Vegetation cover density and disturbance affected arbuscular mycorrhiza fungi spore density and root colonization in a dry Afromontane forest,northern Ethiopia

Emiru Birhane•Nakiguli Fatumah•Kidane Gidey•Amanuel Zenebe•Ssemwanga Mohammed

Introduction

Afromontane forests are known for their species richness around the world(Schmitt et al.2010).In Ethiopia,Afromontane vegetation occupies more than a half of the overall highland area and majority of it being dry Afromontane(Wubet et al.2003).However,the country is highly threatened by increasing rates of deforestation,which has increased the rate of soil erosion and the loss of soil fertility,biodiversity and fragile ecosystems(Chun et al.2003;Lenaerts 2013).These effects of deforestation are increasingly reducing the volume and health of the forestecosystem (Sebhatleab 2012;Lenaerts2013).Restoration and/or re-establishment of this degraded forest ecosystem is,therefore,vital.Restoration of the degraded forest ecosystem can easily be obtained if both the aboveground levels and belowground microorganisms are well conserved(Liu et al.2000).The close linkage between theaboveground systemsand thebelowground soil microorganisms helps to build a healthy ecosystem(Wardle et al.2004).

Belowground soil microorganisms mutually associate with many plant species(Smith and Read 2008);arbuscular mycorrhiza fungi(AMF)are the principal microorganism in these associations(Vani et al.2014).Most woody plant communities(＞80%)mutually associatewith these organisms(Zobel and O¨pik 2014);the AMF obtain carbon compoundsfortheirgrowth and development,and numerous bene fits are obtained by plants and soils(Liu et al.2000;Walder et al.2012),such as more water and nutrients via a fungal tree-like network structure(Babikova et al.2013),reduced stress from salts and heavy metals(Hildebrandt et al.2007).Arbuscular mycorrhiza fungi also increase the plants’ability to fight pathogens and pests(Eyles et al.2010).Although AMF provide numerous functions in the natural ecosystem,their spatial and temporal distributions and functioning are still poorly understood(Oliveira and Oliveira 2010).Despite the fact that several research studies have been conducted on how seasons affect the distribution and functioning of AMF in nature(Birhane et al.2010),consistent seasonal patterns in the development of these organisms have not yet been observed(Panwar et al.2011).Moreover,the short-term seasonal patterns and timing of AMF sporulation and colonization have not been investigated thoroughly in the forest ecosystems(Panwar et al.2011).Limited research on the effect of vegetation cover density on AMF has been done in Ethiopia.In addition,Wardle et al.(2004)reported that aboveground systems receive most research attention,while soil microorganisms are often neglected.Hence,a need to understand the in fluence of seasons,vegetation cover density and edaphic and anthropogenic factors on the AMF SD and RC in the Afromontane forest ecosystems is essential.This study was conceived to answer calls for more research-based actions to help restore and re-establish degraded forest ecosystems by maintaining populations of microorganisms aboveground and belowground(Liu et al.2000).

Although many environmental and biotic factors in fluence the distribution and development of these microorganisms,climate, flora and disturbance are the chief factors(Rodrı´guez-Echeverrı´a et al.2008).Physicochemical soil properties and plant species are additional in fluences on AMF activities and distributions(Vyas and Gupta 2014).However,the level of information on the prevalence of AMF in nature is still unsatisfactory(Muthukumar and Udaiyan 2000).Consequently,there is a need for a deeper understanding of these microorganisms for the bene fit of management and maintenance of the health of the entire natural(forest)ecosystem components.This paper,therefore,was aimed at determining the in fluence of seasons,vegetation cover density,edaphic and anthropogenic factors on AMF SD and RC in a forest ecosystem.This paper investigated the AMF SD and RC of trees in wet and dry seasons and in the fenced and unfenced permanent plots having different vegetation cover density.

