Nematode numbers,biomass and respiratory metabolism in a beech woodland—Wytham Woods,Oxford

Summary The mean annual population density of nematodes in the litter and upper 6 cm of soil was found to be 368,000 m^-2. Mean individual live weight biomass approximated 0.2 g and mean biomass was calculated to be 74.6 mg live weight m^-2. No evidence of seasonal vertical migration between the litter, 0–3 cm and 3–6 cm strata was found and on average these strata contained 21.9, 46.2 and 31.9% respectively of the total number of nematodes recovered. The equivalent biomass values were 26.14, 56.57, and 17.29%. Total numbers revealed a general picture of low densities in spring and high ones in early winter, whereas biomass m^-2 was low in late summer — autumn and high in winter. The annual oxygen consumption of the extracted nematodes was calculated to approximate 0.211 m^-2 (4.0 kJ m^-2) but when corrected for the effect of individual biomass (weight specific oxygen uptake) was equivalent to an energy expenditure 6.0 kJ m^-2 which in its turn, because of the efficiencies of extraction, probably accounts for only 87% of the total energy expenditure by the nematode fauna. The nematodes were estimated to be responsible for a minimum of 0.11% to a maximum of 0.13% of the total soil respiration. A production/biomass ratio of 5.16 was estimated as was a net population production efficiency of 36.63%.     

Snail numbers,biomass and respiratory metabolism in a beech woodland — Wytham Woods,Oxford

Summary Two methods of extraction were used in the estimation of snail population densities in woodland litter. The time-consuming-Vágvölgyi technique proved to be 6.25 times more efficient than infra-red heat extraction but it was shown that the results obtained by the latter method could be easily corrected to conform with those of the former.Snail density varied with season (Winter, 1,000–1,250 m^-2, Summer, 50–600 m^-2), the annual mean density being 645 m^-2. The annual mean ash-free dry weight biomass was 176 mg m^-2 while annual population metabolism equalled 0.8941 O₂ (=17.84 kJ m^-2 yr^-1).Two independent estimates of the energy equivalent of food consumption gave rise to values of 25.37 and 57.98 kJ m^-2 yr^-1, these respectively account for 0.54 and 1.23% of the known ground litter disappearance of 4,716.58 kJ (=235 g dry wt. m^-2 yr^-1).     

Lignin properties in topsoils of a beech/oak forest after 8 years of manipulated litter fall: relevance of altered input and oxidation of lignin

Background and aims

We studied the response of lignin oxidation in soils of a beech/oak forest to changes in litter fall. Additionally we considered possible factors in lignin oxidation, including altered (i) input of fresh organic matter and (ii) fungi-to-bacteria ratios.

Methods

The field-based experiment included (i) doubling and (ii) exclusion of litter fall and (iii) controls with ambient litter fall. Soil (0–20 cm depth) was sampled after 8 years. We analyzed (i) lignin using the CuO oxidation method, (ii) stocks of free and mineral-bound organic carbon (OC), (iii) the response of soil organic matter (SOM) decomposition to addition of labile organic compounds in laboratory incubations, and (iv) ratios of fungal- vs. bacterial-derived amino sugars (F/B ratios).

Results

Litter exclusion increased stocks of free-light fraction OC, F/B ratios, the ability of the microbial community to use labile compounds for SOM decomposition, as well as acid-to-aldehyde ratios of vanillyl-type lignin phenols in A horizons. Litter addition had no such effects. We assume that litter exclusion caused enhanced transport of organic debris from lower forest floor horizons with rainwater into the A horizon. Enhanced input of organic debris might have increased (i) the availability of labile compounds and (ii) F/B ratios. Consequently, lignin oxidation increased.

Conclusions

Enhanced input of organic debris from forest floors can increase lignin oxidation in mineral topsoils of the studied forest. The expected gradual changes in litter fall due to climate change likely will cause no such effects.     

