平茬措施对天然沙冬青生理特性的影响

沙冬青(Ammopiptanthus mongolicus(Maxim.)Cheng f.)是我国二级珍稀濒危植物,由于自然条件的不断恶化使这一古老残遗物种种群受到威胁。本文以西鄂尔多斯国家级自然保护区内生长的天然沙冬青为材料,对平茬后经过3年恢复生长的萌蘖灌丛和未平茬的沙冬青灌丛的地上部生物量、叶片相对含水量(RWC)、叶水势(WPB)、净光合速率(Pn)、蒸腾速率(Tr)、水分利用效率(WUE)、气孔导度(Gs)和胞间CO2浓度(Ci)等指标进行了测定,并对平茬处理的各项生理指标变化进行了研究。结果显示:平茬后的沙冬青萌蘖灌丛经过3年的生长能恢复到平茬前的生物量;平茬与未平茬(对照)沙冬青叶片相对含水量差异不显著(P0.05),但平茬后的沙冬青叶水势日间(7∶00-19∶00)均显著高于对照(P0.05);平茬与未平茬沙冬青日间净光合速率、蒸腾速率均出现两个高峰值,且均有"午休"现象,平茬后的沙冬青萌蘖丛Pn日均值比对照升高了15.73%、Tr日均值比对照升高了15.57%、WUE日均值比对照升高了13.92%(P0.05);Gs日均值比对照也有所上升,且与Pn、Tr的变化趋势基本一致,但Ci的变化趋势与Gs、Pn和Tr相反。说明平茬处理对增加地上部生物量、提高其生理指标均有明显作用,能提高沙冬青潜在的生产力。     

平茬措施对柠条生理特征及土壤水分的影响

通过对比试验,研究了平茬措施对柠条的净光合速率、蒸腾速率、水分利用效率、枝水势,以及土壤水分含量的影响。结果表明:(1)平茬措施对柠条生理特征的影响因其生长发育阶段而异。其中,在花期(6月份),平茬柠条日平均净光合速率较对照(未平茬柠条)降低14.72%,日平均蒸腾速率提高27.31%,水分利用效率较对照低33.33%;随着柠条的生长发育(7月、8月、9月),平茬柠条日平均净光合速率逐渐升高最终高于对照,日平均蒸腾速率的差距也不断缩小;相应的其水分利用效率增加较快(对照柠条、平茬柠条增幅分别达108.3%、222.5%),至自然生长末期(9月),平茬柠条较对照高出4.76%。(2)平茬柠条枝水势的日变化和月变化均高于对照。(3)在整个生长季,平茬柠条地的平均土壤含水量在50—240 cm范围内均明显高于对照,且平茬措施显著降低了0—300 cm剖面各层土壤水分变异情况。(4)相关分析显示,平茬措施对柠条生理特征及土壤水分有重要影响。可见,采取平茬措施的第1年,平茬措施对柠条同时产生消极的生理影响和积极的土壤水分效应。弄清平茬措施的更新复壮机理,需要开展更多的深入研究工作。     

平茬对四翅滨藜补偿生长及水分生理特征的影响

【目的】四翅滨藜是荒漠化防治区广泛引种的优质旱生灌木,平茬是其主要抚育管理措施,揭示其平茬后恢复过程中的适应性和补偿生长机制,可为四翅滨藜发展成荒漠区优质饲料提供理论支撑。【方法】以人工种植的5年生四翅滨藜植株为研究对象,在平茬处理(留茬高度10 cm)后,测定四翅滨藜恢复过程中的株高、冠幅、光合反应、叶片水势、叶片导水率和水分利用效率,并探讨功能性状间的关系。【结果】(1)四翅滨藜平茬后的株高、冠幅和地上生物量经过1个生长季后能恢复至平茬前状态;(2)平茬植株的叶水势、叶导水率、水分利用效率、光合参数均高于对照植株;(3)线性拟合分析显示,平茬植株的正午叶水势和气孔导度与生长速率呈显著正相关。【结论】四翅滨藜平茬后具有良好的补偿生长能力;平茬植株在恢复生长前期表现出较高的补偿生长能力和典型的获取性策略,后期随着水力状况降低又转向保守性策略;平茬植株会将更多的生物量和资源分配到枝、叶等地上组织的生长,后期的资源分配又转向促进地下部分生长。     