Materials and methods

Study sites

The research was done in Desa’a dry Afromontane forest located at 39°43′E and 13°45′N in northern Ethiopia(Fig.1).The forest is situated in a semi-arid area with the climate greatly in fluenced by topographic features(Nyssen et al.2005).Annual precipitation in this area is less than 1000 mm with short,seasonal,erratic and irregularly distributed unimodal rainfall with the highest amount between June and September(Aynekulu et al.2011).Annual average rainfall is within 406–700 mm,and the average minimum and maximum temperature varies within 7.5–19.3 °C and 22.6 °C and 33.4 °C,respectively(Fig.2).

The elevation of study site is 1000–2760 m a.s.l(Aynekulu et al.2011).Desa’a forest is located in a matrix of agricultural and heavily grazed land(Sebhatleab 2012).The dominant tree species areJuniperus proceraandOlea europaea(Mokria et al.2015),which are increasingly replaced byAcaciaspecies at lower altitudes.

Study plots

Three permanent study blocks measuring 160×100 m(16,000 m2)with homogeneous soil and vegetation density were established in the study site as described by Giday(2013).The study blocks were established in areas with poor,medium and dense vegetation cover densities.In each of the three study blocks,two management plots of 40×160 m with a 20-m buffer zone between them were established in 2013.One of the two plots from each block was selected randomly and fenced to check for the absence of both human and livestock pressure and deter their potentialeffectonAMF SD andRC.Withinthe 40×160 m plots,40×40 m experimental subplots were established using a split plot design.In the 40×40 m subplots,there were 20×20 m plots for root and rhizosphere soil sampling and 5×5 m plots for physicochemical soil properties.

Fig.1 Location of Desa’a Forest in northern Ethiopia

Fig.2 Average total rainfall,maximum and minimum temperature for 10 years(2006–2015)at the study area

Root and rhizosphere soil sampling

Sampling was carried out in both wet and dry seasons in the months of August 2015 and January 2016 respectively.Within the 20×20 m plots,three dominant tree species were identi fied for root and rhizosphere soil samples and replicated twice,for a total of 144 tree species from the 160×40 m plots.In total,488 trees were sampled for each season.For each of the selected tree species,root samples were collected by digging out the soil in four directions with a hand hoe beginning from the tree trunk base around the tree to expose the fine roots.Fine roots were collected around the tree,then mixed well to make a composite sample.The sample was placed in a sampling bottle with 97%ethanol to preserve the roots until processing for colonization analysis.Rhizosphere soils were collected to a depth of 50 cm(Sewnet and Tuju 2013)and mixed to make composite samples.These samples were labelled,then taken to the laboratory for enumerating AMF spores.

AMF root colonization assessment

The ethanol and soil particles were washed from the roots by running tap water through them.They were then cut into 1 cm lengths and placed in autoclave resistant bottles containing 10%KOH and heated at 90°C for 1 h(Phillips and Hayman 1970).These samples were washed again using distilled water then placed in 10%H2O2for 15 min for further bleaching.They were then cleaned using distilled water and placed in 1%HCl for 1 h for acidi fication,then stained using Trypan blue(0.05 g)solution in 1:1:1 lactic acid–glycerol–distilled water for 12 h(Das and Kayang 2008).

The stained root pieces were mounted lengthwise on slides in replicates of nine after being washed and placed into 50%glycerol for 1 h and observed with a compound light microscope at 400×to observe AMF arbuscules,hyphae and vesicles.The gridline intersection method was used to observe fungal structures(Giovannetti and Mosse 1980).The method of Brundrett et al.(1994)was used to analyze AMF colonization.

