Annual Biomass Production Research Articles

Green foliage decomposition in tree plantations on degraded, irrigated croplands in Uzbekistan, Central Asia

Afforestation is a prospective strategy to improve soil fertility of salt-affected, irrigated croplands in Central Asia. The effect of macro- and mesofauna and microflora on the decomposition of tree leaves, collected ca. 2 weeks before natural fall, was monitored during 367 days. The three-year-old tree plantations consisted of Elaeagnus angustifolia L., Ulmus pumila L., and Populus euphratica Oliv. The leaf decay rate was determined in 25 × 25 cm sized polyester litterbags with mesh sizes of 10,000 μm (coarse), 250 μm (medium), and 20 μm (fine). Decomposition in the coarse litterbags, allowing access by the entire decomposer community, was highest in P. euphratica at 61% weight loss after 367 days. In the same period, the weight loss in E. angustifolia was 51% and in U. pumila 52%. Combined correlation and multiple regression analyses revealed that decomposability was determined by mesh size, initial C/N ratio, crude fiber-to-N (CF/N) ratio, leaf area, and specific leaf area. A high correlation existed between traits impacting decomposition by the entire decomposer population and the digestibility of leaves by animals as measured in the laboratory (the in vitro digestibility). Initial leaf N (34 g N kg−1 DM) content was highest in E. angustifolia, followed by 23 g N kg−1 DM in U. pumila and 22 g N kg−1 DM in P. euphratica. The C/N ratio followed the order of P. euphratica (21.8) > U. pumila (19.4) > E. angustifolia (13.1). The CF/N ratio followed the order P. euphratica (5.2) > E. angustifolia (3.9) > U. pumila (2.9). Despite a lower decay rate and a higher N content remaining in leaves after 367 days in comparison to both other species, E. angustifolia had the highest potential for soil bio-amelioration. This was due to its foliage production (6 t ha−1 on average), which was about 2.5 times higher than that of the other species, giving a total leaf N loss of about 97 kg N ha−1 in coarse mesh bags. The N loss from U. pumila and P. euphratica leaves amounted to 33 and 23 kg N ha−1, respectively. The potential of leaf decomposition for supplementing soil N in the region depends on the decay rate, the initial leaf N content, the annual leaf biomass production, and differences between N contents over the course of the decomposition period. These can be additional criteria for selecting tree species suitable for afforestation of the degraded, irrigated croplands in Central Asia.

Simulating the temporal pattern of waste production in farmed gilthead seabream ( Sparus aurata), European seabass ( Dicentrarchus labrax) and Atlantic bluefin tuna ( Thunnus thynnus)

Most fish farming waste output models provide gross waste rates as a function of stocked or produced biomass for a year or total culture cycle, but without contemplating the temporality of the discharges. This work aims to ascertain the temporal pattern of waste loads by coupling available growth and waste production models and developing simulation under real production rearing conditions, considering the overlapping of batches and management of stocks for three widely cultured species in the Mediterranean Sea: gilthead seabream ( Sparus aurata), European seabass ( Dicentrarchus labrax) and Atlantic bluefin tuna ( Thunnus thynnus). For a similar annual biomass production, the simulations showed that waste output and temporal dumping patterns differ between the three species as a result of the disparities in growth velocity, nutrient digestibility, maintenance metabolic budget and husbandry. The simulations allowed the temporal patterns including the periods of maximum discharge and the dissolved and particulate nitrogen and phosphorus content in the wastes released to be determined, both of which were seen to be species-specific.

Response of temperate grasslands at different altitudes to simulated summer drought differed but scaled with annual precipitation

Abstract. Water is an important resource for plant life. Since climate scenarios for Switzerland predict an average reduction of 20% in summer precipitation until 2070, understanding ecosystem responses to water shortage, e.g. in terms of plant productivity, is of major concern. Thus, we tested the effects of simulated summer drought on three managed grasslands along an altitudinal gradient in Switzerland from 2005 to 2007, representing typical management intensities at the respective altitude. We assessed the effects of experimental drought on above- and below-ground productivity, stand structure (LAI and vegetation height) and resource use (carbon and water). Responses of community above-ground productivity to reduced precipitation input differed among the three sites but scaled positively with total annual precipitation at the sites (R2=0.85). Annual community above-ground biomass productivity was significantly reduced by summer drought at the alpine site receiving the least amount of annual precipitation, while no significant decrease (rather an increase) was observed at the pre-alpine site receiving highest precipitation amounts in all three years. At the lowland site (intermediate precipitation sums), biomass productivity significantly decreased in response to drought only in the third year, after showing increased abundance of a drought tolerant weed species in the second year. No significant change in below-ground biomass productivity was observed at any of the sites in response to simulated summer drought. However, vegetation carbon isotope ratios increased under drought conditions, indicating an increase in water use efficiency. We conclude that there is no general drought response of Swiss grasslands, but that sites with lower annual precipitation seem to be more vulnerable to summer drought than sites with higher annual precipitation, and thus site-specific adaptation of management strategies will be needed, especially in regions with low annual precipitation.

