太行山南麓山区栓皮栎-扁担杆生态系统水分利用策略

分析了太行山南麓低丘山区降水、泉水、地下水、土壤水以及栓皮栎、扁担杆的氢氧稳定同位素特征,结合Iso Source模型确定了栓皮栎和扁担杆水分来源的季节性差异,并对栓皮栎和扁担杆水分利用策略进行分析。结果表明,同一生态系统中的栓皮栎和扁担杆枝条水的δ18O和δD值差别明显。雨季中栓皮栎和扁担杆水分来源较浅,以0—20 cm土壤水分为主,但旱季中栓皮栎和扁担杆水分主要来源均比雨季明显加深,其中栓皮栎主要利用40—60 cm土壤水分,扁担杆则主要利用20—40 cm土壤水分。此外,旱季后期栓皮栎还利用部分泉水,其比例达到了19.6%。二者水分来源的不同,使得栓皮栎与扁担杆在旱季期间能避开用水冲突。旱季中生长在生态系统上层的栓皮栎中午部分气孔关闭,蒸腾速率下降,生长在生态系统下层的扁担杆日均蒸腾速率、气孔导度则分别比栓皮栎下降了46.94%和30.58%。栓皮栎和扁担杆分别采取了深水源及部分气孔关闭和浅水源及低蒸腾耗散的水分利用策略来利用旱季中有限的水分,因而其组成的生态系统表现出较强地适合太行山南麓脆弱环境的生态适应性。     

干旱胁迫对沙枣和孩儿拳头的生理特性的影响

以沙枣和孩儿拳头2年生盆栽苗为材料,采用称重控水的方法对4个梯度土壤干旱胁迫条件对沙枣和孩儿拳头生理特性的影响进行了研究.结果显示:(I)干旱胁迫造成了两物种体内水分的严重亏缺,重度胁迫(6.4%～8.0%)下,两物种自然饱和亏为对照的3～4倍;同一干旱胁迫梯度下沙枣自然饱和亏总高于孩儿拳头,但水分临界饱和亏和需水程度低于孩儿拳头;沙枣自由水含量随干旱胁迫加剧下降幅度较大,自由水向束缚水转化率较高;沙枣最高水势的下降幅度低于孩儿拳头,最低水势的下降幅度高于孩儿拳头,且沙枣的绝对水势比孩儿拳头低.(2)随着干旱胁迫程度的加剧,两物种叶片中的脯氨酸含量、可溶性总糖含量均有不同程度的增加,特别是在重度干旱胁迫下,脯氨酸含量高出对照4倍多,且孩儿拳头脯氨酸含量明显高于沙枣,但可溶性总糖含量低于沙枣;沙枣本身的可溶性蛋白含量较孩儿拳头高,随干旱胁迫的加重沙枣的可溶性蛋白含量先增加后下降,而孩儿拳头逐渐下降.结果表明,沙枣和孩儿拳头对干旱胁迫均具有积极的水分生理响应方式,推测两种植物的水分耐受极限为6.4%～8.0%,但物种间生理响应方式存在差异,沙枣较孩儿拳头具有更强的防御干旱的生理机制.     

Disentangling facilitation and seed dispersal from environmental heterogeneity as mechanisms generating associations between savanna plants

Question: How can we disentangle facilitation and seed dispersal from environmental heterogeneity as mechanisms causing spatial associations of plant species? Location: Semi‐arid savanna in the Kimberley Thorn Bushveld, South Africa. Methods: We developed a two‐step protocol for the statistical differentiation of association‐promoting mechanisms in plants based on the Acacia erioloba–Grewia flava association. Individuals of the savanna shrub G. flava and the tree A. erioloba were mapped on four study plots. Disentangling the mechanism causing the association of G. flava and A. erioloba involved tests of three spatial and one non‐spatial null model. The spatial null models include homogeneous and heterogeneous Poisson processes for spatial randomness based on the bivariate spatial point patterns of the four plots. With the non‐spatial analysis, we determined the relationship between the canopy diameter of A. erioloba trees and presence or absence of G. flava shrubs in the tree understorey to find whether shrub presence requires a minimum tree canopy diameter. Results: We first showed a significant positive spatial association of the two species. Thereafter, the non‐spatial analysis supported an exclusion of environmental heterogeneity as the sole cause of this positive association. We found a minimum tree size under which no G. flava shrubs occurred. Conclusions: Our two‐step analysis showed that it is unlikely that heterogeneous environmental conditions caused the spatial association of A. erioloba and G. flava. Instead, this association may have been caused by seed dispersal and/or facilitation (e.g. caused by hydraulic lift and/or nitrogen fixation by the host tree).     

