Changes In Biomass Production Research Articles

Fire increases aboveground biomass, seed production and recruitment success of Molinia caerulea in dry heathland

During the last decades, the perennial tussock grass Molinia caerulea has shown an increased abundance in European heathlands, most likely as a result of increased nitrogen deposition and altered management schemes. Because of its deciduous nature, Molinia produces large amounts of litter each year, which may affect the intensity and frequency of accidental fires in heathlands. These fires may influence plant population dynamics and heathland community organization through their effects on plant vital attributes and competitive interactions. In this study, fire-induced changes in competitive ability and invasiveness of Molinia through changes in biomass production, seed set and seed germination under both natural and laboratory conditions were investigated. We found that fire significantly increased aboveground biomass, seed set and germination of Molinia. Seed set was twice as high in burned compared to unburned heathland. Two years after fire, seedling densities in natural conditions were on average six times higher in burned than in unburned heathland, which resulted in increased abundance of Molinia after burning. The seed germination experiment indicated that seeds harvested from plants in burned heathland showed higher germination rates than those from unburned heathland. Hence, our results clearly demonstrate increased invasive spread of Molinia after large and intense fires. Active management guidelines are required to prevent further encroachment of Molinia and to lower the probability of large fires altering the heathland community in the future.

Stimulated growth of Betula pubescens and Molinia caerulea on ombrotrophic bogs: role of high levels of atmospheric nitrogen deposition

Summary 1 In order to test whether the observed invasion of ombrotrophic bogs in the Netherlands by Molinia caerulea and Betula pubescens is the result of long‐term high nitrogen (N) loads, we conducted a 3‐year fertilization experiment with Sphagnum fallax turfs. Six different N treatments were applied ranging from 0 (control) to 4 g N m−2 year−1. 2 During the experimental period, ammonium concentrations in the peat moisture remained very low due to high uptake rates by Sphagnum. Tissue N concentrations in S. fallax showed a linear response to the experimental N addition. Excess N was accumulated as N‐rich free amino acids such as arginine, asparagine and glutamine, especially at N addition rates of 0.25 g m−2 year−1 or higher, indicating N‐saturation. 3 Despite the high tissue N : P ratio (above 35), above‐ground biomass production by Molinia was still stimulated at N addition rates of 4 g m−2 year−1, and foliar nutrient concentrations were unaffected compared to the control. In contrast to Molinia, Betula was unable to increase its above‐ground biomass. Foliar N concentrations in Betula were significantly higher at N addition rates of 4 g m−2 year−1 and excess N was stored in foliar arginine, making up 27% of the total N concentration. Evapotranspiration was increased at higher N addition rates due to stimulated total above‐ground biomass production of the vegetation. 4 N addition at the actual Dutch deposition rate of 4 g m−2 year−1 stimulated the growth of Molinia in this experiment, providing evidence that the observed dominance of Molinia on ombrotrophic bogs in the Netherlands is caused by high N deposition levels. Based on the observed changes in biomass production and tissue nutrient concentrations, we assume that a long‐term deposition of 0.5 g N m−2 year−1, or higher, leads to undesirable changes in species composition and increased risk of desiccation.

Effects of environmental biomass-producing factors on Cd uptake in two Swedish ecotypes of Pinus sylvestris

A factorial design was used to study direct effects of external biomass-producing factors such as light, temperature and photoperiod on cadmium (Cd) uptake and indirect effects, via change in biomass production in two ecotypes of Scots pine ( Pinus silvestris). The aim was to find out if the external factors affect the Cd uptake directly or via change in biomass production, and if the effect differs between ecotypes. Seedlings were grown under 10 combinations of external factors, i.e. temperature (15 and 20 °C), light intensity (50 and 200 μmol photons m −2 s −1), photoperiod (18 h light/8 h darkness and continuous light) and external Cd concentration (totally 1.88 and 7.50 μmol). The treatment lasted for 18 days and Cd concentrations in roots and shoots were determined by AAS. The results showed that an increased biomass production increased the total Cd uptake but had a dilution effect on the Cd concentration, especially in the root tissues. The external factors tested did not have any direct effects on the Cd uptake, only in the case of Cd translocation to the shoot did the higher temperature show a direct increase, but only in the southern ecotype. The two ecotypes reacted differently in Cd uptake and translocation to the external factors studied. The relative Cd uptake increased with increasing photoperiod in the northern but not in the southern ecotype. The southern ecotype decreased the Cd concentration in the shoot with increased light intensity caused by a dilution effect due to extensive shoot growth of this ecotype. The conclusion is that the uptake in pine seedlings is mainly regulated via biomass production, and not directly by light and temperature and that resulting plant Cd contents to a certain extent depend on plant origin.

