中国温带旱柳物候期对气候变化的时空响应

为了揭示中国温带植物物候随时间变化和植物物候对气候变化响应的空间格局及其生态机制,利用52个站点1986—2005年的旱柳展叶始期、开花始期、果实成熟期、叶变色始期和落叶末期的物候数据,分析其时间序列的线性趋势,并通过建立基于最佳期间日均温的物候时间模型,确定物候发生日期对气温年际变化的响应。在研究的时段内,区域平均旱柳展叶始期、开花始期和果实成熟期的发生日期分别以-4.2 d/10 a、-3.8 d/10 a和-3.3 d/10 a的平均速率显著提前,而区域平均旱柳叶变色始期和落叶末期的发生日期则分别呈不显著推迟和以2.4 d/10 a的平均速率显著推迟的趋势。单站展叶始期、开花始期和果实成熟期发生日期的线性趋势以提前为主,显著提前的站点分别占40%、41%和29%;叶变色始期发生日期呈显著提前和显著推迟趋势的站点数相当,分别占17%和19%;落叶末期发生日期的线性趋势以推迟为主,显著推迟的站点占23%。各站展叶始期、开花始期和果实成熟期发生日期的线性趋势空间序列与相应的最佳期间日均温的线性趋势空间序列之间呈显著负相关,表明一个站点前期气温升高的速率越快,该站这些物候期发生日期提前的速率就越快。在物候期对气温年际变化的响应方面,区域平均春季最佳期间日均温每升高1℃,展叶始期、开花始期和果实成熟期的发生日期分别提前3.08 d、2.83 d和3.54 d;区域平均秋季最佳期间日均温每升高1℃,叶变色始期和落叶末期的发生日期分别推迟1.69 d和2.28 d。单站展叶始期和落叶末期发生日期对气温年际变化的响应表现出在温暖地区的站点比在寒冷地区的站点更为敏感的特点。总体上看,基于日均温的物候时间模型对春、夏季物候期的模拟精度明显高于对秋季物候期的模拟精度。建立了基于最佳期间日均温和日累积降水量的改进秋季物候模型,该模型使旱柳叶变色始期和落叶末期的模拟精度显著提高。由此可见,旱柳叶变色始期和落叶末期的发生日期受到前期气温和降水量的综合影响。     

民勤荒漠区16种植物物候持续日数及其积温变化

中国西北荒漠区植物物候随气温变暖表现为提前趋势。本文以甘肃民勤荒漠区16种植物34年的物候观测资料,采用一次趋势线方程研究了荒漠区植物在物候提前的过程中,物候日数变化和物候期积温变化。结果表明,随着气温升高,物候持续日数表现出一定的增长趋势。物候持续期积温增加显著,而且春、秋两季是积温变化较敏感的季节。积温的增减在很大程度上是由物候持续日数增加或减少引起的,其次才是由于气温增高引起的。表明,随着气温的增高或降低,植物的物候持续日数并不能无限制地缩短或延长。     

祁连山中部低海拔地区青海云杉径向生长的气候响应机制

利用生理模型开展树木径向生长的气候响应机制研究对理解树木生长的生理机制、预估气候变化情景下森林生态系统的变化、提供森林保护管理的建议有重要意义。以祁连山中部低海拔地区青海云杉树轮记录为依据,利用Vaganov-Shashkin模型模拟青海云杉(Picea crassifolia)的径向生长,探讨青海云杉径向生长的生理机制。结果表明:降水对祁连山中部低海拔地区青海云杉径向生长起着决定性作用,5—8月份的降水直接影响当年青海云杉的径向生长,9月份的降水量影响翌年青海云杉的径向生长。根据本研究结果,水分是限制青海云杉径向生长的主要因子,建议青海云杉人工林种植时,可在5—8月份对青海云杉增加灌溉量。     

