陕北黄土丘陵沟壑区14种植物的萌发特性

在实验室条件下观测了陕北黄土丘陵沟壑区14种植物的萌发特性,结果发现：萌发率在80%以上的植物有杠柳、铁杆蒿和茭蒿;在60%～80%之间的物种有白羊草、紫丁香、阿尔泰狗娃花、大针茅、沙棘和猪毛蒿;长芒草为37.3%;小于20%的植物有达乌里胡枝子、刺槐、虎榛子和狼牙刺。14种植物的萌发时滞最短的为2 d,最长的为8 d;几乎所有植物种子达到T50的时间都在其萌发开始后的7 d以内,且大部分物种在萌发开始后的15 d完成总萌发量的90%;萌发持续时间最短的为6 d,有刺槐、狼牙刺、虎榛子、沙棘4种,最长的为猪毛蒿,达32 d。这些植物种子的萌发特性及生态适宜性决定了它们在陕北黄土丘陵沟壑区植被演替中的角色与地位。     

冷蒿对三种禾本科植物种子萌发和幼苗生长的化感作用

研究了冷蒿茎叶水浸提液及冷蒿斑块土壤对羊草草原3种禾本科植物(羊草、克氏针茅和糙隐子草)种子萌发及幼苗生长的影响.结果表明:冷蒿茎叶水浸提液使受试植物种子的发芽指数降低,平均发芽时间延长.羊草、克氏针茅和糙隐子草幼苗苗高及克氏针茅幼苗根长均受冷蒿茎叶水浸提液抑制;浸提液浓度≥0.075g.ml-1时显著抑制羊草幼苗根长生长,≤0.05g.ml-1时则无显著影响;而茎叶水浸提液对糙隐子草幼苗根长有"低促高抑"的作用.冷蒿斑块土壤抑制受试植物幼苗生长;3种植物对冷蒿化感效应的敏感性依次为克氏针茅羊草糙隐子草,且幼苗根长的敏感性均大于苗高.     

降水对鄂尔多斯高原克隆植物分布的影响

鄂尔多斯高原地处半干旱区到干旱区的过渡带。通过沿鄂尔多斯高原从东到西的天然降水梯度的样带调查,分析了克隆植物的分布特征与降水的关系。结果表明:克隆植物的物种数量、占物种总数的比例和重要值以及根状茎型克隆植物的物种数量均与降水量呈显著正相关。5种优势植物克氏针茅、本氏针茅、黑沙蒿、赖草和短花针茅均为克隆植物,它们的分布也受降水影响。克氏针茅的密度、本氏针茅的盖度和密度、黑沙蒿的高度、盖度和密度以及赖草的高度均与降水量呈显著正相关。然而,赖草的盖度以及短花针茅的高度、盖度和密度均与降水量成负相关。因此,克隆植物在鄂尔多斯高原植被中具有重要作用,而且其作用随着降水量的增加而加强。     

黄土丘陵区不同立地条件下猪毛蒿种内、种间竞争

猪毛蒿(Artemisia scoparia)通常是黄土丘陵区撂荒演替前期群落优势种,在无人为干扰的情况下,猪毛蒿群落通常会向冰草(Agropyron cristatum)群落或阿尔泰狗娃花(Heteropappus altaicus)群落,或长芒草(Stipa bungeana)群落等演替。该文通过河阶地和梁峁阴坡中猪毛蒿生长特征的调查和种内、种间竞争田间试验,从植物竞争角度对猪毛蒿群落的演替机制给予了解释。结果表明:1)两类样地中猪毛蒿的生长都趋于小型化,有少数大个体和多数小个体,都存在异速生长现象,说明两类样地存在竞争,且对猪毛蒿的生长形态具有塑造作用; 2)由于单位地上生物量竞争效应排除了立地条件和个体大小的影响,因而比总竞争效应更能说明种对间的相对竞争能力。梁峁阴坡地和一、二级河阶地三种立地条件下,7种测试植物中对猪毛蒿的相对竞争能力以演替后期多年生植物较高,而演替前期一年生植物较低,说明演替后期种对前期种的竞争抑制是演替驱动力之一; 3)以各测试植物对猪毛蒿单位重量竞争抑制程度平均值来看,以梁峁阴坡地最大,二级河阶地次之,一级河阶地最小,说明立地条件越差,土壤资源可利用水平越低,竞争越激烈; 4)一级河阶地和梁峁阴坡地各测试植物对猪毛蒿的竞争等级发生了显著变化,说明环境条件差别较大时,植物的竞争等级会发生变化。     

