Plant Community Productivity Research Articles

Effects of Dynamic Changes of Soil Moisture and Salinity on Plant Community in the Bosten Lake Basin

To estimate the potential risks of plant diversity reduction and soil salinization in the Bosten Lake Basin, the dynamic changes in the plant community and species diversity affected by soil moisture and salinity were analyzed from 2000 to 2020 based on remote sensing technology and field experiments. A model for simulating soil moisture, salinity, and the productivity of the plant communities was proposed. The results demonstrated that: (1) The soil moisture index (SMI) increased but the soil salinity index (SSI) decreased from 2000 to 2020 in the study areas. Accordingly, the plant community productivity indices, including the vegetation index (NDVI), enhanced vegetation index (EVI), and ratio vegetation index (RVI), exhibited an increasing trend. It was found that the Alpine meadow, Alpine steppe, and temperate steppe desert were the main types of plant communities in the study areas, accounting for 69% of its total area. (2) With increasing SMI or decreasing SSI, the vegetation productivity such as NDVI, RVI, and EVI all exhibited an increasing trend. With the increment of SMI, the species diversity indices of the Simpson, Shannon–Wiener, and Margalef exhibited a distinctly increasing trend. However, the indices of the Simpson, Shannon–Wiener, and Alatalo increased with the decreasing SSI. (3) The study discovered from the SVM model that the species diversity index was optimal when the soil salinity was 0–15 g/kg and the soil moisture was 12–30% in the study areas. It was found that soil moisture, not soil salinity, controls the plant species diversity change in the study areas. (4) A multiple linear regression model was established for simulating the effect of soil water-salinity on the vegetation productivity index at the watershed scale. The model indicated that higher salinity would reduce vegetation productivity and higher soil moisture would promote vegetation growth (except for RVI). The SSI had a higher impact on NDVI and EVI than the SMI in the study areas. This study would support decision-making on grassland ecosystem restoration and management in the other arid areas.

Disentangling the effects of biomass and productivity in plant competition.

The relationship between competition and productivity in plant communities is unclear, and this is likely to be due to (1) a confusion in the literature between productivity and biomass, (2) the lack of studies assessing variation in competition in all combinations of biomass and productivity. We assessed the outcome of plant-plant interactions by removing the neighbors around five focal species in 14 herbaceous communities with contrasting biomasses and productivities: meadows with high biomass and productivity, heathlands with high biomass and low productivity, understory communities of deciduous forests with low biomass and high productivity and calcareous grasslands with low biomass and low productivity. Competition intensity was quantified with the relative interaction index (RII) calculated for both survival and growth of the transplanted targets assessed with the increase in leaf number. To examine which traits better explain variation in competition and what drives variation in diversity, we also quantified litter decomposition rate, species composition and diversity and six morphological traits related to plant size and growth rate for eight dominant species of each community. Our main questions were: (1) Is competition mostly related to biomass or productivity? (2) Which traits of the community dominants better explain variation in competition? (3) Is variation in competition and related traits correlated with variation in diversity? Competition for survival significantly increased with increasing community biomass (but not productivity). In addition, competition for survival increased with the size traits and competitive effects of the dominant species of the communities, whereas diversity decreased. Competition for growth also increased with increasing productivity, but only for high-biomass communities. Additionally, the increase in competition for growth with increasing soil fertility, as measured with litter decomposition rate, was only due to an increase in target growth in plots without neighbors and was unrelated to community competitive effects and species diversity. The results of our study illustrate how the confusion between productivity and biomass could have contributed to the long-standing debate on variation in competition along productivity gradients and its consequence for diversity.

Quality of cowpea seeds: A food security strategy in the tropical environment.

