Growth And Physiological Response To Soil Water Change Of Two Native Species In Loess Hilly-gully Region Under Intercropping

The semiarid loess hilly region is the typical environmental fragile area on the Loess Plateauof China. Drought and littled rain are the main factors that affect the structure and function ofnatural ecosystem in the area. The response of natural vegetation ecosystem to soil waterchange dependent on the adaptability of dominant species in the community. To clarify thephysiological and ecological adaptability of dominant species to soil water change willprovide theoretical basis for re-vegetation purposes and ecological restoration in the regions.Two native dominant species, Bothriochloa ischaemum and Lespedeza davurica in the loesshill-gully area were used under potted condition. The effects of soil water change on thephysiological process, biomass allocation, water use efficiency and relative competitiveability of two native species were investigated. Our aim are to identify the co-existence andcompetition mechanisms of both co-occurring species based on their eco-physiologycharacteristics under lower water availability, and eventually to find appropriate measures forusing them in practice. A replacement series design method was used at a density of12plantsper pot, and seven sowing ratios of B. ischaemum to L. davurica of0:12,2:10,4:8,6:6,8:4,10:2and12:0. The response of the species to their mutual presence at the different ratioswater evaluated at the three soil water regimes [80%±5%FC (field capacity)(HW),60%±5%FC (MW) and40%±5%FC (LW)]. Besides, at the three main growth periods (budding,flowering and grain filling stage), soil water contents were improved in2012, while the soilwater regimes were corresponding reduced in2013. The leaf chlorophyll fluorescence,photosynthetic gas exchange, biomass allocation, water use efficiency and relativecompetitive ability of two native species were determined during each experiment. The mainresults were as follows:(1) Non-photochemical quenching values (NPQ) of B. ischaemum were significantlyhigher than those of L. davurica, but the maximum relative electron transport rate (rETRmax)and minimum saturating irradiance (Ik) values of B. ischaemum were significantly lower thanL. davurica under each water regime. Under HW and MW regimes, the averaged maximumphotochemical efficiency (Fv/Fm) values of B. ischaemum in mixtures at the HP weresignificantly higher than in monoculture, and the mean rETRmaxvalues of B. ischaemumduring the HP and FP in mixtures were significantly higher than in monoculture. During the MP, the averaged Fv/Fm values of L. davurica in mixtures was significantly higher than inmonoculture under the HW regime, and the mean rETRmaxvalues of L. davurica in mixtureswere significantly higher than in monoculture under each water regime.(2) During each growth period, the averaged PNvalues of B. ischaemum in mixtures weresignificantly higher than in monoculture under each water regime, but the averaged PNvaluesfor L. davurica in mixtures were significantly lower than in monoculture under the HWregime, while these value of L. davurica in the MP was significantly higher than inmonoculture under MW or LW regimes. Mixture planting improved the photosyntheticperformances of both species depending on their developmental stage of the component plant,i.e, B. ischaemum showed the maximal photosynthetic capacity in the HP or FP while L.davurica in the MP under water stress.(3) Soil water change significantly affected the biomass production of B. ischaemum andL. davurica under different mixture ratios, especially for both species at the heading periods,and the fomer species was more sensitive to soil water change than the latter species. In mosttreantments, the highest total biomass production was obtained when grown at10:2B.ischaemum:L. davurica mixture proportion.(4) Under soil water unchanged conditions, the significantly higher water use efficiency(WUE) of both species was obtained when grown at10:2B. ischaemum:L. davurica mixtureproportion; WUE of B. ischaemum and L. davurica were improved under soil water decreasedconditions, while those values has been reduced by soil water incressed treatments.(5) Under most treamtments, relative yield total (RYT) values were all greater than1.0,and the aggressivity (A) of B. ischaemu were bigger than zero, indicating partial resourdecomplementarity between both species and the competion ability of B. ischaemu was strongerthan L. davurica; Relative competition intensity (RCI) of B. ischaemu were bigger than zero,and RCI of L. davurica were saller than zero, indicating that intraspecific competion wasmore higher while the interspecific competion of L. davurica was more higher; water stressdecreased the competions ability of B. ischaemu while increased that of L. davurica.In summary, it is advantageous to grow the two species to accelerate vegetationestablishment in the semiarid Loess Plateau, and the recommended mixture raio was10:2of B.ischaemum and L. davurica. In addtions, water supplyment could effectively improve the totalbiomass production and water use effiency before the flowering period of both species.