Abstract
A wide range of C3 and C4 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 C3 and C4 plants. Thus, the objective was to compare varied mycorrhizal symbiotic relationship between C3 and C4 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 (C3 vs. C4) and plant functional groups, (iii) soil texture and level of salinity and (iv) experimental condition (greenhouse vs. field). Results indicate that both C3 and C4 plants under saline condition responded positively to AMF inoculation, thereby overcoming the predicted effects of symbiotic efficiency. Although C3 and C4 plants showed positive effects under low (EC < 4 ds/m) and high (>8 ds/m) saline conditions, C3 plants showed significant effects for mycorrhizal inoculation over C4 plants. Among the plant types, C4 annual and perennial plants, C4 herbs and C4 dicot had a significant effect over other counterparts. Between single and mixed AMF inoculants, single inoculants Rhizophagus irregularis had a positive effect on C3 plants whereas Funneliformis mosseae had a positive effect on C4 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 C3 and C4 plants. This influence, owing to mycorrhizal inoculation, was significantly higher in K uptake in C4 plants. For our analysis, we concluded that AMF-inoculated C4 plants showed more competitive K+ ions uptake than C3 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 C3 and C4 mycorrhizal plants under salt stress is lacking, and this needs to be explored.
Highlights
70% of the farm soils on earth are either saltaffected or subjected to salinity (Munns and Tester, 2008)
The selected publications were checked for the following inclusion criteria (i) plant biomass and nutrient uptake, (ii) crop plants, (iii) influence on arbuscular mycorrhizal fungi (AMF) inoculation compared with uninoculated control and (iv) the experiments that were performed in saline conditions, or at least an EC ≤ 4 dS/m and/or >40 mM NaCl levels
We found that AMF inoculation increased K uptake by 21.7 and 22.8% for C3 and C4 plants, respectively
Summary
70% of the farm soils on earth are either saltaffected or subjected to salinity (Munns and Tester, 2008). Plants can be divided in to three different types in terms of the way in which they use photosynthesis, C3, C4, and CAM The difference between these types is how plant uses carbon dioxide in the growth process. As described previously in detail, Zhu et al (2008) and de Bossoreille de Ribou et al (2013) reported that the conversion efficiency (from solar energy to biomass) during photosynthesis is 4.6% for C3 and 6% for C4 plants. Mane et al (2011) reported a higher shoot/root ratio at 300 mM NaCl in the C4 plant Bajra, in which plant biomass production was increased by 29.17%. Shoot and root growth of C3 plants wheat (Mohammad et al, 1998) and tomato (Datta et al, 2009) were decreased proportionately with the increase in NaCl concentration up to 125 mM. Earlier researchers (Omoto et al, 2012; Ivlev et al, 2013) have attributed this successful salttolerance effect in C4 plants to the CO2 concentrating mechanism of these plants under stress conditions
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