Higher Aboveground Biomass Production Research Articles

Effects of perennial biomass yield energy grasses and fertilization on soil characteristics and nutrient balances

AbstractBesides its bioenergy potential, perennial grasses can also have positive impacts on soil quality. However, responses of soil organic carbon (SOC) and total nitrogen (TN) depend on multiple factors, including grass species selection and N and P addition. We investigated the effect of four N and P fertility treatments (control = 0 kg N + 0 kg P ha–1 [N0P0]; 100 kg N + 0 kg P ha–1 [N1P0]; 0 kg N + 100 kg P ha–1 [N0P1]; 100 kg N + 100 kg P ha–1 [N1P1] applied annually] across 9 yr in Uruguay on soil nutrient balances, C and N pools, and biomass yields of elephantgrass (EG) (Pennisetum purpureum Schum.), giant reed (GR) (Arundo donax L.), and switchgrass (SW) (Panicum virgatum L.). Across years, EG had the highest biomass yield, followed by GR and SW (18.9, 16.3, and 14.1 Mg ha–1 yr–1, respectively). Across species, aboveground biomass increased by 46% with N addition. Yield response to P fertilization was lower (+11%). Elephantgrass had the highest N and P negative balance. Soil organic C and TN concentration were affected by species but not by fertilizer treatments. Giant reed had the highest SOC content gain in the first 0–40 cm (540 kg C ha– yr–1), and was the only species maintaining TN content from the beginning of the study. Giant reed could be an excellent option as a bioenergy crop due to its high aboveground biomass production, and its positive impacts on SOC and TN pools.

Plant Morphoecological Traits, Grass-Weed Interactions and Water Use Efficiencies of Grasses Used for Restoration of African Rangelands

Degradation characterized by depleted vegetation cover is a serious environmental problem in African rangelands. It poses a serious threat to millions of pastoralists and agropastoralists who depend on livestock as a source of livelihood. Consequently, there has been a growing global interest to consolidate efforts to restore degraded ecosystems. For example, the UN decade of Ecosystem Restoration initiative aims at uniting the world behind a common goal of preventing, halting and reversing the degradation of ecosystems. Grass reseeding using native perennial species has been identified as one of the practical ecological strategies for restoring degraded African rangelands, enhancing vegetation cover and forage production. Knowledge of the multifaceted performance of African rangeland grasses in terms of morphoecological traits, interaction with weeds and water use efficiencies is however largely limited and often elusive. Perennial grasses indigenous to African rangelands Cenchrus ciliaris L. (African foxtail grass), Enteropogon macrostachyus (Hochst. Ex A. Rich.) Monro ex Benth. (Bush rye grass) and Eragrostis superba Peyr. (Maasai love grass), were established in an African semi-arid rangeland under natural conditions to fill this knowledge gap. Morphoecological plant traits: aboveground biomass (shoot, leaf and stem) production, plant densities, basal cover, tiller densities and plant height were measured 9 months after establishment. Interaction between the target grass species and weeds and water use efficiencies (WUE) were also determined. Enteropogon macrostachyus displayed significantly higher values for plant densities, tiller densities and basal cover, indices commonly used to estimate the potential of grasses for ecological restoration. Eragrostis superba produced the highest shoot biomass and water use efficiencies. This is attributed to its higher leafy biomass fraction. Higher aboveground biomass production of E. superba demonstrate its suitability for enhancing rangeland productivity. Cenchrus ciliaris suppressed the weeds. This is linked to its aggressive and allelopathic nature. In conclusion, the three perennial grasses displayed distinct morphoecological traits. In order to achieve successful seed-based restoration of degraded African rangelands using native perennial grasses, careful selection species to maximize on their unique traits is recommended. Ultimately, this selection process should match the desired restoration outcomes and subsequent use of the rangeland.

Oak sprouts grow better than seedlings under drought stress

Abstract: This study focused on the comparison of two contrasting forest regeneration types and their susceptibility to drought stress. Transpiration and biomass production were studied on young sessile oak trees Quercus petraea (Matt.) Liebl. regenerated as sprouts and seedlings, and grown in a coppice experimental site in the Czech Republic. Biomass production was estimated using destructive methods, while transpiration was derived from sap flow measurements and assessed according to the plant biometry and microclimatic conditions. Sprouts were characterized by a significantly higher diameter, height, leaf area and above-ground biomass and by a lower wood density as compared with seedlings of the same age. Moreover, the sap flow of sprouts was higher than that of seedlings, which was explained by the plant dimension. Transpiration, expressed as sap flow scaled to plant leaf area, did not differ between seedlings and sprouts when soil water was not limiting. However, during drought periods, when soil water potential dropped below -1.4 MPa, sprouts transpired significantly more than seedlings. Our results confirm that sprouts have access to a larger water pool via the old stump root system and are able to draw more water under drought. Moreover, sprouts seemed to be less susceptible to water limitations than seedlings of similar age. Less influence of drought on sprouts may partially explain their higher above-ground biomass production. Based on our results, coppice could be an appropriate management system to be adopted in sites characterized by frequent or extreme drought periods.