What is the relation between seed quality and food security? Here we built a summary diagram that links the development stages of the seeds with their potential of providing grain yield. This idea was tested using cowpea as a model crop, grown in a tropical environment. Initially, seed quality attributes such as water content, dry weight, germination, vigor, and longevity were characterized during seed development. With this, we were able to elucidate at which point the late maturation phase and the acquisition of seed with superior physiological quality starts. From these data, the proposed summary diagram highlighted the seed quality as a technological basis for generating a more productive plant community. It also showed that only seeds with a high-quality profile have a better chance to establishment in an increasingly challenging agricultural environment. Overall, we bring the concept that cowpea seeds with superior quality besides being the essential input for tropical agriculture is also a strategy that can contribute food security.

Grazing season regulates plant community structure and production by altering plant litter mass in a typical steppe

AbstractAimsGrazing different grasslands with seasonal changes is the tradition in pastoral systems in natural grassland regions worldwide. The effects and mechanisms of different grazing seasons on semi‐arid steppe vegetation are less explored on the Mongolian Plateau. Therefore, we assessed the impact and underlying mechanisms of grazing seasons on grassland community structure and production.LocationXilingol, Inner Mongolia, China.MethodsWe conducted a three‐year experiment to investigate the effects of grazing in four different seasons under the same grazing intensities on plant community structure and production in a typical steppe rangeland. The experiment was a random‐block design, with 20 grassland paddocks of 50 m × 50 m, representing five treatments (i.e., early spring, summer, autumn, mid‐winter, and no grazing), replicated by four blocks. We monitored the changes in soil properties, plant litter mass (i.e., standing dead biomass and dead plant material on the soil surface) and plant species composition and production across grazing treatments.ResultsPlant community height and above‐ground biomass were higher under early spring and winter grazing than autumn and summer grazing and no grazing. This divergence in plant community structure was mainly mediated by the seasonal patterns of plant litter mass across the grazing regimes. A high plant litter mass enhanced soil moisture by accumulating snow in winter and reducing soil evaporation during the growing season, which benefit plant growth. The removal of plant litter before the growing season increased the reception of solar radiation, thus improving soil temperature and plant production. The changes in community microenvironment and selective grazing led to the changes in plant species composition especially under summer and autumn grazing.ConclusionsOur results imply that grazing in winter or in early spring before plants start to turn green is more efficient than the complete animal exclusion for the natural recovery of degraded grassland in Inner Mongolia. It is suitable to incorporate cold‐season grazing in the development of sustainable grassland management systems.

Intensification of disturbance destabilizes productivity through effects on dominant species

• Both intensification and cessation of disturbance destabilized plant productivity. • Community stability was mainly driven by the stability of dominant species. • Maintaining disturbance may be an appropriate strategy for community stability. Disturbances, including anthropogenic disturbances, are integral to the maintenance of grassland ecosystems. Most research on anthropogenic disturbances focuses on the effects of intensification, yet cessation of disturbance can have equally important effects on grassland biodiversity and ecosystem functioning. Natural disturbances have largely been replaced by anthropogenic disturbance, which has pronounced effects on community function and structure in grassland ecosystems. It is still unclear how changing disturbance intensity affects community stability and its mechanisms. We examined the temporal stability of above-ground net primary productivity (ANPP) in a seven-year field mowing experiment which included normal disturbance (control, mowing annually at 5 cm stubble height), increasing disturbance (mowing annually at 2 cm stubble height) and ceasing disturbance (no mowing) in a typical steppe in Inner Mongolia. Overall, ceasing disturbance increased ANPP of whole community but increasing disturbance had no significant effect on community ANPP, which was driven by ANPP of dominant species; and species richness and asynchrony were independent of changing disturbance. Despite having no effect on species richness, both intensification and cessation of disturbance destabilized plant community productivity, primarily through effects on the stability of the dominant species. This highlights the importance of dominant species in driving community dynamics. Maintaining disturbance intensity is an appropriate strategy to maintain hay production and community stability in typical steppe in Inner Mongolia, and may be beneficial to the development of sustainable utilization of grassland and may ensure the income of resident population.

