CO2浓度倍增与干旱胁迫对油松（Pinus tabulaeformis）相对分枝级水力结构的影响

在密闭式生长箱内经过13个月高CO2浓度培养的5年生油松(Pinus tabulaeformis)为实验对象,采用改良冲洗法研究了CO2浓度倍增(720μmolmol-1)与干旱胁迫交互作用对油松相对分枝级水力结构参数的影响.通过测定油松不同分枝级的水力结构参数分别在720μmolmol-1 CO2和380μmolmol-1 CO2(大气现有CO2浓度)浓度下随着干旱胁迫的变化,得出不同分枝级的导水率(Kh)、比导率(Ks)和胡伯尔值(Hv)在2个CO2浓度下均随着干旱胁迫的增加而逐渐下降,叶比导率(Lsc)在720μmolmol-1CO2浓度下随着干旱胁迫的增加非线性变化(0级>2级>1级)不同于380μmolmol-1 CO2(0级>1级>2级).同期干旱胁迫条件下,720μmolmol-1CO2浓度下的Kh、Ks、Lsc 和Hv均大于380μmolmol-1 CO2且差异显著.根据整株苗木的水势将苗木的水分状况分为4个梯度,在正常水分(-0.45～-0.65MPa)、轻度干旱(-1.15～-0.75MPa)和中度干旱(-1.95～-1.35MPa)胁迫时,3个分枝级均在720μmolmol-1CO2条件下的Kh和Ks较380μmolmol-1 CO2增加,说明交互作用能提高导水能力,同时加快水分运输效率.在重度干旱(＜-2.80MPa)胁迫时Kh比380μmolmol-1 CO2增加,而Ks比380μmolmol-1 CO2减小,即交互作用提高了水分运输的安全性,却减少了有效性.     

Phenotypic variation and covariation indicate high evolvability of acoustic communication in crickets

Studying the genetic architecture of sexual traits provides insight into the rate and direction at which traits can respond to selection. Traits associated with few loci and limited genetic and phenotypic constraints tend to evolve at high rates typically observed for secondary sexual characters. Here, we examined the genetic architecture of song traits and female song preferences in the field crickets Gryllus rubens and Gryllus texensis. Song and preference data were collected from both species and interspecific F1 and F2 hybrids. We first analysed phenotypic variation to examine interspecific differentiation and trait distributions in parental and hybrid generations. Then, the relative contribution of additive and additive‐dominance variation was estimated. Finally, phenotypic variance–covariance ( P ) matrices were estimated to evaluate the multivariate phenotype available for selection. Song traits and preferences had unimodal trait distributions, and hybrid offspring were intermediate with respect to the parents. We uncovered additive and dominance variation in song traits and preferences. For two song traits, we found evidence for X‐linked inheritance. On the one hand, the observed genetic architecture does not suggest rapid divergence, although sex linkage may have allowed for somewhat higher evolutionary rates. On the other hand, P matrices revealed that multivariate variation in song traits aligned with major dimensions in song preferences, suggesting a strong selection response. We also found strong covariance between the main traits that are sexually selected and traits that are not directly selected by females, providing an explanation for the striking multivariate divergence in male calling songs despite limited divergence in female preferences.     

Reliability and robustness of muscle architecture measurements obtained using diffusion tensor imaging with anatomically constrained tractography

For detailed analyses of muscle adaptation mechanisms during growth, ageing or disease, reliable measurements of muscle architecture are required. Diffusion tensor imaging (DTI) and DTI tractography have been used to reconstruct the architecture of human muscles in vivo. However, muscle architecture measurements reconstructed with conventional DTI techniques are often anatomically implausible because the reconstructed fascicles do not terminate on aponeuroses, as real muscle fascicles are known to do. In this study, we tested the reliability of an anatomically constrained DTI-based method for measuring three-dimensional muscle architecture. Anatomical magnetic resonance images and diffusion tensor images were obtained from the left legs of eight healthy participants on two occasions one week apart. Muscle volumes, fascicle lengths, pennation angles and fascicle curvatures were measured in the medial and lateral gastrocnemius, soleus and the tibialis anterior muscles. Averaged across muscles, the intraclass correlation coefficient was 0.99 for muscle volume, 0.81 for fascicle length, 0.73 for pennation angle and 0.76 for fascicle curvature. Measurements of muscle architecture obtained using conventional DTI tractography were highly sensitive to variations in the stopping criteria for DTI tractography. The application of anatomical constraints reduced this sensitivity significantly. This study demonstrates that anatomically constrained DTI tractography can provide reliable and robust three-dimensional measurements of whole-muscle architecture. The algorithms used to constrain tractography have been made publicly available.     