七种云杉针叶非结构性碳与光合特性随物候期的动态变化特征

云杉作为我国东北和西部高山地区的主要树种,在森林碳汇、水源涵养、生态安全屏障等方面具有重要的意义,其非结构性碳(NSC)的动态变化为研究森林碳储存和碳供应提供重要参考.为探究不同云杉树种针叶NSC含量与光合特性随物候期的动态变化特征,对同质园内7个云杉属树种幼树的物候期进行了观测,并测量了各物候期一年生和当年生叶中NSC的含量以及净光合速率.结果表明:各树种的萌动期从早到晚依次为粗枝云杉<青扦<白扦<林芝云杉<青海云杉<川西云杉<红皮云杉,伸展期从早到晚依次为白扦<青海云杉<粗枝云杉<青扦<红皮云杉<川西云杉<林芝云杉,顶芽期则无显著差异;物候期的差异不仅存在对当前生境如有效积温(R=0.996^*)、土壤含水量(R=-0.807^*)等的响应,也存在对原生境的适应;各树种NSC含量随物候期变化规律一致,当年生和一年生叶中淀粉含量均呈单峰型变化,可溶性糖含量则是先升高后趋于稳定;当年生叶中NSC含量均低于一年生,其中淀粉含量变化范围分别是20~50、70~ 150 mg·g^-1,可溶性糖含量变化范围分别是80~150、200~350 mg·g^-1.此外,不论在新老龄叶片中,淀粉含量下降后光合速率均会升高,净光合速率与淀粉和可溶性糖含量存在协调性.以上结果为全面理解云杉属树种NSC的季节动态及种间差异的变化规律提供了重要参考.     

青海云杉叶寿命与比叶重随海拔变化特征

以祁连山北坡中部的青海云杉纯林为对象,沿海拔梯度调查了7个样点的叶寿命、比叶重及相应的土壤温度和水分状况,探讨其叶寿命和比叶重随海拔梯度变化特征及其与水分、温度的关系.结果表明:(1)青海云杉叶寿命变化范围为10.4～13.2年(平均11.8年),不同海拔间具有极显著差异(P<0.001);青海云杉当年叶比叶重变化范围为261.78～324.31 g·m-2(平均303.45 g·m-2),一年叶比叶重变化范围为299.04～355.85 g·m-2(平均324.05 g·m-2);青海云杉比叶重与叶寿命之间存在显著正相关关系(P<0.05),当年叶和1年叶的相关系数分别为0.806 2和0.871 8.(2)青海云杉分布带土壤水分变化范围为19.9%～50.9%,沿海拔梯度增加呈现上升趋势,土壤年均温度变化范围为-1.67℃～1.45℃,沿海拔梯度增加呈现递减趋势.(3)青海云杉叶寿命、比叶重与土壤水分、温度之间存在显著的二次曲线关系,在土壤水分较低、温度较高的低海拔地带,以及土壤水分较高、温度较低的高海拔地带,叶寿命和比叶重均较高,且二者最大值均分布在林线地带.可见,青海云杉对于干旱、低温环境具有强烈适应性,土壤温度对其比叶重和叶寿命的影响较水分更为明显.     

西安木本植物物候与气候要素的关系

根据1963–2007年中国物候观测网西安观测站的物候和气温、降水资料,分析了西安站34种木本植物春季展叶始期、展叶盛期、始花期和盛花期等4个关键物候期的变化趋势、对气候变化的阶段响应特点及其与气温、降水变化的关系。结果表明,1963年以来,西安地区气温呈显著上升趋势,特别是1994年前后,气温发生明显突变,上升趋势更加明显;西安春季物候变化主要呈现提前趋势。在45年中,观测到的34种植物的展叶始期平均提前1天,展叶盛期平均提前1.4天,始花期平均提前9天,盛花期平均提前12天;以突变点为界,34个物种1995–2007年的4种物候期比1963–1994年平均提前了4.34±0.77天;春季物候期的早晚主要受春季气温的影响,特别是春季物候期发生当月和上一月的平均气温对物候期的影响最为显著。叶物候和物候发生期前一月的降水量有较为明显的相关关系,花物候期和降水的关系不明显。     

