Exploitation of neighbouring subsoil for nutrient acquisition under annual-perennial strip intercropping systems

Little is known of how the deep root systems of perennial crops contribute to deeper and better resource use when intercropped with annuals in arable fields. Therefore, we aimed at measuring the capacity of perennial deep roots, alfalfa (Medicago sativa L.) and curly dock (Rumex crispus L.) to access the nutrient source located under the neighboring annuals at 1.0 and 2.5 m of soil depth. Alfalfa and curly dock were able to access the tracer-labelled source placed at a distance under the annual crop strips. As a result, the reliance on deeper soil layer for nutrient uptake under intercroppings became greater compared with sole-croppings. Combination of an annual cereal (winter rye) and a perennial legume (alfalfa) with contrasting root systems exhibited higher resource complementarity compared with intercroppings having similar root systems or absence of legumes. Our results demonstrated that the deep-rooted perennials when intercropped with annuals can induce vertical niche complementarity, especially at deeper soil layers. This was assumed to be due to the vertically stratified root activity between the crop components, however, the magnitude of the effects depended on choice of crop combinations, and on types of tracers. Future studies should include estimates such as relative yield total and land equivalent ratio to quantitatively determine the effects of resource acquisition under annual-perennial intercropping in arable fields.

Diverse phylogenetic neighborhoods enhance community resistance to drought in experimental assemblages

Although the role played by phylogeny in the assembly of plant communities remains as a priority to complete the theory of species coexistence, experimental evidence is lacking. It is still unclear to what extent phylogenetic diversity is a driver or a consequence of species assembly processes. We experimentally explored how phylogenetic diversity can drive the community level responses to drought conditions in annual plant communities. We manipulated the initial phylogenetic diversity of the assemblages and the water availability in a common garden experiment with two irrigation treatments: average natural rainfall and drought, formed with annual plant species of gypsum ecosystems of Central Spain. We recorded plant survival and the numbers of flowering and fruiting plants per species in each assemblage. GLMMs were performed for the proportion of surviving, flowering, fruiting plants per species and for total proportion of surviving species and plants per pot. In water limited conditions, high phylogenetic diversity favored species coexistence over time with higher plant survival and more flowering and fruiting plants per species and more species and plants surviving per pot. Our results agree with the existence of niche complementarity and the convergence of water economy strategies as major mechanisms for promoting species coexistence in plant assemblages in semiarid Mediterranean habitats. Our findings point to high phylogenetic diversity among neighboring plants as a plausible feature underpinning the coexistence of species, because the success of each species in terms of surviving and producing offspring in drought conditions was greater when the initial phylogenetic diversity was higher. Our study is a step forward to understand how phylogenetic relatedness is connected to the mechanisms determining the maintenance of biodiversity.

Positive Effects of Legumes on Soil Organic Carbon Stocks Disappear at High Legume Proportions Across Natural Grasslands in the Pyrenees

Soil is the largest terrestrial carbon pool, making it crucial for climate change mitigation. Soil organic carbon (SOC) is suggested to depend on biodiversity components, but much evidence comes from diversity-function experiments. To disentangle the relationships of plant guild diversity with SOC storage (kg m−2) at broad spatial scales, we applied diversity-interaction models to a regional grassland database (n = 96) including wide environmental conditions and management regimes. The questions were: (1) Are the effects of plant guilds on SOC stocks in natural grasslands consistent with those found in experimental systems? (2) Are plant guild effects on SOC stocks independent of each other or do they show interactive—synergistic or antagonistic—effects? (3) Do environmental variables, including abiotic and management, modify guild effects on SOC stocks? Among our most novel results we found, legume effects on grassland SOC vary depending on legume proportion consistently across broad spatial scales. SOC increased with legume proportion up to 7–17%, then decreased. Additionally, these effects were strengthened when grasses and forbs were codominant. Grazing intensity modulated grass proportion effects on SOC, being maximum at relatively high intensities. Interpreting our results in terms of existing contrasted ecological theories, we confirmed at broad spatial scales and under wide-ranging environmental conditions the positive effects of plant guild diversity on SOC, and we showed how legumes exert a keystone effect on SOC in natural grasslands, probably related to their ability to fix inorganic N. Niche complementarity effects were illustrated when codominance of forbs and grasses at optimum legume proportions boosted SOC storage, whereas grass dominance increased SOC stocks at medium–high grazing intensities. These findings can facilitate the preparation of regional and local strategies to ameliorate the soil capacity to absorb carbon.

