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Thus, soil organic C storage is linked to N availability and can result in N immobilization in SOM with feedbacks to plant productivity. In-N-Out: A hierarchical framework to understand and predict soil carbon storage and nitrogen recycling Conversely, when N is available in excess of plant and microbial demand, the C and N cycles decouple, and N is lost from the system. We further hypothesize that C input-limited systems have N in excess of demand, resulting in decoupling of the N and C cycles, and the opening of N cycle to losses from the soil. [Extracted from the article]

Elevated CO2 increases intrinsic water use efficiency ( WUE i) of forests, but the magnitude of this effect and its interaction with climate is still poorly understood., We combined tree ring analysis with isotope measurements at three Free Air CO2 Enrichment ( FACE, POP- EUROFACE, in Italy; Duke FACE in North Carolina and ORNL in Tennessee, USA) sites, to cover the entire life of the trees. We used δ13C to assess carbon isotope discrimination and changes in water-use efficiency, while direct CO2 effects on stomatal conductance were explored using δ18O as a proxy., Across all the sites, elevated CO2 increased 13C-derived water-use efficiency on average by 73% for Liquidambar styraciflua, 77% for Pinus taeda and 75% for Populus sp., but through different ecophysiological mechanisms., Our findings provide a robust means of predicting water-use efficiency responses from a variety of tree species exposed to variable environmental conditions over time, and species-specific relationships that can help modelling elevated CO2 and climate impacts on forest productivity, carbon and water balances. [ABSTRACT FROM AUTHOR]

Volcanic eruptions impact the global and the hemispheric climate, but it is still unknown how and to what degree they force the climate system and in particular the global carbon cycle. In this paper, the relationships between individual eruptions (reconstructed for the past using written records), tree primary productivity (estimated using ring widths), photosynthetic rate and stomatal conductance (assessed by carbon and oxygen isotope data) are investigated, to understand the impact of volcanic eruptions on net primary production. Data from a mixed stand of Fagus sylvatica L. and Acer pseudoplatanus L. located in the area of the Vesuvio volcanic complex (Southern Italy) showed a significant decrease in ring width following each eruption. Isotope analyses indicate a change in climatic conditions after such events. Specifically, the lower oxygen isotope ratio in the tree-ring cellulose strongly suggests an increase in relative humidity and a decrease in temperature, with the latter resulting in a strong limitation to tree-ring growth. The carbon isotope ratio was only moderately but not significantly reduced in the years of volcanic eruption, suggesting no major changes in C fixation rates. This work is a case study on the effects of volcanic eruptions resulting in strong climatic changes on the local scale. This is an opportunity to explore the process and causal relationships between climatic changes and the response of the vegetation. Thus, we propose here a realistic model scenario, from which we can extrapolate to global scales and improve our interpretations of results of global studies. [ABSTRACT FROM AUTHOR]

Abstract Within the framework of the Kyoto Protocol, the potential mitigation of greenhouse gas emissions by terrestrial ecosystems has placed focus on carbon sequestration following afforestation of former arable land. Central to this soil C sequestration are the dynamics of soil organic matter (SOM). In North Eastern Italy, a mixed deciduous forest was planted on continuous maize field soil with a strong C4 isotopic C signature 20 years ago. In addition, a continuous maize field and a relic of the original permanent grassland were maintained at the site, thus offering the opportunity to compare the impacts on soil C dynamics by conventional agriculture, afforestation and permanent grassland. Soil samples from the afforested, grassland and agricultured systems were separated in three aggregate size classes, and inter- vs. intra-aggregate particulate organic matter was isolated. All fractions were analyzed for their C content and isotopic signature. The distinct 13 C signature of the C derived from maize vegetation allowed the calculation of proportions of old vs. forest-derived C of the physically defined fractions of the afforested soil. Long-term agricultural use significantly decreased soil C content (-48%), in the top 10 cm, but not SOM aggregation, as compared to permanent grassland. After 20 years, afforestation increased the total amount of soil C by 23% and 6% in the 0–10 and in the 10–30 cm depth layer, respectively. Forest-derived carbon contributed 43% and 31% to the total soil C storage in the afforested systems in the 0–10 and 10–30 cm depths, respectively. Furthermore, afforestation resulted in significant sequestration of new C and stabilization of old C in physically protected SOM fractions, associated with microaggregates (53–250 μm) and silt&clay (<53 μm). [ABSTRACT FROM AUTHOR]

A correction to the article "Trends and Methodological Impacts in soil CO2 efflux partitioning: a meta-analytical review" , Vol. 12, 921-943, is presented.