气候变暖背景下青藏高原草本植物物候变化空间换时间预测

气候变暖背景下的植物物候变化广受关注, 然而常用的植物物候变化预测模型未充分考虑植物对环境的适应性, 给预测结果带来了较大的不确定性。该文基于2002-2011年青藏高原10个站点的地面物候观测资料以及年平均气温数据, 对空间换时间模型预测车前(Plantago asiatica)和蒲公英(Taraxacum mongolicum)各主要物候事件(展叶始期、开花始期和黄枯普遍期)变化的可行性及其在升温背景下的变化规律进行了分析。首先利用不同海拔高度的气温和物候事件分别与地理因子(经度、纬度和海拔)建立多元线性回归模型, 然后在此基础上剔除经度和纬度的影响, 单独考察海拔变化所引起的气温与植物物候变化, 最后以海拔高度作为桥梁来考察物候变化与温度变化的关系。结果表明, 采用各站点对应的海拔高度来模拟年平均气温空间差异的R²均大于0.89, 表明海拔梯度可以用来反映时间尺度下的年际温度变化; 车前和蒲公英各物候事件发生日期拟合值均与海拔高度变化关系显著, R²均大于0.70, 表明海拔变化是影响它们各物候事件变化的主要地理因子; 在物候事件发生日期拟合值和年平均气温拟合值的回归方程中, R²均大于0.93, 说明基于不同海拔高度模拟得到的年平均气温变化可以对时间尺度上车前和蒲公英的物候事件变化进行预测。空间换时间预测表明, 温度每升高1 ℃, 车前展叶始期和开花始期分别提前5.1和5.4 d, 而黄枯普遍期推迟4.8 d; 蒲公英展叶始期和开花始期分别提前6.5和7.8 d, 而黄枯普遍期推迟6.7 d。     

祁连山优势树木碳水化合物资源分配的海拔和树种效应

海拔梯度造成的温度、水分和土壤肥力等环境异质性会影响树木的生长, 但是不同树木的生理差异也决定了树木资源分配权衡还存在很多不确定性。为探明祁连山地区青海云杉(Picea crassifolia)和祁连圆柏(Juniperus przewalskii)非结构碳水化合物(NSC)含量的海拔和树种效应差异, 该研究以祁连山两个优势针叶树种青海云杉和祁连圆柏为研究对象, 分别设置了高海拔(3 300 m)和低海拔(2 850 m)两个采样高度, 采用t检验和多因素方差分析比较了不同海拔两个树种NSC及其组分(可溶性糖、淀粉)含量的差异, 分析叶、树干、粗根和细根间的NSC及其组分含量的资源分配权衡特征, 明晰不同海拔青海云杉和祁连圆柏生长限制因素和生理生态适应机理。结果表明: (1)低海拔青海云杉整株和各器官NSC及其组分含量均显著高于高海拔青海云杉; 而低海拔祁连圆柏整株和各器官NSC及其组分含量均显著低于高海拔祁连圆柏; (2)不同海拔两个优势针叶树种可溶性糖主要投资在叶, 而淀粉主要投资在粗根和树干; (3)高海拔青海云杉的可溶性糖与淀粉的比值显著高于低海拔青海云杉, 说明高海拔青海云杉将更多的碳用于生长, 而低海拔青海云杉将更多的碳用于储存; (4)海拔、树种、器官以及它们的交互作用显著地影响NSC及其组分含量及可溶性糖:淀粉, 其中树种分别解释了NSC、淀粉总变异的38%和37%; 器官分别解释了可溶性糖、可溶性糖:淀粉总变异的68%和42%。该研究结果阐明了不同海拔青海云杉和祁连圆柏的生长限制因素及其资源分配权衡, 为理解不同海拔和不同树种的生态适应机理以及祁连山森林生态系统的保护提供了科学参考。     

