Root morphological and architectural plasticity in wheat/faba bean intercropping

Background

Intercropping has been widely applied by smallholder farmers in Africa, Latin America and parts of Asia for centuries. In resource limited areas, intercrops have the potential of increasing productivity, and thus income, and of reducing the risk of crop failure. Generally, intercropping systems have a higher resource (land, nutrient, radiation and water) use efficiency compared to monocultures. Intercropped crops benefit from facilitation (species helping each other in taking up resources) and niche complementary (species looks for resources in different places or at different moments), which may eventually lead to overyielding.  

Popular intercropping systems contain a cereal (monocot) and a legume (dicot) species. Monocots and dicots have different foraging and acquisition strategies for edaphic resources. As a result, they may show different plastic responses to competition for soil resources. Most monocot species have a fibrous root system consisting of embryonic primary root and seminal roots, and post embryonic shoot borne roots and lateral roots. In contrast, dicots mainly form a tap root system comprising a single embryonically initiate primary root with initiated lateral roots, adventitious roots, and hypocotyl-borne basal roots. In legume/non-legume intercrops the legume root system is confined to the shallower soil layer due to the strong competition from the companion non-legume crop.  

In below-ground, at the early growth stages when the root systems of both species are not fully developed yet, the soil exploration rate is of critical for soil resource competition. This root system exploration at early stages is determined by resource availability and the time of germination. Hence the advantage of one species could result in suppression of root growth of the other species and eventually influence crop performance in later stages. This priority effect on root growth and below-ground competition have hardly been studied in agroecosystems, but mainly in natural ecosystems.  

The canopies of intercropping systems typically consist of crop species of different heights. This heterogeneous distribution of the canopy results in patterns of light capture (photosynthetically active radiation, PAR) and light signalling (red to far-red ratio, R:FR) different to sole crops, whose are much more uniform. R/FR ratio is used by plants as an indicator of plant proximity. Low R/FR ratio induces plastic responses in shoot and root system development. How plant use this light signal received by photoreceptors to regulate their development belowground, and what this means for plant performance, is rarely studied. This shoot to root communication might help plants coordinate resource partitioning under interspecific competition in intercropping systems, and therefore play an important part in determining intercrop performance benefits. 

Project description

The present work aims to evaluate the interspecific interactions during vegetative stage for the intercropping system of agricultural interests. This knowledge could eventually help in intercropping in terms of deciding timing and spacing of planting and levels of plasticity in used cultivars. The project is consists of four parts.

1. Nutrient viability

The root forging behaviours under levels of Nitrogen levels will be studied in the wheat/faba bean row intercropping system. This study will provide a further understanding of the root distribution and nitrogen uptake under competitive interactions in the crop mixture. 

2. Time of arrival

It is aimed to quantify the priority effect during early development stage for the wheat/faba bean mixture system. Such knowledge is crucial in the understanding of intercrop performance and the optimization of crop system management for high yielding crops at sustainable input levels. 

3. Light signalling

This study aims to understand if the difference of light conditions (R/FR) in the mixed stand (intercropping) and mono stand (sole crop) will trigger altered root system development. The research on interactions between above- and belowground plant–plant signalling is will improve our understanding of the mechanisms of interactions in intercropping. 

4. Model simulation

FSP modelling will be used to understand the role of plant root morphology plasticity on resource capture, and to develop strategies for optimisation of intercropping cultivation and breeding in terms of underground resource capture. An existing FSP model will be parameterized using root traits observed in the experiments. Then, virtual “transplantation” experiments will be carried out in the model environment to explore the effect of intercrop and sole crop plant phenotypes for above and belowground traits on the growth and resource capture.