Axis differentiation in two South American Nothofagus species (Nothofagaceae)

An analysis was carried out on the length, diameter and number of leaves, and the ratios between these variables for current-year growth units (sibling growth units) derived from different nodes of previous-year growth units (parent growth units) of young Nothofagus dombeyi and Nothofagus pumilio trees. Changes in sibling growth unit length, diameter, and number of leaves with position on the parent growth unit were assessed. In both species, sibling-growth unit morphology varied according to both the axis type of the parent growth unit and the position of the sibling growth unit on its parent growth unit. For the largest parent growth units, the length, diameter and number of leaves of their sibling growth units decreased from distal to proximal positions on the parent growth unit. Distal sibling growth units had a more slender stem and longer internodes than proximal sibling growth units. Sibling growth units in equivalent positions tended to have a more slender stem for N. dombeyi than for N. pumilio. Long main-branch growth units of N. pumilio had longer internodes than those of N. dombeyi; the converse was true for shorter growth units. The growth unit diameter/leaf number ratio was consistently higher for N. pumilio than for N. dombeyi. Nothofagus pumilio axes would go through a faster transition from an 'exploring' morphology to an 'exploiting' morphology than N. dombeyi axes. Within- and between-species variations in growth unit morphology should be considered when assessing the adaptive value of the branching pattern of plants.     

黑石顶自然保护区南亚热带常绿阔叶林的凋落物

分析了黑石顶自然保护区南亚热带常绿阔叶林凋落物的季节变化及１８种常见种的落叶规律．结果表明凋落物有明显的季节变化,４ａ平均凋落量为４．６３０ｔ·ｈｍ－２·ａ－１．凋落物具体峰值出现的时期有一定程度的年际变化,雨季的４～９月和旱季的１０～３月各有一个高峰期．植物的落叶习性是适应外界环境变化的反映,根据不同种凋落叶高峰出现的时期可将植物分为３种不同类型．     

Cellulase and polygalacturonase involvement in the abscission of leaf and fruit explants of peach

Ethylene-induced abscission in leaf and fruit explants of peach involves different enzymes. In leaves abscission is accompanied by increased occurrence of cellulase forms differing in isoelectric point (pI 6.5 and 9.5). A polypeptide with a molecular mass of 51 kDa gives in a western blot a strong cross-reaction with an antibody raised against a maturation cellulase from avocado fruit. Cellulase activity is also found in abscising fruit explants but the amount is very low compared to that of the leaf explants. A northern analysis with a cellulase clone from avocado reveals the presence of two hybridizing mRNAs with a size of 2.2 kb and 1.8 kb, respectively. The steady-state level of the 2.2 kb mRNA is significantly increased by treatment with ethylene.Polygalacturonases are not detected in abscising leaves, but are strongly induced by ethylene in fruit explants. Of the three forms found, two are exopolygalacturonases while the third is an endoenzyme. Ethylene activates preferentially the endoenzyme and the basic exoenzyme but depresses the acid exopolygalacturonases. A northern analysis carried out with a cDNA coding for tomato endopolygalacturonase shows hybridization only with one endopolygalacturonase mRNA from in the fruit abscission zone. Treatment with ethylene causes an increase in the steady-state level of this mRNA. The differences in the enzyme patterns observed in fruit and leaf abscission zones and a differential enzyme induction suggest the feasibility to regulate fruit abscission in peach with the aid of antisense RNA genes.     

Detecting successional changes in long-term empirical data from subalpine conifer forests

The gap dynamics of two Nothofagus pumilio (lenga) stands have been investigated. We evaluated and compared tree diameter distributions, spatial patterns, tree fall and gap characteristics and regeneration responses in gaps in two old-growth forests of Nothofagus pumilio in Southern Chile (Shangri-La: 36°60 S, 71°30 W; Reserva Coyhaique: 45°52 S, 72°00 W). In addition, we describe relationships between gap size and regeneration characteristics. We detected some differences in tree and sapling densities between sites. The causes of gap formation and the gap size distribution, mean gap area, and gap fraction were similar, but gap abundance was different at the two sites. The Reserva Coyhaique site had 15 gaps/ha compared to 10 gaps/ha for Shangri-La. Sizes of clumps of trees were within the range of sizes of canopy gaps at both sites. The density of saplings was higher in gaps than under closed forest at R. Coyhaique, but not at Shangri-La. We found that sapling densities were unrelated to gap size in both sites. The lower sapling density in gaps at Shangri-La might be explained by the presence of Chusquea quila, a competitive pioneer bamboo species. The height increment was related to gap size at Shangri-La, but not at R. Coyhaique. Gap size itself does not account for all the variation in recruitment performance in these Southern beech stands.     

