Changes in arbuscular mycorrhiza fungi spore density and root colonization of woody plants in response to exclosure age and slope position in the highlands of Tigray, Northern Ethiopia
Introduction
The idea of exclosure involves a protection system, exclusion of the degrading agent, to allow the lands to re-establish itself through natural succession process. Exclosures are areas that exclude human and livestock interference for rehabilitation of degraded lands in the drylands (Seyoum et al., 2015). Degraded lands that almost lost their production potentials left for nature based rehabilitation, and if properly managed and rehabilitated through exclosure system, allow native vegetation to restore. Many case studies conducted in highlands showed that exclosures are effective in enhancing composition, diversity, and density of vegetation (Yayneshet et al., 2009). Species that disappeared long time ago restored following the establishment of exclosures. For instance, species that could not be observed for many years in some parts of eastern Tigray, namely Olea europaea subsp. cuspidata and Juniperus procera, reappeared, densities and diversities of the flora, particularly of grasses, and fauna increased, soil erosion decreased and even dead springs started to flow after exclosures were established (Birhane et al., 2007).
The restoration and re-establishment of degraded ecosystems should include not only the aboveground systems but also the below ground microorganisms which are linked functionally with plants (Li et al., 2007). The success of any ecosystem restoration efforts are likely to depend on the establishment of mycorrhizas, and Arbuscular Mycorrhiza Fungi (AMF) should receive special consideration in restoration of degraded ecosystem (Wubet et al., 2003). Owing to the multiple beneficial effects on plant performance and soil health, AMF are essential for the restoration and re-establishment of the vegetation in degraded ecosystems (Dhillion and Gardsjord, 2004). AMF are more commonly distributed than other types of mycorrhizal associations (Smith and Read, 2008) and are keystone organisms that form an interface between soils and plant roots, and are sensitive to changes in soil and plant environment.
Disturbance can affect the incidence of AM fungi in both agricultural and natural ecosystems. Land use change and/or disturbance of soil can reduce mycorrhizal infection and several factors may be responsible. Soil disturbance negatively affect the functionality of AMF (Trejo et al., 2016). There may be effects of tillage on root growth affecting the degree of root colonization by mycorrhizal fungi (Borie et al., 2006). The influence of grazing on soil nutrient availability and host plant productivity may cause inconsistent effects on AMF community composition and structure (Bai et al., 2013). Grazing of pasture grasses in the field has been found to affect the amount of root length infected by decreasing root length per unit volume of soil (Yang et al., 2013). Grazers also influence allocation to AMF morphological structures by changing soil nutrient condition through direct inputs of N and P in dung and urine deposition (van der Waal et al., 2011, Schnyder et al., 2010). AMF differ in their response to the mineral environment of the soil (Brundrett, 2004).
One way by which plants can potentially enlarge ecosystem productivity and stability is by forming mycorrhizal associations (Eriksson, 2001). Plants are most likely to form associations with and benefit from mycorrhizal fungi under situations in which availability of one or more soil nutrients, including water, is low (Smith and Read, 2008). Tropical savanna soils have been eroded and poor in nutrients resulting to reduced plant productivity (Pimentel, 2006). AMF are of particular significance to the plant in soils that are nutrient poor (Jeffries et al., 2003). Moreover, AMF serve as sensitive indicators of ecological soil quality if they respond to environmental variation in a predictable way (Verbruggen et al., 2012). Information about species composition of AMF community appears important to recognize mycorrhizal function in the ecosystems. It is evident that AMF are essential for the functioning of terrestrial ecosystems. Therefore, understanding the impact of land use on AMF abundance in tropical soils is important. Forest restoration in protected exclosures has become a widespread practice to fight land degradation in the highlands of Northern Ethiopia (Mekuria and Aynekulu, 2013). Exclosures have been implemented in grazing areas for the past decades in Ethiopia and have been effective in regenerating natural vegetation, controlling soil erosion and increasing soil fertility (Baudron et al., 2015). Despite this effort, studies that evaluate the effectiveness of different exclosure habitat types to restore degraded soils and vegetation, their role to the enhancement of microorganisms in soils are lacking. Besides, it is hardly possible to find studies that evaluate the benefits of exclosures to restore arbuscular mycorrhiza fungi (AMF). This paper aimed at investigating the spore density and root colonization of AMF in relation to land use, age and slope positions of the exclosures and the dynamic with soil nutrients. The research questions answered in this paper were; is conversion of free grazing land to exclosure increased AMF spore density in rhizosphere soils and colonization of plant roots? Does age of exclosures at different elevation gradient influence the availability of AMF spore density and percent of root colonization? What is the relationship of AMF spore density and root colonization in relation to the available nutrients?
