The Importance Of Soil Respiration

The aim of this chapter is to explain the importance and roles soil respiration has in top-ics which is related with, as the ecosystem carbon balance, nutrient processes, carbon cycling, carbon storage or a topic that is always present talking about nature, climate change.

2.5.1 Soil respiration and ecosystem carbon balance

The carbon cycle in an ecosystem starts with photosynthesis, where plants take CO2 from the air and convert it to organic compounds. Some of these compounds are used to grow leaves, stems and roots; and some are broken down to supply energy to the plant. (Lou & Zhou 2006, 17-18).

During this process, CO2 is released again to the atmosphere by plant respiration. Dead plant materials are decomposed by microorganisms to

At the beginning of the decomposition, the mineralized nitrogen from litter is simultaneously immobilized by microbes for their own growth, leading to an increased nitrogen concen-tration in the mixture of litter substrate and microbes. This carbon release and nitrogen immobilization causes an increase of carbon-nitrogen ratio (C:N) until mineralized nitro-gen is greater than needed for microbial growth. When this happens, litter decomposi-tion leads to a net release of nitrogen. (Lou & Zhou 2006, 21-22).

Because of the carbon and nitrogen release, the rate of mineralized nitrogen (Nmin) is usually correlated with respiration (Rm). For example, Zak et al. (1993) found this rela-tionship: Rm = 15.9 Nmin + 27.4 with r = 0.853 for litter and Rm = 7.1 Nmin + 159.9 with r = 0.616 for soil organic matter from laboratory incubation. (Lou & Zhou 2006, 22).

2.5.3 Soil respiration and carbon cycling

The carbon cycling consists in the exchanges of CO2 between the atmosphere, biosphere, oceans and the earth´s crust. Soil respiration is an important factor of this cycle (figure 2.5.3). (Lou & Zhou 2006,

Global carbon cycle. Pools in Pg (= 1015 g) C and fluxes in Pg C yr−1 as indicated by arrows (Wikipedia).

Photosynthesis takes about 120 PgC per year from the atmosphere and a similar amount is released back due to respiration. Oceans and atmosphere exchange like 90 PgC per year. Through the human activity, approximately 7.2 PgC per year are released to the atmosphere. This amount seems to be very small compared with the natural fluxes, but only a small change it is necessary to perturb the balance. (Lou & Zhou 2006, 123-24).

The soil pool from which soil respiration releases carbon (3150 PgC) is much bigger than the atmospheric pool (750 PgC), so a little change in soil respiration can seriously alter the CO2 concentration balance. Therefore, soil respiration has to be well studied for pre-dicting changes in the carbon cycle. (Lou & Zhou 2006, 23-24).

Soil respiration is very sensitive to environmental changes, and the human activity caus-es an increase of the CO2 concentration in the atmosphere, which induces at the same time to an increase of the global temperature. As seen in chapter 2.4.2, temperature af-fect a lot to soil respiration, so the global balance will be disturbed. (Lou & Zhou 2006,