Species-Level Versus Community-Level Responses to Microhabitat Type and Diversity in an Experimental Plant Community

Soil heterogeneity has been theoretically predicted to promote plant performance, but empirical evidence is often mixed. By focusing on a gradient of microhabitats (single, three and six types of microhabitats), we tested the hypothesis that increasing the number of microhabitats promotes the diversity and productivity of plant communities. We created different types of microhabitats by adding different forms of nitrogen (NH4+, NO3− and glycine) or combinations of these nitrogen in an even or patchy way. Community biomass, but not evenness, differed in different types of single-microhabitat. Increasing the number of microhabitat types did not alter community growth or evenness, but it increased the difference in the relative abundance of plant species within the community. These results suggest that microhabitat diversity can influence plant competitive hierarchies, and that this effect can lead to changed community growth, but may not be decisive for plant evenness.

Long-term effects of artificial nighttime lighting and trophic complexity on plant biomass and foliar carbon and nitrogen in a grassland community.

The introduction of artificial nighttime lighting due to human settlements and transport networks is increasingly altering the timing, intensity, and spectra of natural light regimes worldwide. Much of the research on the impacts of nighttime light pollution on organisms has focused on animal species. Little is known about the impacts of daylength extension due to outdoor lighting technologies on wild plant communities, despite the fact that plant growth and development are under photoperiodic control. In a five‐year field experiment, artificial ecosystems (“mesocosms”) of grassland communities both alone or in combination with invertebrate herbivores and predators were exposed to light treatments that simulated street lighting technologies (low‐pressure sodium, and light‐emitting diode [LED]‐based white lighting), at ground‐level illuminance. Most of the plant species in the mesocosms did not exhibit changes in biomass accumulation after 5 years of exposure to the light treatments. However, the white LED treatment had a significant negative effect on biomass production in the herbaceous species Lotus pedunculatus. Likewise, the interaction between the white LED treatment and the presence of herbivores significantly reduced the mean shoot/root ratio of the grass species Holcus lanatus. Artificial nighttime lighting had no effect on the foliar carbon or nitrogen in most of the grassland species. Nevertheless, the white LED treatment significantly increased the leaf nitrogen content in Lotus corniculatus in the presence of herbivores. Long‐term exposure to artificial light at night had no general effects on plant biomass responses in experimental grassland communities. However, species‐specific and negative effects of cool white LED lighting at ground‐level illuminance on biomass production and allocation in mixed plant communities are suggested by our findings. Further studies on the impacts of light pollution on biomass accumulation in plant communities are required as these effects could be mediated by different factors, including herbivory, competition, and soil nutrient availability.

Plant responses to soil biota depend on precipitation history, plant diversity, and productivity.

Soil biota are critical drivers of plant growth, population dynamics, and community structure and thus have wide-ranging effects on ecosystem function. Interactions between plants and soil biota are complex, however, and can depend on the diversity and productivity of the plant community and environmental conditions. Plant-soil biota interactions may be especially important during stressful periods, such as drought, when plants can gain great benefits from beneficial biota but may be susceptible to antagonists. How soil biota respond to drought is also important and can influence plant growth following drought and leave legacies that affect future plant responses to soil biota and further drought. To explore how drought legacies and plant community context influence plant growth responses to soil biota and further drought, we collected soils from 12 grasslands varying in plant diversity and productivity where precipitation was experimentally reduced. We used these soils as inoculum in a growth chamber experiment testing how precipitation history (ambient or reduced) and soil biota (live or sterile soil inoculum) mediate plant growth and drought responses within an experimental plant community. We also tested whether these responses differed with the diversity and productivity of the community where the soil was collected. Plant growth responses to soil biota were positive when inoculated with soils from less diverse and productive plant communities and became negative as the diversity and productivity of the conditioning community increased. At low diversity, however, positive soil biota effects on plant growth were eliminated if precipitation had been reduced in the field, suggesting that diversity loss may heighten climate change sensitivity. Differences among species within the experimental community in their responses to soil biota and drought suggest that species benefitting from less drought sensitive soil biota may be able to compensate for some of this loss of productivity. Regardless of the plant species and soil origin, further drought eliminated any effects of soil biota on plant growth. Consequently, soil biota may be unable to buffer the effects of drought on primary productivity or other ecosystem functions as extreme events increase in frequency.

