Presentation Title

Will nutrient limitation worsen climate change?

Authors' Names

Alanna Shaw

Presentation Type

Oral Presentation

Abstract

Many climate models predict increasing atmospheric carbon dioxide (CO2) concentrations will increase the amount of carbon (C) terrestrial ecosystems can store. Higher levels of C storage in terrestrial ecosystems may slow the pace of climate warming caused by human activities. Nutrients must be available in sufficient quantities to support increased C storage, however, and when these predictions are adjusted for their availability they are muted or even reversed, with terrestrial ecosystems releasing CO2 instead of storing more C. Therefore, an increase in productivity and C storage levels would require new nutrient inputs or an increase in the rates of nutrient recycling– or reuse – within terrestrial ecosystems. The two main nutrients that limit C storage in terrestrial ecosystems are nitrogen (N) and phosphorus (P). Multiple pathways of new N inputs exist and there is some evidence that climate warming could increase N recycling rates. By contrast, P inputs to ecosystems are very low and temperature effects on P recycling rates remain poorly understood. Under current conditions, recycled P supports more than half of P demand for the growth of tropical rain forests, which are responsible for a disproportionately large share of C storage for the size of their land mass. Future increases in C storage would require elevated P recycling rates to keep up with elevated demand. To test the effects of temperature on P recycling rates, we incubated soils from two tropical rain forest sites at a range of temperatures below and above the average annual temperature for each site, respectively. We measured P recycling rates and the activities of the enzymes responsible for this recycling process. We predicted that rates of P recycling would increase with temperature because enzymatic recycling processes tend to be sensitive to temperature increases.

The rate of P recycling increased with temperature at both sites, but only significantly so when temperatures were at least 10oC greater than the site average annual temperature. The P recycling rate response to temperature was stronger at the site with less P. Even though the direct predictions of global climate warming only predict 3-5oC temperature increases by 2100, our results suggest that ecologically relevant increases in P recycling rates in tropical rainforests likely require temperature increases much greater than those predicted for human caused climate warming. Therefore, while terrestrial ecosystems may be able to overcome potential nutrient constraints to C storage by recycling nutrients more quickly, our preliminary results suggest that climate warming driven increases in nutrient recycling rates are insufficient to meet the future nutrient demands of elevated C storage.

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Apr 27th, 9:40 AM Apr 27th, 9:55 AM

Will nutrient limitation worsen climate change?

UC Ballroom, Pod #2

Many climate models predict increasing atmospheric carbon dioxide (CO2) concentrations will increase the amount of carbon (C) terrestrial ecosystems can store. Higher levels of C storage in terrestrial ecosystems may slow the pace of climate warming caused by human activities. Nutrients must be available in sufficient quantities to support increased C storage, however, and when these predictions are adjusted for their availability they are muted or even reversed, with terrestrial ecosystems releasing CO2 instead of storing more C. Therefore, an increase in productivity and C storage levels would require new nutrient inputs or an increase in the rates of nutrient recycling– or reuse – within terrestrial ecosystems. The two main nutrients that limit C storage in terrestrial ecosystems are nitrogen (N) and phosphorus (P). Multiple pathways of new N inputs exist and there is some evidence that climate warming could increase N recycling rates. By contrast, P inputs to ecosystems are very low and temperature effects on P recycling rates remain poorly understood. Under current conditions, recycled P supports more than half of P demand for the growth of tropical rain forests, which are responsible for a disproportionately large share of C storage for the size of their land mass. Future increases in C storage would require elevated P recycling rates to keep up with elevated demand. To test the effects of temperature on P recycling rates, we incubated soils from two tropical rain forest sites at a range of temperatures below and above the average annual temperature for each site, respectively. We measured P recycling rates and the activities of the enzymes responsible for this recycling process. We predicted that rates of P recycling would increase with temperature because enzymatic recycling processes tend to be sensitive to temperature increases.

The rate of P recycling increased with temperature at both sites, but only significantly so when temperatures were at least 10oC greater than the site average annual temperature. The P recycling rate response to temperature was stronger at the site with less P. Even though the direct predictions of global climate warming only predict 3-5oC temperature increases by 2100, our results suggest that ecologically relevant increases in P recycling rates in tropical rainforests likely require temperature increases much greater than those predicted for human caused climate warming. Therefore, while terrestrial ecosystems may be able to overcome potential nutrient constraints to C storage by recycling nutrients more quickly, our preliminary results suggest that climate warming driven increases in nutrient recycling rates are insufficient to meet the future nutrient demands of elevated C storage.