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Xiao-min Liu, Xin-zhi Zhang, Yi-min Shi and Dong-qin Tang

Genetic diversity of Narcissus was systematically studied on both morphological and molecular levels. Twenty-four characteristics of nine narcissi were observed and their differences evaluated by clustering method. The results showed that nine narcissi can be divided into two subclusters: one comprised by Narcissus pseudonarcissus, the other by Chinese Narcissus. The morphological diversity among five cultivars of N. pseudonarcissus is higher than that among four ecotypes of Chinese Narcissus (Narcissus tazetta var. chinensis). There are seven morphological characteristics in N. pseudonarcissus presenting obvious variations with coefficients from 33.33% to 91.67%. Only five morphological characteristics in Chinese Narcissus present certain variations with coefficients from 37.04% to 51.79%. On DNA level, two clusters are distantly related too. Based on the random amplified polymorphic DNA (RAPD) markers, 13 out of 40 random primers yielded scorable polymorphisms between samples. Wide variations in banding profiles between cultivars or between ecotypes were observed with nearly every primer tested. Among 95 band positions that were scored for all the 9 narcissi, 81 are polymorphic (85.26%). Cluster analysis of the calculated similarity matrix revealed that the genetic diversity between these individuals within the same section is low. However, the genetic diversity between two sections is obviously higher. Taken together, the methods combined morphological characteristics and RAPD technique allow a deep evaluation of the variation of Narcissus on both section level and cultivar/ecotype level.

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Zhi Quan, Bin Huang, Caiyan Lu, Yi Shi, Yanhong Cao, Yongzhuang Wang, Chuanrui He, Guangyu Chi, Jian Ma and Xin Chen

Much nitrogen (N) is lost in high-input protected cropping systems mainly via leaching of not only nitrate-N but also extractable organic N (EON), but the role of EON in this process is poorly appreciated. A consecutive 3-year plot experiment was conducted to investigate the impact of co-application of manures with chemical N fertilizer on N accumulation and loss in a greenhouse soil rotationally planted with cucumber or tomato and lettuce. Application of manures significantly enhanced the average contents and stocks of NO3 -N, EON, and total N (TN) in 0- to 60-cm soil layer, although EON accumulated within growing season, while NO3 -N accumulated with fluctuation, and TN accumulated gradually throughout the 3-year experiment. With application rate at 120 or 180 t dry manures per hectare per 3 years, the corresponding apparent N surplus was 2710 or 3924 kg⋅ha−1 per 3 years. Due to little increase of biomass N uptakes during vegetable seasons, the accumulated N in soil profile would be a potential loss source, largely via leaching of both nitrate and EON. Application of manures slowed soil acidification but intensified secondary salinization of the greenhouse soil. Considering the manures-induced high soil N accumulation and loss, well-balanced evaluation of the role of manures in high-input agricultural ecosystems is needed.

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Yi Zhang, Xiao-Hui Hu, Yu Shi, Zhi-Rong Zou, Fei Yan, Yan-Yan Zhao, Hao Zhang and Jiu-Zhou Zhao

We studied the effects of exogenous spermidine (Spd) on plant growth and nitrogen metabolism in two cultivars of tomato (Solanum lycopersicum) that have differential sensitivity to mixed salinity-alkalinity stress: ‘Jinpeng Chaoguan’ (salt-tolerant) and ‘Zhongza No. 9’ (salt-sensitive). Seedling growth of both tomato cultivars was inhibited by salinity-alkalinity stress, but Spd treatment alleviated the growth reduction to some extent, especially in ‘Zhongza No. 9’. Exogenous Spd may help reduce stress-induced increases in free amino acids, ammonium (NH4 +) contents, and NADH-dependent glutamate dehydrogenase (NADH-GDH) activities; depress stress-induced decreases in soluble protein and nitrate content; and depress nitrate reductase, nitrite reductase, glutamine synthetase (GS), NADH-dependent glutamate synthase (NADH-GOGAT), glutamate oxaloacetate transaminase (GOT), and glutamate pyruvate transaminase (GPT) activities, especially for ‘Zhongza No. 9’. Based on our results, we suggest that exogenous Spd promotes the assimilation of excess toxic NH4 + by coordinating and strengthening the synergistic action of NADH-GDH, GS/NADH-GOGAT, and transamination pathways, all during saline-alkaline stress. Subsequently, NH4 + and its related enzymes (GDH, GS, GOGAT, GOT, and GPT), in vivo, are maintained in a proper and balanced state to enable mitigation of stress-resulted damages. These results suggest that exogenous Spd treatment can relieve nitrogen metabolic disturbances caused by salinity-alkalinity stress and eventually promote plant growth.