AMF spore assessment

AMF spores were analysed using the decanting and sieving method described by Gerdemann and Nicolson(1963)using mycorrhizalEndogonespecies spores.The wet sieving and decanting procedures were carried out based on 100 g of air-dried soil in each rhizosphere soil sample.Samples were then centrifuged in water and then in 1:1 sucrose to water(Walker et al.1982).Air-dried,sieved rhizosphere soil(10 g)was added to a container of 100 mL of tap water,shaken for 30 min and left to stand for about 5 min to separate the decant from the filtrate.The suspension was passed through 850,300,100 and 50 μm sieves,placed on each other in the order of decreasing size.The 850 μm sieve was used to remove rocks,woods and other unnecessary material which might have remained during sieving.The suspensions in each of the different sieves were carefully poured into a plastic jar,water was added,then the jar was covered tightly and centrifuged at 2000 rpm for 5 min.Samples were washed again with tap water,then sieved using the 50 μm sieve.The samples were poured into the plastic jar and centrifuged again using 50%sucrose at 2000 rpm for 1 min.Samples were again poured into the 50 μm sieve and rinsed with running tap water to rinse off the sucrose.Lastly,each of these samples was poured on filter paper and left to dry.The filter papers containing spores were kept in inverted Petri dishes divided into sections to simplify spore counting.A stereomicroscope with 100 times magni fication was used for viewing and quantifying the spores.AMF fungal propagules in the form of spores and sporocarps were quanti fied by observing all sieve sizes(300,100 and 50 μm)of the filter papers with the microscope.Total AMF spore density was calculated for 100 g of dried soil.To identify morphospecies,spores were separated by colour and size,then placed in Petri dishes and crushed under a cover slip in a drop of 1:1 polyvinyl alcohol lactoglycerol–Melzer’s reagent(Morton et al.1993),and observed with a compound light microscope at 400×using the density measurement procedures described by Bundrett et al.(1996).

Soil property analysis

Soil for the physiochemical soil analysis was sampled from each of the 5×5 m plots using a soil augur at a depth of 0–50 cm in both the fenced plot(FP)and unfenced plot(NFP)in an ‘‘X’’pattern within a single plot and mixed to form a bulk sample for the whole plot;1000 g of the bulked soil was stored in tightly closed polyethene bags to avoid evaporation.The pH and electrical conductivity(EC)in the soil were determined using a soil suspension at a ratio of 1:5 soil to water(Gee and Bauder 1986).Soil moisture content was obtained using the gravimetric method and 10 g of fresh soil oven-dried at 105°C for 24 h.Organic carbon was determined using the Walkley–Black procedure(Walkley and Black 1934).Available phosphorous was determined using the phosphorous analysis protocol of Olsen et al.(1982).Total nitrogen was determined using the Kjeldahl procedure(Bremner and Mulvaney 1982).

Data analyses

Data were analysed using SPSS statiscical software version 20.0(SPSS,Chicago,IL,USA).Variations in AMF SD and total RC among vegetation cover densities were analysed using two-way an ANOVA.Post-hoc Tukey’s test was used for multiple comparison tests between the vegetation cover densities.Differences in AMF genera were determined using the Kruskal–WallisHtest.Variations in SD and RC between management practices as well as seasons were tested using an independentttest.Before analysis,spore density was log10-transformed.All tests were true at 5%con fidence interval.Correlations in AMF SD and RC with soil variables were tested using Pearson’s correlation test.

Results

Vegetation cover density and edaphic factors

Soil variables did not differ significantly (p＞0.05)between the vegetation cover densities except for available potassium and total nitrogen(Table 1).Generally,the soil pH for the poor and medium vegetation cover density was moderately alkaline and strongly alkaline(8.0)for the dense vegetation cover density.Electrical conductivity values were＜2 that indicated that the soils were not saline in all the vegetation cover densities.All the nutrients decreased with a decrease in the vegetation cover density(Table 1).

Management practices,season and edaphic factors

None of the soil variables differed significantly(p＞0.05)between the FP and NFP except for available phosphorus and total nitrogen.All the nutrients were higher in the FP than in the NFP(Table 2).Apart from available phosphorus,total nitrogen,OC and OM,there were signi ficant(p＜0.05)differences in soil moisture content,pH,EC and available potassium between the dry and rainy seasons(Table 2).Soil pH increased significantly with an increase in rain.

