Background In the Mediterranean climate, plants have evolved under conditions of low soil-water and nutrient availabilities and have acquired a series of adaptive traits that, in turn exert strong ...feedback on soil fertility, structure, and protection. As a result, plant-soil systems constitute complex interactive webs where these adaptive traits allow plants to maximize the use of scarce resources. Scope It is necessary to review the current bibliography to highlight the most know characteristic mechanisms underlying Mediterranean plant-soil feed-backs and identify the processes that merit further research in order to reach an understanding of the plant-soil feedbacks and its capacity to cope with future global change scenarios. In this review, we characterize the functional and structural plant-soil relationships and feedbacks in Mediterranean regions. We thereafter discuss the effects of global change drivers on these complex interactions between plants and soil. Conclusions The large plant diversity that characterizes Mediterranean ecosystems is associated to the success of coexisting species in avoiding competition for soil resources by differential exploitation in space (soil layers) and time (year and daily). Among plant and soil traits, high foliar nutrient re-translocation and large contents of recalcitrant compounds reduce nutrient cycling. Meanwhile increased allocation of resources to roots and soil enzymes help to protect against soil erosion and to improve soil fertility and capacity to retain water. The long-term evolutionary adaptation to drought of Mediterranean plants allows them to cope with moderate increases of drought without significant losses of production and survival in some species. However, other species have proved to be more sensitive decreasing their growth and increasing their mortality under moderate rising of drought. All these increases contribute to species composition shifts. Moreover, in more xeric sites, the desertification resulting from synergic interactions among some related process such as drought increases, torrential rainfall increases and human driven disturbances is an increasing concern. A research priority now is to discern the effects of long-term increases in atmospheric CO₂ concentrations, warming, and drought on soil fertility and water availability and on the structure of soil communities (e.g., shifts from bacteria to fungi) and on patching vegetation and root-water uplift (from soil to plant and from soil deep layers to soil superficial layers) roles in desertification.
This study examined the literature in ISI Web of Science to identify the effects that the main drivers of global change have on the nutrient concentrations and C:N:P stoichiometry of organisms and ...ecosystems, and examined their relationship to changes in ecosystem structure and function. We have conducted a meta-analysis by comparing C:N:P ratios of plants and soils subjected to elevated CO2 with those subjected to ambient CO2. A second meta-analysis compared the C:N:P ratios of plants and soils that received supplemental N to simulate N deposition and those that did not receive supplemental N. On average, an experimental increase in atmospheric CO2 increased the foliar C:N ratios of C3 grasses, forbs, and woody plants by 22%, but the foliar ratios of C4 grasses were unaffected. This trend may be enhanced in semi-arid areas by the increase in droughts that have been projected for the coming decades which can increase leaf C:N ratios. The available studies show an average 38% increase in foliar C:P ratios in C3 plants in response to elevated atmospheric CO2, but no significant effects were observed in C4 grasses. Furthermore, studies that examine the effects of elevated atmospheric CO2 on N:P ratio (on a mass basis) are warranted since its response remains elusive. N deposition increases the N:P ratio in the plants of terrestrial and freshwater ecosystems, and decreases plants and organic soil C:N ratio (25% on average for C3 plants), reducing soil and water N2 fixation capacity and ecosystem species diversity. In contrast, in croplands subjected to intense fertilization, mostly, animal slurries, a reduction in soil N:P ratio can occur because of the greater solubility and loss of N. In the open ocean, there are experimental observations showing an ongoing increase in P-limited areas in response to several of the factors that promote global change, including the increase in atmospheric CO2 which increases the demand for P, the warming effect that leads to an increase in water column stratification, and increases in the N:P ratio of atmospheric inputs. Depending on the type of plant and the climate where it grows, warming can increase, reduce, or have no effect on foliar C:N ratios. The results suggest that warming and drought can increase C:N and C:P ratios in warm-dry and temperate-dry terrestrial ecosystems, especially, when high temperatures and drought coincide. Advances in this topic are a challenge because changes in stoichiometric ratios can favour different types of species and change ecosystem composition and structure.
Biogenic volatile emissions from the soil PEÑUELAS, J; ASENSIO, D; THOLL, D ...
