Belowground Biomass Production Research Articles

Forage and tree seedling growth in a soil with an encased swine sludge layer

The closure of swine farms requires decommissioning of lagoons that contain large amounts of swine solids (sludge). Sludge is typically transported and land applied to soils. However, in some cases this process could be economically prohibitive and/or unpractical. An alternative idea is to encase sludge with lagoon soil berms after removing overlying effluent, followed by establishment of forages or short-rotation woody crops on the encased sludge. The objective of this study was to investigate growth potential for several forages and tree species into a pure layer of swine sludge. Alfalfa (Meticago sativa), bermudagrass (Cynodon dactylon), switchgrass (Panicum virgatum), green ash (Fraxinus pennsylvanica), black locust (Robinia pseudoacacia), and sycamore (Platanus occidentalis) were established in 40 cm deep pots consisting of a lagoon berm soil overlaying a sludge layer for 12 w followed by analysis of aboveground and belowground biomass production. “New” and “old” sludge was collected from an active 10 year old lagoon and decommissioned 50 year old lagoon, respectively. A control (soil only) was used. Encased sludge treatments increased forage biomass production. Sycamore and green ash were sensitive to new sludge but not old sludge as these species had less biomass production in new sludge than control and showed tissue trace nutrient deficiencies. While both sludge materials contained adequate nutrients, the new sludge had a salt concentration 1.8 times higher than old sludge as indicated by electrical conductivity (12.4 mS). Thus, the forage crops and black locust were able to thrive in new sludge due to their salt tolerance.

Long-term study of above- and below-ground biomass production in relation to nitrogen and carbon accumulation dynamics in a grey alder (Alnus incana (L.) Moench) plantation on former agricultural land

In the Northern and Baltic countries, grey alder is a prospective tree species for short-rotation forestry. Hence, knowledge about the functioning of such forest ecosystems is critical in order to manage them in a sustainable and environmentally sound way. The 17-year-long continuous time series study is conducted in a grey alder plantation growing on abandoned agricultural land. The results of above- and below-ground biomass and production of the 17-year-old stand are compared to the earlier published respective data from the same stand at the ages of 5 and 10 years. The objectives of the current study were to assess (1) above-ground biomass (AGB) and production; (2) below-ground biomass: coarse root biomass (CRB), fine root biomass (FRB) and fine root production (FRP); (3) carbon (C) and nitrogen (N) accumulation dynamics in grey alder stand growing on former arable land. The main results of the 17-year-old stand were as follows: AGB 120.8 t ha−1; current annual increment of the stem mass 5.7 t ha year−1; calculated CRB 22.3 t ha−1; FRB 81 ± 10 g m−2; nodule biomass 31 ± 19 g m−2; fine root necromass 11 ± 2 g m−2; FRP 53 g DM m−2 year−1; fine root turnover rate 0.54 year−1; and fine root longevity 1.9 years. FRB was strongly correlated with the stand basal area and stem mass. Fine root efficiency was the highest at the age of 10 years; at the age of 17 years, it had slightly reduced. Grey alder stand significantly increased N and Corg content in topsoil. The role of fine roots for the sequestration of C is quite modest compared to leaf litter C flux.

Belowground interactions shift the relative importance of direct and indirect genetic effects