Robinia pseudoacacia L.: A Lesser Known Tree Species for Biomass Production

Experiments with fast-growing tree species for biomass production in Germany have been mainly focused on the growth performance of Populus and Salix spp. Among the lesser-known species for energy plantations is Robinia pseudoacacia L. Special features of this species are its drought tolerance and its ability to fix nitrogen. Given the large share of marginal arable land in NE-Germany and the predicted climate change, R. pseudoacacia is expected to grow in importance. In order to evaluate the growth performance of this species under extreme conditions, four experiments were established in the post-mining landscape of the Lusatian lignite-mining district (NE-Germany). Biomass production was estimated for 3- to 14-year-old shoots on 4- to 14-year-old roots. Results for the annual production of oven-dried biomass of R. pseudoacacia ranged between 3 and 10 t ha−1, which was substantially greater than the biomass of poplar and willow clones established on the same site. Economic analysis results show that the rotation period, the duration of the plantation, and the harvesting costs are important parameters for the economic return and cash flow in short-rotation coppice cultivation. The results show that the cultivation of R. pseudoacacia is an economically competitive land-use strategy for the post-mining landscapes considered in our study.

The Effects of Topographic Factors on Aboveground Biomass Production of Grasslands in the Atacora Mountains in Northwestern Benin

The Atacora Mountain range is an important mountain chain in the West African landscape. It extends from northern Benin to Togo and Ghana. More and more cattle are starting to graze on the Beninese part of this range, although there is a critical lack of basic data on its ecological function. The present study assesses the effects of topography and aspect on the grassland biomass production of these mountains. The results show that annual grassland biomass production averages 5.29 tonnes dry matter (DM)/ha. This biomass production is significantly impacted by aspect (east facing versus west facing). Biomass is lower on east-facing sides (4.97 tonnes DM/ha) than on west-facing sides (6.10 tonnes DM/ha) and hilltops and valleys (6.24 tonnes DM/ha). This effect may be explained by direct exposure of east-facing sides to the harmattan, a northeast dry wind blowing from the Sahara Desert. No significant impact of topography on biomass production is observed.

Woody biomass and bioenergy potentials in Southeast Asia between 1990 and 2020

Forests in Southeast Asia are important sources of timber and other forest products, of local energy for cooking and heading, and potentially as sources of bioenergy. Many of these forests have experienced deforestation and forest degradation over the last few decades. The potential flow of woody biomass for bioenergy from forests is uncertain and needs to be assessed before policy intervention can be successfully implemented in the context of international negotiations on climate change. Using current data, we developed a forest land use model and projected changes in area of natural forests and forest plantations from 1990 to 2020. We also developed biomass change and harvest models to estimate woody biomass availability in the forests under the current management regime. Due to deforestation and logging (including illegal logging), projected annual woody biomass production in natural forests declined from 815.9 million tons (16.3 EJ) in 1990 to 359.3 million tons (7.2 EJ) in 2020. Woody biomass production in forest plantations was estimated at 16.2 million tons yr −1 (0.3 EJ), but was strongly affected by cutting rotation length. Average annual woody biomass production in all forests in Southeast Asia between 1990 and 2020 was estimated at 563.4 million tons (11.3 EJ) yr −1 declining about 1.5% yr −1. Without incentives to reduce deforestation and forest degradation, and to promote forest rehabilitation and plantations, woody biomass as well as wood production and carbon stocks will continue to decline, putting sustainable development in the region at risk as the majority of the population depend mostly on forest ecosystem services for daily survival.

