Abstract: Based on the interactions between life cycle strategy and plant ecological process such as interspecific competition,natural evolution,and artificial selection,it is crucial to determine the possible mechanism involving the mutual adaptation and regulation from species according to ecosystem ecology principles.The dynamics of aboveground biomass and interspecific competition under the monoculture and mixture of Astragalus adsurgens Pall.and Medicago sativa L.were investigated by the replacement series experiment in one-year field trials.The aboveground biomass and the absolute growth rate of M.sativa in monoculture were significantly higher than those of A.adsurgens and increased with the sowing density and positively correlated with the days after returning green.Among the three densities,M.sativa displayed a maximum productivity in June of 2005 irrespective of the monoculture or the mixture.M.sativa and A.adsurgens exhibited a discontinuity in interspecific competition and shared the same resources under different densities.The degree of resource share was negatively correlated with the density,which was contrary to the interspecific competition.During the entire tested periods,M.sativa showed a stronger competency than A.adsurgens under medium and high densities.Under low density,the predominant competition started from the time of returning green and increased with the development stages.The stronger competition of M.sativa in comparison to A.adsurgens was accounted by the density factors andcould be determined by the mutual promotion relationship between productivity and relative growth superiority.Therefore,the response of productivity to interspecific relationship was possibly the main characteristics in the life history of M.sativa and A.adsurgens in arid highland environments of the Loess Plateau in Northern China.

Key words: Weibei arid highland, Astragalus adsurgens Pall., Medicago sativa L., Interspecific competition, Productivity response

摘要： 大田条件下采用生态替代试验对沙打旺(Astragalus adsurgens Pall.)和紫花苜蓿(Medicago sativa L.)单播及混播的当年草地进行地上生物量动态及种间竞争的研究。结果表明:单混播苜蓿地上生物量与其绝对生长速率显著大于沙打旺,并且随播种密度升高而增大,3种密度下苜蓿单混播生产力均在2005年6月最高,其中两牧草地上生物量的累积与返青天数均呈显著正相关。不同密度处理下两牧草表现为阶段性的资源共享和资源竞争关系,随密度增大,资源共享程度降低,而资源竞争反之。但中高密度下整个生育期内苜蓿的相对竞争力均高于沙打旺,低密度在返青后开始出现种间竞争关系,随生育期变化竞争增强。混播当年苜蓿竞争力始终大于沙打旺,其中密度效应为两者种间关系调节的重要影响因素。混播中苜蓿生物量与苜蓿对沙打旺的竞争优势为性状互利关系。因此,植物生产力对物种种间关系的积极响应可能为旱生环境中植物生活史对策的重要特征。

关键词: 渭北旱塬, 紫花苜蓿, 沙打旺, 种间竞争, 生产力响应