1 UIUC ATMOS 397G Biogeochemical Cycles and Global Change Lecture 15: Biosphere and Nutrients Don...
-
Upload
beatrix-horn -
Category
Documents
-
view
212 -
download
0
Transcript of 1 UIUC ATMOS 397G Biogeochemical Cycles and Global Change Lecture 15: Biosphere and Nutrients Don...
1
UIUCUIUC
ATMOS 397GATMOS 397GBiogeochemical Cycles and Global ChangeBiogeochemical Cycles and Global Change
Lecture 15: Biosphere and NutrientsLecture 15: Biosphere and Nutrients
Don WuebblesDon Wuebbles
Department of Atmospheric SciencesDepartment of Atmospheric Sciences
University of Illinois, Urbana, ILUniversity of Illinois, Urbana, IL
March 18, 2003March 18, 2003
4
UIUCUIUC
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
UIUCUIUC
Terrestrial EcosystemsTerrestrial Ecosystems
C/N in leaf tissue 50 NPP globally ~ 60 x 1015 gC/yr 1.2 x 1015 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
UIUCUIUC
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
UIUCUIUC
Nutrient Intrasystem CyclingNutrient 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
10
UIUCUIUC
Nutrient BalanceNutrient 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 NH4+ as N source tend to acidify the
immediate zone around their roots (NO3- uptake
has opposite effect)
13
UIUCUIUC
Nitrogen Assimilation and Nitrogen FixationNitrogen Assimilation and Nitrogen Fixation
Availability of NH4+ or NO3
- depends on environmental conditions
Waterlogged soils: NH4+
Desert conditions: NO3-
Most species show preference for NO3- even
though NH4+ is assimilated easier
NH4+ reacts easier in the soil
Rate of delivery of NO3- to roots is higher
Nitrification vs. denitrification
16
UIUCUIUC
Inorganic nitrogen cycle
•no nitrogen is found in native rock
•the ultimate source of nitrogen for ecosystems is molecular nitrogen (N2) in the atmosphere (78.1% by volume)
•N2 may dissolve in water
•virtually all nitrogen would occur as N2 if not for biological processes occurring in the presence of oxygen
Molecular nitrogen enters biological pathways through nitrogen fixation by certain microorganisms: