Enhanced Biomass Accumulation Research Articles

Potential of biogas recirculation to enhance biomass accumulation on supporting media.

Two lab-scale anaerobic hybrid reactors (AHR) were operated to investigate the effect of recirculated biogas on the development of biomass on supporting media during the start-up. The reactor comprised of two distinct zones; sludge bed on the bottom and packed bed using nylon fiber as the media on the upper half of the reactor. Both reactors were continuously fed with cassava starch wastewater. The organic loading rate (OLR) was increased from 0.3 to 5.5 g COD/L/day by gradually decreasing the hydraulic retention time (HRT) from 37 to 3.5 days in two months. The biogas at 2.6 L/L/day was recirculated merely in the first month of the operation in order to allow the attached biomass to grow according to the organic matters present in the reactor at the final stage of the start up. Chemical oxygen demand (COD) removal efficiency of over 80% was achieved throughout the study. The result demonstrated a better COD removal efficiency for the reactor with biogas recirculation, especially at low HRTs. The amounts of biomass accumulated on the media in both reactors were slightly different with 11.9 gVSS found on the one with biogas recirculation compared to 9.8 gVSS on the other. In addition, 16.3% increase of the sludge bed was achieved with biogas recirculation as opposed to 9% in the control one. The attached biomass activity test indicated a greater amount and more favorable ratio of the methanogenic bacterial group on the media with the recirculation correlating well to a relatively higher methane content in biogas. As a result, the recirculation of biogas has a potential of improving the characteristics of the AHR especially in terms of biomass accumulation.

Plant diversity enhances ecosystem responses to elevated CO2 and nitrogen deposition

Human actions are causing declines in plant biodiversity, increases in atmospheric CO2 concentrations and increases in nitrogen deposition; however, the interactive effects of these factors on ecosystem processes are unknown. Reduced biodiversity has raised numerous concerns, including the possibility that ecosystem functioning may be affected negatively, which might be particularly important in the face of other global changes. Here we present results of a grassland field experiment in Minnesota, USA, that tests the hypothesis that plant diversity and composition influence the enhancement of biomass and carbon acquisition in ecosystems subjected to elevated atmospheric CO2 concentrations and nitrogen deposition. The study experimentally controlled plant diversity (1, 4, 9 or 16 species), soil nitrogen (unamended versus deposition of 4 g of nitrogen per m2 per yr) and atmospheric CO2 concentrations using free-air CO2 enrichment (ambient, 368 micromol mol-1, versus elevated, 560 micromol mol-1). We found that the enhanced biomass accumulation in response to elevated levels of CO2 or nitrogen, or their combination, is less in species-poor than in species-rich assemblages.

Effects of submergence on the growth of Phragmites australis seedlings

Colonisation by reed seedlings, Phragmites australis (Cav.) Trin. ex Steud. is rare and usually occurs after drawdown and when shallow water prevails. P. australis seeds have high rates of germination but successful colonisation is dependent upon subsequent water depths. We investigated the capacity of young reed plants to resist a 4 weeks submergence stress within a 5 months period, and their subsequent recovery. A pond experiment examined the interactions between submergence depth and the age of the seedlings at submergence. Four submergence treatments were used. In two partial submergence treatments, 50 and 80% of the initial leaf area was submerged. In two total submergence treatments, plants were either submerged at 125% of their initial height with possible subsequent development of emerged leaves, or the water was deepened as they grew to maintain total submergence for 4 weeks. The ages at submergence were 40, 60 and 80 days. Plants were harvested at 5 months. Shoot elongation, biomass allocations to aerial biomass, roots and rhizomes, and photosynthetic activity of aerial leaves were measured. Redox potential was measured for a subsample. Mortality (18.7%) occurred only in the permanent submergence treatment for 40-day-old seedlings. In all treatments, submerged leaves senesced, except the terminal (youngest) leaves of permanently submerged plants. Submergence differentially affected shoot length and biomass, depending upon the intensity of the treatment and the seedling age. The major differences were found between the two partial and two total submergence treatments. Partial submergence (50 and 80%) significantly enhanced biomass accumulation and growth, whereas total submergence largely decreased biomass production and growth in length, with less effect on shoot numbers. The 80-day-old seedlings tolerated submergence better but growth was poorest in medium-aged plants (60-day-old). Increased elongation of the growing internodes of up to 140% was caused by submergence, and photosynthetic activity was enhanced by 85% in emergent leaves of plants initially submerged but allowed to produce emerged leaves during the treatment period. Young P. australis plants require shallow water levels without long lasting submergence to grow and survive. Tolerance to submergence increases with age. These processes contribute to define the conditions for colonisation via seeds in P. australis.

Effect of elevated CO2 and soil fertilization on whole-plant growth and water use in seedlings of a tropical pioneer tree, Ficus insipida Willd.