Carbon input, loss and storage in sub-tropical Indian Inceptisol under multi-ratooning sugarcane

Changes in residue management and incorporation of organic manures may help in carbon sequestration, restoring soil organic carbon (SOC) and sustaining the productivity of land under a cropping system. An experiment of multi-ratooning sugarcane ( Saccharum officinarum L.) was initiated in 2003 in Inceptisols of Indian subtropics, to assess the effect of different organic manures and chemical fertilizer, on the crop productivity and soil quality. The annual sugarcane shoot biomass production in organic manure treatments was at par with the chemically fertilized treatment. Gross input of carbon (GIC) by the sugarcane crop was estimated to be 11.7–12.4 t ha −1 y −1 in different organic manure treatments compared to 8.4 and 5.0 t ha −1 y −1 in NPK and control treatments, respectively. The respiratory loss of C (RLC) increased linearly with increasing input of C in soil and it ranged from 3.3 to 4.1 t ha −1 y −1 in different treatments with maximum in FYM and minimum in control treatment. The sugarcane biomass added in the soil humified at a rate constant of 0.38 in sub-tropical conditions and an addition of 3.9 t C ha −1 y −1 is required to maintain SOC in equilibrium. After 5 years of sugarcane cropping (one plant + four ratoons) an increase of 2.3–17.1 t ha −1 in SOC over initial content was recorded with different treatments. Results in coming years from this long-term experiment shall add to the present calculated relationships between carbon addition and storage in sugarcane multi-ratooning crop production system under sub-tropical condition of India.

Responses of CO2 Exchange and Primary Production of the Ecosystem Components to Environmental Changes in a Mountain Peatland

The complexity of natural ecological systems presents challenges for predicting the impact of global environmental changes on ecosystem structure and function. Grouping of plants into functional types, that is, groups of species sharing traits that govern their mechanisms of response to environmental perturbations, reduce the complexity of species diversity to a few key plant types for better understanding of ecosystem responses. Chambers were used to measure CO2 exchange in grass and moss growing together in a mountain peatland in southern Germany to assess variations in their response to environmental changes and how they influence ecosystem CO2 exchange. Parameter fits and comparison for net ecosystem exchange (NEE) in two ecosystem components were conducted using an empirical hyperbolic light response model. Annual green biomass production was 320 and 210 g dwt m−2, whereas mean maximum NEE was –10.0 and –5.0 μmol m−2 s−1 for grass and moss, respectively. Grass exhibited higher light use efficiency (α) and maximum gross primary production [(β+γ)2000]. Leaf area index explained 93% of light use and 83% of overall production by the grass. Peat temperature at 10-cm depth explained more than 80% of the fluctuations in ecosystem respiration (R eco). Compared to grass, moss NEE was more sensitive to ground water level (GWL) draw-down and hence could be more vulnerable to changes in precipitation that result in GWL decline and may be potentially replaced by grass and other vegetation that are less sensitive.

Impacts of micro-basin water harvesting structures in improving vegetative cover in degraded hillslope areas of north-east Ethiopia

Water is one of the most important entry points to improve rural livelihoods in drought affected areas of the north-eastern Amhara region in Ethiopia. Various attempts have been made to overcome this problem by making use of different water harvesting structures. However, the choice of structures has been difficult because of a lack of empirical evidence on the relative effectiveness of the different structures. An experiment was conducted from 2002 to 2004 to compare and evaluate three different water harvesting structures (eye-brow basin, half-moon and trench) against the normal seedling plantation practice by farmers (normal pit) as a control. Data on root collar diameter (RCD), diameter at breast height (DBH), height and survival rate of Acacia saligna tree seedlings was collected at 3-month intervals after planting and annual grass biomass production was also measured. Trench and eye-brow basin structures produced 68, 95, 52 and 44% increases in RCD, DBH, height and survival rate, respectively, 15 months after planting compared with the normal pit. Trench structures increased grass biomass by 41.1% compared with normal pits. Eye-brow basins are recommended on hillsides where stone is available while trenchs could be used where stone is scarce. The results indicated that well designed water harvesting micro-basin structures can mitigate the effect of dry spell shocks on tree seedling performance and land cover rehabilitation. They were also very effective in increasing grass biomass production indicating the potential for improving livestock feed on the available barren hillsides.