Microbial contributions to the evolution of the ‘steady state’ carbon dioxide system

Various processes for the production of carbon dioxide by microorganisms are presented. It is postulated that a microniche developed in a reducing environment; a symbiotic relationship between alga-like organisms and bacterium-like organisms in the microniche governed the production of carbon dioxide resulting in the establishment of the steady state carbon dioxide system in the sea.     

Spiders in mofette fields—Survival of the toughest in natural carbon dioxide springs?

In mofette fields, natural carbon dioxide springs, organisms have to stand extreme CO₂ concentrations up to 100%. These hostile conditions are spatially small-scaled and further influenced by earth tides, wind and temperature. The present project investigated the influence of increased atmospheric CO₂ concentration on spiders as representatives of above-ground organisms by means of pitfall traps in three mofette fields, differing in habitat conditions in the Plesná valley, eastern Cheb Basin, Czech Republic.Among the 71 recorded spider species four were rarely found in the Czech Republic. A canonical correspondence analysis revealed significant influences of environmental parameters on the spider assemblages. Two groups of spiders are clearly distinguishable, one being positively influenced by humidity and the second by temperature. A cluster analysis showed distinct and congruent results: spider assemblages of pitfall traps at spots with a mean CO₂ concentration above 7.6% grouped close together and this grouping was independent of site. At >7.6% CO₂ significantly fewer individuals and species were found in comparison to areas with lower CO₂ concentration. Between 2.5 and 10% CO₂, spiders indicated increased CO₂ concentrations much more sensitively than endogeic organisms (Nematoda, Collembola) in a nearby mofette field. Unlike in nematodes, collembolans and plants, no mofettovageous or mofettophilous spiders were detected. In contrast to humidity, CO₂ concentration and temperature, the vegetation cover was not among the factors, which significantly influenced spiders. This is explained by the fact that mofettophilous plants occurred at spots where almost no spiders could live. In a field experiment, most Pardosa pullata males tested passed a 30 cm long corridor with increased carbon dioxide concentration. These results and that of pitfall traps showed that relatively large and wandering specimens respectively were able to transit moderately hostile spots. Further experiments are necessary to find out if there is any active avoidance of high-CO₂ areas by spiders.     

Atmospheric carbon dioxide: a driver of photosynthetic eukaryote evolution for over a billion years?

Exciting evidence from diverse fields, including physiology, evolutionary biology, palaeontology, geosciences and molecular genetics, is providing an increasingly secure basis for robustly formulating and evaluating hypotheses concerning the role of atmospheric carbon dioxide (CO(2)) in the evolution of photosynthetic eukaryotes. Such studies span over a billion years of evolutionary change, from the origins of eukaryotic algae through to the evolution of our present-day terrestrial floras, and have relevance for plant and ecosystem responses to future global CO(2) increases. The papers in this issue reflect the breadth and depth of approaches being adopted to address this issue. They reveal new discoveries pointing to deep evidence for the role of CO(2) in shaping evolutionary changes in plants and ecosystems, and establish an exciting cross-disciplinary research agenda for uncovering new insights into feedbacks between biology and the Earth system.     

Stable carbon isotope ratio of tree leaves, boles and fine litter in a tropical forest in Rondônia, Brazil

Leaves of 208 trees were collected for isotopic analysis together with wood from 36 tree boles and 18 samples of fine litter from a terra-firme forest located at Samuel Ecological Reserve, Rondônia State, in the southwestern Amazon region. The range of δ¹³C values in leaves was from ?28 to ?36‰, with an average (±1 SD) of ?32.1?±?1.5‰, which was more negative than the δ¹³C values of bole samples (?28.4?±?2.0‰) and fine litter (?28.7?±?2.0‰). These values are within the range found for tropical and subtropical forests. Pooling the δ¹³C values for leaf samples from trees of the same height gave averages which were positively correlated with plant height at a highly significant level, with a slope of 0.06 and an intercept of ?33.3‰ and a correlation coefficient r ²=0.70 (P<0.001).     

