Authors:W. Qi, X. Zhou, M. Ma, J. M. H. Knops, W. Li, and G. Du
Despite a long history of alpine meadows studies, uncertainty remains about the importance of environmental factors in structuring their assembly. We examined the functional and phylogenetic structure of 170 alpine Tibetan meadow communities in relation to elevation, soil moisture and shade. Functional community structure was estimated with both communityweighted mean (CWM) trait values for specific leaf area (SLA), plant height and seed mass and functional diversity (Rao’s quadratic index) for their traits individually and in combination (multivariate functional diversity). We found that shade induced by woody plants significantly increased the phylogenetic diversity and functional diversity of SLA of co-occurring species, suggesting that woody plants behave as “ecosystem engineers” creating a different environment that allows the existence of shade tolerant species and thereby facilitates the coexistence of plant species with different light resource acquisition strategies. We also found evidence for a clear decrease in phylogenetic diversity, CWM and functional diversity related to plant height in the two extreme, both the dry and wet, soil moisture conditions. This indicates that both drought and excess moisture may act as environmental filters selecting species with close phylogenetic relationships and similar height. Moreover, we detected significant decreases in both CWM and functional diversity for seed mass along elevational gradients, suggesting that low net primary productivity (NPP) limits seed size. Finally, because of different individual trait responses to environmental factors, the multivariate functional diversity did not change across environmental gradients. This lack of multivariate response supports the hypothesis that multiple processes, such as environmental filtering, competition and facilitation, may operate simultaneously and exert opposing effects on community assembly along different niche (e.g., water use, light acquisition) axes, resulting in no overall functional community structure change. This contrast between individual and multivariate trait patterns highlights the importance of examining individual traits linked with different ecological processes to better understand the mechanisms of community assembly.
There are two main methods for estimating seed density and species composition of soil seed banks: manual seed extraction and seedling emergence. These methods were used to determine and compare seed density and species composition in the soil of a natural grassland in Patagonia. Additionally, known amounts of seeds of different sizes from Patagonian grassland species were mixed with soil to evaluate the efficiency of the seed extraction method, and determine their recovery percentage. Seed density found in the grassland soil with the extraction method was four times higher than that found with the seedling emergence method. Through the use of these two methods, there was very little overlap found in species composition. Small seeds (< 1 mm) were only found with the seedling emergence method, whereas the seeds of species with specific germination requirements were found with the seed extraction method. Seed recovery of grassland species varied from 2.5% for smaller seeds (Erophila verna) to 100% for larger seeds (Rumex acetosella) with the seed extraction method. This method was more effective in detecting seeds of large-seeded species. Discrepancies in seed detection between both methods may be related to seed dormancy, specific germination requirements, seed size and mass. These two methods are necessary to describe seed density and seed bank composition.
Authors:H. Bu, X. Chen, Y. Wang, X. Xu, K. Liu, and G. Du
In this paper, 633 species (involving 10 classes, 48 families, 205 genera) collected from the alpine meadow on the eastern Qinghai-Tibet plateau were studied. We tested potential factors affecting variation in mean germination time (MGT), i.e., plant traits (adult longevity, dispersal mode and seed size) or phylogeny, to evaluate if these factors were independent or they had interaction. Nested ANOVA showed that taxonomic membership accounted for the majority of MGT variation (70%), and in the generalized linear model, family membership could explain independently the largest proportion of MGT variation (29%). The strong taxonomic effect suggests that MGT variation within taxonomic membership is constrained. The other plant traits could also explain MGT variation independently (1% by adult longevity and dispersal mode, respectively, and 2% by seed size). Thus, the phylogeny was an important constraint to maintain the stability of species, and we could simplify the question if we regarded the phylogeny as an individual factor, but we could not negate the adaptive significance of the relationship between other plant traits and seed MGT. In addition, a large percentage of the variance remained unexplained by our model, thus important selective factors or parameters may have been left out of this analysis. We suggest that other possible correlates may exist between seed germination time and additional ecological factors (for example, altitude, habitat and post-dispersal predation) or phylogenetic related morphological and physiological seed attributes (e.g., endosperm mass) that were not evaluated in this study.
investigations were made on the relationship between plant density and plant height, and on the yield, thousand seed mass, and ratio of diseased and broken seeds of varieties with different seed sizes. Experiments were carried out to analyse the effects of potassium on the yield, bacterial diseases and nutritive quality of the seed of bean varieties. Three dry bean cultivars representing the small, medium and large seed size groups were investigated. Six plant density treatments were chosen based on theoretical seed norms, taking the germinative value of the seeds into consideration. The correlation between plant density and yield average showed that the volume of yield increased for varieties with large and medium-sized seeds up to a plant density of 285-400 thousand/ha, after which it declined. On the basis of the results, yield averages at plant densities of 285-334 thousand plants/ha were 0.17 t/ha higher than those achieved at low density (200 thousand plants/ha). At greater plant density the plant height increased in the case of large-seeded varieties and there was a considerable decrease in the thousand seed mass. With an adequate water supply a high level of potassium decreased the number of pods and seeds per plant compared with the basic level, which gave a yield of 2.5 t/ha. The use of high rates of potassium fertilizer decreased the number of infected seeds, but the differences were only significant for the small-seeded variety. A moderately high potassium level was advantageous for food quality, particularly during drought.
