只是一个地域的历史名词,泛指今天的长白山以北广大地区,后泛指地处世界三大黑土带之一的我国东北原始大荒原。历史发展到今天,狭义的北大荒,就是指现在的黑龙江垦区。     

穿越云间花园(二) 重游“秘密花园”

<正>无须讳言,今日的长白山已美色大减。风倒木生产、红松种子生产和旅游大开发这几场重度的人为干扰破坏已经侵蚀了这一块稀世净土。有年轻的朋友问,当初的长白山是什么样子?到哪儿能多少感受一下长白山给你的最初的震撼和那种美妙的感觉?     

穿越云间花园(四) 穿越火山口,饱览“上花园”

<正>从长白山南坡穿越到西坡是一路下行,有如闲庭信步,轻松自如:然而从西坡穿越到北坡则是一路上行,特别是要翻越火山口上的几座峥嵘险峻的山峰,如同探险,需要有一定的体力和胆量,也需要有一定登山经验的领队才能完成。我约了精于此道的长白山自然博物馆馆长朴龙国,他带了三名助手到长白山西坡和我的一行(也是四人)会合。     

Limitations within "The Limits to Tree Height"1

Koch et al. (Nature 428: 851-854) measured various parameters that were thought to limit the height of Sequoia sempervirens from northern California and concluded that the maximum height for this species is 122-130 m because within this range: (1) Irreversible embolism formation was proposed to occur when the xylem pressure was less than -1.9 MPa. (2) The leaf mass to area ratio exponentially approached 833 g×m(-2). (3) The discrimination against (13)CO(2) exponentially approached -20. (4) Light-saturated photosynthesis per unit leaf mass decreased to zero, indicating no net gain in leaf biomass. These conclusions are questioned here by reassessing the assumed limits to the biophysical parameters and by reexamining the proposed linear and exponential relationships between these parameters and tree height. It is concluded that: (1) Embolism repair mechanisms could have occurred at -2.7 MPa. (2) The leaf mass to area ratio could be a result of, rather than a determinant of, the large differential between cellular turgor and the xylem pressure. (3) The discrimination against (13)CO(2) may show two populations of foliage with apparent linear relationships with height rather than one exponential relationship. (4) The light-saturated photosynthesis per unit leaf mass as a measure of biomass investment in leaf expansion excludes investment in branch and trunk wood. As a result, tree height may be limited by a long-term balance between dieback and continued growth.     

长城之父

长城现代已经成了中华民族的象征,不过,又有多少人知道最早的长城是什么样子,在什么地方,因为什么而修筑?过去的地方文献中并没有关于它的记载,因此,长城的先祖——楚长城,其地理位置和状况一直都是一个谜……而今在河南南阳宝天曼生物圈保护区附近,我们发现了她的“芳踪”,就让我们以放松的心情慢慢地走入历史,走入那片绿色的天地,一同去探寻神秘的楚长城。     

A response to: Limitations within "The Limits to Tree Height"

Here we respond to the communication in American Journal of Botany (96: 542-544 in this issue) by Netting, who proposes several ways in which our paper "The Limits to Tree Height" (Nature 428: 851-854) may have erred in estimating the biophysical limits to height growth in Sequoia sempervirens. We first explain that because embolism repair requires long time periods and is generally incomplete, xylem vulnerability characteristics offer a sound basis for estimating performance limits in woody plants. We reaffirm our earlier use of vertical gradients of foliar carbon isotope composition with new data for S. sempervirens. We support these arguments with reference to studies in other tree species. We take exception with Netting's view that the turgor pressure-cell expansion relationship for Zea mays is applicable to S. sempervirens. Finally, we second Netting's call for more work on carbon allocation vis a vis height growth limits.     

Father absence and age at menarche

Life history data, attractiveness ratings of male photographs, and attitudes towards partnership and child-rearing of 321 women were used to test four evolutionary models (quantitative reproductive strategy, male short-age, polygyny indication, and maternal reproductive interests) which attempt to explain the influence of family composition on reproductive strategies. Links between early menarche and other markers of reproductive strategy were investigated. Childhood stress and absence of a father figure, whether genetically related or not, were found to have accelerated menarche whereas having younger siblings decelerated it. Early menarche was associated with attractiveness ratings, the number of partners desired for the immediate future, and the early onset of intimate relationships. It was not linked with sociosexual orientation, mate choice criteria, and investment in the subjects’ own children, but these three markers were interrelated. The implications of the findings for the four evolutionary models are discussed.