Plants can suffer ammonium (NH4 +) toxicity, particularly when NH4 + is supplied as the sole nitrogen source. However, our knowledge about the underlying mechanisms of NH4 + toxicity is still largely unknown. Lemna minor, a model duckweed species, can grow well in high NH4 + environment but to some extent can also suffer toxic effects. The transcriptomic and physiological analysis of L. minor responding to high NH4 + may provide us some interesting and useful information not only in toxic processes, but also in tolerance mechanisms. The L. minor cultured in the Hoagland solution were used as the control (NC), and in two NH4 + concentrations (NH4 + was the sole nitrogen source), 84 mg/L (A84) and 840 mg/L (A840) were used as stress treatments. The NH4 + toxicity could inhibit the growth of L. minor. Reactive oxygen species (ROS) and cell death were studied using stained fronds under toxic levels of NH4 +. The malondialdehyde content and the activities of superoxide dismutase and peroxidase increased from NC to A840, rather than catalase and ascorbate peroxidase. A total of 6.62G nucleotides were generated from the three distinct libraries. A total of 14,207 differentially expressed genes (DEGs) among 70,728 unigenes were obtained. All the DEGs could be clustered into 7 profiles. Most DEGs were down-regulated under NH4 + toxicity. The genes required for lignin biosynthesis in phenylpropanoid biosynthesis pathway were up-regulated. ROS oxidative-related genes and programmed cell death (PCD)-related genes were also analyzed and indicated oxidative damage and PCD occurring under NH4 + toxicity. The first large transcriptome study in L. minor responses to NH4 + toxicity was reported in this work. NH4 + toxicity could induce ROS accumulation that causes oxidative damage and thus induce cell death in L. minor. The antioxidant enzyme system was activated under NH4 + toxicity for ROS scavenging. The phenylpropanoid pathway was stimulated under NH4 + toxicity. The increased lignin biosynthesis might play an important role in NH4 + toxicity resistance.

Fritillaria cirrhosa D. Don is a renowned traditional Chinese medicine plant that is mainly distributed in the southeastern margin of the Qinghai–Tibet Plateau. The overexploitation in the recent years has led to a sharp decline of this undomesticated resource. Analyzing the impact of climate change on the geographic distribution of F. cirrhosa is meaningful for its conservation and domestication. In this study, the maximum entropy model (Maxent) was used to simulate the distribution of F. cirrhosa in relation to the current and future climatic conditions. The maximum temperature of the warmest month (Bio 5) and the precipitation of the warmest quarter (Bio 18) were the two most important bioclimatic variables determining the distribution of F. cirrhosa. Based on the predicted level of climatic warming, a further reduction of the geographic distribution of F. cirrhosa is to be expected. This study demonstrated the necessity and urgency of establishing more effective ways to protect the natural F. cirrhosa resources and developing artificial cultivation methodology.