Developing understanding of biotic turnover

Abstract

Over the last 50 years A.A. Titlyanova with her colleagues from the Laboratory of Biogeocenology in the Institute of Soil Science and Agrochemistry of the Siberian Branch of the Russian Academy of Sciences has been actively studying biotic turnover components and processes: the flow of carbon and its stocks in various ecosystem blocks were estimated, and turnover regimes revealed. The performed field experiments showed that the nearer an ecosystem is to the stationary state, the more closed its biotic turnover becomes, and the lesser role is played by abiotic processes. The studies in diverse ecosystems confirmed that climatic and weather conditions, soil properties as well as ecosystem’s relief position and exposition are the main factors driving the net primary production of grassland ecosystems. The article presents and discuss earlier results about phytomass dynamics and provides estimates of the net primary production, both above- and belowground. The belowground plant organs, i.e. roots and rhizomes, preserve life of a grassland ecosystem under any climatic conditions. Sustainability of grasslands in time depends on the changes in plant species composition, diverse survival strategies, high productivity of the dominant plant species, soil seed bank and their aeolian and water transportation from other ecosystems, rapid release of nutrients from residues by mineralization. Analysis of different successions in ecosystems allowed concluding that the number of succession types is higher than only two main types of primary and secondary succession. The primary succession refers only to those successions that occur by spontaneous revegetation at sites without any history of previous vegetation, whereas the secondary successions are more diverse and include pyrogenic (renovating succession), pasture (continuous and reversible), abandoned field successions and others. Not only the biotic turnover, but strong in- and outcoming flows of matter and energy operate in each and every ecosystem. Presently turnover can be better described as a network of diversified processes, rather than a circle per se.