Intraspecific genetic variation can affect decomposition, nutrient cycling, and interactions between plants and their associated belowground communities. However, the effects of genetic variation on ecosystems can also be indirect, meaning that genes in a focal plant may affect ecosystems by altering the phenotype of interacting (i.e., neighboring) individuals. We manipulated genotype identity, species identity, and the possibility of belowground interactions between neighboring Solidago plants. We hypothesized that, because our plants were nitrogen (N) limited, the most important interactions between focal and neighbor plants would occur belowground. More specifically, we hypothesized that the genotypic identity of a plant's neighbor would have a larger effect on belowground biomass than on aboveground biomass, but only when neighboring plants were allowed to interact belowground. We detected species- and genotype-level variation for aboveground biomass and ramet production. We also found that belowground biomass and ramet production depended on the interaction of neighbor genotype identity and the presence or absence of belowground interactions. Additionally, we found that interspecific indirect genetic effects (IIGEs; changes in focal plant traits due to the genotype identity of a heterospecific neighbor) had a greater effect size on belowground biomass than did focal genotype; however, this effect only held in pots that allowed belowground interactions. These results expand the types of natural processes that can be attributed to genotypes by showing that, under certain conditions, a plant's phenotype can be strongly determined by the expression of genes in its neighbor. By showing that IIGEs are dependent upon plants being able to interact belowground, our results also provide a first step for thinking about how genotype-based, belowground interactions influence the evolutionary outcomes of plant-neighbor interactions.

Response of rice-rice ecosystem productivity and yield stability to long-term fertilization

The productivity and yield stability of rice-rice ecosystem in Huazhong with different fertilizers were investigated using experimental data from the Chinese Ecosystem Research Network at Taoyuan Station of Agro-ecology Research,Chinese Academy of Sciences.The field trials included no fertilizer(CK),chemical fertilizer(NPK),rice straw with low N,K and high P(optimal fertilization,OF) and rice straw with some amount of NPK(general fertilization,GF).The results showed that fertilization was the basic mode of maintaining or increasing productivity of rice in paddy ecosystem.Productivity and stability were different in paddy ecosystems with different fertilizers.The total rice biomass was significantly higher in fertilizer treatments than in no fertilizer treatments;0.33~1.23 times higher for the period of 2005 to 2010.The order of stability from high to low was OF GF NPK CK.OF treatment improved total biomass stability in the study area.Yield under fertilizer treatments was 0.35~1.02 times higher than under no fertilizer treatment for the period of 2005 to 2010.It was 0.35 times higher in GF than CK in 2005,0.82 times higher in NPK than CK in 2007 and 1.02 times higher in OF than CK in 2010.The stability of rice yield was high in OF treatment and significantly low in CK treatment.Yearly variation coefficient under CK,NPK,OF and GF treatments was 22.4%,15.8%,10.3% and 15.7%,respectively.Productivity of underground biomass was significantly higher in fertilizer treatments than in no fertilizer treatment.Also ecological stability was significantly higher under GF treatment than the other treatments.In conclusion,rice productivity and production stability were highest under OF treatment and lowest under CK treatment.While fertilizers influenced rice yield stability and total or over-ground rice biomass,they little affected the stability of below-ground biomass productivity.

Effects of shading onVallisneria natans(Lour.) H. Hara growth

Effects of surface shading were measured on above- and below-ground biomass and fruit production of Vallisneria natans (Lour.) H. Hara plants grown from seed in replicated microcosm experiments, based on a control (no shading) and four treatments (25%, 50%, 75% and 90% shading). Above- and below-ground biomass was significantly reduced at treatments above 50% shading and first pistillate and staminate florescence dates were significantly delayed above 75% and 50% shading, respectively. Ratios of mature to unripe fruits produced (both in number or dry weight) did not differ between shading treatments, but dry weight fruit production was significantly reduced at 90% shading. We conclude that above 50% surface shading, V. natans plants suffer reductions in accumulated biomass and investment in sexual reproduction. We contend that recent expansions in the extent of the native floating water chestnut Trapa spp. at seasonally inundated wetlands in the Yangtze River floodplain could, by shading, have contributed to the reduction in annual biomass and seed production of V. natans , contributing to declines in distribution and abundance.

