Inactive and inefficient: Warming and drought effect on microbial carbon processing in alpine grassland at depth
Inactive and inefficient: Warming and drought effect on microbial carbon processing in alpine grassland at depth
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DOI：
10.1111/gcb.15541
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发表时间：
2021-02
影响因子：
11.6
通讯作者：
Erxiong Zhu;Z. Cao;J. Jia;Chengzhu Liu;Zhenhua Zhang;Hao Wang;Guohua Dai;Jinsheng He;Xiaojuan Feng
中科院分区：
文献类型：
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作者：
Erxiong Zhu;Z. Cao;J. Jia;Chengzhu Liu;Zhenhua Zhang;Hao Wang;Guohua Dai;Jinsheng He;Xiaojuan Feng
底土含有全球土壤有机碳（SOC）的50%以上，但在其对气候变化的响应方面仍处于研究阶段。最近的证据表明，温暖，干燥的条件下，在高山草原诱导不同的反应，在SOC分解和碳积累的顶部与底土。然而，对微生物活性的长期影响（即，分解代谢呼吸与合成代谢生长）和地下碳循环还没有得到很好的理解。在这里，我们利用青藏高原的野外操作实验，在有和没有13 C标记的草凋落物的情况下进行了110天的土壤培养，以评估在5年的变暖和干旱处理后，微生物在表层（0-10 cm）和下层（30 - 40 cm）中作为SOC“分解者”和“贡献者”的作用。微生物矿化的SOC和添加的垃圾进行了检查，在串联与潜在的胞外酶活性，而微生物生物量的合成和necromass积累进行了分析，分别使用磷脂脂肪酸和氨基糖加上13 C分析。我们发现，变暖和较小程度的干旱降低了底土中无机氮（N）与水提取有机碳的比例，加剧了深层的氮限制。土壤有机碳和凋落物矿化减少，这也可能与氮限制，证明了较低的水解酶活性（特别是亮氨酸氨肽酶）和微生物效率降低（较低的生物质合成和necromass积累相对于呼吸）。然而，在表土中没有观察到这些影响，这表明土壤微生物在底土环境中变得不活跃且效率低下，但在表土环境中则不然。由于在这个高寒草原在变暖的地下生产力增加，升高的根存款和减少微生物活性可能有助于新的碳积累在底土。然而，植物生长的可持续性和持久性的土壤有机碳库需要进一步研究，在长期内，考虑到加剧的N限制在深度。
Subsoils contain >50% of soil organic carbon (SOC) globally yet remain under‐investigated in terms of their response to climate changes. Recent evidence suggests that warmer, drier conditions in alpine grasslands induce divergent responses in SOC decomposition and carbon accrual in top‐ versus subsoils. However, longer term effects on microbial activity (i.e., catabolic respiration vs. anabolic growth) and belowground carbon cycling are not well understood. Here we utilized a field manipulation experiment on the Qinghai‐Tibetan Plateau and conducted a 110‐day soil incubation with and without 13C‐labeled grass litter to assess microbes' role as both SOC “decomposers” and “contributors” in the top‐ (0–10 cm) versus subsoils (30−40 cm) after 5 years of warming and drought treatments. Microbial mineralization of both SOC and added litter was examined in tandem with potential extracellular enzyme activities, while microbial biomass synthesis and necromass accumulation were analyzed using phospholipid fatty acids and amino sugars coupled with 13C analysis, respectively. We found that warming and, to a lesser extent, drought decreased the ratio of inorganic nitrogen (N) to water‐extractable organic carbon in the subsoil, intensifying N limitation at depth. Both SOC and litter mineralization were reduced in the subsoil, which may also be related to N limitation, as evidenced by lower hydrolase activity (especially leucine aminopeptidase) and reduced microbial efficiency (lower biomass synthesis and necromass accumulation relative to respiration). However, none of these effects were observed in the topsoil, suggesting that soil microbes became inactive and inefficient in subsoil but not topsoil environments. Given increasing belowground productivity in this alpine grassland under warming, both elevated root deposits and diminished microbial activity may contribute to new carbon accrual in the subsoil. However, the sustainability of plant growth and persistence of subsoil SOC pools deserve further investigation in the long term, given the aggravated N limitation at depth.