Publications from IMPAC3

Juliane Streit, Catharina Meinen & Rolf Rauber (2019): Intercropping effects on root distribution of eight novel winter faba bean genotypes mixed with winter wheat. Field Crops Res. 235, 1-10.

The spatial root distribution of plant species is generally altered by intra- and interspecific competition. The assessment of species specific root distribution in intercrops was limited so far because of the difficulties to identify roots on a species level. We investigated horizontal and vertical root distribution of eight winter faba bean genotypes (Vicia faba L.) and one winter wheat cultivar (Triticum aestivum L.) grown in sole stands and in 50/50 substitutive row intercrops.
Root samples were taken within and between rows with a root auger down to 60 cm soil depth in May 2015 and May 2016 at a field site in central Germany. We used Fourier transform infrared (FTIR) spectroscopy for root species identification. Vertical root distribution was described by the equation y=1 - βd according to Gale and Grigal (1987).
Horizontal root distribution did not differ between bean and wheat and between sole stands and intercrops averaged across the eight bean genotypes: Bean and wheat root biomass was on average 65% lower between rows than within rows in sole stands and in intercrops. Both species proliferated into the soil space between the rows and into the intercropping partner’s row to a similar extent. Bean developed 36% of its root biomass in 0–10 cm soil depth, while wheat had 51%. Bean and wheat had shallower roots within their own row in intercrops (βbean=0.933; βwheat=0.858) compared to their own row in sole stands (βbean=0.945; βwheat=0.902). In the intercrops both species occupied deeper soil layers within their partner’s row (βbean=0.947; βwheat=0.960) compared to their own row (βbean=0.933; βwheat=0.858). This change in vertical root distribution was more pronounced for wheat than for bean. Bean genotypes grown in sole stands did not differ in their horizontal and vertical root distribution. However, there were significant differences between bean genotypes within wheat rows in the intercrops: bean genotype Vf6 had the largest horizontal spread but the most shallow root growth within the wheat row, while Vf5 showed the lowest horizontal spread and the highest root fractions in deep soil layers within the wheat row. The alteration of the vertical root distribution of both species in intercrops, compared to the sole crops, could lead to a better resource utilization and an intercrop advantage.

Juliane Streit, Catharina Meinen, William Nelson, Daniel Siebrecht-Schöll, Rolf Rauber (2019): Above- and belowground biomass in a mixed cropping system with eight novel winter faba bean genotypes and winter wheat using FTIR spectroscopy for root species discrimination. Plant Soil,

Legume-cereal mixtures are often characterized by higher biomass and grain yields compared to their sole crop equivalents due to complementary resource use. Little is known about the contribution of the root system to this overyielding potential and the related cultivar differences. This study investigated pure stands and mixtures of eight winter faba bean (Vicia faba L.) genotypes and one winter wheat cultivar (Triticum aestivum L., cv. Genius) with regard to their intra- and interspecific variation of shoot and root biomass and overyielding potential at full flowering of the bean. Shoot biomass of 1 m2 was harvested and roots were sampled with a root auger down to 0.6 m soil depth in two sampling years. Fourier transform infrared (FTIR) spectroscopy was successfully used to determine species specific root biomasses in mixtures. Statistics were performed using linear mixed effects models. Mixtures of winter faba bean and winter wheat overyielded more below- than aboveground. Bean genotypes grown in mixtures with wheat differed significantly in their root biomass, root:shoot ratio and overyielding potential but not in their shoot biomass. Genotype differences in root biomass and overyielding indicate breeding potential of winter faba bean cultivars for mixed cropping.