Effects of adaptation to winter stress on biomass production, growth and morphology of three contrasting white clover cultivars

Changes in biomass production and partitioning, together with morphology and growth of three white clover (Trifolium repens L.) cultivars after exposure to winter stress were recorded in a controlled environment study. The cultivars used were Grasslands Huia (H, New Zealand), AberHerald (AH, bred in UK from material of Swiss origin) and Sandra (S, Sweden), sub‐populations of these (survival populations), and a wild ecotype from the Uppsala area. The sub‐populations were collected after 2 (with the exception of S) and 4 years of winter stress, respectively, at Uppsala (59°49′ N, 17°39′ E). In the controlled environment study the photoperiod was 12 h and there were two temperature regimes, namely 24/18 and 12/9°C (day/night), respectively. The experimental plants were cloned from eight different plants of each population. There were few interactions between populations and temperature regimes. Biomass production was lowest in the Swedish populations and in the surviving populations of the other cultivars collected after 4 years of exposure to winter stress. However, biomass partitioning, with the exception of allocation to branches, remained unaffected. Morphology differed significantly between cultivars, but, with the exception of internode length, was unaffected by exposure to winter stress. Internode length was significantly reduced in surviving populations of both H and AH after exposure to four winters, when its value was similar to that of the Swedish populations. The reduced internode length was a result of a greater reduction in the stolon extension rate than in the leaf appearance rate of survival populations compared with the original populations. It is hypothesised that reduced internode length would have implications for the carbon economy of the plant.

Seasonal responses of six Poaceae to differential levels of solar UV-B radiation

The effects of changes in solar UV-B on the growth and pigmentation of six grass species from cold-temperate grasslands (Lolium perenne, Lolium multiflorum, Festuca arundinacea, Festuca rubra, Phleum pratense and Dactylis glomerata) in spring and summer were studied. The grasses were grown in greenhouses with different foils, resulting in three treatments: no UV-B, 80% of ambient and 90% of ambient UV-BBE.(biologically effective UV-B). The results indicated important effects of ambient UV-B levels on grass, but the different species reacted in very different ways. Both morphology and biomass production were influenced by UV-B in some species. However, changes in biomass production did not necessarily occur within the same species as changes in morphology. The grasses were more sensitive in summer. Overall, only F. rubra was positively influenced by UV-B under all circumstances. The biomass of D. glomerata and L. perenne was reduced by UV-B in spring and summer. Morphological changes included reduced height and increased tillering. The sensitivity of the different species was partially explained by their ability to reduce their specific leaf area in response to UV-B. Only the more sensitive species showed increased production of protective pigments. Overall, there were important differences between the effect of a low level of UV-B, and the further increase in UV-B, indicating that several mechanisms are operating at different light levels.

Continental water cycle and carbon reservoirs and their relationships in the past

In this short review paper, the author discusses the importance of studies on changes in the continental water cycle for a better understanding of temporal changes in biomass production and carbon storage. All calculations made for the late Pleistocene and Holocene should take into consideration not only the subsequent rises in temperature, precipitation and carbon storage, but also secondary hydrologic variations, which differ spatially due to climatic zonation as well as to orography, lithology and other factors. To a large extent, the present-day picture of the water cycle and biomass production is transformed by man.