Recruitment limitation has been hypothesized to promote the maintenance of high species diversity in forests by slowing down competitive exclusion. However, the difference of recruitment limitation for tree species with varying seed masses, which is a common phenomenon in tropical or subtropical forests, is largely unknown. In this study we conducted a seed sowing experiment for five dominant tree species with varying seed mass (a proxy of dispersal ability) in a subtropical evergreen broad-leaved forest at different successional stages to test the hypothesis that the determinants of species recruitment vary with their seed masses in Heishiding Nature Reserve (Guangdong Province, China). The effects of seed predators, soil pathogens, light conditions, plant litter, seed additions, and the presence of adult conspecific trees on the performance of seeds and seedlings for the five species were examined. We particularly investigated the effects of habitat hazards and seed size on the relative importance of dispersal limitation and establishment limitation. The results show that all five sowing species experienced recruitment limitation at the microsite level, although the causes of the limitation of these species varied between pathogen infection, animal predation, litter covering and shading. Seedling recruitment of the wind-dispersed, small-seeded species was mostly limited by microsite condition, while large-seeded species were mostly limited by dispersal ability.
Authors:M. Dainese, M. Scotton, F. Clementel, A. Pecile, and J. Lepš
We studied the floristic composition in the pastures of the Southern Alps (Trento Province, Italy). One hundred and five plots in seven different pasture plant communities were sampled: (1) nitrophilous, (2) montane mesic, (3) subalpine mesic, (4) calcareous montane, (5) calcareous subalpine, (6) acid montane, and (7) acid subalpine pastures. Forward selection and variation partitioning were applied to identify the most important factors controlling the species composition and plant traits in the pastures. Aggregated weighted averages were calculated for each plot using the published values of average height, specific leaf area, and seed mass for each species. Explanatory variables were recorded for each site to reflect climate, soil properties, and grazing pressure. We hypothesised that species composition and functional variation in pastures of the Southern Alps are controlled by three main environmental filters: climate, resource availability, and grazing pressure. We found that variables of climate and soil properties had a major role in explaining the species composition and variations in plant traits, while grazing pressure showed a lower independent effect. Species composition and plant traits depended mainly on temperature, soil fertility, and variables of bedrock type — soil pH. Our results confirm the importance of taking the effects of climate and resource availability into account when describing plant and community functions of grasslands.
The influence of white-water flooding and treefall gap formation on terra firme forest regeneration was investigated in Yasuni National Park of western Ecuador. I set up seed traps, collected seed rain and soil samples, and set out seeds and seedlings in unflooded terra firme forest (dry) and its gaps, and in nearby white-water floodplain várzea forest (wet) and its gaps. I found that (1) total number of dispersed seeds was greatest in the dry gaps with more seeds and greater richness in the gaps than the forest for both forest types, (2) the greatest number of seedlings germinated from wet gap soils with the least from the dry forest with gaps having more seedlings compared to their respective forests, (3) on average 30% of seeds remained after two weeks in the field and species seed losses were significantly different in all but one of the four sites, (4) more large seeds than small seeds were lost to pathogens and those losses were greater in the forests than the gaps, (5) as seed mass increased seedlings survival rates also increased but growth rates declined, and (6) more seedlings survived in gaps compared to closed forests where they grew faster with a larger leaf area ratio. Past sampling has shown that species composition differed between forest types, and present results show that the greatest seed and seedlings losses and the slowest growth rates were in intact terra firme forest, there were medium losses and medium growth rates in terra firme gaps and in the intact várzea forest, and the smallest losses and fastest growth rates were found in várzea gaps.
The effect of the foliar fertilizer Campofort Special-Zn (CSZn) and the plant growth regulator Rastim 30 DKV (RM) on growth, yield parameters and seed protein content was studied in mung bean [
(L.) Wilczek] plants grown under greenhouse and field conditions. CSZn at a dose of 10 l per ha, and RM at doses of 3, 30 and 60 g per ha were applied alone or in combination (before flowering and 14 days after first application). The initiation of flowering and ripening processes and the chlorophyll content Chl (
) were evaluated. At harvest, total yield and yield components (number of pods per plant, seed number per pod, single pod mass, seed mass per pod), germination of seeds and seed protein content were determined. RM applied alone induced intensive flowering, increased the number of pods and yield components per plant, accelerated the ripening of the pods, increased the Chl content in the leaves and delayed senescence in treated plants. The mixture of RM with CSZn (60 g + 10 l per ha) and RM alone at a dose of 60 g per ha had a retarding and morphogenic effect on the growth of treated plants and also decreased the protein content and germination of the seeds. The best results for all studied parameters were achieved in the field at a dose of 30 g RM + 10 l CSZn and under greenhouse conditions at a dose of 3 g RM + 10 l CSZn.
Authors:P. Török, E. Tóth, K. Tóth, O. Valkó, B. Deák, B. Kelbert, P. Bálint, Sz. Radócz, A. Kelemen, J. Sonkoly, T. Miglécz, G. Matus, A. Takács, V. A. Molnár, K. Süveges, L. Papp, L. Papp Jr., Z. Tóth, B. Baktay, G. Málnási Csizmadia, I. Oláh, E. Peti, J. Schellenberger, O. Szalkovszki, R. Kiss, and B. TÓthmérész
and seedmass . – New Phytol. 173 : 422 – 437 . http://dx.doi.org/10.1111/j.1469-8137.2006.01919.x
Cappers , R. T. J. , Bekker , R. M. and Jans , J. E. A. ( 2012 ): Digital