Nematode biomass changes along an elevational gradient are trophic group dependent but independent of body size

Aboveground, large and higher trophic-level organisms often respond more strongly to environmental changes than small and lower trophic-level organisms. However, whether this trophic or size-dependent sensitivity also applies to the most abundant animals, microscopic soil-borne nematodes, remains largely unknown. Here, we sampled an altitudinal transect across the Tibetan Plateau and applied a community-weighted mean (CWM) approach to test how differences in climatic and edaphic properties affect nematode CWM biomass at the level of community, trophic group and taxon mean biomass within trophic groups. We found that climatic and edaphic properties, particularly soil water-related properties, positively affected nematode CWM biomass, with no overall impact of altitude on nematode CWM biomass. Higher trophic-level omnivorous and predatory nematodes responded more strongly to climatic and edaphic properties, particularly to temperature, soil pH, and soil water content than lower trophic-level bacterivorous and fungivorous nematodes. However, these differences were likely not (only) driven by size, as we did not observe significant interactions between climatic and edaphic properties and mean biomasses within trophic groups. Together, our research implies a stronger, size-independent trophic sensitivity of higher trophic-level nematodes compared with lower trophic-level ones. Therefore, our findings provide new insights into the mechanisms underlying nematode body size structure in alpine grasslands and highlight that traits independent of size need to be found to explain increased sensitivity of higher trophic-level nematodes to climatic and edaphic properties, which might affect soil functioning.

Ellenberg Indicator Values Disclose Complex Environmental Filtering Processes in Plant Communities along an Elevational Gradient

Ellenberg indicator values (EIVs) express plant preferences for temperature, light, continentality, soil moisture, pH, and soil nutrients, and have been largely used to deduce environmental characteristics from plant communities. However, EIVs might also be used to investigate the importance of filtering mechanisms in shaping plant communities according to species ecological preferences, a so far overlooked use of EIVs. In this paper, we investigated how community-weighted means (CWM), calculated with EIVs, varied along an elevational gradient in a small mountain in Central Italy. We also tested if species abundances varied according to their ecological preferences. We found that the prevalence of thermophilous species declines with elevation, being progressively replaced by cold-adapted species. Heliophilous species prevail at low and high elevations (characterized by the presence of open habitats), whereas in the middle of the gradient (occupied by the beech forest), sciophilous species predominate. Variations for moisture and soil nutrient preferences followed a similar pattern, probably because of the high moisture and nutrient levels of forest soils with a lot of humus. No distinct pattern was detected for EIVs for pH and continentality since these factors are subject to more local variations. These results highlight the possible role of EIVs to investigate how environmental gradients shape plant communities.

Above- and Belowground Plant Functional Composition Show Similar Changes During Temperate Forest Swamp Succession

Plant functional composition, defined by both community-weighted mean (CWM) traits and functional diversity, can provide insights into plant ecological strategies and community assembly. However, our understanding of plant functional composition during succession is largely based on aboveground traits. Here we investigated community-level traits and functional diversity for six pairs of analogous leaf and fine root traits of understory plants in a temperate forest swamp during succession with a decrease in soil pH and nutrient availability. CWMs of traits related to resource acquisition (including specific leaf area, specific root length, leaf N, leaf P, root N, and root P) decreased with succession, whereas those related to resource conservation (leaf dry matter content, root dry matter content, leaf tissue density, leaf C, and root C) increased along the forest swamp successional gradient. Multi-trait functional dispersion (FDis) of both leaf and fine root traits tended to decrease along the successional gradient, but functional richness and evenness were highest at the middle successional stage. Moreover, FDis of individual plant traits except N showed the same pattern as multi-trait FDis. Soil pH and nutrient availability were the main drivers of successional changes in both CWM traits and FDis. The changes of community-level traits along succession indicated a shift from acquisitive to conservative strategy of understory plants during forest swamp succession. Similar trends in leaf and fine root functional diversity along succession may indicate above- and belowground functional diversity are coordinated during the processes of plant community assembly. These findings of linkages between above- and belowground plant functional composition have important implications for plant community dynamics and assembly rules.

Plant and soil biodiversity have non-substitutable stabilising effects on biomass production

The stability of plant biomass production in the face of environmental change is fundamental for maintaining terrestrial ecosystem functioning, as plant biomass is the ultimate source of energy for nearly all life forms. However, most studies have focused on the stabilising effect of plant diversity, neglecting the effect of soil biodiversity, the largest reservoir of biodiversity on Earth. Here we investigated the effects of plant and soil biodiversity on the temporal stability of biomass production under varying simulated precipitation in grassland microcosms. Soil biodiversity loss reduced temporal stability by suppressing asynchronous responses of plant functional groups. Greater plant diversity, especially in terms of functional diversity, promoted temporal stability, but this effect was independent of soil biodiversity loss. Moreover, multitrophic biodiversity, plant and soil biodiversity combined, was positively associated with temporal stability. Our study highlights the importance of maintaining both plant and soil biodiversity for sustainable biomass production.

