Abstract
The freezing–thawing cycle is a basic feature of a frozen soil ecosystem, and it affects the growth of alpine vegetation both directly and indirectly. As the climate changes, the freezing–thawing mode, along with its impact on frozen soil ecosystems, also changes. In this research, the freezing–thawing cycle of the Nagqu River Basin in the Qinghai–Tibet Plateau was studied. Vegetation growth characteristics and microbial abundance were analyzed under different freezing–thawing modes. The direct and indirect effects of the freezing–thawing cycle mode on alpine vegetation in the Nagqu River Basin are presented, and the changing trends and hazards of the freezing–thawing cycle mode due to climate change are discussed. The results highlight two major findings. First, the freezing–thawing cycle in the Nagqu River Basin has a high-frequency mode (HFM) and a low-frequency mode (LFM). With the influence of climate change, the LFM is gradually shifting to the HFM. Second, the alpine vegetation biomass in the HFM is lower than that in the LFM. Frequent freezing–thawing cycles reduce root cell activity and can even lead to root cell death. On the other hand, frequent freezing–thawing cycles increase microbial (Bradyrhizobium, Mesorhizobium, and Pseudomonas) death, weaken symbiotic nitrogen fixation and the disease resistance of vegetation, accelerate soil nutrient loss, reduce the soil water holding capacity and soil moisture, and hinder root growth. This study provides a complete response mechanism of alpine vegetation to the freezing–thawing cycle frequency while providing a theoretical basis for studying the change direction and impact on the frozen soil ecosystem due to climate change.
Highlights
The freezing–thawing cycle (FTC) data that were used to determine the impact on plant growth were from 1 January to 30 June
Through the analysis of freezing–thawing cycle characteristics, this study showed that the freezing–thawing cycle mode fluctuates between the high-frequency mode (HFM) and the low-frequency mode (LFM) in the Nagqu River Basin of the Qinghai–Tibet Plateau
With the influence of climate change, the LFM is gradually shifting to the HFM
Summary
Vegetation is an important part of the soil ecosystem and is critical for soil and water conservation, soil remediation, the development of animal husbandry, and ecosystem function and services [1,2,3,4,5,6].As a special soil ecosystem [7,8], the frozen soil ecosystem contains unique alpine vegetation [9,10].Alpine vegetation is sensitive to environmental factors [11,12,13,14], and the freezing–thawing cycle is the most important environmental factor affecting vegetation growth and survival in alpine regions.Water 2019, 11, 2122; doi:10.3390/w11102122 www.mdpi.com/journal/wateralpine vegetation is a useful indicator of changes in environmental factors due toWater 2019, 11, x FOR PEER REVIEW climate change.The freezing–thawing cycle (FTC) is a phenomenon in which the soil undergoes repeated freezingThe freezing–thawing cycle (FTC) is a phenomenon in which the soil undergoes repeated and melting as a result of seasonal or diurnal temperature change [15]. Alpine vegetation is sensitive to environmental factors [11,12,13,14], and the freezing–thawing cycle is the most important environmental factor affecting vegetation growth and survival in alpine regions. The freezing–thawing cycle (FTC) is a phenomenon in which the soil undergoes repeated freezing. The freezing–thawing cycle (FTC) is a phenomenon in which the soil undergoes repeated and melting as a result of seasonal or diurnal temperature change [15]. Frequent low-temperature freezing and melting as a result of seasonal or diurnal temperature change [15]. Frequent lowdisturbances can damage vegetation roots and directly affect vegetation growth [16,17,18]. Among the temperature disturbances can damage vegetation roots and directly affect vegetation growth [16,17,18]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
