Waring Bonnie G, Hawkes Christine V
Section of Integrative Biology, University of Texas at Austin, Austin, TX, USA,
Microb Ecol. 2015 May;69(4):843-54. doi: 10.1007/s00248-014-0436-z. Epub 2014 Jun 3.
Many wet tropical forests, which contain a quarter of global terrestrial biomass carbon stocks, will experience changes in precipitation regime over the next century. Soil microbial responses to altered rainfall are likely to be an important feedback on ecosystem carbon cycling, but the ecological mechanisms underpinning these responses are poorly understood. We examined how reduced rainfall affected soil microbial abundance, activity, and community composition using a 6-month precipitation exclusion experiment at La Selva Biological Station, Costa Rica. Thereafter, we addressed the persistent effects of field moisture treatments by exposing soils to a controlled soil moisture gradient in the lab for 4 weeks. In the field, compositional and functional responses to reduced rainfall were dependent on initial conditions, consistent with a large degree of spatial heterogeneity in tropical forests. However, the precipitation manipulation significantly altered microbial functional responses to soil moisture. Communities with prior drought exposure exhibited higher respiration rates per unit microbial biomass under all conditions and respired significantly more CO2 than control soils at low soil moisture. These functional patterns suggest that changes in microbial physiology may drive positive feedbacks to rising atmospheric CO2 concentrations if wet tropical forests experience longer or more intense dry seasons in the future.
许多潮湿的热带森林储存着全球陆地生物量碳储量的四分之一，在下个世纪，这些森林的降水模式将会发生变化。土壤微生物对降雨变化的反应可能是生态系统碳循环的一个重要反馈，但支撑这些反应的生态机制却鲜为人知。我们在哥斯达黎加的拉塞尔瓦生物站进行了为期6个月的降水排除实验，研究了降雨减少如何影响土壤微生物的丰度、活性和群落组成。此后，我们通过在实验室中将土壤暴露于可控的土壤湿度梯度下4周，研究了田间湿度处理的持续影响。在野外，对降雨减少的组成和功能反应取决于初始条件，这与热带森林中高度的空间异质性相一致。然而，降水控制显著改变了微生物对土壤湿度的功能反应。在所有条件下，先前经历过干旱的群落每单位微生物生物量的呼吸速率更高，并且在低土壤湿度下，其呼出的二氧化碳比对照土壤显著更多。这些功能模式表明，如果潮湿的热带森林在未来经历更长或更强烈的旱季，微生物生理变化可能会对大气二氧化碳浓度上升产生正反馈。