Short Communication: Forage mixture responses to water stress in semi-arid prairie grassland: a pot experiment

Wang, Z., Schellenberg, M. P., Biligetu, B., Zhao, M. L. and Han, G. D. 2012. Short Communication: Forage mixture responses to water stress in semi-arid prairie grassland: a pot experiment. Can. J. Plant Sci. 92: 1259–1261. As a negative result of changing climate, drought has become a worldwide concern, particularly in arid and semiarid regions. Under drier conditions, seeding multiple forage species may produce higher biomass than single species. A randomized complete block design experiment was carried out in a growth chamber over a 4-mo period to examine the effect of watering regimes (100, 85 and 70% of field capacity of semiarid grassland) on above- and below-ground biomass of various combinations of five forage species. Alfalfa monoculture and mixtures containing alfalfa produced significantly higher above- and below-ground biomass (P<0.05) than the other species or species combinations when grown at field capacity. They were also among the highest biomass producers under restricted water supply, although differences were not always statistically different. Winterfat showed a good tolerance to water deficit and its below-ground biomass production was not significantly affected by water restriction. The findings suggest that a mixture of native plant species with alfalfa would be important for forage seedling production in the semi-arid prairie grassland under water-limiting conditions.

Greenhouse Gas Potentials of Shrub Willow Biomass Crops Based on Below- and Aboveground Biomass Inventory Along a 19-Year Chronosequence

Shrub willow biomass crops (SWBC) have been developed as a biomass feedstock for bioenergy, biofuels, and bioproducts in the northeastern and midwestern USA as well as in Europe. A previous life cycle analysis in North America showed that the SWBC production system is a low-carbon fuel source. However, this analysis is potentially inaccurate due to the limited belowground biomass data and the lack of aboveground stool biomass data. This study provides new information on the above- and belowground biomass, the carbon–nitrogen (C/N) ratio, and the root/shoot (R/S) ratio of willow biomass crops (Salix × dasyclados [SV1]), which have been in production from 5 to 19 years. The measured amounts of biomass were: 2.6 to 4.1 odt ha−1 for foliage, 4.9 to 10.9 odt ha−1 for aboveground stool (AGS), 2.9 to 5.7 odt ha−1 for coarse roots (CR), 3.1 to 10.2 odt ha−1 for belowground stool (BGS), and 5.6 to 9.9 odt ha−1 for standing fine root (FR). The stem biomass production ranged from 7.0 to 18.0 odt ha−1 year−1 for the 5- and 19-year-old willows, respectively. C/N ratios ranged from 23 for foliage to 209 for belowground stool. An average R/S ratio of 2.0, calculated as total belowground biomass (BGS, CR, and FR) plus AGS divided by annual stem biomass, can be applied to estimate the total belowground biomass production of a mature SWBC. Based on AGS, BGS, and CR and standing FR biomass data, SWBC showed a net GHG potential of −42.9 Mg CO2 eq ha−1 at the end of seven 3-year rotations.

Ecosystem Biomass, Carbon, and Nitrogen Five Years after Restoration with Municipal Solid Waste

Escalating municipal solid waste generation coupled with decreasing landfill space needed for disposal has increased the pressure on military installations to evaluate novel approaches to handle this waste. One approach to alleviating the amount of municipal solid waste being landfilled is the use of a new garbage‐processing technology that sterilizes and separates waste into inorganic and organic components. Thus, a study was initiated to evaluate the effectiveness of using the organic component (Fluff) as a soil amendment for establishing native prairie grasses on disturbed U.S. Army training land. The Fluff material was incorporated (10–20 cm) into a highly degraded sandy loam soil located in a borrow pit at Fort Benning Military Reservation, GA, in 2003. The Fluff was applied at rates of 0, 18, 36, 72, and 143 Mg ha−1 and seeded with native prairie grasses to assess its effect on aboveground and belowground biomass production and C and N cycling after 5 yr. An unseeded control (no Fluff) treatment was also evaluated as a comparison of natural recovery. After 5 yr, revegetation resulting from natural recovery in the unseeded control was sparse. However, Fluff addition improved native grass establishment, with greater biomass production being observed with increasing rates. Fluff addition also decreased soil bulk density and increased soil C and N concentrations. These results show that Fluff can be effectively used in land rehabilitation and revegetation practices as well as to improve C and N cycling of highly degraded soils for periods exceeding 5 yr after application.

