1 UIUC ATMOS 397G Biogeochemical Cycles and Global Change Lecture 15: Biosphere and Nutrients Don Wuebbles Department of Atmospheric Sciences University of Illinois, Urbana, IL March 18, 2003

2 UIUC The Biosphere (AVHRR measurements)

3 UIUC The Biosphere over Time

4 UIUC Leafing Dates of Oak (1746–present) - This graph shows how the leafing dates of oaks in southeastern England have changed over the past 256 years.

5 UIUC Terrestrial Ecosystems C/N in leaf tissue  50 NPP globally ~ 60 x gC/yr  1.2 x gN needed each year N and P are often limited  supply of these elements may control NPP Nutrients in greater quantities, e.g., Ca and S, have NPP determine their rate of cycling in ecosystems and losses to streamwaters The atmosphere is the major source of C, N, and S in terrestrial ecosystems Rock weathering is the major source for most remaining biochemical elements, e.g., Ca, Mg, K, Fe, P

6 UIUC detailed overlay of N deposition patterns with ecosystem types was key to predicting possible C storage. Where high N deposition occurs on forested systems, there is a potential for significant C storage because forest vegetation has large C:N ratios and long tissue lifetimes in wood. Thus, a map of modeled C uptake using spatially defined estimates of fossil fuel N deposition suggested potential carbon sink hotspots in the mid-latitude forests of the northern hemispere, while at the same time showed that high deposition regions over grassland or agricultural areas, such as the Great Plains, were not likely to produce much carbon storage

7 UIUC Nutrient Intrasystem Cycling Nutrient Intrasystem Cycling Cycling of N within an ecosystem is often 10 to 20X greater than the amount received from outside. Soil chemical reactions (ion exchange, mineral solubility) set constraints for plant uptake of essential elements Plants can release organic compounds that enhance solubility Uptake of N and P is so rapid, and soil concentration so low, that there is often none of these in the vicinity of roots. Diffusion of P is slow and limits supply Plants respond by increasing root/shoot ratio Some plants respond by putting out enzymes to extract nutrients

8 UIUC Nutrients Needed for Growing Corn

9 UIUC Nutrient Uptake by Wheat

10 UIUC Nutrient Balance Plant growth is affected by the balance of nutrients in soil Some trees 100 N:15 P: 50 K: 5 Ca: 5 Mg: 10 S More nutrients occur as positively charged ions in the soil solution Plants will often release H + to maintain balance of charge Plants using NH 4 + as N source tend to acidify the immediate zone around their roots (NO 3 - uptake has opposite effect)

11 UIUC Nutrient Availability Depends on pH of the Soil

12 UIUC Nitrogen Assimilation in Roots of Plants

13 UIUC Nitrogen Assimilation and Nitrogen Fixation Availability of NH 4 + or NO 3 - depends on environmental conditions Waterlogged soils: NH 4 + Desert conditions: NO 3 - Most species show preference for NO 3 - even though NH 4 + is assimilated easier NH 4 + reacts easier in the soil Rate of delivery of NO 3 - to roots is higher Nitrification vs. denitrification

14 UIUC Nitrogen in the Plant

15 UIUC Nitrogen Fixation in Trees

16 UIUC Inorganic nitrogen cycle no nitrogen is found in native rock the ultimate source of nitrogen for ecosystems is molecular nitrogen (N 2 ) in the atmosphere (78.1% by volume) N 2 may dissolve in water virtually all nitrogen would occur as N 2 if not for biological processes occurring in the presence of oxygen Molecular nitrogen enters biological pathways through nitrogen fixation by certain microorganisms:

17 UIUC