Abstract
The issue of how to alleviate the negative effects imposed by water stress is an interesting problem. Plant growth-promoting rhizobacteria (PGPR) colonize the rhizosphere of plants and are known to promote the growth of crops. However, there are few studies characterizing the physiological response of plants to drought stress after PGPR inoculation. The aim of this study was to investigate the effectiveness of different PGPRs in arid environments and then investigated the effects of PGPR inoculation under drought stress on the physiological characteristics and growth of North China red elder (Sambucus williamsii) nursery container seedlings. The viable count of different PGPRs under drought stress varies widely, and the drought tolerance of Acinetobacter calcoaceticus X128 was significantly higher than that of other PGPRs. In comparison with non-inoculation, inoculation with X128 in an arid environment significantly increased stomatal conductance and mitigated the inhibition of net photosynthetic rate caused by drought stress; this mitigating effect of inoculation is enhanced as the level of drought stress increases. Relative to non-inoculated seedlings, cytokinin levels in the leaves increased by 91.17% under severe drought stress conditions in inoculated seedlings. However, X128 inoculation decreased this deficit to only 44.54%. Compared with non-inoculated seedlings, the relative water content of inoculated seedlings under severe drought stress increased by 15.06%, however the relative conductivity decreased by 12.48%. Consequently, X128 could increase dry matter accumulation of S. williamsii regardless of watering status, indicative of the greater benefits of PGPR on shoot growth than root. Therefore, inoculation of A. calcoaceticus X128 under drought conditions play a significant role for alleviating the negative effects imposed by water stress and promoting plant growth.
Highlights
Drought stress is among the most destructive abiotic stresses that increased in intensity over the past decades affecting world’s food security [1] and may range from moderate and short to extremely severe and prolonged duration, restricting the crop yields [2]
The effective viable counts of SC2, Z77, and T026 (GE3) were nearly 0 at days 19, 21, and 24 of drought, respectively, and the effective viable count of X128 in the nursery substrate was still 417 CFU g-1 on day 25 of drought stress. This shows that different plant growth-promoting rhizobacteria’ (PGPR) have very different drought resistances, and that the drought tolerance of X128 is higher than the drought tolerance of the other strains
Compared with the corresponding well-watered seedlings, photosynthetic rate (Pn) decreased by 22.16% and gs decreased by 39.02% for the non-inoculated seedlings under severe drought stress, and Pn decreased by 14.40% and gs decreased by 25.53% for the inoculated seedlings under severe drought stress
Summary
Drought stress is among the most destructive abiotic stresses that increased in intensity over the past decades affecting world’s food security [1] and may range from moderate and short to extremely severe and prolonged duration, restricting the crop yields [2]. Studies have shown that inoculation of Bacillus amyloliquefaciens 5113 under drought stress can promote dry matter accumulation in wheat and increase wheat yield [4]. A study by Mayaka et al (2004) found that Achromobacter piechaudii ARV8 producing ACC-deaminase could not inhibit the decrease in the relative water content of tomato and pepper leaves under drought stress, but did promote the rapid recovery of relative water content after rehydration [26]. These studies have shown that the action of PGPR is close ly associated with plant drought
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