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.

The kinetics of asymbiotic nitrogenase activity in three strains of the actinomycete Frankia were studied. Decay rates for enzyme activity were determined by adding chloramphenicol to active acetylene-reducing cells and measuring the time required for all activity to cease. Synthesis rates were measured by bubbling oxygen through actively-reducing cells (which totally destroyed all activity) and then measuring the time required for activity to return to normal. Decay rates (t
1/2) for these three strains were approximately 30 to 40 min. Synthesis rates were slower and initial nitrogenase activities were recorded about 110 min (DDB 011610) or 210 min (DDB 020210 and WgCc1.17) after return to air-equilibrated cultures. Frankia strain WgCc1.17 showed a greater sensitivity to oxygen and nitrogenase activity was totally lost when cells were bubbled only with atmospheric concentrations of oxygen. The results presented here indicate that nitrogenase activity turnover time is relatively rapid, on the order of minutes rather than hours or days. However, regulation of nitrogenase activity will differ from one strain to another and asmmbiotic characterization will be useful for understanding nitrogenase regulation in the bacterial-plant symbiosis.

Effects of oxygen and chloramphenicol on Frankia nitrogenase activity

A clone of Alnus incana (L.) Moench was grown in symbiosis with a local source of Frankia or with Frankia Ar14. Seven to 9-week-old plants were given 20 mM NH4Cl (20 mM KCl = control) for 3 days. Nitrogenase activity of intact plants decreased gradually within the 3 days of treatment to about 10% of the initial rates. Hydrogen evolution in air and total nitrogenase activity responded similarly to the treatment. Relative efficiency of nitrogenase thus remained the same throughout the study period. Control plants were not affected. Measurements of nitrogenase activity in root nodule homogenates (in vitro measurements) indicated loss of active nitrogenase rather than shortage of energy for nitrogenase activity in Frankia from ammonium-treated plants. Shoots were exposed to 14CO2 and translocation of 14C to Frankia vesicle clusters prepared from root nodules was studied. Frankia vesicle clusters from ammonium-treated plants contained about half as much 14C as those of control plants during all 3 days studied. One explanation for the observed effects is that a reduced supply of carbon to Frankia vesicles in the root nodules caused a reduced metabolic rate, including reduced protein synthesis and synthesis of nitrogenase.

Nitrogenase activity decay and energy supply in Frankia after addition of ammonium to the host plant Alnus incana

Some plants live in symbiosis with N2-fixing bacteria. Frankia, a genus of soil actinomycetes, can infect roots and induce root nodules on so-called actinorhizal plants. These are about 200 species of essentially woody angiosperms belonging to eight families. The root nodule is a unique organ where the plant anatomy and metabolism has adapted to facilitate the hosting of Frankia. In exchange for carbon compounds Frankia provides plant-available nitrogen rendering the host independent of soil nitrogen. When free-living, Frankia is capable of fixing N2 for its own growth, and an important characteristic are specialized cells, so-called vesicles, where dinitrogenase can function in an aerobic environment. Among actinorhizal genera there is a broad range of anatomical and biochemical adaptations in Frankia and the host plant to enable both N2 fixation and aerobic metabolism in the root nodules. Plant and bacterial metabolism form a complex intertwined network with bacterial and plant metabolites shuttled across membranes. N2 fixation is energy costly and nodules represent strong carbon sinks. The plant provides the nodules with photosynthates mostly in the form of sucrose. Dicarboxylates are imported to Frankia to support bacterial development and N2 fixation. Ammonium is assumed to be exported from Frankia to the cytoplasm of the infected cells and converted to appropriate amino acids and amides for transport to the nitrogen sinks of the plant. The N2 fixation activity in Frankia is controlled by external factors such as the plant's photosynthetic activity, which affects the carbon supply to the nodule, and nitrogen availability in the plant.

Physiology of Actinorhizal Nodules

Nitrogenase Activity in the Lichen Stereocaulon paschale: Recovery after Dry Storage

Inhibition of nitrogenase (EC 1.18.6.1) activity by O2 has been suggested to be an early response to disturbance in carbon supply to root nodules in the Frankia-Alnus incana symbiosis. Intact nodulated root systems of plants kept in prolonged darkness of 22 h were used to test responses to O2 and short-term N2 deprivation (1 h in Ar:O2). By using a Frankia lacking uptake hydrogenase it was possible to follow nitrogenase activity over time as H2 evolution in a gas exchange system. Respiration was simultaneously recorded as CO2 evolution. Dark-treated plants had lower initial nitrogenase activity in N2:O2 (68% of controls), which declined further during a 1-h period in the assay system in N2:O2 at 21 and 17% O2, but not at 13% O2. When dark-treated plants were deprived of N2 at 21 and 17% O2 nitrogenase activity declined rapidly to 61 and 74%, respectively, after 20 min, compared with control plants continuously kept in their normal light regime. In contrast, there was no decline in dark-treated plants at 13% O2, and only a smaller and temporary decline in control plants at 21% O2. When dark-treated plants were kept at 21% O2 during 45 min prior to N2 deprivation at 17% O2 the decline was abolished. This supports the idea that the decline in nitrogenase activity observed in N2:O2 at 21% O2 and during N2 deprivation was caused by O2, which affected a sensitive nodule fraction. Nodule contents of the amino acids Gln and Cit decreased during N2 deprivation, suggesting decreased assimilation of NH4+. Contents of ATP and ADP in nodules were not affected by short-term N2 deprivation. ATP/ADP ratios were about 5 indicating a highly aerobic metabolism in the root nodule. We conclude that nitrogenase activity of Alnus plants exposed to prolonged darkness becomes more sensitive to inactivation by O2. It seemed that dark-treated plants could not adjust their nodule metabolism at higher perceived pO2 and during cessation of NH4+ production.

Kerstin Huss-Danell

Papers

Effects of oxygen and chloramphenicol on Frankia nitrogenase activity

Nitrogenase activity decay and energy supply in Frankia after addition of ammonium to the host plant Alnus incana

Physiology of Actinorhizal Nodules

Nitrogenase Activity in the Lichen Stereocaulon paschale: Recovery after Dry Storage

Nitrogenase activity and root nodule metabolism in response to O2 and short-term N2 deprivation in dark-treated Frankia-Alnus incana plants