Section snippets
Study area
The study was conducted in the highlands of Tigray region, Northern Ethiopia in four zones and four districts (Fig. 1). There were 12 sites having exclosures and a grazing land. Exclosure is a method of rehabilitating land by protecting an area from the interference of animals and human encroachment for limited period of time, depending on site capacity and vegetation re-establishment (Seyoum et al., 2015). The grazing lands are areas open for grazing continuously by livestock. The exclosures
Woody plants AMF spore abundance in exclosure and grazing land
Land use type, slope and age were the main source of variation for significant difference in AMF spore density (Table 1). The interaction effect land use *slope, land use *age was significantly different (P < 0.05), but the interaction effect among slope*age and land use*age*slope was not significantly different (Table 1).
AMF spore density ranged from 40 spores 100 g−1 to 2980 spores 100 g−1 of dry soil in exclosures and 30 spores 100 g−1 to 2200 spores 100 g−1 of dry soil in grazing lands. The
Discussion
Arbuscular mycorrhiza fungi were present in all woody plant roots and rhizosphere soil samples. There was a significant variation in the abundance of AMF spores in the rhizosphere soil of tree species and their families. The difference in AMF spore density between samples could be due to the difference in micro climatic and edaphic properties, spatial and temporal variation, vegetation, and host specificity between fungi and woody plants, age of the host plants, disturbance, and differential
Conclusion
Exclosures improved the spore abundance and woody plant root colonization of arbuscular mycorrhiza fungi of restored lands. The middle slope had more AMF within the exclosures. Age difference brought a significant difference on AMF spore density, woody plant root colonization and nutrient availability. Exclosures are important in restoring AMF in disturbed degraded areas. Age and slope position are key parameters to enumerate the AMF spore density and root colonization to validate the
Acknowledgement
The Steps towards sustainable forest management with the local communities in Tigray, Northern Ethiopia (ETH 13/0018) project funded by NORAD under the NORHED programme fully fund the study. We are grateful to the two anonymous referees for constructive comments on an earlier version of this manuscript.
References (57)
- et al.
Impact of farmland exclosure on the productivity and sustainability of a mixed crop-livestock system in the Central Rift Valley of Ethiopia
Agric. Ecosyst. Environ.
(2015) - et al.
Arbuscular mycorrhizal associations in Boswellia papyrifera (frankincense-tree) dominated dry deciduous woodlands of Northern Ethiopia
For. Ecol. Manage.
(2010) - et al.
Effects of tillage systems on soil characteristics, glomalin and mycorrhizal propagules in a Chilean Ultisol
Soil. Tillage. Res.
(2006) - et al.
Analysing arbuscular mycorrhizal fungal diversity in shrub-associated resource islands from a desertification threatened semiarid Mediterranean ecosystem
Appl. Soil Ecol.
(2004) - et al.
Temporal variation in the arbuscular mycorrhizal communities colonising seedlings in a tropical forest
FEMS Microbiol. Ecol.
(2002) - et al.
Distribution of roots and arbuscular mycorrhizal associations in tropical forest types of Xishuangbanna, southwest China
Appl. Soil Ecol.
(2003) - et al.
The influence of grazing exclosure on soil C stocks and dynamics, and ecological indicators in upland arid and semi-arid rangelands
Ecol. Indic.
(2014) - et al.
Mycorrhizal status of indigenous trees in dry Afromontane forests of Ethiopia
For. Ecol. Manag.
(2003) - et al.
The effects of exclosures in restoring degraded semi-arid vegetation in communal grazing lands in northern Ethiopia
J. Arid. Environ.
(2009) - et al.
Impacts of livestock grazing on selected soil chemical properties in intensively managed pastures of Peninsular Malaysia
J. Trop. Agric. Sci.
(2011)
Community structure of arbuscular mycorrhizal fungi associated with pioneer grass species Miscanthus sinensis in acid sulfate soils: habitat segregation along pH gradients
J. Plant Nutr. Soil Sci.
Arbuscular mycorrhizal fungi associated with vegetation and soil parameters under rest grazing management in a desert steppe ecosystem
Mycorrhiza
Enclosures to enhance woody species diversity in the dry lands of eastern Tigray, Ethiopia
East Afr. J. Sci.