Plant, cell & environment/Plant, cell and environment,
August 2014, Volume:
37, Issue:
8
Journal Article
Peer reviewed
Open access
Volatile compounds are usually associated with an appearance/presence in the atmosphere. Recent advances, however, indicated that the soil is a huge reservoir and source of biogenic volatile organic ...compounds (bVOCs), which are formed from decomposing litter and dead organic material or are synthesized by underground living organism or organs and tissues of plants. This review summarizes the scarce available data on the exchange of VOCs between soil and atmosphere and the features of the soil and particle structure allowing diffusion of volatiles in the soil, which is the prerequisite for biological VOC‐based interactions. In fact, soil may function either as a sink or as a source of bVOCs. Soil VOC emissions to the atmosphere are often 1–2 (0–3) orders of magnitude lower than those from aboveground vegetation. Microorganisms and the plant root system are the major sources for bVOCs. The current methodology to detect belowground volatiles is described as well as the metabolic capabilities resulting in the wealth of microbial and root VOC emissions. Furthermore, VOC profiles are discussed as non‐destructive fingerprints for the detection of organisms. In the last chapter, belowground volatile‐based bi‐ and multi‐trophic interactions between microorganisms, plants and invertebrates in the soil are discussed.
Soil phosphatase levels strongly control the biotic pathways of phosphorus (P), an essential element for life, which is often limiting in terrestrial ecosystems. We investigated the influence of ...climatic and soil traits on phosphatase activity in terrestrial systems using metadata analysis from published studies. This is the first analysis of global measurements of phosphatase in natural soils. Our results suggest that organic P (P
), rather than available P, is the most important P fraction in predicting phosphatase activity. Structural equation modeling using soil total nitrogen (TN), mean annual precipitation, mean annual temperature, thermal amplitude and total soil carbon as most available predictor variables explained up to 50% of the spatial variance in phosphatase activity. In this analysis, P
could not be tested and among the rest of available variables, TN was the most important factor explaining the observed spatial gradients in phosphatase activity. On the other hand, phosphatase activity was also found to be associated with climatic conditions and soil type across different biomes worldwide. The close association among different predictors like P
, TN and precipitation suggest that P recycling is driven by a broad scale pattern of ecosystem productivity capacity.
We studied the impacts of anthropogenic changes in land use on the stoichiometric imbalance of soil carbon (C), nitrogen (N), phosphorus (P) and potassium (K) in Phragmites australis wetlands in the ...Minjiang River estuary. We compared five areas with different land uses: P. australis wetland (control), grassland, a mudskipper breeding flat, pond aquaculture and rice cropland. Human activity has affected the elemental and stoichiometric compositions of soils through changes in land use. In general, soil C and N concentrations were lower and total soil K concentrations were higher at the sites under human land uses relative to the control site, and total soil P concentrations were generally not significantly different. The close relationship between total soil C and N concentrations in all cases, including fertilization with N, suggested that N was the most limiting nutrient in these wetlands. Lower soil N concentrations and similar soil P concentrations and higher soil K concentrations under human land-use activities suggest that human activity has increased the role of N limitation in these wetlands. Only grassland use increases soil N contents (only in the 0–10cm of soil). Despite N fertilization, lower soil N concentrations were also observed in the rice cropland, indicating the difficulty of avoiding N limitation in these wetlands. The observed lower soil N:P ratio, together with higher soil P and K availabilities in rice croplands, is consistent with the tendency of human activity to change the competitive relationships of plants, in this case favoring species adapted to high rates of growth (low N:P ratio) and/or favoring plants with high demands for P and K. Both, soil C storage and respiration were higher in grasslands, likely due to the introduction of grasses, which led to a high density of plants, increased grazing activity and soil compaction. Soil C storage and respiration were lower under human land uses, except in the rice cropland, with respect to natural wetland. Using overall data, soil C storage and respiration were correlated, indicating that soil respiration was correlated with plant productivity. In this wetland area the impacts of different human land-uses on soil stoichiometry and C-cycle can be very different depending on the activity. Further regeneration of natural communities can be determined by the previous type of land-use.
•Human activity increases total soil K and available-P concentrations.•Despite low soil N:P ratio, human activities decrease even more the soil N:P ratios.•These decreases of soil N:P are linked with the presence of high growth rate species.•Human activities decrease soil C and N concentrations affecting C storing capacity.•These soil stoichiometry changes can influence the regeneration of natural vegetation.
