Agroforestry systems for the production of woody biomass for energy transformation purposes

In the temperate zone, agroforestry systems come increasingly into focus as they offer an approach for the production of fuelwood, thus matching the increasing demand for a self-supply with bioenergy in rural decentralized areas. Because of the large area potential of marginal land, research activities aimed at a reliable estimation of the minimum productivity of fast–growing tree species under most unfavourable site conditions.Two agroforestry systems were established on reclaimed mine sites in NE-Germany (Lusatia) and Central Germany (Helmstedt). The yield potential and the sustainability of yields were studied for different clones of poplar (Populus spp.), willow (Salix viminalis L.), and black locust (Robinia pseudoacacia L.), considering different rotation periods (3-, 6-, and 9-year-rotation) and approaches of soil amelioration (mineral fertiliser, compost).On both sites the highest yields of woody biomass were found for R. pseudoacacia L. regardless of rotation period and amelioration measures. On loamy substrates in the Helmstedt mining district, all tree species and clones responded positively to soil amelioration measures.In the agroforestry system in Lusatia, special emphasis was given to the interaction between trees (R. pseudoacacia) and crops (Medicago sativa L.). Considering the land equivalent ratio (LER), R. pseudoacacia hedgerows have practically no negative influence on yields of M. sativa. Hence, with regard to an increasing demand for woody biomass, alley cropping with R. pseudoacacia and crops such as M. sativa may provide a promising alternative for future land use in the temperate zone.     

Higher phenotypic plasticity does not confer higher salt resistance to <Emphasis Type="Italic">Robinia pseudoacacia</Emphasis> than <Emphasis Type="Italic">Amorpha fruticosa</Emphasis>

A greenhouse experiment was conducted in which two leguminous species commonly used in the Yellow River Delta for vegetation restoration, Robinia pseudoacacia and Amorpha fruticosa, were subjected to five salt treatments: 0, 50, 100, 150, and 200 mmol L^?1. We aimed to determine which of the two species would be better suited for growth in a saline environment, and whether the acclimation capacity to salinity resulted from an inherently higher phenotypic plasticity. The results showed that salinity affected most growth and biomass parameters but had no effects on most leaf traits and physiological parameters of the two species. Height, relative growth rate of crown area, root biomass, and leaf mass ratio of R. pseudoacacia were reduced by higher salinity, while A. fruticosa was not affected. Chlorophyll a-to-chlorophyll b ratio and total antioxidative capacity of A. fruticosa increased with higher salinity, whereas those of R. pseudoacacia remained unchanged. Root mass ratio and vitamin C concentration of both species were not affected by salinity, whereas vitamin C concentration of A. fruticosa was higher than that of R. pseudoacacia. The root-to-shoot ratio of A. fruticosa was higher than that of R. pseudoacacia in most salt treatments. Of all leaf traits, only leaf area differed between treatments. R. pseudoacacia generally exhibited a greater plasticity than A. fruticosa in response to salinity, but A. fruticosa was more resistant to the higher salinities than R. pseudoacacia, and was thus a better candidate for vegetation restoration in saline areas.     

Impacts of climate change on forest growth in saline-alkali land of Yellow River Delta,North China

Climate change is an important factor affecting forest growth. Therefore, approaching the impacts of climate change on forest growth is of great significance to ameliorate this degraded land and push up forestry development. This paper initially probes the impacts of climate change on tree growth in Yellow River Delta region and responds of different tree species on the change. In this study, five species of 22-year-old trees were selected, and the tree biomass was measured by standard site methods and tree ring sampling to pursue the impacts of climate change on forest growth. Besides, growth models of the different tree species were established and verified using Robinia pseudoacacia as an example. The results showed: (1) In the Yellow River Delta, the most adapted tree species are Fraxinus chinensis and R. pseudoacacia. (2) Precipitation is the main meteorological factor affecting tree growth, while temperature and air pressure are also significantly correlated with tree growth. (3) Linear and power function models can simulate tree growth well. From the verification results, the modified R. pseudoacacia biomass is 294.54 t/ha, and the simulated biomass of the linear function model is close to the value. It is expected that the research not only provides a theoretical basis for forestry development in saline lands, but also helps to rehabilitate saline-alkali lands and cope with climate change.     

