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Abstract
Soil microbes play an essential role in the forest ecosystem as an active component. This study examined the hypothesis that soil microbial community structure and metabolic activity would vary with the increasing stand ages in long-term pure plantations of Pinus elliottii. The phospholipid fatty acids (PLFA) combined with community level physiological profiles (CLPP) method was used to assess these characteristics in the rhizospheric soils of P. elliottii. We found that the soil microbial communities were significantly different among different stand ages of P. elliottii plantations. The PLFA analysis indicated that the bacterial biomass was higher than the actinomycic and fungal biomass in all stand ages. However, the bacterial biomass decreased with the increasing stand ages, while the fungal biomass increased. The four maximum biomarker concentrations in rhizospheric soils of P. elliottii for all stand ages were 18:1ω9c, 16:1ω7c, 18:3ω6c (6,9,12) and cy19:0, representing measures of fungal and gram negative bacterial biomass. In addition, CLPP analysis revealed that the utilization rate of amino acids, polymers, phenolic acids, and carbohydrates of soil microbial community gradually decreased with increasing stand ages, though this pattern was not observed for carboxylic acids and amines. Microbial community diversity, as determined by the Simpson index, Shannon-Wiener index, Richness index and McIntosh index, significantly decreased as stand age increased. Overall, both the PLFA and CLPP illustrated that the long-term pure plantation pattern exacerbated the microecological imbalance previously described in the rhizospheric soils of P. elliottii, and markedly decreased the soil microbial community diversity and metabolic activity. Based on the correlation analysis, we concluded that the soil nutrient and C/N ratio most significantly contributed to the variation of soil microbial community structure and metabolic activity in different stand ages of P. elliottii plantations.
Highlights
Pinus elliottii is a tree species native to the southeastern United States, and has been widely planted in China since 1980s due to its forage characteristics of high yield and fast growth [1]
The goal of this study was to answer two questions: (1) how different stand ages of P. elliottii plantations affect soil microbial community structure and metabolic activity? and (2) What are the possible environmental factors leading to these differences? For these objectives, phospholipid fatty acids (PLFA) combined with community level physiological profiles (CLPP) methods were used to detect the variation of soil microbial community structure and metabolic activity in P. elliottii plantations
Our study demonstrated that soil microbial community diversity and metabolic activity decreased with increasing stand ages in P. elliottii plantations
Summary
Pinus elliottii is a tree species native to the southeastern United States, and has been widely planted in China since 1980s due to its forage characteristics of high yield and fast growth [1]. It covers 11 provinces and has become one of the most important economic tree species in China [2]. Previous studies have shown that continuous cultivation of a single species resulted in degradation of the soil [4] This phenomenon has been observed in many cultivated tree species, such as Cunninghamia lanceolata, Larix gmelinii, Pinus massoniana, Eucalyptus spp., and Populus spp. Restricted by soil ecosystem complexity and reliable experimental methods, the effects of P. elliottii long-term pure plantation patterns on the below-ground soil microbial community has not yet been reported
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