Håkan Marstorp

Field and pulping performances of transgenic trees with altered lignification

The agronomic and pulping performance of transgenic trees with altered lignin has been evaluated in duplicated, long-term field trials. Poplars expressing cinnamyl alcohol dehydrogenase (CAD) or caffeate/5-hydroxy-ferulate O-methyltransferase (COMT) antisense transgenes were grown for four years at two sites, in France and England. The trees remained healthy throughout the trial. Growth indicators and interactions with insects were normal. No changes in soil microbial communities were detected beneath the transgenic trees. The expected modifications to lignin were maintained in the transgenics over four years, at both sites. Kraft pulping of tree trunks showed that the reduced-CAD lines had improved characteristics, allowing easier delignification, using smaller amounts of chemicals, while yielding more high-quality pulp. This work highlights the potential of engineering wood quality for more environmentally benign papermaking without interfering with tree growth or fitness.

Influence of soluble carbohydrates, free amino acids, and protein content on the decomposition of Lolium multiflorum shoots

The aim of the present investigation was to determine how the chemical composition of L. multiflorum (var. Imperial) shoots influences the initial dynamic decomposition phase. Decomposition in soil was monitored by taking semicontinuous respiration measurements with a resolution of 1 h. Shoots with six different total N contents(2.0–5.2%) were compared. The carbohydrate content of the shoots decreased with increasing total N content, whereas the free amino acid and protein contents increased. Two respiration peaks were observed during the 1-week-long incubation. Comparisons of C mineralisation curves for water-extracted and whole shoots showed that the first peak was derived from water-soluble plant components. Lengths of lag phases and values of specific microbial growth rates obtained from respiration curves of sugars and amino acids implied that these substances were mineralised during the time of the first respiration peak. Amounts of CO2-C evolved from the shoots during the first peak increased linearly as a function of the sum of the content of glucose, fructose, sucrose, fructans, and free amino acids in the shoots. The shoots with two highest N contents showed net N mineralisation during the first respiration peak, whereas at a lower N content there was net immobilisation. It was concluded that soluble carbohydrates and free amino acids were important C and energy sources for the decomposers during the time encompassed by the first respiration peak. The second peak was derived from both water-soluble and water-insoluble plant components, and the amount of C respired increased with an increasing protein content.

A study of the structure and metal tolerance of the soil microbial community six years after cessation of sewage sludge applications

Changes in soil microbial community structure and development of metal tolerance as a result of past applications of unamended sewage sludge and metal-amended sewage sludge were found in soils of a long-term field experiment at Braunschweig, Germany. Both the rate of sewage sludge application and metal amendment affected the size and activity of the microbial biomass and had caused changes in microbial community structure as seen by differences in phospholipid fatty acid (PLFA) profiles. Past sewage sludge additions and metal amendment had an effect on the microbial respiratory response to 15 different C substrates, but both the magnitude and the direction of this response were substrate dependent. Differences between the soils in the respiratory response to the substrates were therefore probably largely determined by differences in the composition of the microbial consortia utilizing the substrates. The level of metal tolerance of the soil bacterial community determined by the thymidine incorporation technique and that of the microbial consortium growing on glucose in situ (determined from respiration measurements) increased with the level of metal contamination of the soil. Metal tolerance measurements could identify the metal with the largest toxicity effect in this experiment with multiple metal-polluted sewage sludge.

Carbon and Nitrogen Mineralization and Crop Uptake of Nitrogen from Six Green Manure Legumes Decomposing in Soil

Abstract Carbon and nitrogen mineralization from six green-manure legumes was studied in an incubation experiment. The values measured were fitted to a two-component and a one-component first-order model, respectively. Estimated parameters were compared. During 115 days of incubation approximately 30–35% of total N in white clover, black medic and subterranean clover was mineralized. Red clover and persian clover mineralized only 20% and egyptian clover 17%. White clover, black medic and subterranean clover showed a net mineralization during the whole incubation period. Red clover, persian clover and egyptian clover showed apparently an initial immobilization followed by a net mineralization after approximately 2 weeks. In a pot experiment, N uptake in rye grass from the six legumes was measured and comparisons were made with the incubation experiment after corrections for temperature differences. The amount of N harvested in the pot experiment was approximately 90% of the net N mineralization during deco...

Carbohydrate composition of plant materials determines N mineralisation

To improve the synchrony between N mineralisation and crop N demand itis important to identify properties of the plant materials that can be used topredict the N mineralisation. We hypothesised that the timing of decompositionof plant carbohydrates relative to that of plant proteins could be used todetermine the course of net N mineralisation. We started by studying thedecomposition of several plant carbohydrates, both as single substrates and incombination, to find out how they affected the net N mineralisation fromproteins. As the next step, we combined nitrogen-rich Medicagosativa leaves with Phleum pratense thatcontained large amounts of sugars and fructans. We also combined M.sativa leaves with Trifolium pratense thatcontained large amounts of pectic substances and hemicellulose. Finally, wecombined M. sativa leaves with Loliumperenne that contained large amounts of lignocellulose but lowamounts of sugars and fructans. With the addition of P.pratense, the course of N release changed to an initial Nimmobilisation followed by a net N mineralisation. Addition of L.perenne only slightly affected the N mineralisation rate ofM. sativa leaves initially, but reduced amounts of Nmineralised thereafter. The effect of T. pratense wasintermediate between that of P. pratense and L.perenne. Our results show that by combining plant materials withdifferent carbohydrate and protein compositions it is possible to affect the Nmineralisation. However, to utilise subtle differences between plant materials,detailed analysis of non-cellulose polysaccharides may be necessary.