AMF spore genera between tree species

Common tree species at all vegetation cover densities includedJ.procera,O.europaea,Maytenus arbutifolia,Carissa spinarumandDodonaea angustifolia.AMF SD varied slightly among the plant species but no signi ficant(p＞0.05)differences were found.The SD ranged from 50 to 4467 with an average of 624 spores.Glomus,Acaulospora,Gigaspora,ScutellosporaandEntrophosporawere the spore genera identi fied.Glomuswas the most abundant genus followed byAcaulospora,Gigaspora,ScutellosporaandEntrophosporawith mean spore density of 153,86,25,4,and 0.2,respectively.All the genera differed signi ficantly among the vegetation cover densities whereas the management practices had no signi ficant effect on the AMF spore genera except forGlomus(Table 3).

AMF root colonization between species

All the species were AMF colonized and the internal hyphae,external hyphae,vesicles and arbuscules structures were observed in the roots of the studied plants at a variable degree.Hyphal colonization(HC)was the highestfollowed by mycorrhizal hyphal colonization(MHC),vesicular colonization(VC)and arbuscular colonization(AC)with a mean percentage of 78.74,64.71,42.27 and 37.12,respectively.The AMF structural colonization differed significantly between the species(Table 4).

Table 1 Mean plot soil characteristics(±SE)in each of the vegetation cover density

Table 2 Mean soil characteristics(±SE)in management plots during the dry and rainy season(n=22)

Table 3 Number of morphospecies in plots with different vegetation cover densities and management in studied fields

The RC ranged between 4 and 95%and with an average of 54%.Olea europaeahad the highest colonization by AM followed byCarissa spinarumandDodonaea angustifoliawas the least colonized.The total AMF root colonization between species was significantly different(Fig.3).

AMF spore density and root colonization between vegetation cover types

The highest and the lowest spore density were from the poor and dense vegetation cover densities,respectively(Fig.4a),whereas percentage root colonization showed a reverse trend(Fig.4b).The mean spore density of 989,675 and 364 per 100 g soil were observed in poor,medium and dense vegetation densities,respectively.The root colonization percentage ranged between 4–90,0–80 and 0–76 in the dense,medium and poor vegetation cover densities,respectively.Both spore densities and root colonization differed significantly(p＜0.05)among the vegetation cover densities.

Management and seasonal effect on AMF spore density and root colonization

AMF SD and RC were significantly(p＜0.05)higher in the wet period than in the dry period.The spore densities during the rainy season were 2-fold higher than the spore densities in the dry season(Table 5).AMF SD and RC were significantly higher in the fenced plots than in the unfenced plots(Table 5).The interactions between the main factors were significantly different for both AMF SD and RC(Table 6).

Table 4 AMF root structure colonization and species

Fig.3 Total root colonization percentage between dominant species found in Desaa’dry Afromontane forest.Error bars indicate standard error.J:Juniperus procera,O:Olea europaea,M:Maytenu sarbutifolia,C:Carissa spinarum and D:Dodonaea angustifolia.Bars with different letters differ significantly at p＜0.05

Correlation between AMF SD,RC with edaphic factors and elevation

A positive and signi ficant relationship was observed between AMF SD and RC(p＜0.05).Soil pH was negatively correlated with both SD and RC(Table 7).Organic carbon ranged from low(1.24)to medium levels(4.82)and showed an inverse relationship with AMF SD and a positive relationship with AMF RC.Both SD and RC inversely related with total nitrogen,available phosphorus and available potassium.There was a negative correlation between altitude and SD,whereas RC was positively correlated with altitude(Table 7).

