Abstract
The effects of conversion of an Indian dry tropical forest ecosystem into savanna, on mineral nitrogen (N), net N-mineralization rate and microbial biomass carbon (MBC), nitrogen (MBN) and phosphorus (MBP) in soil were studied for two years. There was a marked seasonal variation in all the above parameters at both (upper, 0-10 cm and lower, 10-20 cm) the soil depths of forest and savanna ecosystems. In forest ecosystems the mean annual values of mineral N, net nitrification rate, net N-mineralization rate, MBC, MBN and MBP at both depths were 17.41 and 13.2 µg g -1 , 18.76 and 10.96 µg g -1 mo -1 , 23.54 and 12.83 µg g -1 mo -1 , 623 and 195µg g -1 , 116 and 29µg g -1 , 16 and 9µg g -1 , respectively; while in savanna ecosystems the values were 20.15 and 15.73 µg g-1, 10.74 and 6.29 µg g-1mo-1, 16.59 and 10.11 µg g -1 mo -1 , 453 and 150µg g -1 , 79 and 21.7µg g -1 , 13 and 6µg g -1 , respectively. The soil microbial biomass was positively related to root biomass and total plant biomass (i.e., above- and below-ground biomass). Interestingly, seasonal soil moisture and temperature are reciprocally related to microbial biomass and mineral N and directly related to nitrification and N-mineralization. The microbial biomass, nitrification and N-mineralization are negatively related to clay content. Savannization caused significant loss of soil mean organic carbon (OC), total N (TN) total mean annual nitrification, N-mineralization, MBC, MBN and MBP by 40, 42, 27, 27, 29 and 7%, respectively at upper soil depth and 18, 21, 42, 29 and 22%, respectively at lower soil depth. The reflectances of soil microbial biomass to OC were 1.22 and 1.06 folds at upper and lower soil depths, respectively. Thus, conversion of dry tropical forests into savanna affects remarkably the soil N transformation; microbial biomass and loss of soil organic C which adds to the environmental pollution.
Highlights
Much of the earth’s grasslands are over used and poorly managed [1], and significant amounts of native forest, shrub land, and woodland have been converted to grassland [2]
The objectives of this study were to determine the effects of conversion of a tropical forest into savanna on plant available N-pool, nitrification and N-mineralization rates and soil microbial biomass carbon (MBC), MBN and MBP
The study sites were located in Similipal Biosphere Tiger Reserve in Mayurbhanj District of Orissa state (India)
Summary
Much of the earth’s grasslands are over used and poorly managed [1], and significant amounts of native forest, shrub land, and woodland have been converted to grassland [2]. In Ecuador less than 2% of the original extent of this forest type remains, a statistic which is characteristic of most tropical dry forest regions in the world; in Central America sadly less than one-tenth of one percent remains. Because of these tremendous rates of loss, organisms that once were common in these forests face extinction, merely for lack of habitat. Because few functioning dry forest ecosystems remain (the forest is reduced to small, isolated patches in most parts of the world), their ecology is poorly studied (http://www.ceiba.org/ loorecology.htm accessed on 24/11/2010)
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