不同氮（N）水平下玉米的生理和代谢差异是田间合理氮素营养管理的基础，对提高氮肥利用率和减少环境污染具有重要作用。本文在明确长期不同氮肥处理下玉米氮效率和产量响应的前提下，利用非靶代谢组学方法分析了相应的差异代谢物及其代谢途径的差异。结果表明，氮胁迫（包括缺乏和过量），通过调节碳代谢产物（包括糖醇和TCA循环中间体）和氮代谢产物（包含各种氨基酸及其衍生物）影响碳氮代谢的平衡。缺氮胁迫时，L-丙氨酸、L-苯丙氨酸、L-组氨酸和L-谷氨酰胺显著下调，而过量氮时，L-缬氨酸、脯氨酸和L-组氨酸显著上调。除了上述碳氮代谢中的糖醇和氨基酸外，在该实验条件下，一些次生代谢物如黄酮类化合物（包括山奈酚、木犀草素、芸香素和香叶木素）和激素类（包括吲哚乙酸、反式玉米素和茉莉酸）可以初步被筛选作为氮胁迫诊断的指标。本研究还表明，N2处理（120 kg·ha^-1 N）和N3处理（180 kg·ha^-1 N）的叶片代谢水平相似，这与12年试验中两处理之间生理指标和产量的变化趋势一致。本研究在代谢水平上验证了氮肥减施即施用量从180 kg·ha^-1（当地推荐）减少到120 kg·ha^-1的可行性，为不降低产量条件下减少氮肥施用，进而提高氮肥利用率和保护生态环境提供了理论基础。

磷（P）是一种不可再生资源，也是植物生长的关键营养元素，对作物产量的提高起着重要作用。磷肥的过量施用在农业生产中很普遍，这不仅浪费了磷肥资源，还造成了磷的积累和地下水污染。为了获得较高的产量和磷素利用效率（PUE），我们假设农业系统的表观磷平衡可以作为确定磷投入阈值的关键指标。因此，我们进行了长达12年的定位田间试验，包括6个施磷处理，施磷量分别为0、45、90、135、180和225 kg P₂O₅ ha^–1，以明确作物产量、PUE和土壤Olsen-P对磷平衡的反应并优化磷投入。结果表明，当磷肥施用量超过某一水平时，周年产量不再增加，当周年磷肥施用量为90–135 kg P₂O₅ ha^–1时可以实现较高的产量和PUE。当磷平衡阈值为2.15–4.45 kg P ha^–1时可以实现最佳产量和最小的环境风险。基于磷平衡阈值估算的磷投入为95.7–101 kg P₂O₅ ha^–1，施磷量在此阈值内时可以协同提高产量与PUE（90.0–94.9%）。此外，本研究发现磷投入-产出平衡框架的建立有助于评估土壤Olsen-P在未来的变化，其中土壤磷平衡每增加100 kg P ha^–1，有效磷含量上升4.07 mg kg^–1。总之，磷平衡可以作为农业生产中磷管理的一个重要指标，为限制磷过剩和制定更高产、高效和环保的磷肥管理策略提供有力参考。

Maize is one of the most important crops worldwide, but it suffers from salt stress when grown in saline-alkaline soil. There is therefore an urgent need to improve maize salt tolerance and crop yield. In this study, the SsNHX1 gene of Suaeda salsa, which encodes a vacuolar membrane Na⁺/H⁺ antiporter, was transformed into the maize inbred line 18-599 by Agrobacterium-mediated transformation. Transgenic maize plants overexpressing the SsNHX1 gene showed less growth retardation when treated with an increasing NaCl gradient of up to 1%, indicating enhanced salt tolerance. The improved salt tolerance of transgenic plants was also demonstrated by a significantly elevated seed germination rate (79%) and a reduction in seminal root length inhibition. Moreover, transgenic plants under salt stress exhibited less physiological damage. SsNHX1-overexpressing transgenic maize accumulated more Na⁺ and K⁺ than wild-type (WT) plants particularly in the leaves, resulting in a higher ratio of K+/Na+ in the leaves under salt stress. This result revealed that the improved salt tolerance of SsNHX1-overexpressing transgenic maize plants was likely attributed to SsNHX1-mediated localization of Na⁺ to vacuoles and subsequent maintenance of the cytosolic ionic balance. In addition, SsNHX1 overexpression also improved the drought tolerance of the transgenic maize plants, as rehydrated transgenic plants were restored to normal growth while WT plants did not grow normally after dehydration treatment. Therefore, based on our engineering approach, SsNHX1 represents a promising candidate gene for improving the salt and drought tolerance of maize and other crops.

   Zea nicaraguensis, a wild relative of cultivated maize (Zea mays subsp. mays), is considered to be a valuable germplasm to improve the waterlogging tolerance of cultivated maize. Use of reverse genetic-based gene cloning and function verification to discover waterlogging tolerance genes in Z. nicaraguensis is currently impractical, because little gene sequence information for Z. nicaraguensis is available in public databases. In this study, Z. nicaraguensis seedlings were subjected to simulated waterlogging stress and total RNAs were isolated from roots stressed and non-stressed controls. In total, 80 mol L^–1 Illumina 100-bp paired-end reads were generated. De novo assembly of the reads generated 81 002 final non-redundant contigs, from which 5 261 full-length transcripts were identified. Among these full-length transcripts, 3 169 had at least one Gene Ontology (GO) annotation, 2 354 received cluster of orthologous groups (COG) terms, and 1 992 were assigned a Kyoto encyclopedia of genes and genomes (KEGG) Orthology number. These sequence data represent a valuable resource for identification of Z. nicaraguensis genes involved in waterlogging response.

