Lagomarsino A, Moscatelli M C, De Angelis P, Grego S
Department of Agrobiology and Agrochemistry, University of Tuscia, VITERBO, Italy.
Sci Total Environ. 2006 Dec 15;372(1):256-65. doi: 10.1016/j.scitotenv.2006.08.031. Epub 2006 Oct 4.
Soil carbon (C) long term storage is influenced by the balance among ecosystem net primary productivity (NPP), the rate of delivery of new organic matter to soil pools and the decomposition of soil organic matter (SOM). The increase of NPP under elevated CO(2) can result in a greater production and higher turnover of fine roots or root exudation and, in turn, in an increase of labile C belowground. The aim of this work was to detect if changes in labile C substrates influenced the organic C storage in soils, verifying (i) whether treatments with elevated CO(2) and N fertilization induced changes in the amount and quality of labile C pools and in microbial C immobilization and (ii) whether these changes provoked modifications in the microbial C mineralization activity, and therefore changes in soil C losses. The effect of elevated CO(2) was a significant increase in both seasons (June and October 2004), of all labile C fractions: microbial biomass C (MBC), K(2)SO(4) extractable C (ExC), and water soluble C (WSC). The C/N ratio of the microbial biomass and of the K(2)SO(4) extractable SOM presented a seasonal fluctuation showing higher values in June, whereas the elevated CO(2) increased significantly the C/N ratio of these fractions independent of the season and the N addition, indicating a lower quality of labile SOM. Microbial respiration was more than doubled in October compared to June, confirming that changes in substrate quality and nutrient availability, occurring in the plantation at the beginning and at the end of the vegetative period, influenced the microbial activity in the bulk soil. Furthermore, the microbial respiration response to N fertilization was dependent on the season, with an opposite effect between June and October. The kinetic parameters calculated according to the first-order equation C(m)=C(0)(1-e(-kt)) were unaffected by elevated CO(2) treatment, except C(0)k and MR(basal), that showed a significant reduction, ascribable to (i) a lower quality of labile pools, and (ii) a more efficient microbial biomass in the use of available substrates. The C surplus found in elevated CO(2) soils was indeed immobilized and used for microbial growth, thus excluding a priming effect mechanism of elevated CO(2) on SOM decomposition.
土壤碳（C）的长期储存受生态系统净初级生产力（NPP）、新有机物质向土壤库的输送速率以及土壤有机质（SOM）分解之间平衡的影响。CO₂浓度升高下NPP的增加可导致细根或根系分泌物的产量增加和周转加快，进而使地下不稳定碳增加。本研究的目的是检测不稳定碳底物的变化是否影响土壤中的有机碳储存，验证（i）CO₂浓度升高和氮肥处理是否会引起不稳定碳库的数量和质量以及微生物碳固定的变化，以及（ii）这些变化是否会引发微生物碳矿化活性的改变，从而导致土壤碳损失的变化。CO₂浓度升高的影响是在两个季节（2004年6月和10月）中，所有不稳定碳组分均显著增加：微生物生物量碳（MBC）、K₂SO₄可提取碳（ExC）和水溶性碳（WSC）。微生物生物量和K₂SO₄可提取SOM的C/N比呈现季节性波动，6月的值较高，而CO₂浓度升高显著增加了这些组分的C/N比，与季节和氮肥添加无关，表明不稳定SOM的质量较低。与6月相比，10月微生物呼吸增加了一倍多，证实了在生长季开始和结束时种植园中底物质量和养分有效性的变化影响了表层土壤中的微生物活性。此外，微生物呼吸对氮肥的响应取决于季节，6月和10月的影响相反。根据一级方程C(m)=C(0)(1-e(-kt))计算的动力学参数不受CO₂浓度升高处理的影响，但C(0)k和MR(basal)显著降低，这归因于（i）不稳定库质量较低，以及（ii）微生物生物量在利用可用底物方面更高效。在CO₂浓度升高的土壤中发现的碳盈余确实被固定并用于微生物生长，因此排除了CO₂浓度升高对SOM分解的激发效应机制。
