Humic Acid Composition and Characteristics of Soil Organic Matter in Relation to the Elevation Gradient of Moso Bamboo Plantations

Abstract

Studying the influence of climatic and/or site-specific factors on soil organic matter (SOM) along an elevation gradient is important for understanding the response of SOM to global warming. We evaluated the composition of SOM and structure of humic acids along an altitudinal gradient from 600 to 1400 m in moso bamboo (Phyllostachys edulis) plantations in central Taiwan using NMR spectroscopy and photometric analysis. Total organic C and total nitrogen (N) content increased with increasing elevation. Aromaticity decreased and ΔlogK (the logarithm of the absorbance ratio of humic acids at 400 and 600 nm) increased with increasing elevation, which suggests that SOM humification decreased with increasing elevation. High temperature at low elevations seemed to enhance the decomposition (less accumulation of total organic C and N) and humification (high aromaticity and low ΔlogK). The alkyl-C/O-alkyl-C (A/O-A) ratio of humic acids increased with increasing elevation, which suggests that SOM humification increased with increasing elevation; this finding was contrary to the trend observed for ΔlogK and aromaticity. Such a discrepancy might be due to the relatively greater remaining of SOM derived from high alkyl-C broadleaf litter of previous forest at high elevations. The ratio of recalcitrant C to total organic C was low at low elevations, possibly because of enhanced decomposition of recalcitrant SOM from the previous broadleaf forest during long-term intensive cultivation and high temperature. Overall, the change in SOM pools and in the rate of humification with elevation was primarily affected by changes in climatic conditions along the elevation gradient in these bamboo plantations. However, when the composition of SOM, as assessed by NMR spectroscopy and photometric analysis was considered, site-specific factors such as residual SOM from previous forest and intensive cultivation history could also have an important effect on the humic acid composition and humification of SOM.

Effects of temperature on the composition and diversity of bacterial communities in bamboo soils at different elevations

“…The Mucilaginibacter species of Bacteroidetes are capable of degrading polysaccharides (Pankratov et al, 2007); thus, the increase in their abundance can be explained by the increase in plant residues in the soil. A previous study suggested the relationship of elevation and temperature with the decomposition of recalcitrant C (Wang et al, 2016a). After decomposition of labile C, the availability of recalcitrant C can strongly affect the community.…”

“…The increasing concentration of recalcitrant C with increasing elevation (Wang et al, 2016a) could be helpful in providing more carbon resources to the community at high elevation. Together, these findings indicate that bamboo soil bacterial communities with higher diversity could be more capable of maintaining soil community and function when exposed to climatic changes and subjected to management at high elevation (1800 m).…”

“…The three sampling sites were all dominated by moso bamboo with few understory plants. Based on weather station records and the temperature-elevation correlation, the annual mean air temperature was estimated as 20.3 • C at 600 m, 17.2 • C at 1200 m, and 14.1 • C at 1800 m with a decrease of 0.52 • C per 100 m elevation gain (Wang et al, 2016a). At each elevation, three 25 m×25 m plots were established along transect lines in March 2015.…”

“…Our parallel study showed that invasion of bamboo into adjacent forest soils increased humification of soil organic matter (SOM) (Wang et al, 2016b). In addition, changes in the SOM pool and the rate of humification with elevation were primarily affected by changes in climatic conditions along the elevation gradient in the bamboo plantations (Wang et al, 2016a). However, it is not known whether bamboo soil bacterial groups respond to temperature changes.…”

Response of Humic Acids and Soil Organic Matter to Vegetation Replacement in Subtropical High Mountain Forests

“…The changes in SOM stability and decomposability impact the local and regional C cycles, and the CO 2 exchange process between the soil and atmosphere (Larionova et al, ; Stockmann et al, ). SOM humification and soil C accumulation are sensitive to climatic and local environmental fluctuations and changes in land use and soil management (Wang et al, ; Wang et al, ).…”