Search

Convergence of eco-physiological function in harsh habitats due to environmental filtering is well-known, however, some evidence of eco-physiological divergence in coexisting species also exists. Experimental data to verify whether divergence of eco-physiological function in coexisting species increases with increasing environmental stress remain limited. Here, we measured bulk leaf oxygen isotope and functional traits along a climatic stress gradient in a grassland in Tibetan Plateau where drought, excess radiation, and temperature increased from east to west. Enrichment (Δ18O) in bulk leaf oxygen isotope was used as proxy for time-integrated gs. We found that the leaf water use (Δ18O and leaf area [LA]) spectrum was independent of the leaf economic spectrum, indicating that coexisting species shifted from high nitrogen use efficiency (high ratio of leaf carbon to nitrogen) and water loss (high LA) in low-stress habitats to high photosynthetic capacity (high leaf nitrogen) and low water loss (low gs) in high-stress habitats. As the stress intensity of climate increases, higher mean and maximum and lower skewness (varying from positive to negative values) of Δ18O in coexisting species confirmed that the abundance of water-saving species increased to cope with climatic stress, while the greater standard deviation and kurtosis further indicated that climatic stress drove the divergence in gs in coexisting species. This study revealed that coexisting species adopt more diversified water use strategies and the abundance of water-saving species increases to cope with climatic stress, regardless of decreases in overall species abundance.

Environmentally persistent free radicals are pollutants recently detected in most environmental matrices such as fly ash, aerosols, soils and sediments. Their generation and transformation is poorly known, notably in the atmopshere. Here we modeled the effect of dioxygen O2, hydroxyl radical •OH, and nitrate radical NO3 on Cu(II)O surface-bound phenoxyl radical, using quantum chemical calculations and kinetics analysis. Results show that additional stabilization of the surface-bound phenoxyl radical is provided by the metal-oxide surface, implying that self-decomposition is not likely to occur. The addition reactions of hydroxyl and nitrate radicals with surface-mediated radicals are both thermodynamically and kinetically favorable, whereas the role of O2 appears negligible. The tropospheric lifetime of the Cu(II)O-based surface-bound phenoxyl radical is only few seconds to about one hour, in agreement with experimental observations from the literature. [ABSTRACT FROM AUTHOR]

Abstract Background Stellera chamaejasme L. is a poisonous plant widely distributes in degraded grasslands in China. The mechanism underlying its spread remains unknown. In some degraded grasslands, S. chamaejasme has gradually replaced previous dominant species, such as Leymus chinensis, Stipa krylovii, Artemisia eriopoda on typical steppes. Apart from its unpalatability by livestock, we hypothesized that the survival strategy (nutrient uptake and water use efficiency) of S. chamaejasme in degraded grasslands could be distinct from other coexisting species in the community. Recently, ecological stoichiometry has been suggested as a new approach for studying the demand for natural resources of plants in a changing world, and the leaf carbon isotopic composition (δ13C leaf) as a rapid and effective high throughput phenotyping method for water use efficiency (WUE), both of which can reveal the survival and adaptive strategies of plants. Therefore, in this study we aimed to fill the knowledge gap concerning ecological stoichiometry in the leaf, stem, and root of S. chamaejasme and its surrounding soil on grasslands with different degrees of degradation, and comparing the leaf nutrient content and δ13C of S. chamaejasme with the coexisting species (L. chinensis, S. krylovii, A. eriopoda) in the communities. Toward this goal, we conducted a field survey in which plants and soils were sampled from four different degraded grasslands on typical steppes in China. Results Our results showed that there is no significant difference of carbon content (C%) and nitrogen content (N%) in leaves of S. chamaejasme in different degraded grasslands, and all element contents and element ratios in stems did not differ significantly. Meanwhile, ecological stoichiometry of S. chamaejasme is distinct from the coexisting species, with low C%, high N% and phosphorus content (P%) in the leaf, indicating high nutrient uptake efficiency of S. chamaejasme in nutrient-poor environments like degraded grasslands. Additionally, S. chamaejasme showed significant higher WUE than other species. Conclusions Our results indicated that high nutrient uptake efficiency and high WUE of S. chamaejasme might together contribute to the spread of S. chamaejasme in degraded grasslands.

