Warming and nitrogen deposition are interactive in shaping surface soil microbial communities near the alpine timberline zone on the eastern Qinghai–Tibet Plateau, southwestern China

Abstract

Changes to global climate patterns have the potential to alter the structure of soil microbial communities which are key components of terrestrial ecosystems. High altitude ecosystems are both temperature and Nitrogen-limited and the biota therein is sensitive to these conditions. Temperatures and nitrogen (N) depositions in the eastern Qinghai–Tibet Plateau are predicted to sharp rise by the end of this century. This study aimed to better understand the effects of warming and N addition treatments alone and in combination on an alpine meadow ecosystem near the timberline zone in the eastern region of the Qinghai–Tibet Plateau. The field experiment included replicated plots with an ambient treatment alone or with low N (5gNm−2a−1), intermediate N (15gNm−2a−1), and high N (30gNm−2a−1) (Control, LN, MN, HN) and open top chambers warming treatment alone, or LN and HN additions (W, WLN, WHN) to study the interactive effects of the warming and N additions on the soil microbial community as determined by phospholipid fatty acids (PLFAs). Microbial communities and their allied soil and plant properties were examined after 3 years of the treatments. The strength of the relationship between the treatments and their direct and indirect effects on the microbial communities, soil and plant properties were determined using a structural equation model (SEqM). The results indicated that N addition significantly changed surface soil microbial communities, in particular, decreased the fungi: bacteria ratio (F:B) (p<0.01). The warming differentially influenced some specific microbial biomarkers, such as fungal PLFAs which decreased, and actinobacterial PLFAs, which increased, under warming (p<0.05). The combination of the warming and N addition showed significantly positive interactive effects (p<0.001) on soil microorganisms (i.e. the biomass of general bacteria, Gram-positive bacteria, fungi and etc.) in these alpine soils. The SEqM results show the direct effects of the warming treatment on soil microorganisms were less than those from the N additions. Moreover, warming and N addition had stronger indirect, than direct, effects on the soil microbial community via induced changes in soil properties and plant community. The total effect of warming on the soil microbial community was stronger than that of the N additions. The results suggested interactive effects of the warming and N addition on soil microorganisms in an near timberline alpine ecosystem in the eastern Qinghai-Tibet Plateau.