Growing Ulva (Chlorophyta) in integrated systems as a commercial crop for abalone feed in South Africa: a SWOT analysis

Over 1,000t fresh weight of Ulva was cultivated on South African abalone farms in 2007, primarily for feed, but in one case to allow partial re-circulation by nutrient removal. The potential of this new commercial crop is analysed. Material is collected from natural free-floating populations and at least four species are commonly grown, with different ecophysiological characteristics. A brown epiphyte, Myrionema strangulans, causes a disease of the Ulva, which is currently managed by farmers by re-stocking. The main potential threat is that some farmers are wary of integrated systems, fearing they may promote disease in abalone, although Ulva has been grown in abalone effluent and fed back to the abalone on one farm for 6 years without adverse effects. Opportunities exist for the expansion of Ulva cultivation via further spread of the abalone industry, the inclusion of seaweed raceways in proposed fish-farming activities, or the potential for the inclusion of high quality cultivated Ulva as a constituent in aquafeed. A conservative estimate of production over a full year from these raceway systems was 26.1 g dw m−2 day−1 (2006) and 19.7 g dw m−2 day−1 (2007), similar to maximum figures for total annual microalgal biomass production in outdoor systems.

Lagged effects of experimental warming and doubled precipitation on annual and seasonal aboveground biomass production in a tallgrass prairie

AbstractGlobal climate change is expected to result in a greater frequency of extreme weather, which can cause lag effects on aboveground net primary production (ANPP). However, our understanding of lag effects is limited. To explore lag effects following extreme weather, we applied four treatments (control, doubled precipitation, 4 °C warming, and warming plus doubled precipitation) for 1 year in a randomized block design and monitored changes in ecosystem processes for 3 years in an old‐field tallgrass prairie in central Oklahoma. Biomass was estimated twice in the pretreatment year, and three times during the treatment and posttreatment years. Total plant biomass was increased by warming in spring of the treatment year and by doubled precipitation in summer. However, double precipitation suppressed fall production. During the following spring, biomass production was significantly suppressed in the formerly warmed plots 2 months after treatments ceased. Nine months after the end of treatments, fall production remained suppressed in double precipitation and warming plus double precipitation treatments. Also, the formerly warmed plots still had a significantly greater proportion of C4 plants, while the warmed plus double precipitation plots retained a high proportion of C3 plants. The lag effects of warming on biomass did not match the temporal patterns of soil nitrogen availability determined by plant root simulator probes, but coincided with warming‐induced decreases in available soil moisture in the deepest layers of soil which recovered to the pretreatment pattern approximately 10 months after the treatments ceased. Analyzing the data with an ecosystem model showed that the lagged temporal patterns of effects of warming and precipitation on biomass can be fully explained by warming‐induced differences in soil moisture. Thus, both the experimental results and modeling analysis indicate that water availability regulates lag effects of warming on biomass production.

Secondary production, longevity and resource consumption rates of freshwater shrimps in two tropical streams with contrasting geomorphology and food web structure

Summary1. Freshwater shrimps often dominate the biomass of tropical island streams and are known to have strong effects on stream ecosystem structure and function, but little effort has been dedicated toward quantifying basic energetic and life history attributes such as growth, production and longevity. Such information is critical for understanding both the role of shrimps in ecosystem dynamics and the gravity of threats to shrimp populations posed by human activities such as shrimp harvesting, dam construction and water withdrawal.2. We quantified growth rates and secondary production of dominant freshwater shrimps for 3 years in two Puerto Rican headwater streams that differ in food web structure because of the presence or absence of predatory fishes that are excluded from reaches above waterfalls. Using growth data, we constructed a minimum longevity model to explore the likely minimum life spans of the two dominant taxa (Atya spp. and Xiphocaris elongata). Finally, we used a bioenergetics model to quantify annual consumption rates of major basal resources by the two taxa.3. Daily growth rates ranged from −0.001 to 0.011 day−1, were inversely related to body size, and were higher for small individuals of X. elongata than Atya spp. Mean annual shrimp biomass and secondary production were an order of magnitude higher in the stream that lacked predatory fishes (biomass: 4.34 g AFDM m−2; production: 0.89 g AFDM m−2 year−1) than in the stream with predatory fishes (biomass: 0.12 g AFDM m−2; production: 0.02 g AFDM m−2 year−1). Production : biomass ratios ranged from 0.01 to 0.38.4. Our longevity model predicted a minimum life span of 8 years for Atya spp. and 5 years for X. elongata in the stream lacking predatory fishes. In contrast, due to a larger average size of X. elongata in the stream with predatory fishes, our model predicted a minimum life span of 11 years. Actual life spans of these taxa are likely to be much longer based on long‐term observations of marked individuals.5. Estimated consumption rates from the bioenergetics model indicated that Atya spp. and X. elongata are important processors of organic matter resources in streams where they occur at high densities. Atya spp. and X. elongata appeared capable of consuming a large proportion of algal and insect production and the proportion of direct leaf litter inputs consumed was also appreciable (c. 40–60%). However, the consumption of suspended fine particulate organic matter (SFPOM) by Atya spp. is probably only a minor proportion of total SFPOM flux in these streams.6. Our study suggests that geomorphic features such as waterfalls may play an important role in controlling the distribution and production of freshwater shrimps through their effects on predatory fish movement. Spatial differences in shrimp densities result in landscape‐scale variation in the significance to ecosystem processes of these long‐lived organisms, particularly as processors of major organic matter resources.