Copyright of Acta Prataculturae Sinica is the property of Acta Prataculturae Sinica Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Relationships among twig size, leaf size and leafing intensity are essential for predicting structure and function of twigs and leaves and ability of plants to acquire different environmental resources. We aimed to test whether trade-offs between twig and leaf traits for species would be influenced by forest successional status and sampling orientation within canopy. We measured four twig and leaf traits for seven coexisting broadleaf species across successional statuses in mixed broadleaved-Korean pine (Pinus koraiensis) forests in Northeast China. The results showed that both twig and leaf traits varied with successional status and twig level explained the largest variations in traits. Slopes of regression of leaf traits (i.e. individual leaf area, total leaf area and volume-based leafing intensity) against twig cross-sectional area were late-successional species > middle-successional species > early-successional species. Relationships between twig cross-sectional area and total leaf area in upper south and lower north canopy orientations did not vary with successional status of species. However, slopes of regression of twig cross-sectional area against total leaf area varied with successional status in other four sampling orientations. Our results highlight the importance of successional status and sampling orientation within canopy in controlling variations and trade-offs between twig and leaf traits. [ABSTRACT FROM AUTHOR]

In a fragmented landscape, transitional zones between neighboring habitats are common, and our understanding of community organizational forces across such habitats is important. Edge studies are numerous, but the majority of them utilize information on species richness and abundance. Abundance and taxonomic diversity, however, provide little information on the functioning and phylogeny of the co‐existing species. Combining the evaluation of their functional and phylogenetic relationships, we aimed to assess whether ground beetle assemblages are deterministically or stochastically structured along grassland–forest gradients. Our results showed different community assembly rules on opposite sides of the forest edge. In the grassland, co‐occurring species were functionally and phylogenetically not different from the random null model, indicating a random assembly process. Contrary to this, at the forest edge and the interior, co‐occurring species showed functional and phylogenetic clustering, thus environmental filtering was the likely process structuring carabid assemblages. Community assembly in the grassland was considerably affected by asymmetrical species flows (spillover) across the forest edge: more forest species penetrated into the grassland than open‐habitat and generalist species entered into the forest. This asymmetrical species flow underlines the importance of the filter function of forest edges. As unfavorable, human‐induced changes to the structure, composition and characteristics of forest edges may alter their filter function, edges have to be specifically considered during conservation management. [ABSTRACT FROM AUTHOR]

Characterizing patterns of variation in plant traits across species and environmental gradients is critical for understanding performance of species in ecosystems. One‐dimensional pattern of variation has been demonstrated in leaf traits, which is known as the leaf economic spectrum. However, it is unclear whether such a spectrum exists for root traits.For roots of 15 species from temperate grasslands, we determined respiration rate, relative growth rate, life span and 10 morphological, chemical and anatomical root traits. We further evaluated pairwise and multiple‐trait relationships by Pearson's correlation and principle component analysis including phylogenetic contrasts.We found that root functions were related to three clusters of variation. Root respiration rate and relative growth rate were positively correlated with average root diameter (AD), but they were negatively correlated with specific root length (SRL). In contrast, root life span was not correlated with AD, but it was positively correlated with SRL. These results are inconsistent with the presumption of the root economic spectrum.The principle components analysis revealed a multi‐dimensional pattern of variation in root traits among the 15 coexisting herbaceous species. Moreover, species within the same phylogenetic clades tended to have similar root trait syndromes. Most of the root traits exhibited a significant phylogenetic signal.Synthesis. Our results do not support a one‐dimensional root economic spectrum in the coexisting herbaceous species of temperate grasslands. In contrast, the pattern of variation in root traits was multi‐dimensional. We further demonstrated that species in different phylogenetic clades possess diverse root trait syndromes for efficient resource acquisition. Our findings provide a next step in understanding root functions and plant strategies in temperate grasslands. Our results do not support a one‐dimensional root economic spectrum in the coexisting herbaceous species of temperate grasslands. In contrast, the pattern of variation in root traits was multi‐dimensional. We further demonstrated that species in different phylogenetic clades possess diverse root trait syndromes for efficient resource acquisition. Our findings provide a next step in understanding root functions and plant strategies in temperate grasslands. [ABSTRACT FROM AUTHOR]

