Effects of Pre-Planting Soaking on Growth and Survival of Black Willow Cuttings

Black willow (Salix nigra) uses periodic flood events for dispersal of vegetative propagules, subjecting them to periods of soaking before their deposition along the streambank. It was hypothesized that this life history trait results in optimal conditions for willow growth and survival. To test this hypothesis, a greenhouse experiment was conducted using 1.2‐m‐long black willow cuttings (posts) with a basal diameter of 5 cm. Cuttings were subjected to three soaking treatments (0, 3, and 10 days) and then grown under four soil moisture regimes (control, drought, permanently flooded, and intermittently flooded). Growth, biomass, and survival were recorded. Results showed that soaking posts for 10 days was most beneficial in the control soil moisture regime, enhancing root, shoot, leaf, and total biomass production. Shoot abundance and growth were also enhanced by 10 days of soaking in the control and permanently flooded moisture regimes. Finally, survival increased significantly in control and drought moisture regimes in response to the 10‐day soaking treatment. Results clearly demonstrated that soaking had significant effects on willow post success when evaluated across all soil moisture regimes. Posts subjected to the 10‐day soaking treatment consistently had greatest growth and biomass and displayed a doubling of the survival rate. Therefore, soaking willow cuttings before planting is a simple, inexpensive technique that may be used to bolster streambank restoration success.     

Growth Response of Coyote Willow (Salix exigua) Cuttings in Relation to Alluvial Soil Texture and Water Availability

A common approach to re‐establishing cottonwood–willow habitat along regulated rivers is through installing dormant, rootless cuttings, yet there is little published information exploring floodplain characteristics that optimize growth of southwestern riparian willows planted in this manner. The goal of this project was to evaluate relationships between growth attributes of Salix exigua and soil texture and soil water availability. Monitoring plots were established in five willow swales planted with dormant S. exigua cuttings along the banks of the Middle Rio Grande in central New Mexico. Data analysis revealed significantly higher aerial cover, height, and stem density for S. exigua plants installed in plots with intermediate levels (15–25%) of fine textured soils distributed through the soil profile. Similar relationships were found in relation to soil water availability. Regression analysis of percent fines and available water at different depth increments provided limited explanation of variability in willow growth attributes at different plots. Findings indicate that S. exigua plants established from cuttings can achieve heights and aerial cover values similar to naturally established willow bars if the floodplain soil profile contains intermediate levels of fine textured soils and the maximum depth to groundwater is within 1.5 m of the ground surface. Where sites are dominated by coarse sand, S. exigua growth may be improved if maximum depth to groundwater is within 1 m of the ground surface.     

Taming the Beast: Managing Hydrology to Control Carolina Willow (Salix caroliniana) Seedlings and Cuttings

Historically, wetlands along the St. Johns River, Florida, were dominated by herbaceous marshes. However, in the last 50 years many areas transformed to shrub‐dominated wetlands, at the same time a system of levees and canals was constructed to control flooding. We tested the role of water management in controlling Carolina willow (Salix caroliniana), a native shrub that accounts for most of this shift. We assessed survival and growth of seedlings and cuttings on four artificial islands. We planted willow seedlings and cuttings at the spring waterline and at three higher levels (+17.5, +35, and +50 cm) and evaluated their responses to natural hydrologic fluctuations. Overall, seedlings had lower survival than cuttings. Highest mortality occurred during summer floods and willows greater than 50 cm above marsh surface had the highest survivorship. Surviving seedlings attained similar height and biomass among elevations, but the cuttings had greater stem diameter, stem height, and biomass at higher elevations. In the second experiment, we planted seedlings and short (25 cm) and tall (50 cm) cuttings at the waterline and at three higher levels (+25, +35, and +50 cm) in artificial ponds with controlled water levels. Before flooding, seedlings at the highest elevation suffered some mortality due to desiccation, but after flooding, they had the highest survival. Elevation did not affect cutting survival, but those at the lowest elevation had the greatest height and biomass. Hydrologic manipulation can be a powerful tool to control willow establishment. However, its success depends on timely and prolonged inundation or water drawdown .     

