Global warming effects on forest soil processes

土壤有机质（SOM）动态是陆地生态系统对全球变暖的响应中最不清楚的一个。温度的升高增加了土壤有机质的分解和CO2向大气中N2 O的排放。氮（N）和磷（P）等养分的可用性以及它们与土壤碳循环的相互作用也会增加。然而，温度对土壤碳和养分循环的影响不一定是线性的。气候变暖会逐渐耗尽可分解的有机质。微生物生理学可以适应较温暖的条件和有机物的C：N：P化学计量随时间的潜在变化。因此，土壤碳和养分循环的长期响应可能与短期响应有很大不同。在Achenkirch的土壤变暖实验中，自2004年以来，我们已经将土壤温度提高了4°C。我们的目标是将变暖实验再延长3年，因为我们观察到土壤CO2（~ 40%，2005-2017）和N2 O排放量（~ 50%，2005-2009）的持续增长。迄今为止，在森林生态系统中还没有观察到土壤CO2排放量如此强烈和持续的增加。我们的实验是世界范围内为数不多的监测土壤变暖影响超过10年的研究之一。我们将继续进行土壤CO2排放调查，并评估长期变暖如何影响土壤N2 O通量。长期数据集将允许量化变暖引起的土壤碳损失，方法是（i）碳通量预算（15年土壤CO2排放与碳输入）和（ii）碳库比较（2004年、2013年和2019年碳存量）。我们将评估细根和土壤的放射性碳（14 C）特征，并应用新一代14 C模型来估计细根和土壤C的周转。将评估变暖对溶解的有机和无机C的浸出的影响。通过结合所有数据，我们将提出一个长期的情况下，高温下的土壤C动态的石灰性森林土壤。土壤C，N和P循环之间的相互作用将进行评估，特别关注根/土壤界面（根际）。将监测真菌化和真菌分解者群落的结构。我们将进一步测试变暖对根系分泌物的影响。此外，我们将遵循变暖对原位土壤C，N和P的有效性和通量，以及相关的微生物过程的影响。这些数据将使我们能够分析由季节变化和土壤变暖引发的根系，土壤，微生物生物量和土壤酶的C：N：P化学计量的变化，提供土壤微生物群落元素限制变化的代理。Achenkirch土壤变暖实验使一个有意义的预测有机碳和养分储量和循环在一个温暖的地球上的高山森林土壤。

Soil organic matter (SOM) dynamics are one of the least understood responses of terrestrial ecosystems to global warming. Rising temperature increases SOM decomposition and CO2 efflux from soil to the atmosphere of N2O. The availability of nutrients such as nitrogen (N) and phosphorus (P), and thus their interactions with the soil C cycle, can increase as well. The temperature effect on soil C and nutrient cycling is however not necessarily linear over time. Warming can gradually deplete the pool of decomposable SOM. Microbial physiology can adapt to warmer conditions and to potential changes in the stoichiometry of C:N:P of organic matter over time. Therefore, the long-term response of soil C and nutrient cycling can differ substantially from the short-term response. In the soil warming experiment Achenkirch, we have increased the soil temperature by 4°C since 2004. The goal is to prolong the warming experiment for further 3 years as we observed a strong sustained increase of soil CO2 (~ 40%, 2005-2017) and N2O efflux (~50%, 2005-2009). Such a strong and persisting increase in soil CO2 efflux has not been observed in forest ecosystems so far. Our experiment is one of a mere handful of studies world-wide monitoring the effects of soil warming for more than 10 years. We will continue the soil CO2 efflux survey and asses how long-term warming affects soil N2O fluxes. The long-term dataset will allow quantifying the warming induced soil C loss by (i) budgeting of C fluxes (15 years of soil CO2 efflux vs. C input) and (ii) C pool comparisons (C stock 2004, 2013, and 2019). We will assess the radiocarbon (14C) signature of fine roots and soil and apply a new generation 14C model to estimate the turnover of fine roots and soil C. Warming effects on the leaching of dissolved organic and inorganic C will be evaluated. By combining all data, we will come up with a long-term scenario of soil C dynamics under elevated temperature for this calcareous forest soil.Interactions between soil C, N, and P cycles will be assessed with a special focus on the root/soil interface (rhizosphere). Mycorrhization and the structure of fungal decomposer communities will be monitored. We will further test for warming effects on root exudation. Additionally, we will follow warming effects on in-situ soil C, N and P availabilities and fluxes, and related microbial processes. These data will enable us to analyze shifts in the C:N:P stoichiometry of roots, soil, microbial biomass, and soil enzymes as triggered by seasonal variations and soil warming, providing a proxy of shifts in element limitation of the soil microbial communities. The Achenkirch soil warming experiment enables a meaningful forecast of organic C and nutrient stocks and cycling in Alpine forest soils on a warmer earth.