Postharvest growth dynamic of <Emphasis Type="Italic">Schoenoplectus californicus</Emphasis> along fluvio-estuarine and flooding gradients

The emergent wetland plant Schoenoplectus californicus is used as fiber in several American countries, but the effects of harvesting on this species have not previously been studied. We analyzed the biomass production, stem density and morphometry of this species along fluvio-estuarine and flooding gradients and evaluated the effects of harvesting on growth and recovery capacity in the Santa Lucía River (Uruguay), comparing river sections and surface elevations. Differences in biomass, length and stem density were associated with the dynamics of the hydrological regime. The mean biomass and length growth rates were 3.0 ± 2.8 g day^?1 and 0.8 ± 0.5 cm day^?1, respectively. The analysis of the postharvest growth dynamic showed variation among the stems, suggesting the existence of mechanisms of plant compensation for the harvest effect. Six months after the harvest, S. californicus had recovered, e.g., in stem length and density, while the biomass showed a slower recovery. Our results suggest that the recovery capacity of this species depends on the population structure before the harvest and on favorable conditions during the recovery period. Based on our results, we recommend strategies for sustainable harvest management.     

A water-centred framework to assess the effects of salinity on the growth and yield of wheat and barley

We conducted a field experiment in two alpine meadows to investigate the short-term effects of nitrogen enrichment and plant litter biomass on plant species richness, the percent cover of functional groups, soil microbial biomass, and enzyme activity in two alpine meadow communities. The addition of nitrogen fertilizer to experimental plots over two growing seasons increased plant production, as indicated by increases in both the living plant biomass and litter biomass in the Kobresia humilis meadow community. In contrast, fertilization had no significant effect on the amounts of living biomass and litter biomass in the K. tibetica meadow. The litter treatment results indicate that litter removal significantly increased the living biomass and decreased the litter biomass in the K. humilis meadow; however, litter-removal and litter-intact treatments had no impact on the amounts of living biomass and litter biomass in the K. tibetica meadow. Litter production depended on the degree of grass cover and was also influenced by nitrogen enrichment. The increase in plant biomass reflects a strong positive effect of nitrogen enrichment and litter removal on grasses in the K. humilis meadow. Neither fertilization nor litter removal had any impact on the grass biomass in the K. tibetica meadow. Sedge biomass was not significantly affected by either nutrient enrichment or litter removal in either alpine meadow community. The plant species richness decreased in the K. humilis meadow following nitrogen addition. In the K. humilis meadow, microbial biomass C increased significantly in response to the nitrogen enrichment and litter removal treatments. Enzyme activities differed depending on the enzyme and the different alpine meadow communities; in general, enzyme activities were higher in the upper soil layers (0–10 cm and 10–20 cm) than in the lower soil layers (20–40 cm). The amounts of living plant biomass and plant litter biomass in response to the different treatments of the two alpine meadow communities affected the soil microbial biomass C, soil organic C, and soil fertility. These results suggest that the original soil conditions, plant community composition, and community productivity are very important in regulating plant community productivity and microbial biomass and activity.     

Growth of microalgae Botryococcus sp. in domestic wastewater and application of statistical analysis for the optimization of flocculation using alum and chitosan

Microalga biomass has been recognized as a sustainable bio-product to replace terrestrial biomass in biofuel production. The microalga industry has high operating costs, specifically on harvesting and biomass recovery. Therefore, the development of an efficient harvesting method is crucial to the minimization of production cost. A statistical analysis through response surface methodology was used to investigate the optimization of harvesting efficiency using alum and chitosan as a coagulant. Growth rate and biomass productivity were also determined. This research revealed that the harvesting efficiency using alum was 99.3%, with optimum dosage and pH of 177.74 mg L^?1 and 8.24, respectively. Chitosan achieved 94.2% biomass recovery at an optimal dosage of 169.95 mg L^?1 at pH of 12. Moreover, Botryococcus sp. achieved the maximum growth of 0.7551 µ_max d^?1, with an average total biomass productivity of 9.81 mg L^?1?d^?1 in domestic wastewater. Overall, this study shows that both alum and chitosan coagulants have great potential for efficient microalgal biomass recovery. It suggests that domestic wastewater as a potential growth medium for the large-scale production of microalga biomass.     

