Biota can be described in terms of elemental composition, expressed as an atomic ratio of carbon:nitrogen:phosphorus (refs 1-3). The elemental stoichiometry of microoorganisms is fundamental for understanding the production dynamics and biogeochemical cycles of ecosystems because microbial biomass is the trophic base of detrital food webs. Here we show that heterotrophic microbial communities of diverse composition from terrestrial soils and freshwater sediments share a common functional stoichiometry in relation to organic nutrient acquisition. The activities of four enzymes that catalyse the hydrolysis of assimilable products from the principal environmental sources of C, N and P show similar scaling relationships over several orders of magnitude, with a mean ratio for C:N:P activities near 1:1:1 in all habitats. We suggest that these ecoenzymatic ratios reflect the equilibria between the elemental composition of microbial biomass and detrital organic matter and the efficiencies of microbial nutrient assimilation and growth. Because ecoenzymatic activities intersect the stoichiometric and metabolic theories of ecology, they provide a functional measure of the threshold at which control of community metabolism shifts from nutrient to energy flow.

and peroxide, respectively, as electron acceptors, catalyze the oxidative degradation of lignin and the formation of humus. These choices are partially methodological; it is easier to assay activities using soluble substrates that yield soluble products than to study the degradation of insoluble polymers or humic complexes. This bias has value in that reactions that yield assimilable products are the ones most directly linked to microbial metabolism (Meyer-Reil 1987, Hoppe et al. 1988, Münster 1991). In the molecular sieve model (Burns 1978), such enzymes are intermediate agents in reaction pathways that connect the activities of polymer-degrading enzymes distributed throughout the environmental matrix and cell membrane permeases that transport substrates into the cell. In many cases, the enzymes that catalyze the terminal reactions in polymer degradation are localized on cell surfaces and periplasmic spaces.

Abstract. The carbon use efficiency (CUE) of microbial communities partitions the flow of C from primary producers to the atmosphere, decomposer food webs and soil C stores. CUE, usually defined as the ratio of growth to assimilation, is a critical parameter in ecosystem models, but is seldom measured directly in soils because of the methodological difficulty of measuring in situ rates of microbial growth and respiration. Alternatively, CUE can be estimated indirectly from the elemental stoichiometry of organic matter and microbial biomass, and the ratios of C to nutrient-acquiring ecoenzymatic activities. We used this approach to estimate and compare microbial CUE in >2000 soils from a broad range of ecosystems. Mean CUE based on C:N stoichiometry was 0.269 ± 0.110 (SD). A parallel calculation based on C:P stoichiometry yielded a mean CUE estimate of 0.252 ± 0.125 (SD). The mean values and frequency distributions were similar to those from aquatic ecosystems, also calculated from stoichiometric models, and to those calculated from direct measurements of bacterial and fungal growth and respiration. CUE was directly related to microbial biomass C with a scaling exponent of 0.304 ± 0.067 (95% CI) and inversely related to microbial biomass P with a scaling exponent of -0.234 ± 0.055 (95% CI). Relative to CUE, biomass specific turnover time increased with a scaling Accepted ArticleThis article is protected by copyright. All rights reserved. exponent of 0.509 ± 0.042. CUE increased weakly with mean annual temperature. CUE declined with increasing soil pH reaching a minimum at pH 7.0, then increased again as soil pH approached 9.0, a pattern consistent with pH trends in the ratio of fungal:bacteria abundance and growth. Structural equation models that related geographic variables to CUE component variables showed the strongest connections for paths linking latitude and pH to ß-glucosidase activity and soil C:N:P ratios. The integration of stoichiometric and metabolic models provides a quantitative description of the functional organization of soil microbial communities that can improve the representation of CUE in microbial process and ecosystem simulation models.

An experiment in >1000 river and riparian sites found spatial patterns and controls of carbon processing at the global scale.

Riparian ecosystems support mosaics of terrestrial and aquatic plant species that enhance regional biodiversity and provide important ecosystem services to humans. Species composition and the distribution of functional traits – traits that define species in terms of their ecological roles – within riparian plant communities are rapidly changing in response to various global change drivers. Here, we present a conceptual framework illustrating how changes in dependent wildlife communities and ecosystem processes can be predicted by examining shifts in riparian plant functional trait diversity and redundancy (overlap). Three widespread examples of altered riparian plant composition are: shifts in the dominance of deciduous and coniferous species; increases in drought‐tolerant species; and the increasing global distribution of plantation and crop species. Changes in the diversity and distribution of critical plant functional traits influence terrestrial and aquatic food webs, organic matter production and processing, nutrient cycling, water quality, and water availability. Effective conservation efforts and riparian ecosystems management require matching of plant functional trait diversity and redundancy with tolerance to environmental changes in all biomes.