Competition and soil fungi affect the physiological and growth traits of an alien and a native tree species

Competition plays an important role in the replacement of native species by alien plants. A greenhouse experiment was conducted to investigate whether the competition pattern of alien Robinia pseudoacacia L. and native Quercus acutissima Carr. is affected by soil sterilization. Physiological traits, such as gas-exchange parameters and chlorophyll (Chl) content, and growth traits, such as the biomass accumulation of the two species, were examined in natural soil or in soil sterilized with benomyl. The results show that native Q. acutissima inhibits the growth of R. pseudoacacia in natural soil. When the two plants coexisted and competed under sterilization treatment, R. pseudoacacia was less inhibited by Q. acutissima and the competition of R. pseudoacacia decreased the growth of Q. acutissima in terms of biomass, Chl a, Chl b, total Chl, and Chl a/b. These results suggest that soil sterilization benefits the growth of R. pseudoacacia and changes the competition pattern by the changed soil biota. Soil sterilization increased the biomass of root nodules, which ultimately benefits the growth of R. pseudoacacia and root nodule bacteria may be important in the dispersal and invasion process of nitrogen-fixing alien plants such as R. pseudoacacia.     

Drought enhances symbiotic dinitrogen fixation and competitive ability of a temperate forest tree

General circulation models project more intense and frequent droughts over the next century, but many questions remain about how terrestrial ecosystems will respond. Of particular importance, is to understand how drought will alter the species composition of regenerating temperate forests wherein symbiotic dinitrogen (N₂)-fixing plants play a critical role. In experimental mesocosms we manipulated soil moisture to study the effect of drought on the physiology, growth and competitive interactions of four co-occurring North American tree species, one of which (Robinia pseudoacacia) is a symbiotic N₂-fixer. We hypothesized that drought would reduce growth by decreasing stomatal conductance, hydraulic conductance and increasing the water use efficiency of species with larger diameter xylem vessel elements (Quercus rubra, R. pseudoacacia) relative to those with smaller elements (Acer rubrum and Liriodendron tulipifera). We further hypothesized that N₂ fixation by R. pseudoacacia would decline with drought, reducing its competitive ability. Under drought, growth declined across all species; but, growth and physiological responses did not correspond to species’ hydraulic architecture. Drought triggered an 80 % increase in nodule biomass and N accrual for R. pseudoacacia, improving its growth relative to other species. These results suggest that drought intensified soil N deficiency and that R. pseudoacacia’s ability to fix N₂ facilitated competition with non-fixing species when both water and N were limiting. Under scenarios of moderate drought, N₂ fixation may alleviate the N constraints resulting from low soil moisture and improve competitive ability of N₂-fixing species, and as a result, supply more new N to the ecosystem.     

Comparison of biomass production and total lipid content of freshwater green microalgae cultivated under various culture conditions

The growth and total lipid content of four green microalgae (Chlorella sp., Chlorella vulgaris CCAP211/11B, Botryococcus braunii FC124 and Scenedesmus obliquus R8) were investigated under different culture conditions. Among the various carbon sources tested, glucose produced the largest biomass or microalgae grown heterotrophically. It was found that 1 % (w/v) glucose was actively utilized by Chlorella sp., C. vulgaris CCAP211/11B and B. braunii FC124, whereas S. obliquus R8 preferred 2 % (w/v) glucose. No significant difference in biomass production was noted between heterotrophic and mixotrophic (heterotrophic with light illumination/exposure) growth conditions, however, less production was observed for autotrophic cultivation. Total lipid content in cells increased by approximately two-fold under mixotrophic cultivation with respect to heterotrophic and autotrophic cultivation. In addition, light intensity had an impact on microalgal growth and total lipid content. The highest total lipid content was observed at 100 μmol m^?2s^?1 for Chlorella sp. (22.5 %) and S. obliquus R8 (23.7 %) and 80 μmol m^?2s^?1 for C. vulgaris CCAP211/11B (20.1 %) and B. braunii FC124 (34.9 %).     

