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Peatlands in the Sanjiang Plain could be more vulnerable to global warming because they are located at the southernmost boundary of northern peatlands. Unlike bacteria, fungi are often overlooked, even though they play important roles in substance circulation in the peatland ecosystems. Accordingly, it is imperative that we deepen our understanding of fungal community structure and diversity in the peatlands. In this study, high-throughput Illumina sequencing was used to study the fungal communities in three fens in the Sanjiang Plain, located at the southern edge of northern peatlands. Peat soil was collected from the three fens which developed during different periods. A total of 463,198 fungal ITS sequences were obtained, and these sequences were classified into at least six phyla, 21 classes, more than 60 orders and over 200 genera. The fungal community structures were distinct in the three sites and were dominated by Ascomycota and Basidiomycota. However, there were no significant differences between these three fens in any α-diversity index (p > 0.05). Soil age and the carbon (C) accumulation rate, as well as total carbon (TC), total nitrogen (TN), C/N ratio, and bulk density were found to be closely related to the abundance of several dominant fungal taxa. We captured a rich fungal community and confirmed that the dominant taxa were those which were frequently detected in other northern peatlands. Soil age and the C accumulation rate were found to play important roles in shaping the fungal community structure. [ABSTRACT FROM AUTHOR]

Understanding the fire evolution history and its driving mechanisms can provide useful insights into the fire regimes and their potential impacts in the future. Here, we present a well-dated peat profile with high-resolution charcoal and pollen records to reconstruct the fire and vegetation history in the Sanjiang Plain over the last 6000 yr. The regional and local fire frequencies were reconstructed with the microscopic (< 125 μm) and macroscopic (> 125 μm) charcoal fractions, respectively. During the interval ~ 6.0–4.5 ka BP, both the regional and local fires exhibited much low frequencies responding to the strong summer monsoon. Thereafter, the fire frequencies increased significantly with the decline of the summer monsoon, and the highest frequencies corresponded well with the weak monsoon intervals around 4.0, 2.7, and 0.8 ka BP. As for the local fires, in addition to the climate changes, the local vegetation conditions have also served an important role in driving their occurrences. During the last 300 yr, the gradually increased fire frequencies were attributed to the intensified human activities instead of the climate and vegetation influences. [ABSTRACT FROM AUTHOR]

Compared to the well-studied the grain-size depositional process in hydraulic and aeolian sediments, the process in wetlands is still poorly understood. In this study, the grain-size components of a well-dated mud/peat profile (SJ2) in the Sanjiang Plain were partitioned using a lognormal distribution function. The results suggest that the lacustrine deposits contain four distinct unimodal grain-size distributions, C-1 through C-4, with their modal sizes ranging 0.7–1.6, 2.4–8.7, 15.7–27.8, and 380.2–529.6 μm respectively. Only the C-1 and C-3 were identified in the peat layers. A grain-size depositional modal was introduced to explain the environmental meanings of the four components. C-3, as a nearshore suspension component, was the most sensitive component to the variation of local hydraulic conditions. Based on the variation of C-3 percentages of the profile SJ2, the local hydraulic conditions were tentatively reconstructed, and the results showed a close relation with the monsoon variations during the Holocene. Accordingly, we suggest the relative coarse component of the polymodal peat deposits in monsoonal regions can be used as a sensitive indicator for the hydraulic conditions and the monsoon circulations in the geological past. [ABSTRACT FROM AUTHOR]

Principal component analysis (PCA) and enrichment factor (EF) were used to investigate the trace and major element concentrations in peat soils of Sanjiang Plain, northeast China. The results showed that elements and paleoenvironmental proxies could be divided into four factoring trends in the late Holocene: (1) soil character change (conservative trace elements and chemical changes) (F1), (2) water table change (aerobic/anaerobic changes) (F2), (3) ability of heavy metal storage change (F3), and climate dry/wet change (F4). In addition, carbon accumulation rates were affected by climate dry/wet change and human activities influence in the recent 1000 years. Furthermore, the results suggested that the concentrations of pollution elements were controlled by both nature and human activities. Anthropogenic influences are the main source of heavy metals in the study sites in the last 200 years. [ABSTRACT FROM AUTHOR]