Intraspecific trait variation in generalist animals is widespread in nature, yet its effects on community ecology are not well understood. Newts are considered opportunistic feeders that may co-occur in different syntopic conditions and represent an excellent model for studying the role of individual feeding specialization in shaping the population dietary strategy. Here, we investigated the diet of three newt species from central Italy occurring in artificial habitats in different coexistence conditions to test the predictions of the niche width (NW) variation hypotheses. Population NW did not vary among species and between presence and absence of coexisting species. An overall positive relationship between individual specialization and population NW was observed. However, this pattern was disrupted by the condition of syntopy with newt populations showing an individual NW variation invariant with population NW in presence of coexisting species, whereas it was larger in populations occurring alone. The observed pattern of newt behavior was not consistent with any of the proposed scenarios. We found a consistent pattern with the degree of individual specialization being (1) size-dependent (specialized individuals increasing within larger sized species) and (2) assemblage-complexity-dependent (specialized individuals increasing in syntopic populations in comparison to singly populations).

• Overall species abundance decreased to cope with climatic stress. • Abundance of water-saving species increased to cope with climatic stress. • Climatic stress drove divergence of stomatal conductance in coexisting species. Convergence of eco-physiological function in harsh habitats due to environmental filtering is well-known, however, some evidence of eco-physiological divergence in coexisting species also exists. Experimental data to verify whether divergence of eco-physiological function in coexisting species increases with increasing environmental stress remain limited. Here, we measured bulk leaf oxygen isotope and functional traits along a climatic stress gradient in a grassland in Tibetan Plateau where drought, excess radiation, and temperature increased from east to west. Enrichment (Δ18O) in bulk leaf oxygen isotope was used as proxy for time-integrated gs. We found that the leaf water use (Δ18O and leaf area [LA]) spectrum was independent of the leaf economic spectrum, indicating that coexisting species shifted from high nitrogen use efficiency (high ratio of leaf carbon to nitrogen) and water loss (high LA) in low-stress habitats to high photosynthetic capacity (high leaf nitrogen) and low water loss (low gs) in high-stress habitats. As the stress intensity of climate increases, higher mean and maximum and lower skewness (varying from positive to negative values) of Δ18O in coexisting species confirmed that the abundance of water-saving species increased to cope with climatic stress, while the greater standard deviation and kurtosis further indicated that climatic stress drove the divergence in gs in coexisting species. This study revealed that coexisting species adopt more diversified water use strategies and the abundance of water-saving species increases to cope with climatic stress, regardless of decreases in overall species abundance. [ABSTRACT FROM AUTHOR]

