| Population density is one of the selection pressures during plant growth,and plays a key role in intraspecific and interspecific competition.As a perennial herb of Gramineae,Agropyron mongolicum plays an important role in regional ecological restoration.In order to understand the response of phenotypic traits,resource allocation and physiological characteristics of A.mongolicum to density changes,a pot control experiment was conducted to study the growth parameters,leaf functional traits,root architecture,module distribution and physiological characteristics of A.mongolicum under four different sowing densities(1 plant/pot,4 plant/pot,9 plant/pot,16 plant/pot).The seeds which were collected from four different natural populations(D,Q,H and G populations)of A.mongolicum in Dashuikeng Town,Qingshan Township,Huamachi Town and Gaoshawo Town in Yanchi County in Ningxia were used as materials.To explore the response of phenotypic plasticity,resource balance and physiological characteristics of A mongolicum to density changes..The main results are as follows:(1)A.mongolicum could respond to the increase of density by changing stem diameter,leaf number,tiller number and plant height.The plant height increased with the increase of density,and of which 16 plants/pot was significantly higher than other density treatments(P<0.05).The stem diameter was the largest of 1 plant/pot from population D,which was 1.32 mm.The number of leaves and tillers decreased significantly with the increase of density,ranging from 23 to 71 and 24 to 28 respectively of 1 plant/pot,and from 22 to 24 and 8 to 12 respectively of 16 plants/pot.(2)The leaf functional traits of A.mongolicum showed a certain coordination in adapting to density changes.Leaf dry matter content,leaf length,leaf width and leaf area increased with the increase of density.Leaf thickness and specific leaf area decreased with the increase of density(P<0.05).The leaf thickness of Q population was the highest,with an average of 0.24 mm.The specific leaf area of D and G populations was higher,with an average of 187.93 cm2·g-1 and 187.32 cm2·g-1.(3)The total root length of A.mongolicum with different population sources and planting densities ranged from 663.14 mm to 1379.94 mm.The root surface area,total root volume and average root diameter decreased with the increase of density,and were significantly higher of 1 plant/pot than those of 16 plant/pot(P<0.05).For 16 plants/pot,A.mongolicum from various populations had larger specific root length.There was no obvious regularity in the change of root tip number with density.From the perspective of population sources,the specific root length of G population was the highest,with an average of 1442.59 cm·g-1.The average root diameter of Q population was the highest,and the number of root tips was the lowest,which were 0.57 mm and 4140.50,respectively.(4)The total biomass and the biomass accumulation of each component of A.mongolicum showed density-dependent effects.The total individual biomass was the largest with 1 plant/pot.Different population sources showed H>D>Q>G,with an average of 3.42 g,3.39 g,3.00 g and 2.81 g,respectively.With the increase of density,A.mongolicum could respond to density changes by reducing root biomass allocation,decreasing root-shoot ratio,and increasing the allocation ratio of stem and leaf biomass to respond to increased density.(5)There were significant differences in sucrose,chlorophyll B and starch contents among different populations of A.mongolicum.The sucrose content increased first and then decreased with the increase of planting density.The highest sucrose content was found in D and H populations of 9 plants/pot,with an average of 2.29 g·kg-1 and 1.51 g·kg-1,which was significantly higher than that of 1 plant/pot.The content of chlorophyll B from D and Q populations changed greatly with the increase of density,and 16 plants/pot were the highest or the second highest,with an average of 0.82 g·kg-1 and 0.72 g·kg-1,which were significantly higher than that of 1 plant/pot.The starch content in D,Q and H populations of 1 plant/pot was significantly higher than that of 9 plant/pot.The content of malondialdehyde decreased significantly with the increase of density in Q and G populations.The soluble sugar content of D population was the highest with the density of 4 plants/pot and 9 plants/pot;there was no obvious change law in superoxide dismutase activity.The nitrate reductase activity was the lowest at 1 plant/pot.(6)Based on the results of correlation analysis,16 indexes of phenotypic traits,component allocation and physiological characteristics of A.mongolicum were selected for redundancy analysis.Six factors(leaf area,root average diameter,leaf width,root surface area,specific root length and root allocation ratio)had extremely significant or significant effects on the growth of A.mongolicum t(P<0.01 or P<0.05).These indexes were the key traits of A.mongolicum growth status in response to density changes.In summary,phenotypic plasticity,resource allocation and physiological characteristics of A.mongolicum had a certain response to density changes.With the increase of density,the larger and thinner leaves of A.mongolicum could be formed,and the accumulation of individual biomass was limited.The number of tillers,root surface area,total root volume and average root diameter decreased,the input of stem and leaf resources increased,and the activity of nitrate reductase increased. |
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