. Productivity changes of wetland and grassland ecosystems along a latitudal gradient

Abstract

The aim of the study. Analysis of changes in the productivity of dwarf shrub-moss-lichen, pine-dwarf shrub-sphagnum and sedge-sphagnum and grass ecosystems along the latitudinal gradient. Methodology. For a number of bog and grass ecosystems located along a latitudinal gradient from 65 to 50° N in the range of longitudes from 63 to 95° E the stocks of live and dead, aboveground and belowground phytomass, as well as the values of aboveground (ANP), belowground (BNP) and total production (NPP) were analyzed. The data are given for 45 ecosystems grouped into 12 types from forest-tundra mires to desert steppes. The vegetation of ecosystems is represented by bog one (mosses, shrubs and grasses) to the steppe (mesoxerophytic and xerophytic grasses). Since the spread of data on stocks and production for individual ecosystems is large, we present averaged data for ecosystem types. Main results. The largest stock of green phytomass was obtained for floodplain meadows (7 t/ha), the smallest stock was found in the desert steppes (0.8 t/ha). The stock of dead aboveground phytomass was maximal in the fens of the forest-steppe zone (10 t/ha) and minimal in the oligotrophic hollows of boreal bogs (0.3 t/ha). The stock of living belowground organs decreases along a latitudinal gradient from 20 (true steppes) to 3 t/ha (desert steppes), whereas the stock of dead belowground organs decreased from 79 (fens of the forest-steppe zone) to 4 t/ha (in the ryams of the middle taiga and desert steppes). Above-ground production was estimated as highest in the fens of the forest-steppe zone (12), decreasing along the latitudinal gradient down to the desert steppes (1 t/ha per year). Belowground production in all types of ecosystems studied was higher than the above-ground one, ranging from 45 (fens of the forest-steppe zone) to 3 t/ha per year (mires in the forest-tundra). The NPP value in some of the studied ecosystems varied from 57 (fens of the forest-steppe zone) to 5 t/ha per year (mires in the forest-tundra). The BNP/ANP ratio averaged over ecosystem types was maximal in the desert steppes (5.9) and minimal in floodplain meadows (1.9). In the range of latitudes 56-52°N, where steppe meadows, meadow steppes and true steppes located, the NPP, averaged over these ecosystems, varied from 22 to 24 t/ha per year. These ecosystems the most fertile soils of the region, i.e. meadow chernozem and ordinary chernozem (Phaeozems) were developed. To the north and south of this area, the NPP value decreases: to the north due to the lack of heat, and to the south due to lack of moisture. Conclusions. In the biotic cycle in mires differs from that in meadows and steppes by the annual sequestration of a part of the carbon influx in the forming peat. This amount of carbon sequestration is about 10% of the NPP of the wetland ecosystem. In the climax grass ecosystems, the carbon influx is equal to its outflux. These ecosystems are acting as gas exchangers between plants, soil and atmosphere. In contrast to grasslands, wetlands are acting as carbon accumulators that lower the CO2 in the air.