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Aggregate Distribution of Soil Amidohydrolases in Different Ecosystem Rahele sadat aletaha maki sr aletahamakikoohbanani@ag iut ac ir 2012 College of Agriculture Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Farshid Nourbakhsh farshid@cc iut ac ir Abstract The location of extracellular enzymes with the soil architecture and their association with the various soil components affects their catalytic potential Soil enzyme activities are thought to be central in nutrient cycling in the natural and agroecosystems Amidohydrolases including L glutaminase L asparaginase Urease Amidase and L aspartase play important roles in mineralization of nitrogen This study was conducted to investigate a aggregate distribution of L glutaminase L asparaginase and Urease in different ecosystems including Gisum forst Delvara forest and Hanna rangeland b the effect of the location on their respective kinetics A wet sieving procedure was used to separate soil aggregate into classes of 2 2 1 1 0 5 0 5 0 25and 0 25 0 1 Soil amidohydrolases which are thought to be of different origins were measured either in bulk soil or in the separated aggregates as well as soil organic C SOC Results indicated that in the Gisum forest pine standing has resulted in increasing SOC content Moreover small macro and micro aggregates were more abundant in the maple compared to the pine standing The activity of L glutaminas and Urease were similar in the both standings but the activity of L asparaginase was greater in the maple standing compared to the pine standing The enzyme activities enhanced as the aggregate size increased in both pine and maple standings In the Delvara oak forest and Hanna rangeland the enzyme activities showed to be highly sensitive to management practices while L glutaminase L asparaginase and Urease decreased significantly as cultivation practiced in the ecosystems The activity of the enzymes was distributed unequally in the aggregate size fractions The greater fractions showed higher enzyme activity Multiplying the mass fraction of each aggregate class to the enzyme activities bring about the aggregate derived enzyme activity which is affected by both the initial activity of the enzymes and the aggregate mass fraction Exceptionally due to high prevalence of small aggregates in the Hanna rangeland aggregate derived enzyme activity was decreased as the aggregate size increased In other word the greatest fraction of total soil enzyme activity is concentrated in the small macro and microaggregates Changing the land use could not influence the predominance of the L glutaminase Enzyme kinetics parameters vmax and km were estimated for L glutaminase in Delvara forest The results showed that not all aggregates were equally enzymatically active The Michaelis constant km varied among aggregates indicating that the association of enzyme with different aggregation affected its substrate affinity The response of the enzyme kinetics to the management practices caused unequal distribution of the aggregate derived activity in the two counterparts of the ecosystems This clearly indicates that land use change not only influences the total soil enzyme activity but also modifies the distribution of the enzyme molecules in the soil aggregates Our study showed that soil management practices including tillage would enhance the mass fraction of either small macroaggregate or microaggregates and therefore would increase their aggregate derived activity also significantly affect soil biological and biochemical properties which may lead to changes in nitrogen cycling including N mineralization in soil aggregates Key words Amidohydrolases Aggregate Aggregate distribution of enzyme Management and land use Enzyme Kinetic

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توزيع خاكدانه اي آميدوهيدرولازها در اكوسيستم هاي مختلف

توزيع خاكدانه اي آنزيم ها , مديريت و كاربري اراضي , سينتيك آنزيمي