Search

Ferriferous savannas, also known as cangas in Brazil, are nutrient-impoverished ecosystems adapted to seasonal droughts. These ecosystems support distinctive vegetation physiognomies and high plant diversity, although little is known about how nutrient and water availability shape these ecosystems. Our study was carried out in the cangas from Carajás, eastern Amazonia, Brazil. To investigate the N cycling and drought adaptations of different canga physiognomies and compare the findings with those from other ecosystems, we analyzed nutrient concentrations and isotope ratios (δ13C and δ15N) of plants, litter, and soils from 36 plots distributed in three physiognomies: typical scrubland (SB), Vellozia scrubland (VL), and woodland (WD). Foliar δ15N values in cangas were higher than those in savannas but lower than those in tropical forests, indicating more conservative N cycles in Amazonian cangas than in forests. The lower δ15N in savanna formations may be due to a higher importance of mycorrhizal species in savanna vegetation than in canga vegetation. Elevated δ13C values indicate higher water shortage in canga ecosystems than in forests. Foliar and litter nutrient concentrations vary among canga physiognomies, indicating differences in nutrient dynamics. Lower nutrient availability, higher C:N ratios, and lower δ15N values characterize VL, whereas WD is delineated by lower δ13C values and higher soil P. These results suggest lower water restriction and lower P limitation in WD, whereas VL shows more conserved N cycles due to lower nutrient availability. Differences in nutrient and water dynamics among physiognomies indicate different ecological processes; thus, the conservation of all physiognomies is required to ensure the maintenance of functional diversity in this unique ecosystem. [ABSTRACT FROM AUTHOR]

The Brazilian cerrado occurs interspersed with the semi-deciduous seasonal forest, and soil fertility is considered as the main determinant of the abrupt transitions between both vegetation types. We aimed to study patterns across chemical traits of green leaves in 121 cerrado and seasonal forest woody species from southeastern Brazil, their response to soil nutrient status, and their effects on decomposition rates. We compared leaf traits of both cerrado and forest species and constructed multilevel models to account for partitioning of variance in each trait. We calculated the community-weighted mean of each trait to assess their response to soil nutrient status and their effects on decomposition rates of standard plant material. Most of the traits were significantly correlated among themselves, with cerrado species having lower nutrient concentrations than the seasonal forest. Taxonomy accounted for 52 % of the total variance in leaf traits, whereas vegetation type accounted for 19 %. All leaf traits but leaf manganese and aluminium concentrations were significantly related to soil properties. Decomposition rates were affected indirectly by soil features through its effects on leaf traits. Contrary to the expected, the higher the leaf nitrogen concentration in the surrounding litter, the lower the decomposition rate. Even with a large effect of taxonomy on leaf nutrient-related traits, soil exerted an important role on the chemical traits. Strategies of both cerrado and seasonal forest species were carried out through multi-element control of soil on leaf nutrient composition. The effect of such different strategies on functioning was, however, less prominent. [ABSTRACT FROM AUTHOR]

The study aimed to examine the effect of the invasion of the two congeneric species Impatiens glandulifera and Impatiens parviflora on species richness and composition across a wide range of communities in North-western Germany. We applied a space-for-time substitution approach, comparing invaded plots with adjacent, environmentally similar uninvaded plots, based on the assumption that the latter represent the situation prior to an invasion. Even though the dominance of the invasive species resulted in a lower Shannon diversity in the invaded plots, species richness was not ( I. parviflora) or only weakly ( I. glandulifera) reduced. Also the community composition of the invaded sites was only marginally different. Invaded and uninvaded plots in general had similar habitat conditions, but both Impatiens species occurred in slightly shadier sites compared to the uninvaded areas, and the plots invaded by I. parviflora tended to have higher nutrient concentrations. These results suggest that dense populations of invading species may often be found at particular microsites. The relatively low impact of Impatiens on the vegetation is most likely caused by the annual life strategy of the species: while I. glandulifera shows large fluctuations in numbers between years and has a later phenological development than most other species in its habitat, I. parviflora establishes preferably in dark and acidic, often disturbed woodlands where it competes with few other species. [ABSTRACT FROM AUTHOR]