The Driving Factors of Subtropical Mature Forest Productivity: Stand Structure Matters

Forest productivity (increment of above-ground biomass) is determined by biodiversity but also by stand structure attributes. However, the relative strengths of these drivers in determining productivity remain controversial in subtropical forests. In this study, we analyzed a tree growth data from 500 plots with in a 20 ha mature subtropical forest in eastern China. We used spatial simultaneous autoregressive error models to examine the effects of diversity variables (species richness, evenness, and composition), stand structural attributes (stand density, tree size range and diversity), environmental factors (topography and soil), and initial above-ground biomass (AGB) on productivity. We also applied structural equation models to quantify the relative importance of diversity, stand structure, environmental factors, and initial AGB in determining forest productivity. Our results showed that stand structure together with diversity and initial AGB governed forest productivity. Tree size diversity (DBH Shannon’s diversity index) had the largest positive effect on forest productivity. These results provide new evidence that structural explanatory variables have greater contributions to productivity for mature subtropical forests, strongly supporting the niche complementarity hypothesis. Our work highlights the importance of tree size diversity in promoting high forest productivity, and suggests that regulating and conserving complexity of forest stand structure should be among the most important goals in subtropical forest management.

Illuminating key microbial players and metabolic processes involved in the remineralization of particulate organic carbon in the ocean’s twilight zone by metaproteomics

The twilight zone (from the base of the euphotic zone to the depth of 1000 m) is the major area of particulate organic carbon (POC) remineralization in the ocean, and heterotrophic microbes contribute to more than 70% of the estimated remineralization. However, little is known about the microbial community and metabolic activity directly associated with POC remineralization in this chronically understudied realm. Here, we characterized the microbial community proteomes of POCs collected from the twilight zone of three contrasting sites in the Northwest Pacific Ocean using a metaproteomic approach. The particle-attached bacteria from Alteromonadales, Rhodobacterales, and Enterobacteriales were the primary POC remineralizers. Hydrolytic enzymes, including proteases and hydrolases, that degrade proteinaceous components and polysaccharides, the main constituents of POC, were abundant and taxonomically associated with these bacterial groups. Furthermore, identification of diverse species-specific transporters and metabolic enzymes implied niche specialization for nutrient acquisition among these bacterial groups. Temperature was the main environmental factor driven the active bacterial groups and metabolic processes, and Enterobacteriales replaced Alteromonadales as the predominant group under low temperature. This study provides insight into the key bacteria and metabolic processes involved in POC remineralization, and niche complementarity and species substitution among bacterial groups are critical for efficient POC remineralization in the twilight zone. IMPORTANCE The Ocean’s twilight zone is a critical zone where more than 70% of the sinking particulate organic carbon (POC) are remineralized. Therefore, the twilight zone determines the size of biological carbon storage in the ocean, and regulates the global climate. Prokaryotes are major players that govern remineralization of POC in this region. However, knowledge of microbial community structure and metabolic activity is still lacking. This study unveiled microbial communities and metabolic activities of POCs collected from the twilight zone of three contrasting environments in the Northwest Pacific Ocean using a metaproteomic approach. Alteromonadales, Rhodobacterales and Enterobacteriales were the major remineralizers of POC. They excreted diverse species-specific hydrolytic enzymes to split POC to solubilized POC or dissolved organic carbon. Temperature played a crucial role in regulating the community composition and metabolism. Furthermore, niche complementarity or species substitution among bacterial groups guaranteed the efficient remineralization of POC in the twilight zone.

Testing hypotheses of habitat use and temporal activity in relation to body plan in a Mediterranean lizard community

A body plan (= bauplan) is a suite of morphological characters shared by phylogenetically related animals at some point during their development. Despite its value, the bauplan concept is still rarely employed to characterize functional groups in community ecology. Here, we examine habitat use and spatio-temporal activity correlates of an entire seven-species community of lizards with different bauplans. The study was carried out in three locations in central Italy, encompassing a complex landscape with a patchy mosaic of a wide variety of habitats and microclimates. We tested four hypotheses regarding niche breadth, habitat use and activity patterns. The first hypothesis, niche complementarity, in which species with similar body shapes should non-randomly partition available habitats, was not supported. By contrast, the hypotheses that larger-bodied species should have a wider niche breadth, that slower species should inhabit habitat types of higher cover, and species inhabiting open sunny habitats should exhibit more seasonally variable activity patterns, were all supported by the data. Sympatric lizard communities in our study area were clearly organized by autecological constraints and eco-physiological attributes.

