Post-silking nitrogen accumulation and remobilization are associated with green leaf persi

Post-silking nitrogen accumulation and remobilization are associated with green leaf

persistence and plant density in maize

ZHANG Li-li1, 2, ZHOU Xiang-li3, FAN Ye2, FU Jun2, HOU Peng4, YANG Hai-long2, QI Hua1

【摘 要】Abstract Stay green (SG) maize was found to have higher grain yield and post-silking nitrogen (N) uptake (PostN) compared with a non-stay green (NSG) hybrid. To understand the effects of plant density on grain yield (GY) and N efficiency in modern maize hybrids, we compared two modern hybrids (SG hybrid DY508 and NSG hybrid NH101) with similar maturity ratings at three plant densities (45 000, 60 000, and 75 000 pl ha-1) in 2014 and 2015. GY, leaf senescence, dry matter (DM) accumulation,N accumulation, PostN, and post-silking N remobilization (RemN) were analyzed. DY508 and NH101 had similar GY, but DY508 had higher thousand kernel weight (TKW) and lower kernel number (KN) than NH101. Plant density significantly increased GY in the two hybrids. On average, over the two years, plant density improved GY in DY508 and NH101 by 18.5 and 11.1%, respectively, but there were no differences in total dry matter (TDM) and post-silking DM (PostDM) between the two hybrids. Plant density improved leaf N, stem N, and grain N at the silking and maturity stages in 2014 and 2015. DY508 was lower in harvest index (HI), nitrogen harvest index (NHI), and grain N

concentration (GNC) than NH101. Grain N in DY508 was 2.61 kg ha-1 less than in NH101, and this was caused by lower GNC and leaf RemN. On the average, DY508 was 1.62 kg ha-1 less in leaf remobilized N (leaf RemN) than NH101, but was similar in stem remobilized N (stem RemN；2.47 kg ha-1 vs. 3.41 kg ha-1). Maize hybrid DY508 shows delayed leaf senescence in the upper and bottom canopy layers in the later stages of growth. The present study provides evidence that the NH101, which has rapid leaf senescence at the late grain-filling stage, has gained equivalent GY and higher leaf RemN, and was more efficient in N utilization.

【期刊名称】《农业科学学报（英文版）》 【年(卷),期】2019(018)008 【总页数】11

【关键词】Keywords: maize, N remobilization, post-silking N uptake, stay green, plant density

Received 2 April, 2018 Accepted 25 July, 2018 Correspondence QI Hua, E-mail: qihua10@163.com

? 2019 CAAS. Published by Elsevier Ltd. This is an open access article under

the

CC

BY-NC-ND

license

(http://creativecommons.org/licenses/by-nc-nd/4.0/).

1. Introduction

Grain yield (GY) in maize has increased steadily over the past 50 years

due to genetic and agronomic improvements(Duvick et al. 2005； Tollenaar and Lee 2010). An extended post-silking period and delayed leaf senescence are two important factors that increase canopy function in modern

maize hybrids. This is beneficial for post-silking dry matter accumulation (PostDM) and post-silking nitrogen (N) uptake(PostN), which improves GY (Tollenaar and Wu 1999； Borrell and Hammer 2000； Valentinuz and Tollenaar 2004). Modern maize hybrids can accumulate more than 10% DM and N during grain filling than older hybrids (Rajcan and Tollenaar 1999). Stay green (SG) maize hybrids have late-senescing leaves and can produce higher GY, particularly in the context of a warming climate (Liu et al. 2013； Xiao and Tao 2016).Evidence from field experiments indicated that SG hybrids did not have higher GY and accumulated less N in grain(Ciampitti and Vyn 2012, 2013； Kosgey et al. 2013). Grain N (GrainN) content is closely correlated with GY in maize,indicating the importance of N in yield potential (Antonietta et al. 2016). GrainN in maize is derived mainly from PostN and N remobilization (RemN) from other organs, and an inverse correlation between PostN and RemN was found(Chen et al. 2014； Chen et al. 2015). Indeed, SG maize hybrids have higher PostN but lower RemN (He et al. 2004；Pommel et al. 2006), because SG hybrids require a large amount of applied N to maintain high foliar N levels, which is

associated with chloroplasts integrity (Tollenaar and Lee 2006). The SG period is associated with PostN and RemN,an increase in PostN and a decrease in RemN to the grain can extend the SG period (Rajcan and Tollenaa 1999； Mi et al. 2003).

Delayed leaf senescence is the most important difference between SG and NSG hybrids. For both SG and NSG maize hybrids, leaves senesce starts in the lower canopy layer,then in the top layer, and lastly in the middle layer of the canopy (Valentinuz and Tollenaar 2004). The difference in senescence between SG and NSG hybrids occurs mainly in the lower canopy leaves； the onset of leaf senescence is delayed and the rate is lower (He et al. 2004； Antonietta et al.2014). However, green leaves in the lower canopy layer cannot contribute to a higher photosynthesis rate due to low irradiance levels, but they consume more stored assimilates late in the growing period (Antonietta et al. 2014). Delayed senescence in SG maize hybrids can result in a higher DM,which mainly accumulates in the stem rather than in the grain compared to NSG hybrids (Pommel et al. 2006). The assimilate distribution cann't guarantee a promised grain yield for SG maize hybrids, but likely increase the stem tolerance to lodging.

Increasing plant density is an important strategy to increase maize yield (Tollenaar and Wu 1999； Sangoi et al.2002； Duvick et al. 2005； Boomsma et al. 2009； Assefa et al. 2016). High plant density can lead

to weak stems and lodging in maize, partly as a result of the fast remobilization of DM and N at the early post-silking stage (Rajcan and Tollenaa 1999). Furthermore, a higher PostDM was found in newer hybrids grown at high density compared to older hybrids (Tollenaar et al. 1991). However, there is limited information about the effects of plant density on PostN and RemN in modern maize hybrids that differ in the leaf senescence trait.

In the present study, we compared canopy senescence,dry matter accumulation, N accumulation and remobilization between silking and maturity stages in two modern SG and NSG maize hybrids that differed with respect to leaf senescence at different plant densities. The objectives were to (1) test the leaf senescence behavior in the canopy during the grain-filling stage, (2) understand the GY, N, and DM accumulation and partitioning at the post-silking stage in response to increasing plant density, and (3) evaluate the effects of plant density on RemN and PostN between silking and physiological maturity stages in the SG and NSG hybrids.

2. Materials and methods

2.1. Field site and experimental design

The experiments were conducted in 2014 and 2015 at the experimental station of Dandong Academy of Agricultural Sciences (40°28′N, 124°06′E), Fengcheng, Dandong City,Liaoning Province, China. The soil