Effects of microbial fertilizer and irrigation amount on growth, physiology and water use efficiency of tomato in greenhouse

•Adding microbial fertilizers relieve drought stress on tomato.•Microbial fertilizers improve the growth, physiology and nitrogen use efficiency.•Microbial fertilizers influence the nitrogen uptake of tomato plant.•Bacillus subtilis fertilizer combined with moderate irrigation is optimal. A pot experiment was conducted to investigate the effect of microbial fertilizer and irrigation regime on growth, physiology, water use efficiency (WUE) of tomato plants and soil nutrients. Microbial fertilizers: bacillus subtilis fertilizer (B.s.), bacillus polymyxa fertilizer (B.p.) and combined bacillus species (B.c.) were used as microbial fertilizers in the study, and plants treated without bacillus fertilizer were taken as control (CK). Three irrigation levels were set, i.e., full irrigation (I1) which plants were irrigated to 95 % field capacity (θf), and two deficit irrigations which were 2/3 I1 (I2) and 1/3 I1 (I3), respectively. The result showed that microbial fertilizers enhanced leaf photosynthesis rate (An), transpiration rate (Tr), relative chlorophyll content (CHL), nitrogen index balance (NBI) and leaf water potential (Ψl) in addition to increased plant root length, root surface area, root volume; and promoted plant water consumption, dry matter (DM) and plant water use efficiency (WUE). The content of nitrogen in leaf ([N]leaf), nitrogen use efficiency (NUE), the mineral nitrogen and soil microbial nitrogen content (MBN) were significantly improved by microbial fertilizer. Compared to CK, B.s., B.p. and B.c. increased An by 17.96 %, 11.77 % and 6.83 %, respectively. B.s. fertilizer significantly increased MBN and root length by 21.99 % and 55.08 % than CK. Deficit irrigations decreased An, Tr, stomatal conductance (gs), and improved intrinsic water use efficiency (WUEi) and instantaneous water use efficiency (WUEinst). Deficit irrigation depressed leaf area, Ψl, CHL, NBI, root length, root surface area and root volume, hereby declined plant water consumption, and optimized plant WUE. In this study, microbial fertilizers mitigated negative effects of deficit irrigation on photosynthesis and DM and improved WUE. Compare to CK and other microbial fertilizers, B.s fertilizer treated plants possessed enhanced plant water status, higher leaf gas exchange rates, more developed root system, higher plant nitrogen accumulation and NUE. Hereby, the B.s. fertilizer is an optimal strategy to mitigate water stress in tomato plants and promoted plants growth.