Carbon and nitrogen pools in Chinese fir and evergreen broadleaved forests and changes associated with felling and burning in mid-subtropical China

Abstract. Nitrogen (N) and phosphorus (P) additions to forest ecosystems are known to influence various above-ground properties, such as plant productivity and composition, and below-ground properties, such as soil nutrient cycling. However, our understanding of how soil microbial communities and their functions respond to nutrient additions in subtropical plantations is still not complete. In this study, we added N and P to Chinese fir plantations in subtropical China to examine how nutrient additions influenced soil microbial community composition and enzyme activities. The results showed that most soil microbial properties were responsive to N and/or P additions, but responses often varied depending on the nutrient added and the quantity added. For instance, there were more than 30 % greater increases in the activities of β-Glucosidase (βG) and N-acetyl-β-D-glucosaminidase (NAG) in the treatments that received nutrient additions compared to the control plot, whereas acid phosphatase (aP) activity was always higher (57 and 71 %, respectively) in the P treatment. N and P additions greatly enhanced the PLFA abundanceespecially in the N2P treatment, the bacterial PLFAs (bacPLFAs), fungal PLFAs (funPLFAs) and actinomycic PLFAs (actPLFAs) were about 2.5, 3 and 4 times higher, respectively, than in the CK. Soil enzyme activities were noticeably higher in November than in July, mainly due to seasonal differences in soil moisture content (SMC). βG or NAG activities were significantly and positively correlated with microbial PLFAs. There were also significant relationships between gram-positive (G+) bacteria and all three soil enzymes. These findings indicate that G+ bacteria is the most important microbial community in C, N, and P transformations in Chinese fir plantations, and that βG and NAG would be useful tools for assessing the biogeochemical transformation and metabolic activity of soil microbes. We recommend combined additions of N and P fertilizer to promote soil fertility and microbial activity in this kind of plantation.

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Measuring the Labile and Recalcitrant Pools of Carbon and Nitrogen in Forested and Agricultural Soils: A Study under Tropical Conditions

Forests ◽

10.3390/f10070544 ◽

2019 ◽

Vol 10 (7) ◽

pp. 544

Author(s):

Risely Ferraz de Almeida ◽

Joseph Elias Rodrigues Mikhael ◽

Fernando Oliveira Franco ◽

Luna Monique Fonseca Santana ◽

Beno Wendling

Keyword(s):

Agricultural Soils ◽

Soil Surface ◽

Environmental Stability ◽

Management Systems ◽

Human Intervention ◽

Carbon And Nitrogen ◽

Nitrogen Pools ◽

Tropical Conditions ◽

Recalcitrant Carbon ◽

The Impact

Soil organic carbon and nitrogen can be divided into labile and recalcitrant pools according to the time it takes to be cycled. The way in which carbon and nitrogen pools are cycled and distributed between labile and recalcitrant pools can directly relate to soil quality. This paper tested the hypothesis that labile and recalcitrant pools of carbon and nitrogen vary between agricultural soils with different species and fertilization management systems (nitrogen, phosphorus, and potassium need) under tropical conditions. This study aimed to examine the impact of land-uses on stocks and losses of carbon and nitrogen under tropical conditions. We explored labile (soil microbial biomass and labile carbon) and recalcitrant carbon pools (humin, humic acid, and fulvic acid) in forested and agricultural soils, defined as latosol (forest, fertilized pasture, and unfertilized pasture) and cambisol (forest, coast pasture, sugarcane, and silage corn). Forested soil was used as an appropriate use to soil conservation in tropical that presents levels adequate of carbon and nitrogen stocks and biological condition in soil. Results showed that pools of labile and recalcitrant carbon are different on soil layers and the use of soil. Forest use in cambisol and latosol promoted higher labile and recalcitrant pools of carbon and nitrogen due to the greater environmental stability without human intervention. On the other hand, human intervention occurred in fertilized pasture and coast pasture; however, both uses presented similar recalcitrant carbon and nitrogen pools when compared to forested soil on the soil surface due to fertilizer uses and the high volume of the grass root system. Overall, our findings reveal that under tropical conditions, agriculture and forested soil can present similar recalcitrant pools of carbon and nitrogen if agricultural soils are associated with the appropriate fertilizer management. Pasture with adequate fertilization management systems can be used as an alternative to recover degraded areas with low levels of recalcitrant carbon and nitrogen pools.

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