Biology subjects

Schoeb, C.

Publications and source records attributed to Schoeb, C..

6 recordsLinked to original sources

bioRxiv2022

Assessing the accuracy of paired and random sampling for quantifying plant-plant interactions in natural communities

Interactions among plant species in extreme ecological systems are often inferred from spatial associations and quantified by means of paired sampling. Yet, this method might be confounded by habitat-sharing effects, in particular when microenvironmental heterogeneity and stress are high. Here, we address whether paired and random sampling methods provide similar results at varying levels of environmental heterogeneity. Furthermore, we investigate how the relationship between species preferences and abiotic severity influences the outcome of these two methods. We quantified spatial associations with the two methods at three sites that encompass different micro-environmental heterogeneity and stress levels: semi-arid environments in Canary Islands, Spain and Sardinia, Italy and a cold alpine environment in Hokkaido (Japan). Then, we simulated plant communities with different levels of species micro-habitat preferences, environmental heterogeneity and stress levels. We found that differences in species associations between paired and random sampling were indistinguishable from zero in our model simulations. At each site, there were strong differences between beneficiary species in their spatial association with benefactor species, and associations became more positive with increasing stress in Spain. Most importantly, there were no differences in the results yielded by the two methods at any of the different stress levels at the Spanish and Japanese sites. At the Italian site, although micro-environmental heterogeneity was low, we found weakly significant differences between methods that were unlikely due to habitat-sharing effects. We conclude that the paired sampling method can provide significant insights into net, long-term effects of plant interactions in spatially conspicuous environments.

ecology↗

bioRxiv2022

Rapid transgenerational adaptation in response to intercropping increases facilitation and reduces competition

By capitalising on positive biodiversity-productivity relationships, intercropping provides opportunities to improve agricultural sustainability1. However, intercropping is generally implemented using commercial seeds that were bred for maximal productivity in monocultures, which might limit the benefits of crop diversity on yield2,3. Plants can adapt over generations to the level of surrounding plant diversity, notably through increases in niche differentiation4. However, this adaptation potential and the corresponding yield benefit potential have not been explored in annual crop systems. Here we show that plant-plant interactions among annual crops evolved towards increased facilitation and reduced competition when the plants coexistence history matched their current diversity setting, which led to an increase in overyielding of up to 58%. These higher yield benefits were linked to character convergence between species sharing the same coexistence history for two generations. Notably, the six crop species tested converged towards taller phenotypes with lower leaf dry matter content when grown in mixtures. This study provides the first empirical evidence for the importance of parental diversity affecting plant-plant interactions and ecosystem functioning of the following generations in annual cropping systems. These results have important implications for diversified agriculture as they demonstrate the yield potential of targeted cultivars for intercropping, which can be achieved through specific breeding for mixtures.

ecology↗

bioRxiv2021

Using spatially-explicit plant competition models to optimise crop productivity in intercropped systems

Intercropping, by capitalizing on positive biodiversity-productivity relationships, represents a promising option to increase agricultural sustainability. However, the complexity and context-dependency of plant-plant interactions can make it challenging for farmers to find suitable crop combinations. Furthermore, intercropping is usually implemented with standard inter-row spacing and plant densities based on monoculture practices, which might not be the ideal configuration to maximise yield. Therefore, here we present a spatially-explicit method based on plant ecological interaction models that allowed to optimize crop species combinations and spatial configurations for maximal yield in intercropped systems. We tested this method with three crop species, namely oat, lupin, and camelina. In a first step, field experiments in which crop density was varied provided us with indications on which species would compete more with each other. The results showed us that oat and camelina strongly competed with each other. In addition, the distance experiments allowed us to understand how the changes in yield associated with the presence of neighbours vary with distance. This allowed us to find the sets of parameters (identity of neighbours, sowing density, distances between individuals) that optimises intercrop yield (measured as Land Equivalent Ratio [LER]) for the three considered species. Specifically, we show that alternating rows of species led to higher LERs than a homogeneous species mixing. In addition, for each spatial configuration considered, we provide indications for the optimal inter- and intra-row distances and information about relative yield losses with suboptimal planting patterns. By modelling crop yield from simple and reproducible density and distance experiments, our results allow to optimize crop mixtures in terms of species combinations and spatial configurations.

ecology↗

bioRxiv2021

Temporal differentiation of resource capture and biomass accumulation as a driver of yield increase in intercropping

