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Flujos de CO2 en ecosistemas mediterráneos: Influencia de factores bióticos y abióticos
| Content Provider | Semantic Scholar |
|---|---|
| Author | Puig, Carme Estruch |
| Copyright Year | 2016 |
| Abstract | In this Thesis we address the effect of the main biotic and abiotic factors on CO2 fluxes in drylands. With this purpose, we assessed the effect of plant communities and soil properties on CO2 fluxes, and their relationship with soil humidity and temperature. From these CO2 fluxes we focused our analyses in soil respiration, and in several cases we also analyzed atmosphere CO2 fixation by plants (photosynthesis) Specifically, our objectives were to analyze 1) the effect of plant communities in soil respiration and their relationship with seasonal changes in temperature and humidity, 2) soil respiration responses to sudden changes in soil moisture in a range of temperatures typical of arid zones, and relate them to the composition of the microbial community involved, 3) the contribution to soil respiration of the three main soil biota groups involved in soil respiration (roots, mycorrhiza and bulk soil), and 4) the links between plant community fluxes and soil respiration in a chronosequence of abandoned land to determine ecosystem capacity to act as a carbon source or carbon sink. In the first chapter we addressed soil respiration under different plant species canopies and bare soil. The different plant species influence CO2 emissions through specific effects on soil humidity, temperature, C allocation, organic matter or microbial communities. We determined CO2 emissions in soils beneath different plant species and bare soils their response to temperature in a semiarid environment over a 20-mo manipulative experiment. We altered soil temperature under the canopy of four plant species differing in functional type and activity, and in bare soil, and measured monthly fluxes to establish seasonal patterns of CO2 release. We found an exponential relationship between soil respiration and soil temperature that shifted from negative in the dry and warm season to positive in the relatively wet and cool season. A model that include soil temperature, soil water content and plant species identity effects on CO2 emissions explained 74% of the seasonal variation in soil respiration rate in this system, species identity playing a significant and probably the strongest effect on soil respiration rate. Our data showed the importance that plant species composition plays on annual CO2 emissions at the community level. In the second chapter we addressed the soil respiration response to water pulses in a range of high temperatures (30oC-60oC) that are typical in arid and semiarid environments. We determined optimal soil respiration temperature after rapid rewetting with different water pulses, and assessed soil microbial communities (SMC) in three different soils from contrasted semiarid environments. We used short incubation times with four temperatures and three watering regimes and determined the structure of soil microbial communities (SMC). Soil respiration responses to water supply depended on temperature and soil origin. Optimum temperatures in sandy soils (desert and alpine) were well above 50oC while in clay soils were lower. Soils showed marked differences in SMC, and differed with depth. Our data show that soil respiration pulses depended on temperature if not completely dry, and that optimum temperatures were well above the general assumption of 35oC in these semiarid environments. Our results also evidenced the dependence of soil respiration responses on soil depth, which showed higher respiration pulses in the upper soil layers. In the thirds chapter we addressed the contribution of the three main soil community groups (roots, mycorrhiza and the bulk soil community) in the total soil respiration. In order to determine the sensitivity of these components to environmental drivers we set up an experiment to address the effect of plant community composition, soil age and warming on soil respiration rate during the 2014-2015 winter. We tested differences among microbial, fungal and root respiration using an exclusion technique to assess the effect of plant community (open grasslands vs oak woodland) in two field sites differing in geologic soil age (92 and 137 kyr). We also used open top chambers (OTC) to simulate global change effects on grasslands. Our results showed that arbuscular mycorrhizal fungi were the main drivers of differences recorded between soils of different age, and that those differences were linked to nutrient availability. Bulk soil respiration was more sensitive to temporal variation than mycorrhizal or root respiration. Soil age affected CO2 flux from grasslands but not under oak canopies, likely due to differences in SOM content which moderate CO2 fluxes. Overall our study shows that the ability of grasslands to mitigate CO2 emissions depends on interactions between vegetation and their rhizosphere and soil microbial communities. In the fourth chapter we addressed changes in the carbon balance along a chronosequence from abandoned farmlands, in a semiarid environment. We addressed changes in C balance along a chronosequence of land abandonment in a semiarid environment and assessed the consequences of secondary succession on C sequestration capacity at community scale. We used a closed-chamber method to estimate the contribution of whole-plants and bare soil to whole-ecosystem C exchange. Plant community composition and cover strongly affected C balance. Overall, whole-ecosystem C exchange shifted from C source to C sink with succession. However, only after 63 years of agriculture abandonment the system did recover its natural C sequestration capacity. Thus, the capacity of semiarid ecosystems to recover native plant communities after anthropogenic disturbance may contribute to decrease C emissions in the long term. This information is important to understand the role of drylands in the global carbon cycle. Moreover, brings information relevant in understanding the function of different ecosystems components and their implication in the net carbon balance. The information generated by this thesis is useful to improve predictions about carbon cycling in terrestrial ecosystems limited by water. |
| Starting Page | 1 |
| Ending Page | 1 |
| Page Count | 1 |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://roderic.uv.es/bitstream/handle/10550/55868/Tesis_Carme.Estruch.Puig.Final2_Portada.pdf?isAllowed=y&sequence=1 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
