Mirco Rodeghiero

Redefinition and global estimation of basal ecosystem respiration rate

Basal ecosystem respiration rate (BR), the ecosystem respiration rate at a given temperature, is a common and important parameter in empirical models for quantifying ecosystem respiration (ER) globally. Numerous studies have indicated that BR varies in space. However, many empirical ER models still use a global constant BR largely due to the lack of a functional description for BR. In this study, we redefined BR to be ecosystem respiration rate at the mean annual temperature. To test the validity of this concept, we conducted a synthesis analysis using 276 site-years of eddy covariance data, from 79 research sites located at latitudes ranging from similar to 3 degrees S to similar to 70 degrees N. Results showed that mean annual ER rate closely matches ER rate at mean annual temperature. Incorporation of site-specific BR into global ER model substantially improved simulated ER compared to an invariant BR at all sites. These results confirm that ER at the mean annual temperature can be considered as BR in empirical models. A strong correlation was found between the mean annual ER and mean annual gross primary production (GPP). Consequently, GPP, which is typically more accurately modeled, can be used to estimate BR. A light use efficiency GPP model (i.e., EC-LUE) was applied to estimate global GPP, BR and ER with input data from MERRA (Modern Era Retrospective-Analysis for Research and Applications) and MODIS (Moderate resolution Imaging Spectroradiometer). The global ER was 103 Pg C yr (-1), with the highest respiration rate over tropical forests and the lowest value in dry and high-latitude areas.

Current status, uncertainty and future needs in soil organic carbon monitoring☆

Increasing human demands on soil-derived ecosystem services requires reliable data on global soil resources for sustainable development. The soil organic carbon (SOC) pool is a key indicator of soil quality as it affects essential biological, chemical and physical soil functions such as nutrient cycling, pesticide and water retention, and soil structure maintenance. However, information on the SOC pool, and its temporal and spatial dynamics is unbalanced. Even in well-studied regions with a pronounced interest in environmental issues information on soil carbon (C) is inconsistent. Several activities for the compilation of global soil C data are under way. However, different approaches for soil sampling and chemical analyses make even regional comparisons highly uncertain. Often, the procedures used so far have not allowed the reliable estimation of the total SOC pool, partly because the available knowledge is focused on not clearly defined upper soil horizons and the contribution of subsoil to SOC stocks has been less considered. Even more difficult is quantifying SOC pool changes over time. SOC consists of variable amounts of labile and recalcitrant molecules of plant, and microbial and animal origin that are often operationally defined. A comprehensively active soil expert community needs to agree on protocols of soil surveying and lab procedures towards reliable SOC pool estimates. Already established long-term ecological research sites, where SOC changes are quantified and the underlying mechanisms are investigated, are potentially the backbones for regional, national, and international SOC monitoring programs.

Temperature sensitivity of the turnover times of soil organic matter in forests

Soils represent the largest carbon pool in the terrestrial biosphere, and climate change might affect the main carbon fluxes associated with this pool. These fluxes are the production of aboveground litter and root litter, and decomposition of the soil organic matter (SOM) pool by soil microorganisms. Knowledge about the temperature sensitivity of the decomposition of different SOM fractions is crucial in order to understand how climate change might affect carbon storage in soils. In this study, the temperature sensitivity of the turnover times of three different SOM fractions (labile, intermediate, and stabilized) was investigated for 11 forest sites along a temperature gradient. Carbon-14 isotope analyses of the SOM fractions combined with a model provided estimates of their turnover times. The turnover times of the labile SOM fraction were not correlated with mean annual soil temperature. Therefore it was not possible to estimate temperature sensitivity for the labile SOM fraction. Given considerable evidence elsewhere for significant temperature sensitivities of labile SOM, lack of temperature sensitivity here most likely indicates limitations of the applied methodology for the labile SOM fraction. The turnover times of the intermediate and the stabilized SOM fractions were both correlated with mean annual soil temperatures. The temperature sensitivity of the stabilized SOM fraction was at least equal to that of the intermediate SOM fraction and possibly more than twice as high. A correction for confounding effects of soil acidity and clay content on the temperature sensitivities of the intermediate and stabilized SOM fractions was included in the analysis. The results as observed here for the three SOM fractions may have been influenced by (1) modeling assumptions for the estimation of SOM turnover times of leaf and needle longevities, constant annual carbon inputs, and steady-state SOM pools, (2) the occurrence of summer drought at some sites, (3) differences between sites in quality of the SOM fractions, or (4) the relatively small temperature range. Our results suggested that a 1 degree C increase in temperature could lead to decreases in turnover times of 4-11% and 8-16%, for the intermediate and stabilized SOM fractions, respectively.

