Joint control of terrestrial gross primary productivity by plant phenology and physiology.

Terrestrial gross primary productivity (GPP) varies greatly over time and space. A better understanding of this variability is necessary for more accurate predictions of the future climate-carbon cycle feedback. Recent studies have suggested that variability in GPP is driven by a broad range of biotic and abiotic factors operating mainly through changes in vegetation phenology and physiological processes. However, it is still unclear how plant phenology and physiology can be integrated to explain the spatiotemporal variability of terrestrial GPP. Based on analyses of eddy-covariance and satellite-derived data, we decomposed annual terrestrial GPP into the length of the CO2 uptake period (CUP) and the seasonal maximal capacity of CO2 uptake (GPPmax). The product of CUP and GPPmax explained >90% of the temporal GPP variability in most areas of North America during 2000-2010 and the spatial GPP variation among globally distributed eddy flux tower sites. It also explained GPP response to the European heatwave in 2003 (r(2) = 0.90) and GPP recovery after a fire disturbance in South Dakota (r(2) = 0.88). Additional analysis of the eddy-covariance flux data shows that the interbiome variation in annual GPP is better explained by that in GPPmax than CUP. These findings indicate that terrestrial GPP is jointly controlled by ecosystem-level plant phenology and photosynthetic capacity, and greater understanding of GPPmax and CUP responses to environmental and biological variations will, thus, improve predictions of GPP over time and space.

Trends in future N2O emissions due to land use change.

Better insight in the possible range of future N2O emissions can help to construct mitigation and adaptation strategies and to adapt land use planning and management to climate objectives. The Dutch fen meadow landscape is a hotspot of N2O emission due to high nitrogen inputs combined with moist peat soils due to land use change. Socio-economic developments in the area are expected to have major impacts on N2O emission. The goals of this study are to estimate changes in N2O emissions for the period 2006-2040 under three different scenarios for the Dutch fen meadow landscape (rural production, rural fragmentation, and rural multifunctionality) and to quantify the share of different emission sources. Three scenarios were constructed and quantified based on the Story-And-Simulation approach. The rural production and the rural fragmentation scenarios are characterized by globalization and a market-oriented economy; in the rural production scenario dairy farming has a strong competitive position in the study region, while under the rural fragmentation scenario agriculture is declining. Under the rural multifunctionality scenario, the global context is characterized by regionalization and stronger regulation toward environmental issues. The N2O emission decreased between 2006 and 2040 under all scenarios. Under the rural production scenario, the N2O emission decreased by 7%. Due to measures to limit peat mineralization and policies to reduce agricultural emissions, the rural multifunctionality scenario showed the largest decrease in N2O emissions (44%). Under the rural fragmentation scenario, in which the dairy farming sector is diminished, the emission decreased by 33%. Compared to other uncertainties involved in N2O emission estimates, the uncertainty due to possible future land use change is relatively large and assuming a constant emission with time is therefore not appropriate.

Nocturnal accumulation of CO2 underneath a tropical forest canopy along a topographical gradient.

Flux measurements of carbon dioxide and water vapor above tropical rain forests are often difficult to interpret because the terrain is usually complex. This complexity induces heterogeneity in the surface but also affects lateral movement of carbon dioxide (CO2) not readily detected by the eddy covariance systems. This study describes such variability using measurements of CO2 along vertical profiles and along a toposequence in a tropical rain forest near Manaus, Brazil. Seasonal and diurnal variation was recorded, with atmospheric CO2 concentration maxima around dawn, generally higher CO2 build-up in the dry season and stronger daytime CO2 drawdown in the wet season. This variation was reflected all along the toposequence, but the slope and valley bottom accumulated clearly more CO2 than the plateaus, depending on atmospheric stability. Particularly during stable nights, accumulation was along lines of equal altitude, suggesting that large amounts of CO2 are stored in the valleys of the landscape. Flushing of this store only occurs during mid-morning, when stored CO2 may well be partly transported back to the plateaus. It is clear that, for proper interpretation of tower fluxes in such complex and actively respiring terrain, the horizontal variability of storage needs to be taken into account not only during the night but also during the mornings.

Changing monsoon patterns, snow and glacial melt, its impacts and adaptation options in northern India: synthesis.

This paper gives a synthesis of this special issue on the sensitivity to climate change of the main bio-physical processes in the Hindukush-Karakoram-Himalayas. It also describes the impacts on the water resources with a special focus on the Ganges. Consequences of changes in water resources and possible adaptation measures for different sectors are discussed.

Changing monsoon patterns, snow and glacial melt, its impacts and adaptation options in northern India: setting the stage.

To set the stage of this special issue this paper gives a short introduction to the sensitivity to climate change of the main bio-physical processes in the Hindukush-Karakoram-Himalayas. It also describes the socio-economic setting of the Ganges basin in northern India as the main focal point of the impact and adaptation studies in this special issue.