陕北黄土丘陵区撂荒群落共存种活性氧清除指标对水分胁迫的响应

群落共存种对环境变化的生理生态响应差异是群落演替的重要因素,其中活性氧清除是生理生态响应的重要方面。该研究以黄土丘陵区10个常见撂荒群落共存种(阿尔泰狗娃花、猪毛蒿、铁杆蒿、茭蒿、小花棘豆、达乌里胡枝子、白羊草、冰草、中华隐子草和无芒隐子草)为研究对象,测定了不同水分处理条件下(适宜水分、中度胁迫及重度胁迫)生长季中3个月份(8、9和10月)个体和种群的生长表现(个体株高、生物量和种群存活率),及主要活性氧清除指标［类胡萝卜素含量、超氧化物歧化酶(SOD)活性和谷胱甘肽(GSH)含量］,分析群落共存种的生态适合度和活性氧清除指标对水分处理的响应差异及其相互关系,以明确演替生态位置上各指标的变化趋势。结果表明：(1)随水分胁迫程度的增加,演替前期种——猪毛蒿的的适合度有所下降,后期种——白羊草有所上升。(2)GSH和类胡萝卜素含量均随水分胁迫程度增强显著升高。(3)类胡萝卜素含量、SOD活性和GSH含量存在显著的种间差异,其中达乌里胡枝子的类胡萝卜素含量、小花棘豆的SOD活性、中华隐子草的SOD活性和GSH含量、无芒隐子草的类胡萝卜素含量和GSH含量均相对较高,且这3个指标的生长季变化也较为明显,8月份类胡萝卜素含量和GSH含量相对较高,而10月份GSH含量和SOD活性相对较高。(4)演替生态位置上,10个共存种在演替序列上以前期种的适合度和类胡萝卜素含量相对较低,而演替后期种相对较高,表明演替后期的植物较为耐旱。     

云雾山铁杆蒿茎叶浸提液对封育草地四种优势植物的化感效应

为了揭示铁杆蒿群落在植被演替中的作用,通过研究铁杆蒿茎叶浸提液对铁杆蒿草地4种优势植物(百里香、大针茅、本氏针茅和赖草)的种子萌发及幼苗生长的干扰,结果表明:高浓度的铁杆蒿浸提液(甲醇浸提液和水浸提液)使得百里香、大针茅、本氏针茅和赖草的种子发芽指数降低,发芽率、芽长和根长低于对照,种子平均发芽时间延长达1.13-2.16 d。而低浓度浸提液(0.005 g/mL)使得百里香的发芽要高于对照11.63%(水浸提液)、15.12%(甲醇浸提液)。在幼苗生长期,铁杆蒿浸提液对4种受试植物幼苗芽和根的生长受到不同程度的抑制,不同浓度的浸提液对植物的化感作用强度不同,随浓度的增加,抑制作用越强,0.1 g/mL相对其他浓度有显著性差异;其中0.005 g/mL浸提液对本氏针茅和赖草的幼苗生长有促进作用,幼根生长高出对照19.00%、16.06%,水浸提液对幼芽促进了2.33%、9.06%,在0.1 g/mL浓度下,本氏针茅或大针茅的生长完全受到抑制,芽长和根长抑制率为100%;同一浓度下的不同浸提液对植物的抑制作用也不同,其中百里香对铁杆蒿浸提液的敏感度是最低的;甲醇浸提液的化感作用要强于水浸提液。在封育过程中,百里香群落向铁杆蒿群落的过渡,铁杆蒿的化感作用是该草地演替的一个重要影响因子。     

氮沉降和降雨变化对荒漠草原凋落物分解的影响

以荒漠草原凋落物为研究对象,通过设置自然降雨(CK)、增雨30%(W)和减雨30%(R) 3种水分处理和0 (N0)、30(N30)、50 (N50)和100 kg hm~(-2) a~(-1)(N100)4种氮素(NH_4NO_3)水平处理,用分解袋法,研究内蒙古短花针茅荒漠草原短花针茅(Stipa breviflora)、冷蒿(Artemisia frigida)、无芒隐子草(Cleistogenes songorica)和木地肤(Kochia prostrata)凋落物分解过程,旨在阐明荒漠草原凋落物分解过程及其对氮沉降和降雨变化的响应特征,为荒漠草原生态系统物质循环过程响应气候变化研究提供基础数据。结果表明:1)经过270 d分解后,短花针茅、冷蒿、木地肤和无芒隐子草干物质残留率分别为69.95%—78.67%、68.89%—79.89%、64.68%—79.23%、66.89%—79.38%,分解速率为木地肤无芒隐子草冷蒿短花针茅。2)氮沉降和降雨对短花针茅和冷蒿凋落物分解速率产生显著影响(P0.05),其交互作用对这两种凋落物分解速率不显著(P0.05)。氮沉降和降雨以及交互作用均对无芒隐子草和木地肤凋落物分解速率产生显著影响(P0.05)。3)单一水分或氮素的添加均提高土壤微生物量碳氮含量,而水氮交互作用下更为显著。4)凋落物分解速率受生物及非生物因子的影响,相关分析表明:冷蒿、无芒隐子草、木地肤与土壤微生物量碳呈极显著正相关(P0.01);冷蒿、木地肤、短花针茅与土壤微生物量氮呈极显著正相关(P0.01);木地肤和短花针茅与土壤含水量呈极显著正相关(P0.01);冷蒿、木地肤、短花针茅与地上生物量呈极显著正相关(P0.01)。     