Drivers of invasive tree and shrub natural regeneration in temperate forests

We assessed drivers of ecological success along resource availability gradients for three invasive woody species: Prunus serotina Ehrh., Quercus rubra L. and Robinia pseudoacacia L. We aimed to check how much of invasion success, measured by invader biomass, is explained by propagule pressure and plant community invasibility. Using 3 years of observations from 372 study plots (100 m² each) in temperate forests of Wielkopolski National Park (Poland) we investigated the hierarchy of predictors and partial dependencies using the random forest method. Our study indicated that propagule pressure explained more variance in success of invaders than invasibility—describing availability of resources and competitors in understory vegetation. We also found different responses of seedlings and saplings, connected with dependence on stored carbohydrates, which decreased seedling responses to resource availability gradients. However, resource availability (light and leaf litter predictors) had greater influence than predictors describing understory vegetation. Based on importance and response strength the species studied may be arranged by decreasing requirements for soil fertility and acidity: P. serotina?<?Q. rubra?<?R. pseudoacacia, whereas for light requirements and competition vulnerability the order is: P. serotina?>?Q. rubra?>?R. pseudoacacia. However, low light requirements of R. pseudoacacia may be biased by high proportion of sprouts supplied by parental trees. Results provide guidelines for effective management of invasive woody species in forest ecosystems and describe complex interactions between factors studied on ecological success of invaders.     

Mixotrophic and photoautotrophic cultivation of 14 microalgae isolates from Saskatchewan, Canada: potential applications for wastewater remediation for biofuel production

Northern regions are generally viewed as unsuitable for microalgal biofuel production due to unfavorable climate and solar insolation levels. However, these conditions can potentially be mitigated by coupling microalgal cultivation to industrial processes such as wastewater treatment. In this study, we have examined the biomass and lipid productivity characteristics of 14 microalgae isolates (Chlorophyta) from the Canadian province of Saskatchewan. Under both photoautotrophic and mixotrophic cultivation, a distinct linear trend was observed between biomass and lipid productivities in the 14 SK isolates. The most productive strain under cultivation in TAP media was Scenedesmus sp.-AMDD which displayed rates of biomass and fatty acid productivities of 80 and 30.7?mg?L^?1?day^?1, respectively. The most productive strain in B3NV media was Chlamydomonas debaryana-AMLs1b which displayed rates of biomass and fatty acid productivities of 51.7 and 5.9?mg?L^?1?day^?1, respectively. In 11 of the isolates tested, secondary municipal wastewater (MCWW) supported rates of biomass productivity between 21 and 33?mg?L^?1?day^?1 with Scenedesmus sp.-AMDD being the most productive. Three strains, Chlamydomonas debaryana-AMB1, Chlorella sorokiniana-RBD8 and Micractinium sp.-RB1b, showed large increases in biomass productivity when cultivated mixotrophically in MCWW supplemented with glycerol. High relative oleic acid content was detected in 10 of the 14 isolates when grown mixotrophically in media supplemented with acetate. There was no detectable effect on the fatty acid profiles in cells cultivated mixotrophically in glycerol-supplemented MCWW. These data indicate that biomass and lipid productivities are boosted by mixotrophic cultivation. Exploiting this response in municipal wastewater is a promising strategy for the production of environmentally sustainable biofuels.     

The influence of black locust (Robinia pseudoacacia) flower and leaf fall on soil phosphate

To investigate the influence of black locust (Robinia pseudoacacia) flower and leaf fall on soil phosphate, we monitored litterfall, litter decomposition, and soil membrane phosphate in a R. pseudoacacia forest on Mt. Ilzasan, Seoul, Korea. R. pseudoacacia flower litter was 30–50% of total litter production in May and the flowers decomposed rapidly. More than 11% of R. pseudoacacia leaf litter decomposed from February to May, while that of Quercus spp. decomposed very little. Fast decomposition of R. pseudoacacia flower and leaf litter significantly increased membrane phosphate in the soil. The rapid nutrient-cycling of R. pseudoacacia through flower litterfall and rapid decomposition benefits the plant itself in the growing season when nutrients demand is increasing. Rapid nutrient-cycling might be a strategy that helps R. pseudoacacia to persist in poor soil environments.     

