Abstract
Efficient use of nitrogen inputs for concurrent improvements in grain yield and nitrogen use efficiency (NUE) has been recognized as a viable strategy for sustainable agriculture development. Yet, there is little research on the possible physiological basis of maize hybrid heterosis for NUE and measurable traits that are corresponding to the NUE heterosis. A field study was conducted for two years to evaluate the heterosis for NUE and determine the relationship between NUE and its physiological components. Two commercial hybrids, ‘Xianyu335’ and ‘Zhengdan958’, and their parental inbred lines, were grown at 0 (0 N) and 150 kg N ha−1 (150 N), in a randomized complete block design with four replications each year. Compared to their parental lines, both hybrids displayed a significant heterosis, up to 466%, for NUE. N internal efficiency (NIE) accounted for 52% of the variation in heterosis for NUE, while there was generally negligible heterosis for nitrogen recovery efficiency (NRE). Heterosis for NIE and thereby for NUE in maize was ascribed to (i) an earlier establishment of pre-anthesis source for N accumulation, which phenotypically exhibited as a faster leaf appearance rate with higher maximum LAI and photosynthetic nitrogen use efficiency; (ii) a larger amount of N being remobilized from the vegetative tissues, especially from leaves, during the grain filling. Phenotypically, there was notably a rapid reduction in post-anthesis specific weights of leaf and stalk, but with maintained functionally stay-green ear leaves; and (iii) a higher productive efficiency per unit grain N, which was characterized by a reduced grain N concentration and enhanced sink strength.
Highlights
The global challenge of meeting increased food demand and protecting environmental quality calls for improving nitrogen use efficiency in maize production systems
Ma and Dwyer[12] and Subedi & Ma13,14 suggested that hybrids with greater yields or higher nitrogen use efficiency (NUE) were accompanied with greater BM production and more N uptake during the grain-filling period, but their results showed no indication of greater allocation of N to the grain in hybrids with higher yields or NUE13
The results showed that the absolute heterosis for maize NUE was approximately 13.1 to 24.8 kg grain kg−1 N, representing 174% to 422% of the mid-parental heterosis for NUE
Summary
The global challenge of meeting increased food demand and protecting environmental quality calls for improving nitrogen use efficiency in maize production systems. Evaluation of the two components is useful to advance the understanding of physiological mechanisms of NUE This is achieved through examining N uptake, assimilation, translocation and remobilization[3]. Ciampitti and Vyn[11] reviewed the physiological mechanisms of changes over time in maize NUE They suggested that New Era genotypes, which exhibited a higher NUE, showed higher total biomass (BM) accumulation and N uptake during the post-silking period. Shading stress during the presilking and silking periods resulted in a greater heterosis of maize hybrids for grain yield, which was highly associated with heterosis for kernel number. A field experiment was conducted on two contrasting commercial maize hybrids and their parental inbred lines, to investigate yield, NUE, N uptake and remobilization, and the related traits. Our objective was to illuminate the main physiological basis of heterosis for maize NUE
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