Substantial understory contribution to the C sink of a European temperate mountain forest landscape.

CONTEXT: The contribution of forest understory to the temperate forest carbon sink is not well known, increasing the uncertainty in C cycling feedbacks on global climate as estimated by Earth System Models. OBJECTIVES: We aimed at quantifying the effect of woody and non-woody understory vegetation on net ecosystem production (NEP) for a forested area of 158 km2 in the European Alps. METHODS: We simulated C dynamics for the period 2000-2014, characterized by above-average temperatures, windstorms and a subsequent bark beetle outbreak for the area, using the regional ecosystem model LandscapeDNDC. RESULTS: In the entire study area, woody and non-woody understory vegetation caused between 16 and 37% higher regional NEP as compared to a bare soil scenario over the 15-year period. The mean annual contribution of the understory to NEP was in the same order of magnitude as the average annual European (EU-25) forest C sink. After wind and bark beetle disturbances, the understory effect was more pronounced, leading to an increase in NEP between 35 and 67% compared to simulations not taking into account these components. CONCLUSIONS: Our findings strongly support the importance of processes related to the understory in the context of the climate change mitigation potential of temperate forest ecosystems. The expected increases in stand replacing disturbances due to climate change call for a better representation of understory vegetation dynamics and its effect on the ecosystem C balance in regional assessments and Earth System Models.

Processes that determine the interplay of root exudation, methane emission and yield in rice agriculture.

Rice is the most important staple food for half of the world's population, but also accounts for about 10% of all anthropogenic CH4 emissions. In spite of a wealth of information on the mechanistic basis and the importance of the rice plant in mediating these emissions, the significance of root exudation for CH4 emissions and the processes that determine root exudation are not well understood. Root exudates derive from photosynthate allocated to the root and subjected to root anabolic and catabolic processes. Key processes in roots that determine the extent of root exudation and, hence, CH4 emission from rice agriculture, include (i) deviation of metabolites from root anabolic and catabolic pathways facilitating root exudation, but also (ii) xylem loading and transport of potential root exudates for reallocation to the leaves, and (iii) xylem loading of sucrose in roots for its transport into reproductive organs, both suppressing root exudation. These processes are modulated by plant development and metabolic requirements resulting from different functions of root exudation. In the present report the interplay of root exudation, CH4 emission and yield are discussed.

Sampling frequency affects estimates of annual nitrous oxide fluxes.

Quantifying nitrous oxide (N2O) fluxes, a potent greenhouse gas, from soils is necessary to improve our knowledge of terrestrial N2O losses. Developing universal sampling frequencies for calculating annual N2O fluxes is difficult, as fluxes are renowned for their high temporal variability. We demonstrate daily sampling was largely required to achieve annual N2O fluxes within 10% of the 'best' estimate for 28 annual datasets collected from three continents--Australia, Europe and Asia. Decreasing the regularity of measurements either under- or overestimated annual N2O fluxes, with a maximum overestimation of 935%. Measurement frequency was lowered using a sampling strategy based on environmental factors known to affect temporal variability, but still required sampling more than once a week. Consequently, uncertainty in current global terrestrial N2O budgets associated with the upscaling of field-based datasets can be decreased significantly using adequate sampling frequencies.