Mycorrhizal Symbiotic Efficiency on C(3) and C(4) Plants under Salinity Stress – A Meta-Analysis

A wide range of C(3) and C(4) plant species could acclimatize and grow under the impact of salinity stress. Symbiotic relationship between plant roots and arbuscular mycorrhizal fungi (AMF) are widespread and are well known to ameliorate the influence of salinity stress on agro-ecosystem. In the present study, we sought to understand the phenomenon of variability on AMF symbiotic relationship on saline stress amelioration in C(3) and C(4) plants. Thus, the objective was to compare varied mycorrhizal symbiotic relationship between C(3) and C(4) plants in saline conditions. To accomplish the above mentioned objective, we conducted a random effects models meta-analysis across 60 published studies. An effect size was calculated as the difference in mycorrhizal responses between the AMF inoculated plants and its corresponding control under saline conditions. Responses were compared between (i) identity of AMF species and AMF inoculation, (ii) identity of host plants (C(3) vs. C(4)) and plant functional groups, (iii) soil texture and level of salinity and (iv) experimental condition (greenhouse vs. field). Results indicate that both C(3) and C(4) plants under saline condition responded positively to AMF inoculation, thereby overcoming the predicted effects of symbiotic efficiency. Although C(3) and C(4) plants showed positive effects under low (EC < 4 ds/m) and high (>8 ds/m) saline conditions, C(3) plants showed significant effects for mycorrhizal inoculation over C(4) plants. Among the plant types, C(4) annual and perennial plants, C(4) herbs and C(4) dicot had a significant effect over other counterparts. Between single and mixed AMF inoculants, single inoculants Rhizophagus irregularis had a positive effect on C(3) plants whereas Funneliformis mosseae had a positive effect on C(4) plants than other species. In all of the observed studies, mycorrhizal inoculation showed positive effects on shoot, root and total biomass, and in nitrogen, phosphorous and potassium (K) uptake. However, it showed negative effects in sodium (Na) uptake in both C(3) and C(4) plants. This influence, owing to mycorrhizal inoculation, was significantly higher in K uptake in C(4) plants. For our analysis, we concluded that AMF-inoculated C(4) plants showed more competitive K(+) ions uptake than C(3) plants. Therefore, maintenance of high cytosolic K(+)/Na(+) ratio is a key feature of plant salt tolerance. Studies on the detailed mechanism for the selective transport of K in C(3) and C(4) mycorrhizal plants under salt stress is lacking, and this needs to be explored.