Forest soil respiration is the sum of heterotrophic (microbes, soil fauna) and auto- trophic (root) respiration. The contribution of each group needs to be understood to evaluate implications of environmental change on soil carbon cycling and sequestration. Three primary methods have been used to distinguish hetero- versus autotrophic soil respiration including: integration of components contributing to in situ forest soil CO2 efflux (i.e., litter, roots, soil), comparison of soils with and without root exclusion, and application of stable or radioactive isotope methods. Each approach has advantages and disadvantages, but isotope based methods provide quantitative answers with the least amount of disturbance to the soil and roots. Pub- lished data from all methods indicate that root/rhizosphere respiration can account for as little as 10 percent to greater than 90 percent of total in situ soil respiration depending on vegetation type and season of the year. Studies which have integrated percent root contribution to total soil respiration throughout an entire year or growing season show mean values of 45.8 and 60.4 percent for forest and nonforest vegetation, respectively. Such average annual values must be extrapolated with caution, however, because the root contribution to total soil respiration is commonly higher during the growing season and lower during the dormant periods of the year. Abbreviations: TScer -t otal soil CO 2 efflux rate; f - fractional root contribution to TS cer; RC - root contribution to TScer

/pdf/separating-root-and-soil-microbial-contributions-to-soil-422u2gsu0s.pdf

Separating root and soil microbial contributions to soil respiration: A review of methods and observations

Summary Biodiversity is responsible for the provision of many ecosystem services; human well-being is based on these services, and consequently on biodiversity. In soil, earthworms represent the largest component of the animal biomass and are commonly termed ‘ecosystem engineers’. This review considers the contribution of earthworms to ecosystem services through pedogenesis, development of soil structure, water regulation, nutrient cycling, primary production, climate regulation, pollution remediation and cultural services. Although there has been much research into the role of earthworms in soil ecology, this review demonstrates substantial gaps in our knowledge related in particular to difficulties in identifying the effects of species, land use and climate. The review aims to assist people involved in all aspects of land management, including conservation, agriculture, mining or other industries, to obtain a broad knowledge of earthworms and ecosystem services.

/pdf/a-review-of-earthworm-impact-on-soil-function-and-ecosystem-1kvj0nuth5.pdf

A review of earthworm impact on soil function and ecosystem services

Several experimental approaches have been taken to demonstrate the importance of soil fauna in nitrogen mineralization, but there have been difficulties interpreting the results We have supplemented the experimental approach with theoretical calculations of nitrogen transformations in a shortgrass prairie The calculations incorporate a wide array of information on decomposer organisms, including their feeding preferences, nitrogen contents, life spans, assimilation efficiencies, productio:assimilation ratios, decomposabilities, and population sizes The results are estimates of nitrogen transfer rates through the detrital food web, including rates of N mineralization by bacteria, fungi, root-feeding nematodes, collembolans, fungal-feeding mites, fungal-feeding nematodes, flagellates, bacterial-feeding nematodes, amoebae, omnivorous nematodes, predaceous nematodes, nematode-feeding mites, and predaceous mites Bacteria are estimated to mineralize the most N (45 g N m−2 year−1), followed by the fauna (29), and fungi (03) Bacterial-feeding amoebae and nematodes together account for over 83% of N mineralization by the fauna The detrital food web in a shortgrass prairie is similar to that of a desert grassland The shortgrass detrital web seems to be divided into bacteria- and fungus-based components, although these two branches are united at the level of predaceous nematodes and mites

The detrital food web in a shortgrass prairie

To meet the challenge of feeding a growing world population with minimal environmental impact, we need comprehensive and quantitative knowledge of ecological factors affecting crop production. Earthworms are among the most important soil dwelling invertebrates. Their activity affects both biotic and abiotic soil properties, in turn affecting plant growth. Yet, studies on the effect of earthworm presence on crop yields have not been quantitatively synthesized. Here we show, using meta-analysis, that on average earthworm presence in agroecosystems leads to a 25% increase in crop yield and a 23% increase in aboveground biomass. The magnitude of these effects depends on presence of crop residue, earthworm density and type and rate of fertilization. The positive effects of earthworms become larger when more residue is returned to the soil, but disappear when soil nitrogen availability is high. This suggests that earthworms stimulate plant growth predominantly through releasing nitrogen locked away in residue and soil organic matter. Our results therefore imply that earthworms are of crucial importance to decrease the yield gap of farmers who can't -or won't- use nitrogen fertilizer.