Deciphering role of technical bioprocess parameters for bioethanol production using microalgae

Microalgae biomass is considered an important feedstock for biofuels and other bioactive compounds due to its faster growth rate, high biomass production and high biomolecules accumulation over first and second-generation feedstock. This research aimed to maximize the specific growth rate of fresh water green microalgae Closteriopsis acicularis, a member of family Chlorellaceae under the effect of pH and phosphate concentration to attain enhanced biomass productivity. This study investigates the individual and cumulative effect of phosphate concentration and pH on specific growth characteristics of Closteriopsis acicularis in autotrophic mode of cultivation for bioethanol production. Central-Composite Design (CCD) strategy and Response Surface Methodology (RSM) was used for the optimization of microalga growth and ethanol production under laboratory conditions. The results showed that high specific growth rate and biomass productivity of 0.342 day⁻¹ and 0.497 g L⁻¹ day⁻¹ respectively, were achieved at high concentration of phosphate (0.115 g L⁻¹) and pH (9) at 21st day of cultivation. The elemental composition of optimized biomass has shown enhanced elemental accumulation of certain macro (C, O, P) and micronutrients (Na, Mg, Al, K, Ca and Fe) except for nitrogen and sulfur. The Fourier transform infrared spectroscopic analysis has revealed spectral peaks and high absorbance in spectral range of carbohydrates, lipids and proteins, in optimized biomass. The carbohydrates content of optimized biomass was observed as 58%, with 29.3 g L⁻¹ of fermentable sugars after acid catalyzed saccharification. The bioethanol yield was estimated as 51 % g ethanol/g glucose with maximum of 14.9 g/L of bioethanol production. In conclusion, it can be inferred that high specific growth rate and biomass productivity can be achieved by varying levels of phosphate concentration and pH during cultivation of Closteriopsis acicularis for improved yield of microbial growth, biomass and bioethanol production.     

连栽杉木林林下植被生物量动态格局

用空间一致时间连续的定位研究方法,在湖南会同杉木林生态系统国家野外科学观测研究站试验基地的第2集水区,对连栽杉木林林下植被生物量进行了12 a的监测,研究了林下植被种类的变化、生物量动态特征、生物量的组成与分布变化格局。结果表明:连栽杉木林在14a生长发育过程中,林下植物种类呈现波动性的减少趋势,其中木本植物物种数下降率为40.0%,草本植物物种数下降率为47.1%。林下植被生物量由杉木林3年生29.48 t/hm²下降至14年生的2.53 t/hm²,其中木本植物生物量由7.07 t/hm²,下降至1.25 t/hm²,下降了82.3%;草本植物由22.41 t/hm²,下降至1.28 t/hm²,下降了94.3%。在此期间,木本与草本植物生物量的高低均出现波动现象。3年生杉木林下木本植物以乔木树种生物量6068.97 kg/hm²最高,占总生物量85.88%,藤本植物生物量736.97 kg/hm²为次,占10.44%,灌木植物生物量259.87 kg/hm²最低,仅占3.68%。14年生杉木林下木本植物以灌木植物生物量881.87 kg/hm²为首,占总生物量70.73%,藤本植物生物量247.07 kg/hm²为次,占19.82%,乔木树种生物量117.87 kg/hm²最少,只占9.45%。3年生杉木林下草本植物以蕨类植物生物量8391.44 kg/hm²最高,占总生物量的37.44%,过路黄生物量36.77 kg/hm²最低,仅占0.16%。杉木14年生时,以芒生物量573.00 kg/hm²最大,占总生物量44.78%,金毛耳草生物量2.93 kg/hm²最小,仅占0.23%。研究结果,可为研究杉木林养分循环、碳平衡、维护和提高林地地力及可持续经营管理提供科学依据。     

Recovery of grassland after clear-cutting of invasive Robinia pseudoacacia – Long-term study in Prague (Czech Republic)

