Ozone fumigation of Quercus ilex L. slows down leaf litter decomposition with no detectable change in leaf composition

Context

The evaluation of changes in litter decomposition rate due to increasing trend in tropospheric ozone is an emerging field of investigation, providing relevant information on long-term forest ecosystem sustainability.

Aims

This research aims to clarify the effects of ozone exposure on Quercus ilex leaf chemical composition and decomposition slow down.

Methods

Young plants were fumigated in growth chambers at a cumulative dose of 17.15 ppm h. To assess the fumigation effectiveness, stomatal conductance and net photosynthesis were monitored. Leaves were analysed for C, N, S, Ca, Mg, K, Fe, Zn, Mn, total soluble sugars, starch, acid-detergent fibre (ADF), lignin and cellulose prior to the incubation in litter bags in mesocosms, and during decomposition along 395 days.

Results

Ozone-exposed leaves showed a significant reduction in net photosynthesis and stomatal conductance but did not differ from control leaves in all the chemical parameters analysed. Nevertheless, leaf decomposition rate was lower in treated leaves. The main differences between the models describing the mass loss in exposed and control leaves were played by ADF for exposed leaves and by lignin for control leaves, as well as by N, that showed a greater contribution in the model for the exposed leaves.

Conclusion

Ozone fumigation of Q. ilex results in leaf litter decomposition slowing down, mainly due to ADF joint dynamics with the other variables describing mass decay, even if no detectable changes in initial leaf composition occur.     

A microwave tomographic system for wood characterization in the forest products industry

Abstract

Nondestructive testing and evaluation techniques able to extract information about the internal structure of the samples under test are very important in the wood industry. Microwave imaging systems have been considered for a long time promising apparatuses for this task. In this framework, approaches exploiting the full scattering phenomena for creating images of the distributions of the dielectric properties of the targets have been developed in the last few years. In this paper, a prototype of microwave tomographic system is presented and several experimental validation confirming its suitability for the use in the wood and forest product industry are reported.     

Nitrogen dynamics during ecosystem development in tropical forest restoration

We considered whether ecological restoration using high diversity of native tree species serves to restore nitrogen dynamics in the Brazilian Atlantic Forest. We measured δ¹⁵N and N content in green foliage and soil; vegetation N:P ratio; and soil N mineralization in a preserved natural forest and restored forests of ages 21 and 52 years. Green foliage δ¹⁵N values, N content, N:P ratio, inorganic N and net mineralization and nitrification rates were all higher, the older the forest. Our findings indicate that the recuperation of N cycling has not been achieved yet in the restored forests even after 52 years, but show that they are following a trajectory of development that is characterized by their N cycling intensity becoming similar to a natural mature forest of the same original forest formation. This study demonstrated that some young restored forests are more limited by N compared to mature natural forests. We document that the recuperation of N cycling in tropical forests can be achieved through ecological restoration actions.     

Diurnal and seasonal variability in radial distribution of sap flux density: Implications for estimating stand transpiration

Daily and seasonal patterns in radial distribution of sap flux density were monitored in six trees differing in social position in a mixed coniferous stand dominated by silver fir (Abies alba Miller) and Norway spruce (Picea abies (L.) Karst) in the Alps of northeastern Italy. Radial distribution of sap flux was measured with arrays of 1-cm-long Granier probes. The radial profiles were either Gaussian or decreased monotonically toward the tree center, and seemed to be related to social position and crown distribution of the trees. The ratio between sap flux estimated with the most external sensor and the mean flux, weighted with the corresponding annulus areas, was used as a correction factor (CF) to express diurnal and seasonal radial variation in sap flow. During sunny days, the diurnal radial profile of sap flux changed with time and accumulated photosynthetic active radiation (PAR), with an increasing contribution of sap flux in the inner sapwood during the day. Seasonally, the contribution of sap flux in the inner xylem increased with daily cumulative PAR and the variation of CF was proportional to the tree diameter, ranging from 29% for suppressed trees up to 300% for dominant trees. Two models were developed, relating CF with PAR and tree diameter at breast height (DBH), to correct daily and seasonal estimates of whole-tree and stand sap flow obtained by assuming uniform sap flux density over the sapwood. If the variability in the radial profile of sap flux density was not accounted for, total stand transpiration would be overestimated by 32% during sunny days and 40% for the entire season.     

Vertical foliage distribution determines the radial pattern of sap flux density in Picea abies

Understanding the causes determining the radial pattern of sap flux density is important both for improving knowledge of sapwood functioning and for up-scaling sap flow measurements to canopy transpiration and ecosystem water use. To investigate the anatomical connection between whorls and annual sapwood rings, pruning-induced variation in the radial pattern of sap flux density was monitored with Granier probes in a 35-year-old Picea abies (L.) Karst tree that was pruned from the crown bottom up. Modifications in the radial pattern of sap flux density were quantified by a shape index (SI), which varies with the relative contribution of the outer and inner sapwood to tree transpiration. The SI progressively diminished during bottom up pruning, indicating a significant reduction in sap flow contribution of the inner sapwood. Results suggest that the radial pattern of sap flux density depends mainly on the vertical distribution of foliage in the crown, with lower shaded branches hydraulically connected with inner sapwood and upper branches connected with the outer rings.     

