Long-term elevated precipitation induces grassland soil carbon loss via microbe-plant-soil interplay.

Global climate models predict that the frequency and intensity of precipitation events will increase in many regions across the world. However, the biosphere-climate feedback to elevated precipitation (eP) remains elusive. Here, we report a study on one of the longest field experiments assessing the effects of eP, alone or in combination with other climate change drivers such as elevated CO2 (eCO2 ), warming and nitrogen deposition. Soil total carbon (C) decreased after a decade of eP treatment, while plant root production decreased after 2 years. To explain this asynchrony, we found that the relative abundances of fungal genes associated with chitin and protein degradation increased and were positively correlated with bacteriophage genes, suggesting a potential viral shunt in C degradation. In addition, eP increased the relative abundances of microbial stress tolerance genes, which are essential for coping with environmental stressors. Microbial responses to eP were phylogenetically conserved. The effects of eP on soil total C, root production, and microbes were interactively affected by eCO2 . Collectively, we demonstrate that long-term eP induces soil C loss, owing to changes in microbial community composition, functional traits, root production, and soil moisture. Our study unveils an important, previously unknown biosphere-climate feedback in Mediterranean-type water-limited ecosystems, namely how eP induces soil C loss via microbe-plant-soil interplay.

Dissolved carbon fluxes in a vegetation restoration area of an eroding landscape.

Dissolved carbon (DC) is a critical component of the global carbon (C) cycle. DC transport occurs through water-driven erosion and infiltration during rain storms. To explore the specific role of DC flux in topsoil C pool dynamics during rainfall events and predict the trend of ratios of lateral versus vertical DC efflux from topsoil in a vegetation restoration area, we measured the major DC fluxes at four runoff plots, during rainfall events in an eroding soil landscape on the Chinese Loess Plateau. The results show that topsoil vertical DC efflux into deep soil layers accounted for approximately 98.7 (±1.0) % of the total dissolved carbon efflux in plots with vegetation versus 95.3% in a plot without vegetation. The carbon sequestration capacity of the top soil would be underestimated by up to 38 (±5) % if the vertical DC efflux was omitted. The ratios of lateral versus vertical DC efflux tended to increase with rainfall intensity. The results of this study improve understanding of the carbon cycle processes during rainfall events in general and estimation of carbon sequestration rates in vegetation restoration regions such as the Chinese Loess Plateau in particular.

Heterogeneity of carbon loss and its temperature sensitivity in East-European subarctic tundra soils.

Arctic peatlands store large stocks of organic carbon which are vulnerable to the climate change but their fate is uncertain. There is increasing evidence that a part of it will be lost as a result of faster microbial mineralization. We studied the vulnerability of 3500-5900 years old bare peat uplifted from permafrost layers by cryogenic processes to the surface of an arctic peat plateau. We aimed to find biotic and abiotic drivers of CLOSS from old peat and compare them with those of adjacent, young vegetated soils of the peat plateau and mineral tundra. The soils were incubated in laboratory at three temperatures (4°C, 12°C and 20°C) and two oxygen levels (aerobic, anaerobic). CLOSS was monitored and soil parameters (organic carbon quality, nutrient availability, microbial activity, biomass and stoichiometry, and extracellular oxidative and hydrolytic enzyme pools) were determined. We found that CLOSS from the old peat was constrained by low microbial biomass representing only 0.22% of organic carbon. CLOSS was only slightly reduced by the absence of oxygen and exponentially increased with temperature, showing the same temperature sensitivity under both aerobic and anaerobic conditions. We conclude that carbon in the old bare peat is stabilized by a combination of physical, chemical and biological controls including soil compaction, organic carbon quality, low microbial biomass and the absence of plants.