- Intercropping, i.e. the simultaneous cultivation of different crops on the same field, has demonstrated yield advantages compared to monoculture cropping. These yield advantages have often been attributed to complementary resource use, but few studies quantified the temporal complementarity of nutrient acquisition and biomass production. Our understanding of how nutrient uptake rates of nitrogen (N) and phosphorous (P) and biomass accumulation change throughout the growing season and between different neighbors is limited. - We conducted weekly destructive harvests to measure temporal trajectories of N and P uptake and biomass production in three crop species (oat, lupin and camelina) growing either as isolated single plants, in monocultures or as intercrops. Additionally, we quantified organic acid exudation in the rhizosphere and biological N2-fixation of lupin throughout the growing season. Logistic models were fitted to characterize nutrient acquisition and biomass accumulation trajectories. - Nutrient uptake and biomass accumulation trajectories were curtailed by competitive interactions, resulting in earlier peak rates and lower total accumulated nutrients and biomass compared to cultivation as isolated single plants. Different pathways led to overyielding in the two mixtures. The oat-camelina mixture was characterized by a shift from belowground temporal niche partitioning of resource uptake to aboveground competition for light during the growing season. The oat-lupin mixture showed strong competitive interactions, where lupin eventually overyielded due to reliance on atmospheric N and stronger competitiveness for soil P. - Synthesis: This study demonstrates temporal shifts to earlier peak rates of plants growing with neighbors compared to those growing alone, suggesting that the observed temporal shifts in our experiment are driven by competitive interactions rather than active plant behavior to reduce competition. The two differing pathways to overyielding in the two mixtures highlight the importance of examining temporal dynamics in intercropping systems to understand the underlying mechanisms of overyielding.

ecology↗

bioRxiv2020

Positive effects of crop diversity on productivity driven by changes in soil microbial composition

Intensive agriculture has major negative impacts on ecosystem diversity and functioning, including that of soils. The associated reduction of soil biodiversity and essential soil functions, such as nutrient cycling, can restrict plant growth and crop yield. By increasing plant diversity in agricultural systems, intercropping could be a promising way to foster soil microbial diversity and functioning. However, plant-microbe interactions and the extent to which they influence crop yield under field conditions are still poorly understood. In this study, we performed an extensive intercropping experiment using eight crop species and 40 different crop mixtures to investigate how crop diversity affects soil microbial diversity and functions, and whether these changes subsequently affect crop yield. Experiments were carried out in mesocosms under natural conditions in Switzerland and in Spain, two countries with drastically different soils and climate, and our crop communities included either one, two or four species. We sampled and sequenced soil microbial DNA to assess soil microbial diversity, and measured soil basal respiration as a proxy for soil activity. Results indicate that in Switzerland, increasing crop diversity led to shifts in soil microbial community composition, and in particular to an increase of several plant-growth promoting microbes, such as members of the bacterial phylum Actinobacteria. These shifts in community composition subsequently led to a 15 and 35% increase in crop yield in 2 and 4-species mixtures, respectively. This suggests that the positive effects of crop diversity on crop productivity can partially be explained by changes in soil microbial composition. However, the effects of crop diversity on soil microbes were relatively small compared to the effects of abiotic factors such as fertilization (3 times larger) or soil moisture (3 times larger). Furthermore, these processes were context-dependent: in Spain, where soil resources were limited, soil microbial communities did not respond to crop diversity, and their effect on crop yield was less strong. This research highlights the potential beneficial role of soil microbial communities in intercropping systems, while also reflecting on the relative importance of crop diversity compared to abiotic drivers of microbiomes, thereby emphasizing the context-dependence of crop-microbe relationships.

ecology↗

bioRxiv2020

Weeds are not always evil: crop-weed relationships are context-dependent and cannot fully explain the positive effects of intercropping on yield

O_LIImplementing sustainable weed control strategies is a major challenge in agriculture. Intercropping offers a potential solution to control weed pressure by reducing the niche space available for weeds; however, available research on the relationship between crop diversity and weed pressure, and its consequences on crop yield is not fully conclusive yet. C_LIO_LIIn this study, we performed an extensive intercropping experiment using eight crop species and 40 different species mixtures to examine how crop diversity affects weed communities and how the subsequent changes in weeds influence crop yield. Field experiments were carried out in Switzerland and in Spain, which differ drastically in terms of climate and soil, and included monocultures, 2- and 4-species mixtures, and a control treatment without crops. Weed communities were assessed in terms of biomass, species richness and evenness, and community composition. C_LIO_LIResults indicate that intercropping per se does not reduce weed performance or diversity, but crop species composition does. In particular, the presence of cereals in crop mixtures significantly reduced weed biomass and diversity. C_LIO_LIDespite the lack of crop diversity effect on weeds, crop yield increased with crop species richness, particularly in Switzerland. Moreover, in Switzerland, where soil resources were abundant, increasing crop yield correlated with increased weed suppression and reduced weed diversity. In Spain, where water and nutrients were limited, crop yield was not related to weed biomass or diversity. C_LIO_LISynthesis and applications: We demonstrate that in our study, increased crop yield in mixtures was not due to increased weed suppression in diverse crop communities, but must be the result of other ecological processes. We also show that crop-weed relationships vary across environmental conditions, which emphasizes the need for a better understanding of weed communities assembly mechanisms, as well as locally adapted weed management strategies. C_LI

ecology↗