Hypothesis-testing methods for multivariate data are needed to make rigorous probability statements about the effects of factors and their interactions in experiments. Analysis of variance is particularly powerful for the analysis of univariate data. The traditional multivariate analogues, however, are too stringent in their assumptions for most ecological multivariate data sets. Non-parametric methods, based on permutation tests, are preferable. This paper describes a new non-parametric method for multivariate analysis of variance, after McArdle and Anderson (in press). It is given here, with several applications in ecology, to provide an alternative and perhaps more intuitive formulation for ANOVA (based on sums of squared distances) to complement the description pro- vided by McArdle and Anderson (in press) for the analysis of any linear model. It is an improvement on previous non-parametric methods because it allows a direct additive partitioning of variation for complex models. It does this while maintaining the flexibility and lack of formal assumptions of other non-parametric methods. The test- statistic is a multivariate analogue to Fisher's F-ratio and is calculated directly from any symmetric distance or dissimilarity matrix. P-values are then obtained using permutations. Some examples of the method are given for tests involving several factors, including factorial and hierarchical (nested) designs and tests of interactions.

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A new method for non-parametric multivariate analysis of variance

Organic acids, such as malate, citrate and oxalate, have been proposed to be involved in many processes operating in the rhizosphere, including nutrient acquisition and metal detoxification, alleviation of anaerobic stress in roots, mineral weathering and pathogen attraction. A full assessment of their role in these processes, however, cannot be determined unless the exact mechanisms of plant organic acid release and the fate of these compounds in the soil are more fully understood. This review therefore includes information on organic acid levels in plants (concentrations, compartmentalisation, spatial aspects, synthesis), plant efflux (passive versus active transport, theoretical versus experimental considerations), soil reactions (soil solution concentrations, sorption) and microbial considerations (mineralization). In summary, the release of organic acids from roots can operate by multiple mechanisms in response to a number of well-defined environmental stresses (e.g., Al, P and Fe stress, anoxia): These responses, however, are highly stress- and plant-species specific. In addition, this review indicates that the sorption of organic acids to the mineral phase and mineralisation by the soil's microbial biomass are critical to determining the effectiveness of organic acids in most rhizosphere processes.

Organic acids in the rhizosphere: a critical review

B6nassy, C., 1955. R6marques sur deux Aphelinid6s: Aphelinus mytilaspidis Le Baron et Aphytis proclia Walker. Annls l~piphyt. 6: 11-17. Lord, F. T. & MacPhee, A. W., 1953. The influence of spray programs on the fauna of apple orchards in Nova Scotia II. Oyster shell scale. Can. Ent. 79: 196-209. Pickett, A. D., 1946. A progress report on long term spray programs. Rep. Nova Scotia Fruit Grow. Ass. 83 : 27-31. Pickett, A. D., 1967. The influence of spray programs on the fauna of apple orchards in Nova Scotia XIV. Can. Ent. 97: 816-821. Tothill, J. D., 1918. The predacious mite Hemisarcoptes malus Shimer and its relation to the natural control of the oyster shell scale Lepidosaphes ulmi L. Agric. Gaz. Can. 5 : 234-239.

http://link.springer.com/content/pdf/10.1007/BF01976688.pdf

Soil enzymes: Kuprevich, V. F. & Shcherbakova, T. A.: Translated from the Russian edition (1966), published by the Indian National Scientific Documentation Centre, New Delhi 1971. 392 pp., offset printing from type script, paper cover. Obtainable from U.S. Department of Commerce, National Technical Information Service, Springfield, Va. 22151