枝条覆盖对平茬花棒生长特征和浅层土壤水分的影响

为了综合评价枝条覆盖对不同立地(平地、丘顶、丘间低地)平茬花棒(Hedysarum scoparium)生长特征和浅层土壤水分的影响,以吉兰泰荒漠-绿洲过渡区平茬花棒为研究对象,于2017年4—10月对覆盖与无覆盖平茬花棒物候期、土壤容积含水量、土壤储水量和生长指标等相关指标进行测定。实验结果表明:(1)枝条覆盖有利于平茬花棒提前萌芽,较无覆盖提前5 d以上。(2)枝条覆盖使不同立地平茬花棒生长初期和生长末期0—100 cm土层平均土壤容积含水量增加20.12%以上,且土壤含水量变异系数随土层深度增加变化减缓;土壤储水量在生长初期和生长末期枝条覆盖较无覆盖增加27%以上。(3)枝条覆盖使平茬花棒株高、新生枝数、基径、冠幅较无覆盖增加10.91%以上,同时其生物量鲜重和干重较无覆盖分别增加4.45%—24.17%和3.78%—18.93%。尤其丘间低地平茬花棒生物量增加效果更加明显(P0.05)。但枝条覆盖不能改变平茬花棒生物量分配格局;(4)枝条覆盖和平茬对花棒生长均具有积极作用,枝条覆盖对丘间低地平茬花棒生长促进作用最好。     

平茬高度对四合木生长及生理特性的影响

为改善珍稀濒危植物四合木种群衰退现状,促进其更新复壮及可持续发展,对四合木老龄化植株进行了0 cm、5 cm、10 cm、15 cm（文中定义为A、B、C、D）四种平茬高度处理,以未平茬老龄植株为对照（CK）,跟踪测定各处理的生长指标和生理指标变化规律,结果表明：（1）平茬能够促进四合木老龄化植株更新复壮,平茬后第一生长季各处理组株高生长量极显著大于CK（p<0.01）,处理B、C、D冠幅年生长量极显著大于CK（p<0.01）,各处理组新生萌条数量大于CK、萌条基径和萌条枝长极显著大于CK（p<0.01）,其中处理B株高和冠幅生长量分别较对照组增加241.43 %和417.21 %,平均萌条数量为324枝分别大于处理A、C、D和CK的293枝、229枝、221枝159枝;（2）对照植株净光合速率及蒸腾速率日变化均为双峰曲线,四种平茬处理植株平茬后第一个生长季7月份净光合速率和蒸腾速率为单峰曲线,而平茬后第二个生长季7月份变为双峰曲线;（3）平茬后前两个生长季7月份净光合速率日均值排序均为：处理B>D>C>A>CK,其中,处理B日均值分别为CK的2.07倍和1.94倍;（4）平茬处理改善了四合木植株水分状况,提高了四合木抵御干旱胁迫的能力,处理组蒸腾速率和水势均高于对照组;（5）平茬处理提高了四合木水分利用效率,其中,处理B提高程度最为明显,前两个生长季的水分利用效率分别是CK的1.38倍和1.42倍;（6）在平茬后前两个生长季内,5 cm平茬较其他高度平茬在生长和生理特性均有明显优势,但随平茬年限的增加其状况如何尚需进一步研究。     

长期水淹条件下香根草(Vetiveria zizanioides)、菖蒲(Acorus calamus)和空心莲子草(Alternanthera philoxeroides)的存活及生长响应