Future threats to agricultural food production posed by environmental degradation, climate change, and animal and plant diseases - a risk analysis in three economic and climate settings

Global food security is one of the most pressing issues for humanity, and agricultural production is critical for achieving this. The existing analyses of specific threats to agricultural food production seldom bring out the contrasts associated with different levels of economic development and different climatic zones. We therefore investigated the same biophysical threats in three modelled types of countries with different economic and climatic conditions. The threats analysed were environmental degradation, climate change and diseases and pests of animals and plants. These threats were analysed with a methodology enabling the associated risks to be compared. The timeframe was 2012–2050 and the analysis was based on three underlying assumptions for 2050: the world population will have increased to 9 billion people, there will be a larger middle class in the world and climate change will be causing more extreme weather events, higher temperatures and altered precipitation. It is suggested that the risks, presented by the biophysical threats analysed, differ among the three modelled types of countries and that climate zone, public stewardship and economic strength are major determinants of these differences. These determinants are far from evenly spread among the world’s major food producers, which implies that diversification of risk monitoring and international assessment of agricultural production is critical for assuring global food security in 2050.

Interactions in microbial use of soluble plant components in soil

Glucose, glutamic acid, alanine, valine, and albumin were used as model substances to represent readily available soluble plant components. Their mineralisation in soil was monitored by making hourly measurements of total CO2 evolution and periodic measurements of 14CO2 during a 5-day incubation period. When glucose and the amino acids were combined in dual substrates the two components were mineralised simultaneously. In each combination the component with the shortest lag phase or highest specific growth rate (μ) was mineralised preferentially. Glucose accelerated the mineralisation of the amino acids that had longer lag phases than glucose (i.e., alamine and valine). During the first 8 h, glucose mineralisation was reduced in the dual substrates compared with its mineralisation as a single substrate. The smaller the difference between the lag phase of glucose and the amino acid, the greater was the reduction in the glucose mineralisation rate. During the exponential phase, the effects on glucose mineralisation were dependent on the nature and concentration of the amino acid. The interactions observed between glucose and amino acid decomposition indicated that these substances were mineralised, at least partly, by the same microorganisms. In contrast, glucose and the soluble protein albumin were decomposed independently of each other.

Calculation of N Mineralization from Six Green Manure Legumes under Field Conditions from Autumn to Spring

Abstract Mean soil temperature values and optimal moisture conditions were incorporated into a kinetic first-order model to describe net nitrogen mineralization from above-ground legume material under field conditions. Calculations showed that red clover, persian clover and egyptian clover would mineralize 1 to 2 kg N ton-1 above-ground legume dry matter from autumn to early spring, whereas white clover, black medic and subterranean clover would mineralize between 6 and 13 kg N ton-1 of dry matter during the same time period. Late ploughing (December 1) compared to early ploughing (October 15) had a substantial effect on the initial amounts of N released but differences decreased and were small in May. Assuming an above-ground legume biomass of 3 tonnes of dry matter, up to 40 kg N per hectare can be mineralized from autumn to early spring depending on the legume species. The species had a larger influence on the mineralized amounts of N than the location and the time of ploughing.

Mulch N recycling in green manure leys under Scandinavian conditions

Nitrogen (N) recycling to the regrowth of mulched red clover (Trifolium pratense L.) and mulched mixed red clover/perennial ryegrass (Lolium perenne L.) leys was determined in field experiments during three consecutive years using 15N-labelled shoot material. Nitrogen recycling was greater in the pure clover stands than in the mixed stands in the beginning of the growing season, but increased successively in the mixed stands so that it was similar (14–15.5%) in both stands at the end of the season. This recycling of N from the mulch led to increased biomass accumulation but did not alter stand composition in the mixed stands. Mulch-derived N was incorporated into the soil organic N in both pure clover and mixed stands which thus contributed to building up soil fertility. An approximately similar proportion of N remained unaccounted for in mulched pure clover and mixed stand leys and presumably represented gaseous losses. To exploit the benefits of green manure leys in the humid temperate zone while minimising the negative environmental impact, these should be harvested rather than mulched.

N release pattern from green manures can be modified through species composition

Abstract This study examined whether the N release pattern during decomposition of plant materials used as green manures can be modified in the short term through mixing plant materials with different levels of easily degradable compounds. In a lysimeter study, white clover shoots were mixed with perennial ryegrass shoots or chicory roots. Leaching of clover N was decreased more by inclusion of chicory than by ryegrass. However, decreased leaching losses over the non-growing season did not lead to enhanced N uptake by the crop during the following growing season.