Simulating the impacts of land use in northwest Europe on Net Ecosystem Exchange (NEE): the role of arable ecosystems, grasslands and forest plantations in climate change mitigation.

In this study, we compared measured and simulated Net Ecosystem Exchange (NEE) values from three wide spread ecosystems in the southeast of Ireland (forest, arable and grassland), and investigated the suitability of the DNDC (the DeNitrification-DeComposition) model to estimate present and future NEE. Although, the field-DNDC version overestimated NEE at temperatures >5 °C, forest-DNDC under-estimated NEE at temperatures >5 °C. The results suggest that the field/forest DNDC models can successfully estimate changes in seasonal and annual NEE from these ecosystems. Differences in NEE were found to be primarily land cover specific. The annual NEE was similar for the grassland and arable sites, but due to the contribution of exported carbon, the soil carbon increased at the grassland site and decreased at the arable site. The NEE of the forest site was an order of magnitude larger than that of the grassland or arable ecosystems, with large amounts of carbon stored in woody biomass and the soil. The average annual NEE, GPP and Reco values over the measurement period were -904, 2379 and 1475 g C m(-2) (forest plantations), -189, 906 and 715 g C m(-2) (arable systems) and -212, 1653 and 1444 g C m(-2) (grasslands), respectively. The average RMSE values were 3.8 g C m(-2) (forest plantations), 0.12 g C m(-2) (arable systems) and 0.21 g C m(-2) (grasslands). When these models were run with climate change scenarios to 2060, predictions show that all three ecosystems will continue to operate as carbon sinks. Further, climate change may decrease the carbon sink strength in the forest plantations by up to 50%. This study supports the use of the DNDC model as a valid tool to predict the consequences of climate change on NEE from different ecosystems.

Thermal optimality of net ecosystem exchange of carbon dioxide and underlying mechanisms.

• It is well established that individual organisms can acclimate and adapt to temperature to optimize their functioning. However, thermal optimization of ecosystems, as an assemblage of organisms, has not been examined at broad spatial and temporal scales. • Here, we compiled data from 169 globally distributed sites of eddy covariance and quantified the temperature response functions of net ecosystem exchange (NEE), an ecosystem-level property, to determine whether NEE shows thermal optimality and to explore the underlying mechanisms. • We found that the temperature response of NEE followed a peak curve, with the optimum temperature (corresponding to the maximum magnitude of NEE) being positively correlated with annual mean temperature over years and across sites. Shifts of the optimum temperature of NEE were mostly a result of temperature acclimation of gross primary productivity (upward shift of optimum temperature) rather than changes in the temperature sensitivity of ecosystem respiration. • Ecosystem-level thermal optimality is a newly revealed ecosystem property, presumably reflecting associated evolutionary adaptation of organisms within ecosystems, and has the potential to significantly regulate ecosystem-climate change feedbacks. The thermal optimality of NEE has implications for understanding fundamental properties of ecosystems in changing environments and benchmarking global models.

A review of indicators of climate change for use in Ireland.

Impact indicators are systems/organisms, the vitality of which alters in response to changes in environmental condition. The indicators assessed in this review fall within the impact category of the driver-pressure-state-impact-response (DPSIR) framework. Instrumental records have shown unequivocal changes in climatic conditions over the past 30 years at a global level but impact indicators allow these changes to be monitored at a finer resolution. Our main aim was to review sets of indicators of climate change currently used in various countries and to make recommendations for their use in the Irish environment. We review a preliminary set of climate change impact indicators in five sectors: agriculture; plant and animal distribution patterns; phenology; palaeoecology and human health. Currently, the most effective impact indicators of climate change have proved to be phenological observations of tree developmental stages. The strongest factor limiting the use of indicators is the lack of long-term data sets from which a climatic signal can be extracted.

Seasonal changes in tissue elasticity and water transport efficiency in three co-occurring Mediterranean shrubs under natural long-term CO2 enrichment.

Seasonal changes in hydraulic properties and tissue elasticity were evaluated in Erica arborea L., Myrtuscommunis L. and Juniperus communis L., three Mediterranean shrubs that differ in adaptations to drought. These parameters were analysed over 12 months under field conditions, by comparing plants grown in the proximity of a natural CO2 spring (about 700 µmol mol-1 atmospheric CO2 concentration, [CO2]) with plants in ambient conditions. Plants at the CO2-spring site have been growing for generations at elevated [CO2]. At both sites, stem hydraulic and structural properties followed the prevailing climatic constraints. However, these shrub species co-occurring in the same environment differed in their capacity to tolerate water deficits, in xylem efficiency, and in strategies for regulating water movement between plant compartments. Either an increase or a decrease in tissue elasticity was effective in promoting resistance to drought stress, depending on the species. Long-term elevated [CO2] influenced all the studied parameters. Species-dependent differences existed in hydraulic architecture between the CO2-spring plants and control plants of E. arborea and M. communis, while J. communis plants rarely showed differences between sites. Less distinct differences between sites were observed for wood structure. The three species showed somewhat lower tissue elasticity under elevated [CO2], in particular during stress periods. The effects of elevated [CO2] on stem hydraulic pathway and structure and shoot elastic properties persist in the long term, but differ in absolute values and sign among the studied species and with the seasonal course, and thus might alter competitive relations between these shrubs.