/pdf/earthworms-increase-plant-production-a-meta-analysis-c4ejxyl7y6.pdf

Earthworms increase plant production: a meta- analysis

Summary
The ability of mycorrhizal (M) and non-mycorrhizal (NM) plants of Pinus contorta (Dougl. ex Loud) to utilize protein as a nitrogen source was examined. Mycorrhizas were synthesized with the fungal symbionts Paxillus involutus, Rhizopogon roseolas, Suillus bovines and Pisolithus tinctorius. The plants were grown under aseptic conditions and provided with nitrogen in the form of either protein or ammonium.

Dry weight yields of plants infected with P. involutus, R. roseolus and S. bovinus were significantly higher than those of NM plants when grown on protein as the N source. In these associations yields of M plants on protein were similar to those obtained on ammonium-N. Non-mycorrhizal plants had little ability to use protein N and the same was true of plants infected with P. tinctorius.

Plants in those associations which provided a yield increase also contained larger quantities of N. Calculations show that in all these cases some of the increases of N content arise through utilization of protein.

The implications of the results are discussed in relation to the nitrogen nutrition of the plant and to the pattern of N mobilization in soil. It is proposed that the ability of mycorrhizal associations to utilize protein N will lead not only to an increased supply of N to the plant but also to more effective competition with the decomposer population and to an overall tightening of the nitrogen cycle.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.1986.tb02886.x

The role of proteins in the nitrogen nutrition of ectomycorrhizal plants

This book is the Proceedings of the 6th International Soil Zoology Colloquium held in Uppsala in June 1976. The major theme is the interactions of plant roots, microorganisms, and soil animals. Four subthemes were chosen for the plenary sessions. These were: (i) Community structure and niche separation; (ii) The role of soil organisms in nutrient cycling; (iii) Plant roots in the soil system; and (iv) Models of soil organisms and their environment. In addition tothe 51 papers (14, 16, 13, and 8) presented in the above sessions, there are summarized versions of 41 papers given in poster session. The individual papers range from excellent to poor, with about one-fourth in the poor category. About half the remainder are autecological in subject matter treatment and lack the perspective promised in the colloquium title. Most of the papers in the first plenary session are on niche exploitation and responses by members of the soil fauna rather than on their roles as ecosystem components. The papers on nutrient cycling are, with few exceptions, excellent contributions. Particularly commendable is the comprehensive discussion offered by D. E. Reichle. The bulk of the papers in the third session concern either the activities or the effects on plants of rhizophagic invertebrates. Good discussions are given by Vancura and associates on quantitative aspects of root exudation and by Sihanonth and Todd on transfer of nutrients by ectomycorrhizal fungi. Readers expecting to find any noteworthy array of simulation models on soil organisms will be disappointed. Most of the papers in this session might have been placed just as appropriately in some other session. The closing session address by J. E. Satchell is thought-provoking as well asentertaining. The reader, while being told that earthworms are the trombones of the grave, gains the impression that as a group, the soil zoologists are alive and well. Mechanistically the book is soft cover and generally excellently edited. There are about 200 illustrations, mostly line graphs and histograms, but also some light microscope and scanning electron micrographs. Unfortunately, some of the hand-drawn diagrams are so overcrowded with small-scale details as to be practically unreadable. This volume belongs primarily in the personal libraries of invertebrate zoologists. Its reading by systems ecologists and soil scientists will be, in part, time well spent.--FRANCIS E. CLARK, Federal Research, Western Region, U.S. Department of Agriculture, P.O. Box E, Fort Collins, CO 80522.

Francis E. Clark

Papers

Soil Organisms as Components of Ecosystems