Diurnal and seasonal variations of soil respiration rate under different row-spacing in a Panicum virgatum L. field on semi-arid Loess Plateau of China

Soil respiration (SR) in crop field is affected by environmental factors, agronomic practices and crop types. To clarify how planting density affects the SR dynamics in switchgrass (Panicum virgatum L.) field on the semi-arid Loess Plateau, this research investigated diurnal and seasonal changes of soil respiration rate (RS) under three different row-spacing treatments (20, 40 and 60 cm) in the fourth growing year of switchgrass. Results showed that RS presented a pronounced seasonality under all row-spacing treatments. The highest daily average RS values appeared in August, while the lowest (P<0.05) were in September for each row-spacing. Diurnal variations of RS exhibited single-peak curves in each month. Daily average RS increased significantly as row-spacing enlarged during May and August but there was no significant difference among row-spacing treatments in September. Soil water storage in the depth of 0–100 cm had no significant difference (P>0.05) among the row-spacing treatments, and similar results were found for soil temperature in 0–15 cm soil depth. Soil respiration temperature sensitivity (Q10) values were 1.0–3.7 during the growing months, which were strongly correlated with air temperature in May and June and the soil temperature at 15 cm depth in August. Higher aboveground biomass production and lower RS in most growth months indicated that 20 cm row-spacing treatment was beneficial for increasing the carbon fixation in switchgrass field. Results also implied that it is necessary to take into account the influence of phenology and root growth of switchgrass on soil respiration for accurately evaluating the carbon cycle in the region.

Tissue chemistry and morphology affect root decomposition of perennial bioenergy grasses on sandy soil in a sub‐tropical environment

AbstractSecond‐generation biofuels and bio‐based products derived from lignocellulosic biomass are likely to replace current fuels derived from simple sugars and starch because of greater yield potential and less competition with food production. Besides the high aboveground biomass production, these bioenergy grasses also exhibit extensive root systems. The decomposition of root biomass greatly influences nutrient cycling and microbial activity and subsequent accumulation of carbon (C) in the soil. The objective of this research was thus to characterize root morphological and chemical differences in six perennial grass species in order to better understand root decomposition and belowground C cycling of these bioenergy cropping systems. Giant reed (Arundo donax), elephantgrass (Pennisetum purpureum), energycane (Saccharum spp.), sugarcane (Saccharum spp.), sweetcane (Saccharum arundinaceum), and giant miscanthus (Miscanthus × giganteus) were established in Fall 2008 in research plots near Gainesville, Florida. Root decomposition rates were measured in situ from root decomposition bags over 12 months along with initial and final root tissue composition. Root potential decomposition rate constant (K) was higher in elephantgrass (3.64 g kg−1 day−1) and sweetcane (2.77 g kg−1 day−1) than in sugarcane (1.62 g kg−1 day−1) and energycane (1.48 g kg−1 day−1). Notably, K was positively related to initial root tissue total C (Total C), total fiber glucose (TFG), total fiber xylose (TFX), and total fiber carbohydrate (TFC) concentrations, but negatively related to total fiber arabinose (TFA) and lignin (TL) concentrations and specific root volume (SRV). Among the six species, elephantgrass exhibited root traits most favorable for fast decomposition: high TFG, high TFX, high TFC, high specific root length (SRL), and a low SRV, whereas giant reed, sugarcane, and energycane exhibited slow decomposition rates and the corresponding root traits. Thus, despite similar aboveground biomass yields in many cases, these species are likely to differentially affect soil C accumulation.

