Deep-rooted pigeon pea promotes the water relations and survival of shallow-rooted finger millet during drought—Despite strong competitive interactions at ambient water availability

Abstract

Bioirrigation has been defined as the transfer of hydraulically lifted water by a deep-rooted plant to a neighbouring shallow-rooted plant which cannot access deep soil moisture. In this study, we tested if facilitative effects of bioirrigation or the competition for water dominate the interaction of two intercropped plants-deep-rooted pigeon pea (PP) and shallow-rooted finger millet (FM) before and during a drought. Additionally, we tested how the presence of a common mycorrhizal network (CMN) affects the balance between facilitative (i.e. bioirrigation) and competitive interactions between two intercropping species. Our results show that PP can indeed promote the water relations of FM during a drought event. Specifically, stomatal conductance in FM controls dropped to low values of 27.1 to 33.6 mmol m-2 s-1 , while FM in intercropping treatments were able to maintain its stomatal conductance at 60 mmol m-2 s-1. In addition, the presence of PP reduced the drought-induced foliar damage and mortality of FM. The observed facilitative effects of PP on FM were partially enhanced by the presence of a CMN. In contrast to the facilitative effects under drought, PP exerted strong competitive effects on FM before the onset of drought. This hindered growth and biomass production of FM when intercropped with PP, an effect that was even enhanced in the presence of a CMN. The results from our study thus indicate that in intercropping, deep-rooted plants may act as "bioirrigators" for shallow-rooted crops and that a CMN can promote these facilitative effects. However, the interspecific competition between the intercropped plants under conditions of abundant moisture supply can be strong and are enhanced by the presence of a CMN. In more general terms, our study shows that the extent by which the antagonistic effects of facilitation and competition are expressed in an intercropping system strongly depends on the availability of resources, which in the case of the present study was water and the presence of biotic interactions (i.e. the presence of a CMN).

Intercropping—A Low Input Agricultural Strategy for Food and Environmental Security

“…Bio-irrigation is another beneficial phenomenon by which shallow-rooted crops obtain support from deep-rooted ones in intercropping under limited moisture conditions. The experimental results clearly indicated that deep-rooted pigeon pea played the role of bio-irrigators and shared moisture for shallow-rooted finger millet [67,68].…”

“…The transported water to the upper layer of the soil is utilized by lateral secondary branches of the roots of the same crop and neighbouring crops also share it. The experimental results clearly indicated that deep-rooted pigeon pea shared played the role of bio-irrigators and shared moisture for shallowrooted finger millet [67,68]. Moreover, Chai et al [142] mentioned that WUE was increased by 95% in a maize + pea intercropping system over the pure stand of pea.…”

Assessment of Nitrogen Fixation by Mungbean Genotypes in Different Soil Textures Using 15N Natural Abundance Method

“…Annual global estimates of N fixed by legumes in symbiosis with soil rhizobia were reported to be 21.5 Tg (Herridge et al 2008) of which up to 30% is estimated to be returned to soils (Reeves et al 2016). Other reported benefits of including legumes into crop rotations are greater microbial and crop diversity, soil fertility, and reduction of pest incidence (Diatta et al 2016a;Franke et al 2018;Giller 2001;Matusso et al 2014;Singh et al 2020;Vanlauwe et al 2019). In addition, legume crops are an important and economic source of protein, minerals, and vitamins in human diets and animal feed under smallholder agriculture (Diatta et al 2016b;Graham and Vance 2003;Tharanathan and Mahadevamma 2003).…”

Spatial arrangement and biofertilizers enhance the performance of legume – millet intercropping system in rainfed areas of southern India

“…Our recent work has shown that a CMN plays a key role in facilitating the transfer of water between the rhizospheres of two intercropped partners in a greenhouse and can in turn improve the water relations of shallow rooted crops during soil drying (Singh et al ., 2019). However, a further experiment with bigger pots (50 L) than in the previous experiment did not show an effect of the CMN on water-relations but treatments with CMN had lower foliar damage than treatments without CMN during drought (Singh et al ., 2020).…”