Trophic relationships of polychaetes associated with different algal growth forms

The trophic relations of the polychaete species associated with four different algal growth forms (filamentous, fan-shaped, bush-like and encrusting) were studied in the North Aegean Sea. Samples for the spatial analysis were collected in summer with a quadrate sampler (400 cm²) at a depth range of 15–40 m. Filamentous and encrusting forms were also seasonally sampled in order to detect the temporal changes. A total of 5,494 individuals belonging to 79 species were classified to 12 feeding guilds, considering the type of food, the feeding apparatus and the motility patterns involved. Carnivores dominated, followed by herbivores and filter-feeders, among all the algal forms studied, excepting the fan-shaped form where filter-feeders prevailed mainly due to a massive recruitment of spirorbids. With respect to the abundance of the various feeding guilds, filamentous and fan-shaped forms discriminated, whereas bush-like and encrusting forms showed high similarity. The occurrence of polychaete feeding guilds among both filamentous and encrusting forms showed seasonal changes, with summer and spring samples, respectively, discriminating. The results of the trophic group analysis conformed to previous information provided by a taxon composition analysis of the dominated by the same algae communities. However, a functional study can give additional information and is thus a useful tool for the study of hard bottom communities.     

Standardized diet compositions and trophic levels of skates (Chondrichthyes: Rajiformes: Rajoidei)

Skates by virtue of their abundance and widespread occurrence appear to play an influential role in the food webs of demersal marine communities. However, few quantitative dietary studies have been conducted on this elasmobranch group. Therefore, to better understand the ecological role of skates, standardized diet compositions and trophic level (TL) values were calculated from quantitative studies, and compared within and among skate and shark taxa. Prey items were grouped into 11 general categories to facilitate standardized diet composition and TL calculations. Trophic level values were calculated for 60 skate species with TL estimates ranging from 3.48 to 4.22 (mean TL = 3.80 ± 0.02 SE). Standardized diet composition results revealed that decapods and fishes were the main prey taxa of most skate species followed by amphipods and polychaetes. Correspondingly, cluster analysis of diet composition data revealed four major trophic guilds, each dominated by one of these prey groups. Fish and decapod guilds were dominant comprising 39 of 48 species analyzed. Analysis of skate families revealed that the Arhynchobatidae and Rajidae had similar TL values of 3.86 and 3.79 (t-test, P = 0.27), respectively. The Anacanthobatidae were represented by a single species, Cruriraja parcomaculata, with a TL of 3.53. Statistical comparison of TL values calculated for five genera (Bathyraja, Leucoraja, Raja, Rajella, Rhinoraja) revealed a significant difference between Bathyraja and Rajella (t-test, P = 0.03). A positive correlation was observed between TL and total length (L _T) with larger skates (e.g. >100 cm L _T) tending to have a higher calculated TL value (>3.9). Skates were found to occupy TLs similar to those of several co-occurring demersal shark families including the Scyliorhinidae, Squatinidae, and Triakidae. Results from this study support recent assertions that skates utilize similar resources to those of other upper trophic-level marine predators, e.g. seabirds, marine mammals, and sharks. These preliminary findings will hopefully encourage future research into the trophic relationships and ecological impact of these interesting and important demersal predators.     

Natural hybridization between a deciduous (Nothofagus antarctica, Nothofagaceae) and an evergreen (N. dombeyi) forest tree species: evidence from morphological and isoenzymatic traits