人工构建三峡库区消落区植被是控制消落区水土流失、保护消落区生态环境的重要措施,选择能够耐受长时间完全水淹的植物物种是该措施实施的关键.为了验证香根草、菖蒲、空心莲子草能否用于消落区植被的构建,实验模拟消落区的长期完全水淹条件,设置30d、60d、90d、120d、150d和180d等6个完全水淹时间水平,研究了3种植物在完全水淹条件下生长、生物量积累及存活状况.结果发现:(1)3种植物在经受长时间的完全水淹后有较高的存活率,180d全淹处理后,香根草、菖蒲和空心莲子草的存活率分别为87.5%、100%和50%.(2)这3种植物有不同的水下生长能力.全淹条件下,香根草生长缓慢,几乎没有产生新的叶片,总叶长也没有显著变化;菖蒲能够持续产生较对照植株更为细长的叶片,空心莲子草只在水淹初期(30d内)能够快速伸长地上部分的枝条,并迅速产生新叶片,但随水淹时间的延长,总枝条长及总叶片数没有再显著增加.(3)与对照植株相比,全淹处理抑制了3种植物总生物量的增加,但对3种植物的地上、地下部分生物量抑制程度不同.全淹条件下,香根草的地上部分和地下部分生物量与水淹0d水平(水淹处理开始前一天,下同)相比无显著变化,根冠比高于对照植株;菖蒲的地上部分生物量随水淹时间延长而降低,但却高于对照植株,地下部分生物量始终低于水淹0d水平,根冠比低于对照植株;空心莲子草的地上部分生物量与水淹0d水平相比无显著差异,但地下部分生物量与水淹0d水平相比大幅降低,根冠比低于对照植株.结果表明,这3种植物都有很强的水淹耐受能力,可应用于三峡库区消落区植被的构建.同时,发现植物对长期完全水淹的耐受能力很大程度上与植株在水下的生长情况及植株的营养储备水平相关,剧烈的水下生长会消耗大量的营养储备,进而造成植株存活率降低.植株在全淹条件下有限的生长能力及丰富的营养储备可能是耐淹物种的重要特征.     

平茬对塔里木沙漠公路沙拐枣防护林生长与土壤水盐分布的影响

对塔里木沙漠公路防护林示范段老化衰败的沙拐枣林分进行平茬复壮试验,并对平茬后沙拐枣生长与土壤水盐分布进行动态监测.结果表明:两次平茬后,沙拐枣萌蘖株的株高、冠幅、地径和萌蘖数均迅速增加.与对照相比,平茬后第3年,沙拐枣萌蘖株的平均株高超过对照,冠幅和最大地径分别达到对照的92.0％和73.0％;萌蘖株的枝鲜质量、同化枝鲜质量、枝干质量、同化枝干质量、地上部分总鲜质量和总干质量分别达到对照的80.0％、115.0％、80.0％、116.0％、93.5％和88.0％.平茬4年后地上生物量达到甚至超过对照.平茬能增加土壤含水量,且影响达到极显著水平;平茬能降低土壤含盐量,但影响不显著.对老化衰败的沙拐枣林进行重复平茬,能增加其土壤含水量,降低根系分布层土壤含盐量,有效促进其复壮更新.     

荒漠草原区柠条林平茬和牧草补播对地面节肢动物群落的影响

以荒漠草原区25年龄柠条林为研究对象,通过调查未平茬未补播、补播、平茬和既平茬又补播牧草的柠条林地中地面节肢动物群落特征,分析了补播和平茬及其交互作用对柠条林间和林下地面节肢动物个体数和类群数分布的影响.结果表明:在未平茬未补播牧草的林地中,林间地面节肢动物个体数和类群数均显著低于林下.与未平茬未补播牧草林地相比,补播、平茬和既平茬又补播牧草均显著增加柠条林间地面节肢动物个体数和类群数,而对柠条林下地面节肢动物个体数和类群数分布无显著影响,经过不同管理措施处理后,柠条林下与林间的地面节肢动物分布无显著差异.平茬和补播对柠条灌丛内外地面节肢动物分布影响具有类同效应,而且相互之间存在缓冲作用,补播与平茬处理、平茬与既平茬又补播处理、补播与既平茬又补播处理之间,林间和林下地面节肢动物的分布均无显著差异.在荒漠草原区柠条人工林中,平茬、补播和既平茬又补播牧草均可以显著提高柠条林地特别是林间地面节肢动物多样性,有利于退化草地生物多样性保护、生态系统恢复和柠条人工林的有效管理.     

