4.3 Relationships among GRSP, SOC, and soil variables
GRSP content was significantly
positively correlated with SOC and TN. GRSP comprises carbon and
nitrogen and is highly correlated with the carbon and nitrogen content
in the soil (Vasconcellos et al., 2016). Other studies have also shown a
positive relationship between GRSP with SOC and TN (Zhang et al., 2015;
Wang et al., 2018; Qiao et al., 2019). C and N contents in glomalin
represent 4–5% of the total soil C and N (Rillig et al., 2001). GRSP
content was associated with SOC probably because GRSP is also a
component of soil organic matter (Rillig et al., 2001). Besides, GRSP
and SOC depend on similar ecosystem component (photosynthetic
productivity) and contribute to similar ecosystem functions (feeding
decomposer community and formation of soil aggregates) (Kumar et al.,
2018). Moreover, GRSP promotes soil C pools in native grasslands for a
soil binding agent (Purin et al. 2006). In summary,
GRSP regulates the accumulation
and circulation of SOC in alpine grassland soils. Meanwhile, GRSP is an
N-linked glycoprotein that increases soil N levels (Wright and
Upadhyaya, 1998).
GRSP content was negatively correlated with pH, consistent with other
studies (Wang et al., 2014; Wang et al., 2017). Antibus et al. (2006)
also indicated that EE-GRSP is negatively correlated with pH. Previous
studies have also shown that soil pH regulates GRSP accumulation,
precipitated under acidic conditions, and soluble under alkaline pH
conditions (Singh et al., 2017). Decreased soil pH facilitates GRSP
accumulation (Wang et al., 2017), explaining the negative correlation
between GRSP and pH.
5. CONCLUSION
This study demonstrated that livestock grazing can change GRSP stability
in alpine grassland. Also, T-GRSP and EE-GRSP contents were gradually
decreased as grazing intensity increased. Grazing also affects SOC
fixation. The succession process of alpine grassland also causes various
soil organic carbon succession. GRSP is strong positive correlated with
SOC and TN, and GRSP contributing 3.7-14.18% of SOC. N and P nutrient
addition for five years increases the available N and P content, but it
does not affect SOC and GRSP contents. Therefore, GRSP is a stable
organic carbon and regulates SOC fixation. Moreover, short-term grazing
cannot affect GRSP stability, but long-term overgrazing can gradually
reduce GRSP stability. This study showed the impact of grazing and
fertilization on GRSP and another indicator of stable soil carbon.
Therefore, it provides insights into the changes of soil carbon pool and
ecological stoichiometry during grassland succession on the
Qinghai-Tibet plateau.
ACKNOWLEDGEMENTS
This work was financially supported by the National Natural Science
Foundation of China (32171650, 31400483, 41730752), the National Program
on Key Basic Research Project (2014CB954002). We thank Xun ke, Yanan
Sun, Shuli Liu, Jingzheng Ouyang from the Northwest Institute of Plateau
Biology, Chinese Academy of Sciences, for assistance in soil sampling.
We also heartily acknowledge the input from anonymous reviewers and
editors that improved earlier versions of this manuscript.