Factors modulating cottongrass seedling growth stimulation to enhanced nitrogen and carbon dioxide: compensatory tradeoffs in leaf dynamics and allocation to meet potassium-limited growth

Eriophorum vaginatum is a characteristic species of northern peatlands and a keystone plant for cutover bog restoration. Understanding the factors affecting E. vaginatum seedling establishment (i.e. growth dynamics and allocation) under global change has practical implications for the management of abandoned mined bogs and restoration of their C-sequestration function. We studied the responses of leaf dynamics, above- and belowground biomass production of establishing seedlings to elevated CO(2) and N. We hypothesised that nutrient factors such as limitation shifts or dilutions would modulate growth stimulation. Elevated CO(2) did not affect biomass, but increased the number of young leaves in spring (+400 %), and the plant vitality (i.e. number of green leaves/total number of leaves) (+3 %), both of which were negatively correlated to [K(+)] in surface porewater, suggesting a K-limited production of young leaves. Nutrient ratios in green leaves indicated either N and K co-limitation or K limitation. N addition enhanced the number of tillers (+38 %), green leaves (+18 %), aboveground and belowground biomass (+99, +61 %), leaf mass-to-length ratio (+28 %), and reduced the leaf turnover (-32 %). N addition enhanced N availability and decreased [K(+)] in spring surface porewater. Increased tiller and leaf production in July were associated with a doubling in [K(+)] in surface porewater suggesting that under enhanced N production is K driven. Both experiments illustrate the importance of tradeoffs in E. vaginatum growth between: (1) producing tillers and generating new leaves, (2) maintaining adult leaves and initiating new ones, and (3) investing in basal parts (corms) for storage or in root growth for greater K uptake. The K concentration in surface porewater is thus the single most important factor controlling the growth of E. vaginatum seedlings in the regeneration of selected cutover bogs.

Quantifying field-scale effects of elevated carbon dioxide concentration on crops

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 54:35-47 (2012) - DOI: https://doi.org/10.3354/cr01096 Quantifying field-scale effects of elevated carbon dioxide concentration on crops Eline Vanuytrecht1,*, Dirk Raes1, Patrick Willems2, Sam Geerts1 1Division of Soil and Water Management, Department of Earth and Environmental Sciences 2Hydraulics Laboratory, Department of Civil Engineering, KU Leuven University, 3001 Heverlee, Belgium *Email: eline.vanuytrecht@ees.kuleuven.be ABSTRACT: Climate change will affect crop growth and agricultural production worldwide. Crop production will be affected not only by modified rainfall patterns, increased air temperatures and changes in evaporative demand, but also elevated atmospheric CO2 concentrations ([CO2]). This study used meta-analytic techniques to quantify field-scale effects of elevated [CO2] (mainly 541 to 620 µmol mol−1) on agricultural crops in free air CO2 enrichment (FACE) conditions. Overall, crops benefit from elevated [CO2] by improving water productivity (+23% for biomass production and +27% for yield production), which is achieved through production increases in biomass (+15% for aboveground biomass) and yield (+16%), in combination with a decrease in seasonal evapotranspiration (–5%). Increased root:shoot ratios (+24%) indicate a more than proportional stimulation of belowground biomass production. Less critical, yet statistically significant are changes in canopy development rate and in phenology. Certain statistically significant differences existed between C3 and C4 crops, and between levels of environmental stress (nitrogen and water availability). Once the effect of elevated [CO2] is well understood and quantified, crop modellers can investigate the interactions with other climatic factors, providing better estimates of potential impacts on food production. KEY WORDS: CO2 · Climate change · Crop productivity · FACE · Field-scale effects · Meta‑analysis Full text in pdf format Supplementary material PreviousNextCite this article as: Vanuytrecht E, Raes D, Willems P, Geerts S (2012) Quantifying field-scale effects of elevated carbon dioxide concentration on crops. Clim Res 54:35-47. https://doi.org/10.3354/cr01096 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 54, No. 1. Online publication date: August 03, 2012 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2012 Inter-Research.