平茬对半干旱黄土丘陵区柠条林地土壤水分的影响

半干旱黄土丘陵区多年生柠条人工林地发生土壤旱化,研究柠条林平茬对土壤水分影响对于防治土壤旱化具有重要意义。采用中子仪测定土壤水分,对未平茬和平茬柠条林地土壤水分进行测定,分析了平茬对土壤水分的影响。结果表明:未平茬和平茬柠条林地降雨补给量(R₁,R₂)同降雨量(P)显著正相关(P<0.05)。定义降雨耗损量(林冠截留量和地表径流之和)占降雨量的百分比为降雨耗损率,未平茬林地降雨损耗率(L₁)和平茬柠条林地降雨损耗率(L₂)分别与其降雨前土壤表层(0-20 cm)含水量(S₁,S₂)呈明显指数关系(P<0.05):L₁=2.54exp(0.22S₁),L₂=2.40exp(0.27S₂),表层含水量相同时,平茬林地降雨损耗率明显高于未平茬林地。平茬后,林地降雨最大入渗深度减小,土壤水分利用深度减小;短时间内(2个月左右)林地20-160 cm含水量增加,之后平茬林地土壤含水量与未平茬林地土壤含水量接近;丰水年和丰水年后的第一年,平茬林地含水量低于未平茬林地,0-400 cm土壤储水量比未平茬林地最多低45.9 mm。平茬后200-400 cm土层土壤水分有少量增加,但是0-200 cm土层土壤含水量损失更严重。平茬3a后,平茬对柠条林地土壤水分的影响减弱。     

平茬密度对荒漠草原人工柠条林间生境的影响

合理平茬对柠条林更新复壮及科学利用具有重要意义。以宁夏荒漠草原6 m带距人工柠条林（中间锦鸡儿,Caragana intermedia）林间草原为研究对象,研究了全平（QP）、隔一带平茬两带（G1P2）、隔一带平茬一带（G1P1）、隔两带平茬一带（G2P1）、未平茬（WP）五种密度（间距）平茬后柠条林间植被和土壤性状、小气候和土壤风蚀特征等变化。结果表明：（1）G2P1处理下林间植被物种总数、密度、高度和地上生物量最高,物种丰富度、多样性指数以G1P1、G2P1较高。（2）0-40 cm土壤容重以G1P1、G2P1较低,但机械组成无明显变化规律;土壤有机质、速效钾、全氮和速效氮以G2P1最高,但速效磷G1P1最高;土壤平均含水量以G2P1较高,达到8.33%,G1P2和WP最低,WP水分垂直变异系数最大。（3）处理间气温和风速无显著差异;风蚀量以QP、G1P2和WP较高,G1P1与G2P1较小。研究认为,适宜的密度平茬对人工柠条林间生境有改善作用,宁夏荒漠草原人工柠条林平茬时可采取隔两带平茬一带的方式。     

3个木薯品种嫩茎叶中氢氰酸、总黄酮及主要营养成分含量的变化

以木薯(Manihot esculenta Crantz)品种'华南7号'('South China 7')、'华南9号'('South China 9')和'华南205号'('South China 205')为研究对象,分别对种植后90、120、150、180和210 d的3个木薯品种嫩茎叶中氢氰酸、总黄酮及主要营养成分含量的变化进行了分析;在此基础上,明确供试3个品种嫩茎叶作为饲料的最佳采收期.结果表明:随种植后时间延长,3个品种嫩茎叶中的氢氰酸和总黄酮含量变化均呈波动趋势,其中,'华南7号'嫩茎叶的氢氰酸含量在种植后150和210 d显著降低(分别为347843和320507 mg·kg-1),'华南9号'嫩茎叶的氢氰酸含量在种植后150 d最低(313643 mg·kg-1),'华南205号'嫩茎叶的氢氰酸含量在种植后210 d最低(75103 mg·kg-1);'华南7号'和'华南205号'嫩茎叶的总黄酮含量在种植后120 d最高(分别为1963%和1917%),而'华南9号'嫩茎叶的总黄酮含量则在种植后210 d最高(1801%).不同生长期3个木薯品种嫩茎叶的粗蛋白质和粗灰分含量均符合相关动物饲料的标准,而总磷含量均较低.其中,'华南7号'嫩茎叶的粗蛋白质、粗脂肪、粗纤维、粗灰分和总钙含量在种植后150 d相对较高,分别为25273%、7687%、23077%、7157%和1660%,其无氮浸出物含量(26823%)相对较低;'华南9号'嫩茎叶的上述5种营养成分含量在种植后120 d相对较高,分别为28050%、6990%、21557%、8467%和1493%,其无氮浸出物含量(24723%)相对较低;'华南205号'嫩茎叶的粗蛋白质、粗脂肪和粗灰分含量在种植后120 d相对较高,分别为24273%、7080%和7633%,其粗纤维(18470%)、无氮浸出物(32037%)和总钙(1323%)含量相对较低.综合分析结果显示:'华南7号'、'华南9号'和'华南205号'嫩茎叶作为饲料的最佳采收时间分别为种植后150、120和120 d.     