Root turnover is a critical component of ecosystem nutrient dynamics and carbon sequestration and is also an important sink for plant primary productivity. We tested global controls on root turnover across climatic gradients and for plant functional groups by using a database of 190 published studies. Root turnover rates increased exponentially with mean annual temperature for fine roots of grasslands (r2 = 0.48) and forests (r2 = 0.17) and for total root biomass in shrublands (r2 = 0.55). On the basis of the best-fit exponential model, the Q10 for root turnover was 1.4 for forest small diameter roots (5 mm or less), 1.6 for grassland fine roots, and 1.9 for shrublands. Surprisingly, after accounting for temperature, there was no such global relationship between precipitation and root turnover. The slowest average turnover rates were observed for entire tree root systems (10% annually), followed by 34% for shrubland total roots, 53% for grassland fine roots, 55% for wetland fine roots, and 56% for forest fine roots. Root turnover decreased from tropical to high-latitude systems for all plant functional groups. To test whether global relationships can be used to predict interannual variability in root turnover, we evaluated 14 yr of published root turnover data from a shortgrass steppe site in northeastern Colorado, USA. At this site there was no correlation between interannual variability in mean annual temperature and root turnover. Rather, turnover was positively correlated with the ratio of growing season precipitation and maximum monthly temperature (r2 = 0.61). We conclude that there are global patterns in rates of root turnover between plant groups and across climatic gradients but that these patterns cannot always be used for the successful prediction of the relationship of root turnover to climate change at a particular site.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1469-8137.2000.00681.x

Global patterns of root turnover for terrestrial ecosystems

https://www.ess.uci.edu/researchgrp/sites/default/files/jranders/files/1995rsefieldetal.pdf

Global net primary production: Combining ecology and remote sensing

The objective of this study was to evaluate for an 8-yr period the ecosystem-level impacts of no grazing vs. sustained moderate and heavy cattle grazing in terms of: (1) plant species basal cover, density, and composition; (2) aboveground net primary production (ANPP), N content of ANPP (ANPP-N), belowground net primary production (BNPP), and N content of BNPP (BNPP-N); (3) litter and root decomposition and N loss; and (4) soil C, total soil N, and net in situ soil N mineralization. Moderate and heavy grazing treatments were designed to achieve an end-of-the-grazing-season residual vegetation of 50% and 10%, respectively, of the long-term average ANPP of comparable ungrazed sites. The main factor affecting the vegetation response was the increase in precipitation after the drought of 1988; few differences were due to grazing intensity. The total absolute basal cover of grasses increased steadily in all treatments, from an average of 4% during the drought of 1988 to 14% in 1993. Forb density and diversity increased from 51 plants/m2 and 14 species in 1988 to 412 plants/m2 and 36 species in 1995. Grazing, however, increased the relative composition of Poa pratensis and Achillea millefolium, but reduced the relative composition of Bouteloua gracilis and Aster ericoides. ANPP and ANPP-N were correlated with rainfall, but not with grazing intensity. Heavy grazing led to declines in standing dead biomass, litter, peak root biomass and biomass-N, root N concentrations, and in situ net soil N mineralization. There was an increase in root decomposition and N loss with grazing. From this study, we reached the following conclusions about the northern mixed-grass prairie: (1) climatic variations, in particular droughts, control major trends in plant species composition and production, with grazing playing a secondary role; (2) heavy grazing leads to declines in standing dead biomass and biomass-N, litter biomass and biomass-N, peak root biomass and biomass-N, and in situ net soil N mineralization, which may have a significant long-term impact on range condition; and (3) grazing pressures that lead to a removal of 50% of ANPP, however, seem to be sustainable and compatible with the maintenance of range condition.

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Grazing intensity and ecosystem processes in a northern mixed-grass prairie, usa

The relationship between secondary succession, soil disturbance, and soil biological activity were studied on a sagebrush community (Artemisia tridentata) in the Piceance Basin of northwestern Colorado, U.S.A. Four levels of disturbance were imposed. I: the vegetation was mechanically removed and as much topsoil as possible was left; 2: the vegetation was mechanically removed and the topsoil scarified to a depth of 30 cm; 3: topsoil and subsoil were removed to a depth of 1 m, mixed and replaced; 4: topsoil and subsoil were removed to a depth of 2 m and replaced in a reverse order. Plant species composition, dehydrogenase and phosphatase enzymatic activity, mycorrhizae infection potentials, and percent organic matter were the variables measured. Treatment 4 drastically altered the pattern of vegetation succession. Treatments 2, 3, and 4 started with Salsola iberica as the dominant species but six years later, 3 and to lesser extent 2 changed in the direction of the species composition of 1, dominated by perennial grasses and perennial forbs. Treatment 4 developed a shrub dominated community. The rate of succession was not decreased by the increased levels of disturbance. Both dehydrogenase enzyme activity and mycorrhizae infection potential (MIP) increased with the change from Salsola iberica to a vegetation dominated by either perennial grasses and forbs or shrubs. The intensity of disturbance in 2, 3, and 4 reduced drastically dehydrogenase activity and MIP, but in six years they recovered to levels comparable to 1. Phosphatase enzyme activity and organic matter were unrelated to species composition but related to treatment and time elapsed. In both cases a significant decrease was observed throughout the six-year period.

