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We drilled a core in Tingming Lake (located at the tree line) to conduct pollen and diatom analyses. The pollen record shows that the vegetation ecosystem is very stable and has no obvious regime shift signals, although the vegetable belt has moved gradually upward or downward under the backdrop of climate change. There may be a positive relationship between the vegetation ecosystem stability and the turnover component (β sim). Diatoms, which record the lake ecosystem, show an obvious regime shift signal in 1929 AD, which was possibly was due to environmental changes or decreased nutrient inputs. However, there were fluctuations in species richness and species dissimilarity and there was a slightly increased β diversity (β sor), which was mainly interpreted by the increased turnover component (β sim). It is difficult to determine the relationship between the unstable stability and diversity fluctuations. Therefore, the relationships between diversity and stability in the adjacent vegetation and lake ecosystems are different. It is possible that β diversity partitioning may lead to an improved understanding of ecosystem stability. [ABSTRACT FROM AUTHOR]

There is no doubt that the diversity and stability of freshwater ecosystems have suffered dramatic changes as a result of intensified human activities. However, the relationship between community diversity and stability is still debated. In this study, we used biological and geochemical records from the recent sediments of two lakes to test the hypothesis that different aspects of the diversity of the chironomid community have different relationships with community stability. Yangzong Lake (YZ) and Chenghai Lake (CH) are large and deep alpine lakes in SW China. We conducted a multi-proxy study of the sedimentary records spanning the last 200 years from the two lakes. Our focus was on subfossil chironomid remains, but analyses of chemical elements, total organic carbon (TOC) and total nitrogen (TN) were also conducted. The principal results are as follows: 1) Both nutrient and chironomid assemblages underwent a critical transition in 1990 at YZ and in 1998 at CH. 2) The response of species richness varied between the two lakes, but the trends of their respective β diversity indices are consistent, despite the fact that the contributors to β diversity are different. 3) The stability of the chironomid communities has decreased in both lakes since the mid-20th century. 4) The relationship between diversity and stability varies in relation to the type of diversity. Overall, our results emphasize the importance of considering the complex nature of diversity and stability when studying community assemblages. Unlabelled Image • Chironomid in two lakes were used for assessing community diversity and stability. • Chironomid communities experienced critical transitions in 1990s. • Definition of diversity determines its relationship with stability. • β diversity partitioning revealed the mechanisms behind this relationship. [ABSTRACT FROM AUTHOR]