Corsa Lok Ching Liu, Oleksandra Kuchma, Konstantin V. Krutovsky (2018): Mixed-species versus monocultures in plantation forestry: Development, benefits, ecosystem services and perspectives for the future. Global Ecology and Conservation 15 (2018) e00419

Plantation forests are increasing rapidly in the world in order to alleviate deforestation and degradation of natural forests, along with providing various goods and services. While monoculture plantations have been the dominant type of plantation in practice and wellrecorded in research, in the face of intensifying climate change and resource scarcity, there is a growing interest in mixed-species plantations. Agroforestry systems are also catching the attention of foresters, smallholders and landowners. However, there are relatively limited number of studies on successful species mixtures. This paper first reviews the progression of monocultures and mixed-species, followed by the comparisons of advantages, disadvantages and effects on the surrounding natural ecosystems between these two types of plantations. The paper further investigates combinations of species with complementary traits for efficient use of limiting resources associated with improvement in growth development and production of tree species, as well as examining some other challenges in mixed-species. In addition, it is helpful to select and combine tree/crop species in mixtures based on complementary traits that maximise positive and minimise negative interactions and using the advance molecular technologies for genetic analysis. With careful design and proper management, mixed-species plantations with two, three or four species can be more productive and have more advantages in biodiversity, economy and forest health over monocultures. Many researchers are still working on different projects to explore the potential benefits and to promote the applications of mixed-species plantations and agroforestry.

Sandra Granzow, Kristin Kaiser, Bernd Wemheuer, Birgit Pfeiffer, Rolf Daniel, Stefan Vidal and Franziska Wemheuer (2017): The Effects of Cropping Regimes on Fungal and Bacterial Communities of Wheat and Faba Bean in a Greenhouse Pot Experiment Differ between Plant Species and Compartment. Front. Microbiol. 8:902. doi: 10.3389/fmicb.2017.00902

Many bacteria and fungi in the plant rhizosphere and endosphere are beneficial to plant nutrient acquisition, health, and growth. Although playing essential roles in ecosystem functioning, our knowledge about the effects of multiple cropping regimes on the plant microbiome and their interactions is still limited. Here, we designed a pot experiment simulating different cropping regimes. For this purpose, wheat and faba bean plants were grown under controlled greenhouse conditions in monocultures and in two intercropping regimes: row and mixed intercropping. Bacterial and fungal communities in bulk and rhizosphere soils as well as in the roots and aerial plant parts were analyzed using large-scale metabarcoding. We detected differences in microbial richness and diversity between the cropping regimes. Generally, observed effects were attributed to differences between mixed and row intercropping or mixed intercropping and monoculture. Bacterial and fungal diversity were significantly higher in bulk soil samples of wheat and faba bean grown in mixed compared to row intercropping. Moreover, microbial communities varied between crop species and plant compartments resulting in different responses of these communities toward cropping regimes. Leaf endophytes were not affected by cropping regime but bacterial and fungal community structures in bulk and rhizosphere soil as well as fungal community structures in roots. We further recorded highly complex changes in microbial interactions. The number of negative inter-domain correlations between fungi and bacteria decreased in bulk and rhizosphere soil in intercropping regimes compared to monocultures due to beneficial effects. In addition, we observed plant species-dependent differences indicating that intra- and interspecific competition between plants had different effects on the plant species and thus on their associated microbial communities. To our knowledge, this is the first study investigating microbial communities in different plant compartments with respect to multiple cropping regimes Granzow et al. Cropping Regimes and Microbial Communities using large-scale metabarcoding. Although a simple design simulating different cropping regimes was used, obtained results contribute to the understanding how cropping regimes affect bacterial and fungal communities and their interactions in different plant compartments. Nonetheless, we need field experiments to properly quantify observed effects in natural ecosystems.

Dominic Lemken, Mandy Knigge, Stephan Meyerding and Achim Spiller (2017): The Value of Environmental and Health Claims on New Legume Products: A Non-Hypothetical Online Auction. Sustainability 2017, 9, 1340; doi:10.3390/su9081340

Legumes are valued in agricultural systems, as they can contribute to a more sustainable land use. However, their economic value is low. Despite health and environmental benefits, marketers struggle to communicate the worth of legumes to consumers. We evaluate the worth of health and, in particular, environmental claims that would spread consumers’ awareness of ecological advantages.Utilizing a large consumer sample, we execute binding online auctions. Comparing claim-treated and untreated subjects (between design), we model the price premium that potential customers are willing to pay (WTP) for having pasta in a legume instead of a wheat version. We find that claims may increase the WTP, however, a mix of environmental and health claims is superior to individual claims. Effect sizes suggest that the mix of claims increases the WTP by roughly 35% (20 cents). The link of WTP and food attitudes, such as concern for health in eating habits or social reservations towards legumes, varies depending on whether the green-pea or chickpea pasta was evaluated. A critical perception of legumes’ association with flatulence reduces the WTP. Developing the online auction may enable researchers to increase the external validity of consumer samples. We discuss implications for researchers and marketers.