Historical context modifies plant diversity–community productivity relationships in alpine grassland

Abstract While most studies yield positive relationships between biodiversity (B) and ecosystem functioning (EF), awareness is growing that BEF relationships can vary with ecological context. The awareness has led to increased efforts to understand how contemporary environmental context modifies BEF relationships, but the role of historical context, and the mechanisms by which it may influence biodiversity effects, remains poorly understood. We examined how historical context alters plant diversity–community productivity relationships via plant species interactions in alpine grassland. We also tested how historical context modifies interactions between plants and arbuscular mycorrhizal (AM) fungi, which can potentially mediate the above processes. We studied biodiversity effects on plant community productivity at two grassland sites with different histories related to grazing intensity—heavy versus light livestock grazing—but similar current management. We assembled experimental communities of identical species composition with plants from each of the two sites in disturbed soil from a contemporary heavily grazed grassland, ranging in species richness from one to two, three and six species. Moreover, we carried out a mycorrhizal hyphae‐exclusion experiment to test how plant interactions with AM fungi influence plant responses to historical context. We detected a significantly positive diversity–productivity relationship that was driven by complementarity effects in communities composed of plants from the site without heavy‐grazing history, but no such relationship in plant communities composed of plants from the site with heavy‐grazing history. Plants from the site with heavy‐grazing history had increased competitive ability and increased yields in low‐diversity communities but disrupted complementarity effects in high‐diversity communities. Moreover, plants of one species from the site with heavy‐grazing history benefitted more from AM fungal communities than did plants from the site without such history. Synthesis. Using the same experimental design and species, communities assembled by plants from two sites with different historical contexts showed different plant diversity–community productivity relationships. Our results suggest that historical context can alter plant diversity–community productivity relationships via plant species interactions and potentially plant–soil interactions. Therefore, considering historical contexts of ecological communities is of importance for advancing our understanding of long‐term impacts of anthropogenic disturbance on ecosystem functioning.

Plant–soil feedbacks help explain plant community productivity

Plant productivity often increases with species richness, but the mechanisms explaining this diversity-productivity relationship are not fully understood. We tested if plant-soil feedbacks (PSF) can help to explain how biomass production changes with species richness. Using a greenhouse experiment, we measured all 240 possible PSFs for 16 plant species. At the same time, 49 plant communities with diversities ranging from one to 16 species were grown in replicated pots. A suite of plant community growth models, parameterized with (PSF) or without PSF (Null) effects, was used to predict plant growth observed in the communities. Selection effects and complementarity effects in modeled and observed data were separated. Plants created soils that increased or decreased subsequent plant growth by 25%±10%, but because PSFs were negative for C3 and C4 grasses, neutral for forbs, and positive for legumes, the net effect of all PSFs was a 2%±17% decrease in plant growth. Experimental plant communities with 16 species produced 37% more biomass than monocultures due to complementarity. Null models incorrectly predicted that 16-species communities would overyield due to selection effects. Adding PSF effects to Null models decreased selection effects, increased complementarity effects, and improved correlations between observed and predicted community biomass. PSF models predicted 26% of overyielding caused by complementarity observed in experimental communities. Relative to Null models, PSF models improved the predictions of the magnitude and mechanism of the diversity-productivity relationship. Results provide clear support for PSFs as one of several mechanisms that determine diversity-productivity relationships and help close the gap in understanding how biodiversity enhances ecosystem services such as biomass production.