Canopy manipulations of exotic Bitter Willow (Salix elaeagnos) forest for indigenous seedling recruitment: A pilot study

The invasive exotic tree species Bitter Willow (Salix elaeagnos; Salicaceae) has colonised areas of rank exotic grassland and has been found to contain indigenous seed, dispersed by frugivorous birds into the monospecific stands. This small pilot study examined whether indigenous seedlings that have germinated in the understorey of exotic Bitter Willow stands could be stimulated to establish through the creation of small‐scale canopy gaps. In Bitter Willow forest, four single Bitter Willow trees were poisoned to create canopy gaps. Light transmission and seedling regeneration of tree and shrub species were assessed beneath both the four manipulated and three comparable intact Bitter Willow canopies. Over 3 years, seedling height and density increased more beneath opened compared to intact Bitter Willow canopies. These results suggest that Bitter Willow can fill the roles of both a facilitative nurse and a perch tree. Larger‐scale canopy manipulation experiments of both Bitter Willow and other Salix species are needed to determine the full potential of canopy manipulations for forest restoration.     

酸枣叶对土壤水分的生理生化响应

酸枣(Ziziphus jujuba var.spinosa)分布广、适应性强、极耐旱,是研究植物响应干旱气候的优良试验材料。通过覆膜技术控制酸枣根系附近土壤水分含量,研究了不同土壤水分条件对酸枣叶片组织含水量、叶绿素含量、丙二醛、可溶性糖含量等生理生化指标的影响,以期探明酸枣适应干旱的生理机制。结果显示：随着土壤含水量的降低,处理组酸枣叶片的相对含水量与绝对含水量均降低,但都保持在较高水平,与对照相比,差异显著（p<0.05）;自然饱和亏呈下降趋势且维持在较低水平,较对照差异均显著（p<0.05）;随着土壤水分的减少,处理组酸枣叶片较对照组组织水势和渗透势减小（p<0.05）,较对照差异显著（p<0.05）,吸水能力提高;处理组酸枣叶片的叶绿体色素含量随土壤干旱程度的加深,均表现为低于对照且逐渐减少（p<0.05）;随着处理时间的延长,处理组与对照组相比,电导率随之增大,MDA含量也随之升高,质膜受到损伤;处理组酸枣叶片中渗透调节物质可溶性糖含量和游离脯氨酸含量均有不同程度的增加,平均增幅为1.29、1.5倍。结果表明,酸枣叶片在不同的土壤水分条件下,具有积极的生理响应方式,适应性强,具有较强的抗旱耐旱能力。     

Plant and Soil Responses to Created Microtopography and Soil Treatments in Bottomland Hardwood Forest Restoration

Although microtopographic heterogeneity is common in bottomland hardwood forests, it is rarely considered in bottomland restoration efforts. The objective of this study was to determine the responses of hydrologic condition, soil physiochemical properties, and introduced and colonizing vegetation to created microtopography and soil treatments at a landfill borrow pit in northern Texas. A series of mounds and pools were created and planted with fast‐growing pioneer species as well as more desirable, later‐successional species. Erosion control mats were installed on half the plots as a source of organic matter. Erosion control mats had little influence on introduced seedling survival or colonizing species abundance, but microtopography strongly influenced hydrologic condition, soil properties, seedling survival and growth, and colonizing species abundance and distribution. Pools were flooded during much of the summer months and had significantly higher nitrate and total nitrogen concentrations than mounds. Topographic position had little effect on survival of pioneer species, but mortality of most later‐successional species was highest in pools. Colonizing species distribution and abundance were also strongly related to topographic position. Despite differences in soil nutrient concentration among topographic zones, hydrologic condition likely had the strongest influence on growth and survival of planted species and distribution of colonizing species. Creating microtopography resulted in a spatially heterogeneous system that reflected variations in natural bottomlands, and introducing a mix of species (pioneer and later‐successional) across topographic and hydrologic gradients may improve the establishment and survival of a diverse community when hydrologic condition is highly variable or difficult to predict.     

