Effects of experimental nitrogen deposition on soil organic carbon storage in Southern California drylands
Effects of experimental nitrogen deposition on soil organic carbon storage in Southern California drylands
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DOI：
10.1111/gcb.16563
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发表时间：
2022-12-27
影响因子：
11.6
通讯作者：
Homyak, Peter M.
中科院分区：
文献类型：
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作者：
Puspok, Johann F.;Zhao, Sharon;Homyak, Peter M.
大气氮 (N) 沉降使生物群落中的土壤富含氮。土壤氮富集可以提高植物生产力并影响微生物活动，从而增加土壤有机碳（SOC），但这种反应因生物群落而异。旱地覆盖了地球陆地面积的 45%，储存的 SOC 相当于表层 1 m 土壤中全球 33% 的有机碳。因此，施氮肥可能会对碳（C）循环产生不成比例的影响，但旱地土壤有机碳储存量是否会随着施氮量的增加而增加仍不清楚。为了了解氮富集如何改变 SOC 存储，我们在南加州的四个氮沉降实验点将 SOC 分为植物来源的颗粒有机碳 (POC) 和主要微生物来源的矿物相关有机碳 (MAOC)。理论表明，如果土壤 pH 值保持恒定，氮富集会提高微生物构建 MAOC（碳稳定效率）的效率。但如果土壤酸化（这是氮富集的常见反应），那么微生物生物量和酶促有机物腐烂可能会减少，从而增加 POC，但不会增加 MAOC。我们发现，除了某一位点的 MAOC 减少外，氮富集对 C 分数没有影响。具体而言，尽管据报道三个地点的植物生物量增加，而两个酸化地点的微生物生物量和细胞外酶活性降低，但 POC 并未增加。此外，非酸化位点中微生物 C 的利用和稳定效率增加，但 MAOC 没有增加。相反，MAOC 在酸化位点之一下降了 16%，可能是因为与对照相比，它损失了 47% 的可交换钙 (Ca)。事实上，MAOC 受到 Ca 的强烈而积极的影响，Ca 直接并通过其对微生物量的积极影响，解释了 MAOC 变化的 58%。施氮肥对旱地 SOC 储存的长期影响本质上是非生物的，因此 SOC 普遍存在钙稳定作用且土壤酸化的旱地最有可能发生碳显着损失。
Atmospheric nitrogen (N) deposition is enriching soils with N across biomes. Soil N enrichment can increase plant productivity and affect microbial activity, thereby increasing soil organic carbon (SOC), but such responses vary across biomes. Drylands cover similar to 45% of Earth's land area and store similar to 33% of global SOC contained in the top 1 m of soil. Nitrogen fertilization could, therefore, disproportionately impact carbon (C) cycling, yet whether dryland SOC storage increases with N remains unclear. To understand how N enrichment may change SOC storage, we separated SOC into plant-derived, particulate organic C (POC), and largely microbially derived, mineral-associated organic C (MAOC) at four N deposition experimental sites in Southern California. Theory suggests that N enrichment increases the efficiency by which microbes build MAOC (C stabilization efficiency) if soil pH stays constant. But if soils acidify, a common response to N enrichment, then microbial biomass and enzymatic organic matter decay may decrease, increasing POC but not MAOC. We found that N enrichment had no effect on C fractions except for a decrease in MAOC at one site. Specifically, despite reported increases in plant biomass in three sites and decreases in microbial biomass and extracellular enzyme activities in two sites that acidified, POC did not increase. Furthermore, microbial C use and stabilization efficiency increased in a non-acidified site, but without increasing MAOC. Instead, MAOC decreased by 16% at one of the sites that acidified, likely because it lost 47% of the exchangeable calcium (Ca) relative to controls. Indeed, MAOC was strongly and positively affected by Ca, which directly and, through its positive effect on microbial biomass, explained 58% of variation in MAOC. Long-term effects of N fertilization on dryland SOC storage appear abiotic in nature, such that drylands where Ca-stabilization of SOC is prevalent and soils acidify, are most at risk for significant C loss.