Constraints on light interception efficiency due to shoot architecture in broad-leaved Nothofagus species

Shoot architecture may significantly alter mean quantum flux on foliage and thus, photosynthetic productivity. There is currently only limited information about plastic alterations in shoot structure caused by within-canopy variation in mean integrated irradiance (Q(int)) in broad-leaved trees. We studied leaf and shoot structure, and nitrogen and carbon content in late-successional, widely distributed, temperate, broad-leaved Nothofagus taxa to determine the architectural controls on light harvesting and photosynthetic performance. Nothofagus fusca (Hook. f.) Oersted has larger leaves and less densely leaved shoots than the N. solandri varieties. Nothofagus solandri var. solandri (Hook. f.) Oersted is characterized by rounder leaves that potentially have a larger overlap than the ovate-triangular leaves of N. solandri var. cliffortioides (Hook. f.) Poole. Leaf dry mass (M(A)) and nitrogen content (N(A)) per unit area increased with increasing Q(int) in all species, demonstrating enhanced investment of photosynthetic biomass in high light. Although M(A) differed between species at a common irradiance, there was a uniform relationship between N(A) and Q(int) across species. Leaf carbon content per dry mass and leaf dry mass to fresh mass ratio also scaled positively with irradiance, suggesting greater structural investments in high light. In all species, shoots became more horizontal and flatter at lower Q(int), implying an enhanced use efficiency of direct irradiance in natural leaf positions. In contrast, irradiance effects on leaf aggregation varied among species. Across the data, leaf overlap or leaf area density was often greater at lower irradiances, possibly as a result of limited carbon availability for shoot axis extension growth. In N. fusca, leaves of which were more aggregated in high light, the shoot silhouette to total leaf area ratio (S(S)) declined strongly with increasing irradiance, demonstrating a lower light harvesting efficiency at high Q(int). This effect was only moderate in N. solandri var. cliffortioides and S(S) was independent of Q(int) in N. solandri var. solandri. Although the efficiency of light interception at high irradiances was lowest in N. fusca, this species had the greatest nitrogen content per unit shoot silhouette area (2N(A)/S(S)), indicating superior shoot-level photosynthetic potential. These data collectively demonstrate that shoot architecture significantly affects light interception and photosynthesis in broad-leaved trees, and that structural carbon limitations may constrain leaf light harvesting efficiency at low irradiance.     

Simulation of soil types in Teramo province (Central Italy) with terrain parameters and remote sensing data

Soil surveys are an essential source of information for land management although a limited budget often reduces the amount of data available. Even if the dataset is limited, geostatistics can provide a valid estimation tool through a weighted moving average interpolation (kriging). Often, however, the spatial variability of soil properties appears smoothed and short range variability is underestimated by this kind of interpolation technique. A more realistic distribution of a given variable on the territory can be obtained through models based on stochastic simulation.     

Biological and Artificial Matrixes as PAH Accumulators: An Experimental Comparative Study

In order to find out a new effective accumulator of polycyclic aromatic hydrocarbons (PAHs) useful for monitoring studies on a large scale and low costs, the accumulation capacity of both biological and artificial matrixes (mosses and polyester fibers, respectively) has been tested. For this purposes, Hypnum cupressiforme and dacron® were exposed to pollution airborne in two sites located nearby an active iron industry and in center of the town of Trieste, where high PAH pollution spots, due to vehicular traffic, are usually detected. The samplers were exposed in six sampling sessions for 21 days. The results obtained were compared with data collected by active PAH samplers, usually employed for official widespread monitoring. The level of correlation between the data sets was calculated. Furthermore, a repeatability study of data was performed. According to the results, both matrixes are good PAH accumulators, though they show different skills.     

Heavy Metal Contents and Distribution in Coastal Sediments of the Gulf of Trieste (Northern Adriatic Sea, Italy)

A set of ten heavy metals (Al, As, Cd, Cr, Cu, Hg, Ni, Pb, V, and Zn) was investigated in surface sediments (0–5 cm) collected in 21 sites of the Gulf of Trieste, Northern Adriatic Sea (Italy). The aim of this work was to obtain a preliminary assessment about the levels and spatial distribution of these selected elements. Ancillary parameters such as grain size, total organic carbon, and total nitrogen were also determined. The enrichment factor was calculated to discriminate if a natural condition or a status of anthropogenic contamination occurs. In addition, a set of sediment quality guidelines, mean effect low range and effect medium range quotients, was also applied in order to predict the probability of adverse biological effects on the benthic community.     

三种南方典型水稻土长期试验下有机碳积累机制研究Ⅲ.两种水稻土颗粒有机质结构特征的变化

采用固体交叉极化魔角自旋¹³C核磁共振(CPMAS¹³C-NMR)波谱技术对长期不同施肥处理下红壤性水稻土和太湖地区黄泥土本体土壤以及水稳性团聚体中颗粒有机质（POM）的化学结构特征进行了研究。结果表明,不同施肥处理下本体土壤和不同粒径水稳性团聚体中POM的结构组成相似,主要由烷氧C、烷基C和芳香C组成,其中以烷氧C含量最高。施肥改变了本体土壤POM中各类C原子的相对百分含量,有机肥以及化肥配施有机肥条件下烷氧C含量明显降低,芳香C和酚基C含量有不同程度的增加,表明POM的稳定性增强;单施化肥下烷氧C含量最高,而烷基C、芳香C和芳香度均最低,POM的稳定性减弱,不利于POM的积累。施肥改变了黄泥土不同粒径水稳性团聚体中POM各类C原子的相对百分含量,从而使得不同粒径中POM对其团聚体的稳定性作用发生变化;而红壤性水稻土不同粒径水稳性团聚体POM各类C原子的相对百分含量并未明显受到施肥措施的影响。