The Role of Inter- and Intraspecific Variations in Grassland Plant Functional Traits along an Elevational Gradient in a Mediterranean Mountain Area

Elevational gradients offer special opportunities to investigate the relative role of intraspecific and interspecific trait variations in relation to stress gradients. We used an altitudinal gradient in the Mediterranean (Mt Velino, Central Italy) to study (1) how community-weighted means (CWM) and nonweighted means (CM) vary with elevation for plant height, specific leaf area, and seed mass; and (2) how variation patterns differ for inter- and intraspecific functional variability. We tested (1) if elevation influences community functional composition on the basis of the adaptive value of plant traits and (2) if the latter shows intraspecific variations according to the species' ability to cope with local conditions. We found that different traits showed different patterns, which can be linked to the function they express. Differences between communities were influenced more by differences between their traits (CM) than by the relative species coverage (CWM). Both highest and lowest elevations were the most selective due to their particularly severe climatic conditions. Intermediate elevations were the most favorable thanks to less constraining climatic conditions. Interspecific trait variability was the most relevant component, indicating a low plant ability to cope with environmental variations through phenotypic plasticity.

Direct and indirect facilitation affect community productivity through changes in functional diversity in an alpine system

BACKGROUND AND AIMS

Facilitation is an important ecological process for plant community structure and functional composition. Although direct facilitation has accrued most of the evidence so far, indirect facilitation is ubiquitous in nature and it has an enormous potential to explain community structuring. In this study, we assess the effect of direct and indirect facilitation on community productivity via taxonomic and functional diversity.

METHODS

In an alpine community on the Tibetan Plateau, we manipulated the presence of the shrub Dasiphora fruticosa and graminoids in a fenced meadow and a grazed meadow to quantify the effects of direct and indirect facilitation. We measured four plant traits: height, lateral spread, specific leaf area (SLA) and leaf dry matter content (LDMC) of forbs; calculated two metrics of functional diversity [range of trait and community-weighted mean (CWM) of trait]; and assessed the responses of functional diversity to shrub facilitation. We used structural equation modelling to explore how shrubs directly and indirectly drove community productivity via taxonomic diversity and functional diversity.

KEY RESULTS

We found stronger effects from herbivore-mediated indirect facilitation than direct facilitation on productivity and taxonomic diversity, regardless of the presence of graminoids. For functional diversity, the range and CWM of height and SLA, rather than lateral spread and LDMC, generally increased due to direct and indirect facilitation. Moreover, we found that the range of traits played a primary role over taxonomic diversity and CWM of traits in terms of shrub effects on community productivity.

CONCLUSIONS

Our study reveals that the mechanism of shrub direct and indirect facilitation of community productivity in this alpine community is expanding the realized niche (i.e. expanding range of traits). Our findings indicate that facilitators might increase trait dispersion in the local community, which could alleviate the effect of environmental filters on trait values in harsh environments, thereby contributing to ecosystem functioning.

Functional and environmental determinants of bark thickness in fire-free temperate rain forest communities

PREMISE OF THE STUDY

In fire-prone ecosystems, variation in bark thickness among species and communities has been explained by fire frequency; thick bark is necessary to protect cambium from lethal temperatures. Elsewhere this investment is deemed unnecessary, and thin bark is thought to prevail. However, in rain forest ecosystems where fire is rare, bark thickness varies widely among species and communities, and the causes of this variation remain enigmatic. We tested for functional explanations of bark thickness variation in temperate rain forest species and communities.

METHODS

We measured bark thickness in 82 tree species throughout New Zealand temperate rain forests that historically have experienced little fire and applied two complementary analyses. First, we examined correlations between bark traits and leaf habit, and leaf and stem traits. Second, we calculated community-weighted mean (CWM) bark thickness for 272 plots distributed throughout New Zealand to identify the environments in which thicker-barked communities occur.

KEY RESULTS

Conifers had higher size-independent bark thickness than evergreen angiosperms. Species with thicker bark or higher bark allocation coefficients were not associated with "slow economic" plant traits. Across 272 forest plots, communities with thicker bark occurred on infertile soils, and communities with thicker bark and higher bark allocation coefficients occurred in cooler, drier climates.

CONCLUSIONS

In non-fire-prone temperate rain forest ecosystems, investment in bark is driven by soil resources, cool minimum temperatures, and seasonal moisture stress. The role of these factors in fire-prone ecosystems warrants testing.