择伐强度对中亚热带天然针阔混交林林分空间结构的影响

利用混交度、大小比数和角尺度3个结构参数,研究4种不同择伐强度（弱度13.0%、中度29.1%、强度45.8%、极强度67.1%）对中亚热带天然针阔混交林林分空间结构的影响。结果表明：弱度择伐后林木的平均混交度最大,中度择伐次之,极强度择伐林木单种聚集的比例最高;不同择伐强度对林木的大小分化程度影响不大,但各主要树种的地位都有一定程度变化;择伐并未改变林木的空间分布格局,各样地林分整体和主要树种均为聚集分布,极强度择伐林木多呈团状分布,而弱度、中度择伐树种大多处于不均匀和随机分布。总的来说,弱度和中度择伐有利于林分空间结构的优化。     

Influence of Ethephon on Nitrate Reductase, Protein Amino Nitrogen and Nitrate Content of Solanum tuberosum L.

Nitrate reductase activity was stimulated in roots and stems,but suppressed in leaves of potato plants grown in nutrientculture by 30 mg.liter^–1 ethephon applied to the culturesolution. In stems, nitrate reductase activity was stimulatedafter 5 h and by 24 h it was more than two fold that of thecontrol. The magnitude of stimulation by ethephon was less inroots compared to stems. Ethephon treatment enhanced ethyleneproduction by roots, stems and leaves but the level of productionwas not significantly different in these organs. The stimulationof nitrate reductase activity was prevented by cycloheximideand cordycepin suggesting the involvement of new protein synthesis. Ethephon enhanced TCA precipitable protein levels in both rootsand stems while that in leaves was not significantly affected.Amino nitrogen content increased in parallel with protein contentin response to ethephon, with roots exhibiting substantial stimulation.Nitrate accumulation in stem tissues was not affected by ethephontreatment but was increased in roots at 24 and 48 h. Leaf NO³content declined with time in both ethephon-treated and controlplants and after 24 h significantly less NO³ accumulated intreated leaves. These results are explained in terms of ethephonstimulated protein synthesis and increase in cellular metabolismand permeability. (Received August 21, 1984; Accepted January 7, 1985)     

淀山湖周丛动物群落的初步研究

作者于1991年11月至1992年11月对淀山湖水生植物上周丛动物进行了初步研究。共观察到84种周丛动物,以原生动物(38.10%)和轮虫(22.62%)占多数。按个体大小,分为小型周丛动物群落和大型周丛动物群落两种群落类型。小型周丛动物群落的优势种为似钟虫、角突臂尾轮虫等,个体数量受周丛原生动物支配,一年中有两次高峰(3-4月份和11月份),生物量在3月份最大,主要受周丛轮虫控制。大型周丛动物群落的优势种为线虫和螺类,一年只有一次数量高峰(6-8月),生物量中螺类占绝对优势(96.4%)。周丛动物在不同水生植物上的分布数量不同,沉水植物中以金鱼藻最多,大茨藻最少;并且叶上的数量明显高于茎上。漂浮植物上一般多于沉水植物,且根部最多,茎、叶相近。水生植物上周丛动物多为广布种,特有种罕见,主要出现于小型周丛动物群落中。       