Predicting phenology shifts of herbaceous plants on the Qinghai-Xizang Plateau under climate warming with the space-for-time method

气候变暖背景下的植物物候变化广受关注, 然而常用的植物物候变化预测模型未充分考虑植物对环境的适应性, 给预测结果带来了较大的不确定性。该文基于2002-2011年青藏高原10个站点的地面物候观测资料以及年平均气温数据, 对空间换时间模型预测车前(Plantago asiatica)和蒲公英(Taraxacum mongolicum)各主要物候事件(展叶始期、开花始期和黄枯普遍期)变化的可行性及其在升温背景下的变化规律进行了分析。首先利用不同海拔高度的气温和物候事件分别与地理因子(经度、纬度和海拔)建立多元线性回归模型, 然后在此基础上剔除经度和纬度的影响, 单独考察海拔变化所引起的气温与植物物候变化, 最后以海拔高度作为桥梁来考察物候变化与温度变化的关系。结果表明, 采用各站点对应的海拔高度来模拟年平均气温空间差异的R²均大于0.89, 表明海拔梯度可以用来反映时间尺度下的年际温度变化; 车前和蒲公英各物候事件发生日期拟合值均与海拔高度变化关系显著, R²均大于0.70, 表明海拔变化是影响它们各物候事件变化的主要地理因子; 在物候事件发生日期拟合值和年平均气温拟合值的回归方程中, R²均大于0.93, 说明基于不同海拔高度模拟得到的年平均气温变化可以对时间尺度上车前和蒲公英的物候事件变化进行预测。空间换时间预测表明, 温度每升高1 ℃, 车前展叶始期和开花始期分别提前5.1和5.4 d, 而黄枯普遍期推迟4.8 d; 蒲公英展叶始期和开花始期分别提前6.5和7.8 d, 而黄枯普遍期推迟6.7 d。     

民勤荒漠植被对气候变化的响应

运用民勤荒漠区1974-2009年物候观测资料和2002-2010年植被样方观测资料以及同期气象资料,分析了荒漠植被对气候变化的响应.结果表明:1961-2010年,民勤荒漠区气温升高,空气湿度增大,年均气温升高速率大于全球水平和中国近百年平均水平;植物对气温变化的响应主要表现在春季物候提前、秋季物候推迟、生长季延长;植被对降水量变化的响应主要表现为植被盖度和纯盖度随降水量减少而降低,植株密度、植物多度随降水量变化而波动;植被盖度和纯盖度与年降水量的相关性较高,然后依次为6-7月和4-5月的降水量;植株密度和植物多度与9月降水量呈正相关;植物春季物候提前的次序是芽初膨大期＞芽开放期＞开花始期＞展叶始期和展叶盛期＞花蕾序出现＞开花盛期＞开花末期＞果实成熟期;秋季物候推迟的次序是叶全变色期＞落叶始期＞叶初变色期＞落叶末期.春季气温升高对民勤荒漠区植物物候的影响大于秋季气温升高对物候的影响.     