The potential use of papyrus (Cyperus papyrus L.) wetlands as a source of biomass energy for sub‐Saharan Africa

Four of five people in sub‐Saharan Africa rely on the traditional use of solid biomass, mainly fuelwood, for cooking. In some areas, the current rate of fuelwood consumption will exhaust biomass reserves within the next decade or two. A largely unrecognized source of biomass are tropical wetland ecosystems which have been shown to be some of the most productive ecosystems globally, exhibiting rates of net primary productivity comparable with high‐input, intensively managed agricultural systems. Papyrus (Cyperus papyrus L.) is an emergent sedge with C₄ photosynthesis which is native to the wetlands, river valleys and lakes of central, eastern and southern Africa. The mean standing dry matter of culms and umbels measured at a number of locations throughout East Africa is 38.3 ± 21.6 tDM ha^?1, and the aerial net primary productivity ranges between 25.9 and 136.4 tDM ha^?1 yr^?1. Papyrus vegetation can be harvested by hand and stacked on the rhizome mat for partial air‐drying, and it has been demonstrated that an annual harvesting regime has no negative impacts on long‐term productivity. The use of papyrus as a biofuel for cooking and heating depends on converting it to a suitably combustible form, such as compressed or carbonized briquettes with a calorific value approximately one‐third less than wood charcoal. While papyrus has significant potential as a biofuel, we argue that an integrated management and decision‐making framework for the sustainable utilization of papyrus wetlands is required, in which all ecosystem services including the provision of biomass energy need to be assessed. Sustainability of papyrus wetlands requires management which combines the strength of traditional communal governance and modern legislation to promote its utilization. In this way, local communities can benefit from the inherent advantages of tropical wetlands as very productive ecosystems.     

Rapid Recovery of Gross Production and Respiration in a Mesic Mountain Big Sagebrush Ecosystem Following Prescribed Fire

The impact of land management actions such as prescribed fire remains a key uncertainty in understanding the spatiotemporal patterns of carbon cycling in the Western USA. We therefore quantified carbon exchange and aboveground carbon stocks following a prescribed fire in a mountain big sagebrush ecosystem located in the northern Great Basin, USA. Specifically, we examined the changes in plant functional type, leaf area index, standing aboveground carbon stocks, net ecosystem production (NEP), gross ecosystem production (GEP), and ecosystem-level respiration (R_eco) for 2 years before and 7 of 9 years after a prescribed fire. Post-burn GEP and R_eco exceeded pre-burn GEP and R_eco within 2 years and remained elevated. The variation in GEP and R_eco provided no evidence of a large and prolonged net efflux of carbon in the 9 years after the fire. Rather, NEP indicated the site was a sink before and after the fire, with little change in sink strength associated with the burn. Re-sprouting and recruitment of grasses and forbs drove the post-burn increase in GEP. Woody shrub growth was the dominant control on aboveground biomass accumulation after fire, with shrub aboveground biomass reaching ~ 11% of pre-burn biomass after 5 years. The rapid recovery of GEP and the growth of mid-successional shrubs suggest ecosystem-level carbon fluxes and stocks can recover rapidly after fire in mesic mountain big sagebrush ecosystems.     

Effect of caffeine concentration on biomass production, caffeine degradation, and morphology of Aspergillus tamarii

The aim of the present study was to evaluate the effect of the initial caffeine concentration (1–8 g/L) on growth and caffeine consumption by Aspergillus tamarii as well as pellet morphology, in submerged fermentation. Caffeine was used as sole nitrogen source. At 1 g/L of initial caffeine concentration, caffeine degradation was not affected, resulting in a production of 8.7 g/L of biomass. The highest biomass production (12.4–14.8 g/L) was observed within a range of 2 to 4 g/L of initial caffeine concentration. At these initial caffeine concentrations, after 96 h of fermentation, 41–51 % of the initial caffeine was degraded. Using an initial caffeine concentration of 2–3 g/L, the highest specific growth rate was observed (μ?=?0.069 1/h). Biomass production decreased at 8 g/L of initial caffeine concentration. A. tamarii formed mainly pellets at all concentrations tested. The size of the pellet decreased at a caffeine concentration of 8 g/L.     

