Microbial Biomass Responses to Soil Drying-Rewetting and Phosphorus Leaching

Abstract

Soil drying-rewetting is known to enhance soil phosphorus leaching, which in part is due to osmotic shock and lysis of microbial cells upon rewetting. However, it is not entirely clear how this may be influenced by the intensity and duration of soil drying. We hypothesized that the intensity and duration of soil drying play important roles in determining the extent of dissolved reactive phosphorus (DRP) leaching resulting from microbial biomass mortality. To test this hypothesis soil sub-samples of a loamy grassland soil were dried (30 or 40 • C for 2 or 14-days), rewetted, and the leachate was analyzed for DRP. Soil drying at 30 • C for 2 and 14-days resulted in leachate DRP concentrations which were 71 and 271%, respectively, higher than those in leachate from a control moist counterpart. Relatively greater DRP leaching losses occurred from the soil dried at 40 • C for 2 and 14-days (143 and 300%, respectively). To determine the contribution of the microbial biomass to the DRP in leachate, soil sub-samples were fumigated with chloroform either before or after drying (30 or 40 • C for 2 or 14-days). All soil treatments were then either leached with water and analyzed for DRP or extracted with 0.5 M sodium bicarbonate solution and analyzed for microbial biomass phosphorus. Fumigating soil samples before or after drying reduced microbial biomass phosphorus. However, the effect of chloroform fumigation was more pronounced in terms of microbial biomass reduction in the DF (drying followed by fumigation) treatment. Moreover, results revealed that in the DF treatment, soils dried at 30 • C for 2-days and 14-days had 22 and 13%, respectively, more microbial biomass phosphorus than their counterparts dried at 40 • C for 2 and 14-days, respectively. These results suggest that soil drying at higher intensity and for prolonged periods significantly (p < 0.05) affect microbial biomass and subsequently increases soil phosphorus leaching following rewetting, due to enhanced contributions from the microbial biomass. These findings, however, need to be verified over a range of soil types under natural field conditions to better assess soil drying-rewetting effects on nutrient leaching.

Short-term soil drying–rewetting effects on respiration rate and microbial biomass carbon and phosphorus in a 60-year paddy soil

“…Therefore, in these conditions, moisture stress is not affected by the short-term drying stress. Also, our results are consistent with the results of Butterly et al (2011) and Venterink et al (2002), but not with those of Sun et al (2018), Chen et al (2016), and Khan et al (2019). Soil respiration and biomass activity are enhanced by drying-rewetting cycles, because dead microorganisms release intra-cellular osmolytes due to the change in water pressure, fracture of soil aggregates, and uncoupling of enzymatic activity from cellular respiration (Moyano et al 2013).…”

Phosphorus Leaching From Naturally Structured Forest Soils Is More Affected by Soil Properties Than by Drying and Rewetting

“…MRP showed a tendency to increase after more intense desiccation, especially above pF 4. This is in agreement with the results of Khan et al (2019), who observed increased leaching of dissolved inorganic P when soils were more desiccated prior to rewetting. Our results partially agree with findings of Brödlin et al (2019), who observed (in organic and topsoil material from LUE and BBR) a considerably greater mobilization of inorganic, but also organic P after an initiate harsh dry spell (drying at 40 • C for 72 h) compared to a subsequent moderate one (drying at 20 • C for one month).…”

“…Apart from the magnitude of desiccation (i.e., the achieved matric potential), the established drying phase in our experiment was possibly too short to induce a substantial release of P from microbial cell lysis. For example, Khan et al (2019) found that after an intensive drying period of 14 days, rewetting released significantly more microbially derived P from soils than after two days of intensive drying. Lower survival of bacteria with increasing desiccation time was also observed by Meisner et al (2015Meisner et al ( , 2017, while fungi probably survived desiccation better (Schimel, 2018).…”

“…Microbial cell lysis has been found to enhance leaching mainly of organic P (Turner and Haygarth, 2001;Blackwell et al, 2009). However, also the leaching of inorganic P has been associated with cell lysis (Brödlin et al, 2019;Khan et al, 2019), possibly due to the rapid mineralization of released organic compounds rich in P (Annaheim et al, 2013;Dinh et al, 2016). Apart from biotic processes, abiotic processes may release both organic and inorganic P upon DRW.…”

Phosphate-Solubilizing Microorganisms: Mechanism and Their Role in Phosphate Solubilization and Uptake

“…Investigation showed that soil drying with subsequent fumigation for a varied number of days, i.e., for 2 and 14 days at 40°C resulted in a decline in microbial biomass phosphorus by 61 and 70%, respectively. This finding proposed the correlation between soil drying, the mortality of microbial cells, and microbial biomass phosphorus, indicating the indirect mode of microbial contribution to available phosphorus in soil (Khan et al 2019b).…”