Deactivation of isoamylase and β-amylase in the agitated reactor under supercritical carbon dioxide

The current research examines the impact of agitation on deactivation of isoamylase and β-amylase under supercritical carbon dioxide (SC-CO₂). Our experimental results showed that the activity of either enzyme decreased with increasing pressure or speed of agitation. The degree of enzymatic deactivation caused by pressure became more prominent in the presence of agitation, suggesting that the agitation plays an important role in enzymatic deactivation in SC-CO₂ environment. Moreover, the enzymatic deactivation behavior associated with agitation and pressure was further quantitatively analyzed using a proposed inactivation kinetic model. Our analysis indicated that isoamylase and β-amylase exhibited significantly different relationships between the inverse of percentage residual activity and the product of number of revolution per time and time elapsed under pressurized carbon dioxide. We believe that the outcome from this work may provide a better understanding of the effects of agitation and pressure in enzyme deactivation behavior under SC-CO₂.     

How does drought stress influence the decomposition of plant litter with contrasting quality in a grassland ecosystem?

Background and aims

Plant litter quality and water availability both control decomposition. The interaction of both parameters was never studied. We used a grassland site, where litter of contrasting quality, i.e. green litter (fresh leaves; high quality) and brown litter (dead leaves, which underwent senescence but which are still attached to the plant; low quality), is returned to soil. Green and brown litter were exposed in the field under regular weather and drought conditions. The objective of this study was to evaluate the effect of drought on the decomposition of both litter types.

Methods

We incubated green and brown litter of three different grassland species (Lolium perenne, Festuca arundinacea and Dactylis glomerata) alone or as litter mixture (1/3 of each of the three grassland species) in litterbags for 28?weeks. Drought conditions were simulated by rainfall exclusion. After incubation, litter residues were analysed for C and nitrogen (N) content and stable isotope composition. Additionally, we determined the response of the lignin and carbohydrate signatures to the contrasting conditions.

Results

C decomposition kinetics of green and brown litter under drought conditions could be explained by two pools of contrasting turnover times. Drought decreased leaf litter C and N decomposition by more than 50% compared to regular weather conditions, mainly by strongly decreasing the decomposition rate constants. The lowest C decomposition occurred for mixtures of litter from all three grassland species. Brown litter showed on average 15% higher reduction in carbon decomposition than green litter following drought. Lignin content remained similar for green and brown litter after drought and regular weather conditions, while sugar content remained similar in green litter and decreased by 18% for brown litter under drought conditions.

Conclusions

Our results showed different response of decomposition of litter with contrasting quality to drought. Low quality brown litter is likely to be more affected than high quality green litter. Thus, litter quality must be taken into account, when assessing the effect of drought on decomposition.     

On the origin and evolution of new genes——a genomic and experimental perspective

The inherent interest on the origin of genetic novelties can be traced back to Darwin. But it was not until recently that we were allowed to investigate the fundamental process of origin of new genes by the studies on newly evolved young genes. Two indispensible steps are involved in this process:origin of new gene copies through various mutational mechanisms and evolution of novel functions, which further more leads to fixation of the new copies within populations. The theoretical framework for the former ...     

On the origin and evolution of new genes——a genomic and experimental perspective

The inherent interest on the origin of genetic novelties can be traced back to Darwin, But it was not until recently that we were allowed to investigate the fundamental process of origin of new genes by the studies on newly evolved young genes. Two indispensible steps are involved in this process: origin of new gene copies through various mutational mechanisms and evolution of novel functions, which fur-ther more leads to fixation of the new copies within populations. The theoretical framework for the former step formed in 1970s. Ohno proposed gene duplication as the most important mechanism producing new gene copies. He also believed that the most common fate for new gene copies is to become pseudogenes. This classical view was validated and was also challenged by the characterization of the first functional young gene jingwei in Drosophila. Recent genome-wide comparison on young genes of Drosophila has elucidated a compre-hensive picture addressing remarkable roles of various mechanisms besides gene duplication during origin of new genes. Case surveys revealed it is not rare that new genes would evolve novel structures and functions to contribute to the adaptive evolution of organisms.Here, we review recent advances in understanding how new genes originated and evolved on the basis of genome-wide results and ex-perimental efforts on cases, We would finally discuss the future directions of this fast-growing research field in the context of functional genomics era.     