Invasive species belong to the main threats to dry grassland biodiversity. That́s why nature conservation managers seek the best ways to remove them and to support the restoration process of original natural habitats. We studied the effect of clear-cutting of invasive black locust (Robinia pseudoacacia L.) on the recovery of former species rich dry grassland vegetation. Ten permanent plots where R. pseudoacacia was cut down were long-term monitored in nature reserves protecting dry grasslands. The representation of dry grassland plants has been increased four times and the representation of synanthropic plants has been decreased two times during 40 years of succession even though R. pseudoacacia still relatively successfully resisted eradication efforts. During the succession after R. pseudoacacia cutting down, the Ellenberg indicator values for nutrients have decreased significantly, but no decrease in the nitrate content of the soil was observed. The long-term monitoring revealed that the restoration of dry grasslands invaded by R. pseudoacacia is possible but very time consuming.     

Analysis of interactions between the invasive tree-of-heaven (<Emphasis Type="Italic">Ailanthus altissima</Emphasis>) and the native black locust (<Emphasis Type="Italic">Robinia pseudoacacia</Emphasis>)

Invasive exotic plants can persist and successfully spread within ecosystems and negatively affect the recruitment of native species. The exotic invasive Ailanthus altissima and the native Robinia pseudoacacia are frequently found in disturbed sites and exhibit similar growth and reproductive characteristics, yet each has distinct functional roles such as allelopathy and nitrogen fixation, respectively. A four-month full additive series in the greenhouse was used to analyze the intraspecific and interspecific interference between these two species. In the greenhouse experiment, the inverse of the mean total biomass (g) response per plant for each species was regressed on the density of each species and revealed that the performance of the plants was significantly reduced by interspecific interference and not by intraspecific interference (p < 0.05). Other biomass traits such as root dry weight, shoot dry weight, stem dry weight, and leaf dry weight were also negatively affected by interspecific interference. Competition indices such as Relative Yield Total and Relative Crowding Coefficient suggested that A. altissima was the better competitor in mixed plantings. Ailanthus altissima consistently produced a larger above ground and below ground relative yield while R. pseudoacacia generated a larger aboveground relative yield in high density mixed species pots.     

Symbiosis of Arbuscular Mycorrhizal Fungi and Robinia pseudoacacia L. Improves Root Tensile Strength and Soil Aggregate Stability

Robinia pseudoacacia L. (black locust) is a widely planted tree species on Loess Plateau for revegetation. Due to its symbiosis forming capability with arbuscular mycorrhizal (AM) fungi, we explored the influence of arbuscular mycorrhizal fungi on plant biomass, root morphology, root tensile strength and soil aggregate stability in a pot experiment. We inoculated R. pseudoacacia with/without AM fungus (Rhizophagus irregularis or Glomus versiforme), and measured root colonization, plant growth, root morphological characters, root tensile force and tensile strength, and parameters for soil aggregate stability at twelve weeks after inoculation. AM fungi colonized more than 70% plant root, significantly improved plant growth. Meanwhile, AM fungi elevated root morphological parameters, root tensile force, root tensile strength, Glomalin-related soil protein (GRSP) content in soil, and parameters for soil aggregate stability such as water stable aggregate (WSA), mean weight diameter (MWD) and geometric mean diameter (GMD). Root length was highly correlated with WSA, MWD and GMD, while hyphae length was highly correlated with GRSP content. The improved R. pseudoacacia growth, root tensile strength and soil aggregate stability indicated that AM fungi could accelerate soil fixation and stabilization with R. pseudoacacia, and its function in revegetation on Loess Plateau deserves more attention.     