Miscanthus clones for cellulosic bioethanol production: Relationships between biomass production, biomass production components, and biomass chemical composition

The perennial miscanthus crop is a promising feedstock for cellulosic ethanol production due to its high yield, low input and low environmental impacts. To be suitable for cellulosic ethanol production, cultivated Miscanthus clones need to present not only high aboveground biomass production, but also high cellulose and hemicellulose contents and low lignin, soluble, and ash contents. By testing M.×giganteus, M. sacchariflorus, and M. sinensis clones, we investigated the relationships between biomass production and biomass composition traits at two harvest dates over 3 years. High aboveground biomass production was associated with high canopy height, high stem diameter, late flowering, and high cellulose and lignin contents but low hemicellulose, soluble, and ash contents. The aboveground biomass production was positively correlated with the potential yields of cellulose, hemicelluloses, and lignins. These relationships were consistent throughout the years and the harvest dates. The most productive Miscanthus clones displayed high cellulose contents and low soluble and ash contents; however, they displayed low hemicellulose contents and high lignin contents. The total aboveground biomass composition was closer to the stem composition than to the leaf composition. Nevertheless, the leaves were interesting because of their high hemicellulose and low lignin contents. Lastly, all of the studied factors were significant, but the biomass production traits were mainly affected by the year of cultivation or clone, while the biomass composition traits were mainly affected by the harvest date. All of the traits showed low interaction effects. These results will guide the breeding of Miscanthus clones that are tailored for biofuel production.

Moving on from Metabolic Scaling Theory: hierarchical models of tree growth and asymmetric competition for light

Summary1. Coomes &amp; Allen (2009)showed that the Metabolic Scaling Theory of Plant Growth (MST‐PG) has no empirical support, because the only piece of confirmatory evidence was an analysis of a small and noisy data set from which it was impossible to draw strong inferences. Our re‐analyses showed that MST‐PG predictions were contained within very broad 95% confidence intervals, creating an illusion of close adherence to theoretical predictions. In a response to our paper,Stark, Bentley &amp; Enquist (2010)acknowledge these shortcomings.2. We reasoned that MST‐PG makes inaccurate predictions because asymmetric competition for light is not included in the theoretical model. We argued that asymmetric competition has its greatest impact on small trees within populations, such that the mean size‐scaling relationship of the population has a greater exponent than that of trees growing without competitors (i.e. the slope predicted by MST‐PG).Stark, Bentley &amp; Enquist (2010)appear to dispute this logic and criticize the statistical approach we developed to test our hypothesis.3. Here we use Bayesian hierarchical models (BHMs) to re‐examine three forest data sets, and find no support for MST‐PG. Based on a large data set from New Zealand, the majority of tall tree species have scaling exponents greater than predicted by MST‐PG, suggesting that asymmetric competition may have influenced the scaling relationships. Parameters for many small tree and shrub species were very poorly estimated, in part because their size ranges were narrow, so these species cannot be used to argue for, or against, MST‐PG.4. We hypothesize that scaling relationships are most affected by asymmetric competition in high‐productivity forests because, as many ecologists argue, competition for light is intense in such forests (the productivity‐dependent scaling hypothesis). We estimate growth scaling exponents forNothofagusforest sites which differed in above‐ground biomass (AGB) production. As predicted, scaling exponents were greater in sites with high AGB production and close to MST‐PG predictions in sites with low AGB production.5. Synthesis.Competition from taller neighbours has strong effects on tree growth, particularly in forests growing in productive locations. We continue to advocate for the inclusion of asymmetric competition into general models of tree growth, mortality, recruitment and size structure.

Biomass production, water use and photosynthesis of Salix clones grown in a wastewater purification system

Abstract An objective of the study was to identify leaf morphophysiological characteristics indicative of high aboveground woody biomass production of Salix clones growing in the vegetation filter of a wastewater purification system. It was hypothesized, that in these extra irrigated stands, the characteristics of photosynthesis are stronger determinants of the production than the characteristics of leaf water relations. The biomass production of the clones was correlated with numerous characteristics of leaf water relations and photosynthesis. Significant correlation was found between the biomass production and the following characteristics of top foliage leaves: daily decrease in water potential, stomatal conductance, stomatal sensitivity to increase in light intensity, and hydraulic conductance (positive); daily minimum and maximum water potentials, instantaneous water use efficiency, and stomatal sensitivity to decrease in leaf water potential (negative); maximum rate of photosynthetic electron transport, chlorophyll content, and the partitioning coefficient for leaf nitrogen into bioenergetics associated with electron transport (positive). In the most productive clones, the vertical gradient (through foliage) of values of almost all the characteristics was the smallest. The biomass correlated more strongly with the characteristics of photosynthesis light stage than with the characteristics of water relations. We conclude that the characteristics of photosynthesis light stage – high maximum rate of photosynthetic electron transport, high chlorophyll content, and also flat vertical gradient (through foliage) in values of the characteristics could be the strongest indicators of high biomass production of Salix clones growing in vegetation filter.