3种园林树木种子萌发期耐盐性研究

以杠柳、白蜡和孩儿拳3种绿化树种为材料,在室内设置5个NaCl胁迫梯度,系统测定了其种子的萌发、生长和生理生化指标及其耐盐临界值,并用隶属函数法综合评价了它们在种子萌发期的耐盐性.结果表明:随着盐胁迫浓度的增加,杠柳、白蜡和孩儿拳种子的萌发率、萌发指数、胚根生长速率、胚轴生长速率、种子活力指数和相对含水量均呈逐渐下降趋势,且相同盐处理的指标值及各指标的耐盐临界值均表现为杠柳>白蜡>孩儿拳;随着盐胁迫浓度的增加,杠柳和白蜡的SOD活性、POD活性和MDA含量分别呈现先降后升、先升后降和保持较低水平的趋势,而孩儿拳则分别表现出先升后降、持续下降和大幅先降再升的趋势;各树种隶属函数法综合评价的耐盐性依次为杠柳>白蜡>孩儿拳.可见,各树种种子萌发和生长均受到不同程度盐胁迫伤害,杠柳的耐盐性明显强于白蜡和孩儿拳.     

Cyanobacterial soil crusts and woody shrub canopies in Kalahari rangelands

Intensive grazing of Kalahari rangelands has led to woody plant encroachment, notably of Acacia mellifera and Grewia flava. The mechanisms causing this process, and the ecological stability of woody plant encroached ecosystems, remain uncertain. Past studies suggest that canopy–soil relations may enhance woody plant competitive dominance. This study aims to investigate one element of this ecological change by examining the spatial distribution of cyanobacterial soil crusts in two vegetation sub‐habitats at sites of different disturbance. Crust burial by litter was also assessed to analyse the dynamics of canopy–crust relations. Our results show there is enhanced cyanobacterial crust cover under A. mellifera canopies and that unlike G. flava canopies, the crust cover remains under A. mellifera even at highly disturbed sites. This canopy–crust association suggests A. mellifera encroachment exhibits intrinsic resilience because of the crusts ability to stabilize the soil surface and increase nutrient retention. Crust burial by litter that accumulates under larger woody plants restricts crust development under canopies. Disturbance restricts crust development in plant interspaces and under G. flava. These two mechanisms combine to restrict crust development to an observed 40% threshold, with nonlinear models required to explain spatial patterns of crust dynamics.     

云南扁担杆属二新种

云南扁担杆属二新种＠钱义咏￥云南省思茅行暑林业局扁担杆属;思茅扁担杆;景洪扁担杆云南扁担杆属二新种钱义咏（云南省思茅行暑林业局,思茅６６５０００）ＴＷＯＮＥＷＳＰＥＣＩＥＳＯＦＧＲＥＷＩＡＦＲＯＭＹＵＮＮＡＮＱｉａｎＹｉｙｏｎｇ（ＦｏｒｅｓｔｒｙＢｕｒｅａ...     

云南扁担杆属植物评注

云南扁担杆属植物计有14种3变种,本文对其中9种1变种作了分类学评注,并确认中国新记录2种．云南新记录1种,新组合1变种及新异名6个。     

干旱胁迫下沙枣和孩儿拳头叶绿素荧光特性研究

以沙枣和孩儿拳头2年生盆栽苗为材料,采用称重控水的方法设置对照（土壤含水量为25.6%~27.2%）,轻度胁迫（19.2%~20.8%）,中度胁迫（12.8%~14.4%）,重度胁迫（6.4%~8.0%）4个梯度,研究了干旱胁迫对沙枣和孩儿拳头色素含量和叶绿素荧光特性的影响。结果表明：（1）随着干旱胁迫的加剧,两物种叶绿素a含量,叶绿素a/b比值,总叶绿素含量呈下降趋势,且叶绿素a对干旱胁迫的反应较叶绿素b敏感,但两物种叶绿素b含量和胡萝卜素含量变化规律不一致。（2）随着干旱胁迫的加剧,孩儿拳头F_m、F_v呈下降趋势,沙枣相反,但两物种F₀呈增加趋势,F_v/F₀、F′_v/F′_m呈下降趋势,F_v/F_m差异不显著;PhiPS2、ETR、qP先升高后降低,NPQ则先降低后升高。（3）虽然两物种表现出较强的抗旱性,但在重度干旱胁迫下（6.4%~8.0%）,光合色素含量、叶绿素荧光参数受到较大影响,推测此时的土壤水分含量为两物种光合色素、光系统Ⅱ的耐受极限;物种间相比,孩儿拳头更为敏感,在今后的园林管护中,要根据土壤水分状况和物种间的差异做好园林灌溉。     

云南扁担杆属植物评注

云南扁担杆属植物计有14种3变种,本文对其中9种1变种作了分类学评注,并确认中国新记录2种,云南新记录1种,新组合1变种及新异名6个。     

广西扁担杆属（椴树科）一新种—阔腺扁担杆

灌木,高1—1．8m,茎、枝灰褐色：小枝淡褐色,具圆形小皮孔,嫩枝密被白色星状毛。叶纸质,椭圆形至长圆形,长2.2—10cm,宽1.2—3．4cm,有时两侧稍不对称,上面绿色,被细小星状毛,中脉微凸起,侧脉及细脉微凹,两面淡绿色,密被星状毛,叶脉明显凸起,先端渐尖至长渐尖．少为饨尖,基部近圆形或圆形,