Domestication effects on nitrogen allocation, internal recycling and nitrogen use efficiency in the perennial new crop Silphium integrifolium (Asteraceae)

Abstract

Improvements in seed yield during domestication and breeding are frequently achieved moving plants from the conservative syndrome of the plant economic spectrum towards the more acquisitive side, changing how plants acquire, allocate, use and store C and nutrients in relation to their wild relatives. The aims were to evaluate if domestication changed the N allocation, the internal plant N recycling (N resorption efficiency and proficiency, and N storage) and N-use-efficiency, in the perennial new crop Silphium integrifolium. We compared in a field experiment repeated in two locations (Kansas and Patagonia), a Wild (W) and two improved accessions, with high- (HYI) and low-seed yield improved (LYI) accessions. HYI accessions produced more than twice the biomass and acquired twofold more N than LYI and Wild accessions. Changes in proportional N allocation were similar in both improved accessions (HYI and LYI) and locations: higher allocation to leaves and lower to the crown at pre-anthesis (growth-storage trade-off) and higher allocation to seeds and lower to the crown at maturity (reproduction-storage trade-off). HYI and LYI allocated 50% more N to seeds in average, reducing a 31% the N allocated to the crown in relation to the Wild. Nitrogen use efficiency (NUE) and mean residence time (MRT) of N were reduced in both improved accessions. In HYI, the lower MRT was related to the lower storage of N in the crown and N removal through seed production, and in LYI was the result of the N lost through leaf senescence. HYI produced litter with lower N concentration (more proficient) that the wild accession. These could decrease the net N mineralization rate and soil N availability at long term. HYI plants should require higher external N inputs to the soil to sustain their N uptake requirements. LYI and Wild accessions, had lower resorption efficiency, but N recycled was allocated to the crown for future remobilization and uses (better internal cycling). The leaf litter type of these accessions with higher N content should sustain faster N-cycles rates and N release to the soil. If the focus is on the ecosystem services, HYI accessions could help achieve a reduction in nitrate leaching by maximizing N uptake, N resorption and N removal through seed (i.e. nitrate catch crop), and also produce crop residues that slow down biogeochemical cycling and soil nutrient retention.