祁连山排露沟流域青海云杉天然更新与土壤水热的关系

青海云杉是祁连山区森林生态系统的建群种,其天然更新对维持祁连山森林生态系统功能具有重要意义。以祁连山排露沟流域青海云杉林天然更新为研究对象,于2021年6-9月测定海拔2700-3300m的0-40cm土层土壤温度和水分数据,并于7月中旬对样地天然更新进行每木检尺,将天然更新划分为幼苗(第一龄级)阶段和幼树(第二龄级)阶段,通过方差分析探究不同海拔更新苗胸径、株高的差异,再进一步建立回归模型拟合更新苗胸径、株高与各层土壤水热的关系,探讨更新苗胸径、株高对土壤水热的响应。结果表明:(1)更新苗胸径、株高随海拔升高而降低,海拔2700m幼苗胸径与3300m幼苗胸径存在显著性差异(P<0.05),海拔2700m、2800m幼苗、幼树株高与3300m幼苗、幼树株高存在显著性差异(P<0.05),幼树胸径在各海拔均不存在显著性差异,表明更新苗胸径对海拔的敏感性要低于更新苗株高。(2)更新苗胸径、株高与土壤温度呈正相关,与土壤水分呈负相关,幼苗胸径与20cm土壤温度和土壤水分的相关系数最大,幼树胸径与40cm土壤温度和土壤水分相关系数最大,幼树株高与40cm土壤温度及20cm土壤水分相关系数最大。(3)回归模型显示幼苗胸径和株高对土壤水热的利用模式相同,而幼树胸径和株高对土壤水热的利用模式存在差异。(4)青海云杉天然更新随着龄级的增加,影响生长的主要因素由土壤温度逐渐变为土壤水分,更新苗胸径对土壤水热的响应也随着龄级的增加在逐渐减弱。     

模拟降水减少对中亚热带杉木人工林土壤甲烷吸收的影响

森林土壤是大气中甲烷重要的汇,降水变化是影响森林土壤甲烷吸收速率(V_(CH_4))的重要因子。以中亚热带地区不同降水减少程度的杉木林土壤为研究对象,采用静态箱-气相色谱法来测定不同模拟降水减少处理样地的土壤甲烷吸收速率。结果表明:模拟降水减少后显著改变了土壤中的含水量,降水减少60%、降水减少20%和对照样地的年均土壤含水量分别为18.87%、23.89%和28.33%。杉木人工林土壤甲烷吸收速率在月变化上存在较大幅度的波动,其中土壤甲烷吸收速率在8月份达到一年中的最大值(对照75μg m~(-2) h~(-1)),2月份达到一年中的最小值(对照10.93μg m~(-2) h~(-1))。3种处理样地的土壤全年均为甲烷汇,与对照样地的甲烷年通量(2.48 kg hm~(-2) a~(-1))相比,降水减少60%和20%样地的甲烷年通量分别增加44%和19%。在对照样地中,土壤甲烷吸收速率与土壤含水量呈现负相关(P=0.001),与温度相关性不显著(P0.05);而模拟降水减少后,土壤甲烷吸收速率与土壤温度呈正相关关系(P=0.006和P=0.034),与土壤含水量相关性不显著(P0.05)。总之,模拟降水减少后不仅提高了杉木人工林土壤甲烷吸收的能力,同时也可能改变影响土壤甲烷吸收的环境因子;在模拟降水减少前土壤甲烷吸收速率与土壤水分相关性更为密切,而模拟降水减少后土壤甲烷吸收速率可能主要受土壤温度的影响。     

川西云杉幼苗非结构性碳水化合物对土壤温度和水分变化的响应

选取5年生川西云杉（Picea balfouriana）幼苗作为试验材料,于生长季模拟土壤温度和水分变化,研究不同土壤温度和水分处理对幼苗各器官生物量和非结构性碳水化合物（NSC）浓度的影响,以期加深对高海拔树木碳水化合物生理的理解,并为全球气候变化下植物的生理生态响应和动态变迁研究提供基础数据。于人工气候室内采用嵌套设计,设置5个土壤温度梯度（2、7、12、17、22℃）,每个温度处理下3个土壤水分处理（干旱处理、正常水分含量处理、饱和水分含量处理）。每9株幼苗为同一个处理,共135株幼苗。试验处理4个月后,测定幼苗各器官生物量、可溶性糖、淀粉和NSC浓度。土壤温度对幼苗总生物量无显著影响,但土壤低温显著降低了根生物量和根冠比;干旱和饱和水分胁迫在较高的土壤温度处理下显著降低了根生物量和根冠比。随着土壤温度降低,各器官可溶性糖、淀粉和NSC浓度并未降低,反而呈现出升高或不变的趋势。。在土壤低温处理下（2和7℃）干旱显著降低了当年生叶的淀粉和NSC浓度以及当年生枝的淀粉浓度;在2和7℃时,干旱和饱和水分胁迫显著降低了根中淀粉和NSC浓度。土壤低温和水分胁迫对幼苗地上地下生物量分配影响显著,分配给光合器官的生物量相对增多。土壤低温并没有导致碳受限,甚至各器官NSC浓度随着土壤温度降低有升高的趋势,因此,土壤低温下非结构性碳水化合物的不足不是限制川西云杉幼苗存活和生长的原因,从侧面支持了林线形成的"生长抑制"假说。此外,干旱胁迫在土壤低温下很可能会导致川西云杉的"碳饥饿"。     