Ecological theory suggests that in harsh environments major abiotic stress factors may act as environmental filters, thereby reducing the range of possible plant strategies through environmental trait selection. This would lead to functional similarity of species coexisting in hostile environments. To test this prediction, we evaluated six functional leaf traits at three different times of year in five species coexisting in a coastal dune ecosystem. The functional traits examined were associated with water status and light interception and use - two of the most limiting factors that lead to stress in dune systems. Species differed in traits associated with light absorption, namely chlorophyll content, the vigour index NDVI, and the proportion of the light absorbed that is used in photochemistry (as expressed by the effective and maximum quantum yield of PSII and the photochemical reflectance index). For most of the traits, the relative performance of species depended significantly on time. This research revealed a significant divergence in functional traits of coexisting species, which does not conform to findings in other harsh environments where species tend to functional convergence. The data provide experimental support for the hypothesis that there is no single combination of traits for a given environment, but that alternative functional designs of similar fitness may evolve in the same environment as a result of complex interactions and trade-offs among traits. This suggests that factors claimed to promote divergence, such as limiting similarity and disturbance processes, may play an important role in structuring the dune community under study. The high variability in functional traits suggests a significant degree of functional diversity and highlights the importance of preserving the species composition of threatened coastal dune habitats in order to preserve distinctive functional processes that may be unique to the systems. [ABSTRACT FROM AUTHOR]

To assess the possible degree of root competition from fruit trees which could potentially be used in agroforestry systems, fine root density of fruit trees Strychnos cocculoides BAK., Strychnos spinosa LAM. (Loganiaceae) and Vangueria infausta BURCH. (Rubiaceae), as well as from the shrubby species, Grewia flava DC. (Tiliaceae) was investigated. Vangueria infausta had the highest fine root densities in both vertical and horizontal extensions. In Vangueria infausta fine root density decreased with increasing soil depth. For the other species in the 80 cm soil profile investigated, no significant changes in fine root density with soil depth were found. For Strychnos cocculoides almost no fine roots were detected in the upper soil horizon (0-20 cm). Using fine root surface area densities, exploration and exploitation indices were calculated. Vangueria infausta had the highest value of the exploration index compared to the other species. For use in agroforestry systems Vangueria infausta was estimated to be the most competitive of the investigated species, whereas Strychnos cocculoides seems to be the less competitive. Strychnos cocculoides has additionally spatial arrangements of fine roots favourable for agroforestry, slowly increasing with depth and additionally low concentrations in upper soil layers. [ABSTRACT FROM AUTHOR]

Intraspecific trait variation in generalist animals is widespread in nature, yet its effects on community ecology are not well understood. Newts are considered opportunistic feeders that may co-occur in different syntopic conditions and represent an excellent model for studying the role of individual feeding specialization in shaping the population dietary strategy. Here, we investigated the diet of three newt species from central Italy occurring in artificial habitats in different coexistence conditions to test the predictions of the niche width (NW) variation hypotheses. Population NW did not vary among species and between presence and absence of coexisting species. An overall positive relationship between individual specialization and population NW was observed. However, this pattern was disrupted by the condition of syntopy with newt populations showing an individual NW variation invariant with population NW in presence of coexisting species, whereas it was larger in populations occurring alone. The observed pattern of newt behavior was not consistent with any of the proposed scenarios. We found a consistent pattern with the degree of individual specialization being (1) size-dependent (specialized individuals increasing within larger sized species) and (2) assemblage-complexity-dependent (specialized individuals increasing in syntopic populations in comparison to singly populations). [ABSTRACT FROM AUTHOR]

We investigate the rate of increase of protists introduced at low density into experimental communities comprising different sets of coexisting species. The experiment separates (1) the main effect of six introduced species, (2) the main effect of eleven resident communities, and (3) the introductioncommunity interaction. Introduced species differ markedly in their capacity to invade, and only one, Paramecium,invades all of the communities. Most of the introduced species invade some communities, and there is a large introductioncommunity interaction that comes about from bringing together particular combinationsof species. For example, the rate of increase of Amoeba is greater when introduced into communities containing Paramecium than when introduced into communities in which Paramecium is absent. The omnivore Blepharisma increases faster in the presence of one of its prey Tetrahymena, notwithstanding the fact that it is also a potential competitorwith this prey for bacteria. There is little indication that the species richness of resident communities (over the limited range available) affects the success of invasion. The results suggest that understanding invasions depends as much on detailed knowledge of idiosyncratic biological interactions as on general properties of community structure. [ABSTRACT FROM AUTHOR]