Biology subjects

Engbersen, N.

Publications and source records attributed to Engbersen, N..

3 recordsLinked to original sources

bioRxiv2020

Using plant traits to understand the contribution of biodiversity effects to community productivity in an agricultural system

O_LIIncreasing biodiversity generally enhances productivity through selection and complementarity effects not only in natural but also in agricultural systems. However, explaining why diversity enhances productivity remains a central goal in agricultural science. C_LIO_LIIn a field experiment, we constructed monocultures, 2- and 4-species mixtures from eight crop species with and without fertilizer and both in temperate Switzerland and semi-arid Spain. We measured environmental factors and plant traits and related these in structural equation models to selection and complementarity effects to explain yield differences between monocultures and mixtures. C_LIO_LIIncreased crop diversity increased yield in Switzerland. This positive biodiversity effect was driven to almost same extents by selection and complementarity effects, which increased with plant height and C:N ratio, respectively. Also, ecological processes driving yield increases from monocultures to mixtures differed from those responsible for yield increases through the diversification of mixtures. C_LIO_LIWhile selection effects were mainly driven by one species, complementarity effects were linked to higher productivity per unit N. Yield increases due to mixture diversification were driven only by complementarity and were not mediated through the measured traits, suggesting that ecological processes beyond those measured in this study were responsible for positive diversity effects on yield beyond 2-species mixtures. C_LI

ecology↗

bioRxiv2020

Diversity increases yield but reduces reproductive effort in crop mixtures

Resource allocation to reproduction is a critical trait for plant fitness1,2. This trait, called harvest index in the agricultural context3-5, determines how plant biomass is converted to seed yield and consequently financial revenue of numerous major staple crops. While plant diversity has been demonstrated to increase plant biomass6-8, plant diversity effects on seed yield of crops are ambiguous9. This discrepancy could be explained through changes in the proportion of resources invested into reproduction in response to changes in plant diversity, namely through changes of species interactions and microenvironmental conditions10-13. Here we show that increasing crop plant diversity from monoculture over 2- to 4-species mixtures increased annual primary productivity, resulting in overall higher plant biomass and, to a lesser extent, higher seed yield in mixtures compared with monocultures. The difference between the two responses to diversity was due to a reduced reproductive effort of the eight tested crop species in mixtures, possibly because their common cultivars have been bred for maximum performance in monoculture. While crop diversification provides a sustainable measure of agricultural intensification14, the use of currently available cultivars may compromise larger gains in seed yield. We therefore advocate regional breeding programs for crop varieties to be used in mixtures that should exploit facilitative interactions15 among crop species.

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↗