Dynamics of large wood in an eastern U.S. mountain stream

Large wood (LW) is an important feature in many streams in northeastern North America, yet the dynamics (recruitment, movement, and export) of large wood remain largely undocumented for streams in this region. In this study we quantify the dynamics of LW in 400 m of a second-order, high gradient, boulder-dominated stream in the eastern Adirondack Mountains, NY. Characteristics and location of all LW (>1-m length, >10-cm diameter) in the 400-m study reach were initially recorded and pieces were individually tagged in November 2000. Subsequent surveys were conducted in late summer/fall of 2001, 2003, and 2004. Twenty-six% of the 112 pieces of LW initially tagged moved 5.0 m or more during the 4 years of this study. Mobile wood was, on average, shorter than non-mobile wood. Nearly all mobile wood was shorter than the 8.0-m bankfull width of the stream. From 2000 to 2004, 2.16 m³ (0.54 m³ 100 m⁻¹; 43 pieces) of LW entered the study reach and 0.7 m³ (0.18 m³ 100 m⁻¹; 13 pieces) left the stream. Retention of wood in debris dams was key to reducing potential export. For this stream, located within a second-growth mixed northern hardwood riparian forest that is approaching maturity, the net wood accumulation rate was estimated as ranging from 0.09 to 0.15 m³ 100 m⁻¹ year⁻¹. Our data support previous observations that LW length strongly influences its potential to move in high gradient streams, though debris dams can reduce LW movement rates and movement distances for wood of all sizes.     

基于SLAF-seq技术的红心火龙果SNP位点开发及遗传分析

为分析不同品种红心火龙果的遗传关系,本研究采集国内14种红心火龙果品种,通过生物信息学分析进行实验方案的系统设计,将所提取基因组进行酶切,筛选特异长度的DNA片断,构建SLAF-seq文库后进行高通量测序,将获得的序列进行分析比较后得到多态SLAF标签,在此标签基础上进一步开发特异性SNP位点,最后建立14种红心火龙果品种的进化树。本研究共开发159 560个SLAF标签,样品的平均测序深度为5.26×;共得到120 294个群体SNP,其中高一致性的群体SNP 51 859个。12种红心火龙果聚类结果发现,样品1、2、6、8、10同缘关系相近;样品3、5、7、9同缘关系相近;样品4、14同缘关系相对较近。研究表明应用SLAF-seq技术开发分子标记的效率比ISSR、RAPD、AFLP等常规技术更高。12种红心火龙果的聚类结果从基因组水平揭示不同地区品种之间的遗传分化关系,为火龙果种质的保护和遗传改良提供参考。     

Growth and survival of the scallop Lyropecten (=Nodipecten) nodosus (L. 1758) in suspended culture in the Cariaco Gulf (Venezuela) during a non-upwelling period

Growth and survival of the scallop Lyropecten nodosus were studied in 1997 at two sites (inner and outer Turpialito Bay) during a non‐upwelling period normally occurring between August and November. Individuals had an initial shell height of 4.86 cm (SD=1.64 cm). Both experimental groups were held in suspended plastic baskets at the same depth (4 m). Measurements of shell height and dry weights of shell, gonad, digestive gland, remaining tissues and shell biofouling were taken at monthly intervals. Environmental parameters, including temperature, phytoplanktonic biomass, total particulate material (TPM) and associated organic (POM) and inorganic (PIM) fractions, were recorded simultaneously. At the end of the study, significant differences in growth and survival of scallops were observed between the two experimental sites. Scallops maintained inside the bay showed a 22% greater increase in shell height (7.41±0.27 cm) than those placed outside the bay (6.37±0.41 cm). Survival of scallops inside the bay was 31% higher compared with scallops outside. The greater availability of food of phytoplanktonic origin during the first two experimental months (July and August) together with greater POM throughout the whole experimental period except September, at the inner bay site, probably explained survival and growth differences observed between the two locations. Results suggest that, during the non‐upwelling period (characterized by low primary productivity and high water temperatures), POM of sedimentary origin may play an important role as an energy source required for metabolic and reproductive activities of L. nodosus.     

