Soil Chemical Analysis

Humans are altering the composition of biological communities through a variety of activities that increase rates of species invasions and species extinctions, at all scales, from local to global. These changes in components of the Earth's biodiversity cause concern for ethical and aesthetic reasons, but they also have a strong potential to alter ecosystem properties and the goods and services they provide to humanity. Ecological experiments, observations, and theoretical developments show that ecosystem properties depend greatly on biodiversity in terms of the functional characteristics of organisms present in the ecosystem and the distribution and abundance of those organisms over space and time. Species effects act in concert with the effects of climate, resource availability, and disturbance regimes in influencing ecosystem properties. Human activities can modify all of the above factors; here we focus on modification of these biotic controls. The scientific community has come to a broad consensus on many aspects of the re- lationship between biodiversity and ecosystem functioning, including many points relevant to management of ecosystems. Further progress will require integration of knowledge about biotic and abiotic controls on ecosystem properties, how ecological communities are struc- tured, and the forces driving species extinctions and invasions. To strengthen links to policy and management, we also need to integrate our ecological knowledge with understanding of the social and economic constraints of potential management practices. Understanding this complexity, while taking strong steps to minimize current losses of species, is necessary for responsible management of Earth's ecosystems and the diverse biota they contain.

/pdf/effects-of-biodiversity-on-ecosystem-functioning-a-consensus-13j8vabcus.pdf

Effects of biodiversity on ecosystem functioning: a consensus of current knowledge

A doubling in global food demand projected for the next 50 years poses huge challenges for the sustainability both of food production and of terrestrial and aquatic ecosystems and the services they provide to society. Agriculturalists are the principal managers of global useable lands and will shape, perhaps irreversibly, the surface of the Earth in the coming decades. New incentives and policies for ensuring the sustainability of agriculture and ecosystem services will be crucial if we are to meet the demands of improving yields without compromising environmental integrity or public health.

/pdf/agricultural-sustainability-and-intensive-production-1h98l920tu.pdf

Agricultural sustainability and intensive production practices

The most unique feature of Earth is the existence of life, and the most extraordinary feature of life is its diversity. Approximately 9 million types of plants, animals, protists and fungi inhabit the Earth. So, too, do 7 billion people. Two decades ago, at the first Earth Summit, the vast majority of the world's nations declared that human actions were dismantling the Earth's ecosystems, eliminating genes, species and biological traits at an alarming rate. This observation led to the question of how such loss of biological diversity will alter the functioning of ecosystems and their ability to provide society with the goods and services needed to prosper.

/pdf/biodiversity-loss-and-its-impact-on-humanity-2d0fgc88mg.pdf

Biodiversity loss and its impact on humanity

When a person looks at an object while exploring it with their hand, vision and touch both provide information for estimating the properties of the object. Vision frequently dominates the integrated visual-haptic percept, for example when judging size, shape or position, but in some circumstances the percept is clearly affected by haptics. Here we propose that a general principle, which minimizes variance in the final estimate, determines the degree to which vision or haptics dominates. This principle is realized by using maximum-likelihood estimation to combine the inputs. To investigate cue combination quantitatively, we first measured the variances associated with visual and haptic estimation of height. We then used these measurements to construct a maximum-likelihood integrator. This model behaved very similarly to humans in a visual-haptic task. Thus, the nervous system seems to combine visual and haptic information in a fashion that is similar to a maximum-likelihood integrator. Visual dominance occurs when the variance associated with visual estimation is lower than that associated with haptic estimation.

Humans integrate visual and haptic information in a statistically optimal fashion.

SUMMARY

Thalli of Stereocaulon paschale (L.) Fr. were collected at approximately monthly intervals during a 13-month period from a pine forest in northern Sweden. The capacity for nitrogenase activity (C2H2-reduction) was studied on each collection under standardized, favourable laboratory conditions. Significantly higher capacities were found in thalli collected from bare ground than in thalli collected under snow, but the capacity decreased in autumn close to the snow covering. At snow melt the increase in capacity was rapid.