Feasibility of SRC Species for Growing in Mediterranean Conditions

The suitability of poplar (Populus × canadensis Moench.—genotype ‘Neva’), black locust (Robinia pseudoacacia L.), and eucalyptus (Eucalyptus bridgesiana R. Baker) growing in short rotation coppice (SRC) system in a Mediterranean area (southern Italy), and under two management regimes, was evaluated in terms of survival, biomass yield, biomass quality, and soil fertility. The high management regime (H treatment) consisted of high plant density (6667 trees ha^?1) and a 2-year harvesting cycle; the low management regime (L treatment) consisted of low plant density (1667 trees ha^?1) and a 4-year harvesting cycle. The dry biomass production was 36, 13, and 9 t dry matter (dm)?ha^?1 in the H treatment and 25, 14, and 7 t dm ha^?1 in the L treatment for eucalyptus, black locust, and poplar, respectively. The analysis of the biomass showed a superior quality for the black locust feedstock because of its low moisture and ash percentages, high heating value (HHV), and low alkali metal concentrations, although, from an environmental point of view, the high N (12.3 g kg^?1) and S (0.7 g kg^?1) biomass concentrations would increase the pollutant emissions generated by combustion. Eucalyptus showed a high HHV, especially for the H treatment (18.70 MJ kg^?1). Its high concentrations of K (4 g kg^?1) and Mg (0.8 g kg^?1) could provoke slagging and fouling in combustion equipment, and the high concentrations of S and N, if leaves are considered in the harvested biomass, indicate the low quality of its feedstock. No specific poplar feedstock stood out, although it had a good HHV (19.02 MJ kg^?1). The soil fertility was not affected negatively after the 4-year SRC cycle, while S content in soil showed a tendency to increase in the case of black locust cultivation.     

Microbial activity in reclaimed and unreclaimed post-mining sites near Sokolov (Czech Republic)

Microbial activity reflects soil conditions and degree of development. The aim of this study was to compare microbial properties of reclaimed and unreclaimed post-mining soil. Microbial biomass, microbial respiration, and cellulose decomposition were quantified in two chronosequences of post-mining sites located in the Sokolov brown-coal mining area. The first chronosequence consisted of five sites reclaimed with an alder plantation (Alnus glutinosa, Alnus incana), and the other consisted of five unreclaimed sites naturally colonized by local vegetation (especially Salix caprea, Betula pendula and Populus tremula). The spoil material of all the studied sites consisted of tertiary clays without any topsoil cover.Microbial respiration per unit of soil mass as well as per unit of soil area decreased as site age increased. Microbial biomass, whether expressed as a function of soil mass or area, increased with site age in both reclaimed and unreclaimed sites. When expressed per m², proportion of deeper soil layers (5–10 cm) on overall microbial biomass in 0–10 cm layer increased with site age. This increase was more pronounced in reclaimed than in unreclaimed sites. Cellulose decomposition was highest in 8-year-old sites in the reclaimed chronosequence and in 17–21-year-old sites in the unreclaimed chronosequence. The cellulose decomposition rate was higher in reclaimed than in unreclaimed sites. In reclaimed sites, the decomposition rate depended on air temperature, while in unreclaimed sites other factors, such as moisture deficiency, seemed to drive decomposition rate in some locations. Overall, microbial activity increased faster in reclaimed than in unreclaimed sites, and this difference was most evident in younger sites.     

An estimation of Scots pine (Pinus sylvestris L.) ecosystem productivity on reclaimed post-mining sites in Poland (central Europe) using of allometric equations

The work presents determination of the productivity of post-mining ecosystems (PME) derived from the aboveground biomass and annual biomass increment of Scots pine (Pinus sylvestris L.) stands. Single tree biomass assessment data from 42 cut trees were used in developing local allometric equations which may be used as an index during post-mining reforestation projects. The total biomass of pine ecosystems was determined from dendrometric measurements of sample plots with the use of elaborated equations. Forest floor vegetation was determined using the harvest method. Control plots were set up in the vicinity of the mining-sites at a managed forest on natural pine sites (NPS). Results confirm wide ecological amplitude of pine and indicate a high PME productivity on all substrates (2.79-4.34 Mg ha⁻¹ yr⁻¹).     