Comparison of Medusahead-Invaded and Noninvaded Wyoming Big Sagebrush Steppe in Southeastern Oregon

Medusahead (Taeniatherum caput-medusae [L.] Nevski) is an exotic, annual grass invading sagebrush steppe rangelands in the western United States. Medusahead invasion has been demonstrated to reduce livestock forage, but otherwise information comparing vegetation characteristics of medusahead-invaded to noninvaded sagebrush steppe communities is limited. This lack of knowledge makes it difficult to determine the cost–benefit ratio of controlling and preventing medusahead invasion. To estimate the impact of medusahead invasion, vegetation characteristics were compared between invaded and noninvaded Wyoming big sagebrush (Artemisia tridentata subsp. wyomingensis [Beetle & A. Young] S. L. Welsh) steppe communities that had similar soils, topography, climate, and management. Noninvaded plant communities had greater cover and density of all native herbaceous functional groups compared to medusahead-invaded communities (P < 0.01). Large perennial grass cover was 15-fold greater in the noninvaded compared to invaded plant communities. Sagebrush cover and density were greater in the noninvaded compared to the medusahead-invaded communities (P < 0.01). Biomass production of all native herbaceous functional groups was higher in noninvaded compared to invaded plant communities (P < 0.02). Perennial and annual forb biomass production was 1.9- and 45-fold more, respectively, in the noninvaded than invaded communities. Species richness and diversity were greater in the noninvaded than invaded plant communities (P < 0.01). The results of this study suggest that medusahead invasion substantially alters vegetation characteristics of sagebrush steppe plant communities, and thereby diminishes wildlife habitat, forage production, and ecosystem functions. Because of the broad negative influence of medusahead invasion, greater efforts should be directed at preventing its continued expansion. La cabeza de medusa (Taeniatherum caput-medusae [L.] Nevski) es una grama anual exótica que invade los pastizales de triguillo crestado en el oeste de los Estados Unidos. Se ha demostrado que la invasión de la cabeza de medusa reduce el forraje para el ganado, sin embargo otra información sobre las estepas de triguillo crestado invadida y no invadida por la cabeza de medusa es limitada. Esta ausencia de conocimiento hace difícil determinar la relación costo–beneficio para controlar y prevenir la invasión de la cabeza de medusa. Para estimar el impacto de la invasión de cabeza de medusa, se compararon las características vegetativas entre las comunidades de estepas de triguillo crestado grande de Wyoming (Artemisia tridentata subsp. wyomingensis [Beetle & A. Young] S. L. Welsh) invadida y no invadida con suelos, topografía, clima, y manejo similares. Las comunidades de plantas no invadidas tuvieron la mayor cobertura y densidad de todos los grupos funcionales de las herbáceas nativas comparadas a las comunidades de cabeza de medusa invadida (P < 0.01). La cobertura grande de grama perene fue 15 veces mayor en las comunidades no invadidas comparada con las comunidades de plantas invadidas. La cobertura del triguillo crestado fue mayor en las comunidades no invadidas comparada con las comunidades de cabeza de medusa invadidas (P < 0.01). La producción de biomasa de todos los grupos funcionales de herbáceas nativas fueron mayor en las no invadidas comparadas con las comunidades de plantas invadidas (P < 0.02). La producción de biomasa de la hierba anual y perene fue de 1.9 y 45 veces más, respectivamente, en las comunidades no invadidas que en las comunidades invadidas. La diversidad y la riqueza de especies fueron mayor en las comunidades no invadidas que en las comunidades de planta invadidas (P < 0.01). Los resultados de este estudio sugieren que la invasión de la cabeza de medusa altera sustancialmente las características vegetativas de las comunidades de estepas de triguillo crestado; y de ese modo, disminuye el hábitat de vida silvestre, la producción de forraje y las funciones del ecosistema. Debido a la amplia influencia negativa en la invasión de la cabeza de medusa mayores esfuerzos deben ser dirigidos para prevenir su continua expansión.

