| Leymus chinensis (Trin.), also called Tzvel, is an important rhizomatous, perennial grass that widely distributed in the northeast of China. It is tolerant to saline-alkali soils, cold extremes, and drought conditions, but also has high forage value and good palatability, making the grass ideal for rangeland use in arid and semiarid regions. However, under native conditions, the sexual reproductive capability of L. chinensis is poor. The low seed yield constrains new stand establishment for herb's production and ecological construction. A randomized complete block design with a spilt was used to examine the effects of different nitrogen (N) application time (i.e., double-ridge stage, spikelet initiation stage, and later seed-filling stage in spring) and rates (equal to 0, 27.6, 55.2 kg ha~-1 pure nitrogen) on yield components, potential seed yield (PSY), and seed yield (SY) during 2005 to 2007. Later, the same designed experiment was conducted to examine the effects of different treatment time (grain filled stage, mid vegetative growing stage, and end of growing season), water regimes (equal to 0, 17 mm, and 34 mm precipitation), and nitrogen application rates (equal to 0, 27.6, 55.2 kg ha~-1 pure nitrogen) on yield component and seed yield during 2008 to 2010. Meanwhile, we experimentally investigated the response of bud bank, clonal growth, and physiological ecology traits to different N rate, drought regimes, and warming through potted Leymus chinensis in a phytotron. The results showed that:(1) Yield components of L. chinensis, were decided over two growing seasons: spike number (SN) is independent on N application time and rate in heading year, it only influenced by experimental year; but SNS and TSW appear dependent on N management and precipitation in the current year. SN is the most important component to seed yield in L. chinensis, the importance of seed number per spike (SNS) and thousand seeds weight (TSW) is less than SN. In this experiment, the largest increase of seed yield was occurred when applied 55.2 kg pure nitrogen per ha at double-ridge stage.(2) Water and N application during grain filled stage was significantly increased the spike number and total density per square meter in following year, meanwhile, the capacity of unit vegetative shoot bear reproductive shoots number also increased. The same treatment applied during the end of growing season can improve the fertility florets per spike, and has the positive effects on SNS and TSW in following year. Among the yield components, the increase of SN was higher than SNS and TSW when water and applied N during the after grain filled stage. When compared to the effect of water on yield component and seed yield, the N application has more significantly effect on it; the seed yield increased more than 6 times when applied 55.2 kg pure nitrogen per ha at grain filled stage that compared to the control. Thus, aim to improve the seed yield in production, we recommend a valuable managing methods that firstly application N at the grain filled stage in the last growing season, and then applies N at double ridge stage in the current year. However, a half of potential seed yield is still not realized.Water and N application can significantly improve the daughter shoot number per square meter; however, the effects of N application on daughter shoot number were better than waters. The daughter shoot number of high leaf age has the greater increase than low leaf age in early time treatment, but in latest treatment has the opposite effect. The daughter shoot was product in autumn all has the heading capacity in following year, and independent with the leaf age. These results suggested that the heading capacity of daughter shoot not related to the development statues of daughter shoot in autumn, it may be only correlated with the survives in winter, that is, adequate soil moisture and low temperature is favorable to daughter shoots survive and heading in following year, but the extreme drought conditions.(3) Nitrogen application significantly increased the aboveground biomass, belowground biomass, the number of total daughter shoot and bud. Importantly, the proportions of daughter apical rhizome shoot to total daughter shoot was significantly increased, which the primary reason lead to the number of total daughter shoot increase; in the case of changed organs of belowground, the N application significantly increased the total bud number, and Secondary rhizome number and length, these changes all related with the axillary rhizome buds. At the mean time, the leaf photosynthetic ability significantly increased, and lead to the plant allocated more energy to aboveground organs growth. This selective growth strategy advantages to reproduction and occupy more resource.Both moderate and severe drought regimes were reduced the clonal growth ability, including the daughter shoot number and aboveground biomass, belowground bud number and biomass, especially in severely drought conditions (SD). SD significantly decreased the number of daughter apical rhizome shoot and axillary shoot bud, finally lead to the proportions of it reduced. As for the bud bank, the horizontal rhizome buds increased in number under moderate drought (MD) condition, as well as SD. The root:shoot ratio also increased, which shows the L. chinensis will reduced the parent shoot biomass, the daughter shoot number and weight, and relatively increased the energy allocate proportions to belowground organs to adopt different drought regimes. Warming significantly decreased the biomass of both parent and daughter shoots, slightly increased the belowground biomass, and lead to a significant increase in root:shoot ratio. Warming reduced the aboveground biomass due to decreases in both parent and daughter shoot biomass; the parent shoot biomass decrease was apparently caused by the reduced photosynthetic ability, but the daughter shoot biomass decrease was caused by the decreased the daughter shoot number. Warming reduced the daughter rhizome shoots number, which led to the decreased total daughter shoots number; meanwhile, the increased horizontal apical rhizome buds number led to the total bud number increased. These results indicate that, as a rhizomatous, perennial grass, L. chinensis to reduce the energy allocated to its aboveground biomass by instead diverting it into developing belowground organs including enhance the rhizome number and length, bud number, resulting in an unbalanced growth strategy It implied the increases of population density will constrained in warming conditions.From the perspective of daughter shoot number that produce in autumn influence the spike number in following year, N application had advantages to increases in spike number, but drought and warming had disadvantages. Inevitably, these factors will enhance or reduce the seed yield per unit area of L. chinensis.We found the importance of some effective regulate methods to improve the yield components and seed yield during two growing seasons based nitrogen application and waters. In practice, these optimum and simple methods can substantially increase the seed yield of L. chinensis. Additionally, a retrospective study was conducted in a controlled phytotron to explain the primary reason of N, water, and temperature affects on seed production through potted L. chinensis. These results are important for improving the seed yields of L. chinensis, can also provide clues for other rhizomatous, perennial grass in practice.
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