Litter decomposition of woody species in shrublands of NW Patagonia: how much do functional groups and microsite conditions influence decomposition?

The study examined the effects of leaf traits, soil microsite, and microclimate characteristics on litter decomposition of the dominant species in two functional groups (FG), deciduous and evergreen, in shrublands in NW Patagonia, Argentina. Leaf traits considered were nutrient concentration (C, N, P, C/N, and N/P) and physical characteristics (area, strength, specific leaf area, and dry matter content). Soil microsite characteristics measured were pH, C, N, P, C/N and water retention capacity, while soil microclimate characteristics recorded were soil and air, temperature and moisture, and solar radiation. Five evergreen and five deciduous woody shrub species were selected. During 1 year, litter and microsite properties were measured below canopy: (i) senescent leaf chemical and physical properties, and the quantity as well as field decomposition of litter and (ii) soil chemistry, and soil and air physical properties. The factors controlling litter decomposition were different for each FG. In deciduous species, C/N ratio had a negative effect on decomposition. In evergreen species, decomposition was affected negatively by leaf carbon and dry matter content. Litter decomposition depended exclusively on the inherent senescent leaves traits. The common decomposition pattern between species of both FG could be attributed to similar leaf traits and the correlation between variables that control decomposition in both groups. Plant nutrient inputs associated with the litter decomposition process did not explain the soil nutrient content. These results suggest that other organic matter sources (roots, branches, and fruits) are more important than leaves on soil fertility.     

Are fire,soil fertility and toxicity,water availability,plant functional diversity,and litter decomposition related in a Neotropical savanna?

Understanding how biodiversity and ecosystem functioning respond to changes in the environment is fundamental to the maintenance of ecosystem function. In realistic scenarios, the biodiversity-ecosystem functioning path may account for only a small share of all factors determining ecosystem function. Here, we investigated the strength to which variations in environmental characteristics in a Neotropical savanna affected functional diversity and decomposition. We sought an integrative approach, testing a number of pairwise hypotheses about how the environment, biodiversity, and functioning were linked. We used structural equation modelling to connect fire frequency, soil fertility, exchangeable Al, water availability, functional diversity of woody plants, tree density, tree height, and litter decomposition rates in a causal chain. We found significant effects of soil nutrients, water availability, and Al on functional diversity and litter decomposition. Fire did not have a significant direct effect on functional diversity or litter decomposition. However, fire was connected to both variables through soil fertility. Functional diversity did not influence rates of litter decomposition. The mediated effects that emerged from pairwise interactions are encouraging not only for predicting the functional consequences of changes in environmental variables and biodiversity, but also to caution against predictions based on only environmental or only biodiversity change.     

Microbial Colonization of Beech and Spruce Litter—Influence of Decomposition Site and Plant Litter Species on the Diversity of Microbial Community

The present study was conducted to investigate the effect of decomposition site and plant litter species on the colonizing microbial communities. For this, litter bag technique using beech and spruce litter was combined with RNA-based fingerprinting and cloning. Litter bags were incubated for 2 and 8 weeks in the A_h horizon of beech and beech–spruce mixed forest sites. Although sugars and starch were rapidly lost, lignin content increased by more than 40% for beech and more than doubled for spruce litter at both soil sites at the end of the experiment. Denaturing gradient gel electrophoresis analysis of 16S and 18S rRNA RT–PCR products was used for screening of differences between bacterial and fungal communities colonizing the two litter types. Development of the microbial community over time was observed to be specific for each litter type and decomposition site. RT–PCR products from both litter types incubated in beech–spruce mixed forest site were also cloned to identify the bacterial and fungal colonizers. The 16S rRNA clone libraries of beech litter were dominated by γ-proteobacterial members, whereas spruce libraries were mainly composed of α-, β-, and γ-proteobacterial members. Ascomycota members dominated the 18S rRNA clone libraries. Clones similar to Zygomycota were absent from spruce, whereas those similar to Basidiomycota and Glomeromycota were absent from beech libraries. Selective effects of litter quality were observed after 8 weeks. The study provides an insight into the bacterial and fungal communities colonizing beech and spruce litter, and the importance of litter quality and decomposition site as key factors in their development and succession.     