Effect of soil humus cover on the establishment and development of mycorrhiza on containerised pinus sylvestris L. and pinus contorta ssp. latifolia Engelm. after outplanting

The presence of humus was evaluated as a factor affecting the establishment and development of mycorrhiza in Scots pine (Pinus sylvestris L.) and lodgepole pine (Pinus contorta ssp. latifolia Engelm.) during the first growing season after outplanting on two clear‐cut sites. Humus proved to be of minor importance for the formation of mycorrhizae. Instead, the colonisation showed a patchy pattern, indicating spatial variation in the amounts of active inoculum. This variation may reflect differences in soil microhabitat and perhaps the mycorrhizal distribution in the logged stands. Total mycorrhizal short‐root frequency increased from 10% at outplanting in June to 40–65% in October. The nursery mycorrhiza accounted for 80–95% of the total mycorrhiza at the end of the investigation. However, by this time 60–90% of the seedlings had, to some extent, indigenous mycorrhiza with fungi from the clear‐cut sites. Piloderma croceum tended to be formed at a higher rate in the presence of humus than in its absence while another mycorrhizal type increased faster in the mineral soil.     

Effect of density of riparian vegetation on effective tractive force

This study aims to clarify the effect of density of riparian vegetation on effective tractive force for various bedload transport conditions. Hydraulic model experiments were performed using a straight channel, and the methods used to calculate the effective tractive force necessary for estimating bedload transport rate in channels with riparian vegetation were studied. An apparatus was developed to directly measure the effective tractive force in a channel with riparian vegetation. Applying the apparatus in a hydraulic experiment allowed accurate direct measurement of effective tractive force, formerly estimated indirectly. Based on the experimental results, the effect of the density of vegetation on the effective tractive force was examined. Then the methods for estimating effective tractive force and bedload transport rate were studied. As a result of the experiment, it was found that the coefficient of velocity U/U_* and the ratio of coefficient of velocity (U/U_*)/(U/U_*) are negatively correlated with the density of vegetation. A very high negative correlation was also obtained between recession coefficient of effective tractive force ( = effective tractive force of a flow with riparian vegetation/effective tractive force of a flow with no riparian vegetation) and the density of vegetation. The friction factor of the channel bed f was positively correlated with the density of vegetation. Methods were presented for accurately estimating effective tractive force using equations including the relationships of the density of vegetation to the coefficient of velocity, the ratio of the coefficient of velocity, and the recession coefficient of effective tractive force. Using the estimated effective tractive force and an existing bedload equation enabled very accurate calculation of bedload transport rate in flows through riparian vegetation. The methods presented in this study have potential to be developed as a tool that can provide guidance in the planning and designing of riparian vegetation that are intended for the prevention and mitigation of floods and resultant sediment transportation.     

Revisiting the relationship between common weather variables and loblolly–shortleaf pine seed crops in natural stands

Seed production was monitored during24 years using seed-collection traps inloblolly–shortleaf pine (Pinus taeda L.–P.echinata Mill.) stands located in southeast Arkansas,north-central Louisiana, and southwest Mississippi onthe southeastern Coastal Plain, USA. Sound seedproduction was correlated with mean monthlyprecipitation and temperature from National Oceanicand Atmospheric Administration weather stationslocated near the seed-collection areas to determinethe potential of weather factors in forecasting pineseed crops. Correlations were restricted to threecritical periods in the pine reproductive cycle –strobili primordia differentiation, pollination, andfertilization. The most important (P 0.05)variables correlated with pine seed production for combined locations were cumulative precipitation (r = +0.60) during July, August, and September at 27 to 25 months before seed dispersal and mean temperature (r = –0.45) in August at 26 months before seed dispersal. Because multiple environmental factors can negatively impact pine seed development during the two yearsfollowing strobili primordia differentiation,seed-production forecasts based on weather variablesshould be verified by on-site cone counts during thesummer preceding autumn seed dispersal.     

