Study On The Eco-physiological Characteristics And Relative Competitive Ability Of Two Native Species Under Mixture In Loess Hilly-gully Region

This study was conducted in the terrace land of loess hilly-gully region, in order to makefull use of native species for establishing artificial mixture grassland. Two native specieswhich were Bothriochloa ischaemum and Lespedeza davurica were chosen as the studymaterals. Field experiment was conducted using replacement series design in whichBothriochloa ischaemum and Lespedeza davurica were sowed at row ratios of0:10,2:8,4:6,5:5,6:4,8:2and10:0in the same plot. The photosynthetic physiological characteristics andseasonal dynamics, the above-ground biomass, soil water use efficiency and the competitionability between B. ischaemum and L. davurica in different mixed sowing ratios wereinvestigated and compared. The aims were to provid scientific theory basis for planting highyield, stable, high-quality mixed artificial grassland in Loess hilly-gully region. The mainresults are as follows:1. The diurnal changes of net photosynthetic rate of B. ischaemum presented adouble-peak pattern cure under different mixture ratios at June and September, and presenteda unimodal curve at August. The diurnal changes of net photosynthetic rate of L. davuricapresented a double-peak pattern cure at at June, while presented a unimodal curve at Augustand September. B. ischaemum at B8D2and B6D4, and L. davurica at B2D8and B6D4mixture ratios had higher daily averaged photosynthetic rate, daily averaged leaf water useefficiency, and lower daily averaged transpiration rate indicating that these two mixturesowing ratios were beneficial to improve the photosynthesis and leaf water use efficiency of B.ischaemum and L. davurica.2. The biomass increased firstly, and then decreased as the growth stage for B.ischaemum and L. davurica in monoculture or mixtures grassland, and the maximum valueappeared in September. Mixed grassland had higer biomass than monoculture grassland. TheB6D4ratio had the highest biomass, while B0D10(i.e. sole L. davurica) ratio had the lowestyearly biomass production.3. After dividing the yearly growth stage into three growth periods, i.e April-June,June-September and total growth period. The mixture grassland uniformly had higher soilwater use efficiency than the monoculture grassland. The B6D4ratio had the highest soilwater use efficiency, and B0D10ratio had the lowest soil water use efficiency.4. The seasonal aboveground biomass production dynamics of absolute growth rate (AGR) and relative growth rate (RGR) in mixture grassland indicated that: RGR peak valueappeared in July10th–August13th in all ratios, and AGR peak values in B10D0, B8D2,B6D4and B5D5ratios appeared in July10th–August13th, while for B4D6, B2D8andB0D10ratios it appeared in August13th–Spetembem15th. B6D4ratio had the fastestcommunity biomass accumulation rate while B10D0ratio had the slowest.5. The relative yield total (RYT) value during the whole growth period was significantlyhiger than1.0, indicating that B. ischaemum and L. davurica in the whole growth period couldmake the best of light, water, nutrients and other environmental resources, and presenting acomplementary relationship.Whereas the competition still existed between Bothriochloaischaemum and L. davurica, and B. ischaemum at B8D2and B6D4ratios had higercompetitive ability than L. davurica, and B. ischaemum and L. davurica had nearly equallcompetive ability at5:5ratio; while L. davurica at B2D8and B4D6ratios had higercompetive ability.6. Considering the photosynthesis rate、biomass prodtuction、soil water use efficiency、competition coefficient (AGR、RGR、RTY、CR), etc, the study pointed out that the B6D4wasthe best mixture ratio to establish B. ischaemum and L. davurica mixture grassland in terraceat semiarid loess hilly-gully region on the Loess Plateau.