Productivity of grassland ecosystems in the Tyva Republic, Russia

The aim of the study. The aim of the study was to estimate biological productivity of Tyva grasslands. Location and time of the study. The living and dead above- and belowground phytomass, as well as net primary production, were estimated in the montane ecosystems and depressions of the Tyva Republic, Russia. Methodology. Field and laboratory studies of the biological production by grasslands were conducted using botanical, geobotanical and ecological methods. Main results. In the montane ecosystems the aboveground phytomass production was shown to range from 1.3 to 3.6 Mg ha-1 yr-1, whereas the belowground production was evaluated as ranging 10-65 Mg ha-1 yr-1. The belowground production was found to vary widely, being associated with location of mountain ridges, slope geomorphology and grazing, but no association was found with the altitude. In depressions the average green phytomass stock changed from 0.7 to 1.9 Mg ha-1, living belowground phytomass varied 3.4 to 19.3 Mg ha-1. From the meadow steppes to the deserted ones the living above- and belowground stocks decreased 2.7 and 5.7 fold, respectively, whereas the above- and belowground production was estimated to decrease 3 and 4 times, respectively. Several indices to characterize the growth and development, hence the productivity, of herbaceous plants was proposed. The values of the indices calculated for the Tyva grasslands suggested high photosynthetic activity: all studied steppes had the same share of belowground production in the total ecosystem production, i.e. 90%. The turnover rate of the living belowground phytomass was estimated to increase from meadow steppes to the deserted ones, whereas green phytomass increment, as related to its stock, slightly decreased. Conclusions. The living belowground phytomass stock was found to exceed the green phytomass stock by 5-8 times, both in montane ecosystems and depressions. Preservation of living belowground organs during hot dry summers and cold winters, when soil freezes through, is apparently indispensable for grassland survival under any climatic conditions.

Soil carbon may be maintained under grazing in a St Lawrence Estuary tidal marsh

SUMMARYProduction of belowground organic matter is critical to sustainability of salt marshes. It plays a role in vertical soil accretion, a process essential for salt marshes to maintain their relative elevation and persist as sea levels rise. This paper examines belowground production and soil carbon of a high-latitude saltmarsh in the St Lawrence Estuary (Québec, Canada), which had been subjected to six years of sheep grazing. In the seventh year, without sheep, organic matter production in grazed and ungrazed sections was assessed by examining harvests of plant litter, end-of-season standing crop, and the roots and rhizomes present in in-growth cores. Excepting salinity, porewater chemistry varied little. The grazed marsh had higher soil carbon density and belowground production, yet lower aboveground biomass. Grazing reduces plant litter and increases solar exposure, soil temperature (at this latitude, soil remained frozen until April) and evapotranspiration, thus raising soil salinity and nitrogen demand, the latter a driver of root production. Grazing may not be detrimental to soil carbon storage. Permitting certain types of grazing on restored salt marshes previously drained for agriculture would provide economic incentive to restore tidal flooding, because the natural carbon sink provided in the recovered marsh would make these lands eligible for carbon payments.

Drought effects on litterfall, wood production and belowground carbon cycling in an Amazon forest: results of a throughfall reduction experiment

The Amazon Basin experiences severe droughts that may become more common in the future. Little is known of the effects of such droughts on Amazon forest productivity and carbon allocation. We tested the prediction that severe drought decreases litterfall and wood production but potentially has multiple cancelling effects on belowground production within a 7-year partial throughfall exclusion experiment. We simulated an approximately 35–41% reduction in effective rainfall from 2000 through 2004 in a 1 ha plot and compared forest response with a similar control plot. Wood production was the most sensitive component of above-ground net primary productivity (ANPP) to drought, declining by 13% the first year and up to 62% thereafter. Litterfall declined only in the third year of drought, with a maximum difference of 23% below the control plot. Soil CO 2 efflux and its 14 C signature showed no significant treatment response, suggesting similar amounts and sources of belowground production. ANPP was similar between plots in 2000 and declined to a low of 41% below the control plot during the subsequent treatment years, rebounding to only a 10% difference during the first post-treatment year. Live aboveground carbon declined by 32.5 Mg ha −1 through the effects of drought on ANPP and tree mortality. Results of this unreplicated, long-term, large-scale ecosystem manipulation experiment demonstrate that multi-year severe drought can substantially reduce Amazon forest carbon stocks.