Determination of soil carbon stocks and changes

INTRODUCTION Soil carbon pools and the global carbon cycle In terrestrial ecosystems soils represent the major reservoir of organic carbon (Table 4.1), but with large and yet unquantified uncertainties in their estimates (mainly due to low soil sample numbers used for global up-scaling and assumptions on mean soil depths). At the global level, the soil organic matter (SOM) pool (estimated to 1 m depth) contains about 1580 Pg of carbon (Pg = 10 15 g), about 610 Pg are stored in the vegetation and about 750 Pg are present in the atmosphere (Schimel, 1995). Carbon is found in soils both in organic and inorganic forms (Table 4.2). Organic carbon is commonly classified into three ‘arbitrary’ pools, mostly for modelling purposes (such as in CENTURY), i.e. fast, slow and passive reflecting the rate of turnover. However, it is difficult to relate these pools to soil carbon fractions (see Section 4.1.5). The total amount of carbonate carbon to 1 m depth is estimated at 695–748 Pg carbon (Batjes, 1996). About one third of organic soil carbon occurs in forests and another third in grasslands and savannas, the rest in wetlands, croplands and other biomes (Janzen, 2004). The global soil organic carbon map (Fig. 4.1, ISLSCP II; ORNL DAAC, http://daac.ornl.gov/) shows the areas of high soil organic carbon predominantly in cold boreal (e.g. Northern Canada) and warm and humid tropical regions (e.g. South-East Asia), reflecting areas of deep organic soils (i.e. peatlands).

New spectral vegetation indices based on the near-infrared shoulder wavelengths for remote detection of grassland phytomass

This article examines the possibility of exploiting ground reflectance in the near-infrared (NIR) for monitoring grassland phytomass on a temporal basis. Three new spectral vegetation indices (infrared slope index, ISI; normalized infrared difference index, NIDI; and normalized difference structural index, NDSI), which are based on the reflectance values in the H25 (863–881 nm) and the H18 (745–751 nm) Chris Proba (mode 5) bands, are proposed. Ground measurements of hyperspectral reflectance and phytomass were made at six grassland sites in the Italian and Austrian mountains using a hand-held spectroradiometer. At full canopy cover, strong saturation was observed for many traditional vegetation indices (normalized difference vegetation index (NDVI), modified simple ratio (MSR), enhanced vegetation index (EVI), enhanced vegetation index 2 (EVI 2), renormalized difference vegetation index (RDVI), wide dynamic range vegetation index (WDRVI)). Conversely, ISI and NDSI were linearly related to grassland phytomass with negligible inter-annual variability. The relationships between both ISI and NDSI and phytomass were however site specific. The WinSail model indicated that this was mostly due to grassland species composition and background reflectance. Further studies are needed to confirm the usefulness of these indices (e.g. using multispectral specific sensors) for monitoring vegetation structural biophysical variables in other ecosystem types and to test these relationships with aircraft and satellite sensors data. For grassland ecosystems, we conclude that ISI and NDSI hold great promise for non-destructively monitoring the temporal variability of grassland phytomass.

Cataloguing Soil Carbon Stocks

In their Report (“Terrestrial gross carbon dioxide uptake: Global distribution and covariation with climate,” 13 August, p. [834][1]), C. Beer et al. joined others ([ 1 ][2], [ 2 ][3]) in estimating global carbon fluxes and their relationship to climate. However, the global role of soil carbon

Phenotypic differences determine drought stress responses in ecotypes of Arundo donax adapted to different environments

