Carbon Storage In Terrestrial Ecosystems Research Articles

Carbon storage in terrestrial ecosystems of China: Estimates at different spatial resolutions and their responses to climate change

The carbon storage of terrestrial ecosystems in China was estimated using acommon carbon density method for vegetation and soils relating to thevegetation types. Usingmedian density estimates, carbon storage of 35.23 Gt (1 Gt = 1015g) in biomass and119.76 Gt in soils with total of 154.99 Gt were calculated based on thebaseline distribution of37 vegetation types. Total carbon storage of the median estimates at differentspatial resolutionswas 153.43, 158.08 and 158.54 Gt, respectively, for the fine (10′),median (20′) and coarse (30′)latitude × longitude grids. There were differences of −1.56, +3.09and +3.55 Gt carbon storagebetween baseline vegetation and those at different spatial resolutions. Changein mappingresolution would change area estimates and hence carbon storage estimates. Thefiner the spatialresolution in mapping vegetation, the closer the carbon storage to thebaseline estimation. Carbonstorage in vegetation and soils for baseline vegetation is quite similar tothat of biomes predictedby BIOME3 for the present climate and CO2 concentration of 340ppmv. Climate changealone as well as climate change with elevated CO2 concentrationwill produce an increasein carbon stored by vegetation and soils, especially a larger increase in thesoils. Total mediancarbon storage of terrestrial ecosystems in China will increase by 5.09 Gt and15.91 Gt for theclimate scenario at CO2 concentration of 340 ppmv and 500 ppmv,respectively. This ismainly due to changes in vegetation areas and the effects of changes inclimate and CO2concentration.

Contribution of increasing CO2 and climate to carbon storage by ecosystems in the United States.

The effects of increasing carbon dioxide (CO2) and climate on net carbon storage in terrestrial ecosystems of the conterminous United States for the period 1895-1993 were modeled with new, detailed historical climate information. For the period 1980-1993, results from an ensemble of three models agree within 25%, simulating a land carbon sink from CO2 and climate effects of 0.08 gigaton of carbon per year. The best estimates of the total sink from inventory data are about three times larger, suggesting that processes such as regrowth on abandoned agricultural land or in forests harvested before 1980 have effects as large as or larger than the direct effects of CO2 and climate. The modeled sink varies by about 100% from year to year as a result of climate variability.

New estimates of carbon transfer to terrestrial ecosystems between the last glacial maximum and the Holocene

Ice core records of atmospheric CO2 show an ≈ 80 ppm rise between the last glacial maximum (LGM) and the mid‐Holocene during a corresponding world‐wide expansion of the terrestrial biomass and changes in ocean chemistry. Therefore, the absolute amount of carbon transferred to the atmosphere, probably from the oceans, remains uncertain. To address this issue, I evaluated changes in terrestrial ecosystem carbon storage and isotopic fractionations between the LGM and the mid‐Holocene using a process‐based terrestrial carbon cycle model forced with two general circulation model (GCM) simulations of each interval. The results indicate that global carbon storage in terrestrial ecosystems (vegetation and soils) increased by 668 Gt C during the last glacial–interglacial transition, a value within the range obtained from a revised global carbon isotope mass‐balance analysis (550–680 Gt C), and consistent with independent estimates from the marine isotopic record.

The sensitivity of terrestrial carbon storage to historical climate variability and atmospheric CO2 in the United States