Drought effects on biomass production and radiation-use efficiency in barley

Changes in biomass production of a barley crop in response to droughts of various timing and duration were analysed using a simple radiation interception model. Decreased growth rates were caused primarily by reductions in radiation-use efficiency when drought was imposed from emergence. In these treatments radiation-use efficiency was depressed even after drought was relieved. In contrast, in treatments where drought was imposed from two weeks before anthesis or later, the primary cause of reduced biomass production was a decrease in the amount of radiation intercepted, mostly associated with more rapid leaf senescence. For the later drought treatments, the radiation-use efficiency was stable and near the maximum value for unstressed crops. However, final biomass was sensitive to drought timing and, in particular, was more sensitive to maximum potential soil moisture deficit for the early than the later drought treatments.

Biomass Production in a Tallgrass Prairie Ecosystem Exposed to Ambient and Elevated CO"2.

Responses to elevated CO"2 have not been measured for natural grassland ecosystems. Global carbon budgets will likely be affected by changes in biomass production and allocation in the major terrestrial ecosystems. Whether ecosystems sequester or release excess carbon to the atmosphere will partly determine the extent and rate that atmospheric CO"2 concentration rises. Elevated CO"2 also may change plant community species composition and water status. We determined above- and belowground biomass production, plant community species composition, and measured and modeled water status of a tallgrass prairie ecosystem in Kansas exposed to ambient and twice-ambient CO"2 concentrations in open-top chambers during the entire growing season from 1989 through 1991. Dominant species were Andropogon gerardii, A. scoparius, and Sorghastrum nutans (C"4 metabolism) and Poa pratensis (C"3). Aboveground biomass and leaf area were estimated by periodic sampling throughout the growing season in 1989 and 1990. In 1991, peak biomass and leaf area were estimated by an early August harvest. Relative root production among treatments was estimated using root ingrowth bags which remained in place throughout the growing season. Latent heat flux was simulated with and without water stress. Botanical composition was estimated annually. Compared to ambient CO"2 levels, elevated CO"2 increased production of C"4 grass species, but not of C"3 grass species. composition of C"4 grasses did not change, but Poa pratensis (C"3) declined, and C"3 forbs increased in the stand with elevated CO"2 compared to ambient. Open-top chambers appeared to reduce latent heat flux and increase water-use efficiency similar to the elevated CO"2 treatment when water stress was not severe, but under severe water stress, the chamber effect on water-use efficiency was limited. In natural ecosystems with periodic moisture stress, increased water-use efficiency under elevated CO"2 apparently would have a greater impact on productivity irrespective of photosynthetic pathway.

Growth and water use of wheat under present and future levels of CO2

A mechanistic simulation model was used to examine the expected responses of wheat to a doubling in atmospheric CO2 concentration in combination with a 2°C rise in temperature. The model produced satisfactory simulations of total biomass, leaf area and canopy transpiration under present climatic conditions. However, soil evaporation was underestimated by up to 35% by the simulations. Model predictions suggested that increased CO2 levels should lead to increased biomass and potential yields of wheat up to about 550ppm, after which photosynthesis under full sunlight increases only gradually with CO2. Higher temperatures are expected to decrease biomass production by shortening the growing season and by increasing plant respiration. A doubling of CO2 concentration and a temperature increase of 2°C is expected to cause only marginal changes in biomass production. Transpiration use efficiency may be enhanced by -20% with a doubling of CO2 above current levels.

Wood Energy Plantation Economics in the Great Plains

Short-rotation intensive culture (SRIC) is a method of producing wood energy feedstocks that is potentially competitive with conventional wood sources in eastern Kansas. Silver maple is used as a representative energy species to examine alternative cutting cycles and planting densities. The sensitivity of discounted average cost is also evaluated with respect to changes in biomass productivity and to changes in production and harvesting costs. The results show that SRIC wood feedstocks can be grown, harvested, and delivered at costs approaching $50/dry tonne. This cost is nearly competitive with prices of delivered wood chips from conventional forest sources in eastern Kansas.

Quiescence, growth and senescence of Egeria densa in Lake Marion

Seasonal changes in biomass production and morphology of the submersed vascular plant Egeria densa Planchon (Brazilian elodea) were followed in Lake Marion, South Carolina, from march 1980 to May 1981. Biomass maxima occurred in late summer and late fall; these were followed by periods of senescence denoted by biomass loss through sloughing and decay of tips and branches. A period of quiescence was observed in the winter. Rootcrowns and stems containing double nodes were verified as the overwintering and propagative structures.