Dominic Lemken, Achim Spiller, Marie von Meyer-Höfer (2017): The Case of Legume-Cereal Crop Mixtures in Modern Agriculture and the Transtheoretical Model of Gradual Adoption. Ecological Economics 137 (2017) 20–28

Mixed cropping (MC), the growing of two or more coexisting crops in one field, specifically the mix of cereal and grain legumes, can contribute to a more sustainable agricultural land use. Despite a variety of ecological benefits and promising grain productivity, applications are scarce among farmers in developed countries. In consideration of MC's potential this study interviews farm managers to profile characteristics of adopters. The transtheoretical model (TTM) is applied to capture adoption and adoption tendencies. The results point to a significant positive role of land owned vs. leased, adoption of reduced tillage and adoption intensity of legumes in general. The perception of technical barriers and the perception of MC's usefulness are also major drivers that proponents need to address. In general, the TTM provides a gradual measure of farmer's willingness to adopt, leading to more variance than binary classifications,which makes TTM especially useful to adoption research of marginalized ecological practices.

Mehmet Senbayram, Christian Wenthe, Annika Lingner, Johannes Isselstein, Horst Steinmann,
Cengiz Kaya and Sarah Köbke (2016): Legume-based mixed intercropping systems may lower agricultural born N2O emissions. Energy, Sustainability and Society (2016) 6:2 DOI 10.1186/s13705-015-0067-3

Background: The area used for bioenergy crops (annual row crops (e.g., wheat, maize), herbaceous perennial grasses, and short-rotation woody crops (e.g., poplar)) is increasing because the substitution of fossil fuels by bioenergy is promoted as an option to reduce greenhouse gas (GHG) emissions. However, biomass used for bioenergy production is not per se environmentally benign, since bioenergy crop production is associated with negative side effects such as GHG emissions from soil (dominated by N2O). N2O emissions vary greatly in space and time; thus, direct comparison of soil N2O fluxes from various agro-ecosystems is certainly crucial for the assessment of the GHG reduction potential from energy crops.
Methods: Therefore, our study aimed to evaluate the two different agro-ecosystems (cropland and agro-forestry) cultivated in central Germany for their environmental impact. In a 1-year field experiment, we compared N2O fluxes from cropland (non-fertilized wheat, N-fertilized wheat, non-fertilized faba bean, and wheat mixed intercropping with faba bean) and agro-forestry (non-fertilized poplar, N-fertilized poplar, non-fertilized Robinia, and poplar mixed intercropping with Robinia) as a randomized split-block design.
Results: Rainfall at the field site was slightly over average during the period from 1 April to 1 July in 2014 (201 mm rain) and considerably below average during the same period in 2015 (100 mm rain). Cumulative mean N2O fluxes were up to five fold higher in agro-forestry than in arable crop treatments during 2014 growing period. We hypothesized that the difference in N2O emissions when comparing arable land and agro-forestry was mainly due to the limited water and nutrient uptake of plantations during the first year. Among the arable crops (wheat, N-fertilized wheat, wheat mixed intercropped with bean, and bean), seasonal and annual N2O emissions were highest in soils when faba bean was grown as a mono-crop. On the other hand, cumulative mean N2O fluxes were 31 % lower (p < 0.05) when faba bean mixed with wheat than in soils planted with N-fertilized wheat.
Conclusions: The latter clearly suggests that using legume crops as intercrop or mixed crop in wheat may significantly mitigate fertilizer-derived N2O fluxes and may be an effective proxy for increasing GHG emission savings for energy crops.