Summary Seedlings of the tropical pioneer tree species Ficus insipida were cultivated at present-ambient and elevated (about twice-ambient) CO 2 concentrations in open-top chambers located in a forest clearing near Panama City, Republic of Panama. To examine potential chamber-specific effects on growth and transpiration, plants were also studied outside chambers at ambient CO 2 levels. Plants were grown individually in 38 litre pots containing a mixture of soil and leaf litter, either in the absence or presence of a slow-release fertilizer. Data from three experiments, lasting 7 to 9 weeks each, are presented. Transpirational water loss of plants was determined gravimetrically. Fertilized plants grew more rapidly than unfertilized plants. Elevated CO 2 strongly enhanced biomass accumulation in fertilized plants. In unfertilized plants, elevated CO 2 enhanced growth in two experiments, but not in a third. Transpiration ratios (TR, g water lost: g dry mass accumulated) of plants grown in open-top chambers ranged from 176 (elevated CO 2 , plus fertilizer) to 336 (ambient CO 2 , minus fertilizer). The addition of fertilizer decreased TR by 15 to 20%, irrespective of the CO 2 concentration, and elevated CO 2 reduced TR by 27 to 35%, irrespective of whether fertilizer was present or not. The reduction in TR in response to elevated CO 2 was independent of whether biomass accumulation was enhanced by elevated CO 2 or not. In all experiments in which biomass accumulation was increased at elevated CO 2 , absolute water expenditure at elevated CO 2 was greater or similar to that at ambient levels – despite the lower TR at elevated CO 2 . In the single experiment in which elevated CO 2 did not lead to increased growth, the absolute water expenditure of plants was lower at elevated than at ambient CO 2 . There was no chamber effect on biomass accumulation, but TR of both fertilized and unfertilized plants was 19 to 31% higher inside compared to outside the open-top chambers.

Interactive effects of elevated atmospheric CO2, mycorrhization and drought on long‐distance transport of reduced sulphur in young pedunculate oak trees (Quercus robur L.)

Pedunculate oak (Quercus robur L.) was germinated and grown under nutrient non‐limiting conditions for a total of 10–15 weeks at ambient CO2 concentration and 1100 μmol mol–1 CO2 either in the presence or the absence of the mycorrhizal fungus Laccaria laccata. Half of the oak trees of these treatments were exposed to drought during final growth by suspending the water supply for 21 d. Mycorrhization and elevated atmospheric CO2 each enhanced total plant biomass per tree. Whereas additional biomass accumulation of trees grown under elevated CO2 was mainly attributed to increased growth of lateral roots, mycorrhization promoted shoot growth. Water deficiency reduced biomass accumulation without affecting relative water content, but this effect was more pronounced in mycorrhizal as compared to non‐mycorrhizal trees. Elevated CO2 partially prevented the development of drought stress, as indicated by leaf water potential, but did not counteract the negative effects of water deficiency on growth during the time studied. Enhanced biomass accumulation requires adaption in protein synthesis and, as a consequence, enhanced allocation of reduced sulphur produced in the leaves to growing tissues. Therefore, allocation of reduced sulphur from oak leaves was studied by flap‐feeding radiolabelled GSH, the main long‐distance transport form of reduced sulphur, to mature oak leaves. Export of radiolabel proceeded almost exclusively in basipetal direction to the roots. The rate of export of radioactivity out of the fed leaves was significantly enhanced under elevated CO2, irrespective of mycorrhization. A higher proportion of the exported GSH was transported to the roots than to basipetal stem sections under elevated CO2 as compared to ambient CO2. Mycorrhization did not affect 35S export out of the fed leaves, but the distribution of radiolabel between stem and roots was altered in preference of the stem. Trees exposed to drought did not show appreciable export of the 35S radioactivity fed to the leaves when grown under ambient CO2. Apparently, drought inhibited basipetal transport of reduced sulphur at the level of phloem loading and/or phloem transport. Elevated CO2 seemed to counteract this effect of drought stress to some extent, since higher leaf water potentials and improved 35S export out of the fed leaves was observed in oak trees exposed to drought and elevated CO2 as compared to trees exposed to drought and ambient CO2.

Effect of Split Nitrogen Application on Growth and Yield of Wheat (T. aestivum L.) Genotypes with Different N‐Assimilation Potential

AbstractA field experiment was conducted with different nitrogen regimes to assess the growth and yield performance of wheat genotypes which differ in nitrate assimilation potential. Genotypic differences in biomass accumulation were observed at different growth stages. The nitrogen treatment had little effect on biomass accumulation at early stages of growth, while at later stages of growth there was enhanced biomass accumulation when N was applied in more than two splits. On an average, genotypes with high nitrate reductase activity (the ‘HNR’ genotypes) accumulated 14.2 % more biomass than the genotypes with low nitrate reductase activity (‘LNR’ genotypes) when an extra dose (40 kg N ha−1) of nitrogen was given at the time of anthesis. The application of nitrogen in more than two splits increased grain yield of both ‘HNR’ and ‘LNR’ genotypes mainly by increasing grain weight per ear. The application of an extra dose of nitrogen (40 kg N ha−1) at the time of anthesis increased grain yield of ‘HNR’ genotypes by 38.5 % as compared to ‘LNR’ genotypes.

Effect of thinning on biophysical soil properties of Cupressus lusitanica stand in Munessa forest, Ethiopia

Forest management practices such as thinning can dramatically change the microenvironment and thereby affect the physicochemical and soil microbiological properties. The aim of this research was to determine the effect of thinning on soil physicochemical properties and microbial biomass under Cupressus lusitanica plantation at Munessa forest. The experiment was carried out in a fenced stand treated differently (thinned and unthinned plots) with a completely randomized design. In each plot, 20 sampling spots were randomly selected for soil sample collection from 0 to 10 cm and 10 to 25 cm depth. Independent t-test was used to compare effects of thinning on biophysical properties of the soil. Results showed that soil organic carbon (SOC) and total nitrogen varied significantly between treatments. SOC concentration was generally lower at the soil depth of 0-10 to 10-25 cm. The concentrations of microbial biomarker used as a proxy for microbial biomass assessment were 22% larger in thinned stands. Soils under the thinned stand contained larger concentration of arbuscular mycorrhizal fungi biomarker. The two forest stands were established at the same time with the same stocking and hence differences in soil quality could be possibly resulted from management intervention. These findings showed that Cupressus thinning could enhance biomass accumulation and organic C input to the soil.