Soil nitrate mediates the responses of plant community production to the frequency of N addition in a temperate grassland: a decadal field experiment

PurposeNitrogen (N) enrichment through either artificial N application or atmospheric N deposition often increases ecosystem aboveground net primary productivity (ANPP). Therefore, results from N addition experiments have been used to assess the effects of atmospheric N deposition on ecosystems. However, the frequency of atmospheric N deposition is higher than that of artificial N addition. Whether the frequency of N addition alters the long-term response of ecosystem ANPP remains unclear.MethodsWe conducted a N addition frequency experiment from 2010 in a temperate grassland, northern China. Plant community ANPP was collected in 2019 and 2020, and soil physicochemical properties were measured in 2020.ResultsPlant community ANPP was significantly enhanced by N addition, whereas these increments declined with the frequency of N addition. The responses of the grasses ANPP were similar to those of the plant community ANPP. Forbs ANPP was not significantly altered. Meanwhile, soil ammonium and nitrate (NO3−–N) concentrations decreased with increasing N addition frequency, while the soil water content (SWC) and pH were similar among the frequencies of N addition. Regardless of the frequency of N addition, SWC and soil NO3−–N jointly promoted grasses ANPP, ultimately increasing the plant community ANPP.ConclusionOur findings demonstrate that the frequency of N addition affects plant community biomass production through altering soil nitrate concentration in the semi-arid grassland. Therefore, this study illustrates that a higher frequency of N addition is more suitable for assessing the long-term impacts of atmospheric N deposition on ecosystems.

Aboveground native plant biomass reduces Potentilla recta growth: the role of a productive native plant community to mitigate reinvasion from the seedbank of invaded northern intermountain grasslands

AbstractSulphur cinquefoil (Potentilla recta L.) is an invasive plant of concern within grasslands in western North America. To better understand the role of native plant communities and soil seedbank in P. recta invasion within grasslands, we conducted two greenhouse studies to examine (1) P. recta growth response when grown with and without fertilizer in established native plant communities of varying functional groups (grasses, forbs, or grasses and forbs), and (2) the prevalence of P. recta and other species in the soil seedbank at varying soil depths (0 to 5 cm, 5 to 10 cm, 10 to 15 cm) of grasslands invaded by P. recta in southeastern British Columbia, Canada. The growth response of P. recta did not differ between the native plant communities. However, P. recta above- and belowground biomass declined as native plant aboveground biomass increased, suggesting a productive plant community may be important to suppress P. recta. Fertilizer did not affect the growth response of P. recta or native plants, suggesting nutrients may not have been a dominant limiting factor under greenhouse conditions. Nine species were identified in the soil seedbank. Seven were nonnative, which included P. recta, and native species represented less than 2% of the seedbank. Of the average number of emerged nonnative seedlings, more than 20% were P. recta. The number of emerged P. recta seedlings was 69% lower at 10- to 15-cm compared with 0- to 5-cm soil depth, although the successful germination of P. recta at greater soil depths suggests viable P. recta seeds are persisting in the seedbank. Active revegetation may be an important strategy to mitigate P. recta reinvasion or secondary invasion by other invasive species from the soil seedbank.

Nitrogen Deposition Shifts Grassland Communities Through Directly Increasing Dominance of Graminoids: A 3-Year Case Study From the Qinghai-Tibetan Plateau.

Nitrogen (N) deposition has been increasing for decades and has profoundly influenced the structure and function of grassland ecosystems in many regions of the world. However, the impact of N deposition on alpine grasslands is less well documented. We conducted a 3-year field experiment to determine the effects of N deposition on plant species richness, composition, and community productivity in an alpine meadow of the Qinghai-Tibetan Plateau of China. We found that 3 years of N deposition had a profound effect on these plant community parameters. Increasing N rates increased the dominance of graminoids and reduced the presence of non-graminoids. Species richness was inversely associated with aboveground biomass. The shift in plant species and functional group composition was largely responsible for the increase in productivity associated with N deposition. Climatic factors also interacted with N addition to influence productivity. Our findings suggest that short-term N deposition could increase the productivity of alpine meadows through shifts in composition toward a graminoid-dominated community. Longer-term studies are needed to determine if shifts in composition and increased productivity will be maintained. Future work must also evaluate whether decreasing plant diversity will impair the long-term stability and function of sensitive alpine grasslands.

