Effects Of Elevated Atmospheric Temperature Research Articles

Elevated atmospheric temperature and CO2 altered the growth, carbon, and nitrogen distribution and the rhizosphere properties of Platanus occidentalis L. seedlings

The effects of elevated atmospheric temperature and CO 2 on the growth and plant carbon and nitrogen allocation of Platanus occidentalis L. and their influence on rhizosphere and soil microbial properties were evaluated through a rhizobag experiment in an environmentally controlled chamber. Seedlings of P. occidentalis L. were established in the central compartment of a rhizobag filled with forest soil and exposed to four treatment combinations (control (25 °C, 400 µmol mol -1 CO 2 ), T2 (30 °C, 400 µmol mol -1 CO 2 ), T3 (25 °C, 800 µmol mol -1 CO 2 ), and T4 (30 °C, 800 µmol mol -1 CO 2 )) for 20 weeks. Elevated temperature and CO 2 enhanced the growth and dry matter yield and altered the C and N distribution of P. occidentalis. The pH, electrical conductivity, and concentration of dissolved sugar and organic carbon in soil solution were also altered, as well as the microbial activity and carbon utilization potential of soil microorganisms in the rhizosphere of P. occidentalis. Overall, the results showed that the changes in plant growth and physiology of P. occidentalis due to exposure to elevated temperature and carbon dioxide extended to the soil biological properties via plant-induced changes in substrate quality and quantity in the rhizosphere.

Below-Ground Microbial Community Development in a High Temperature World

The response of above-ground plant and ecosystem processes to climate change are likely to be influenced by both direct and indirect effects of elevated temperature on soil biota and their activities. This study examined the effects of elevated atmospheric temperature on the development of the soil microbial community in a model terrestrial ecosystem facility. The model system was characterized by a soil of low nutrient availability, a condition that simulates most native terrestrial plant communities. The experiment was run over three plant generations, broadly mimicking the early stages of a plant succession, and showed that microbial biomass, measured using phospholipid fatty acid (PLFA) analysis, increased significantly in response to elevated temperature during the first generation only. This increase was unrelated to changes in plant productivity or soil C-availability, and was largely due to a direct effect of elevated temperature on fast-growing Gram-positive bacteria. Slow growing soil micoorganisms such as fungi and actinomycetes were unaffected by elevated temperature throughout the experimental period. Measures of microbial biomass, microbial respiration and N-mineralization were also unaffected by elevated atmospheric temperature over the three generations. The lack of effects on the soil microbial community is thought to be due to the fact that elevated temperature did not influence root biomass or soil C-availability. We suggest that the observed reductions in above-ground plant productivity, in response to elevated temperature, will become apparent in the longer term when litter decomposition pathways are more established. The temporal measures of PLFA and microbial biomass indicated that over the experimental period rapid initial changes occurred in most soil biological characteristics, followed by periods of stabilization during later plant succession. These changes were associated with increases in above-ground plant productivity and amounts of available C in the soil. In contrast, total microbial biomass declined during the last plant generation. Reductions in the diversity of PLFAs in later plant generations appeared to be associated with an increase in the proportion of fatty acids associated with fungi, relative to those from bacteria. These changes are likely to be related to increased competition for resources within the soil, and an associated reduction in N- and C-availability. These changes appear to be broadly consistent with those reported for other studies on the successional development of soil microbial and plant communities. Overall, our data suggest that elevated atmospheric temperature has little effect on the development of below-ground microbial communities and their activities in soils of low nutrient status.