The natural abundance of C and N can integrate information on the dynamics of C and N, respectively. This study tested whether and how δC and δN of the plant and soil samples (including leaf, forest floor litters, fine roots, and 0-15 cm mineral soil) can detect local variations in community biomass, litter production, and litter turnover rate were explored in eight mature subtropical forests in southern China. Community biomass, litter production, and litter turnover rate were significantly positively correlated with each other and revealed similar correlations with other plant and soil parameters. Leaf δC was significantly negatively correlated with litter production, suggesting the stomatal regulation of leaf gas exchange. Similar correlations were also observed for δC of the mineral soil and other plant materials. Leaf and forest floor litters δN were positively correlated with community biomass, litter production, and litter turnover rate. Such correlations were significantly positively mediated by soil availability of P rather than N, as demonstrated by the multiple regression analysis. In contrast, fine roots δN was not related significantly to community biomass, litter production, or litter turnover rate. Significant differences in δC and δN among forests were related to the species composition, topography conditions, and land use history. Our results suggest that δC and δN of most plant and soil samples can indicate local variations in community biomass, litter production, and litter turnover rate in mature subtropical forests. Better understanding of these linkages could significantly improve our knowledge of C and N dynamics in forest ecosystems. [ABSTRACT FROM AUTHOR]

Pot experiments are frequently used to examine plant, soil, and microbial interactions that cannot be studied in situ. Although impacts of the pot environment on seedling growth have long been recognized, they are rarely addressed directly in current ecological studies. Here we examine how commonly used soil conditioners, often necessary to maintain adequate drainage in pots, can influence nutrient availability and seedling growth. Balsawood ( Ochroma pyramidalis) seedlings were grown in central Panama in soil combined in a 50:50 mix with one of the following soil conditioners: marine sand, pure sand, perlite, vermiculite, or rice husks. Soil nutrient availability, foliar N and P, and seedling growth were compared after 1 month. Rice husks dramatically reduced soil nitrate, seedling growth, and foliar N. Other conditioners had smaller effects on growth, although vermiculite may be a significant source of base cations in infertile soils. Marine sand had a strong neutralizing effect on acidic soil due to the presence of calcareous shell fragments. Effects of soil conditioners need to be added to other known artifacts of the pot environment influencing nutrient availability, including alterations to N mineralization rates relative to bulk soil, and pot-size effects on N:P availability. These artifacts can strongly influence plant performance and therefore the interpretation of ecological studies. [ABSTRACT FROM AUTHOR]

Phenotypic plasticity is an important plant trait associated with invasiveness of alien plants that reflects its ability to occupy a wide range of environments. We investigated the phenotypic response of Chenopodium murale to resource variability and ontogeny. Its plant-level and leaf-level traits were studied at high-resource (HR) and low-resource (LR) sites in peri-urban areas in Indian dry tropics. Plants at LR had significantly higher root length, root/shoot biomass ratio, stem mass and root mass fractions. Plants at HR had higher shoot length, basal diameter, leaf mass fraction and leaf area ratio. Leaf-level traits like leaf area and chlorophyll a were also higher here. Mean plasticity indices for plant- and leaf-level traits were higher at HR. With increasing total plant biomass, there was significant increase in the biomass of leaf, stem, root, and reproductive parts, and root and shoot lengths, whereas root/shoot length ratio, their biomass ratio, and leaf and root mass fractions declined significantly. Allocation to roots and leaves significantly decreased with increasing plant size at both sites. But, at any size, allocation to roots was greater at LR, indicative of optimization of capture of soil nutrients, whereas leaf allocation was higher at HR. Consistently increasing stem allocation equaled leaf allocation at comparatively higher shoot lengths at HR. Reproductive biomass comprised 10-12% of the plant's total biomass. In conclusion, the success of alien weed C. murale across environmentally diverse habitat conditions in Indian dry tropics can be attributed to its high phenotypic plasticity, resource utilization capability in low-resource habitats and higher reproductive potential. These characteristics suggest that it will continue to be an aggressive invader. [ABSTRACT FROM AUTHOR]

In fire-prone ecosystems, plants for the most part persist via either soil-stored seed banks (seeders) or below-ground storage structures (resprouters). Given their greater allocation of resources above ground to growth and reproduction, seeders are likely to have a higher nutrient requirement than resprouters. This may result in discernable differences in habitat nutrition and leaf morphology. These differences are probably accentuated in Cape legumes given their poor adaptation to low-P soils. It was hypothesized that legume seeders occupy habitats with greater fertility and possess larger, less sclerophyllous leaves than resprouters. Site nutrition and leaf morphologies were compared between seeders and resprouters in the genera Otholobium and Psoralea. There were no differences in leaf morphology between seeders and resprouters. Seeders sites had a higher total [N], exchangeable [Ca] and [Mg], and CEC, but lower [Fe] than resprouters. Only within Otholobium, did seeder sites have a higher Bray II [P]. This genus-specific variation in available P is probably a consequence of greater variation in soil type and precipitation between seeders and resprouters. Conversely, niche construction may contribute to the differences in soil fertility between seeders and resprouters in Psoralea. Thus, our data showed a general tendency for seeders to inhabit more fertile sites than resprouters. Caution is required, however, in generalizing these results, as our data indicate a difference in factors affecting soil nutrient availability between legume genera. Changes in soil fertility post-fire may limit legume persistence beyond the early stages of succession. [ABSTRACT FROM AUTHOR]