Site Characteristics Determine the Success of Prescribed Burning for Medusahead (Taeniatherum caput-medusae) Control

AbstractMedusahead is one of the most problematic rangeland weeds in the western United States. In previous studies, prescribed burning has been used successfully to control medusahead in some situations, but burning has failed in other circumstances. In this study, trials were conducted using the same protocol at four locations in central to northern California to evaluate plant community response to two consecutive years of summer burning and to determine the conditions resulting in successful medusahead control. During 2002 through 2003 large-scale experiments were established at two low-elevation, warm-winter sites (Fresno and Yolo counties) and two higher elevation, cool-winter sites (Siskiyou and Modoc counties). Plant species cover was estimated using point-intercept transects, and biomass samples were taken in each plot. After 2 yr of burning, medusahead cover was reduced by 99, 96, and 93% for Fresno, Yolo, and Siskiyou counties, respectively, compared to unburned control plots. Other annual grasses were also reduced, but less severely, and broadleaf species increased at all three sites. In contrast, 2 yr of burning resulted in a 55% increase in medusahead at the coolest winter site in Modoc County. In the second season after the final burn, medusahead cover remained low in burned plots at Fresno and Yolo counties (1 and 12% of cover in unburned controls, respectively), but at the Siskiyou site medusahead recovered to 45% relative to untreated controls. The success of prescribed burning was correlated with biomass of annual grasses, excluding medusahead, preceding a burn treatment. It is hypothesized that greater production of combustible forage resulted in increased fire intensity and greater seed mortality in exposed inflorescences. These results demonstrate that burning can be an effective control strategy for medusahead in low elevation, warm-winter areas characterized by high annual grass biomass production, but may not be successful in semiarid cool winter areas.

Seasonal variation in the biomass, quantity and quality of agar from Gelidiella acerosa (Forsskal) Feldmann et Hamel (Gelidiales, Rhodophyta) from the Gulf of Mannar Marine Biosphere Reserve, India

SUMMARYThe Gulf of Mannar on the southeast coast of India, which has recently been declared as biosphere reserve, is the main harvesting place of Gelidiella acerosa for the Indian agar industry. The biomass harvested from natural stocks was estimated to be over 10 000 tonnes dry weight (DW) in the last two decades and is a serious cause of concern on long term sustainability of this valuable resource from this region. The present study reports the seasonal variation in the biomass and agar yield and quality from G. acerosa in four different habitats such as Rameswaram (rocky intertidal), Ervadi (lower intertidal), Sethukarai (subtidal) and Krusadai Island (lagoon reef area). A maximum biomass of 260 ± 26 g DW m−2 was recorded from Ervadi, whereas Sethukarai showed the highest percentage cover (69.83 ± 4.83%) and density (208.20 ± 30.16 plants m−2). Biomass, percentage cover and density were lowest in Rameswaram and significantly lower (P &lt; 0.001) than the other three stations. A single peak in biomass was observed with autumn maxima in Ervadi and Rameswaram and southwest monsoon maxima in Sethukarai and Krusaidai Island. Length of G. acerosa was maximum (9.65 ± 0.25 cm) in Ervadi and the branch index value was maximum (24.70 ± 4.01 br−1 g−1 DW) for Rameswaram. Agar yield (37.24 ± 7.59%) and gel strength (448.66 ± 6.50 g/cm2) were higher in Sethukarai plants. The agar yields attained a peak in the northeast monsoon and decreased in summer, whereas a reverse trend was observed for gel strength. Evidently, agar yield showed a strong negative correlation with gel strength (P &lt; 0.0001) and gelling (P &lt; 0.0001) and melting temperatures (P &lt; 0.01). The single annual peak in biomass observed in the present study, as compared with two peaks reported earlier, are attributed to the continuous overharvesting that would have had an effect on the overall annual biomass production. The findings of this study reveal that a single harvest during the autumn months (January to March) could yield optimum biomass with moderate agar and that would be the best for sustainable usage and conservation of this resource from this region.

