Abstract
Two incubation experiments were carried out to determine the impact of salinity on microbial activity and biomass when organic carbon is supplied as different proportions of glucose and cellulose or when glucose and cellulose were added every 2 weeks in different order. The first experiment was conducted with a non-saline soil and two saline soils (ECe 11 and 43 dS m-1) amended with 5 g C kg-1 as different percentages of glucose and cellulose: glucose: 100% and 0-20% and cellulose: 0-100%. In the second experiment a non-saline loamy sand soil was used which was salinized to ECe 12.5 and 37.4 dS m-1. The C form was maintained or changed over time by addition of 1.5 g C kg-1 every two weeks as glucose or cellulose. In Experiment 1, mixing glucose with cellulose increased cumulative respiration compared to cellulose alone. Cumulative respiration increased with increasing proportion of glucose in the combined treatments with glucose >2.5%.With 100% glucose, cumulative respiration was significantly lower than in the non-saline soil only in EC43. But with 100% cellulose and all combined treatments, cumulative respiration was significantly lower than in the non-saline soil in EC11 and EC43. Cumulative respiration did not differ between EC11 and EC43 with 100% cellulose but decreased significantly in the mixed treatments except with 10% glucose. In Experiment 2, cumulative respiration in the first period (0-14) was always higher with glucose than with cellulose; it decreased with increasing EC. The impact of salinity was smaller when C was added repeatedly compared to a single addition. Cumulative respiration increased when glucose was added after cellulose addition. In conclusion, mixing small amounts of glucose with cellulose could make microbes more sensitive to salinity compared to 100% cellulose. Further, maintaining high C availability with repeated C addition reduces the negative impact of salinity on soil microbes.
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