A model for vertical distribution of fine roots in Robinia pseudoacacia plantations on the Loess Plateau

Based on a detailed investigation of vertical distributions of fine roots in Robinia pseudoacacia plantations at the Ansai Soil and Water Conservation Station, Shaanxi Province, a model was developed for the deep distribution of fine roots of R. pseudoacacia, which reflects the growth of fine roots affected by the mixed process of infiltration water and deep soil water. The maximum depth of the distribution h _max and the depth of the highest fine root density (FRD) h _p were determined and the maximum depth of infiltration water supplied for fine root growth h _q could also be calculated, h _q was considered as the approximate boundary between infiltration water and deep soil water in support of the growth of fine roots. According to the model, the soil water of R. pseudoacacia woodland in the profile could be classified into three layers: the first layer from the soil surface to h _p was the active water exchange layer, very much affected by precipitation; the second was the soil water attenuation layer, between h _p and h _q and largely affected by the vertical distribution of fine roots; the third was the relatively stable soil water layer below h _q, below which soil water did not change much. The percentage of infiltration water supplied for the growth of fine roots reached a level of 88.32% on the shaded slopes and 85.21% on sunny slopes. This indicated infiltration of precipitation played a crucial role in the growth of R. pseudoacacia in the gully region of the Loess Plateau. The research of interaction between the distribution of fine roots and soil water in the profile will help to explain the reasons for the complete drying out of soils and provide a theoretical basis for continuing the policy of matching tree species with sites on the Loess Plateau. Translated from Scientia Silvae Sinicae, 2006, 42(6): 40–48 [译自: 林业科学]     

The effects of selective logging on stand structure and the regeneration of subboreal forests in Hokkaido, northern Japan

We investigated the effects of selective logging on stand structure and regeneration in selectively logged subboreal forests in Taisetsuzan National Park in Hokkaido in northern Japan. The basal area decreased and the size structure of trees altered in the stands studied due to repeated, intense selective logging, in which larger trees were cut down as a priority. Sapling density in the stands was much lower than that in primary forests. In the simple and multiple regression analyses that were used to estimate the effects of selective logging on sapling density, sapling density had a significant positive correlation with tree density and had little correlation with the density of logged stumps or the height ofSasa (dwarf bamboo) growing on the forest floor. These results suggest that the establishment sites around canopy trees influenced the establishment of saplings, rather than the gaps caused by selective logging. However, both the coefficient of determination and the standardized partial regression coefficient of multiple regression analysis were higher for the stand with a dense cover ofSasa than for the stand with a sparse cover ofSasa. Thus, the success of regenerating forests with selective logging depends on both the site of advanced regeneration and the light conditions that regulate growth.     

Dissolved organic matter originating from the riparian shrub Salix gracilistyla

To estimate the importance of leaching of dissolved organic matter (DOM) as a pathway through which organic matter is supplied to stream ecosystems, we examined the amount of leachate over time and chemical properties of DOM leached from leaves in different conditions. The samples used were green leaves, yellow senescent leaves, and leaf litter of Salix gracilistyla Miq., which is the dominant riparian plant species in the middle reaches of rivers in western Japan. We analyzed dissolved organic carbon (DOC), total sugar, and polyphenol in the leachate of leaf samples collected from a fluvial bar in the middle reaches of the Ohtagawa River in Hiroshima Prefecture, Japan. Considerable leaching of DOC from senescent leaves [37.3 mg g⁻¹ dry weight (dw) leaf] and leaf litter (8.1 mg g⁻¹ dw leaf) occurred within 24 h after immersion. In contrast, DOC leached from green leaves was negligible until 1 week after leaf immersion. Carbon loss of leaves by leaching within 24 h after leaf immersion was estimated to be less than 8%, suggesting that leaching of DOC from S. gracilistyla leaves is a minor pathway through which organic matter is supplied to stream ecosystems. DOM leached from the leaves included sugar and polyphenol, which were among the major chemical forms of DOM leached from the leaves (based on the molecular mass). In a laboratory experiment in which the difference in the stability of DOM between the chemical forms was examined, sugar decomposed more rapidly than polyphenol.