Microbiological Research 183 (2016) 26–41 Contents lists available at ScienceDirect Microbiological Research j ournal homepage: www.elsevier.com/locate/micres Bacteria and fungi can contribute to nutrients bioavailability and aggregate formation in degraded soils a,d,∗ a e Muhammad Imtiaz Rashid , Liyakat Hamid Mujawar , Tanvir Shahzad , a,b a,c a Talal Almeelbi , Iqbal M.I. Ismail , Mohammad Oves a Center of Excellence in Environmental Studies, King Abdulaziz University, P.O Box 80216, Jeddah 21589, Saudi Arabia b Department of Environmental Sciences, King Abdulaziz University, Jeddah 2158, Saudi Arabia c Department of Chemistry, King Abdulaziz University, Jeddah 2158, Saudi Arabia d Department of Environmental Sciences, COMSATS Institute of Information Technology, 61100, Vehari, Pakistan e Department of Environmental Sciences & Engineering, Government College University, 38000, Faisalabad, Pakistan a r t i c l e i n f o a b s t r a c t Article history: Intensive agricultural practices and cultivation of exhaustive crops has deteriorated soil fertility and its Received 13 October 2015 quality in agroecosystems. According to an estimate, such practices will convert 30% of the total world Received in revised form cultivated soil into degraded land by 2020. Soil structure and fertility loss are one of the main causes 16 November 2015 of soil degradation. They are also considered as a major threat to crop production and food security for Accepted 21 November 2015 future generations. Implementing safe and environmental friendly technology would be viable solution Available online 25 November 2015 for achieving sustainable restoration of degraded soils. Bacterial and fungal inocula have a potential to reinstate the fertility of degraded land through various processes. These microorganisms increase the Keywords: nutrient bioavailability through nitrogen fixation and mobilization of key nutrients (phosphorus, potas- Degraded land sium and iron) to the crop plants while remediate soil structure by improving its aggregation and stability. Food security Microbial inocula Success rate of such inocula under field conditions depends on their antagonistic or synergistic interac- Nutrient bioavailability tion with indigenous microbes or their inoculation with organic fertilizers. Co-inoculation of bacteria and Soil fertility fungi with or without organic fertilizer are more beneficial for reinstating the soil fertility and organic Siderophores matter content than single inoculum. Such factors are of great importance when considering bacteria Soil aggregation and fungi inocula for restoration of degraded soils. The overview of presented mechanisms and interac- tions will help agriculturists in planning sustainable management strategy for reinstating the fertility of degraded soil and assist them in reducing the negative impact of artificial fertilizers on our environment. © 2015 Elsevier GmbH. All rights reserved. Contents 1. Introduction . 27 2. Reinstating fertility of degraded soils . 28 2.1. Microbial inocula and soil nutrient bioavailability . 29 2.1.1. Nitrogen fixation . 29 2.1.2. N2 fixation in degraded land . 29 3. Mechanisms used by microbes to reinstate the fertility of degraded soils . 29 3.1. Fungi and N2 fixation . 29 3.1.1. How do fungi influence N2 fixation? . 30 3.2. Phosphorus mobilization. .30 3.3. Potassium. .31 ∗ Corresponding author at: King Abdulaziz University, Center of Excellence in Environmental Studies, P.O Box 80216, Jeddah 21589, Saudi Arabia. Fax: +966 12 6951674. E-mail addresses: [email protected] (M.I. Rashid), [email protected] (M. Oves). http://dx.doi.org/10.1016/j.micres.2015.11.007 0944-5013/© 2015 Elsevier GmbH. All rights reserved. M.I. Rashid et al. / Microbiological Research 183 (2016) 26–41 27 3.3.1. Fungi and K mobilization . 31 3.3.2. How do bacterial and fungal inocula increase K mobilization? . 31 3.4. Role of bacteria in Fe mobilization . 31 3.5. Interaction between bacteria and fungi inocula to improve nutrient bioavailability in soil . 33 4. Soil structure . 33 4.1. Bacteria and soil aggregation . 34 4.2. Fungi and soil aggregation . 34 4.2.1. How do fungi influence soil aggregation? Mechanism . 35 4.3. Interaction between fungi and bacteria to improve soil aggregation and their stability . 35 5. Organic amendments to reinstate soil fertility . 36 5.1. Bacterial and fungal inocula to reinstate the fertility of degraded land . 36 5.2. Application of bacterial and fungal inocula with organic amendments to reinstate the fertility of degraded land . 36 5.3. Gaps in current approaches and way forward to restore the degraded land. .37 6. Future considerations . 37 7. Conclusions . 37 Acknowledgments . 37 References . 38 1. Introduction in many parts of the world. Therefore, efforts are necessary to fig- ure out alternative, innovative, environmental friendly options to The global human population is increasing continuously, that reduce the use of costly and non-environmental friendly chem- has propelled up to 7 billion at present (Godfray et al., 2010; Glick, ical fertilizers. In this context, microbes (i.e., bacteria and fungi) 2015). At this projected growth rate, the world population will rise naturally occurring in soil or supplied as bio-fertilizers, could rep- to about 9.5 billion by 2050, thus exerting immense pressure on resent a promising approach to increase nutrients bioavailability food supplies (Glick, 2015). According to FAO (2009), the global food and improve soil structure. demands in coming decades will raise by 70%, which will enhance Bacterial and fungal inocula and.