Structure of two macrolepidopteran assemblages on Salix nigra (Marsh) and Acer negundo L.: abundance,diversity, richness,and persistence of scarce species

1. Most insect species occur at low abundance but a greater research effort has been devoted to so‐called outbreak species and little research is available on scarce (low abundance) species that are typical of most insect species. 2. Larval free‐feeding macrolepidoptera of two riparian trees Salix nigra (Marsh) (black willow) and Acer negundo L. (box elder) were sampled and sorted by species and abundance. 3. Data collected established that the majority of species in the assemblages in each tree species occurred at low abundance in each of the 5 years when larvae were sampled. 4. Species in the Noctuidae and Geometridae dominated both assemblages. 5. On both trees, assemblages were dominated numerically by relatively few species, a pattern that has been observed for insect assemblages on plants in managed and unmanaged habitats.     

Mapping Grey Willow (Salix cinerea) stand architecture using airborne laser scanning: implications for large‐scale tree weed control

We investigated the potential of airborne laser scanning (ALS) for mapping the stand architecture of Grey Willow (Salix cinerea), an invasive wetland weed in New Zealand. In particular, we focused on two metrics, tree height and canopy density, both of which influence the efficacy and nontarget impacts of herbicides aerially broadcast by helicopter to control tree weeds. We compared ground‐based measures of Grey Willow height and canopy density with ALS‐derived data, and the relationship between canopy density as estimated by each method and aerial herbicide deposition at three wetland sites in New Zealand. Analysis revealed strong linear relationships between ground‐based and ALS metrics, indicating that ALS data could be used to generate accurate, high‐resolution digital maps of Grey Willow height and canopy density. These maps coupled with computer‐guided variable flow rate technologies, which enable optimal placement of herbicide, could maximise Grey Willow mortality while reducing the mortality of nontarget indigenous plants. We recommend the application of ALS‐derived maps and computer‐guided variable flow rate technology is investigated for more targeted large‐scale tree weed control.     

Physiological and Proteomic Responses of Different Willow Clones (Salix fragilis X alba) Exposed to Dredged Sediment Contaminated by Heavy Metals

High biomass producing species are considered as tools for remediation of contaminated soils. Willows (Salix spp.) are prominent study subjects in this regard. In this study, different willow clones (Salix fragilis x alba) were planted on heavy-metal polluted dredging sludge. A first objective was assessment of the biomass production for these clones. Using a Gupta statistic, four clones were identified as high biomass producers (HBP). For comparison, a group of four clones with lowest biomass production were selected (LBP). A second objective was to compare metal uptake as well as the physiological and proteomic responses of these two groups. All these complementary data's allow us to have a better picture of the health of the clones that would be used in phytoremediation programs. Cd, Zn, and Ni total uptake was higher in the HBPs but Pb total uptake was higher in LBPs. Our proteomic and physiological results showed that the LBPs were able to maintain cellular activity as much as the HBPs although the oxidative stress response was more pronounced in the LBPs. This could be due to the high Pb content found in this group although a combined effect of the other metals cannot be excluded.     