BACKGROUND AND AIMS: Trees with a partial leaf-shedding pattern and other morphological features a priori considered intermediate between those of the deciduous Nothofagus antarctica (G. Forster) Oersted and the evergreen N. dombeyi (Mirb.) Oersted (Nothofagaceae) were found in natural stands. The hybridization between a deciduous and an evergreen species of Nothofagus has not been reported so far in natural communities. METHODS: The putative hybrids and the two presumed parental species were compared using 14 enzyme systems as well as shoot, leaf and reproductive morphology. KEY RESULTS: Six enzyme systems showed good resolution (MDH-B, IDH, SKDH, 6-PGDH, GOT and PGI) and in four of them (PGI, MDH-B, SKDH and 6-PGDH) the putative hybrids showed intermediate zymogram patterns between N. antarctica and N. dombeyi. Both principal coordinates analysis on isozyme data and principal components analysis (PCA) on quantitative morphological traits of shoots and leaves separated both parental species and located the putative hybrids closer to N. antarctica than to N. dombeyi. In the PCA, the number of basal cataphylls and the length : width ratio of leaves were the variables most discriminating among shoots of the three entities. The putative hybrids were intermediate between both species regarding leaf vernation, outline and venation, variation in leaf shape (length/width) with position on the parent shoot and in staminate inflorescence and cupule morphology. For other morphological traits, the putative hybrids resembled one of the parental species or differed from both species (e.g. valve morphology). CONCLUSIONS: Isoenzymatic and morphological data sets support the idea of the hybrid nature (probably F1 generation) of the semi-deciduous trees found. Nothofagus antarctica and N. dombeyi are probably more closely related than previously assumed. The relevance of pollen type in revealing evolutionary relationships between Nothofagus species is supported, and that of leaf-shedding pattern is rejected.     

小兴安岭三种林型叶面积指数的估测

利用Winscanopy2006冠层分析仪测定2009年7月初至11月初小兴安岭白桦次生林、谷地云冷杉林、阔叶红松林的有效叶面积指数(LAIe),并将经过木质部分所占比率、冠层水平集聚和簇内集聚校正的11月初LAIe作为真实叶面积指数(LAIt),结合凋落物法测定3种林型的LAIt及其季节动态.结果表明:调查期间,白桦次生林的LAIe在7月达到峰值(2.21),谷地云冷杉林、阔叶红松林的LAIe在8月达到峰值,分别为2.57、2.68.白桦次生林、谷地云冷杉林、阔叶红松林的LAIt均在7月达到峰值,分别为3.44、3.86、6.93;相对于本文探讨的方法,光学仪器所测定的LAIe在最高叶面积指数期分别低估33.1％、32.9％、66.0％;而在整个调查期内,谷地云冷杉林和阔叶红松林LAIe平均低估22.8％和56.5％,白桦次生林平均高估13.2％.     

小兴安岭三种林型叶面积指数的估测

利用Winscanopy2006冠层分析仪测定2009年7月初至11月初小兴安岭白桦次生林、谷地云冷杉林、阔叶红松林的有效叶面积指数(LAI_e),并将经过木质部分所占比率、冠层水平集聚和簇内集聚校正的11月初LAI_e作为真实叶面积指数(LAI_t),结合凋落物法测定3种林型的LAI_t及其季节动态.结果表明： 调查期间,白桦次生林的LAI_e在7月达到峰值(2.21),谷地云冷杉林、阔叶红松林的LAI_e在8月达到峰值,分别为2.57、2.68.白桦次生林、谷地云冷杉林、阔叶红松林的LAI_t均在7月达到峰值,分别为3.44、3.86、6.93;相对于本文探讨的方法,光学仪器所测定的LAI_e在最高叶面积指数期分别低估33.1%、32.9%、66.0%;而在整个调查期内,谷地云冷杉林和阔叶红松林LAI_e平均低估22.8%和56.5%,白桦次生林平均高估13.2%.
     

Temporal and spatial macrofaunal community changes along a salinity gradient in seagrass meadows of Akkeshi-ko estuary and Akkeshi Bay,northern Japan

Changes in water clarity (secchi disc transparency) in relation to the presence/absence of introduced, exotic fish, including rudd (Scardinius erythrophthalmus), tench (Tinca tinca), perch (Perca fluviatilis), brown bullhead catfish (Ameiurus nebulosus), goldfish (Carassius auratus), and koi carp (Cyprinus carpio) were determined for 49 small, North Island, New Zealand lakes. There was a negative association between water clarity and the presence of exotic fish independent of lake depth. Moreover, a ‘before-and-after’ comparison and examination of case-studies indicated that introductions of exotic fish reduce water clarity. The number of species introduced affected the relationship between lake depth and water clarity but the specific role of each species could not be distinguished because most of the lakes (83%) contained more than one exotic fish species. A model incorporating the known mechanisms by which planktivorous, benthivorous and herbivorous fish can influence water clarity in lakes showed that control over just one species or feeding guild may not result in an improvement in water clarity because of the additive and synergistic effects of different species on lake trophic processes. Handling editor J. Cambray