Phosphorus Fractions and Arbuscular Mycorrhizal Fungi as Influenced by Forest Conversion Into Other Land Use Types on Planosols in Nyandarua County

Abstract

Land-use conversion from natural forest to agriculture alter above and belowground biodiversity and soil properties due to reduced organic matter inputs and increased loss of topsoil through soil erosion. A study was conducted to determine the effects of forest conversion to other land uses on soil chemical properties, P fractions distribution, abundance and diversity of AMF on Planosols in South Kinangop Sub-County, Nyandarua County. Four land use types including natural forest, cypress plantation, grazed pasture and cultivated potato field were selected with natural forest considered as the reference point. Soil and plant litter samples were randomly collected from three transects and were analyzed for chemical properties (pH, organic C, total N, P, Ca, Mg, K, CEC and lignin content), Hedley P fractions and quantification of AMF spore abundance, diversity and richness and root samples for root colonization. Soil and plant data were analyzed using generalized linear models (GLMs) while spore abundance and root colonization were analyzed using generalized linear mixed models (GLMMs). AMF diversity and richness was determined using Shannon diversity and taxonomic richness indices, respectively. Whenever significant effects for land use type was observed, Tukey’s Honest Significance Difference (HSD) test was used to separate means at α=0.05. All data was analyzed using R statistical software version 4.0.4. Results showed that land use type had significant effect on all soil chemical properties. Soil pH was higher in natural forest (4.9), while potato fields had relatively acidic soils (3.8). Similarly, total C, N, Mg and Ca were significantly higher in natural forest compared to other land use types. Readily and moderately labile P were highest in potato growing fields (125.1 mg and 186.1 mg kg-1, respectively) and lowest in cypress forest (36.4 mg and 82.7 mg kg-1, respectively). However, non-labile P was highest in natural forest (690.1 mg kg-1) and lowest in cypress forest (324.5 mg kg-1). AMF spore abundance, diversity and richness and root colonization did not differ among land use types. AMF genera showed weak to strong or no correlation with soil chemical properties and P fractions. Acaulospora had a negative association with resin Pi, sonicate NaOH-Po and NaHCO3-Po (p<0.05). Glomus was positively correlated with exchangeable K and residual P (p<0.05) whereas Funneliformis had a positive correlation with exchangeable K (p<0.01), total N, sonicate NaOH-Po and HCL-Pi (p<0.05). Paraglomus had a positive correlation with soil pH, exchangeable K, Ca, CEC (p<0.05), NaHCO3-Po (p<0.05), resin Pi, NaHCO3-Pi, NaOH-Pi, sonicate NaOH-Pi, HCL-Pi and residual P (p<0.01) but was negatively correlated with sonicate NaOH-Po (p<0.001). Scutellospora was positively correlated with soil total N (p<0.01) while Enterophospora and Archaeospora were positively associated with residual P (p<0.01) and NaHCO3-Pi (p<0.05), respectively. The study demonstrate that converting natural forest for other land uses may lead to alteration of soil properties and soil biodiversity with implications in nutrient availability and that soil fertility may not be maintained by other land use types