Energy loss in an aestivating population of the tropical snail pila globosa

The dried peripheral area of pond Idumban (62 ha) increased from 3.2 ha in January to 3 1.9 ha in April. Pila globosa, which were abundant in the littoral area, did not commence aestivation during this period, perhaps due to low temperature and/or high dissolved oxygen content. The number of aestivating snails averaged 0.5/m² in May, 1973 (3.6% of the total population) and it increased to 1.1/M² in September (26.2%). Biomass of the snail increased from 3.5 to 19.9 g dry weight (including shell)/M². Number of aestivating snails increased from 0.4/m² (5.2% of the total population) in May 1974 to 0.8/m² (11.1%) in July and the biomass from 4.1 g/m² to 10.7 g/m². Availability of dried area for aestivation increased from 5.3 to 23.7 ha in 1973 and from 13.5 to 30.2 ha in 1974.Monthly observations made on the marked snails forced to aestivate at 7.5, 15.0, 22.5 and 30.0 cm depth in the pond during May, revealed that temperature above 35°C and moisture below 5% were critical. Mortality and weight loss decreased in the snails forced to aestivate at increasing depth. Random observations indicated that 83% of the aestivating snails buried themselves at 15 cm depth in the pond. On the whole, 98,480 snails (592 Kg) and 115,270 (758 Kg) died during aestivation in 1973 and 1974 respectively. Of the total weight loss, the energy lost via metabolism contributed only a small fraction of 2.2% (12 Kg) and 2.1% (15 Kg) during these years. Considering the total aestivation area, the snails which succumbed averaged only 0.4/m²/year (2.5 g/m²/year). On an average, dry substance equivalent to about 2.6 mg dry weight/ g dry weight of snail/ day (3.7 gcal/ g live snail/ day) was lost on metabolism by the aestivating snails, i.e. the metabolic level of the aestivating snail was about 1 / 18th of that of the actively feeding snail.     

Contribution of root respiration to total soil respiration in a Japanese cedar (Cryptomeria japonica D. Don) artificial forest

Soil respiration was measured for 2 years in an artificial gap and in an undisturbed area in a Japanese cedar (Cryptomeria japonica D. Don) forest to estimate the contribution of root respiration to total soil respiration. Measurement plots were set up at the center of the gap, the edge of the gap, the edge of the surrounding stand and within the stand. Using a small gap (2.5 m × 2.5 m) enabled us to maintain the same soil temperature and soil moisture as found in the stand. Seasonal fluctuations in soil respiration, increasing in summer and decreasing in winter, corresponded to changes in the soil surface temperature. Soil respiration in the gap site did not differ significantly from those in the stand in the first year of gap formation. However, in the second year, the minimum CO₂ flux was observed at the center of the gap and the maximum at the edge of the surrounding stand. Assuming that the differences between soil respiration in the center of the gap and that in the stand were equal to the root respiration, the root respiration rate was calculated from the relationship between the root respiration rates (Rr) and the soil surface temperature (Ts) by Ln(Rr) = 0.07Ts + 3.48. The average contribution of root respiration to total soil respiration, as estimated from the soil surface temperature in the stand by using the above equation, was 49%. After taking root decomposition into consideration, the contribution of root respiration to soil respiration increased from 49 to 57%.     

