Abstract: In this study,horizontally segmented soil columns were sampled to simulate field situation,and to investigate the behavior of non hydraulic root signals and its effect on spring wheat yield under definite water deficiency.Three spring wheat cultivars (A,B,C) were tested in the experiment with three watering treatments:well watered (CT),limited watered from upper soil layer (DIu) and limited watered from deeper soil layer (DId).During 17～28 days after emergence (DAE),the stomatal conductance and transpiration rate in treatments DIu and DId were reduced significantly without any apparent change in leaf water potential,indicating the typical non hydraulic root signals,and the leaf water potentials differed significantly with treatment CTover time. Among the three cultivars,the upper root system of cultivar Bhad a higher SRW (specific root weight) at 34 and 54 DAE and a higher biomass at 54 DAEthan cultivars Aand C,which is favorable to cultivar Bfor its high yield. Comparing with cultivars Aand B,cultivar Chad a higher proportion of total root biomass and total root length in upper root layer in treatment DIu at 34 and 54 DAE,and a relatively smaller proportion in middle root layer. In treatment DId,the allocation pattern of root systems of three cultivars was contrary to that in treatment DIu. It is suggested that cultivar Cwas more sensitive to topsoil moisture and more plastic on root allocation than cultivars Aand B, which also reflected its higher sensitivity to root signals. Cultivars A and B had a relatively poor plasticity of roots,but had a significantly higher grain yield than cultivar C.

Key words: Drought, Spring wheat, Root signals, Stomatal conductance, Yield, ammonia-oxidizing bacteria (AOB), acidic forest soil, ammonia-oxidizing archaea (AOA), N cycling