Cutting affects growth of Potamogeton lucens L. and Potamogeton compressus L

Effects of cutting on the growth of Potamogeton lucens L. and Potamogeton compressus L. were studied indoor under experimental conditions. Plants were cut every time they reached the water surface, applying three depth treatments at which the plants were cut; halfway down the water column, at three-quarters down the water column and at the sediment–water interface. For both species short term negative effects of cutting on biomass production and survival were observed. P. lucens seemed to be the more tolerant species as only below-ground biomass was significantly lower when cutting biomass at the sediment–water interface together with a downward trend in shoot biomass at increasing cutting depth. The low below-ground biomass (less than 20% of that in the controls) was caused by the death of most plants in this treatment. P. compressus was more vulnerable with every treatment resulting in significantly lower below-ground and green shoot biomass production. The lowest biomass for P. compressus was observed when plants were cut at the sediment–water interface with values more than 80% lower compared to the controls, while cutting halfway and at three-quarters resulted in values 30–50% lower compared to the controls. Long term effects of cutting on P. lucens might occur through decreased development of the rhizome network. Long term effects on reproduction of P. compressus might be expected as flowering decreased when cut at the sediment–water interface, while turion formation only occurred in the uncut controls. Additionally, the decreased biomass production by P. compressus may lead to a competitive disadvantage in the field as fast-growing, disturbance tolerant species such as Elodea nuttallii (Planch.) St. John may outcompete the species. Creating patchiness in mowing height and frequency or applying a mowing regime that leads to reduced biomass development while species still survive might create opportunities to both maintain the water transporting function of drainage ditches while preserving the species in the system.

The potential of willow and poplar plantations as carbon sinks in Sweden

Abstract A large share, estimated at 12–25%, of the annual anthropogenic greenhouse gas emissions is attributed to global deforestation. Increasing the forested areas therefore has a positive impact on carbon (C) sequestration and mitigation of high atmospheric CO 2 concentrations. Fast-growing species, such as willow and poplar, are of high interest as producers of biomass for fuel, but also as C sinks. The present study estimated the rate of C sequestration in biomass and soil in willow and poplar plantations. Calculations were based on above- and below-ground biomass production data from field experiments, including fine root turnover, litter decomposition rates, and production levels from commercial plantations. Accumulation of C in woody biomass, above and below ground, was estimated at 76.6–80.1 Mg C ha −1 and accumulation of C in the soil at 9.0–10.3 Mg C ha −1 over the first 20–22 years. The average rates of C sequestration were 3.5–4.0 Mg C ha −1 yr −1 in woody biomass, and 0.4–0.5 Mg C ha −1 yr −1 in the soil. If 400,000 ha of abandoned arable land in Sweden were planted with willow and poplar, about 1.5 Tg C would be sequestered annually in woody biomass and 0.2 Tg C in soils. This would be nearly one tenth of the annual anthropogenic emissions of C in Sweden today. These calculations show the potential of fast-growing plantations on arable land to mitigate the effect of high CO 2 concentrations over a short time span. Knowledge gaps were found during the calculation process and future research areas were suggested.

Response ofMiscanthus × giganteusandMiscanthus sinensisto Postemergence Herbicides