The physical and chemical heterogeneities of soils make the soil spectral different and complicated, and it is valuable to increase the accuracy of prediction models for soil organic matter (SOM) based on pre-classification. This experiment was conducted under a controllable environment, and different soil samples from northeast of China were measured using ASD2500 hyperspectral instrument. The results showed that there are different reflectances in different soil types. There are statistically significant correlation between SOM and reflectence at 0.05 and 0.01 levels in 550–850 nm, and all soil types get significant at 0.01 level in 650–750 nm. The results indicated that soil types of the northeast can be divided into three categories: The first category shows relatively flat and low reflectance in the entire band; the second shows that the spectral reflectance curve raises fastest in 460–610 nm band, the sharp increase in the slope, but uneven slope changes; the third category slowly uplifts in the visible band, and its slope in the visible band is obviously higher than the first category. Except for the classification by curve shapes of reflectance, principal component analysis is one more effective method to classify soil types. The first principal component includes 62.13–97.19% of spectral information and it mainly relates to the information in 560–600, 630–690 and 690–760 nm. The second mainly represents spectral information in 1 640–1 740, 2 050–2 120 and 2 200–2 300 nm. The samples with high OM are often in the left, and the others with low OM are in the right of the scatter plot (the first principal component is the horizontal axis and the second is the longitudinal axis). Soil types in northeast of China can be classified effectively by those two principles; it is also a valuable reference to other soil in other areas.

The effect of long-term straw return on crop yield, soil potassium (K) content, soil organic matter, and crop response to K from both straw and chemical K fertilizer (K2SO4) were investigated in a fixed site field experiment for winter wheat-summer maize rotation in 6 years for 12 seasons. The field experiment was located in northern part of North China Plain with a sandy soil in relatively low yield potential. Two factors, straw return and chemical K fertilizer, were studied with two levels in each factor. Field split design was employed, with two straw treatments, full straw return of previous crop (St) and no straw return, in main plots, and two chemical K fertilizer treatments, 0 and 60 kg K2O ha–1, as sub-plots. The results showed that straw return significantly increased yields of winter wheat and summer maize by 16.5 and 13.2% in average, respectively, and the positive effect of straw return to crop yield showed more effective in lower yield season. Straw return significantly increased K absorption by the crops, with significant increase in straw part. In treatment with straw return, the K content in crop straw increased by 15.9 and 21.8% in wheat and maize, respectively, compared with no straw return treatment. But, straw return had little effect on K content in grain of the crops. Straw return had significant influences on total K uptake by wheat and maize plants, with an increase of 32.7 and 30.9%, respectively. There was a significant correlation between crop yield and K uptake by the plant. To produce 100 kg grain, the wheat and maize plants absorbed 3.26 and 2.24 kg K2O, respectively. The contents of soil available K and soil organic matter were significantly affected by the straw return with an increase of 6.07 and 23.0%, respectively, compared to no straw return treatment. K2SO4 application in rate of 60 kg K2O ha–1 showed no significant effect on wheat and maize yield, K content in crop straw, total K uptake by the crops, soil available K content, and soil organic matter. The apparent K utilization rate (percentage of applied K absorbed by the crop in the season) showed difference for wheat and maize with different K sources. In wheat season, the K utilization rate from K2SO4 was higher than that from straw, while in maize season, the K utilization rate from straw was higher than that from chemical fertilizer. In the whole wheat-maize rotation system, the K absorption efficiency by the two crops from straw was higher than that from K2SO4.

Phosphorus (P) is one of the three primary macronutrients that are required in large amounts for plant growth and development. To better understand molecular mechanism of maize and identify relevant genes in response to phosphorus deficiency, we used Solexa/Illumina’s digital gene expression (DGE) technology to investigate six genome-wide expression profiles of seedling roots of the low-P tolerant maize inbred line 178. DGE studies were conducted at 6, 24 and 72 h under both phosphorus deficient and sufficient conditions. Approximately 3.93 million raw reads for each sample were sequenced and 6 816 genes exhibited significant levels of differential expressions in at least one of three time points in response to P starvation. The number of genes with increased expression increased over time from 6 to 24 h, whereas genes with decreased expression were more abundant at 72 h, suggesting a gradual response process for P deficiency at different stages. Gene annotations illustrated that most of differentially expressed genes (DEGs) are involved in different cellular and molecular processes such as environmental adaptation and carbohydrate metabolism. The expression of some known genes identified in other plants, such as those involved in root architecture, P metabolism and transport were found to be altered at least two folds, indicating that the mechanisms of molecular and morphological adaptation to P starvation are conserved in plants. This study provides insight into the general molecular mechanisms underlying plant adaptation to low-P stress and thus may facilitate molecular breeding for improving P utilization in maize.

Vitamin A deficiency has become a worldwide problem. Biofortified foods can potentially be an inexpensive, locally adaptable, and long-term solution to dietary-nutrient deficiency. In order to improve the b-carotene content in maize grain by breeding and minimize vitamin A deficiency, a complete diallel cross was designed with eight inbred lines of maize, and 64 combinations were obtained in this study. The experimental combinations were planted in Yunnan and Sichuan provinces, respectively, with a random complete block design. The b-carotene contents in the grains of the experimental materials were analyzed by high-performance liquid chromatography. Among the tested materials, the effect difference of general combining ability of the b-carotene content was significant; however, the effect difference of the special combining ability and the reciprocal effect were not significant. The b-carotene content of maize grain was not influenced significantly by the cross and the reciprocal cross. There was a significant correlation about the b-carotene content in the maize grains between the F1 and their parents. The combinations with high b-carotene content were obviously influenced by the environment, and the mean value of b-carotene content for the experimental materials planted in Ya’an of Sichuan was higher than that planted in Yuanjiang of Yunnan, with the results being significant at the 0.01 level.