Discussion

The AMF spore densities recorded in this study were comparable to those observed from the tropics(Tao et al.2004;Muleta et al.2008)and higher than those recorded from the dry tropics(Birhane et al.2010),and in the semiarid area(Mohammad et al.2003).The distribution and variation in AMF spore density are in fluenced by both abiotic and biotic factors(Mohammad et al.2003).AMF spore production varies spatially according to the soil physiochemical properties(Nasrullah et al.2010).Glomushad the highest abundance and found in all rhizosphere soils from all the studied species.Glomusis dominant in different ecosystems and common in semi-arid areas of Ethiopia(Wubet et al.2003),tropical rain forests(Zhao et al.2001),and dry deciduous woodlands(Birhane et al.2010).The domination ofGlomusmight be due to their high reproductive ability compared to other AMF genera(Bever et al.1996).Glomusspecies can adapt to varying soil conditions since they can survive in both acidic and alkaline soils(Pande and Tarafdar 2004)and hence can grow in most environmental conditions with limited trouble.

All the tree species were colonized by AMF,consistent with the study by Wubet et al.(2003)in Ethiopia and by Birhane et al.(2010)in a dry deciduous woodland in northern Ethiopia.Over 80%of the terrestrial plants have a mutual association with AMF(Smith and Read 2008;Zobel and O¨pik 2014).AMF root colonization is higher among wild herbaceous species;over 90% of those examined were colonized by AMF(Gai et al.2006).We observed all types of AMF structures(internal hyphae,external hyphae,vesicles and arbuscules),consistent with the results of Moreira-Souza et al.(2003).Since each structure has a unique role in root colonization(Smith and Read 2008),the presence of all the structure is vital for an effective relationship with the plant host roots.Hyphal colonization(HC)and vesicular colonization(VC)were the highest,which agreed with the findings of Belay et al.(2013).Since hyphae and vesicles are the major structures of AMF and persist longer in the root(Wu et al.2009),this peristence could have been the major reason that they were the chief structures found in the root cortex.The formation and breakdown of arbuscules,however,are quite fast,limiting their abundance in the root cortex.

Fig.4 Variation of AMF SD(a)and RC(b)between vegetation cover densities in forests of Northern Ethiopia.Error bars indicate standard error.Different letters above the bars indicate signi ficant differences among vegetation densities at p＜0.05

Table 5 Mean AMF spore density(per 100 g soil)and RC(%)in the dry and wet periods and between management practices(α=0.05)

Table 6 Analysis of variance on the effect of vegetation cover density,season and management and their interaction on AMF spore density and the effect of vegetation cover density and management and their interaction on AMF root colonization(%)of the five common species found in the study site

The root colonization percentage ranged from 4 to 95,similar to the 0–95%found by Birhane et al.(2010),and to the 3.5–96.3%reported by Carrenho et al.(2007).Generally,arid environments are stressed with limited water and nutrients hence the association of microorganisms with the plant host species tend to increase(Thrall et al.2007).The roots ofOlea europaeawere the most highly colonized of the species probably because AMF root colonization is species speci fic(Likar et al.2008;Vyas and Gupta 2014).Other factors such as host physiological attributes,level of reliance on mycorrhiza,and the soil physiochemical properties surrounding the host can be attributed to the variation in root colonization among species(Wu et al.2009).

Maximum AMF SD was recorded in poor vegetation density and the minimum AMF SD in the dense vegetation density,whereas the percentage RC showed a reverse trend.The hypothesis that AMF SD and RC in dry Afromontane forest vary across vegetation cover density was accepted.Various studies have indicated that vegetation cover density in fluence the functioning and development of AMF(Yimer et al.2006;Rodrı´guez-Echeverrı´a et al.2008).In a harsh environment with lower productivity,plant dependence on soil microbes becomes high(Thrall et al.2007),which could have been the reason for the higher spore density in the poor vegetation cover density.Furthermore,other factors like the nutrient level in the soil and soil pH conditions can never be overlooked(Gong et al.2012).Soil nutrient content levels in fluenced spore production in the present study,as vegetation cover densities and management practice(Table 1 and 2)with higher nutrient levels appeared to have lower spore density(Fig.4a).

