Nitrogen availability and summer drought, but not N:P imbalance, drive carbon use efficiency of a Mediterranean tree‐grass ecosystem,Global Change Biology

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Nitrogen availability and summer drought, but not N:P imbalance, drive carbon use efficiency of a Mediterranean tree‐grass ecosystem
Global Change Biology ( IF 10.8 ) Pub Date : 2024-08-31 , DOI: 10.1111/gcb.17486
Richard Nair _{1,

2} , Yunpeng Luo ₃ , Tarek El-Madany ₂ , Victor Rolo ₄ , Javier Pacheco-Labrador _{5,

6} , Silvia Caldararu ₁ , Kendalynn A Morris ₅ , Marion Schrumpf _{2,

7} , Arnaud Carrara ₈ , Gerardo Moreno ₄ , Markus Reichstein ₂ , Mirco Migliavacca _{2,

9}

Affiliation

All ecosystems contain both sources and sinks for atmospheric carbon (C). A change in their balance of net and gross ecosystem carbon uptake, ecosystem‐scale carbon use efficiency (CUEECO), is a change in their ability to buffer climate change. However, anthropogenic nitrogen (N) deposition is increasing N availability, potentially shifting terrestrial ecosystem stoichiometry towards phosphorus (P) limitation. Depending on how gross primary production (GPP, plants alone) and ecosystem respiration (RECO, plants and heterotrophs) are limited by N, P or associated changes in other biogeochemical cycles, CUEECO may change. Seasonally, CUEECO also varies as the multiple processes that control GPP and respiration and their limitations shift in time. We worked in a Mediterranean tree‐grass ecosystem (locally called ‘dehesa’) characterized by mild, wet winters and summer droughts. We examined CUEECO from eddy covariance fluxes over 6 years under control, +N and + NP fertilized treatments on three timescales: annual, seasonal (determined by vegetation phenological phases) and 14‐day aggregations. Finer aggregation allowed consideration of responses to specific patterns in vegetation activity and meteorological conditions. We predicted that CUEECO should be increased by wetter conditions, and successively by N and NP fertilization. Milder and wetter years with proportionally longer growing seasons increased CUEECO, as did N fertilization, regardless of whether P was added. Using a generalized additive model, whole ecosystem phenological status and water deficit indicators, which both varied with treatment, were the main determinants of 14‐day differences in CUEECO. The direction of water effects depended on the timescale considered and occurred alongside treatment‐dependent water depletion. Overall, future regional trends of longer dry summers may push these systems towards lower CUEECO.

中文翻译：

氮的可用性和夏季干旱，而非氮磷失衡，推动了地中海树-草生态系统的碳利用效率

所有生态系统都包含大气碳 (C) 的源和汇。它们净和总生态系统碳吸收平衡的变化，即生态系统规模碳利用效率（CUEECO），就是它们缓冲气候变化的能力的变化。然而，人为氮（N）沉降正在增加氮的可用性，可能使陆地生态系统的化学计量转向磷（P）限制。根据总初级生产力（GPP，仅植物）和生态系统呼吸（RECO，植物和异养生物）如何受到 N、P 或其他生物地球化学循环中相关变化的限制，CUEECO 可能会发生变化。随着控制 GPP 和呼吸的多个过程及其局限性随时间的变化，CUEECO 也会随季节变化。我们在地中海树草生态系统（当地称为“dehesa”）中工作，其特点是冬季温和潮湿，夏季干旱。我们通过 6 年受控、+N 和 + NP 施肥处理的涡流协方差通量在三个时间尺度上检查了 CUEECO：年度、季节（由植被物候阶段确定）和 14 天聚合。更精细的聚合可以考虑对植被活动和气象条件的特定模式的响应。我们预测，CUEECO 应通过湿润条件增加，并依次通过施氮肥和氮肥施肥来增加。气候温和湿润的年份以及相应较长的生长季节会增加 CUEECO，施氮量也会增加，无论是否添加磷。使用广义相加模型，整个生态系统物候状态和水分亏缺指标均随处理而变化，是 CUEECO 14 天差异的主要决定因素。水效应的方向取决于所考虑的时间尺度，并与依赖于处理的水耗竭同时发生。总体而言，未来较长干旱夏季的区域趋势可能会推动这些系统的 CUEECO 降低。

更新日期：2024-08-31

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