Companion crop performance in relation to annual biomass production, resource supply, and subsoil drying

A field experiment located in NE Victoria compared the productivity of cereals sown into mature lucerne (companion crop) with cereals and lucerne grown as monocultures. Additional nitrogen (N) and water was applied to investigate if increased resource supply could alleviate competition and improve cereal performance in the presence of lucerne. Cereal plant populations, lucerne and cereal biomass, and cereal grain yields and protein were measured throughout the experiment. Soil water content was also monitored over time to determine whether companion cropping compromised the ability of lucerne to extract deep soil water. While companion cropping depressed both lucerne and cereal production, the combined annual biomass production was greater than cereal and lucerne when grown alone. Averaged over the three seasons, companion cropping resulted in a 31% increase (P &lt; 0.05) in total annual biomass compared with the lucerne monoculture, and an 18% increase compared with the cereal monoculture in the 2004–05 and 2005–06 seasons. Cereals growing with lucerne produced fewer tillers, spikes and consequently cereal biomass compared with cereals growing as a monoculture. Therefore, companion crops yielded 25% less (P &lt; 0.05) grain compared with the cereal monoculture over the 3-year study. Competition for N and light in the pre-cereal stem elongation period, were likely causes. Increasing the supply of N and water did not result in a main treatment (monoculture v. companion crop) by additional resource interaction, indicating that cereal responses were the same irrespective of lucerne’s presence. The application of N, water and these combined inputs, resulted in a 13–40%, 35% and 49% increase (P &lt; 0.05) in cereal grain yields, respectively. While companion cropping compromised lucerne’s capacity to extract water from deep soil layers to a degree, this practice was still able to maintain drier subsoil in comparison to the cereal monoculture.

Groundnut/Cassava/Maize Intercrop Yields over Three Cycles of Planted Tree Fallow/Crop Rotations on Ultisol in Southern Cameroon

ABSTRACT Lack of crop yield response to planted tree fallow led to introducing a two-year fallow phase to determine if planted tree fallow can improve soil fertility and yields over a no-tree control. Three cycles of two years fallow followed by slash-and-burn land preparation and one year of groundnut/cassava/maize intercropping were conducted with Senna spectabilis, Flemingia macrophylla and Dactyladenia barteri as planted hedgerow fallows and a no-tree control on an Ultisol in southern Cameroon. The land had been continuously cropped to maize/cassava intercrop for 5 years previous to the first two-year fallow phase. Groundnut grain yields were unaffected by fallow system in 1998 and 2001 and the sum of the three cropping years. Maize grain yield was unaffected by fallow system in 1998. In 2001 and 2004 maize grain yield was highest in the S. spectabilis system. Total maize grain yield across the three cropping years was higher in the F. macrophylla and S. spectabilis systems than in the D. barteri system. Cassava root yields were in all years and the sum of the 3 years unaffected by fallow system. Cassava root (1998, 2001) and groundnut grain (2001) yields had significant spatial responses to the distance from hedgerows, with yield increases with increasing distance from hedgerows. Annual biomass production of hedgerow prunings during cropping phases ranged from zero (D. barteri) to 3.4 Mg ha−1 (S. spectabilis). During the growth of groundnut and maize, hedgerows produced < 1 Mg ha−1 in 1998, < 0.6 Mg ha in 2001 and <0.8 Mg ha at any individual pruning. Combined relative crop yields over the three cycles were lower in planted fallow than in the no-tree control. The N export with groundnut and maize grain and cassava roots, as an indicator of crude protein production was lower in the planted hedgerow fallow systems than in no-tree control. The planted fallow hedgerow system appears unsuitable to improve crop yields because the nutrient supply from prunings is low due to their low biomass production. Yet on short distances, the spatial response of cassava and groundnut indicates competition between hedgerows and crops, which was most pronounced on cassava and groundnut in the S. spectabilis system. The crop combination appears incompatible as benefits realized by the maize were outweighed by losses in groundnut.

Browse biomass production an.regrowth capacity after biomass loss in deciduous and coniferous trees: responses to moose browsing along a productivity gradient