The hypothesis that AMF SD and RC are significantly higher in the fenced plots compared to the non-fenced plots received clear empirical support.The observed results showed similarity with those of Birhane et al.(2010)and Oechel et al.(2000),who reported higher AMF SD and more RC in the exclosures and undisturbed land,respectively.The low AMF spore density in the non-fenced plots could be attributed to the disturbances in the soil due to grazing and vegetation removal that affected both soil and soil organisms,disrupting the entire ecosystem interaction.AMF availability and activity can be affected by vegetation removal,which can result in a signi ficant decrease in SD and RC(Boddington and Dodd 2000).Interference within environment affects both the aboveground ecosystem and soil microorganism functioning(Oechel et al.2000),due to the breakdown of AMF hyphal network during cultivation and grazing,which leads to a reduction in mycorrhizal colonization of the root(Mcgonigle and Miller 1996).

Both SD and RC were highest and differed significantly between the wet period from the dry period,which supports our hypothesis that AMF SD and RC within the dry Afromontane forest ecosystem vary by season.The present results contradicted those of Birhane et al.(2010)and Sivakumar(2013)who observed a low SD in the wet period,but agreed with the findings of Oliveira and Oliveira(2010)and Muchane et al.(2012)who observed higher spore density and root colonization in the wet period than in the dry.These discrepancies in the findings could be due to differences in climate,in time and space,soil fertility and types,elevation,and latitude and longitude of the study sites.Similarly,Lugo and Cabello(2002)also reported more vesicles,arbuscular and highest colonization in the wet period similar to our results.Increased precipitation tends to enhance AMF abundance because photosynthetic materials are readily available to the roots and rhizomes and will enable AMF to sporulate abundantly(Kivlin et al.2013).Furthermore,the higher AMF spore population and root colonization indicate better growth during the rainy season due to the high rate of root development,which provides additional openings on the root for AMF access(Zangaro et al.2013).The observedresults are strongly supported by the fact that increased soil moisture with increasing precipitation during the rainy seasons is directly proportional to AMF root colonization(Oliveira and Oliveira 2010).

Table 7 Correlation between spore density and root colonization with soil variables and elevation

Spore density and root colonization were positively and significantly correlated,similar to the results of Muthukumar et al.(2003a,b)and Songachan et al.(2011)who also reported an increase in AMF SD as RC increased.Variations in the spatial distribution of AMF spores has been reported as the major reason for this relationship(Zhao et al.2001).

Higher AMF spore density was found in neutral and slightly alkaline soil conditions,as did Sreevani and Reddy(2004).Soil pH was negatively correlated with both SD and RC,consistent with the results of Songachan et al.(2011),but not with the findings of Burni et al.(2011)and Panwar and Tarafdar(2006)who reported a direct relationship between pH and SD.Soil pH has been reported to in fluence AMF reproduction potential as well as their structural composition(An et al.2008),but is also linked to other factors such as the host plant.However,extremes in soil pH are reported to suppress spore production and root colonization(Postma et al.2007).

Organic carbon and SD were negatively related,similar to the high spore production found in soil of fields of mungbean and soybean where OC content was low(Hindumathi and Reddy 2011).OC and AMF RC showed a positive relationship in our study in line with the high correlation found between OC and spore production by Liu et al.(2000)and Sivakumar(2013).AMF are thought to positively in fluence the soil carbon pool(Wilson et al.2009)and over the long-term may increase carbon storage(Iversen et al.2012).Of the total carbon fixed during photosynthesis,AMF are reported to use 30%(Drigo et al.2010).Vegetation cover densities with higher OC had higher percentages of root colonization(Table 1 and Fig.4b).The AMF SD and RC were inversely related to the available phosphorus,in good accord with findings by Panwar and Tarafdar(2006)and Birhane et al.(2010).Certain AMF species sporulate abundantly under low P availability in the soil(Table 1)and as observed by Kahiluoto et al.(2001).AMF RC had a negative relationship to available phosphorus,consistent with the findings of Lekberg and Koide(2005),but contradicted with that of Nogueira and Cardoso(2006)and Khade and Rodrigues(2009)who reported a positive relationship between phosphorus and RC.