模拟分类经营对小兴安岭林区森林生物量的影响

运用空间直观景观模型LANDIS 7.0 PRO,模拟了在当前采伐模式和无采伐两个预案下,小兴安岭林区森林生物量及主要树种生物量在2000—2200年间的动态。模拟结果如下:(1)无采伐预案下,森林生物量由最初的93.6 t/hm2逐渐升高,90a后达到最大值258 t/hm2,之后森林生物量在245 t/hm2上下小幅波动;(2)前100a采伐预案会明显降低森林生物量,与无采伐预案相比森林生物量最大可降低21.4 t/hm2,平均减少14.7 t/hm2;后100a采伐对森林生物量的影响逐渐减弱,森林生物量平均减少2.6 t/hm2;(3)当前采伐模式促进保护树种红松和紫椴生长,其生物量分别最大可提高9.0 t/hm2和0.53 t/hm2,占到无采伐预案生物量的56%和15%;(4)采伐预案对云冷杉生物量影响较小,主要降低先锋树种(白桦、山杨)和一些阔叶树种(枫桦、春榆)的生物量。研究结果表明现行采伐模式在未来100 a内会显著影响森林生物量,之后其影响逐渐减小,并且保护政策能提高所保护树种(红松、紫椴)的生物量,但要保持较高的总生物量,仍需要降低目前的采伐强度。     

Bioturbation by the sand dollar <Emphasis Type="Italic">Encope emarginata</Emphasis> (Echinoidea,Mellitidae) changes the composition and size structure of microphytobenthic assemblages

The goal of this study is to examine the suitability of three plants, Typha spp., Phragmites spp. and Iris pseudacorus, in a free-water surface constructed wetland created to treat eutrophic water from Lake Albufera (Valencia, Spain), a wetland of international importance. The growth, coverage and nutrient content of the three plants were studied, and chemical analyses were performed according to standard methods. The maximum standing crops measured for each plant were 1.9, 18.2 and 3.3 kg m^?2, respectively, and their average nutrient concentrations were 2.1, 1.2 and 1.7 g P kg^?1 and 12.1, 11.7 and 10.1 g N kg^?1, respectively. A multiple harvest of Iris pseudacorus revealed that the removal of nutrients could be increased up to 50% for N and 100% for P compared with a single harvest. Biomass decomposition assays showed high values for five-day biochemical oxygen demand (115–207 mg O₂ g^?1, depending on the plant and its age) and a substantial release of phosphorus, up to 100% of that contained in the biomass, highlighting the need to remove the litter fall. This study provides key aspects for vegetation selection and management (planting and harvesting) in a novel application of constructed wetlands to enhance water quality and biodiversity.     

Effects of plateau pika (Ochotona curzoniae) on alpine meadow phytocoenosium and analysis of the strategy it uses to expand habitat

High-density plateau pikas (Ochotona curzoniae) disturbance is one of the main causes of alpine meadow degradation. The response of phytocoenosium to the disturbance of plateau pika may reflect its habitat expanding strategy. We used quadrat sampling method to investigate vegetation height, coverage, and aboveground biomass of non-pika area (NA), transition area (TA), and pika-active area (AA) distributed continuously in alpine meadow located in Guoluo Tibetan Autonomous County of Qinghai Province in 2011 and 2012. The results showed that, from NA to AA (i) vegetation coverage, height, and above-ground biomass decreased (P < 0.01). (ii) While the number of plant species decreased from 41 to 30, and species diversity decreased significantly (P < 0.05), evenness of the alpine meadow showed no significant variations. (iii) Dominant species changed from grasses to weeds. (iv) While plants in TA showed no obvious difference in height between 2011 and 2012, coverage reduced significantly (P < 0.05). These results demonstrate that (i) plateau pikas disturbance on alpine meadow will change plant community structure and composition, directly leading to degeneration of alpine meadow. Additionally, (ii) plateau pikas expand their habitat by altering plant coverage firstly.     

