Meier Ina C, Pritchard Seth G, Brzostek Edward R, McCormack M Luke, Phillips Richard P
Department of Biology, Indiana University, Bloomington, IN, 47405, USA.
Department of Biology, College of Charleston, Charleston, SC, 29401, USA.
New Phytol. 2015 Feb;205(3):1164-1174. doi: 10.1111/nph.13122. Epub 2014 Oct 28.
While multiple experiments have demonstrated that trees exposed to elevated CO₂ can stimulate microbes to release nutrients from soil organic matter, the importance of root- versus mycorrhizal-induced changes in soil processes are presently unknown. We analyzed the contribution of roots and mycorrhizal activities to carbon (C) and nitrogen (N) turnover in a loblolly pine (Pinus taeda) forest exposed to elevated CO₂ by measuring extracellular enzyme activities at soil microsites accessed via root windows. Specifically, we quantified enzyme activity from soil adjacent to root tips (rhizosphere), soil adjacent to hyphal tips (hyphosphere), and bulk soil. During the peak growing season, CO₂ enrichment induced a greater increase of N-releasing enzymes in the rhizosphere (215% increase) than in the hyphosphere (36% increase), but a greater increase of recalcitrant C-degrading enzymes in the hyphosphere (118%) than in the rhizosphere (19%). Nitrogen fertilization influenced the magnitude of CO₂ effects on enzyme activities in the rhizosphere only. At the ecosystem scale, the rhizosphere accounted for c. 50% and 40% of the total activity of N- and C-releasing enzymes, respectively. Collectively, our results suggest that root exudates may contribute more to accelerated N cycling under elevated CO₂ at this site, while mycorrhizal fungi may contribute more to soil C degradation.
虽然多项实验表明，暴露于高浓度二氧化碳环境下的树木能够刺激微生物从土壤有机质中释放养分，但目前尚不清楚根系和菌根引起的土壤过程变化哪个更为重要。我们通过测量通过根窗进入的土壤微位点的细胞外酶活性，分析了根系和菌根活动对暴露于高浓度二氧化碳环境下的火炬松（Pinus taeda）林中碳（C）和氮（N）周转的贡献。具体而言，我们对根尖附近土壤（根际）、菌丝尖端附近土壤（菌丝际）和大块土壤中的酶活性进行了量化。在生长旺季，与菌丝际（增加36%）相比，二氧化碳富集导致根际中氮释放酶的增加幅度更大（增加215%），但与根际（增加19%）相比，菌丝际中难降解碳降解酶的增加幅度更大（增加118%）。施氮仅影响二氧化碳对根际酶活性的影响程度。在生态系统尺度上，根际分别占氮和碳释放酶总活性的约50%和40%。总体而言，我们的结果表明，在该地点，高浓度二氧化碳条件下，根系分泌物可能对加速氮循环的贡献更大，而菌根真菌可能对土壤碳降解的贡献更大。