To understand how large herbivores interact with their food resources and the ecosystem, it is necessary to understand plant growth responses to biomass loss. Tolerance to biomass loss, and the ability to regrow new photosynthetic tissue after herbivore attack, is one such important mechanism. Here we experimentally studied how year‐round browsing corresponding to four different levels of moose, Alces alces, population density affected total annual browse biomass production, which also serves as a proxy for production of new photosynthetic tissue, in birch (Betula pubescens and B. pendula) and Scots pine, Pinus sylvestris, along a habitat productivity gradient. Our results revealed that habitat productivity index was the most important variable determining annual browse biomass production for birch, and that a high moose density and biomass removals of 25–40% annually actually could stimulate birch above‐ground productivity in more productive sites. Contrary to birch, pine was not affected by habitat productivity index, and appeared to have much lower regrowth capacity than birch. For pine, percent biomass removed was the most important factor affecting annual browse biomass production, which decreased with increasing levels of biomass removal. We also tested if birch and pine responded to biomass removal by allocating more resources to browse biomass production at in the lower portion of the stem (0–0.5 m), which was protected from biomass removal in winter. Birch did not allocate more resources to biomass production in the lower portion of the stem, whereas pines subjected to high biomass removal had more biomass in the lower portion of the stem than those protected from losses. Our study thus shows that plant responses can be linear or non‐linear along the range of herbivore densities we studied, and that responses can change from negative to positive along underlying habitat productivity gradients.

Bioremediation efficiency in the removal of dissolved inorganic nutrients by the red seaweed, Porphyra yezoensis, cultivated in the open sea

The bioremediation capability and efficiency of large-scale Porphyra cultivation in the removal of inorganic nitrogen and phosphorus from open sea area were studied. The study took place in 2002–2004, in a 300 ha nori farm along the Lusi coast, Qidong County, Jiangsu Province, China, where the valuable rhodophyte seaweed Porphyra yezoensis has been extensively cultivated. Nutrient concentrations were significantly reduced by the seaweed cultivation. During the non-cultivation period of P. yezoensis, the concentrations of NH 4-N, NO 2-N, NO 3-N and PO 4-P were 43–61, 1–3, 33–44 and 1–3 μmol L −1, respectively. Within the Porphyra cultivation area, the average nutrient concentrations during the Porphyra cultivation season were 20.5, 1.1, 27.9 and 0.96 μmol L −1 for NH 4-N, NO 2-N, NO 3-N and PO 4-P, respectively, significantly lower than in the non-cultivation season ( p<0.05). Compared with the control area, Porphyra farming resulted in the reduction of NH 4-N, NO 2-N, NO 3-N and PO 4-P by 50–94%, 42–91%, 21–38% and 42–67%, respectively. Nitrogen and phosphorus contents in dry Porphyra thalli harvested from the Lusi coast averaged 6.3% and 1.0%, respectively. There were significant monthly variations in tissue nitrogen content ( p<0.05) but not in tissue phosphorus content ( p>0.05). The highest tissue nitrogen content, 7.65% in dry wt, was found in December and the lowest value, 4.85%, in dry wt, in April. The annual biomass production of P. yezoensis was about 800 kg dry wt ha −1 at the Lusi Coast in 2003–2004. An average of 14708.5 kg of tissue nitrogen and 2373.5 kg of tissue phosphorus in P. yezoensis biomass were harvested annually from 300 ha of cultivation from Lusi coastal water. These results indicated that Porphyra efficiently removed excess nutrient from nearshore eutrophic coastal areas. Therefore, large-scale cultivation of P. yezoensis could alleviate eutrophication in coastal waters economically.

Dominant species constrain effects of species diversity on temporal variability in biomass production of tallgrass prairie

Species diversity is thought to stabilize functioning of plant communities. An alternative view is that stability depends more on dynamics of dominant species than on diversity. We compared inter‐annual variability (inverse of stability) of aboveground biomass in paired restored and remnant tallgrass prairies at two locations in central Texas, USA. Data from these two locations were used to test the hypothesis that greater richness and evenness in remnant than restored prairies would reduce variability in aboveground biomass in response to natural variation in rainfall. Restored prairies were chosen to be similar to paired remnant prairies in characteristics other than species diversity that affect temporal variability in biomass. Variability was measured as the coefficient of variation among years (square root of variance/mean; CV), where variance in community biomass equals the sum of variances of individual plant species plus the summed covariances between species pairs. Species diversity over five years was greater by a factor of 2 or more in remnant than restored prairies because richness and evenness were greater in remnant than restored prairies. Still, the CV of community biomass during spring and CV of annual biomass production did not differ consistently between prairie types. Neither the sum of species covariances nor total community biomass differed between prairies. Biomass varied relatively little in restored compared to remnant prairies because biomass of the dominant species in restored prairies (the grassSchizachyrium scoparium) varied less than did biomass of other dominant and sub‐dominant species. In these grasslands, biomass response to natural variation in precipitation depended as much on characteristics of a dominant grass as on differences in diversity.