Impacts of forest biomass removal on soil nutrient status under climate change: a catchment-based modelling study for Finland

The environmental impact of different forest harvesting scenarios on soil nutrient status and water chemistry under current and future (IPCC A2) climate was evaluated for a random sample of lake catchments (n = 1066) covering Finland. Biomass removal scenarios were derived from a management-oriented large-scale forest model based on data from national forest inventories. Forest ecosystem sustainability was assessed by evaluating soil base cation balances as well as temporal changes (2010–2050) in soil base saturation and lake water acid neutralising capacity, using a dynamic hydro-geochemical model. The harvesting scenarios had very different effects on biomass and element removal as well as soil and water quality; only harvesting of above-ground woody biomass (stem-only or stem-and-branches harvesting scenarios) was predicted to be sustainable, i.e. not depleting the soil base cation pools in the long term. The most intensive scenario—whole-tree harvesting (including the removal of stumps and roots)—doubled the removal of biomass, tripled the removal of base cations from the catchment soils, and increased nitrogen removal fourfold. Climate change was predicted to have a positive impact by increasing the future supply of base cations from weathering, thus compensating their removal by biomass harvesting. However, additional inputs of nitrogen and potassium will be required to ensure sustained forest growth under intensive biomass harvesting.     

Biomass Increases Go under Cover: Woody Vegetation Dynamics in South African Rangelands

Woody biomass dynamics are an expression of ecosystem function, yet biomass estimates do not provide information on the spatial distribution of woody vegetation within the vertical vegetation subcanopy. We demonstrate the ability of airborne light detection and ranging (LiDAR) to measure aboveground biomass and subcanopy structure, as an explanatory tool to unravel vegetation dynamics in structurally heterogeneous landscapes. We sampled three communal rangelands in Bushbuckridge, South Africa, utilised by rural communities for fuelwood harvesting. Woody biomass estimates ranged between 9 Mg ha^-1 on gabbro geology sites to 27 Mg ha^-1 on granitic geology sites. Despite predictions of woodland depletion due to unsustainable fuelwood extraction in previous studies, biomass in all the communal rangelands increased between 2008 and 2012. Annual biomass productivity estimates (10–14% p.a.) were higher than previous estimates of 4% and likely a significant contributor to the previous underestimations of modelled biomass supply. We show that biomass increases are attributable to growth of vegetation <5 m in height, and that, in the high wood extraction rangeland, 79% of the changes in the vertical vegetation subcanopy are gains in the 1-3m height class. The higher the wood extraction pressure on the rangelands, the greater the biomass increases in the low height classes within the subcanopy, likely a strong resprouting response to intensive harvesting. Yet, fuelwood shortages are still occurring, as evidenced by the losses in the tall tree height class in the high extraction rangeland. Loss of large trees and gain in subcanopy shrubs could result in a structurally simple landscape with reduced functional capacity. This research demonstrates that intensive harvesting can, paradoxically, increase biomass and this has implications for the sustainability of ecosystem service provision. The structural implications of biomass increases in communal rangelands could be misinterpreted as woodland recovery in the absence of three-dimensional, subcanopy information.     

Harvest residue management effects on tree growth and ecosystem carbon in a Chinese fir plantation in subtropical China

Aims

This study aimed to determine the influence of different harvest residue management strategies on tree growth, soil carbon (C) concentrations, soil nitrogen (N) availability and ecosystem C stocks 15 years after replanting second rotation Chinese fir (Cunninghamia lanceolata), an important plantation species in subtropical China. Such information is needed for designing improved management strategies for reforestation programmes in subtropical environments aimed at mitigating CO₂ emissions.

Methods

Four harvest residue management treatments including slash burning, whole tree, stem-only and double residue retention were applied to sixteen 20 m?×?30 m plots in a randomized complete block design with four replicates. Tree growth was measured annually and soil properties were measured at 3 year intervals over a 15 year period after re-planting.

Results

Cumulative diameter growth at age 15 years was significantly smaller in the slash burning than the whole tree and double residue harvest treatments. Hot water extractable N concentrations increased with the increased organic residue retention levels and significant differences were observed between double residue and slash burning treatments. Harvest residue management had no significant effect on the soil C concentrations to 40 cm depth. ANOVA showed that harvest residue management had no significant effect on total biomass carbon at age 15, but the plantation ecosystem (soil C at 0–40 cm depth plus forest biomass C) had significantly lower C mass in the slash burning treatment compared with whole tree, stem only harvest and double residue harvest treatments.

