Litter Inhibitory Effects on Soil Microbial Biomass, Activity, and Catabolic Diversity in Two Paired Stands of Robinia pseudoacacia L. and Pinus nigra Arn.

Research Highlights: Plant cover drives the activity of the microbial decomposer community and affects carbon (C) sequestration in the soil. Despite the relationship between microbial activity and C sequestration in the soil, potential inhibition of soil microbial activity by plant cover has received little attention to date. Background and Objectives: Differences in soil microbial activity between two paired stands on soil at a very early stage of formation and a common story until afforestation, can be traced back to the plant cover. We hypothesized that in a black locust (Robinia pseudoacacia L.) stand the high-quality leaf litter of the tree, and that of the blackberry (Rubus fruticosus L.) understory had an inhibitory effect on soil microbial community resulting in lower mineralization of soil organic matter compared to the paired black pine (Pinus nigra Arn.) stand. Materials and Methods: We estimated potential mineralization rates (MR), microbial (MB), and active fungal biomass (AFB) of newly-shed litter, forest floor, and mineral soil. We tested the effects of litters' water extracts on soil MR, MB, AFB and its catabolic response profile (CRP). Results: Newly-shed litter of black locust had higher MR than that of blackberry and black pine; MR, MB, and AFB were higher in forest floor and in mineral soil under black pine than under black locust. Water extracts of black locust and blackberry litter had a negative effect on the amount, activity of microorganisms, and CRP. Conclusions: The results demonstrate the potential for black locust and blackberry litter to have a marked inhibitory effect on decomposer microorganisms that, in turn, reduce organic matter mineralization with possible consequences at the ecosystem level, by increasing C sequestration in mineral soil.Peer reviewe

C Stocks in Forest Floor and Mineral Soil of Two Mediterranean Beech Forests

This study focuses on two Mediterranean beech forests located in northern and southern Italy and therefore subjected to different environmental conditions. The research goal was to understand C storage in the forest floor and mineral soil and the major determinants. Relative to the northern forest (NF), the southern forest (SF) was found to produce higher amounts of litterfall (4.3 vs. 2.5 Mg·ha−1) and to store less C in the forest floor (~8 vs. ~12 Mg·ha−1) but more C in the mineral soil (~148 vs. ~72 Mg·ha−1). Newly-shed litter of NF had lower P (0.4 vs. 0.6 mg·g−1) but higher N concentration (13 vs. 10 mg·g−1) than SF. Despite its lower Mn concentration (0.06 vs. 0.18 mg·g−1), SF litter produces a Mn-richer humus (0.32 vs. 0.16 mg·g−1) that is less stable. The data suggest that decomposition in the NF forest floor is limited by the shorter growing season (178 days vs. 238 days) and the higher N concentrations in newly shed litter and forest floor. Differences in C stock in the mineral soil reflect differences in ecosystem productivity and long-term organic-matter accumulation. The vertical gradient of soluble and microbial fractions in the soil profile of SF was consistent with a faster turnover of organic matter in the forest floor and greater C accumulation in mineral soil relative to NF. With reference to regional-scale estimates from Italian National Forest Inventory data, the C stock in the mineral soil and the basal area of Italian beech forests were found to be significantly related, whereas C stock in the forest floor and C stock in the mineral soil were not

BIOREGENERATIVE LIFE SUPPORT SYSTEMS IN THE SPACE (BLSS): THE EFFECTS OF RADIATION ON PLANTS

The growth of plants in Space is a fundamental issue for Space exploration. Plants play an important role in the Bioregenerative Life Support Systems (BLSS) to sustain human permanence in extraterrestrial environments. Under this perspective, plants are basic elements for oxygen and fresh food production as well as air regeneration and psychological support to the crew. The potentiality of plant survival and reproduction in space is limited by the same factors that act on the earth (e.g. light, temperature and relative humidity) and by additional factors such as altered gravity and ionizing radiation. This paper analyzes plant responses to space radiation which is recognized as a powerful mutagen for photosynthetic organisms thus being responsible for morpho-structural, physiological and genetic alterations. Until now, many studies have evidenced how the response to ionizing radiation is influenced by several factors associated both to plant characteristics (e.g. cultivar, species, developmental stage, tissue structure) and/or radiation features (e.g. dose, quality and exposure time). The photosynthetic machinery is particularly sensitive to ionizing radiation. The severity of the damages induced by ionizing radiation on plant cell and tissues may depend on the capability of plants to adopt protection mechanisms and/or repair strategies. In this paper a selection of results from studies on the effect of ionizing radiations on plants at anatomical and eco-physiological level is reported and some aspects related to radioresistance are explored

Estimated nitrogen concentrations in humus based on initial nitrogen concentrations in foliar litter: a synthesis. XII. Long-term decomposition in a Scots pine forest

The final (limit) values for litter decomposition were estimated and, by extrapolating a linear relationship between accumulated litter mass loss and litter N concentration, the N concentration at the limit value (N-limit) was estimated. The values for N-limit were compared with those of the A(01) layer (N-humus) and of newly shed litter (N-init). No difference was found between the A(01) and A(02) layers when their N concentrations were compared with the values for N-limit. There was a highly significant linear relationship between N-limit and N-init (R-2 = 0.769 and p < 0.001). Likewise, there was a highly significant linear relationship between N-humus and N-init. When these two linear relationships were compared, there was no significant difference in slope, while there was a significant difference in the intercepts of 6.76 and 7.25 mg,g(-1) for N-humus and N-init, respectively. Thus, for a given site in our investigation, the estimated value for N concentration in humus would be 6.8% lower than the measured one