The effect of gradual increase in salinity on the biomass productivity and biochemical composition of several marine,halotolerant<Emphasis Type="Bold">,</Emphasis> and halophilic microalgae

Open ponds are the preferred cultivation system for large-scale microalgal biomass production. To be more sustainable, commercial scale biomass production should rely on seawater, as freshwater is a limiting resource, especially in places with high irradiance. If seawater is used for both pond fill and evaporative volume makeup, salinity of the growth media will rise over time. It is not possible for any species to achieve optimum growth over the whole saline spectrum (from seawater salinity level up to salt saturation state). In this study, we investigated the effects of gradual salinity increase (between 35 and 233 ppt) on biomass productivity and biochemical composition (lipid and carbohydrate) of six marine, two halotolerant, and a halophilic microalgae. A gradual and slow stepped salinity increase was found to expand the salinity tolerance range of tested species. A gradual reduction in biomass productivity and maximum photochemical efficiency was observed as a consequence of increased salinity in all tested species. Among the marine microalgae, Tetraselmis showed highest biomass productivity (32 mg L^?1 day^?1) with widest salinity tolerance range (35 to 109 ppt). Halotolerant Amphora and Navicula were able to grow from 35 ppt to 129 ppt salinity. Halophilic Dunaliella was the only species capable of growing between 35 and 233 ppt and showed highest lipid content (56.2%) among all tested species. This study showed that it should be possible to maintain high biomass in open outdoor cultivation utilizing seawater by growing Tetraselmis, Amphora, and Dunaliella one after another as salinity increases in the cultivation system.     

Growth and lipid synthesis promotion in mixotrophic Neochloris oleoabundans (Chlorophyta) cultivated with glucose

In the recent years, the studies concerning the cultivation of Neochloris oleoabundans for biofuel purposes have increased, in relation to its capability to accumulate lipids when grown under nutrient starvation. Unfortunately, this cultivation mode does not allow to reach high biomass densities, which are required to improve the feasibility of the process. Increasing knowledge of the microalgal physiology is necessary to obtain new useful information for the improvement of culture performance in the perspective of large-scale cultivation. In this work, the mixotrophic cultivation of N. oleoabundans in a brackish medium added with different glucose concentrations has been tested under shaking, with the aim of stimulating growth alongside lipid accumulation inside cells. Cell morphology, glucose consumption, photosynthetic pigment content and photosynthetic efficiency were also investigated. Among all tested glucose concentrations (0–30 g L^?1), it was observed that 2.5 g L^?1 was the optimal concentration, allowing to obtain the best compromise between glucose supplement, biomass production and lipid accumulation. Growth was highly enhanced in mixotrophic cultures, linked to the release of cells from sporocysts. A unique feature characterising mixotrophy in N. oleoabundans was the promotion of the maximum quantum yield of Photosystem II. Moreover, when mixotrophic cells entered the stationary phase, high lipid accumulation was induced. This study shows that the addition of glucose to N. oleoabundans remarkably increases the production of biomass enriched in lipids and represents an advancement for the cultivation of this microalga for applied purposes.     

Different factors affect the local distribution,persistence and spread of alien tree species in floodplain forests

Floodplain forests are characterized by high and increasing levels of invasions by plant species, but the factors that drive their spread are insufficiently understood. Using data from 708 plots surveyed twice (1998, 2008) supplemented with further data (management, stand age, distance to dispersal corridors, type of ecosystems invaded) we analyzed the factors which shape the local distribution, growth, persistence and spread of three invasive alien tree species (Acer negundo, Ailanthus altissima, Robinia pseudoacacia) in the National Park Donau-Auen in Austria. Using Generalized Linear Models (GLMs), we found that the distribution of the study species per plot is contingent on stand age (R. pseudoacacia), type of floodplain forest (A. negundo, A. altissima) and distance to the next water body (A. negundo). For all study species, colonization of new plots between both surveys is driven by short distance spread from already established invasion foci. Moreover, recipient habitats (softwood vs. hardwood floodplain forests) modify invasion success in species-specific ways. The probability of occurrence and colonization of plots located in softwood floodplain forests is higher for A. negundo, whereas A. altissima more frequently colonizes hardwood floodplain forests. Persistence of R. pseudoacacia decreases with stand age, whereas its growth rate is significantly higher in plots located in zones where management is allowed than in those which are not managed. Persistence and growth of the other two study species were not related to any explanatory variables analyzed. The on-going spread of the study species in the National Park Donau-Auen suggests that their local distribution is in disequilibrium, i.e. not all suitable habitat patches have yet been colonized. This implies that increased management efforts are necessary to reverse the spread of alien tree species in the study area and to maintain the high conservation value of this iconic area which protects one of the largest floodplain forests in Europe.