Elevated CO2 stimulates grassland soil respiration by increasing carbon inputs rather than by enhancing soil moisture
Elevated CO2 stimulates grassland soil respiration by increasing carbon inputs rather than by enhancing soil moisture
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DOI：
10.1111/j.1365-2486.2011.02484.x
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发表时间：
2011-12-01
影响因子：
11.6
通讯作者：
Hobbie, Sarah E.
中科院分区：
文献类型：
--
作者：
Adair, E. Carol;Reich, Peter B.;Hobbie, Sarah E.
目前尚不清楚是否一致的积极影响，CO2浓度升高对土壤呼吸（土壤碳通量，SCF）的结果，增加植物和微生物活性，由于（i）更大的C的可用性，通过CO2诱导的增加C输入或（ii）增强土壤水分通过CO2诱导的气孔导度和植物水分利用的下降。生物多样性丧失或氮沉降等全球变化也可能影响这些驱动因素，与CO2相互作用影响SCF。为了确定这些因素对SCF的影响，并阐明CO2浓度升高对SCF影响背后的机制，我们在生物多样性，CO2和N（BioCON）实验中测量了整个生长季节的SCF和土壤水分。增加多样性和N引起土壤水分小幅下降。多样性有不一致的小影响SCF通过其对非生物条件的影响，而N有一个小的积极影响，是无关的土壤水分。CO2浓度升高有很大的一致性影响，增加土壤水分26%，SCF 45%。然而，CO2引起的土壤水分变化是SCF的弱驱动因素：CO2对SCF和土壤水分的影响不相关，CO2效应大小不随土壤水分而变化，通过土壤水分的日内CO2效应为中性或弱负，增加C有效性的估计效应是增加土壤水分的14倍。结合先前的BioCON结果表明，CO2浓度升高会增加植物和微生物的碳可用性，我们的研究结果表明，增加SCF是由CO2诱导的底物可用性增加驱动的。我们的研究结果提供了进一步的支持，在CO2浓度升高的地下C循环的速率增加和证据表明，不同的生产力的反应，以提高CO2在BioCON，SCF的反应是不强烈的N限制。因此，N有限的草原是不可能作为一个N汇CO2浓度升高。
It is not clear whether the consistent positive effect of elevated CO2 on soil respiration (soil carbon flux, SCF) results from increased plant and microbial activity due to (i) greater C availability through CO2-induced increases in C inputs or (ii) enhanced soil moisture via CO2-induced declines in stomatal conductance and plant water use. Global changes such as biodiversity loss or nitrogen (N) deposition may also affect these drivers, interacting with CO2 to affect SCF. To determine the effects of these factors on SCF and elucidate the mechanism(s) behind the effect of elevated CO2 on SCF, we measured SCF and soil moisture throughout a growing season in the Biodiversity, CO2, and N (BioCON) experiment. Increasing diversity and N caused small declines in soil moisture. Diversity had inconsistent small effects on SCF through its effects on abiotic conditions, while N had a small positive effect that was unrelated to soil moisture. Elevated CO2 had large consistent effects, increasing soil moisture by 26% and SCF by 45%. However, CO2-induced changes in soil moisture were weak drivers of SCF: CO2 effects on SCF and soil moisture were uncorrelated, CO2 effect size did not change with soil moisture, within-day CO2 effects via soil moisture were neutral or weakly negative, and the estimated effect of increased C availability was 14 times larger than that of increased soil moisture. Combined with previous BioCON results indicating elevated CO2 increases C availability to plants and microbes, our results suggest that increased SCF is driven by CO2-induced increases in substrate availability. Our results provide further support for increased rates of belowground C cycling at elevated CO2 and evidence that, unlike the response of productivity to elevated CO2 in BioCON, the response of SCF is not strongly N limited. Thus, N limited grasslands are unlikely to act as a N sink under elevated CO2.