Sexual competition and N supply interactively affect the dimorphism and competiveness of opposite sexes in Populus cathayana

Several important dioecious species show sexual spatial segregation (SSS) along environmental gradients that have significant ecological effect on terrestrial ecosystem. However, little attention has been paid to understanding of how males and females respond to environmental gradients and sexual competition. We compared eco‐physiological parameters of males and females of Populus cathayana under different sexual competition patterns and nitrogen (N) supply levels. We found that males and females interacting with the same or opposite sex showed significant differences in biomass partition, photosynthetic capacity, carbon (C) and N metabolism, and leaf ultrastructure, and that the sexual differences to competition were importantly driven by N supply. The intersexual competition was enhanced under high N, while the intrasexual competition among females was amplified under low N. Under high N, the intersexual competition stimulated the growth of the females and negatively affected the males. In contrast, under low N, the males exposed to intrasexual competition had the highest tolerance, whereas females exposed to intrasexual competition showed the lowest adaptation among all competition patterns. Sexual competition patterns and N supply levels significantly affected the sexual dimorphism and competitiveness, which may play an important role in spatial segregation of P. cathayana populations.     

Soil carbon stocks,deforestation and land‐cover changes in the Western Ghats biodiversity hotspot (India)

Habitat loss and soil organic carbon (SOC) stock variations linked to land‐cover change were estimated over two decades in the most densely populated biodiversity hotspot in the world, in order to assess the possible influence of conservation practices on the protection of SOC. For a study area of 88 484 km², 70% of which lie inside the Western Ghats Biodiversity Hotspot (WGBH), land‐cover maps for two dates (1977, 1999) were built from various data sources including remote sensing images and ecological forest maps. SOC stocks were calculated from climatic parameters, altitude, physiography, rock type, soil type and land‐cover, with a modelling approach used in predictive learning and based on Multiple Additive Regression Tree. The model was trained on 361 soil profiles data, and applied to estimate SOC stocks from predictor variables using a Geographical Information System (GIS). Comparison of 1977 and 1999 land‐cover maps showed 628 km² of dense forests habitat loss (6%), corresponding to an annual deforestation rate of 0.44%. This was found consistent with other studies carried out in other parts of the WGBH, but not with FAO figures showing an increase in forest area. This could be explained by the different forest definitions used, based on ecological classification in the former, and on percentage tree cover in the latter. Unexpectedly, our results showed that despite ongoing deforestation, overall SOC stock was maintained (～0.43 Pg). But a closer examination of spatial differences showed that soil carbon losses in deforested areas were compensated by sequestration elsewhere, mainly in recent plantations and newly irrigated croplands. This suggests that more carbon sequestration in soils could be achieved in the future through appropriate wasteland management. It is also expected that increasing concerns about biodiversity loss will favour more conservation and reinforce the already prevailing protective measures, thus further maintaining C stocks.     

不同频率电刺激猫中央中核对丘脑束旁核痛放电的抑制效应

用清醒的肌肉麻痹的猫进行实验。观察到:以4Hz、8Hz 和60Hz 的电脉冲刺激中央中核,均可抑制束旁核的痛放电。频率为8Hz 的刺激能产生最强的抑制效应,4Hz 的效应稍差,60Hz 的最差。抑制的表现方式有二:(1)跟随着每个刺激脉冲出现痛放电的短暂遏制,遏制时间约为120ms,而且不随刺激强度的加强而相应延长。这种方式只有在低频刺激时才出现。(2)痛放电的整个时程缩短,高频和低频刺激时均可出现,特別是在使用高强度(5.4—8.5V)刺激时表现得更加明显。刺激丘脑中央中核与刺激外周深部神经或“穴位”,对束旁核痛放电有非常相似的抑制时程和适宜频率。此外,刺激中央中核选择性地抑制束旁核内痛敏细胞的活动,而不抑制非痛敏细胞的活动。实验结果提示我们:中央中核可能在远距离穴位镇痛机制中占重要地位。     