Studies were conducted under greenhouse conditions at Michigan State University and Texas Tech University to investigate the tolerance ofMiscanthus × giganteusandMiscanthus sinensisto POST herbicides.Miscanthus sinensisandM. × giganteuswere treated with 10 and 18 POST herbicide treatments, respectively. Plants were evaluated for injury as well as dry aboveground and belowground biomass production 28 days after treatment. Imazethapyr at 0.069 kg ai ha−1caused 5% injury toM. sinensis, which was greater than the nontreated check. Imazethapyr, imazamox at 0.044 kg ai ha−1, and rimsulfuron at 0.017 kg ai ha−1reduced aboveground biomass ofM. sinensiscompared with the nontreated check. Dicamba at 0.56 kg ai ha−1and halosulfuron at 0.035 kg ai ha−1resulted inM. sinensisaboveground biomass similar to the nontreated check. Injury exhibited byM. × giganteuswas greater than the nontreated check with glyphosate at 0.84 kg ae ha−1(54%), foramsulfuron at 0.037 kg ai ha−1(32%), nicosulfuron at 0.035 kg ai ha−1(28%), and imazamox at 0.044 kg ai ha−1(10%). These treatments also yielded the lowest aboveground biomass values. The results of this study demonstrate thatM. sinensisis more tolerant of the POST herbicides tested here thanM.×x. giganteus. Several herbicide options may be available for weed management inM. sinensisandM. × giganteusstands following additional field trials to validate initial findings.

Differential population response of allocation, phenology, and tissue chemistry in Spartina alterniflora

Phenotypic variation within species is widespread among salt marsh plants. For Spartina alterniflora, the dominant species of low intertidal wetlands across the Altantic and Gulf coasts of the US, distinct phenological and morphological differences among populations from different latitudes have been found. To determine whether S. alterniflora plants from lower latitudes and those regenerated from Delaware tissue cultures would maintain differences from that of native plants, we conducted a field study in a natural salt marsh in Delaware, US. After two growing seasons, plant height, stem density, above- and belowground biomass, elemental composition, and nutrient resorption were measured. Natural variation in porewater salinity influenced physiological traits of Na+/K+ ratio regulation and nitrogen resorption efficiency similarly across populations. While plant height exhibited plasticity where populations tended to converge to a similar height, several other traits remained distinct. Delaware plants had a greater rate of rhizome growth than Georgia and Louisiana plants, which correlated with a greater magnitude of fall senescence. If traits such as seasonal translocation are plastic and can change with the length of the growing season, climate warming may alter belowground biomass production of S. alterniflora in wetlands of the mid-Atlantic.

Biomass production and nitrogen accumulation and remobilisation by Miscanthus × giganteus as influenced by nitrogen stocks in belowground organs

The nitrogen (N) requirement of dedicated crops for bioenergy production is a particularly significant issue, since N fertilisers are energy-intensive to make and have environmental impacts on the local level (NO 3 leaching) and global level (N 2O gas emissions). Nitrogen nutrition of Miscanthus × giganteus aboveground organs is assumed to be dependent on N stocks in belowground organs, but the precise quantities involved are unknown. A kinetic study was carried out on the effect of harvest date (early harvest in October or late harvest in February) and nitrogen fertilisation (0 or 120 kg N ha −1) on aboveground and belowground biomass production and N accumulation in established crops. Apparent N fluxes within the crop and their variability were also studied. Aboveground biomass varied between 24 and 28 t DM ha −1 in early harvest treatments, and between 19 and 21 t DM ha −1 in late harvest treatments. Nitrogen fertilisation had no effect on crop yield in late harvest treatments, but enhanced crop yield in early harvest treatments due to lower belowground biomass nitrogen content. Spring remobilisation, i.e. nitrogen flux from belowground to aboveground biomass, varied between 36 and 175 kg N ha −1, due to the variability of initial belowground nitrogen stocks in the different treatments. Autumn remobilisation, i.e. nitrogen flux from aboveground to belowground organs, varied between 107 and 145 kg N ha −1 in late harvest treatments, and between 39 and 93 kg N ha −1 in early harvest treatments. Autumn remobilisation for a given harvest date was linked to aboveground nitrogen accumulation in the different treatments. Nitrogen accumulation in aboveground biomass was shown to be dependent firstly on initial belowground biomass nitrogen stocks and secondly on nitrogen uptake by the whole crop. The study demonstrated the key role of belowground nitrogen stocks on aboveground biomass nitrogen requirements. Early harvest depletes belowground nitrogen stocks and thus increases the need for nitrogen fertiliser.

