Isotopic evidence for increased carbon and nitrogen exchanges between peatland plants and their symbiotic microbes with rising atmospheric CO2 concentrations since 15000 cal. yr BP

Whether nitrogen (N) availability will limit plant growth and removal of atmospheric CO2 this century is controversial. Studies have suggested that N could progressively limit plant growth, as trees and soils accumulate N in slowly cycling biomass pools in response to increases in carbon sequestration. However, a question remains over the longer-term (decadal to century) feedbacks between climate, CO2 and plant N uptake. The symbiosis between plants and microbes can help plants with mycorrhizal N uptake or biological N2 fixation – the pathway through which N can be rapidly brought into ecosystems and thereby partially or completely alleviate N limitation on plant productivity. Here we present results for plant N isotope composition (δ15N) in a peat core that dates to 15000 cal. yr BP to ascertain ecosystem-level N cycling responses to rising atmospheric CO2 concentrations in the past. We found that an increase in atmospheric CO2 concentration happened with a decrease in δ15N values of b..., 1. Study sites and sampling monoliths
The peat core (42.227° N, 126.525° E) was collected in Hani, a valley peatland situated in the middle of the Longgang Mountain Chain which is part of the western flank of the Changbai Mountains, Northeast China. The present surface vegetation community mainly comprises of Betula ovalifolia, Ledum palustre, Phragmites australis, Vaccinium uliginosum, Carex limosa, S. palustre, S. magellanicum, S. cuspidatum, S. subsecundum, S. imbricatum, Polytrichum strictum and Aulacomnium palustre. The mean annual temperature and precipitation range from 0.8 to 5.4 ℃ and from 490 to 1300 mm, respectively from local instrumental records (Jingyu County) during 1955–2019 AD. The length of this core was 8.77 m. The peat core was described and cut with stainless steel at 1 cm intervals in the field. All of the samples were packed in plastic bags and stored at 4 ℃ in a refrigerator for further analyses.
2. Radiocarbon dating
The chronology of the peat core was based on ...,