猫丘脑中央中核对刺激深部神经的反应

在清醒和肌肉麻痹的猫上,以单个电脉冲刺激“足三里”、“上巨虚”穴位可以在丘脑中央中核引导出短潜伏期(15—40ms)短串(2—4个锋电位)反应。这种反应不为镇痛药物(如芬太尼)所抑制。以8Hz 的连续电脉冲刺激腓深神经或桡深神经可使中央中核细胞放电持续增加,刺激过程中未出现适应现象。停刺激后,多数细胞有大约0.5min 的后作用,然后恢复到对照水平。4Hz 的电刺激也使中央中核细胞放电增加,但有时不如前者明显,而且后作用时间甚短。60Hz 的高频电刺激仅使中央中核在前0.5min 内放电增加,然后出现适应现象,放电频率降到对照水平。由此可见,低频刺激(4—8Hz)深部神经能够最有效地激活中央中核细胞。经电子计算机处理的脉冲密度直方图表明中央中核细胞放电与低频刺激脉冲有时间上的相关关系。中央中核细胞放电的多少与我们前文观察到的束旁核痛放电受抑制的程度似呈平行的关系,这再次表明中央中核在针刺镇痛中起重要的作用。     

黑翅土白蚁的跟踪信息素

黑翅土白蚁Odontotermes formosanus(Shiraki)严重危害堤坝,有明显跟踪行为,其分泌跟踪物质的腹板腺位于腹部第5节腹板前沿中部,分泌细胞呈长形,与腹板呈垂直方向排列。用滤纸双圈法测定黑翅土白蚁跟踪行为。跟踪物质的抽提以正己烷较好,丙酮和二氯甲烷次之。从抽提液柱层析、薄层层析和微化学反应结果推测,其跟踪物质可能是含有双键的醇类化合物。密褐褶孔菌及其感染的腐木块抽提液及白蚁跟踪信息化合物——顺,顺-3,6-十二碳双烯醇都对黑翅土白蚁有较强的跟踪活性。肖若散白蚁和家白蚁抽提液均对黑翅土白蚁有跟踪活性,但肖若散白蚁和家白蚁对黑翅土白蚁抽提液及其柱层析和薄层层析的活性馏份无活性反应。     

意蜂与中蜂血淋巴蛋白质成份的研究

本实验用聚丙烯酰胺凝胶电泳分析了两个蜂种的血淋巴蛋白质成分。意蜂和中蜂都是Apis属,血淋巴蛋白质电泳谱相似。但是,两蜂种以及同一蜂种不同级别、不同发育阶段的电泳谱又各有特点。根据实验,我们把成年蜂血淋巴电泳谱分为11条带,雌蜂电泳谱上的带5是卵黄原蛋白;雄蜂卵黄原蛋白含量很少或测不出。 用Thorun方法,在聚丙烯酰胺凝胶平板电泳上测得意蜂卵黄原蛋白的分子量为185,000。     

Relations between vulnerability to xylem embolism and xylem conduit dimensions in young trees of Quercus corris

Measurements of xylem conduit length and width and the distribution of xylem conduit ends were made in inter-nodes (I), nodes (N) and twig junctions (J) of 1-, 2- and 3-year-old twigs of plants of Quercus cerris L. Parallel measurements were also made of the loss of hydraulic conductivity of twigs subjected to pressure differentials across conduit pit membranes, equalling the leaf water potential at the turgor loss point. The loss of theoretical hydraulic conductivity was calculated as the ratio of i esivr⁴ (where r is the conduit radius) of the non-conducting conduits to that of all the conduits in the outermost wood ring of I, N and J. Stem zones such as 1-year-old nodes and junctions were localized with narrower and shorter xylem conduits and with higher percentages of conduit ends than internodes. Such ‘constricted zonesrsquo; were less vulnerable to embolism than internodes. Latewood conduits were consistently narrower, shorter and less vulnerable to embolism than earlywood ones. A positive relation therefore existed between conduit diameter and length and vulnerability to embolism. The overall vulnerability to embolism of Q. cerris plants is discussed in terms of xylem conduit width and length and of the distribution of conduit ends.     

Water storage in the wood and xylem cavitation in 1-year-old twigs of Populus deltoides Bartr.

The possible role of water expelled from cavitated xylem conduits in the rehydration of water-stressed leaves has been studied in one-year-old twigs of populus deltoides Bartr. Twigs were dehydrated in air. At desired values of leaf water potential (Ψ_l) (between near full turgor and -1.62 MPa), twigs were placed in black plastic bags for 1–2h. Leaf water content was measured every 3–5 min before bagging and every 10 min in the dark. Hydraulic conductivity and xylem cavitation were measured both in the open and in the dark. Cavitation was monitored as ultrasound acoustic emissions (AE). A critical Ψ_l value of -0.96 MPa was found, at which AE increased significantly while the leaf water deficit decreased by gain of water. Since the twigs were no longer attached to roots, it was concluded that water expelled from cavitated xylem conduits was transported to the leaves, thus contributing to their rehydration. Xylem cavitation is discussed in terms of a ‘leaf water deficit buffer mechanism’, under not very severe water stress conditions.