Below-ground biomass production and allometric relationships of eucalyptus coppice plantation in the central highlands of Madagascar

Short rotations of Eucalyptus plantations under coppice regime are extensively managed for wood production in Madagascar. Nevertheless, little is known about their biomass production and partitioning and their potential in terms of carbon sequestration. If above-ground biomass (AGB) can be estimated based on established allometric relations, below-ground (BGB) estimates are much less common. The aim of this work was to develop allometric equations to estimate biomass of these plantations, mainly for the root components. Data from 9 Eucalyptus robusta stands (47–87 years of plantation age, 3–5 years of coppice-shoot age) were collected and analyzed. Biomass of 3 sampled trees per stand was determined destructively. Dry weight of AGB components (leaves, branches and stems) were estimated as a function of basal area of all shoots per stump and dry weight for BGB components (mainly stump, coarse root (CR) and medium root (MR)) were estimated as a function of stump circumference. Biomass was then computed using allometric equations from stand inventory data. Stand biomass ranged from 102 to 130 Mg ha−1 with more than 77% contained in the BGB components. The highest dry weight was allocated in the stump and in the CR (51% and 42% respectively) for BGB parts and in the stem (69%) for AGB part. Allometric relationships developed herein could be applied to other Eucalyptus plantations which present similar stand density and growing conditions; anyhow, more is needed to be investigated in understanding biomass production and partitioning over time for this kind of forest ecosystem.

Advances in the study of photosynthate allocation and its controls.

Photosynthate allocation is influenced by both environmental and biological factors. This paper reviews recent advances in the mechanism of photosynthate allocation and its controls at individual and community/ecosystem levels in order to improve understanding of plant responses to global change. At the individual level, more photosynthate will be allocated to roots under conditions of high light, low water and low nutrient availabilities. The effect of increased atmospheric carbon dioxide concentration on photosynthate allocation depends on soil nitrogen availability. The root mass fraction (RMF) will increase under low nitrogen and is unchanged under high nitrogen. At the community/ecosystem levels, photosynthate allocation is insensitive to environmental change. The RMF decreases with increasing stand age. The functional equilibrium hypothesis (optimal partitioning) can explain the regulation of photosynthate allocation in response to environmental change, the source-sink relationship can reflect the effect of ontogeny on photosynthate allocation and the allometric relationship provides an important theoretical baseline prediction to disentangle the effects of plant size and environmental variation on photosynthate allocation. Research is needed on 1) the fraction of photosynthate allocated to respiration at the ecosystem level, 2) accurate estimation of belowground biomass and belowground net primary productivity (BNPP), 3) comparative study of photosynthate allocations between young and mature forests and between field and greenhouse experiments, 4) effects of multiple factors and their interactions on photosynthate allocation at the ecosystem level and 5) cooperative effects of ontogeny and environmental factors on the regulation of photosynthate allocation.

Carbon-allocation dynamics in reed canary grass as affected by soil type and fertilization rates in northern Sweden

A field experiment was conducted in northern Sweden between 1995 and 1997, with the objectives (1) to quantify the dynamics of carbon accumulation in above- and belowground crop components of reed canary grass (RCG) during the second and third year after sowing and (2) to examine the effect of fertilization and soil type (mineral vs. organic) on C allocation. Across all treatments, carbon accumulation in belowground organs in the top 20 cm was on average 3 and 3.4 Mg C by the end of the second and third year, respectively, with roots and rhizomes accounting for up to 80%. Roots contributed most to belowground C mass during the second growing season but during the preceding winter, root biomass C decreased by 44–67%, and, thereafter, during the third growing season, the proportion of rhizome C increased. The dynamics of root biomass was considerably high, suggesting high root turnover rates. Rhizomes support re-growth during spring and rhizome biomass seems to increase with crop age. Thus, early harvesting before October may impact on the productivity during the following season. Among the factors studied, harvest date was the most influential and affected C allocation in all crop components considerably. Fertilization stimulated growth of shoots, rhizomes, and BSBs (belowground shoot bases) but not that of roots. However, root biomass was higher in the organic than in the mineral soil. In this study, we considered only plant components above 20 cm depth. More detailed studies are needed to calculate more complete soil C balances. However, high belowground biomass production and root turnover indicate a high C input to the soil, which may result in positive soil C balances. Therefore, RCG cropping could have considerable carbon-sequestration potential.