Ranges of nutrient concentrations in Quercus ilex leaves at natural and urban sites

The leaf nutrient concentrations and the N-to-nutrient ratios were analyzed to evaluate the nutritional status of holm oaks (Quercus ilex L.) experiencing various anthropogenic pressures. Leaves (1 year old) of Q. ilex and surface soil (0–5 cm) surrounding the trees were collected at seven natural and seven urban sites in Campania Region (Southern Italy) and analyzed for the concentrations of macro (C, N, P, S) and micronutrients (Mn, K, Na, Cu, Mg, Ca, Fe, Zn). The available soil fraction of micronutrients was also evaluated. The nutrients showed different concentration ranges for the natural and the urban sites in the soil (total and available) and in the leaves, that we reported separately. Organic-matter content and macronutrient concentrations were higher in the natural soils, while the highest leaf N, S, and P concentrations were found at some urban sites. Concentrations of Cu, Na and Zn both in leaves and soil, and Mg and Fe in leaves from the urban sites appeared to be affected by air depositions. Manganese was the only micronutrient to show higher concentrations at the natural than at the urban sites, both in soil and leaves. For this nutrient, in addition, a relationship between leaf and available soil concentrations was found at the natural sites. The ratios between the concentrations of N and each studied nutrient in the leaves highlighted a different nutritional status between the plants from the natural and urban sites

Discriminating between seasonal and chemical variation in extracellular enzyme activities within two Italian beech forests by means of multilevel models

Enzymes play a key-role in organic matter dynamics and strong scientific attention has been given to them lately, especially to their response to climate and substrate chemical composition. Accordingly, in this study, we investigated the effects of chemical composition and seasons on extracellular enzyme activities (laccase, peroxidase, cellulase, chitinase, acid phosphomonoesterase, and dehydrogenase) by means of multilevel models within two Italian mountain beech forests. We used chemical variables as the fixed part in the model, season as random variation and layers (decomposition continuum for leaf litter and 0-5, 5-15, 15-30, and 30-40 cm for soil) as nested factors within the two forests. Our results showed that seasonal changes explained a higher amount of variance in enzyme activities compared to substrate chemistry in leaf litter, whereas chemical variation had a stronger impact on soil. Moreover, the effect of seasonality and chemistry was in general larger than the differences between forest sites, soils, and litter layers

Indirect effects of trophic interactions govern carbon circulation in two beech forest soil ecosystems

Forest soils harbour a vast array of organisms that govern the processing of organic matter. Through their trophic interactions, they give rise to carbon flows that sustain soil ecosystem functioning. Understanding how soil food webs shape carbon flows may enhance our knowledge about the role of biodiversity on soil processes. In this work, we assembled trophic networks representing soil food webs of two beech forests during spring and autumn, and compiled mass-balanced models quantifying carbon flows between their components. These models were investigated using network analysis to identify the role of the components on carbon flow, cycling and functional trophic relationships. Moreover, we explored how the structure of carbon exchanges promote efficiency and stability. Results indicate the importance of indirect interactions. Most trophic groups exhibit a diffuse dependency on all the compartments for their carbon requirement although certain groups such as Collembola play the role of hubs in distributing carbon. Indirect interactions often reverse the impacts of direct trophic relationships being antagonistic to the direction of change predicted based on predator–prey interactions. The high incidence of generalist feeding habits increases the redundancy of energy channels thereby making such food webs more resilient against perturbations but at the expense of carbon transfer efficiency. Although differences can be observed across sites and periods, food web structure rather than environmental variability seems to be the main factor responsible for patterns of carbon flows in the two beech forests. Read the free Plain Language Summary for this article on the Journal blog

The chemical composition of newly shed needle litter of Scots pine and some other pine species in a climatic transect. X Long-term decomposition in a Scots pine forest

Significant differences in the chemical composition of falling needle litter were found among various pine species. A comparison between the needle litter of northern species (Scots pine and lodgepole pine) and that of 17 other, southern species combined showed that concentrations of N, P, Mg, K, and lignin were significantly lower in the northern group. In contrast, the Mn concentration was significantly higher in this northern group. Along a transect from the Barents Sea (69 degrees 45'N) to the Carpathian Mountains (49 degrees 53'N), concentrations of N, P, S, and K in Scots pine litter fall increased significantly. The best-fit regression models described asymptotic curves, suggesting that concentrations of these major nutrients approach their maximum values at sites with high values for actual evapotranspiration (AET). Low values were found in the north. By contrast, Mn concentrations, increased with latitude and decreased with increasing AET. High covariation among concentrations of the major nutrients (N, P, S, and K) can be attributed to their being major constituents of structural compounds. Analysis of various regression models relating the chemical composition of needle litter fall to latitude and AET, together with a factor analysis, suggested that concentrations of N, P, S, and K were related mainly to climatic conditions, whereas those of Mg and Mn were related more to site-specific properties such as soil fertility. A high level of predictability was found for concentrations of N, P, S, and K using multiple regression, with values for R(adj)(2) between 0.63 and 0.93