Abstract
Soil carbohydrates (SC) are important parameters in determining soil fertility in different land uses, particularly in the tropics. There are no tropical studies reported so far on the effect of heterogeneneous land uses on the concentration of SC. Therefore, SC under 13 different land uses including forests and adjacent cultivated lands in Sri Lanka were studied. Soil litter (SL) and soil organic C fractions were evaluated for availability of SC. The study showed that SL is the main factor determining SC composition. Positive relationships between SL and carbohydrates of plant origin (CPO) indicated that SL is the major source of carbohydrates in cultivated lands. Negative relationships were observed between SL and carbohydrates of microbial origin (CMO) in forests. Although the vegetation structure differs, the forests did not show much variation in SC, as soil disturbances, which lead to differences in decomposition rates were minimal or absent. However, the soil management practices among the cultivated lands were highly variable and hence induced significant variations in SC by changing the litter decomposition processes. Intensive soil tillage, agrochemical use and low biomass return reduced the SC to a significant level as shown in potato and tea soils. Three carbohydrates, namely arabinose, xylose and glucose, were not detected in potato cultivation, while ribose and glucose were not detected in tea plantation. The concentration of the other carbohydrates was restricted to the range of 0.12 – 1.75 x 10-6 g kg soil-1 in tea. High biomass return and minimum soil tillage in rubber and coconut plantations respectively increased the SC to 48.6 and 57.79 x 10-6 g kg soil-1 being comparable to their adjacent forests. By comparing SC of forests and the adjacent cultivated lands, both having similar climatic conditions and soil types, the study confirmed that differences in land management practices affected SC concentration. This study provides important guidelines for selecting better land management practices in tropical ecosystems for sustaining soil fertility through SC management. Keywords : Cultivated lands, forests, soil carbohydrates, soil litter, soil organic carbon. DOI: http://dx.doi.org/10.4038/jnsfsr.v39i4.3883 J.Natn.Sci.Foundation Sri Lanka 2011 39 (4):345-353
Highlights
Carbohydrates play an important role in the terrestrial carbon cycle
Regression analysis showed that the Soil litter (SL) content was positively related to the soil carbohydrates of plant origin, arabinose and xylose (CPO) in the cultivated lands (Figure 1)
The SL contents of forests is negatively related to the soil carbohydrates of microbial origin, ramnose, fucose and ribose (CMO) (Figure 2)
Summary
Soil structure formation and supply of energy for soil micro-organisms are the main processes that are governed by soil carbohydrates. Fungal and bacterial polysaccharides may play an important role in soil structure formation (Hu et al, 1995). Carbohydrates derived from various sources are usually considered as readily degradable compounds in soil (Allard, 2006). They are degraded microbially to metabolizable substances, which are the most readily available food for soil organisms (Larre-Larrouy et al, 2004). Plant-derived sugars, especially pentose polymers (arabinose and xylose) serve as the major source of energy and C for soil microorganisms. Carbohydrates play an important role in soil organic matter (SOM) dynamics in tropical soils, only few studies have been conducted in this area. The only available data are those on savannah soils in Congo and Senegal (Larré-Larrouy & Feller, 1997; Sall et al, 2002), native grasslands and forest soils in Costa Rica (Guggenberger & Zech, 1999) and forest and savannah soils in Congo and Brazil (Kouakoua et al, 1999)
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