Changes and Relationships between Components in the Plant-Soil System and the Dominant Plant Functional Groups in Alpine Kobresia Meadows Due to Overgrazing

In the last several decades, overgrazing has led to various changes in the plant communities, soil nutrients and soil microbial communities in alpine Kobresia meadows, which contain various plant communities coexisting on the Qinghai–Tibet Plateau. Investigating the variations in the biomass and concentration of nutrients in the plant–soil system in these communities may improve understanding of the biochemical responses and adaptation strategies they use to resist disturbances due to overgrazing. We therefore assessed 12 factors across four grazing intensities in alpine Kobresia meadows to explore the following three questions. (1) What the responses are in alpine Kobresia meadows to overgrazing. (2) How they affect plant–soil systems in alpine Kobresia meadows under overgrazing. (3) What factors can be used to evaluate the effects of overgrazing on the ecosystem health status of alpine Kobresia meadows. The results gave the following answers to the above questions. (1) Overgrazing caused the total aboveground biomass to decrease from 333.2 ± 17.4 g/m2 to 217.4 ± 30.2 g/m2, the coverage of plant functional groups of Gramineae and Cyperaceae to decrease from 74.2 ± 3% to 22.5 ± 1.9%, and the total belowground biomass to increase from 4028.5 ± 7.3 g/m2 to 6325.6 ± 24.8 g/m2. (2) Overgrazing resulted in variations in plant–soil systems at three levels. The concentrations of carbon (C) in soil nutrients and plant communities, explained 50.9% of the variation of biomass in plant functional groups; the concentration of soil available nutrients, explained 22.2% of the variation; and the ratio of C and N in shoots and soil total N, explained 11.0% of the variation. (3) The variations in C/N stoichiometry in total soil nutrients and soil microorganisms were 3.4–8.4% and 2.0–3.0%, respectively, and the load of (ammonium-nitrogen (NH4+-N) + nitrate-nitrogen (NO3–-N)) to growth of roots tissue increased from 84.1 ± 5.0 g/m2/(mg/kg) via 99.0 ± 1.3 g/m2/(mg/kg) to 86.1 ± 2.1 g/m2/(mg/kg) at 0 to 40 cm soil in an alpine meadow with grazing intensities rising. Overgrazing would thus increase the deficit of those two kinds of inorganic N on roots growing by 11.4%, 17.7% and 2.4% as grazing rates increased by 93.3%, 126.7% and 213.3%, respectively, compared to a meadow grazed at the lowest rate in the research. We concluded that the alpine meadow changed its distribution of biomass in the plant community, which increased the limiting nutrient deficit on production and altered the concentration and ratio of C and N. This destroyed the original balance to enable the plant community to resist overgrazing. Plot “KH”—a pasture with a grazing intensity next to the lowest one—was the key state in which persistent overgrazing could increase the limiting nutrient load on plant community production, change the dominant position of functional plant groups and species, and lead to plant community degradation. Using ratio of Gramineae to Cyperaceae or Kobresia humilis to K. pygmaea to monitor plant community succession could indirectly estimate these limiting nutrients deficit and balance, and their strategy for incorporating matter into roots and shoots. However how to use those outward characteristics to assess the ecosystem health requires further studies.

Polyarenes Distribution in the Soil-Plant System of Reindeer Pastures in the Polar Urals