Conclusions

These observations suggest that organic residue retention during the harvesting could improve the growth and ecosystem C stocks of Chinese fir in second rotation forest plantations in subtropical China and highlight the importance of viewing the ecosystem as a whole when evaluating the impact of harvest residue management on C stocks.     

Establishment of Elymus natans improves soil quality of a heavily degraded alpine meadow in Qinghai-Tibetan Plateau, China

Elymus natans is a dominant native species widely planted to restore the heavily degraded alpine meadows in Qinghai-Tibetan plateau. The objective of this study was to determine how E. natans establishment affected the quality and fertility of a heavily degraded soil. Soil samples (at depths of 0–10, 10–20 and 20–30 cm) were collected from the 3- and 7-year-old E. natans re-vegetated grasslands, and in the heavily degraded alpine meadow (control). The establishment of E. natans promoted plant cover and aboveground biomass. Compared to the non-reseeded meadow, the concentration of total organic C increased by 13% in the soil under 3-year-old reseeded E. natans grassland at 0–10 cm, and by 7–33% in the soil under 7-year-old reseeded E. natans grassland at 0–10, 10–20 and 20–30 cm depths. Rapid increases in total and available N were also observed in two E. natans re-vegetated grasslands, especially in the 0–10 cm soil layer. Across three sampling depths, total P concentration was increased by 17–35% and 18–54% in 3- and 7-year-old reseeded soil respectively, compared to the soil of control. After 3 years of E. natans growth, microbial biomass C increased by 13–58% at 0–10 and 10–20 cm layers; while it increased by 43–87% in 7-year-old reseeded treatment at 0–10, 10–20 and 20–30 cm depths relative to control. A similar increasing trend was observed for microbial biomass N and P generally. Significant increase in neutral phosphatase, urease, catalase and dehydrogenase was also found in 3- and 7-year-old re-vegetated grasslands compared with heavily degraded meadow. Our results suggest a significant positive impact of E. natans establishment on soil quality. Thus, E. natans establishment could be an effective and applicable measure in restoring heavily degraded alpine meadow in the region of Qinghai-Tibetan Plateau.     

Kinetics of growth and ethanol formation from a mix of glucose/xylose substrate by Kluyveromyces marxianus UFV-3

The fermentation of both glucose and xylose is important to maximize ethanol yield from renewable biomass feedstocks. In this article, we analyze growth, sugar consumption, and ethanol formation by the yeast Kluyveromyces marxianus UFV-3 using various glucose and xylose concentrations and also under conditions of reduced respiratory activity. In almost all the conditions analyzed, glucose repressed xylose assimilation and xylose consumption began after glucose had been exhausted. A remarkable difference was observed when mixtures of 5 g L^?1 glucose/20 g L^?1 xylose and 20 g L^?1 glucose/20 g L^?1 xylose were used. In the former, the xylose consumption began immediately after the glucose depletion. Indeed, there was no striking diauxic phase, as observed in the latter condition, in which there was an interval of 30 h between glucose depletion and the beginning of xylose consumption. Ethanol production was always higher in a mixture of glucose and xylose than in glucose alone. The highest ethanol concentration (8.65 g L^?1) and cell mass concentration (4.42 g L^?1) were achieved after 8 and 74 h, respectively, in a mixture of 20 g L^?1 glucose/20 g L^?1 xylose. When inhibitors of respiration were added to the medium, glucose repression of xylose consumption was alleviated completely and K. marxianus was able to consume xylose and glucose simultaneously.     