In a Mediterranean shrubland, we investigated the effects of the projected warming and drought on soil urease, protease and β-glucosidase activities and the relation of the possible changes in the ...activities of these enzymes with the observed changes in soil moisture, soil pH and in C and N stocks in soils, leaves and leaf litter during 1 year (April 2004–May 2005). This investigation was conducted in a long-term experiment of warming and drought manipulation that began in 1999 and is lasting until now. Warming increased soil urease activity by 10% in the study period, mainly by increasing soil urease activity 30% in winter and 10% in spring, and increased β-glucosidase activity 38% in spring. Soil urease and β-glucosidase activities were positively correlated with soil temperatures in winter and negatively in summer. Warming increased soil enzyme activities in winter when soil moisture was highest and in spring coinciding with the greatest biological activity. Warming decreased NH
4
+ soil concentration in the spring of 2004 (by 30%) and 2005 (by 72%), in consonance with the increase in N uptake by plants. Warming decreased N concentration in
Globularia alypum leaf litter, increasing C/N leaf ratio by 30% showing an increase in N mobilization and contributing to a greater total N accumulation in plants. However, the greater NO
3
− availability in soil observed under warming, probably by an increase in nitrification, may lead to a net N loss by leaching under the torrential rainfalls typical of the Mediterranean climate regions. Drought reduced soil protease activity (9%) in the study period, mainly by decreasing it in spring by 13–21%, but did not affect N soil contents because N turn-over reduction was counterbalanced by a decrease in N leaf concentrations. Soil protease activity was positively correlated with soil water content showing a strong dependence of this enzyme on soil water content. Drought did not affect β-glucosidase activity but tended to increase C contents in soils, which together with the increase in C/N in leaves indicate a reduction of C turn-over and a trend to increase C stocks in soil at long term. The effects of warming and drought on soil enzyme activities were due to a direct effect on soil temperature and soil water content, respectively, and not to changes on soil organic matter quantity and nutritional quality.
We conducted a field experiment simulating the warming and drought in a Mediterranean shrubland dominated by Erica multiflora and Globularia alypum with the aim to simulate the next future climate ...conditions predicted by the IPCC and ecophysiological models. As P is frequently a limiting nutrient in Mediterranean ecosystems, we investigated the drought and warming effects on soil phosphatases activities, soil P contents and availability, litter and leaf P concentration, and the capacity of this community to maintain soil P reserves and retain this nutrient in the ecosystem. Warming treatment increased soil and air temperature (an average of 1°C) and drought treatment decreased soil water content in one of the seasons analysed (28% in autum 2004). Warming increased (68%) the activities of soil acid phosphatases in summer and alkaline phosphatase activity (22%) in spring 2004, and increased P concentrations in E. multiflora. Instead, warming decreased P concentrations in litterfall of this same species, E. multiflora, and soil HCO₃-extractable Pi (Olsen-Pi) in some seasons, decreasing total P soil concentration (37%) after 6 years of treatment. The drought treatment did not change soil phosphatase activities, nor available Pi. The effects of climate change on soil P dynamics in Mediterranean areas will thus be strongly dependent on whether the main variable involved in the local change is warming or drought. If warming is the main change without significant changes in water availability, the increases of biological activity can accelerate plant growth, P capture by plants and increase soil-phosphatase activity, altogether decreasing P contents in soil. If drought is the main change, a reduction in P demands by plants is expected, increasing P stocks in soils.