In subarctic ecosystems, plant growth is mostly limited by nutrient availability and harsh climate. Investigating how soil nutrient availability controls the plant community composition may therefore help to understand indirect effects of climate change. The study was conducted in a long-term field experiment on a subarctic-alpine fellfield dominated by woody evergreen shrubs, bryophytes, and lichens. To manipulate nutrient availability additions of NPK fertilizer, labile C, and fungicide (benomyl) were done in a fully factorial design, replicated in six blocks. The treatments were run for 10 years, and the aboveground plant biomass was harvested 4 and 16 years after initiating the experiment. In addition, soil inorganic N and P concentration was analyzed the same years. Increased nutrient availability (NPK fertilizer) largely increased the biomass of graminoids and unexpectedly of bryophytes, but not of other vascular plant groups. Also, limitation of soil nutrient availability caused by labile C addition decreased the relative proportion of green shoots in evergreen shrubs, although these were expected to cope better with the nutrient limitation than the opportunistic graminoids, which, by contrast, were unaffected. Reduced fungal biomass due to benomyl addition was accompanied by increased evergreen shrub and clubmoss biomass. Taken together, the effects of treatments were most pronounced 16 years after initiation of the experiment, but despite changes in biomass the overall plant community composition was resistant to environmental changes. [ABSTRACT FROM AUTHOR]

During the past three decades the Earth has warmed with a rate unprecedented during the past 1000 years. There is already ample evidence that this fast climate warming has affected a broad range of organisms, including plants. Plants from high-latitude and high-altitude sites (‘cold biomes’) are especially sensitive to climate warming. In this paper we (1) review the response in the phenology of plants, changes in their range and distribution, soil nutrient availability, and the effects on the structure and dynamics of plant communities for cold, northern biomes; and (2) we show, by using data from an ongoing snow and temperature manipulation experiment in northern Sweden, that also winter and spring events have a profound influence on plant performance. Both long-term phenological data sets, experimental warming studies (performed in summer or year-round), natural gradient studies and satellite images show that key phenological events are responsive to temperature increases and that recent climate warming does indeed lead to changes in plant phenology. However, data from a warming and snow manipulation study that we are conducting in northern Sweden show that plants respond differently to the various climatic scenarios that we had imposed on these species and that especially winter and spring events have a profound impact. This indicates that it is necessary to include several scenarios of both summer and winter climate change in experimental climate change studies, and that we need detailed projections of future climate at a regional scale to be able to assess their impacts on natural ecosystems. There is also ample evidence that the range shift of herbs and shrubs to more northern regions is for the vast majority of species mainly caused by changes in the climate. This is in line with the observed ‘up-greening’ of northern tundra sites. These rapid northern shifts in distribution of plants as a result of climate warming may have substantial consequences for the structure and dynamics of high-latitude ecosystems. An analysis of warming studies at 9 tundra sites shows that heating during at least 3 years increased net N-mineralization from 0.32±0.31 (SE) g N m−2 yr−1 in the controls to 0.53±0.31 (SE) g N m−2 yr−1 in the heated plots ( p<0.05), an increase of about 70%. Thus, warming leads to higher N availability in high-latitude northern tundra sites, but the variability is substantial. Higher nutrient availability affects in turn the species composition of high-latitude sites, which has important consequences for the carbon and water balance of these systems. [ABSTRACT FROM AUTHOR]

The interrelationships between biomass characteristics and soil properties (including in situ annual nitrogen mineralization) were statistically investigated in a descriptive study using a broad range of plant communities in unfertilized road verges. Not only the dependence of biomass characteristics on soil properties, but also the possibility of inferring soil nutrient availability from biomass characteristics was investigated. Possible effects of vegetation management (mowing) and overstory trees (shading) were accounted for. Annual aboveground biomass production was mainly explained by annual N mineralization, average soil moisture content, shading intensity, and soil pH (optimum at pH-CaCl2 5.7). Average tissue nutrient concentrations were primarily explained by mowing frequency, shading intensity, the availability of the corresponding soil nutrient, and pH (optima between 5.5 and 6.0). Results also implied that making hay twice per year removes more nutrients than a single cut at the end of the season. N mineralization may be inferred from the aboveground biomass production, but only across sites with equal moisture and shading conditions (partial r=0.74). In general, it is concluded that nutrient availability can only be deduced from biomass characteristics if sites with similar moisture content are compared. The only exception to this general rule is K availability. The latter was mainly indicated by the K concentration in vegetation biomass (partial r=0.80), and the confounding effect of other factors was small (bivariate r was still 0.71). Soil available P could not be satisfactorily indicated, even across sites with equal moisture and shading conditions. Also, different nutrients appeared to interact, and should not be considered in isolation. K was the only element with a strong relationship between its soil and tissue concentration. For the other nutrients, tissue concentrations did not depend predominantly on the soil availability. It seems most likely that the species occurring in semi-natural vegetation are adapted to the local fertility by means of their physiology or growth rate. It is concluded that, with the possible exception of K, simple relationships between soil properties and biomass characteristics cannot be expected over wide environmental gradients. [ABSTRACT FROM AUTHOR]

