Chin J Plan Ecolo ›› 2018, Vol. 42 ›› Issue (4): 508-516.

• Research Articles •

### Relationships between carbon and nitrogen contents and enzyme activities in soil of three typical subtropical forests in China

Yong BAO,Ying GAO,Xiao-Min ZENG,Ping YUAN,You-Tao SI*(),Yue-Min CHEN,Ying-Yi CHEN

1. School of Geography Sciences, Fujian Normal University, Fuzhou 350007, China; and State Key Laboratory of Sub-tropical Mountain Ecology (Founded by Ministry of Science and Technology and Fujian Province), Fujian Normal University, Fuzhou 350007, China
• Online:2018-06-01 Published:2018-04-20

Abstract:

Aims Forest conversion is an important factor affecting the ecosystem organic matter cycle, and has an impact on the productivity of forest ecosystems, carbon sequestration and nutrient conservation. This study aims to provide more scientific evidence for better understanding the mechanism of different forest types regulating forest soil carbon and nitrogen cycling in the context of forest conversion.

Methods The study site is located in Sanming City, Fujian Province, in subtropical China. Soil samples in the A horizon from an artificial-assisted natural regeneration forest of Castanopsis carlesii (AR), a natural secondary forest of C. carlesii (SF) and a plantation of Pinus massoniana (PM) sites were collected in November, 2016. We investigated the contents of soil organic carbon, soil organic nitrogen, soil dissolved organic matter (DOM), NH4 +-N and NO3 --N. The spectroscopic characteristics of soil DOM were also measured by means of ultraviolet absorbance and fluorescence emission spectroscopic techniques. The activity of five kinds of enzymes related to carbon and nitrogen cycle were determined to decipher their relationships with soil properties.

Important findings The results showed that, due to different tree species and man-made disturbance, the contents of dissolved organic carbon (DOC), DON, humification index of fluorescence emission spectrum were all in the order SF > AR > PM, whereas the aromatization index was in the order PM > AR > SF. NH4 +-N were significantly richer for SF and AR than for PM, while NO3 --N content was low and similar across the three stands. The β-glucosidase activity of PM was significantly lower than that of SF and AR. The activities of cellulolytic enzyme were in sequence of AR > SF > PM. The activities of polyphenol oxidase enzyme in PM was significantly higher than in SF and AR. There was no significant difference in the type of forest peroxidase. The activity of β-N-acetylglucosaminidase of AR was significantly higher than those of the other two kinds of stands. The redundancy analysis indicates that total nitrogen (TN) and DON are the major environmental factors driving soil enzyme activity. Soil total nitrogen content and NAG activity were positively correlated, and DON may be an important component of the N cycle. Soil microorganisms prefer to use readily decomposable carbon; and there is a certain coupling relationship between carbon and nitrogen cycles. Higher soil N contents would increase the C-related hydrolytic enzyme activity, thereby promoting carbon turnover.