Influence of temperature on colonization of spring barleys by vesicular arbuscular mycorrhizal fungi

The effects of three soil temperatures on growth of spring barleys (Hordeum vulgare L.) and on their root colonization by vesicular arbuscular mycorrhizal (VAM) fungi from agricultural soils in Montana (USA) or Syria at different inoculum concentrations were tested in soil incubators in the greenhouse. The number of mycorrhizal plants as well as the proportion and intensity of roots colonized increased with higher soil temperatures. VAM fungi from Montana, primarily Glomus macrocarpum, were cold tolerant at 11°C while those from Syria, primarily G. hoi, were heat tolerant at 26°C. Inoculum potential of Montana VAM fungi was higher than Syrian VAM fungi in cool soils. Harmal, selected from Syrian barley land races, had the highest colonization by mycorrhizal fungi of the cultivars tested.Journal Series Paper: J-2532 Montana Agricultural Experiment Station.     

A comparison of soil core sampling and minirhizotrons to quantify root development of field-grown potatoes

Root growth of potato (Solanum tuberosum L.) is sensitive to soil conditions. A reduced root system size can result in reduced uptake of water and/or nutrients, leading to impaired crop growth. To understand the mechanisms by which soil conditions affect crop growth, study of temporal and spatial development of roots is required.In field experiments, effects of soil temperature, soil compaction and potato cyst nematodes (Globodera pallida) on root growth of potato cultivars were studied using two methods: core sampling and vertically oriented minirhizotrons.Minirhizotrons showed relatively more roots in deeper soil layers than core sampling, probably because of preferential root growth along the tube. Spatial distribution of roots should therefore be analysed by core sampling.To eliminate differences in spatial distribution, total root systems as measured by both methods were compared. Nematodes, cultivars and time did not affect the relationship between both methods. Soil compaction, however, affected it because of a strong response of root length in bulk soil and small differences in root number against the minirhizotron, suggesting that soil coring has to be used to study effects of different bulk densities.With both methods, sequential measurements of roots give the net effect of root growth and decay. Data on root turnover can only be obtained with minirhizotrons by comparing video recordings of different dates. Other information obtained with minirhizotrons is the average orientation of roots. Moreover, the minirhizotron method has the advantage of demanding less labour.     

Onion fly oviposition as influenced by soil temperature

A direct causal relationship was demonstrated between soil temperature and insect ovipositional propensity. When ovipositional substrates (soils) at 5, 15, 22, 30, 35, and 40°C were presented in multiple treatment (choice) tests with air temperature at 15 or 22°C, onion flies, Delia antiqua (Meigen) (Diptera: Anthomyiidae), laid the most eggs in the 22°C substrate. Only 50 eggs were laid when air temperature was increased to 30°C, as compared to 454 and 1128 eggs at 22 and 15°C, respectively. Thus, an air temperature of 30°C appears to be near the upper limit of onion fly ovipositional activity. The numbers of flies observed (counts taken every 15 min) on substrates ranging from 15 to 40°C were not significantly different. Reduced alightment/arrestment does not explain reduced oviposition on the warmer substrates; however, it may partly explain reduced oviposition on 5°C substrates. The range of substrate temperatures facilitating substantial oviposition was narrower than that eliciting alightment/arrestment on the substrate. The ca. 20°C ovipositional optimum corresponds well with temperatures favoring egg survival and development.