On-farm monitoring of economic and environmental performances of cropping systems: Results of a 2-year study at the field scale in northern Italy

Abstract Cropping systems in northern Italy are intensively managed, but an integrated environmental accounting of these systems has not been published yet. We conducted this study to evaluate cropping systems management in a study area in northern Italy using indicators. The study area is a regional agricultural Park, with cereal and livestock farms, cultivating mostly maize, rice, meadows, and winter cereals. To select the indicators, we identified for the study area the most relevant issues concerning the potential impact of agriculture on the environment: nutrient and pesticide management, use of fossil energy and soil management. Subsequently, we selected indicators from the literature, which could address these issues. We also added indicators describing the economic performance. The data were collected at the field level by periodic face-to-face interviews with seven farm managers over 2 years. Indicators were calculated for all crops cultivated in each field ( n = 266). According to the methodology proposed, the best economic performance (gross margin) was obtained by rice, followed by maize, winter cereals, and forage crops. Nitrogen and phosphorus surpluses were high for maize (due to a large use of animal manures), and moderate for rice and permanent meadows (where mineral fertilisers are not usually applied). Maize used high fossil energy inputs; however, the output/input ratio (an indicator of the dependence of food and feed production on non-renewable energy) was elevated, due to high aboveground biomass production. The potential impact due to pesticide use (evaluated with indicators that consider the toxicity and the exposure to active ingredients) was relevant only for rice, moderate for maize and other cereals, and null for forages. Finally, soil management was evaluated for the 2-year crop succession on each field ( n = 131): permanent meadows are excellent (due to continuous soil cover and large returns of organic carbon to soil), rice-based successions are unsatisfactory (due to low residues and manure application and continuous cropping), and maize successions are intermediate. This work shows that good quality data can be collected on-farm for economic and environmental accounting at field level. The indicators chosen for the analysis describe a range of issues in the study area, and make it possible to clearly separate and characterise different cropping systems. The procedure for their calculation is transparent and sound, and can be applied for ex-ante , ex-post , and monitoring procedures.

Contribution of Spartina maritima to the reduction of eutrophication in estuarine systems

Salt marshes are among the most productive ecosystems in the world, performing important ecosystem functions, particularly nutrient recycling. In this study, a comparison is made between Mondego and Tagus estuaries in relation to the role of Spartina maritima in nitrogen retention capacity and cycling. Two mono-specific S. maritima stands per estuary were studied during 1yr (biomass, nitrogen (N) pools, litter production, decomposition rates). Results showed that the oldest Tagus salt marsh population presented higher annual belowground biomass and N productions, and a slower decomposition rate for litter, contributing to the higher N accumulation in the sediment, whereas S. maritima younger marshes had higher aboveground biomass production. Detritus moved by tides represented a huge amount of aboveground production, probably significant when considering the N balance of these salt marshes. Results reinforce the functions of salt marshes as contributing to a reduction of eutrophication in transitional waters, namely through sedimentation processes.

Effects of trait plasticity on aboveground biomass production depend on species identity in experimental grasslands

Abstract Experimental studies with grassland species found a positive relationship between species richness and community biomass production, however the response of individual species was highly variable. The mechanisms behind these patterns are poorly understood. Here we studied aboveground biomass production and plasticity of growth characteristics of four legumes with similar morphology (Lotus corniculatus, Medicago lupulina, Onobrychis viciifolia, Trifolium hybridum) in experimental grasslands varying in species richness (1, 2, 4, 8, 16 and 60) and composition. We identified O. viciifolia and T. hybridum as species that reached higher biomass production in mixtures than expected from monoculture yields, while L. corniculatus and M. lupulina mostly had lower yields than expected. Variation of morphological traits across the species-richness gradient was lowest in the highly competitive O. viciifolia, but increased in the smaller species. The tall-growing O. viciifolia achieved higher biomass production by both, a higher number of plant individuals and an increase in mean mass per individual. Mean shoot number per individual remained constant, but individuals produced heavier shoots. The medium-sized T. hybridum also increased the number of plant individuals, but mean mass per individual did not respond to community species richness. The average mass per shoot was increased in mixtures, but the species developed less shoots per individual. Shoot length and stem weight ratio of T. hybridum increased with community species richness. Morphological changes in the less successful L. corniculatus and M. lupulina with a smaller growth stature were similarly directed as those of T. hybridum. The observed morphological changes are known as typical shade-avoidance mechanisms in dense vegetation. Our study shows that stress responses to changes in resource availability may be a mechanism to enforce higher aboveground biomass production of individual species in mixtures, but it depends on species identity whether trait plasticity is large enough to exceed stress-induced growth limitations.

