Root-root Interaction And Mechanisms For Improving Phosphorus Use Efficiency By Target Maize When Growing With Different Neighbours

Optimizing the traditional production model which depended on high phosphate fertilizer input and taking advantage of root biological potential for increasing phosphorus (P) use efficiency become an important research for the modern agriculture. Root morphological and physiological traits could be affected by heterogeneous nutrients and neighbouring plants. However, root synergetic responses to both heterogeneous nutrients and neighbouring plants in mixture system and the mechanisms for improving nutrient use efficiency are not fully understood. In the present study, the key methods and techniques for in situ monitoring dynamic processes and related parameters in the root-soil interface are adopted, including root exudate collection technique for examing rhizosphere processes, nutrient localized supply technique, split-root cultural method in soil and sand pot experiment for investigating root distribution, shading for reducing photosynthate for root growth, and in situ monitoring root dynamic growth with a BTC 2 Minirhizotron camera system. The present study focused on investigating the effect of neighbouring maize or faba bean on the P utilization by the target maize, examining root foraging behaviors through observing root growth in situ, and analyzing root responses to neighbour under different light intensity condition to understand the mechanisms for improving P use efficiency in maize-based cropping systems. The main results were listed as follows:(1) The neighbouring faba bean induced P availability increase, stimulated maize root proliferation and thus improved maize P uptake. Maize had longer root length and greater shoot biomass and P content when grown with faba bean than with maize. At each P supply rate, faba bean had a smaller root system than maize but greater exudation of citrate and acid phosphatase, suggesting greater capacity to mobilize P in the rhizosphere. Heterogeneous P availability enhanced root-length density of maize but not faba bean. Maize root proliferation in the P-rich patches was associated with increased shoot P uptake. Increased P availability by localized P application or by the presence of faba bean exudation stimulated root morphological plasticity and increased shoot growth for maize in the maize/faba bean mixture, suggesting that root interaction could be regulated by neighbouring plantsthrough affecting P availability.(2) The presence of neighbouring plants affected root foraging behaviors for P through altering direction of maize root growth. In maize/maize, target maize invested greater root mass in foraging P in the soil volume away from neighbouring roots, but in maize/faba bean the maize preferentially positioned its root growth along faba bean roots. Maize foraging strategies depended on neighbouring species, with a greater proportion of root mass, root length, and fine root length in the P-rich patch in maize/maize than maize/faba bean. Neighbouring maize reduced target maize root’s residence time in the patch compared with faba bean. Faba bean stimulated maize-root growth outside of the patch and decreased root investment to the patch. These results demonstrated that neighbouring fababean modified maize root foraging strategy for heterogeneous P through altering root growth-direction and time in the P-rich patch.(3) The maize root responses to heterogeous P and neighbouring species were dynamic. At early stage, the target maize did not respond to neighbouring maize or faba bean, and root distribution of target maize in mixture system was symmetric; at later stage, the target maize avoided neighbouring maize or faba bean inducing asymmetric root distribution of target maize. The occurring time of root asymmetric distribution was put off when the P supply intensity was increased in the soil volume growing target maize and neighbourin plants. The occurring time of root asymmetric distribution was earlier in maize/faba bean than in maize/maize. The growth stage of neighbouring plants influenced root distribution of target maize.(4) The maize root responses to heterogeous P and neighbouring species depended on the effect of light on neighbouring root growth. In low light treatment, the maize root showed no response to neighbouring heterogeneous P and neighbouring maize in maize/maize comparing with that in high light environment. The target maize avoided neighbouring faba bean, which was determined by the eefect of kin recognition between maize and faba bean. The responses of target maize to faba bean was not influenced by the light intensity but could be buffered by increasing the soil P supplied intensity in the soil volume growing maize and neighbour simultaneously. The kin recognition and nutrient availability played an important role in regulating root interaction in maize/faba bean.