Allocation of Nitrogen and Carbon Is Regulated by Nodulation and Mycorrhizal Networks in Soybean/Maize Intercropping System

Abstract

Soybean/maize intercropping has remarkable advantages in increasing crop yield and nitrogen (N) efficiency. However, little is known about the contributions of rhizobia or arbuscular mycorrhizal fungi (AMF) to yield increases and N acquisition in the intercropping system. Plus, the mechanisms controlling carbon (C) and N allocation in intercropping systems remain unsettled. In the present study, a greenhouse experiment combined with 15N and 13C labeling was conducted using various inoculation and nutrient treatments. The results showed that co-inoculation with AMF and rhizobia dramatically increased biomass and N content of soybean and maize, and moderate application of N and phosphorus largely amplified the effect of co-inoculation. Maize had a competitive advantage over soybean only under co-inoculation and moderate nutrient availability conditions, indicating that the effects of AMF and rhizobia in intercropping systems are closely related to nutrient status. Results from 15N labeling showed that the amount of N transferred from soybean to maize in co-inoculations was 54% higher than that with AMF inoculation alone, with this increased N transfer partly resulting from symbiotic N fixation. The results from 13C labeling showed that 13C content increased in maize shoots and decreased in soybean roots with AMF inoculation compared to uninoculated controls. Yet, with co-inoculation, 13C content increased in soybean. These results indicate that photosynthate assimilation is stimulated by AM symbiosis in maize and rhizobial symbiosis in soybean, but AMF inoculation leads to soybean investing more carbon than maize into common mycorrhizal networks (CMNs). Overall, the results herein demonstrate that the growth advantage of maize when intercropped with soybean is due to acquisition of N by maize via CMNs while this crop contributes less C into CMNs than soybean under co-inoculation conditions.

Little Cross-Feeding of the Mycorrhizal Networks Shared Between C3-Panicum bisulcatum and C4-Panicum maximum Under Different Temperature Regimes

“…Our results thus demonstrate a very balanced investment of the two plants into the CMN and that this investment is not substantially affected by elevated temperature. Our data are thus in direct contrast to previous research showing that one or the other plant dominates the C supply to the CMN ( Walder et al, 2012 ; Wang et al, 2016 ). The previous experiments had all used phylogenetically more distant plant species pairs, and it has been shown that plant size and/or presence of rhizobia could affect the C inputs into the CMN ( Nakano et al, 1999 ; Wang et al, 2016 ; Weremijewicz et al, 2016 ).…”

“…Our data are thus in direct contrast to previous research showing that one or the other plant dominates the C supply to the CMN ( Walder et al, 2012 ; Wang et al, 2016 ). The previous experiments had all used phylogenetically more distant plant species pairs, and it has been shown that plant size and/or presence of rhizobia could affect the C inputs into the CMN ( Nakano et al, 1999 ; Wang et al, 2016 ; Weremijewicz et al, 2016 ). Because we used plant species closely related phylogenetically and of similar size and growth rates (although not necessarily so under all temperatures), such asymmetry in C feeding of the CMN as seen in previous experiments may not have developed in our case.…”

“…This imbalance in cost-benefit exchange, however, could be caused by the use of only one fungal species and thus absence of competition among different fungal species or incompatibility of the fungus with one or the other of the plant species. Wang et al (2016) , on the other hand, found that C 3 - Glycine invested more C into CMN than did C 4 - Zea when intercropped. Here, the results may also have been affected by what could be termed “cheating” by the sole fungal species used in the model experiment.…”

The roles and performance of arbuscular mycorrhizal fungi in intercropping systems

“…With 14 C labeling in rice leaves, both enhanced 14 C activity in watermelon (Citrullus lanatus) leaves and increased P uptake and translocation in rice were shown, thus AM fungus mediated the C and P trade between intercrops (Ren et al, 2013). In a growth chamber 13 CO 2 -labeling experiment, inoculation with AM fungi increased 13 C content in maize shoots and decreased 13 C content in soybean roots, indicating that maize invested less C than soybean into the CMNs (Wang et al, 2016). Walnut (Juglans nigra) tree showed higher ∂ 13 C ( 13 C/ 12 C ratio) in leaves but lower ∂ 13 C in root adjacent mycelium compared to the neighboring maize, suggesting the potential C transfer from walnut to maize via the CMNs (van Tuinen et al, 2020).…”

From Leguminosae/Gramineae Intercropping Systems to See Benefits of Intercropping on Iron Nutrition

“…The maize/legumes intercropping systems enriched the soil biodiversity and spores of AMF in the root-zone soil (Punyalue et al, 2018). Intercropping facilitated nitrogen transfer from soybeans to maize on co-inoculation with AMF, as shown by 15 N labeling (Wang et al, 2016). AMF application in dill/common bean intercropping systems can enhance the Fe, zinc (Zn), and manganese (Mn) contents of dill and its competitive ability against weeds (Weisany et al, 2016a,b).…”