Arundo donax has been identified as an important biomass and biofuel crop. Yet, there has been little research on photosynthetic and metabolic traits, which sustain the high productivity of A. donax under drought conditions. This study determined phenotypic differences between two A. donax ecotypes coming from stands with contrasting adaptation to dry climate. We hypothesized that the Bulgarian (BG) ecotype, adapted to drier conditions, exhibits greater drought tolerance than the Italian (IT) ecotype, adapted to a more mesic environment. Under well-watered conditions the BG ecotype was characterized by higher photosynthesis, mesophyll conductance, intrinsic water use efficiency, PSII efficiency, isoprene emission rate and carotenoids, whereas the IT ecotype showed higher levels of hydroxycinnamates. Photosynthesis of water-stressed plants was mainly limited by diffusional resistance to CO2 in BG, and by biochemistry in IT. Recovery of photosynthesis was more rapid and complete in BG than in IT, which may indicate better stability of the photosynthetic apparatus associated to enhanced induction of volatile and non-volatile isoprenoids and phenylpropanoid biosynthesis. This study shows that a large phenotypic plasticity among A. donax ecotypes exists, and may be exploited to compensate for the low genetic variability of this species when selecting plant productivity in constrained environments.

High Resolution Assessment of Spatio-Temporal Changes in O2 Concentration in Root-Pathogen Interaction

Fusarium wilt, caused by the fungus Fusarium oxysporum f. sp. lycopersici (Fol), is one of the most destructive soil-borne diseases of tomatoes. Infection takes place on the roots and the process starts with contact between the fungus and the roots hairs. To date, no detailed studies are available on metabolic activity in the early stages of the Fol and tomato root interaction. Spatial and temporal patterns of oxygen consumption could provide new insights into the dynamics of early colonization. Here, we combined planar optodes and spatial analysis to assess how tomato roots influence the metabolic activity and growth patterns of Fol. The results shows that the fungal metabolism, measured as oxygen consumption, increases within a few hours after the inoculation. Statistical analysis revealed that the fungus tends to growth toward the root, whereas, when the root is not present, the single elements of the fungus move with a Brownian motion (random). The combination of planar optodes and spatial analysis is a powerful new tool for assessing temporal and spatial dynamics in the early stages of root-pathogen interaction.

Greenhouse Gas Emissions from Temperate European Mountain Forests

Forests are covering a substantial part of European mountains. The elongation of the growing season due to climate change and warmer summers are increasing the rate of soil respiration. However, the effect is at some sites partially compensated by droughts. Temperate mountain forests ecosystems are mostly releasing carbon dioxide whereas nitrogen oxides are of lesser importance. Societal changes are also affecting the greenhouse gas emissions from forests. The structural change in agriculture causes an increase of the forest area. The change in land use from grassland to forest, leads to the formation of an organic litter layer on the soil surface but to a reduction of the carbon input by decaying roots to the mineral layers. Moreover, the effect of the increased carbon sequestration in the biomass of more productive forests is partially offset by losses of carbon dioxide from the soil. Climate change also calls for an adaptation of the strategy of forest management. The economical feasibility of timber production in remote high-elevation forests will not be significantly increased. Nevertheless, even marginally productive mountain forests need to be managed in order to ensure the provision of ecosystem services such as protection against natural hazards. Mountain forests with a stable stand structure can better cope with disturbances such as storms and biotic pressures, thereby reducing the risk of carbon losses to the atmosphere.

Soil Carbon Stocks and Fluxes

The aim of this chapter was to quantify the soil organic carbon (SOC) stock in the top 30 cm of mineral soil for the whole Italian territory, according to the different land use types of the Intergovernmental Panel on Climate Change (IPCC) cropland category (arable land, agroforestry, vineyards, olive groves, orchards and rice fields), as a basis for future land use scenarios and to address mitigation policy at country level. Besides, two independent studies addressing the current status and the future trends of SOC for the whole cropland category at regional level were reported. The subdivision of the cropland category into classes is functional to assess the impacts on the SOC stock due to land use changes from and to agricultural uses, providing the starting or ending point scenario. The differences emphasized for the soils of a subcategory under the different types of climate can be possibly used for future-oriented agricultural practices. The comparison of the total mean values of the different cropland subcategories shows significant differences in the SOC stock. Considering the year 2000 and applying to each subcategory area the specific average SOC stock value found in this study, the total amount of C stored in the upper 30 cm of the whole cropland category results to be 516.3 ± 156.9 Tg C. This amount represents about 17 % of the total SOC estimated for the top 50 cm of soils of total surface of Italy, which reports about 2,900 Tg C, thus indicating the importance to preserve the large amount of SOC stored in cropland category. In conclusion, given the few estimates available at European level, repeated SOC inventories aimed to define the SOC content in cropland soils are important for future stock change evaluation.