Elsevier

Applied Soil Ecology

Volume 31, Issue 3, March 2006, Pages 220-227
Applied Soil Ecology

Seasonal dynamics in soil microbial biomass C, N and P in a mixed-oak forest ecosystem of Manipur, North-east India

https://doi.org/10.1016/j.apsoil.2005.05.005Get rights and content

Abstract

The soil microbial biomass C, N and P were studied in two stands of mixed-oak forest ecosystem of Manipur, North-east India to assess the influence of abiotic variables and difference in forest stand on the seasonal variation in soil microbial biomass. Microbial biomass C, N and P were highest during rainy season and lowest during winter in both the forest stands with the exception of microbial N which was lowest in summer in stand II. Microbial biomass C and P showed a positive significant correlation with abiotic variables, i.e. soil moisture, soil temperature, rainfall, mean air temperature and relative humidity in both the stands. Whereas the microbial N exhibited a positive significant correlation with abiotic variables in stand I, but showed a significant correlation only with soil moisture in stand II. The contribution of microbial C, N and P to total soil organic C, total N and P indicates that microbial biomass is immobilized more in forest stand I in comparison to forest stand II.

Introduction

Soil microbial biomass is an important parameter linking the plants to soil. Soil microbial biomass comprises about 2–3% of total organic carbon in the soil and has been recognized as an important source of nutrients to plants because of its fast turnover (Jenkinson and Ladd, 1981). Influence of environmental factors to microbial population and microbial biomass plays an important role in nutrients cycling in an ecosystem. Soil physico-chemical characteristics also has a great impact on microbial biomass and microbial activity and can be used to measure soil quality (Parr and Papendick, 1997) but it may take years for these parameters to make significant changes in soil. Soil biological and biochemical changes are very sensitive to small changes in soil conditions (degradation, erosion) and thereby gives more accurate and immediate information in soil quality because soil microbial activity has a direct influence in ecosystem stability and fertility (Smith and Papendick, 1993). Insam et al. (1989) also proposed that the ratio of microbial biomass to total organic carbon in a soil might serve as a quantitative indicator of carbon dynamics in the soil.

Information on soil microbial biomass in different forest ecosystems have been reported by several workers (Srivastava and Singh, 1991, Billore et al., 1995, Joergensen et al., 1995, Arunachalam et al., 1996, Mendham et al., 2002, Lee and Jose, 2003) but information on seasonal changes in the microbial biomass in an annual cycle in forest ecosystem is limited (Diaz-Ravina et al., 1995, Arunachalam and Arunachalam, 2000). Therefore, the present study was undertaken to assess the seasonal fluctuation in the microbial C, N and P and the influence of abiotic variables on the microbial biomass (C, N and P) in a sub-tropical mixed-oak secondary forest of Manipur, North-east India.

Section snippets

Materials and methods

The study site is located at 24°45′N latitude and 93°55′E longitude in Langol hills a distance of 7 km from Imphal city at an altitude ranging from 780 to 910 m above sea level. The climate of the area is monsoonic with warm moist summer and cool dry winter. There are three distinct seasons comprising of summer (March–May), rainy season (June–October) and winter (November–February). However, March is the transition month between winter and summer and November between rainy and winter seasons. The

Soil characteristics

The soil was sandy loamy with 51.6–61.4% sand, 13.3–14.8% clay and 22.7–30.7% silt in both the stands. The soil moisture ranges from 24.74 to 28.34%, soil temperature ranged from 16.83 to 17.08 °C, soil pH 4.2–6.1, soil organic carbon 2.6–4.4%, soil total N 0.33–0.54%, total P 0.042–0.082% and bulk density 1.38–1.46 g cm−3, C/N ratio varied from 7.0 to 8.7 across the two stands (Table 1).

Microbial C, N and P

In forest stand I, the microbial C, N and P ranged from 71.1 to 1412.6 μg g−1, from 32.1 to 115.7 μg g−1 and from

Discussion

The microbial C, N and P was significantly higher during the rainy season (P < 0.01) and lower in winter season in both the stands with the exception of microbial N exhibiting lowest value in summer season (Table 2). This may be due to higher immobilization of nutrients by the microbes from the decomposing litters as decomposition rate of litters and microbial activities are at peak during this period. Further, the growth of fungi also increased during this season due to high relative humidity

Conclusion

Thus, it may be concluded that the soil microbial biomass exhibits strong seasonality and is highly influenced by the abiotic variables. However, soil moisture has a strong influence on the microbial biomass. The microbial C:N ratio indicates that soil fertility is influenced by the species composition of the forest stands. High microbial N during the rainy season may be considered as a nutrient conservation strategy. Further, the proportion of microbial C and N to soil C and N indicates that C

Acknowledgement

Financial support received from UGC-SAP is thankfully acknowledged.

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