植株密度和氮素互作对垂穗披碱草生物量分配的影响

垂穗披碱草（Elymus nutans）是高寒地区建植和改良栽培草地的首选草种。虽然合理植株密度和氮素添加量是垂穗披碱草栽培草地稳产的关键因子，但两者之间是否存在最佳互作组合仍不清楚。采用盆栽试验，通过分析不同植株密度（58、102、146株/m²）和氮素添加量（0、200、400 mg/kg）组合状态下垂穗披碱草株高、单株分蘖数、地上生物量、地下生物量、根系体积和地上地下生物量比，以确定理论上是否存在植株密度和氮素添加量的最佳组合。结果表明：随植株密度增加，垂穗披碱草株高、地上生物量和地上地下生物量比值均先增加后降低，而单株分蘖数逐渐减小，根系体积和地下生物量先增加后保持相对稳定；随氮素添加量增加，垂穗披碱草单株分蘖数、地上生物量和地上地下生物量比值均表现为先增加后降低，地下生物量逐渐降低。植株密度与氮素添加量互作虽然对垂穗披碱草的根系体积和单株分蘖数没有显著影响，但两者互作显著影响了垂穗披碱草株高、地上生物量、地下生物量、地上地下生物量比（P<0.01），这些指标与植株密度和氮素添加量的关系均表现为一个开口向下的抛物面。当植株密度为102株/m²和氮素添加量为200 mg/kg时，垂穗披碱草栽培草地产量最大，生物量分配最优。垂穗披碱草植株密度和氮素添加互作时理论上存在最佳组合，这为垂穗披碱草栽培草地的田间管理提供了理论依据。

Effects of interaction between plant density and nitrogen application rate on allocation of above/underground biomass of Elymus nutans

Elymus nutans is the prior crop to establish the pasture or improve the pasture in the alpine regions because it is cold-resistant tolerance with good quality. Although proper plant density and nitrogen application rate are conserved as the key factors to affect the yield stability of Elymus nutans pasture, whether there is an optimally theoretical combination of plant density and nitrogen application rate for maintaining the relative yield of Elymus nutans is not well documented. A pot experiment was conducted in a greenhouse to investigate the effect of different combination of plant densities and nitrogen application rates on the plant height, tiller per plant, aboveground biomass, underground biomass, root volume and aboveground to underground biomass ratio, which can be used to identify an optimally theoretical combination between plant density and nitrogen application rate. In this study, the plant densities consisted of 58, 102, 146 plants per square meter and nitrogen application rate was 0, 200, 400 mg/kg. This study showed that with the increase of plant density, the plant height, aboveground biomass and aboveground to underground biomass ratio of Elymus nutans increased first and then decreased, while the tiller per plant decreased gradually, the root volume and underground biomass increased first and then remained relatively stable. The tiller per plant, aboveground biomass and aboveground to underground biomass ratio of Elymus nutans increased first and then decreased with the increase of nitrogen application rates, and the underground biomass decreased gradually. Interaction between plant densities and nitrogen application rates was found to had no effect on root volume and tiller per plant, whereas it was observed to have significant effects on the plant height, aboveground biomass, underground biomass, and the aboveground to underground biomass ratio. The relationships between above-mentioned parameters (plant height, aboveground biomass, underground biomass, and the aboveground to underground biomass ratio) and nitrogen application rate and plant density showed the downward 3D response surfaces, and this demonstrated that there was an optimally theoretical combination between proper plant density and nitrogen application rate, under which plant height, aboveground biomass, underground biomass, and the aboveground to underground biomass ratio were the best. In this study, the optimal combination of plant density and nitrogen application rate were 102 plants per square meter and the nitrogen application rate was 200 mg/kg. The findings of this study suggest that there is an optimally theoretical combination of plant density and nitrogen application rate for maintaining the relative yield of Elymus nutans pasture, which can provide a scientific basis for high persistence yield and optimal allocation of above/underground biomass of Elymus nutans pasture in the field management.