Facilitative interactions do not wane with warming at high elevations in the Andes

Positive interactions between species are known to play an important role in the structure and dynamics of alpine plant communities. The balance between negative and positive interactions is known to shift along spatial and temporal gradients, with positive effects prevailing over negative ones as the environmental stress increases. Thus, this balance is likely to be affected by climate change. We hypothesized that increases in temperature (a global warming scenario) should decrease the importance of positive interactions for the survival and growth of alpine plant species. To test this hypothesis, we selected individuals of the native grass species Hordeum comosum growing within the nurse cushion species Azorella madreporica at 3,600 m.a.s.l. in Los Andes (Chile), and performed nurse removal and seedling survival experiments under natural and warmer conditions. For warmer conditions, we used open-top chambers, which increased the temperature by 4 °C. After two growing seasons, we compared the effect of nurse removal on the survival, biomass, and photochemical efficiency of H. comosum individuals under warmer and natural conditions. Nurse removal significantly decreased the survival, biomass, and photochemical efficiency of H. comosum, demonstrating the facilitative effects of nurse cushions. Seedling survival was also enhanced by cushions, even under warmer conditions. However, warmer conditions only partially mitigated the negative effects of nurse removal, suggesting that facilitative effects of cushions do not wane under warmer conditions. Thus, facilitative interactions are vital to the performance and survival of alpine species, and these positive interactions will continue to be important in the warmer conditions of the future in high-alpine habitats.     

Mesozooplankton distribution patterns and grazing impacts of copepods and Euphausia crystallorophias in the Amundsen Sea, West Antarctica, during austral summer

The rapid melting of glaciers as well as the loss of sea ice in the Amundsen Sea makes it an ideal environmental setting for the investigation of the impacts of climate change in the Antarctic on the distribution and production of mesozooplankton. We examined the latitudinal distribution of mesozooplankton and their grazing impacts on phytoplankton in the Amundsen Sea during the early austral summer from December 27, 2010 to January 13, 2011. Mesozooplankton followed a latitudinal distribution in relation to hydrographic and environmental features, with copepods dominating in the oceanic area and euphausiids dominating in the polynya. Greater Euphausia crystallorophias biomass in the polynya was associated with lower salinity and higher food concentration (chlorophyll a, choanoflagellates, and heterotrophic dinoflagellates). The grazing impact of three copepods (Rhincalanus gigas, Calanoides acutus, and Metridia gerlachei) on phytoplankton was low, with the consumption of 3 % of phytoplankton standing stock and about 4 % of daily primary production. Estimated daily carbon rations for each of the three copepods were also relatively low (<10 %), barely enough to cover metabolic demands. This suggests that copepods may rely on food other than phytoplankton and that much of the primary production is channeled through microzooplankton. Daily carbon rations for E. crystallorophias were high (up to 49 %) with the grazing impact accounting for 17 % of the phytoplankton biomass and 84 % of primary production. The presence of E. crystallorophias appears to be a critical factor regulating phytoplankton blooms and determining the fate of fixed carbon in the coastal polynyas of the Amundsen Sea.     

Use of sodium bicarbonate to stimulate triacylglycerol accumulation in the chlorophyte Scenedesmus sp. and the diatom Phaeodactylum tricornutum

There is potential for algal-derived biofuel to help alleviate part of the world’s dependency on petroleum based fuels. However, research must still be done on strain selection, induction of triacylglycerol (TAG) accumulation, and fundamental algal metabolic studies, along with large-scale culturing techniques, harvesting, and biofuel/biomass processing. Here, we have advanced the knowledge on Scenedesmus sp. strain WC-1 by monitoring growth, pH, and TAG accumulation on a 14:10 light–dark cycle with atmospheric air or 5% CO₂ in air (v/v) aeration. Under ambient aeration, there was a loss of pH-induced TAG accumulation, presumably due to TAG consumption during the lower culture pH observed during dark hours (pH 9.4). Under 5% CO₂ aeration, the growth rate nearly doubled from 0.78 to 1.53 d^?1, but the pH was circumneutral (pH 6.9) and TAG accumulation was minimal. Experiments were also performed with 5% CO₂ during the exponential growth phase, which was then switched to aeration with atmospheric air when nitrate was close to depletion. These tests were run with and without the addition of 50 mM sodium bicarbonate. Cultures without added bicarbonate showed decreased growth rates with the aeration change, but there was no immediate TAG accumulation. The cultures with bicarbonate added immediately ceased cellular replication and rapid TAG accumulation was observed, as monitored by Nile Red fluorescence which has previously been correlated by gas chromatography to cellular TAG levels. Sodium bicarbonate addition (25 mM final concentration) was also tested with the marine diatom Phaeodactylum tricornutum strain Pt-1 and this organism also accumulated TAG.     