Do soil organisms affect aboveground litter decomposition in the semiarid Patagonian steppe, Argentina?

Surface litter decomposition in arid and semiarid ecosystems is often faster than predicted by climatic parameters such as annual precipitation or evapotranspiration, or based on standard indices of litter quality such as lignin or nitrogen concentrations. Abiotic photodegradation has been demonstrated to be an important factor controlling aboveground litter decomposition in aridland ecosystems, but soil fauna, particularly macrofauna such as termites and ants, have also been identified as key players affecting litter mass loss in warm deserts. Our objective was to quantify the importance of soil organisms on surface litter decomposition in the Patagonian steppe in the absence of photodegradative effects, to establish the relative importance of soil organisms on rates of mass loss and nitrogen release. We estimated the relative contribution of soil fauna and microbes to litter decomposition of a dominant grass using litterboxes with variable mesh sizes that excluded groups of soil fauna based on size class (10, 2, and 0.01 mm), which were placed beneath shrub canopies. We also employed chemical repellents (naphthalene and fungicide). The exclusion of macro- and mesofauna had no effect on litter mass loss over 3 years (P = 0.36), as litter decomposition was similar in all soil fauna exclusions and naphthalene-treated litter. In contrast, reduction of fungal activity significantly inhibited litter decomposition (P < 0.001). Although soil fauna have been mentioned as a key control of litter decomposition in warm deserts, biogeographic legacies and temperature limitation may constrain the importance of these organisms in temperate aridlands, particularly in the southern hemisphere.     

Litter decomposition: what controls it and how can we alter it to sequester more carbon in forest soils?

Key recent developments in litter decomposition research are reviewed. Long-term inter-site experiments indicate that temperature and moisture influence early rates of litter decomposition primarily by determining the plants present, suggesting that climate change effects will be small unless they alter the plant forms present. Thresholds may exist at which single factors control decay rate. Litter decomposes faster where the litter type naturally occurs. Elevated CO₂ concentrations have little effect on litter decomposition rates. Plant tissues are not decay-resistant; it is microbial and biochemical transformations of materials into novel recalcitrant compounds rather than selective preservation of recalcitrant compounds that creates stable organic matter. Altering single characteristics of litter will not substantially alter decomposition rates. Nitrogen addition frequently leads to greater stabilization into humus through a combination of chemical reactions and enzyme inhibition. To sequester more C in soil, we need to consider not how to slow decomposition, but rather how to divert more litter into humus through microbial and chemical reactions rather than allowing it to decompose. The optimal strategy is to have litter transformed into humic substances and then chemically or physically protected in mineral soil. Adding N through fertilization and N-fixing plants is a feasible means of stimulating humification.     

Enhanced decomposition of selenium hyperaccumulator litter in a seleniferous habitat��evidence for specialist decomposers?

Grassland canopy management (spring burn, mowing and residue removal in late-summer, or no management) and native tallgrass species composition (cool season mixture, warm season mixture, or combined cool and warm mixture) effects on C and N in aboveground biomass and soil were investigated at Brookings SD on a previously-plowed Barnes clay loam (fine-loamy, superactive, frigid Calcic Hapludoll). During the last 2 yr of the 9-yr experiment, shoot biomass was affected by canopy management with the burn (2,730 kg ha^?1) and mow (3,421 kg ha^?1) treatments containing less than no management (4,655 kg ha^?1). Burn treatment biomass contained 1,189 kg ha^?1 and 25 kg ha^?1 of C and N, mow contained 1,433 kg ha^?1 and 33 kg ha^?1 of C and N, while no management contained 2,014 kg ha^?1 and 39 kg ha^?1 of C and N, respectively. Soil C accumulation was independent of grass species composition. Soil C accumulation rates, which increased in strong linear fashion (r ² of 0.89 to 0.92) after initial grass establishment, were 387 kg C ha^?1 yr^?1, 503 kg C ha^?1 yr^?1, and 711 kg C ha^?1 yr^?1 for burn, mow, and no management treatments, respectively. Thus, grassland management methods used after conversion of cropland to grassland have important effects on grass biomass and soil C accumulation.     