不同土壤水分条件下小叶扶芳藤叶片光合作用对光的响应

利用CIRAS-2型便携式光合作用仪测定不同土壤水分下3年生小叶扶芳藤(Euonymus fortunei var.radicans Sieb.)叶片净光合速率(Pn)、蒸腾速率(Tr)、水分利用效率(WUE)及光能利用效率(LUE)等生理参数,阐明其光合生理参数对土壤水分和光照强度的响应规律,探讨小叶扶芳藤正常生长发育所需的土壤水分和光照条件.结果表明小叶扶芳藤的Pn、Tr、WUE及LUE对土壤水分和光照强度的变化具有明显的阈值.(1)采用非直角双曲线模型进行模拟光响应过程较好,在土壤相对含水量(RWC)为72.2%和32.3%时,曲角(K)值较小;在其它水分条件下,K值接近于1.随着土壤水分(RWC为22.4%～72.2%)的递增,光补偿点降低,光饱和点、最大净光合速率及表观量子效率均呈现升高趋势,在RWC为72.2%时,光补偿点最低(22.6 μmol·m-2·s-1),光饱和点最高(1 400μmol·m-2·s-1).(2)维持小叶扶芳藤正常生长(同时具有较高Pn、LUE及WUE)的土壤水分范围,在RWC为44.2%～72.2%之间,最佳土壤水分在RWC为72.2%左右,正常生长所允许的最低土壤水分在RWC为32.3%左右.(3)小叶扶芳藤对光照环境的适应性较强,在光合有效辐射强度为600～1 600 μmol·m-2·s-1范围内,Pn和WUE都具有较高水平,饱和光强大约在800～1 400 μmol·m-2·s-1之间,LUE在100～300 μmol·m-2·s-1光强范围内达到峰值.     

The role of reproductive phenology, seedling emergence and establishment of perennial Salix gordejevii in active sand dune fields

BACKGROUND AND AIMS: The function of sexual reproduction of perennials in restoration of vegetation of active dune fields frequently has been underestimated. The objective of this study was to evaluate the role of sexual reproduction of the perennial Salix gordejevii in the revegetation of active dunes. METHODS: Seedling emergence and establishment of S. gordejevii were examined both in controlled experiments (germination at different burial depths with different watering regimes) and in field observations in three dune slacks. The reproductive phenology and soil seed bank of S. gordejevii, the dynamics of soil moisture, the groundwater table and the landform level of three dune slacks were monitored. KEY RESULTS: Seeds of S. gordejevii began maturation on 1 May, and seed dispersal lasted from 8 May to 20 May. Seeds on the soil surface germinated significantly faster than those buried in soil (P<0.05). Seedling emergence was negatively correlated with landform level. When most seedlings emerged, there was a significantly positive correlation between soil moisture and seedling emergence (P<0.01). Rainfall was negatively correlated with seedling emergence. Seedling establishment was significantly and positively correlated with seedling emergence (P<0.05), and 72.3 % of the emergent seedlings were established at the end of the growing season. These results indicated that (a) seeds matured and dispersed before the rainy season; (b) seeds germinated as soon as they contacted a moist surface and relied more on soil moisture than on rainfall; and (c) more seedlings emerged at lower sampling points in dune slacks. CONCLUSIONS: In natural conditions, restoration of active sand dune fields generally commences with revegetation of dune slacks where sexual reproduction of perennials contributes greatly to species encroachment and colonization and hence plays an important role in restoration of active dune fields. Furthermore, aeolian erosion in dune slacks, leading to good soil moisture, facilitates seed germination, seedling emergence and establishment of S. gordejevii.     

土壤水分对高山红景天生长和红景天甙含量的影响

温室中3种土壤水分条件(土壤相对含水量分别为35％～55％、55％～75％和75％～95％)下,以55％～75％土壤相对含水量上生长的高山红景天的株高、生物量、红景天甙含量和产量最高。     

沙打旺种群对土壤水分的影响及其调节

一、前言结合沙打旺种群地上部分生物量形成的研究,观测了2—7年生沙打旺改良草地的土壤水分变化情况,以探索沙打旺种群对土壤生态环境的影响及调节因子。     

Phytoremediation of Metal Contaminated Soil Using Willow: Exploiting Plant-Associated Bacteria to Improve Biomass Production and Metal Uptake