胡杨茎叶化学计量和异速生长关系特征随发育阶段变化的性别差异

胡杨(Populus euphratica Oliv.)是荒漠河岸林防风固沙和水土保持的雌雄异株树种。该研究以不同径阶(8、12、16、20 cm)的胡杨雌雄株为研究对象,通过当年生茎、叶化学计量元素(C、N、P、K)含量及生长关系分析,探讨不同器官化学计量随发育阶段的变化及异速生长关系的性别差异。结果表明：(1)胡杨雌雄株叶片C含量表现为大径阶(20 cm)显著高于小径阶(8 cm),而其叶片N含量随着径阶的增加显著增加;雌雄株茎、叶化学计量随着径阶的增加总体上呈增加趋势,且C、N含量均与径阶呈显著正相关关系;随着径阶的增加,雌株叶片P含量呈下降趋势,与径阶呈显著负相关关系,而雌雄株茎的P、K含量呈上升趋势,且与径阶呈显著正相关关系。(2)雌株各径阶叶片的N含量及8、12、20 cm径阶的叶片P含量均显著大于相应雄株,8、16、20 cm径阶当年生茎C含量以及20 cm径阶茎N、P含量均显著高于相应雄株。(3)雌株叶片C与N在20 cm径阶的斜率指数最大,而雄株在12 cm径阶斜率指数最大,雌雄株在各发育阶段N与P的变化较稳定;在相同C含量时,雄株茎能获得更多的N含量,雌株茎在相同N的情况下能获得更多P元素。研究发现,胡杨雌雄株间茎、叶化学计量元素含量和异速生长关系特征在不同发育阶段存在着明显性别差异,成熟雌株叶片需要更多的化学计量特征含量来满足生殖需求,总体反映了自身生长及环境适应的养分分配策略。     

藏雪鸡(Tetraogallus tibetanus)春夏季食性

藏雪鸡(Tetraogallus tibetanus)生活在青藏高原及其毗邻地区,是国家二级保护动物。2016年5—8月,在青海省尖扎县,采集藏雪鸡新鲜粪便及可能食用的植物,采用粪便显微分析法研究了藏雪鸡食性。结果表明:藏雪鸡能以各种植物器官为食,叶片是其食用的主要器官,茎次之,再次是花和果(种子),根极少;藏雪鸡所食植物器官比例有明显季节变化,叶片的比例逐月下降,花的比例在7月显著增加,而果(种子)比例在8月陡增至28%;藏雪鸡能以生境中24科72种草本植物中的19科49种为食,还取食苔藓和地衣;禾本科和菊科植物是其主要食物,占食物总量的42%;草地早熟禾(Poa pratensis)(22.35%)是主要食物种,蒲公英(Taraxacum mongolicum)等20种植物是其常见食物种;藏雪鸡所食植物种类比例季节变化明显,如草地早熟禾比例5—7月稳定在20%左右,但8月上升到30.20%,而蒲公英比例5—8月持续增加;藏雪鸡所食植物种类数稳定在35~36种,仅7月稍多(41种);不同月份的食物成分相似性较高(>73%),食物的Shannon多样性指数和Pielou均匀度指数相似,但8月食物生态位宽度指数明显低于其他月份。综上,藏雪鸡是广食性鸟类,且食性有明显的季节变化。本研究结果可为藏雪鸡救护和迁地保护时人工饲料配方的设计提供依据。     

OSMOTIC ADJUSTMENT OF PLANTS TO SALINE MEDIA. II. DYNAMIC PHASE

Bernstein , Leon . (U. S. Salinity Lab., Riverside, Calif.) Osmotic adjustment of plants to saline media. II. Dynamic phase. Amer. Jour. Bot. 50(4): 360–370. Illus. 1963.—The time-course of osmotic adjustment in bean and pepper plants to increased salinity of the medium was determined by periodic sampling of plants following salt additions to the medium. Bean plants adjusted to increases of 1 atm OP within a day, the adjustment in roots occurring primarily at night following salt addition at 6 pm , whereas leaves and stems made most of their adjustment in the daytime. Pepper plants did not adjust completely to 1.5 atm NaCl additions in 48 hr, but OP increased by about the same amount in both species (0.5—1.0 atm per day). Diurnal fluctuations in OP of leaves and stems of both species and in roots of pepper were matched by parallel fluctuations in K concentrations. Added NaCl caused increased concentrations of K in leaves and stems which were more or less replaced by more slowly absorbed ions, Ca and Mg in bean leaves and Na in bean stems. Other salts produced comparable immediate effects on K level, but K was replaced more rapidly if the cation added was readily accumulated by the bean (Ca). In roots, Na uptake predominated if Na salts were added but K uptake was important on the CaCl₂ treatment. The K effects suggest a passive distribution of K between the cell and the medium.     