To investigate the decrease in capacity during the autumn, S. paschale was exposed to simulated autumn conditions in the laboratory during 2-week periods. These simulation experiments indicated that the light regime was of importance for nitrogenase activity. Low irradiance during short days caused a marked decrease in the nitrogenase activity, especially in combination with night temperatures above freezing. Night temperatures below zero, per se, did not reduce nitrogenase activity; instead a tendency to stimulate it was found.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.1978.tb01607.x

Seasonal variation in the capacity for nitrogenase activity in the lichen stereocaulon paschale

Grey alder, Alnus incana (L.) Moench, was inoculated with the local source of Frankia and planted in nitrogen-poor soil in northern (63.8°N, 20.3°E) Sweden. Each alder root system was enclosed in a...

Distribution of biomass and nitrogen among plant parts and soil nitrogen in a young Alnus incana stand

Cool-season forage grasses infected with asexual endophytic fungi (Neotyphodium spp.) often have advantages over uninfected grasses, including increased herbivore resistance. Since these fungi reproduce by growing into the developing seeds of the host, hyphal loading (amount of fungal hyphae in the plant) gives important information about the balance between host and endophyte in the symbiosis. This work provides insights into how ecological factors external to the symbiosis may influence the symbiosis. By repeated sampling of the same infected plants, we investigated how hyphal loading changes in Festuca pratensis through the growing season and how it is affected by fertilization and ley age in northern Sweden. Infection frequency in F. pratensis ranged from 25-65%. Hyphal loading, based on standard curves of immunoblot assay imprint intensity versus counts of hyphal density across grass leaf sheaths, increased significantly during the growing season and was correlated with cumulative degree days. There were no clear effects of fertilization treatment or ley age on hyphal loading. The symbiosis deserves furher study with respect to plant physiology, ecology, crop production and forage quality.

Endophytic fungi in Festuca pratensis grown in Swedish agricultural grasslands with different managements.

Frankia vesicle clusters were prepared from Alnus incana (L.) Moench root nodules by a homogenization-filtration procedure. The preparation was examined by transmission electron microscopy and computerized picture analysis to quantify contamination from the host plant. Special attention was paid to plant mitochondria. Mitochondria were only found in 30% of the 50 sections of clusters examined. In sections containing mitochondria the mean number of mitochondria per cluster section was 1.5. The relative volume of all objects found in the vesicle clusters was calculated. More than 98% of the volume of a preparation consisted of Frankia vesicles and hyphae, while only 0.4% of the volume was host plant mitochondria. The frequency of mitochondria in a preparation could be further decreased by osmotic shock. It is concluded that Frankia vesicle clusters, prepared from Alnus incana by the homogenization-filtration technique used here, are sufficiently pure to be used for studies of Frankia metabolism.

Purity of Frankia preparations from root nodules of Alnus incana

Frankia vesicle clusters were prepared from Alnus incana (L.) Moench root nodules containing a local source of Frankia by an improved homogenization-filtration procedure. The capacity of the vesicle clusters to metabolize hexoses was investigated by respirometric and enzymological studies. The vesicle clusters could utilize glucose, glucose-6-phosphate and 6-phosphogluconate provided that appropriate cofactors were added to the preparations. The enzymes hexokinase (EC 2.7.1.1), NADP+: glucose-6-phosphate dehydrogenase (EC 1.1.1.49) and NAD+;6-phosphogluconate dehydrogenase (EC 1.1.1.44) were found in cell-free extracts of the vesicle clusters and kinetic constants for the enzymes were determined. Hexokinase had a lower Km for glucose than for fructose. Extracts from both symbiotic and propionate grown Frankia AvcII also showed activity of these hexose-degrading enzymes, indicating that their presence is not necessarily dependent on sugars as carbon source. The NAD+- dependent 6-phosphogluconate dehydrogenase was only present in Frankia cells and not in alder root cells, which makes this enzyme a useful Frankia-specific marker in these symbiotic systems.

Kerstin Huss-Danell

Papers

Seasonal variation in the capacity for nitrogenase activity in the lichen stereocaulon paschale

Distribution of biomass and nitrogen among plant parts and soil nitrogen in a young Alnus incana stand

Endophytic fungi in Festuca pratensis grown in Swedish agricultural grasslands with different managements.

Purity of Frankia preparations from root nodules of Alnus incana

Capacity for hexose respiration in symbiotic Frankia from Alnus incana