Glomalin related protein and C16:1ω5 PLFA associated with AM fungi as potential signatures for assessing the soil C sequestration under contrasting soil management practices

Arbuscular mycorrhizal fungi (AMF) contribute to the sequestration of soil organic carbon (SOC) by glomalin production through their hyphal network which helps to bind soil aggregates and improve other physical and biological properties of soil. The current study was aimed to assess (i) AMF biomass, glomalin related protein (GRP), SOC stocks and soil quality parameters such as microbial biomass carbon (MBC) and 13-glucosidase activity, and (ii) to find out whether GRP production and PLFA C16:1m5 can be used as consistent indicators of soil quality across seven different rhizosphere soil niches such as zero-tillage with Cenchrus ciliaris and minimum tillage with Chloris barbata; conventional tillage with soybean-wheat system from soybean rhizosphere and raised beds with four mycorrhizal host plants (Fenugreek, maize, marigold and sorghum). Among all the soil niches, AMF biomass, the content of SOC, MBC, soil and root GRP, the activity of 13-glucosidase were significantly higher under zero tillage. The AMF biomass, SOC-sequestration and soil quality parameters established a common trend across all the soil management systems and hosts examined. PLFA C16:1m5 was positively correlated with microscopic estimates of AMF biomass, MBC, 13-glucosidase activity and both the fractions of total (T) GRP (the easily extractable and difficulty extractable) in soil and roots. A significant positive correlation of both the fractions of soil-GRP with MBC (r = 0.78**, 0.83**) and 13-glucosidase activity (r = 0.86**, 0.76**) was also found. In general, soil T-GRP (r = 0.93**), soil T-GRP stocks (0.94**) and PLFA C16:1m5 (r = 0.68**) were highly related to SOC stocks. These findings confirm that zero tillage and raised beds favour AMF activity thus improving SOC sequestration potential and soil quality which can be assessed using GRP and PLFA C16:1m5 as potential indicators.