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.

Effects of soil freeze–thaw cycles differ between experimental plant communities

Soil freeze–thaw cycles (FTC) influence nutrient cycling, but their consequences for productivity and composition of vegetation are not well investigated. Ongoing global warming will increase the recurrence of FTC in cool-temperate and high-latitude regions. Here, we report on the above- and belowground biomass production as well as the nitrogen nutrition of two common vegetation types, grassland and heath, after more frequent FTC in a controlled field experiment in Central Europe. Furthermore, we analyze the duration of the observed effects. Five FTC were induced by buried heating wires in addition to three naturally occurring FTC during winter 2005/06. More frequent FTC significantly increased aboveground production of experimental grassland early in the following growing season. However, no reaction was found for experimental heath within the first growing season. Biomass production of heath communities dropped significantly and C/N ratio increased in the freeze–thaw treated plots in the second year after the manipulation, whereas production in the grassland communities was no longer affected significantly, except for an increase in C/N ratio. This response can at least partly be explained by changes in nutrient availability, as plant available nitrate increased in the manipulated grassland plots and decreased in the manipulated heath plots. The results show the high ecological importance of climate changes during winter, with the outcomes differing strongly between contrasting vegetation types. Furthermore, we show that short term climatic events can cause long-lasting effects, sometimes emerging in the vegetation only after considerable time lags (here: one growing season). Bodenfrostwechsel (FTC) beeinflussen Nährstoffkreisläufe, aber ihre Bedeutung für die Vegetation ist kaum erforscht. Im Zuge der Globalen Erwärmung werden FTC in kühl-gemäßigten Breiten häufiger auftreten. In dieser Arbeit wird die ober- und unterirdische Biomasseproduktion sowie die Stickstoffernährung von zwei weit verbreiteten Vegetationstypen (Grünland und Zwergstrauchheide) nach vermehrten FTC in einem kontrollierten Freilandexperiment verglichen. Darüber hinaus wird die zeitliche Dauer der beobachteten Effekte evaluiert. Zusätzlich zu drei natürlichen FTC wurden im Winter 2005/06 fünf FTC durch Heizkabel erzeugt. Intensivierung von FTC führte in der folgenden Vegetationsperiode zu signifikant erhöhter oberirdischer Produktion in den Grünlandsystemen. In den Heidesystemen erfolgte keine Reaktion innerhalb des ersten Jahres. Deren Biomasseproduktion verringerte sich allerdings in der zweiten Vegetationsperiode nach der FTC-Manipulation, begleitet von einer Erweiterung im C/N-Verhältnis in der Biomasse. Zu dieser Zeit zeigte sich kein Behandlungseffekt mehr in der Biomasseproduktion der Grünlandsysteme, obwohl deren C/N-Verhätnis signifikant verengt war. Diese Effekte können zumindest teilweise durch Veränderungen in der Nährstoffverfügbarkeit erklärt werden. Die Konzentration von pflanzenverfügbarem Nitrat stieg in den FTC-behandelten Grünlandplots an, während sie in den FTC-behandelten Heideplots abnahm. Die Ergebnisse belegen die hohe ökologische Bedeutung von Klimaveränderungen im Winter, wobei die Folgen sich zwischen den untersuchten Vegetationstypen stark unterschieden. Darüber hinaus konnte gezeigt werden, dass kurze klimatische Ereignisse zu langfristigen Veränderungen in der Vegetation führen können, und dass diese zum Teil erst nach deutlicher Verzögerung auftreten.