Do climate and soil influence phenotypic variability in leaf litter,microbial decomposition and shredder consumption?

We tested the hypothesis that water stress and soil nutrient availability drive leaf-litter quality for decomposers and detritivores by relating chemical and physical leaf-litter properties and decomposability of Alnus glutinosa and Quercus robur, sampled together with edaphic parameters, across wide European climatic gradients. By regressing principal components analysis of leaf traits [N, P, condensed tannins, lignin, specific leaf area (SLA)] against environmental and soil parameters, we found that: (1) In Q. robur the condensed tannin and lignin contents increased and SLA decreased with precipitation, annual range of temperature, and soil N content, whereas leaf P increased with soil P and temperature; (2) In A. glutinosa leaves N, P, and SLA decreased and condensed tannins increased with temperature, annual range of temperature, and decreasing soil P. On the other hand, leaf P and condensed tannins increased and SLA decreased with minimum annual precipitation and towards sites with low temperature. We selected contrasting leaves in terms of quality to test decomposition and invertebrate consumption. There were intraspecific differences in microbial decomposition rates (field, Q. robur) and consumption by shredders (laboratory, A. glutinosa). We conclude that decomposition rates across ecosystems could be partially governed by climate and soil properties, affecting litter quality and therefore decomposers and detritivores. Under scenarios of global warming and increased nutrients, these results suggest we can expect species-specific changes in leaf-litter properties most likely resulting in slow decomposition with increased variance in temperatures and accelerated decomposition with P increase.     

What type of diversity yields synergy during mixed litter decomposition in a natural forest ecosystem?

Investigating the relationship of biodiversity and ecosystem function in natural forests allows incorporation of established feedbacks between long-lived plants and soil processes. We studied forested stands in northern Arizona that vary in dominant species richness across small areas. We examined the effects of natural variation in dominant tree biodiversity on ecosystem parameters, particularly litter decomposition. We determined not only whether plant species decompose in mixture as predicted by their individual decomposition rates but also: (1) how particular species affect the decomposition rate of each other in mixture; and (2) whether litter decomposes more rapidly at its site of origin; i.e. is there a “home field advantage” to decomposition? Over a 2-year period, litter mixtures of functionally similar tree species decomposed more rapidly than expected from rates of the individual species alone. Mixtures of conifer species litter decomposed up to 50% faster than expected, with individual conifer members of those mixtures decomposing up to 85% faster than expected. In contrast, more functionally diverse mixtures of litter, which included a deciduous species, did not show synergistic effects during decomposition. We found no significant “home-field advantage” to decomposition. Our study is the first to demonstrate that litter mixtures from more closely related plant species give rise to the most synergistic effects of biodiversity on litter dynamics, indicating that more taxonomically and functionally diverse plant assemblages do not always drive greater emergent effects on ecosystem function.     

Leaf dry matter content as a predictor of grassland litter decomposition: a test of the ��mass ratio hypothesis��

The mass ratio hypothesis provides the key link between plant functional traits (PFTs) and ecosystem processes. Despite its centrality to the field it has had few direct tests. A litter decomposition study using grassland species, singly and in mixtures, was set up to see whether simple leaf traits could be used to predict the decomposition of leaf mixtures. Leaf Dry Matter Content (LDMC) was the trait that performed best. Mass loss in single species bags was best predicted using an exponential model. LDMC explained 48% of the variance in mixture mass loss. There was no significant impact of mixture species richness on mass loss. This study generally confirmed the predictions of the mass ratio hypothesis, but adds some support to other studies that indicate it needs broadening to take into account non-linear and threshold relationships between PFTs and ecosystem processes.