不同放牧强度下短花针茅荒漠草原植被的空间异质性

分析不同放牧强度下植物群落中物种的空间分布特征, 有助于阐明群落在放牧胁迫下的演替规律。该研究基于幂函数法则, 探讨了不同放牧强度下短花针茅(Stipa breviflora)荒漠草原群落植物的频率和空间异质性。结果表明: 不同放牧强度下物种空间分布与幂函数法则能很好地吻合; 不同物种空间异质性具有特异性, 随着放牧强度的增加, 提高群落空间异质性的物种分别由无芒隐子草(Cleistogenes songorica)、冷蒿(Artemisia frigida)、短花针茅、银灰旋花(Convolvulus ammannii)等多个物种逐渐转变为以无芒隐子草、短花针茅为主的少数物种, 同时, 物种空间异质性大于群落空间异质性的物种数逐渐减少。     

不同放牧强度下植物种群密度的季节性变化

采用随机区组的试验方法, 着力于探索内蒙古荒漠草原3 种主要植物种群密度在不同生长季节随放牧强度变化而呈现出季节性的波动规律。研究对象主要是短花针茅(Stipa breviflora)、冷蒿(Artemisia frigida)和无芒隐子草(Cleistogenessongorica)。结果表明: 上述3 种主要植物种群总密度在放牧区均高于对照区; 短花针茅和无芒隐子草枝条总密度的变化趋势基本一致, 冷蒿枝条总密度总体逐月降低。整体分析而言, 放牧期间(6-9 月), 短花针茅、冷蒿和无芒隐子草枝条总密度的峰值均出现在HG(或MG), 说明放牧家畜的持续采食及践踏, 导致了植物种群株丛发生破碎而趋向小型化, HG(或MG)由母株破碎而产生的小株丛多, 故株丛总密度相应增加; 另外, 连续放牧致使大多数植株未能进行生殖生长即被采食, 从而促进了植物的营养繁殖和营养生长, 增加了种群密度。     

陇东黄土高原丘陵沟壑区天然草地群落学特征研究

采用路线调查法和样方法研究了陇东黄土高原丘陵沟壑区天然草地植物群落组成的特征.结果表明,该研究区地带性植被的主要类型为草甸草原和典型草原,草甸草原以蒿类、白羊草和白草为代表群落;典型草原以长芒草、蒿类、百里香和毛沙芦草等为代表群落.草地群落物种组成较为简单,优势种的优势度显著,其中长芒草、山蒿、冷蒿、牛枝子、糙隐子草、铁杆蒿、阿尔泰狗娃花、赖草、猪毛蒿、百里香等是群落物种组成中相对重要的物种;天然草地群落数量特征的平均值为:种数17.1、多度163.5、高度49.2 cm、盖度52.8%、鲜重284.9 g?m-2、干重151.8g?m-2;草甸草原群落的高度、盖度、生物量和物种丰富度值均大于典型草原.     

Lateral root emission in woody taproots of Fraxinus ornus L.

Abstract

We applied environmental stresses, namely dehydration, pruning and bending, to woody taproots of Fraxinus ornus L. in order to: (i) identify a method that could be applied in routine studies of lateral root development from a secondary structure; and (ii) carry out anatomical investigations to identify the tissue involved in the recruitment of lateral root mother cells (LRMC). We found that all three methods induce the formation of new lateral roots from a woody parental root. However, bending stress considerably reduced the zone of the woody parental root (the curvature) for analysis when studying the process of emission of a new lateral root. The trace left by a new lateral root in the taproot secondary xylem forms a V-shaped insertion zone that starts in contact with a growth ring and enlarges toward the periphery. This type of insertion zone suggests that the vascular cambium is the tissue-source of initials that produce the root primordium of a new lateral root. In the case of root bending, the emission of a new lateral root occurs also in the convex side of the curvature and is preceded by the formation, at the same site, of a small amount of reaction wood. Thus, reaction wood and lateral root emission are two aspects of the same response mechanism to bending. Consequently, anatomical and cytological studies of lateral root formation should focus on this part of the woody taproot. By peeling off the bark at this site, one has direct access to the underlying living tissues and can thus investigate lateral root formation also at a biochemical and molecular level.     