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Résumé La température du sol est réglée, dans les pondoirs de D. antiqua, par un thermoblock, tandis que toutes les autres variables, associées au succédané d'oignon servant de stimulus de ponte, sont maintenues constantes. Une relation causale entre température du sol et activité de ponte est mise en évidence. Quand il y a choix entre des substrats de ponte à 5, 15, 22, 30 et 40°C, avec une température de l'air de 22°C, les mouches pondent surtout dans le substrat à 22°C. L'optimum thermique est de 20°C quand la température de l'air est abaissée à 15°C. La ponte n'est que de 50 ufs quand la température de l'air est portée à 30°C, contre respectivement 454 et 1128 ufs à 22 et 15°C. Ainsi, une température de l'air de 30°C paraît proche de la limite supérieure de l'activité de ponte de D. antiqua. Le nombre de mouches observées sur le substrat (toutes les 15 min.) ne varie pas significativement quand la température du substrat est entre 15 et 40°C. La gamme de températures provoquant la fixation sur le substrat est plus large que celle des températures provoquant une ponte importante. L'optimum de 20°C correspond bien aux températures favorables à la survie et à la croissance de D. antiqua.Ce travail montre l'effet important de facteurs abiotiques sur l'acceptation de la plante-hôte.

     

Root nodulation and nitrogen accumulation and partitioning in legume crops as affected by soil solarization

Soil solarization is a preplanting technique used in hot climates to control weeds and soilborne pathogens consisting of mulching the soil surface with polyethylene sheets. The increase in temperature associated with solarized soil could affect nitrogen availability for grain legume crops through effects on nitrogen fixing soil microorganisms or other mechanisms. To examine the effects of solarization on natural root nodulation and nitrogen accumulation and partitioning in the plant, two solarization field experiments were carried out over two planting seasons, involving genotypes of both faba bean (Vicia faba) and chickpea (Cicer arietinum). The effect of sowing date was also studied in the first season. Solarization increased the maximum soil temperature by 9–10 °C in the first, and by 13–15 °C in the second season. At 5 cm below the solarized soil surface, a temperature of over 46 °C prevailed for 146 and 280 h over the two respective seasons, while this temperature was not attained in unmulched soil. Solarization delayed the initiation of nodulation and consistently reduced the nodule number per host plant, but generated an approximate doubling of mean nodule weight. The total nodule mass per plant was not affected by the treatment in the first season, but was reduced in the second season. Solarization significantly increased the concentrations of NO₃^– -N, Na⁺, Zn²⁺, Ca²⁺ and K⁺ in the soil extract, and the total nitrogen accumulated in the whole plant. This latter increase was due to both higher plant growth and a greater plant nitrogen concentration. The increased nitrogen level in the plant was not uniform with respect to plant component, varying from 57% in the roots to 198% in the pods and seeds. The plants grown in non-solarized soil accumulated about 31% of their total N content in the shoots of the parasitic weed Orobanche crenata. Solarization dramatically improved grain yield by 300–900% in both seasons and in all genotypes studied, due to increased N availability in soil, N accumulation in plants, improved plant growth, and complete control of the parasite weed O. crenata. On the basis of these beneficial effects, soil solarization, which avoids site contamination and is suited to organic farming, should be a good opportunity in Mediterranean areas where the level and stability of grain yields are low, and the infestation of O. crenata is high.     

不同时间尺度北京蟒山油松树干液流对环境因子的响应

探究不同时间尺度蒸腾与环境因子的关系并明确其主控因子,对于理解蒸腾对环境响应规律和驱动机制具有重要的理论意义。以北京蟒山国家森林公园的油松为例,开展树干液流及气象指标、土壤温湿度等环境因子的长期定位观测,并分析不同时间尺度油松液流速率与环境因子的关系。研究结果表明,在日尺度上,土壤温度、大气相对湿度、土壤湿度与液流速率呈极显著正相关,这3个因子对液流速率变化的贡献量分别占28.3%、11.7%和10.1%;在月尺度上,土壤温度对液流速率的影响最大,贡献量占比49.7%,土壤湿度和相对湿度的贡献量分别为7.3%和6.4%;在年尺度上,相对湿度对液流速率的年际变化的贡献量高达93.3%,是关键控制因子。随着时间尺度的扩展,环境因子对油松液流速率的控制作用逐渐增强。本研究的结果可以为植物蒸腾的时间尺度转换、未来全球气候变化背景下植物蒸腾耗水特征的预测提供理论依据。