Short rotation coppice (SRC) of willow and poplar is proposed for economic valorization and concurrently as remediation strategy for metal contaminated land in northeast-Belgium. However, metal phytoextraction appears insufficient to effectuate rapid reduction of soil metal contents. To increase both biomass production and metal accumulation of SRC, two strategies are proposed: (i) in situ selection of the best performing clones and (ii) bioaugmentation of these clones with beneficial plant-associated bacteria. Based on field data, two experimental willow clones, a Salix viminalis and a Salix alba x alba clone, were selected. Compared to the best performing commercial clones, considerable increases in stem metal extraction were achieved (up to 74% for Cd and 91% for Zn). From the selected clones, plant-associated bacteria were isolated and identified. All strains were subsequently screened for their plant growth-promoting and metal uptake enhancing traits. Five strains were selected for a greenhouse inoculation experiment with the selected clones planted in Cd-Zn-Pb contaminated soil. Extraction potential tended to increase after inoculation of S. viminalis plants with a Rahnella sp. strain due to a significantly increased twig biomass. However, although bacterial strains showing beneficial traits in vitro were used for inoculation, increments in extraction potential were not always observed.     

The Role of Light and Soil Moisture in Plant Community Resistance to Invasion by Yellow Starthistle (Centaurea solstitialis)

To resist establishment by an invasive plant, a community may require one or more species functionally similar to the invader in their resource acquisition pattern. In this study, communities consisting of native winter annual forbs, non‐native annual grasses, native perennials, or a combination of the two native communities were established with and without Centaurea solstitialis to determine the effect of soil moisture and light availability on plant community invasion resistance. The annual plant communities were unable to resist invasion by C. solstitialis. In the native winter annual forb community, senescence in late spring increased light penetration (>75%) to the soil surface, allowing seeded C. solstitialis to quickly establish and dominate the plots. In addition, native annual forbs utilized only shallow soil moisture, whereas C. solstitialis used shallow and deep soil moisture. In communities containing native perennials, only Elymus glaucus established well and eventually dominated the plots. During the first 2 years of establishment, water use pattern of perennial communities was similar to native annual forbs and resistance to invasion was associated with reduced light availability during the critical stages of C. solstitialis establishment. In later years, however, water use pattern of perennial grass communities was similar or greater than C. solstitialis‐dominated plots. These results show that Central Valley grasslands that include E. glaucus resist C. solstitialis invasion by a combination of light suppression and soil water competition. Spatiotemporal resource utilization patterns, and not just functional similarity, should be considered when developing restoration strategies to resist invasion by many non‐native species.     

Effect of Soil Depth and Moisture on the Vertical Distribution of Steinernema riobrave (Nematoda: Steinernematidae)

The effect of soil moisture on the distribution of Steinernema riobrave in a sand column was determined. Larvae of Pectinophora gossypiella were used to detect S. riobrave infective juveniles (IJ) in each 2.5-cm section of 30-cm-long soil columns. Soil moisture was determined for each section and related to the numbers of nematodes recovered from infected insect baits. Infective juveniles of S. riobrave applied on the sand column surface showed some degree of positive geotaxis. IJ in soil columns with a consistent moisture gradient grouped in the upper 12.7 cm within a water potential range of ¯40 to ¯0.0055 MPa (2% to 14% moisture). Nematodes in sand columns that were gradually dehydrating moved down the soil column, aggregating on the 28th day between 15-23 cm in depth. Nematode redistribution over time allowed IJ to remain within a water potential range of ¯0.1 to ¯0.012 MPa (5.2% to 9.5% moisture).     