Novel temporal, fine-scale and growth variation phenotypes in roots of adult-stage maize (Zea mays L.) in response to low nitrogen stress

There is interest in discovering root traits associated with acclimation to nutrient stress. Large root systems, such as in adult maize, have proven difficult to be phenotyped comprehensively and over time, causing target traits to be missed. These challenges were overcome here using aeroponics, a system where roots grow in the air misted with a nutrient solution. Applying an agriculturally relevant degree of low nitrogen (LN) stress, 30-day-old plants responded by increasing lengths of individual crown roots (CRs) by 63%, compensated by a 40% decline in CR number. LN increased the CR elongation rate rather than lengthening the duration of CR growth. Only younger CR were significantly responsive to LN stress, a novel finding. LN shifted the root system architectural balance, increasing the lateral root (LR)-to-CR ratio, adding ～70 m to LR length. LN caused a dramatic increase in second-order LR density, not previously reported in adult maize. Despite the near-uniform aeroponics environment, LN induced increased variation in the relative lengths of opposing LR pairs. Large-scale analysis of root hairs (RHs) showed that LN decreased RH length and density. Time-course experiments suggested the RH responses may be indirect consequences of decreased biomass/demand under LN. These results identify novel root traits for genetic dissection.     

Asymmetric cytokinin signaling opposes gravitropism in roots

Plants depend on gravity to provide the constant landmark for downward root growth and upward shoot growth. The phytohormone auxin and its cell‐to‐cell transport machinery are central determinants ensuring gravitropic growth. Statolith sedimentation toward gravity is sensed in specialized cells. This positional cue is translated into the polar distribution of PIN auxin efflux carriers at the plasma membrane, leading to asymmetric auxin distribution and consequently, differential growth and organ bending. While we have started to understand the general principles of how primary organs execute gravitropism, we currently lack basic understanding of how lateral plant organs can defy gravitropic responses. Here we briefly review the establishment of the oblique gravitropic set point angle in lateral roots and particularly discuss the emerging role of asymmetric cytokinin signaling as a central anti‐gravitropic signal. Differential cytokinin signaling is co‐opted in gravitropic lateral and hydrotropic primary roots to counterbalance gravitropic root growth.     

Consequences of root growth kinetics and vascular structure on the distribution of lateral roots

It has been proposed that the acropetal initiation of lateral roots is a built‐in process specified as part of the general process of cell division and differentiation in the parent root tip. Conversely, it is commonly reported that root branching is essentially a variable feature. In the present study, the interlateral distance along the parent root has been investigated using three banana varieties (Musa spp.) grown in two substrates. The pattern of lateral root initiation was obscured by variations of root growth patterns and vascular structure among roots, genotypes and substrates. A framework model is formulated showing the influence of growth pattern and vascular structure on branching density. The model raises a distinction between growth components which should not affect the branching density (i.e. rate of cell division) and which may affect it (i.e. size of mature cells and number of transverse divisions performed by cells executing their trajectory in the meristem). It appears also that lateral root density and root growth rate might be independently modulated by appropriate changes of root growth patterns, in banana and presumably many other taxa.     

4,4,4-三氟-3-(吲哚-3-)丁酸和吲哚丁酸对水稻和莴苣幼苗种子根长度及侧根原基发生的影响

适宜浓度的TFIBA 显著促进了莴苣和水稻初生种子根的伸长生长,抑制了水稻种子根侧根原基的发生,但对莴苣侧根原基的发生无任何作用,对根顶端优势的调控与IBA相反.     

Relationship between root elongation rate and diameter and duration of growth of lateral roots of maize

The objective of this work was to describe the relationship between elongation rate and diameter of maize roots and to estimate the length and growth duration of lateral roots of maize. Diameters and elongation rates of roots were measuredin situ on plants grown 5 weeks in small rhizotrons under greenhouse conditions. At the end of the experimental period the roots were harvested and diameters of axile and lateral roots were measured. The frequency distribution of diameters of harvested roots was bimodal with a minimum at 0.6 mm; 97% of axile roots were larger than this value and 98% of the lateral roots were smaller. Root elongation per day increased as diameter increased but the slope of the relationship with lateral roots was about 2.5 times that with axile roots when separate linear regressions were fitted to the two populations. The length of lateral roots found on axillary roots between the base and about 30 cm from the apex was approximately 2.2 cm. All of the data was consistent with the hypothesis that the lateral roots grew for about 2.5 days and then ceased growing. The axillary roots continued to grow throughout the experimental period at a rate of about 3 cm day⁻¹. Contribution from the Department of Agronomy, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca, NY 14853. Agronomy paper No. 1661. This research is part of the program of the Center for Root-Soil Research.