农田防护林木材材质物理特性研究

对早柳和小青杨的年轮宽度、年轮密度、木材纤维长度和干缩率及其径向变异进行了研究．结果表明,木材物理特性受年轮年龄的影响显著,而纤维长度不受年轮宽度影响．综合材质物理特性的径向变异规律,可将旱柳和小青杨整个生长期划分为４个时期：幼林期、速生期、成熟期和更新期,确定了各生长期的年龄值．     

水淹条件下秋华柳亚细胞中镉的分配特征

选取秋华柳(Salix variegata)扦插苗为研究对象,通过设置0、0.5、2、10 mg/kg 4个镉胁迫浓度,研究了水淹条件下秋华柳根、枝、叶亚细胞中镉的分配特征。结果表明:(1)试验各处理组秋华柳存活率均为100%,表现出良好的镉和水淹耐受能力。(2)与对照相比,在水淹条件下,各处理组秋华柳根、枝和叶的细胞壁仍是镉最主要的富集部位。各处理组植株细胞壁中的镉含量显著高于其他组分,质体中镉含量次之,细胞核和线粒体组分中的镉含量始终处于较低水平。(3)水淹显著提高了秋华柳根细胞壁中的镉含量,显著降低了高浓度镉处理(10 mg/kg)下萌枝细胞壁中的镉含量,但对叶细胞壁中的镉含量没有显著影响。(4)水淹显著提高了秋华柳根细胞中质体中的镉含量,对萌枝、叶细胞质体中的镉含量没有显著影响。研究证明,水淹条件下,秋华柳根枝叶细胞壁仍然是镉积累富集的最主要部位,从而减少了重金属对植物细胞的伤害。秋华柳适用于三峡消落带镉污染区域的植物修复。     

CO2浓度和辐射强度变化对沙柳光合作用速率影响的模拟研究

沙柳是毛乌素沙地防护林的主要灌木树种 ,模拟研究沙柳对 CO2 浓度和辐射强度的响应有利于准确有效地制定全球变化下的沙漠化防治和水土流失的战略对策。结果表明 ,沙柳的光合作用速率对 CO2 浓度的响应表现为线性关系 ,对辐射的响应表现为对数函数关系。沙柳光合作用速率有随辐射强度增加和 /或 CO2 浓度的升高而增大的变化规律。CO2 浓度越高 ,沙柳的光合作用速率对辐射的反应越明显。同样 ,辐射越强 ,沙柳的光合作用速率对 CO2 浓度的反应越敏感。在高辐射条件下增加大气中 CO2 的“施肥效应”比低辐射条件下要显著。土壤干旱对沙柳的光合和暗呼吸都有抑制作用 ,使沙柳的生理过程受到影响 ,从而使沙柳对 CO2 浓度和辐射的反应规律不如土壤水分适宜时显著。     

On the significance of photoinhibition of photosynthesis in the field and its generality among species

Photoinhibition was examined in naturally exposed willow leaves in the field. In the afternoon on clear and warm days, the quantum yield of electron transport, derived from gas exchange data, was decreased by 28%. Besides this photoinhibition, decreases in the photosynthetic capacity and in the stomatal conductance were also observed. Of these three limitations of carbon assimilation, photoinhibition was the major one at limiting light only.To investigate the generality of photoinhibition, shade- and sun-acclimated leaves of fourteen different species were compared in a laboratory study. Photoinhibition was quantified by fluorescence measurements following exposure to moderate and high light for 30 min. The extent of photoinhibition was inversely related to the photochemical quenching, q_p, during exposure (the proportion of open PS II traps). This relationship was the same independent of the species, the light-acclimation state of the leaf and the light intensity. However, sun- and shade-acclimated leaves occupied opposite sides of the relationship: the sun-leaves showed lower photoinhibition and higher q_p. The sun-leaves were also more competent than shade-leaves by showing faster recovery from a given level of photoinhibition.Abbreviations F₀, F_V, F_M, F_S minimal, variable, maximal and steady-state fluorescence - q_N, q_i total and photoinhibitory non-photochemical quenching of variable fluorescence - q_p photochemical quenching     