We use the Terrestrial Ecosystem Model (TEM, Version 4.1) and the land cover data set of the international geosphere’biosphere program to investigate how increasing atmospheric CO2 concentration and climate variability during 1900–1994 affect the carbon storage of terrestrial ecosystems in the conterminous USA, and how carbon storage has been affected by land-use change. The estimates of TEM indicate that over the past 95 years a combination of increasing atmospheric CO2 with historical temperature and precipitation variability causes a 4.2% (4.3 Pg C) decrease in total carbon storage of potential vegetation in the conterminous US, with vegetation carbon decreasing by 7.2% (3.2 Pg C) and soil organic carbon decreasing by 1.9% (1.1 Pg C). Several dry periods including the 1930s and 1950s are responsible for the loss of carbon storage. Our factorial experiments indicate that precipitation variability alone decreases total carbon storage by 9.5%. Temperature variability alone does not significantly affect carbon storage. The effect of CO2 fertilization alone increases total carbon storage by 4.4%. The effects of increasing atmospheric CO2 and climate variability are not additive. Interactions among CO2, temperature and precipitation increase total carbon storage by 1.1%. Our study also shows substantial year-to-year variations in net carbon exchange between the atmosphere and terrestrial ecosystems due to climate variability. Since the 1960s, we estimate these terrestrial ecosystems have acted primarily as a sink of atmospheric CO2 as a result of wetter weather and higher atmospheric CO2 concentrations. For the 1980s, we estimate the natural terrestrial ecosystems, excluding cropland and urban areas, of the conterminous US have accumulated 78.2 Tg C yr-1 because of the combined effect of increasing atmospheric CO2 and climate variability. For the conterminous US, we estimate that the conversion of natural ecosystems to cropland and urban areas has caused a 18.2% (17.7 Pg C) reduction in total carbon storage from that estimated for potential vegetation. The carbon sink capacity of natural terrestrial ecosystems in the conterminous US is about 69% of that estimated for potential vegetation.

Historical variations in terrestrial biospheric carbon storage

Changes in carbon storage in terrestrial ecosystems are a consequence of shifts in the balance between net primary production (NPP) and heterotrophic respiration (RH). Historical climatic variations which favored NPP over RH may have led to increased ecosystem carbon storage and might account for at least part of the “missing” sink required to balance the current century's global carbon budget. To test this hypothesis, we employed a georeferenced global terrestrial biosphere model of 0.5° spatial resolution. The model was driven from an assumed equilibrium in 1900 using gridded historical time series of monthly temperature and precipitation and the historical record of changes in atmospheric CO2 concentration. Interannual variability in climate induced interannual changes in terrestrial biospheric carbon storage and net carbon exchange with the atmosphere of the order of 1–2 Gt C yr−1. With climate change alone, global biospheric carbon storage declined by 1% (23 Gt C) over the period 1900–1988. With the addition of a moderate CO2 fertilization response, biospheric carbon storage increased by 3% (57 Gt C), primarily as a consequence of changes in NPP and litter inputs to the soil system. With CO2 fertilization, the model's cumulative carbon sink for the period 1900–1988 accounts for about 69% of the missing sink derived by deconvolution. For the period 1950–1988, the modeled sink is about 56% of the missing sink. Our results suggest that the temporal evolution of the missing sink over the period 1900–1988 could be a response of the terrestrial biosphere to changes in climate and atmospheric CO2 or perhaps climate change alone. The discrepancy in the magnitudes of the modeled and deconvolved sinks may be due to limitations of the biospheric model or to overestimates of the land‐use source flux.

Influence of rhizodeposition under elevated CO2 on plant nutrition and soil organic matter

Atmospheric CO2 concentrations can influence ecosystem carbon storage through net primary production (NPP), soil carbon storage, or both. In assessing the potential for carbon storage in terrestrial ecosystems under elevated CO2, both NPP and processing of soil organic matter (SOM), as well as the multiple links between them, must be examined. Within this context, both the quantity and quality of carbon flux from roots to soil are important, since roots produce specialized compounds that enhance nutrient acquisition (affecting NPP), and since the flux of organic compounds from roots to soil fuels soil microbial activity (affecting processing of SOM). From the perspective of root physiology, a technique is described which uses genetically engineered bacteria to detect the distribution and amount of flux of particular compounds from single roots to non-sterile soils. Other experiments from several labs are noted which explore effects of elevated CO2 on root acid phosphatase, phosphomonoesterase, and citrate production, all associated with phosphorus nutrition. From a soil perspective, effects of elevated CO2 on the processing of SOM developed under a C4 grassland but planted with C3 California grassland species were examined under low (unamended) and high (amended with 20 g m−2 NPK) nutrients; measurements of soil atmosphere δ13C combined with soil respiration rates show that during vegetative growth in February, elevated CO2 decreased respiration of carbon from C4 SOM in high nutrient soils but not in unamended soils. This emphasis on the impacts of carbon loss from roots on both NPP and SOM processing will be essential to understanding terrestrial ecosystem carbon storage under changing atmospheric CO2 concentrations.