Humic substances of soils consist of various organic compounds, including polycyclic aromatic hydrocarbons (PAHs). Soil as a fairly stable medium allows the correct use of polyarenes as markers of the humus formation process. Monitoring of the accumulation of PAHs as resistant organic toxicants is also necessary due to their carcinogenic and mutagenic properties. Natural plant resources serve as the feed base of northern reindeer husbandry. In this study, high-performance liquid chromatography in a gradient mode and gas chromatography-mass spectrometry methods were used to estimate the content of PAHs in mountain tundra and meadows of the Polar Urals (Russia). The accumulation of polyarenes in soils on carbonate rocks of the Bolshoi Paipudynsky ridge occurs mainly in the process of soil formation and largely depends on factors such as productivity of plant communities, the composition of standing biomass, the site’s position in relief, the granulometric composition of soils, cryogenesis process and pyrogenesis. According to the set of polyarenes, their number, and ratio, the studied objects were classified into separate groups by discriminant analysis. The most typical representatives of pedogenic origin are naphthalene and phenanthrene. The accumulation features of dibenz[a,h]anthracene and benz[b]-, benz[k]fluoranthene, benz[ghi]perylene, and benz[a]perylene are shown. In mountain tundra landscapes, the characteristics of PAHs can be used to diagnose the intensity and direction of soil formation processes in general and humification in particular.

Pollen Production of Selected Grass Species in Russia and India at the Levels of Anther, Flower and Inflorescence.

Grasses produce large amounts of pollen and are among the main causes of pollen allergy worldwide. Quantification of the roles of individual grass species in airborne pollen is an important task, because morphologically indistinguishable pollen grains of different species may differ in allergenicity. This requires knowledge of the pollen production of individual grass species; however, accumulated data are insufficient in this respect. Attempting to fill this gap, we studied pollen production per inflorescence in 29 grass species which are widespread in Middle Russia and India. Pollen production per inflorescence is determined by the number of grains per anther, the number of flowers in a spikelet and the number of spikelets per inflorescence, with the latter parameter being the most variable. We support the hypothesis that pollen production per inflorescence differs significantly between annual and perennial grasses. The greater pollen production of perennials can be interpreted as a tendency to guarantee cross-fertilization of species with self-incompatibility. The inferred pollen/ovule (P/O) ratios suggest the occurrence of facultative xenogamy in all annuals and obligate xenogamy in most perennials in the present dataset, though some self-incompatible annuals exist outside our sampling. Earlier data indicated that the P/O ratio of the annual cereal crop rye (Secale cereale) is higher than in any annual or perennial species sampled here. A ratio of pollen production to seed set (P/S ratio) is suggested to be another efficient parameter in reproductive biology of grasses. We highlight a need for detailed studies of reproductive biology in grasses that include both pollen and seed production. We found a correlation between pollen production per anther and anther length. A rough approximation of c. 1000 pollen grains per 1 mm of the length of an anther provides an instrument for estimates of pollen production in plant communities.

Mycorrhizal and rhizobial interactions influence model grassland plant community structure and productivity.

Arbuscular mycorrhizal (AM) fungi and rhizobium are likely important drivers of plant coexistence and grassland productivity due to complementary roles in supplying limiting nutrients. However, the interactive effects of mycorrhizal and rhizobial associations on plant community productivity and competitive dynamics remain unclear. To address this, we conducted a greenhouse experiment to determine the influences of these key microbial functional groups on communities comprising three plant species by comparing plant communities grown with or without each symbiont. We also utilized N-fertilization and clipping treatments to explore potential shifts in mycorrhizal and rhizobial benefits across abiotic and biotic conditions. Our research suggests AM fungi and rhizobium co-inoculation was strongly facilitative for plant community productivity and legume (Medicago sativa) growth and nodulation. Plant competitiveness shifted in the presence of AM fungi and rhizobium, favoring M. sativa over a neighboring C4 grass (Andropogon gerardii) and C3 forb (Ratibida pinnata). This may be due to rhizobial symbiosis as well as the relatively greater mycorrhizal growth response of M. sativa, compared to the other model plants. Clipping and N-fertilization altered relative costs and benefits of both symbioses, presumably by altering host-plant nitrogen and carbon dynamics, leading to a relative decrease in mycorrhizal responsiveness and proportional biomass of M. sativa relative to the total biomass of the entire plant community, with a concomitant relative increase in A. gerardii and R. pinnata proportional biomass. Our results demonstrate a strong influence of both microbial symbioses on host-plant competitiveness and community dynamics across clipping and N-fertilization treatments, suggesting the symbiotic rhizosphere community is critical for legume establishment in grasslands.