Stimulation and Inhibition by Ethephon of Stem and Leaf Growth of Some Gramineae at Different Stages of Development

The effect of ethephon on the growth of leaves and stems ofP. pratensis, Agrostis sp., and A. sativa was investigated.The length of the leaves of all species as well as that of theinternodes of stems of vegetative tillers of Agrostis sp. andof stems of reproductive A. sativa plants was reduced. Epidermalcell length was unchanged or somewhat increased, indicatinga reduction in cell number. The rate of cell elongation maybe decreased, however. A reduction in cell length was observedin the internode of generative oat plants that just startedto elongate at the time of treatment. In vegetative tillers of P.pratensis and A. sativa ethephonpromoted growth of the internodes by increasing cell length.Cell number was little affected. GA3 also promoted internodegrowth, causing an increase in cell length as well as in cellnumber. Application of ethephon and GA3 together gave an additiveeffect on cell length but a reverse effect on cell number. Effects of ethephon were observed for 5 or more weeks aftertreatment. Ethylene production from plants of A sativa increased,but the extra production had already decreased by 90% after11 d. No stimulation of the ethylene production by the plantsother than from the breakdown of ethephon was observed.     

Optical properties and the content of photosynthetic pigments in the stems and leaves of the apple-tree

Optical properties and changes in the content of photosynthetic pigments (chlorophyll and total carotenoids) were investigated in the bark and leaves of the apple-tree during a year. Optical properties of stems change with their age. Light reflectance of current year stems equalled 14.2%, while the one for 3-year-old stems decreased to 10.2%, absorption for the current year stems equalled 55.5% and increased up to 66.4% for 3-year-old ones. Light transmittance for the cork of current year stems equalled 30.2%, and decreased with the age of stems reaching 23.4% for the 3-year-old ones. The cork transmitted less than 5% of light of 400 nm, but the transmittance increased with the increase in the wavelength up to 55% at 700 nm. The reflectance of light by the leaf equalled 6.9%, absorption 89.7%, and transmittance 3.4%. In August the highest amount of chlorophyll pigments (6.2 mg·dm⁻²) and carotenoids (1.63 mg·dm⁻²) was detected in the leaves of the apple-tree, however, the ratio of chl a/b reached the highest value 4.12 in June. For the bark of apple-tree stems the content of chlorophyll pigments increased since spring and reached the maximum content of about 2.8 mg(chl)·dm⁻² for 1-3-year-old stems in the summer months, while for the current year stems in October. The ratio chl a/b was at the same level, about 2.2 during the whole year. The content of carotenoids was lower in stems than in leaves and was at the similar level during the year, however, it increased with the age of stems. Minor changes in the optical properties and the content of photosynthetic pigments occurring with the age of stems may be due to the low increment in cork thickness in the studied age groups of plants.     

Cutting stems before relaxing xylem tension induces artefacts in Vitis coignetiae,as evidenced by magnetic resonance imaging

It was recently reported that cutting artefacts occur in some species when branches under tension are cut, even under water. We used non‐destructive magnetic resonance imaging (MRI) to investigate the change in xylem water distribution at the cellular level in Vitis coignetiae standing stems before and after relaxing tension. Less than 3% of vessels were cavitated when stems under tension were cut under water at a position shorter than the maximum vessel length (MVL) from the MRI point, in three of four plants. The vessel contents remained at their original status, and cutting artefact vessel cavitation declined to <1% when stems were cut at a position farther than the MVL from the MRI point. Water infiltration into the originally cavitated vessels after cutting the stem, i.e. vessel refilling, was found in <1% of vessels independent of cutting position on three of nine plants. The results indicate that both vessel cavitation and refilling occur in xylem tissue under tension following stem cutting, but its frequency is quite small, and artefacts can be minimized altogether if the distance between the monitoring position and the cutting point is longer than the MVL.