The restoration of degraded peat-grasslands is an important nature conservation goal in The Netherlands. We investigated the effects of ceased fertilization (15 years) combined with a groundwater-raised water table (6 years) on the production of the peat-grassland vegetation and soil nutrient availability in a meadow. Furthermore, we evaluated whether and how this difference between meadows affected the balances between nutrient inputs and outputs in the ecosystem. We used an adjacent fertilized meadow in which the water table followed agricultural practice as a control. Yield of the grassland vegetation was significantly lower in the wet than in the control meadow. The tissue concentrations of N, P, and K in the harvested vegetation were significantly lower, but those of Ca higher in the wet than in the control meadow. The difference between both meadows significantly affected the annual nitrification rate, but not the annual C and N mineralization rates and the annual net P and K release rates. The difference between both meadows also significantly affected the seasonal nitrification and K release rates. Season exerted a significant effect on the seasonal C and N mineralization and nitrification rates. The elemental balances and relative contributions of the balance terms to elemental inputs and outputs varied considerably with element. Annually, the wet meadow lost N, P and K, while the control meadow gained these elements. The elemental demand of the grassland vegetation in the wet meadow was met for N for a large part by mineralization and for the remainder by atmospheric deposition, for P it was in the same order of magnitude as the net soil-P release, as it was for K. It is to be expected that the soil resources of N, P and K will continue to decrease under a continued regime of ceased fertilization and a raised water table, with those of N decreasing with the same rate, of P morerapidly and of K more slowly than estimated from regressions. [ABSTRACT FROM AUTHOR]

Three grasses ( Holcus lanatus, Anthoxanthum odoratum and Festuca ovina) and three herbs ( Rumex obtusifolius, Plantago lanceolata and Hieracium pilosella) were grown in a greenhouse at 3 nutrient levels in order to evaluate plant allocation, architecture and biomass turnover in relation to fertility level of their habitats. Four harvests were done at intervals of 4 weeks. Various plant traits related to biomass partitioning, plant architecture, biomass turnover and performance were determined. Differences in nutrient supply induced a strong functional response in the species shoot:root allocation, but architecture and turnover showed little or no response. Architectural parameters like specific leaf area and specific root length, however, in general decreased during plant development. Species from more nutrient-rich successional stages were characterized by a larger specific leaf area and longer specific shoot height (height/shoot biomass), resulting in a higher RGR and total biomass in all nutrient conditions. There was no evidence that species from nutrient-poor environments had a longer specific root length or any other superior growth characteristic. The only advantage displayed by these species was a lower leaf turnover when expressed as the fraction of dead leaves and a shorter specific shoot height (SSH) which might prevent herbivory and mowing losses. The dead leaf fraction, which is a good indicator for biomass and nutrient loss, appeared to be not only determined by the leaf longevity, but was also found to be directly related to the RGR of the species. This new fact might explain the slow relative growth rates in species from a nutrient-poor habitat and should be considered in future discussions about turnover. [ABSTRACT FROM AUTHOR]

English broom (Cytisus scoparius) is an aggressive invasive shrub in native sclerophyll forests of South Australia. We studied its relative growth rate (RGR) and competitive ability in soils from invaded and uninvaded woodlands, in comparison to three native species it commonly displaces:Hakea rostrata, Acacia verniciflua, and A. myrtifolia. Hakea was the slowest growing species throughout the year. Both native species had their highest RGR during spring. The RGR of broom was higher than that of both hakea and acacia in the winter and spring. Despite losing its leaves in the summer, the RGR of broom through the year was higher than that of either of the native species. Soil from the invaded stands had higher organic C, N and soluble P than that from uninvaded sites. Broom and acacia grew better in the higher nutrient soil than in the lower nutrient soil. Competition did not decrease the final biomass of any of the species in low nutrient soil. In the higher nutrient soil the biomass of broom was reduced by competition with acacia, but not by competition with hakea. Competition by broom reduced the biomass of hakea but not that of acacia. Broom's earlier and higher RGR, high competitiveness in nutrient rich soils, and probably its ability to change nutrient availability could be important contributors to the mechanisms by which it invades native woodlands. [ABSTRACT FROM AUTHOR]