Aims

We evaluated the impacts of altered precipitation regimes on multiple aspects of the C cycle, including C fluxes, plant and soil microbial communities, and plant-soil interactions in a south-eastern Australian grassland.

Methods

Our experimental treatments, operated through an automated system, included: (i) reduced and (ii) increased rainfall amount by 50%, (iii) reduced rainfall frequency but no change in amount (i.e., more extreme downpours), (iv) and an extreme summer drought.

Results

Temporal dynamics of ecosystem-level CO₂ fluxes fluctuated seasonally and were driven by variations in soil water availability, soil temperature and photosynthetically active radiation. Reducing the frequency of rainfall events, but without change in the amount of rainfall, resulted in lower ecosystem-level net CO₂ uptake due to relatively greater R_eco stimulation after the heavy downpours, particularly during the late summer season. The extreme summer drought downregulated both respiration and photosynthesis. Microbial abundance and activity did not change in response to rainfall manipulation and were not strongly related to precipitation-driven changes in C cycling. In contrast, a greater proportion of live to dead plant biomass, in turn driven by greater water availability, was a main driver of greater respiration and photosynthesis.

Conclusions

Our study suggests that grasslands could shift from net C sinks to C neutral or even net sources of C under future scenarios of more variable rainfall regimes, thus reinforcing climate change.

中文翻译：

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改变降水方式对澳大利亚东部草原生态系统水平CO 2通量及其驱动因子的季节性影响

目的

我们评估了改变降水方式对碳循环的多个方面的影响，包括碳通量，植物和土壤微生物群落，以及澳大利亚东南草原的植物-土壤相互作用。

方法

我们通过自动化系统进行的实验处理包括：（i）减少和（ii）降雨量增加50％，（iii）降雨频率减少但量没有变化（即，倾盆大雨），（iv）和夏季极端干旱。

结果

生态系统水平的CO ₂通量的时间动态随季节而变化，并受土壤水有效性，土壤温度和光合有效辐射的变化驱动。减少降雨事件的频率，但不改变降雨量，由于相对较高的R _eco，导致生态系统水平的净CO ₂吸收量降低倾盆大雨后尤其是夏季晚些时候受到刺激。夏季极端干旱下调了呼吸和光合作用。微生物的丰度和活性没有响应降雨操纵而变化，并且与碳循环中降雨驱动的变化没有强烈关系。相反，更多的活水推动了活植物至死植物生物量的更大比例，这是更大的呼吸和光合作用的主要驱动力。

结论

我们的研究表明，在降雨情况变化更大的未来情况下，草原可能会从碳净汇向碳中性甚至碳净来源转移，从而加剧了气候变化。