Results of regression analysis between dissimilarities in decomposition activity, lipid profile and substrate quality.

<p>Values within parentheses indicate the 95% confidence intervals estimated by 999 bootstraps. The “ecodist” package of R was used to conduct these analyses. ^†Corresponding to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0080320#pone-0080320-g002" target="_blank">Fig. 2a</a>. ^††Corresponding to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0080320#pone-0080320-g002" target="_blank">Fig. 2b</a>.</p

A Coexisting Fungal-Bacterial Community Stabilizes Soil Decomposition Activity in a Microcosm Experiment

<div><p>How diversity influences the stability of a community function is a major question in ecology. However, only limited empirical investigations of the diversity–stability relationship in soil microbial communities have been undertaken, despite the fundamental role of microbial communities in driving carbon and nutrient cycling in terrestrial ecosystems. In this study, we conducted a microcosm experiment to investigate the relationship between microbial diversity and stability of soil decomposition activities against changes in decomposition substrate quality by manipulating microbial community using selective biocides. We found that soil respiration rates and degradation enzyme activities by a coexisting fungal and bacterial community (a taxonomically diverse community) are more stable against changes in substrate quality (plant leaf materials) than those of a fungi-dominated or a bacteria-dominated community (less diverse community). Flexible changes in the microbial community composition and/or physiological state in the coexisting community against changes in substrate quality, as inferred by the soil lipid profile, may be the mechanism underlying this positive diversity–stability relationship. Our experiment demonstrated that the previously found positive diversity–stability relationship could also be valid in the soil microbial community. Our results also imply that the functional/taxonomic diversity and community ecology of soil microbes should be incorporated into the context of climate–ecosystem feedbacks. Changes in substrate quality, which could be induced by climate change, have impacts on decomposition process and carbon dioxide emission from soils, but such impacts may be attenuated by the functional diversity of soil microbial communities.</p></div

The effects of substrate quality on microbial decomposition tested using separate additive models.

*<p>, **, and ***, indicate significance at <i>P</i><0.05, 0.01, and 0.001, respectively. The statistical formula for this analysis was (decomposition activity)  = s (substrate quality) + residuals. The smoothing function was applied for the term enclosed by s() <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0080320#pone.0080320-Wood1" target="_blank">[35]</a>.</p

Effects of substrate quality and microbial groups on soil decomposition activities.

<p>Each value indicates the proportion of explained variation by each factor, calculated using redundancy analysis (RDA) and a permutation test (999 permutations). All 5 decomposition activities were used as explained variables. Note that the sum of the biomarkers that indicate the same microbial group, and not individual biomarker lipids, was used here to reduce the number of explanatory variables in the RDA. Indicative biomarker lipids are specified in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0080320#s2" target="_blank">Materials and Methods</a>. All variables were scaled before the RDA. *, **, and *** indicate significant effects at <i>P</i><0.05, 0.01, and 0.001, respectively, by the permutation test.</p

Adaptiveness of dispersal.

<p>Adaptiveness was calculated as the difference between the invader fitness of each dispersing population of the inferior and that of their sedentary counterpart. Boundaries of positive and negative values are marked by lines. Note that the color scales are different for different dispersal modes. Parameters are (<i>k</i>₁, <i>k</i>₂) = (0.6, 0.3) for Environment 1 in (A, D, G), (0.8, 0.4) for Environment 2 in (B, E, H), and (1.4, 0.7) for Environment 3 in (C, F, I).</p

Effects of substrate quality on the soil respiration rate (SRR; a) and activities of acid phosphatase (APA; b), <i>N</i>-acetylglucosaminidase (NAG; c), β-d-glucosidase (GLD; d), and cellobiohydrolase (CLB; e).

<p>Each point indicates the mean value of 4 replicates in each treatment. The smoothing lines were drawn using the “mgcv” package of R <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0080320#pone.0080320-Wood1" target="_blank">[35]</a>. Bars indicate 95% confidence interval. Black circles, red squares, and light-blue diamonds indicate the coexisting, bacterial, and fungal communities, respectively.</p

The relationships between substrate-quality dissimilarity and dissimilarity of decomposition activity (a) and microbial community composition (b).

<p>Substrate-quality dissimilarity is calculated as the difference between 2 substrates, whereas activity and community dissimilarity are calculated as the Euclidean distance between data matrices of activity and community composition, respectively. Black, red, and light-blue filled circles indicate the mean values of the coexisting, bacterial, and fungal communities, respectively. Grey circles indicate individual values. Black, red and light-blue solid lines indicate regression lines of the coexisting, bacterial, and fungal communities, respectively. Note that the points are slightly adjusted in the x-axis direction to distinguish the values of different microbial groups. Statistical results are shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0080320#pone-0080320-t003" target="_blank">Table 3</a>. Bars indicate standard errors of the mean.</p

Summarizing the conditions and mechanisms of the two coexistence mechanisms.

<p>Summarizing the conditions and mechanisms of the two coexistence mechanisms.</p

Competition outcomes between two consumer species, depending on moving capacity.

<p>In each panel, the species compositions are denoted as follows: S: superior species dominance, Co: coexistence, and I: inferior species dominance. Stable steady states are indicated by (*), and unstable, periodic, or fluctuation outcomes are indicated by (^∧). Parameters are (<i>k</i>₁, <i>k</i>₂) = (0.6, 0.3) for Environment 1 in (A, D, G), (0.8, 0.4) for Environment 2 in (B, E, H), and (1.4, 0.7) for Environment 3 in (C, F, I).</p

Difference Inadaptive Dispersal Ability Can Promote Species Coexistence in Fluctuating Environments

<div><p>Theories and empirical evidence suggest that random dispersal of organisms promotes species coexistence in spatially structured environments. However, directed dispersal, where movement is adjusted with fitness-related cues, is less explored in studies of dispersal-mediated coexistence. Here, we present a metacommunity model of two consumers exhibiting directed dispersal and competing for a single resource. Our results indicated that directed dispersal promotes coexistence through two distinct mechanisms, depending on the adaptiveness of dispersal. Maladaptive directed dispersal may promote coexistence similar to random dispersal. More importantly, directed dispersal is adaptive when dispersers track patches of increased resources in fluctuating environments. Coexistence is promoted under increased adaptive dispersal ability of the inferior competitor relative to the superior competitor. This newly described dispersal-mediated coexistence mechanism is likely favored by natural selection under the trade-off between competitive and adaptive dispersal abilities.</p> </div