Plant diversity but not productivity is associated with community mycorrhization in temperate grasslands

AbstractAimsMycorrhizal symbiosis influences the performance of plant individuals. However, its impact on plant communities is less well understood. We used a database of plant mycorrhizal traits and investigated how community mycorrhization — the prevalence of mycorrhizal symbiosis in plant communities — is related to plant community productivity and diversity. We analysed: (a) how soil fertility affects community mycorrhization; (b) how plant productivity and diversity are related to community mycorrhization; and (c) whether community mycorrhization directly mediates the relationships between soil fertility and plant productivity and diversity.LocationTwenty‐nine semi‐natural grasslands in the south of Estonia, representing a steep productivity gradient (80–500 g/m2).MethodsWe estimated the proportion of plant biomass associated with mycorrhizal symbiosis (arbuscular mycorrhization index, AMI). The relationships between soil fertility (soil nitrogen [N], phosphorus [P] and potassium [K], accounting for soil moisture and pH), AMI, plant diversity and productivity were analysed using model averaging and pairwise generalized linear models, and support for direct relationships was determined using path analysis.ResultsThere was a positive linear relationship between soil nitrogen and AMI. In turn, plant biomass showed positive, and plant diversity negative linear relationships with AMI. Path analyses indicated that AMI mediates the relationship between soil nitrogen and plant diversity, but not the relationship between soil nitrogen and plant community productivity. Plant productivity and mycorrhization increased along the soil fertility gradient, but plant diversity decreased.ConclusionThese results suggest that community mycorrhization, which is sensitive to soil fertility (N), can modulate community composition in temperate grasslands, probably by enhancing the most dominant plant species in the community.

Structure and productivity of herbaceous plant communities of the Krasnoyarsk forest-steppe

Structure and productivity of herbaceous plant communities of the Krasnoyarsk forest-steppe

Earthworms Modulate Impacts of Soil Heterogeneity on Plant Growth at Different Spatial Scales.

Soil heterogeneity (uneven distribution of soil nutrients and/or other properties) is ubiquitous in nature and can greatly affect plant growth. As earthworm activity can influence nutrient redistribution in the soil, we hypothesize that earthworms may alter the effect of soil heterogeneity on plant growth and this effect may depend on the scale of soil heterogeneity. To test these hypotheses, we grew the clonal grass Leymus chinensis in three soil treatments (heterogeneous large vs. heterogeneous small patch vs. homogeneous soil treatment) with or without earthworms [i.e., Eisenia fetida Savigny (Lumbricidae, epigeic redworm)]. In the heterogeneous treatments, the soil consisted of patches with and without 15N-labeled litter (referred to as high- and low-quality patches, respectively), and in the homogeneous treatment, the soil was an even mixture of the two types of soil patches. Biomass of L. chinensis was significantly higher in the high- than in the low-quality patches, showing the foraging response; this foraging response occurred at both scales and under both earthworm treatments. Compared to the homogeneous treatment, the heterogeneous large patch treatment increased biomass of L. chinensis without earthworms, but decreased it with earthworms. In contrast, biomass of L. chinensis in the heterogeneous small patch treatment did not differ from that in the homogeneous treatment, irrespective of earthworms. Belowground biomass was much greater in the heterogeneous small than in the heterogeneous large patch treatment without earthworms, but it did not differ between these two scale treatments with earthworms. In the heterogeneous treatments, soil 15N was greater in the high- than in the low-quality patches, but this effect became much weaker with than without earthworms, suggesting that earthworm activity homogenized the soil. We conclude that earthworms can change the impact of soil heterogeneity on plant growth via homogenizing the soil, and that this effect of earthworms varies with patch scale. Such scale-dependent interactive effects of soil heterogeneity and earthworms could be a potential mechanism modulating plant community structure and productivity.