The subtropical karst region in southwest China has experienced an increase in temperature over the past decades and is predicted to become warmer in the 21st century. Nevertheless, how climate change influences biological N₂ fixation (BNF) has not been investigated in this region.

Free-living BNF may be the dominant pathway of external N inputs in the ecosystems of lacking (or with a low abundance of) N₂-fixing plants. There is large uncertainty in terms of how BNF will respond to climate change. Furthermore, it remains unclear whether BNF in these ecosystem compartments respond similarly or not.

In order to address the above uncertainties, a team from the Institute of Subtropical Agriculture, Chinese Academy of Sciences (ISA) collected soil, litter and moss samples from a secondary forest with a limited abundance of N₂-fixing plants in a subtropical karst region, southwest China. Then, investigated soil, litter and moss responses of BNF to temperature (15, 25 and 35℃) and moisture (low, intermediate and high levels) over a one-week period under laboratory conditions.

The researchers found that the responses of BNF in moss, litter and soil to temperature and moisture were divergent. Litter and soil BNF rates increased with temperature under the three moisture levels.

However, moss BNF rates were decreased, not changed or increased by warming under low, intermediate and high moisture levels, respectively. The temperature sensitivity of BNF was generally highest for litter, intermediate for soil and lowest for moss.

In contrast, the moisture sensitivity of BNF was generally highest for moss, intermediate for soil, and lowest for litter. The findings suggest that different temperature or moisture sensitivities of BNF for the three substrates should be integrated into terrestrial ecosystem models in order to better predict N inputs via BNF under climate change.

This work was supported by the National Natural Science Foundation of China (41571295), the National Key Research and Development Program of China (2016YFC0502404), the National Key Basic Research Program of China (2015CB452703), the Chinese Academy of Sciences through its Program to Dejun Li.

This study entitled “Divergent responses of biological nitrogen fixation in soil, litter and moss to temperature and moisture in a karst forest, southwest China” has been published online in Soil Biology and Biochemistry (Volume 118, Mar 2018). The details could be found at https://www.sciencedirect.com/science/article/pii/S0038071717306739

Contact: LI Dejun

E-mail: dejunli@isa.ac.cn

Institute of Subtropical Agriculture, Chinese Academy of Sciences

Figure 1. Pictures showing the distribution of moss over the forest floor in the karst region. (Image by Li Dejun)