胡杨幼苗根系生长与构型对土壤水分的响应

胡杨实生幼苗成活率低是制约其更新与人工育苗保存的关键问题,而幼苗根系生长与构型是影响其存活的重要因素。该试验以1年生胡杨幼苗为材料,通过2种给水方式(断续给水和连续给水)下各6个土壤水分梯度处理的控制试验,探究胡杨幼苗根系生长与构型对荒漠地区关键因子水分的响应特征。结果表明:(1)2种给水方式下干旱胁迫均使根冠比增加,且断续给水处理下幼苗根冠比显著大于连续给水。(2)一定程度的干旱处理还可以促进幼苗根系形态发育特征的发展和根系生物量的积累,但过度干旱胁迫或土壤水分含量过多都会抑制根系生长,并以连续给水、土壤含水量15%处理下幼苗根系最为发达。(3)幼苗深扎根能力强,其根宽深比在2种给水方式下均小于1,且断续给水处理显著小于连续给水处理;2种给水方式下根宽深比都与土壤水分含量呈显著正相关。(4)根系拓扑指数在2种给水方式下无显著差异且均接近1,但都与土壤水分含量呈显著负相关。即幼苗根系趋向鱼尾状分支结构,次级分支少,这种根系延伸策略有利于胡杨幼苗在干旱贫瘠的土壤环境中生存。(5)根系构型参数的主成分分析显示,总根长、总根表面积、根宽深比和拓扑指数在2种给水方式下都能很好地表示胡杨幼苗根系构型特征。可见,胡杨幼苗根系通过构筑鱼尾状分支结构、增加垂直根纵向延伸能力和增大根冠比适应干旱环境;水分对于胡杨幼苗根系生长与构型作用显著,根系对水分因子的响应对于胡杨幼苗适应水分异质性环境具有重要意义。     

Soil water availability and rooting depth as determinants of hydraulic architecture of Patagonian woody species

Adaptations of species to capture limiting resources is central for understanding structure and function of ecosystems. We studied the water economy of nine woody species differing in rooting depth in a Patagonian shrub steppe from southern Argentina to understand how soil water availability and rooting depth determine their hydraulic architecture. Soil water content and potentials, leaf water potentials (Ψ_Leaf), hydraulic conductivity, wood density (ρ_w), rooting depth, and specific leaf area (SLA) were measured during two summers. Water potentials in the upper soil layers during a summer drought ranged from −2.3 to −3.6 MPa, increasing to −0.05 MPa below 150 cm. Predawn Ψ_Leaf was used as a surrogate of weighted mean soil water potential because no statistical differences in Ψ_Leaf were observed between exposed and covered leaves. Species-specific differences in predawn Ψ_Leaf were consistent with rooting depths. Predawn Ψ_Leaf ranged from −4.0 MPa for shallow rooted shrubs to −1.0 MPa for deep-rooted shrubs, suggesting that the roots of the latter have access to abundant moisture, whereas shallow-rooted shrubs are adapted to use water deposited mainly by small rainfall events. Wood density was a good predictor of hydraulic conductivity and SLA. Overall, we found that shallow rooted species had efficient water transport in terms of high specific and leaf specific hydraulic conductivity, low ρ_w, high SLA and a low minimum Ψ_Leaf that exhibited strong seasonal changes, whereas deeply rooted shrubs maintained similar minimum Ψ_Leaf throughout the year, had stems with high ρ_w and low hydraulic conductivity and leaves with low SLA. These two hydraulic syndromes were the extremes of a continuum with several species occupying different portions of a gradient in hydraulic characteristics. It appears that the marginal cost of having an extensive root system (e.g., high ρ_w and root hydraulic resistance) contributes to low growth rates of the deeply rooted species.     

延展与解蔽—基于时空体验的景观与建筑的内外交互

基于时空关系与体验,探讨了景观与建筑的交接空间。对其建构方式与体验感知方式进行研究。基于戴维·哈维（David Harvey）的“时空压缩”以及希格弗莱德·吉迪恩（Sigfried Giedion）的“空间时间”理论,通过诠释“厚性”的概念,分析了景观与建筑空间交接的2种基本出发点：基于时空拉伸的“延展”,以及基于时空压缩的“解蔽”;通过案例研究,对其不同的空间组织方法与空间界定材料的使用方式进行解读,并论述与此对应的2种空间感知过程：“可推导性”与“瞬时生成性”;通过分析4个现当代景观实践案例,对景观设计在空间“内外交互”建构中所发挥的主动性与使用方法进行综合研究。最后,对时空建构的基本方法、综合使用等方面进行应用层面的分类与总结。     

Do submerged aquatic plants influence periphyton community composition for the benefit of invertebrate mutualists?

• 1 It has been suggested that submerged aquatic plants can influence the periphyton which grows on their surfaces, making it nutritionally beneficial to snails. In return, preferential feeding by snails clears the plants from a potential competitor, with both plants and grazers gaining from this mutualistic relationship.
• 2 A highly replicated experiment was conducted, in which the nature of the plant (isoetid and elodeid types compared with similar shaped inert substrata), the nutrient availability (10–200 µg L^‐1 P, 0.2–4 mg L^‐1 N) and the influence of periphyton grazers, Physa fontinalis, were controlled. The plants were cleaned of periphyton before use and an algal inoculum added to all treatments. At the end of the growth period, quantitative measures of the periphyton community composition were made and related to the treatments using both ordination and analysis of variance.
• 3 Grazing had the largest influence on community composition and algal numbers. A community of unicellular and adpressed filamentous forms developed in the presence of snails, and of erect filamentous forms in their absence. Three algal species, Cocconeis placentula, Chamaesiphon incrustans and Aphanochaete repens, increased in real numbers in the presence of snails, probably as a result of reduced competition whilst being able to withstand grazing.
• 4 The second largest effect was the influence of host plant. However, differences between the two artificial plants were as great as between the real plants and their artificial counterparts, indicating that physical structure was as important as any active contribution by the plants. Nutrients had a small but significant effect on community composition, but not all species responded in the same way to nutrient enrichment.
• 5 Although submerged aquatic plants exert an influence over the community composition of the periphyton which develops on their surfaces, it is unlikely that they manipulate it to make it more attractive to grazers such as snails.