Establishment of grassland species in monocultures: different strategies lead to success

The establishment pattern of monocultures of 61 species common to Central European semi-natural grasslands was analysed in a field experiment. The objectives were to identify key traits for successful establishment, defined in terms of above-ground biomass production, and to characterize the degree of niche overlap with respect to the use of above-ground resources, such as light and space. Four months after sowing, 15 species reached an above-ground biomass of more than 400 g m(-2). Highly productive monocultures adopted extremely different strategies of space filling in terms of canopy height, biomass density and centre of gravity of vertical biomass distribution. Regression tree analysis identified (1) the number of seedlings and (2) a trade-off between the development of a large number of small-sized shoots of species with intensive clonal growth in contrast to the establishment of fewer large-sized shoots as the two most important traits for successful establishment. Further variables associated with high above-ground biomass production by individual species were traits known to be relevant to the relative growth rate of herbaceous species, such as specific leaf area, leaf nitrogen or allocation between shoots and roots. The principle finding of this study is that the success of the 15 most productive species was not based on a single pathway but on a variable combination of traits. There are clearly many possible combinations of morphological and physiological features that will result in a species becoming productive, and these combinations differ among species in a local species pool.

Competition between two grass species with and without grazing over a productivity gradient

Soil nutrient-level and herbivory are predicted to have opposing effects on the allocation pattern of the competitive dominant plant species. Lower stem and higher leaf allocation are favoured when plants are grazed, whereas a higher stem allocation is favoured at high nutrient levels. Grazing by hares and geese can prevent invasion of the tall Elymus athericus, into short vegetation of Festuca rubra, at unproductive stages of salt-marsh succession but not at more productive stages. We hypothesise that the negative effect of herbivory on Elymus decreases due to increasing soil nitrogen levels and shifts the competitive balance towards this species. We tested how simulated grazing and nitrogen availability affected the competitive balance between adult plants of both grass species in a greenhouse experiment. Elymus had a higher above-ground biomass production, invested relatively more in stem and root tissue and had a larger shoot length than Festuca. The above-ground relative yield of Elymus in mixtures of both species increased with increasing nitrogen levels. This indicates that Elymus was the superior competitor at high soil fertility. Although clipping removed relatively more biomass from Elymus than from Festuca and exceeded the observed biomass removal in field conditions, it did not change the competitive balance between both species. Decreasing effects of herbivory due to increasing nitrogen levels are not a likely explanation for the invasion of Elymus in productive marshes. The results suggest that once Elymus has established it can easily invade vegetation dominated by Festuca irrespective of grazing by herbivores such as hares and geese. Herbivory by small herbivores may mainly retard the invasion of this plant by influencing establishment itself.

Effects of forest type and stand age on litterfall quality and soil N dynamics in Shikoku district, southern Japan

To evaluate the effects of forest type and stand age on forest N dynamics, we investigated the leaf-litter quality and soil N mineralization in four pairs of young and middle-aged forests in Shikoku district, southern Japan. The soil N mineralization rate determined by 28-day laboratory incubation ranges from 7.1 to 206.5 mg N kg −1 and was differed among forest types, decreasing in the order of hardwood > Japanese cedar > Japanese red pine = Hinoki cypress. The soil N mineralization rate was strongly correlated with the lignin/N ratio in leaf-litter. Leaf-litter N concentration and lignin/N ratio were different among forest types. Middle-aged forests had lower lignin concentration in leaf-litter, and marginally higher soil N mineralization than young forests. These results suggest that during stand development, the decrease in leaf-litter lignin concentration is an important mechanism that explains larger N cycling in older forests. In contrast, N concentration in leaf-litter was considered to represent the wide variation of N cycling among forest types. During stand development N use efficiency at the leaf level increased (lower N concentration in leaf-litter), whereas water use efficiency decreased (lower δ 13C in leaf-litter). The result suggests that there is a trade-off between NUE and WUE during stand development. However, in all eight forests, NUE and WUE were positively correlated. Japanese cedar and Hinoki cypress utilize both water and N resources more efficiently than hardwood species. Therefore, the efficient use of water and N of coniferous plantations may be related with high aboveground biomass production.