Multiple Drivers of Biomass Change in Subtropical Natural Forests

Forest ecosystems play an important role in regulating the global carbon, a substantial portion of terrestrial carbon pool which is stored in biomass stocks. However, how multiple biotic (i.e. topography) and abiotic (biodiversity, stand structure, and functional traits) influence forest biomass in natural forests, the relative important of these factors determine biomass is still controversial for subtropical natural forests. We used forest inventory data from nine 1-ha plots at different altitude gradients in China’s subtropical forests. We used multiple analyse to quantify the relative importance of multiple facets of diversity, key functional traits, stand structural attributes, and topography variables in determining forest biomass. We found that multiple facets of diversity and stand structure variables enhances biomass. Specifically, large-diameter trees had a strong positive effect on biomass and were the most important factor in determining biomass. Plant functional traits were closely related to biomass. Community-weighted mean value (CWM) of maximum height positively correlated with biomass, but CWM of wood density negatively correlated biomass. Topographic factors including elevation and slope, had a positive effect on biomass. Moreover, among the aforementioned four types of variables, stand structure had the greatest impact on biomass and is linked to diversity-biomass relationship. Topography mainly indirectly affected biomass by altering multiple diversity and stand structure. Functional traits also directly and indirectly affected biomass. Overall, these results support niche complementarity effect and mass-ratio hypothesis. Our results indicate that biodiversity is essential for maintaining ecosystem functions of species-rich subtropical natural forests. Further, adjusting stand structure may be an effective forest management approach to increase forest carbon storage.

Tree species diversity predicts aboveground carbon storage through functional diversity and functional dominance in the dry evergreen Afromontane forest of Hararghe highland, Southeast Ethiopia

Background Regarding the most important ecological challenges, scientists are increasingly debating the relationship between biodiversity and ecosystem function. Despite this, several experimental and theoretical researches have shown inconsistencies in biodiversity and ecosystem function relationships, supporting either the niche complementarity or selection effect hypothesis. The relationship between species diversity, functional diversity, and aboveground biomass carbon was investigated in this study employing standing aboveground carbon (AGC) stock as a proxy measure for ecosystem function. We hypothesized that (i) effects of diversity on AGC can be transmitted through functional diversity and functional dominance; (ii) effects of diversity on AGC would be greater for functional dominance than functional diversity; and (iii) effects of functional diversity and functional dominance on carbon stock varied with metrics and functional traits. Community-weighted means (CWM) of functional traits (wood density, specific leaf area, and maximum plant height) were calculated to assess functional dominance (selection effects). As for functional diversity (complementarity effects), multi-trait functional diversity (selection effects) indices were computed. We tested the first hypothesis using structural equation modeling. For the second hypothesis, the effects of environmental variables such as slope, aspect, and elevation were tested first, and separate linear mixed-effects models were fitted afterward for functional diversity, functional dominance, and the two together. Results Results revealed that slope had a significant effect on aboveground carbon storage. Functional diversity and functional dominance were significant predictors of the aboveground carbon storage (22.4%) in the dry evergreen Afromontane forest. The effects of species richness on aboveground carbon storage were mediated by functional diversity and functional dominance of species. This shows that both the selection effects and the niche complementarity are important for aboveground carbon storage prediction. However, the functional diversity effects (niche complementarity) were greater than functional dominance effects (selection effects). Conclusions Linking diversity and biodiversity components to aboveground carbon provides better insights into the mechanisms that explain variation in aboveground carbon storage in natural forests, which may help improve the prediction of ecosystem functions.

Rhizosphere Bacterial Networks, but Not Diversity, Are Impacted by Pea-Wheat Intercropping

Plant-plant associations, notably cereal-legume intercropping, have been proposed in agroecology to better value resources and thus reduce the use of chemical inputs in agriculture. Wheat-pea intercropping allows to decreasing the use of nitrogen fertilization through ecological processes such as niche complementarity and facilitation. Rhizosphere microbial communities may account for these processes, since they play a major role in biogeochemical cycles and impact plant nutrition. Still, knowledge on the effect of intecropping on the rhizosphere microbiota remains scarce. Especially, it is an open question whether rhizosphere microbial communities in cereal-legume intercropping are the sum or not of the microbiota of each plant species cultivated in sole cropping. In the present study, we assessed the impact of wheat and pea in IC on the diversity and structure of their respective rhizosphere microbiota. For this purpose, several cultivars of wheat and pea were cultivated in sole and intercropping. Roots of wheat and pea were collected separately in intercropping for microbiota analyses to allow deciphering the effect of IC on the bacterial community of each plant species/cultivar tested. Our data confirmed the well-known specificity of the rhizosphere effect and further stress the differentiation of bacterial communities between pea genotypes (Hr and hr). As regards the intercropping effect, diversity and structure of the rhizosphere microbiota were comparable to sole cropping. However, a specific co-occurrence pattern in each crop rhizosphere due to intercropping was revealed through network analysis. Bacterial co-occurrence network of wheat rhizosphere in IC was dominated by OTUs belonging to Alphaproteobacteria, Bacteroidetes and Gammaproteobacteria. We also evidenced a common network found in both rhizosphere under IC, indicating the interaction between the plant species; this common network was dominated by Acidobacteria, Alphaproteobacteria, and Bacteroidetes, with three OTUs belonging to Acidobacteria, Betaproteobacteria and Chloroflexi that were identified as keystone taxa. These findings indicate more complex rhizosphere bacterial networks in intercropping. Possible implications of these conclusions are discussed in relation with the functioning of rhizosphere microbiota in intercropping accounting for its beneficial effects.