Atmospheric deposition of iron (Fe) plays an important role in controlling oceanic primary productivity. However, the sources of Fe in the atmosphere are not well understood. In particular, the ...combustion sources of Fe and the subsequent deposition to the oceans have been accounted for in only few ocean biogeochemical models of the carbon cycle. Here we used a mass-balance method to estimate the emissions of Fe from the combustion of fossil fuels and biomass by accounting for the Fe contents in fuel and the partitioning of Fe during combustion. The emissions of Fe attached to aerosols from combustion sources were estimated by particle size, and their uncertainties were quantified by a Monte Carlo simulation. The emissions of Fe from mineral sources were estimated using the latest soil mineralogical database to date. As a result, the total Fe emissions from combustion averaged for 1960-2007 were estimated to be 5.3 Tg yr-1 (90% confidence of 2.3 to 12.1). Of these emissions, 1, 27 and 72% were emitted in particles < 1 mu m (PM1), 1-10 mu m (PM1-10), and > 10 mu m (PM> 10), respectively, compared to a total Fe emission from mineral dust of 41.0 Tg yr-1 in a log-normal distribution with a mass median diameter of 2.5 mu m and a geometric standard deviation of 2. For combustion sources, different temporal trends were found in fine and medium-to-coarse particles, with a notable increase in Fe emissions in PM1 since 2000 due to an increase in Fe emission from motor vehicles (from 0.008 to 0.0103 Tg yr-1 in 2000 and 2007, respectively). These emissions have been introduced in a global 3-D transport model run at a spatial resolution of 0.94 degree latitude by 1.28 degree longitude to evaluate our estimation of Fe emissions. The modelled Fe concentrations as monthly means were compared with the monthly (57 sites) or daily (768 sites) measured concentrations at a total of 825 sampling stations. The deviation between modelled and observed Fe concentrations attached to aerosols at the surface was within a factor of 2 at most sampling stations, and the deviation was within a factor of 1.5 at sampling stations dominated by combustion sources. We analysed the relative contribution of combustion sources to total Fe concentrations over different regions of the world. The new mineralogical database led to a modest improvement in the simulation relative to station data even in dust-dominated regions, but could provide useful information on the chemical forms of Fe in dust for coupling with ocean biota models. We estimated a total Fe deposition sink of 8.4 Tg yr-1 over global oceans, 7% of which originated from the combustion sources. Our central estimates of Fe emissions from fossil fuel combustion (mainly from coal) are generally higher than those in previous studies, although they are within the uncertainty range of our estimates. In particular, the higher than previously estimated Fe emission from coal combustion implies a larger atmospheric anthropogenic input of soluble Fe to the northern Atlantic and northern Pacific Oceans, which is expected to enhance the biological carbon pump in those regions.
PM1 (particulate matter with an aerodynamic diameter <1 μm) non-refractory components and black carbon were measured continuously together with additional air quality and atmospheric parameters at an ...urban background site in Barcelona, Spain, during March 2009 (campaign DAURE, Determination of the sources of atmospheric Aerosols in Urban and Rural Environments in the western Mediterranean). Positive matrix factorization (PMF) was conducted on the organic aerosol (OA) data matrix measured by an aerosol mass spectrometer, on both unit mass (UMR) and high resolution (HR) data. Five factors or sources could be identified: LV-OOA (low-volatility oxygenated OA), related to regional, aged secondary OA; SV-OOA (semi-volatile oxygenated OA), a fresher oxygenated OA; HOA (hydrocarbon-like OA, related to traffic emissions); BBOA (biomass burning OA) from domestic heating or agricultural biomass burning activities; and COA (cooking OA). LV-OOA contributed 28% to OA, SV-OOA 27%, COA 17%, HOA 16%, and BBOA 11%. The COA HR spectrum contained substantial signal from oxygenated ions (O:C: 0.21) whereas the HR HOA spectrum had almost exclusively contributions from chemically reduced ions (O:C: 0.03). If we assume that the carbon in HOA is fossil while that in COA and BBOA is modern, primary OA in Barcelona contains a surprisingly high fraction (59%) of non-fossil carbon. This paper presents a method for estimating cooking organic aerosol in ambient datasets based on the fractions of organic mass fragments at m/z 55 and 57: their data points fall into a V-shape in a scatter plot, with strongly influenced HOA data aligned to the right arm and strongly influenced COA data points aligned to the left arm. HR data show that this differentiation is mainly driven by the oxygen-containing ions C3H3O+ and C3H5O+, even though their contributions to m/z 55 and 57 are low compared to the reduced ions C4H7+ and C4H9+. A simple estimation method based on the markers m/z 55, 57, and 44 is developed here and allows for a first-order-estimation of COA in urban air. This study emphasizes the importance of cooking activities for ambient air quality and confirms the importance of chemical composition measurements with a high mass and time resolution.
The eddy-covariance (EC) micro-meteorological technique and the ecology-based biometric methods (BM) are the primary methodologies to quantify CO
exchange between terrestrial ecosystems and the ...atmosphere (net ecosystem production, NEP) and its two components, ecosystem respiration and gross primary production. Here we show that EC and BM provide different estimates of NEP, but comparable ecosystem respiration and gross primary production for forest ecosystems globally. Discrepancies between methods are not related to environmental or stand variables, but are consistently more pronounced for boreal forests where carbon fluxes are smaller. BM estimates are prone to underestimation of net primary production and overestimation of leaf respiration. EC biases are not apparent across sites, suggesting the effectiveness of standard post-processing procedures. Our results increase confidence in EC, show in which conditions EC and BM estimates can be integrated, and which methodological aspects can improve the convergence between EC and BM.
PDF