Rust disease (Melampsora epited) of willow (Salix spp.) grown as short rotation coppice (SRC) in inter- and intra-species mixtures

Twenty inter‐ and intra‐species genotypes of willows (Salix spp.) were grown in large mono‐plots and incorporated into five, 10,15 and 20–way mixtures. In each growing season from 1996 to 2001 the level of rust disease caused by Melampsora epitea was recorded on each genotype where it was growing as a mono‐plot or as part of a mixture. Three genotypes, S. schwerinii×viminalis×dasyclados’V7531′, S. schwerinii×aquatica‘V7533’ and S. viminalis‘Gigantea’ remained virtually rust free through the six yr of the trial. It is, however, argued that there are benefits of including such genotypes in a mixture in order to reduce the risk of them developing rust susceptibility. S. burjatica‘Germany’, S. dasyclados×aquatica‘V7511’ and S. dasyclados×caprea‘V794’ were severely affected by rust, although levels tended to be less when included in mixtures. The levels of rust on S. mollissima‐undulata‘SQ83’ were much higher in the first three‐year harvest cycle than during the second cycle. On a number of genotypes, e.g. S. burjatica‘Germany’ and S. dasyclados×aquatica‘V7511’ rust was more severe on the regrowth from freshly coppiced stools.     

Differentiation of metallicolous and non‐metallicolous Salix caprea populations based on phenotypic characteristics and nuclear microsatellite (SSR) markers

The Salicaceae family comprises a large number of high‐biomass species with remarkable genetic variability and adaptation to ecological niches. Salix caprea survives in heavy metal contaminated areas, translocates and accumulates Zn/Cd in leaves. To reveal potential selective effects of long‐term heavy metal contaminations on the genetic structure and Zn/Cd accumulation capacity, 170 S. caprea isolates of four metal‐contaminated and three non‐contaminated middle European sites were analysed with microsatellite markers using Wright's F statistics. The differentiation of populations North of the Alps are more pronounced compared to the Southern ones. By grouping the isolates based on their contamination status, a weak but significant differentiation was calculated between Northern metallicolous and non‐metallicolous populations. To quantify if the contamination and genetic status of the populations correlate with Zn/Cd tolerance and the accumulation capacity, the S. caprea isolates were exposed to elevated Cd/Zn concentrations in perlite‐based cultures. Consistent with the genetic data nested anova analyses for the physiological traits find a significant difference in the Cd accumulation capacity between the Northern and Southern populations. Our data suggest that natural populations are a profitable source to uncover genetic mechanisms of heavy metal accumulation and biomass production, traits that are essential for improving phytoextraction strategies.     

Dependence of Soil Respiration on Soil Temperature and Soil Moisture in Successional Forests in Southern China

The spatial and temporal variations in soil respiration and its relationship with biophysical factors In forests near the Tropic of Cancer remain highly uncertain. To contribute towards an Improvement of actual estimates, soil respiration rates, soil temperature, and soil moisture were measured In three successional subtropical forests at the Dlnghuahan Nature Reserve （DNR） In southern China from March 2003 to February 2005. The overall objective of the present study was to analyze the temporal variations of soil respiration and Its biophysical dependence in these forests. The relationships between biophysical factors and soil respiration rates were compared In successional forests to test the hypothesis that these forests responded similarly to biophysical factors. The seasonality of soil respiration coincided with the seasonal climate pattern, with high respiration rates in the hot humid season （April-September） and with low rates In the cool dry season （October-March）. Soil respiration measured at these forests showed a clear Increasing trend with the progressive succession. Annual mean （± SD） soil respiration rate In the DNR forests was （9.0 ± 4.6） Mg CO2-C/hm^2 per year, ranging from （6.1 ± 3.2） Mg CO2-C/hm^2 per year in early successional forests to （10.7 ± 4.9） Mg CO2-C/hm^2 per year in advanced successional forests. Soil respiration was correlated with both soil temperature and moisture. The T/M model, where the two biophysical variables are driving factors, accounted for 74%-82% of soil respiration variation In DNR forests. Temperature sensitivity decreased along progressive succession stages, suggesting that advanced-successional forests have a good ability to adjust to temperature. In contrast, moisture Increased with progressive succession processes. This increase is caused, in part, by abundant respirators In advanced-successional forest, where more soil moisture is needed to maintain their activities.