Total nitrogen had an inverse relationship with both AMF RC and SD in agreement with those of Deepak et al.(2015),Khade and Rodrigues(2008,2009),who also found a negative association between SD and total nitrogen.However,the results contradicted those of Abubacker et al.(2014)who found a positive relationship between SD and total N.AMF abundance and diversity change greatly with nitrogen content(Egerton-Warburton and Allen 2000).For example,high and low N content in the soil has been reported to respectively suppress and induce AMF SD and RC(Bago et al.2004).Based on current observations,vegetation cover densities with higher total N are associated with low spore density(Table 1,Fig.4a),which further supports the argument.

AMF SD and RC were negatively correlated with available potassium like those of Khanam et al.(2006)and Khade and Rodrigues(2009),but they contradicted those of Gaur and Kaushik(2011),and Abubacker et al.(2014)who determined a positive relationship between available potassium and SD.A negative correlation between available potassium and RC was also reported by Ardestani et al.(2011)in their analysis of the in fluence of different K concentrations on RC.An inverse relationship between RC and available potassium could be due to the fact that AMF tends to lose their potential to develop their structural components such as arbuscules as the K concentration levels increase(Vogel-Mikusˇet al.2005).Generally,high levels of nutrient elements in soil have been reported to decrease mycorrhizal colonization(Liu et al.2000).

There was an inverse relationship between altitude and SD,whereas RC was positively correlated with altitude,supporting the hypothesis that AMF SD and RC in the dry Afromontane forest vary following an altitude gradient.The current results contradicted the decrease in AMF RC with increasing altitude found by Posada et al.(2008),which might be due to a difference in species diversity becauseOlea europaeaspecies,that was most colonized,was found at a higher altitude than all the other species.Human in fluence is also lower with the increase in the altitude.However,poor soil status and unfavourable ecological conditions increase with increasing altitude(Ko¨rner 2003).Plants,therefore,require associations that can assist them in acquiring more water and nutrients in such harsh environments(Pellissier et al.2013).The inverse relationship between SD and altitude might also have resulted from soil erosion.Forces that move soil from one location to another in fluence AMF spores(Smeenk and Ianson 2010).In the current study,soil erosion could have caused the higher number of spores at the low altitude.

Conclusion

Vegetation cover density strongly in fluenced AMF SD and RC.Poor vegetation cover density is more prone to human invasion;soils and vegetation in this block are therefore unstable,which disrupt the ecosystem and microbial activities.AMF SD and RC increased in the wet period and were lower in the dry period.AMF SD and RC changed within the seasons,and precipitation has a positive in fluence on the rate of belowground microbial activity.Although edaphic factors in fluenced SD and RC,management practices had a higher in fluence through vegetation removal and the subsequent effect on the soil.significantly higher SD and RC were observed in the fenced plots as compared to the unfenced plots.Thus,soil disturbance and poor management of the forest ecosystems are some of the major factors affecting AMF development and distribution in the forest ecosystem.Hence,proper management is vital in the AMF development and enhancing ecosystem health at large.

AcknowledgementWe would like to acknowledge the Transdisciplinary Training for Resource Ef ficiency and Climate Change Adaptation in Africa(TRECCAfrica),which funded the second author for the MSc.studies in Climate and Society at Mekelle University.We are also grateful to TRECCAfrica and Norwegian Programme for Capacity Development in Higher Education and Research for Development(NORHED)project which supported the field research including experimentation and data collection and analysis.The valuable suggestions made by anonymous referees is gratefully acknowledged.

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