Effect of root competition on growth and resource allocation of two spring wheat varieties cultivated at different times

Belowground competition among individuals of the same genotype can result in root proliferation, a pattern called "tragedy of the commons". Reducing or eliminating root proliferation could increase seed yield. However, it is not clear whether root competition effect has been influenced by breeding. A greenhouse pot experiment was conducted using an old spring wheat landrace 'Monkhead' and a modern cultivar '92-46'. Root interactions were set up by adding a mesh partition or a plastic partition between two plants from the same variety. Root competition was also encouraged by placing two plants on the same side of the plastic partition. There were two nutrition treatments: 1 time nutrition application and 2 times nutrition application. We examined the effect of root competition by comparing biomass and resource allocation patterns among the partition treatments. Biomass data showed that plants in the 'mesh partition' treatment produced similar root biomass to those in the 'plastic partition' treatment without competition, but their shoot biomass and total biomass were higher. 'Monkhead' plants in the 'mesh partition' treatment produced similar seed biomass to those in the 'plastic partition' treatment without competition, whereas seed biomass of '92-46' plants in the 'mesh partition' treatment was higher. Root biomass and seed biomass in the '2 times nutrition-plastic partition with competition' treatment were similar to those in the '1 time nutrition-plastic partition without competition' treatment, but their shoot biomass and total biomass were lower. A standardized major axis regression analysis (SMA) showed that root allocation of 'Monkhead' was not affected by root competition, but root allocation of '92-46' was decreased slightly ('mesh partition' vs. 'plastic partition without competition'). Root competition had no effect on shoot allocation and seed allocation for both varieties. In addition, Our results revealed composition differences between two varieties. 'Monkhead' produced more roots and shoots, but less seeds than '92-46'. 'Monkhead' also allocated more resources to shoots and less to seeds than '92-46', whereas root allocation was similar between two varieties in most partition sets except for '1 time nutrition-plastic partition without competition'. We conclude that the presence of roots from a neighboring plant does not result in 'the tragedy of the commons' pattern in either 'Monkhead' or '92-46', but affect the resource allocation pattern in '92-46' to some extent. Modern '92-46' is somehow able to develop restraining and cooperative behaviour characteristics in the presence of roots from neighboring plants, whereas 'Monkhead' does not show any responses. The differences in resource allocation patterns between two varieties support Darwinian agriculture, which suggests that in order to enhance yield, crop breeding has consciously selected varieties associated with lower competitiveness.