The effect of agricultural practices on the development of indigenous arbuscular mycorrhizal fungi. II. Studies in experimental microcosms
Plant. Soil
Nitrogen total
Diversity and classification of mycorrhizal associations
Biol. Rev.
The mosaic of habitats in the high-altitude Brazilian rupestrian fields is a hotspot for arbuscular mycorrhizal fungi
Appl. Soil Ecol.
Indigenous Arbuscular mycorrhizae in areas with different successional stages at a tropical dry forest biome in Brazile
Afr. J. Microbiol. Res.
Diversity of arbuscular mycorrhizal fungi in soils of yam (Dioscorea spp.) cropping systems in four agroecologies of Nigeria
Arch. Agron. Soil Sc.i
Arbuscular mycorrhizas influence plant diversity, productivity, and nutrients in boreal grasslands
Can. J. Bot.
Studies on the status of arbuscular mycorrhizal fungi on the fodder crop Sorghum bicolor (L.) moench
Trop. Life Sci. Res.
Ethiopian Metrological Agency
Arbuscular mycorrhiza in relation to management history, soil nutrients and plant species diversity
Plant Ecol.
Effect of tillage and farming system upon VAM fungus populations and mycorrhizas and nutrient uptake of maize
Plant Soil
Particle size analysis
Occurrence and abundance of arbuscular mycorrhizal fungi (AMF) in agro forestry systems of Rubavu and Bugesera Districts in Rwanda
Afr. J. Microbiol. Res.
Arbuscular mycorrhizal association of indigenous agroforestry tree species and their infective potential with Maize in the rift valley, Ethiopia
Agrofor. Syst.
Cited by (29)
Arbuscular mycorrhizal fungi community in soils under desertification and restoration in the Brazilian semiarid
2022, Microbiological ResearchCitation Excerpt :On the other hand, Glomus fasciculatum, Glomus etunicatum, and Acaulospora foveata were abundant in the soil under grazing-exclusion. Species belonging to the genus Glomus present great adaptability and survival under varying soil conditions (Burni et al., 2011) and were highly abundant in enclosure or fenced soils in Northern Ethiopia (Birhane et al., 2017). AMF diversity was found to be higher in the soil under grazing-exclusion, probably due to the presence of legume species, such as Mimosa tenuiflora (Oliveira Filho et al., 2019) that develop mutualistic interactions with AMF (de Souza et al., 2016).
Environmental drivers of grazing effects on arbuscular mycorrhizal fungi in grasslands
2020, Applied Soil EcologyCitation Excerpt :Results of studies investigating the response of AMF to long-term herbivory are contradictory. For example, the response of AMF root colonization to grazing is variable with either positive (Eom et al., 2001; Hokka et al., 2004; Techau et al., 2004; Wearn and Gange, 2007; Nishida et al., 2009), negative (Wardle et al., 2002; Ba et al., 2012; Barber et al., 2012; Birhane et al., 2017; Cavagnaro et al., 2019; Soka and Ritchie, 2018) or neutral effects (Yang et al., 2013; van der van der Heyde et al., 2017). Grazing has been shown to stimulate AMF sporulation (van der van der Heyde et al., 2017), however, negative (Mendoza et al., 2011; Birhane et al., 2017) and null grazing effects (Burke et al., 2019) on AM fungal spore density have also been documented.
The response of grassland mycorrhizal fungal abundance to a range of long-term grazing intensities
2020, RhizosphereCitation Excerpt :Similarly, van der Heyde et al. (2017) reported no grazing effect on mycorrhizal root colonization in grazed sites compared to non-grazed ones in nine grasslands in Canada. However, both positive (Eom et al., 2001; Wearn and Gange, 2007), and negative (Ba et al., 2012; Birhane et al., 2017; Cavagnaro et al., 2018) effects of large herbivores on root colonization have also been documented. It is worth considering that total length of root colonized may decrease following herbivory but percent root colonization, as a relative measure, may remain unchanged (van der Heyde et al., 2017).
Reconciling disparate responses to grazing in the arbuscular mycorrhizal symbiosis
2019, RhizosphereCitation Excerpt :Similarly, low-intensity grazing cab stiumulate productivity by limiting self-shading (Troughton, 1957). At high grazing intensity, carbon limitation would cause even spore production to decrease (Ba et al., 2012; Birhane et al., 2017b, 2017a). Further, fungal diversity may decrease with high intensity grazing as only AM fungi adapted for carbon limitation would be able to survive.