Research article Effects of nitrogen and tiller type on grain yield and physiological responses in rice Yang Wang 1 , Jianwei Lu 1 , Tao Ren 1 , Saddam Hussain 1,2 , Chen Guo 1 , Sen Wang 1 , Rihuan Cong 1 and Xiaokun Li 1 * 1 Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Ministry of Agriculture, Microelement Research Centre, College of Resources and Environment, Huazhong Agricultural University, No.1 Shizishan Street, Hongshan District, Wuhan 430070, China 2 Department of Agronomy, University of Agriculture, Jail Road, Faisalabad, Punjab 38040, Pakistan Received: 30 July 2016; Editorial decision: 14 March 2017; Accepted: 29 March 2017; Published: 30 March 2017 Associate Editor: Abdelbagi M. Ismail Citation: Wang Y, Lu J, Ren T, Hussain S, Guo C, Wang S, Cong R, Li X. 2017. Effects of nitrogen and tiller type on grain yield and physiological responses in rice. AoB PLANTS 9: plx012; doi:10.1093/aobpla/plx012 Abstract. The increasing food demands from an expanding population necessitate global efforts to increase crop production and ensure food security. The rate of nitrogen (N) fertilizer application is strongly related to crop yield. However, although the application of N fertilizer significantly increases the number of tillers in rice, late emerging tillers usually produce lower yields compared with early emerging tillers. Understanding the physiological constraints of late emerging rice tillers is critical for further increasing rice grain yields. Two-year field experiments, consisting of four nitro- gen fertilizer levels, were conducted in order to study variations in the physiological characteristics of different types of tillers. The results revealed that the contributions of late emerging tillers to population rice grain yields improved with increased N levels. However, spikelets per panicle and the grain filling of late emerging tillers were significantly lower than that of the main stems or early emerging tillers under all N levels. The nitrogen harvest index of late emerging till- ers was lower than that of main stems and early emerging tillers, and differences gradually increased under higher N rates. Nutrient source deficiency was a primary factor for the low productivity of late emerging tillers. Additionally, rapid malondialdehyde accumulation and delayed emergence determined the short growth duration of late emerging tillers. Further, low actual photochemistry efficacy (U PSII ) resulted in insufficient photosynthetic assimilate supply in late emerging tillers, whereas highly constitutive non-photochemical energy dissipation (U NO ) might damage the photosyn- thetic system. Moreover, the low activity of SuSase and spikelets per panicle revealed both inadequate sink activities and storage sites. The identification of these limiting factors in late emerging rice tillers will assist in closing the ‘yield gap’ between late emerging tillers and early emerging tillers, and contribute to further increasing rice grain yields. Keywords: Chlorophyll fluorescence; nitrogen; nitrogen harvest index; rice; senescence; tiller; vascular bundle. Introduction Branching comprises a protective mechanism for higher plants, by assisting with reducing the impacts of injury, and facilitating adaptation to the environment (Horvath et al. 2003). Gramineous plants have a special type of side shoot referred to as a tiller. which is distinct from * Corresponding author’s e-mail address: lixiaokun@mail.hzau.edu.cn V C The Authors 2017. Published by Oxford University Press on behalf of the Annals of Botany Company. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/ licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. AoB PLANTS www.aobplants.oxfordjournals.org V C The Authors 2017 100 Downloaded from https://academic.oup.com/aobpla/article/9/2/plx012/3093634 by guest on 12 June 2022