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Secondary successional patterns in a sagebrush (Artemisia tridentata) community as they relate to soil disturbance and soil biological activity

Two distribution-free permutation techniques are described for the analysis of ecological data. These methods are completely data dependent and provide analyses for the commonly-encountered completely-randomized and randomized-block designs in a multivariate framework. Euclidean distance forms the basis of both techniques, providing consistency with the observed distribution of data in many ecological studies.

Data-dependent permutation techniques for the analysis of ecological data

A 2 year study in south central North Dakota determined the responses of (1) litter and root decomposition and nitrogen (N) release, and (2) soil N mineralization to grazing intensity. The treatments were: long term not grazed, moderate grazing, and heavy grazing. The moderate grazing and the heavy grazing treatments removed 45% and 77% of annual above-ground growth respectively. The moderate grazing treatment resulted in higher decomposition and soil N mineralization rates, and lower N releases via decomposition than the long term not grazed and heavy grazing treatments. No consistent differences were found between the long term not grazed and heavy grazing treatments. Annual litter and root decomposition rates in the moderate grazing treatment averaged 55% for 1989-1990 and 63% for 1990-1991 while the long term not grazed and heavy grazing treatments had rates for the same periods of 13% and 19%. The moderate grazing treatment had a net soil N mineralization of 60 micrograms.g-1 and 269 micrograms.g-1 during the 1989 and 1990 growing seasons whereas the long term not grazed and heavy grazing treatments had net soil immobilization for the same periods of -59 micrograms.g-1 and -115 micrograms.g-1. Annual N release from litter and root decomposition in the heavy grazing and long term not grazed treatments averaged 70% and 38% respectively during the 1989-1990 incubation period, and 51 % and 23% during 1990-1991. The equivalent values for the moderate grazing treatment were 47% and -6% (net N immobilization) for 1989-1990 and 41% and 23% for 1990-1991. Results from this study seem to indicate that the standard grazing rule of "take half leave half" may have a significant impact in N conservation and the supply of mineral N for plant growth.

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Grazing intensity effects on litter decomposition and soil nitrogen mineralization

The effects of fire season on forb diversity patterns, density, and composition were determined for a northern Mixed Prairie site, USA. Repeated spring burns (dormant season), summer burns, fall burns (dormant season), and unburned treatments were compared over a 3-yr period characterized by wet and dry moisture conditions. Alpha and beta diversity were highest on unburned and summer burn treatments, while landscape mosaic diversity was highest on fall burns. Forb density was highest on fall and spring burn sites. Nine forb species comprised 82% of total densities and were significantly affected by fire season and year to year variations in moisture. Forb composition for unburned and spring burn treatments was similar, but both treatments were different from the summer burn and fall burn treatments which were similar to each other. Fire alone did not appear to be an intense enough disturbance to initiate drastic changes in the forb component of vegetation patches. Specific fire seasons did appear to either mask or enhance forb structure arising from other disturbance(s). Fire season also affected the scales of forb organization in the landscape. Contrasting spatial characteristics of the forb component of prairie plant communities may provide a diagnostic technique for exposing the interaction of disturbances at different temporal and spatial scales.

Mario E. Biondini

Papers

Grazing intensity and ecosystem processes in a northern mixed-grass prairie, usa

Secondary successional patterns in a sagebrush (Artemisia tridentata) community as they relate to soil disturbance and soil biological activity

Data-dependent permutation techniques for the analysis of ecological data

Grazing intensity effects on litter decomposition and soil nitrogen mineralization

Seasonal fire effects on the diversity patterns, spatial distribution and community structure of forbs in the Northern Mixed Prairie, USA