不同气候情景下四子柳的亚洲潜在地理分布格局变化预测

四子柳(Salix tetrasperma Roxb.)为杨柳科柳属为数不多的分布区扩展到热带的物种之一,广泛分布于华南和东南亚地区,但其生境破碎化较为严重。该物种具有较高的园林绿化价值和生态价值,预测不同气候情景下该物种的地理分布将为四子柳的资源开发和合理利用乃至柳属的起源和分化研究提供重要的科学依据。利用四子柳全面且精确的分布信息和高分辨率环境数据,基于Maxent模型和ArcGIS空间分析,构建其末次间冰期、末次盛冰期、当代以及未来(2050,2070)的潜在空间分布格局,评价环境因子对分布模型的重要性,定量确定未来受到威胁的适宜生境区域和面积。结果表明,四子柳目前的适宜生境面积为234.65×10~4 km~2,主要位于东亚、南亚和东南亚的热带地区,气温年较差和年均降水量是限制其分布的主要环境因子。总体而言,从冰期至未来,四子柳的分布中心有南北往返迁移的趋势。四子柳在末次盛冰期时向西北方向扩张并开始出现于热带地区,表明该物种开始适应热带气候,进入全新世中期以后种群收缩并退缩到云贵高原的河谷地区和印度尼西亚的平原区域。随着全球气候变暖,在不同二氧化碳浓度路径下2050年和2070年四子柳的潜在适生境有可能破碎化增加,建议对缅甸东部及中部成片减少的边缘群体进行实时监测。     

Contrasting levels of β-diversity and underlying phylogenetic trends indicate different paths to chemical diversity in highland and lowland willow species

Diverse specialised metabolites contributed to the success of vascular plants in colonising most terrestrial habitats. Understanding how distinct aspects of chemical diversity arise through heterogeneous environmental pressures can help us understand the effects of abiotic and biotic stress on plant evolution and community assembly. We examined highland and lowland willow species within a phylogenetic framework to test for trends in their chemical α-diversity (richness) and β-diversity (variation among species sympatric in elevation). We show that differences in chemistry among willows growing at different elevations occur mainly through shifts in chemical β-diversity and due to convergence or divergence among species sharing their elevation level. We also detect contrasting phylogenetic trends in concentration and α-diversity of metabolites in highland and lowland willow species. The resulting elevational patterns contribute to the chemical diversity of willows and suggest that variable selective pressure across ecological gradients may, more generally, underpin complex changes in plant chemistry.     

Somatic Mutation Analysis in Salix suchowensis Reveals Early-Segregated Cell Lineages

Long-lived plants face the challenge of ever-increasing mutational burden across their long lifespan. Early sequestration of meristematic stem cells is supposed to efficiently slow down this process, but direct measurement of somatic mutations that accompanies segregated cell lineages in plants is still rare. Here, we tracked somatic mutations in 33 leaves and 22 adventitious roots from 22 stem-cuttings across eight major branches of a shrub willow (Salix suchowensis). We found that most mutations propagated separately in leaves and roots, providing clear evidence for early segregation of underlying cell lineages. By combining lineage tracking with allele frequency analysis, our results revealed a set of mutations shared by distinct branches, but were exclusively present in leaves and not in roots. These mutations were likely propagated by rapidly dividing somatic cell lineages which survive several iterations of branching, distinct from the slowly dividing axillary stem cell lineages. Leaf is thus contributed by both slowly and rapidly dividing cell lineages, leading to varied fixation chances of propagated mutations. By contrast, each root likely arises from a single founder cell within the adventitious stem cell lineages. Our findings give straightforward evidence that early segregation of meristems slows down mutation accumulation in axillary meristems, implying a plant “germline” paralog to the germline of animals through convergent evolution.     

Phytoremediation of groundwater contaminated with pesticides using short-rotation willow crops: A case study of an apple orchard

The occurrence of pesticides in groundwater represents an important health issue, notably for population whose drinking water supply source is located in agricultural areas. However, few solutions have been considered with regard to this issue. We tested the efficacy of a vegetal filtering system made of shrub willows planted at a high density (16,000 plants ha^?1) to filter or degrade pesticides found in the groundwater flowing out of an apple orchard. Ethylene urea (EU), ethylene thiourea (ETU), tetrahydrophthalimide (THPI), atrazine, and desethylatrazine were monitored in the soil solution in willow and control plots over one growing season. ETU and atrazine concentrations were lower in the willow plots relative to the control plots, whereas desethylatrazine concentration was higher in the willow plots. No significant difference was detected for EU and THPI. Furthermore, pesticide concentrations displayed complex temporal patterns. These results suggest that willow filter systems can filter or degrade pesticides, notably ETU and atrazine, and could be used for phytoremediation purposes. Yet, this potential remains to be quantified with further studies using experimental settings allowing more estimation in time and space.     

Effects of nutrients and arbuscular mycorrhizal colonization on the growth of Salix gracilistyla seedlings in a nutrient-poor fluvial bar

A field survey and a pot culture experiment were conducted to examine the effects of nutrients (N and P) and arbuscular mycorrhizal (AM) fungi on the growth of Salix gracilistyla, a pioneer plant in riparian habitats. The plants growing in the field were colonized by AM and/or ectomycorrhizal fungi. However, the direct effect of AM colonization on seedling growth was not detected in the pot culture experiment. In contrast, N application significantly promoted plant growth, suggesting that the growth of S. gracilistyla seedlings is largely limited by the availability of N in the field.     

Host selection,oviposition behaviour and leaf traits in a specialist willow sawfly on species of Salix (Salicaceae)

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