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.     

The effect of brackish water irrigation on the above- and below-ground development of pollarded Acacia saligna shrubs in an arid environment

The regrowth capacity after pollarding of a short-rotation plantation of Acacia saligna (Labill.) H. Wendl. was investigated in a field trial. This shrub has been proposed as a provider of biomass (fuelwood and fodder) in an arid environment, using local marginal water resources such as surface runoff and brackish groundwater. The specific objective of this study was to examine the effects of water quality, irrigation frequency and annual runoff flooding onthe above- and belowground development of the pollarded shrubs. Treatments consisted of drip-irrigation with freshwater or brackish water, at low (twice a month) or high (weekly) frequency, with or without annual freshwater flooding, and on a well-watered basis (twice a week) without flooding. Each 15?×?5 m² plot contained four rows of four shrubs. After 5 years of growth, the shrubs were pollarded to a height of 1.5 m and during the subsequent year of regrowth, root development was monitored non-destructively using the minirhizotron, shoot growth was estimated from trunk cross-sectional area and allometric equations (obtained at the end of the measuring period by measurements and destructive sampling), and plant water status was monitored by measuring pre-dawn leaf water potential. Dry fodder (leaves and thin branches) production was between 3.50 and 9.75 t ha^?1 and dry wood was between 3.50 and 15.50 t ha^?1. The highest biomass production was obtained in the well-watered freshwater treatment, which also had the highest number of roots and highest predawn leaf water potential throughout the year. Shrubs irrigated with brackish water at low frequency without supplemental flooding produced the lowest yields. Water quality significantly affected shoot development only in the well-watered treatments although root development was reduced wherever brackish water was applied. Flooding the plots with freshwater once a year led to an increase in the number of roots outside the drip-irrigation zone, especially in brackish water treatments. A continued root growth with time was observed in all treatments even though the shoots were pollarded. In fact total root increments and aboveground biomass production were positively linearly related. Moreover the linear response of shoot and root increments to increasing water availability and not to water quality suggests that irrigation frequency was the main factor determining the regrowth capacity and amount of above- and belowground biomass production. Based on the above, runoff water and brackish groundwater could be used in a complementary manner for the sustainable production of fuelwood and fodder in a short-rotation plantation of this shrub.     

Temperature thresholds for the onset of xylogenesis in alpine shrubs on the Tibetan Plateau

Key message

The threshold minimum air temperature driving xylem growth of alpine  Rhododendron aganniphum is lower than that commonly observed at the treeline of conifers.

Abstract

Understanding how alpine shrubs grow and which environmental factors drive their biomass gain could help to functionally differentiate trees and shrubs. The cambium is the main meristem responsible for wood formation in trees and shrubs. Thus, a better knowledge of cambium growth dynamics in alpine shrubs would allow explaining why shrubs displace trees above the treeline. Here, we aim to investigate the timings and dynamics of xylogenesis and to identify the thermal thresholds controlling the onset of xylem growth of Rhododendron aganniphum, a tall shrub growing above the alpine treeline on the Tibetan Plateau. Timings of xylogenesis and radial growth rates were assessed from anatomical observations of the developing xylem during three growing seasons (2011, 2012, and 2013). The threshold temperature at which xylogenesis had a 0.5 probability of being active was calculated with logistic regressions. The onset of xylogenesis was observed between mid and late June, whereas the end of xylogenesis lasted from mid to late September. Overall, the duration of xylem growth lasted 88–101 days, and 94 % of the ring was formed from June to August. The threshold for the onset of xylem growth was observed at 2.0 ± 0.6 °C for the minimum air temperature, lower than that commonly observed for treeline conifers (ca. 6 °C). This low thermal threshold allows alpine shrubs to have a growing season long enough to complete xylem production and maturation during the warmest summer months. Our results suggest that the time required to complete xylogenesis is critical to understand why shrubs displace trees above the treeline.