Plant root-shoot biomass allocation over diverse biomes: A global synthesis

Among-population variation in drought responses is consistent across life stages but not between native and non-native ranges

Understanding how widespread species adapt to variation in abiotic conditions across their ranges is fundamental to ecology. Insight may come from studying how among-population variation (APV) in the common garden corresponds with the environmental conditions of source populations. However, there are no such studies comparing native vs non-native populations across multiple life stages. We examined APV in the performance and functional traits of 59 Conyza canadensis populations, in response to drought, across large aridity gradients in the native (North America) and non-native (Eurasia) ranges in three experiments. Our treatment (dry vs wet) was applied at the recruitment, juvenile, and adult life stages. We found contrasting patterns of APV in drought responses between the two ranges. In the native range, plant performance was less reduced by drought in populations from xeric than mesic habitats, but such relationship was not apparent for non-native populations. These range-specific patterns were consistent across the life stages. The weak adaptive responses of non-native populations indicate that they can become highly abundant even without complete local adaptation to abiotic environments and suggest that long-established invaders may still be evolving to the abiotic environment. These findings may explain lag times in invasions and raise concern about future expansions.

Effect of biodegradable and conventional microplastic exposure in combination with seawater inundation on the coastal terrestrial plant Plantago coronopus

Coastal ecosystems face a multitude of pressures including plastic pollution and increased flood risk due to sea level rise and the frequency and severity of storms. Experiments seldom examine multiple stressors such as these, but here we quantified the effect of microplastics (polyethylene terephthalate (PET): a durable plastic and polybutylene adipate terephthalate (PBAT): a biodegradable polymer), in combination with simulated seawater inundation on the coastal species Plantago coronopus. After 35-days exposure to plastic (0.02 g.Kg-1, <300 μm diameter), P. coronopus were flooded to pot height with artificial seawater for 72-h, drained and grown for a further 24-days. Plant mortality, necrosis and photosynthetic efficiency (Fv/Fm) were recorded throughout, with root:shoot biomass and scape production (flower stalks) quantified at harvest. There were significant interactions between microplastics and seawater on the root:shoot ratio; a measure of resource allocation. The allocation to belowground biomass increased significantly under the PET + inundation treatment compared to the PBAT + inundation and the no plastic + inundation treatments, with potential consequences on the capture of water, nutrients and sunlight, which can affect plant performance. Plant necrosis significantly increased, and Fv/Fm declined as a result of seawater inundation. While not significant, plant Fv/Fm responses were influenced by microplastics (17% and 7% reduction in PBAT and PET exposure respectively compared to the no plastic control). Plants mediated this stress response with no discernible treatment-specific effects detected in Fv/Fm 14-days after seawater introduction. Plastic exposure significantly influenced potential reproductive output, with lower average scape numbers across PBAT treatments, but higher in PET treatments. This study highlights the complex interactions and potential for microplastics to present an elevated risk when in combination with additional stressors like seawater flooding; establishing the threat presented to ecosystem resilience in a changing world is a priority.

Is urbanization a driver of aboveground biomass allocation in a widespread tropical shrub, Turnera subulata (Turneroideae - Passifloraceae)?

Plant biomass allocation is mainly affected by the environment where each individual grows. In this sense, through the rapid global expansion of impermeable areas, urbanization has strong, albeit poorly understood, consequences on the biomass allocation of plants found in this environment. Nevertheless, the comprehension of biomass allocation processes in urban shrubs remains unclear, because most studies of urban ecology focus on tree species. This is an important gap of knowledge because a great part of urban vegetation is composed of shrubs and their association with trees have positive impacts in urban ecosystem services. In this study, we explored the ecological and potential selective pressure effects of an urbanization gradient on the biomass allocation patterns of aboveground organs of Turnera subulata, a widely distributed tropical shrub. We have demonstrated that, for certain reproductive organs, biomass allocation decreases in locations with higher urbanization. Unlike expected, the biomass of vegetative organs was not affected by urbanization, and we did not observe any effect of urbanization intensity on the variance in biomass allocation to vegetative and reproductive organs. We did not record urbanization-mediated trade-offs in biomass allocation for reproductive and vegetative organs. Instead, the biomass of these structures showed a positive relationship. Our data suggest that urbanization does not result in radical changes in biomass allocation of T. subulata, and neither in the variation of these traits. They indicate that the ability of T. subulata to thrive in urban environments may be associated with life history and morphological mechanisms. Our findings contribute to the understanding of shrub plant responses to urbanization and highlight urbanization as a potential factor in resource allocation differences for different structures and functions in plants living in these environments.

Measuring leaf and root functional traits uncovers multidimensionality of plant responses to arbuscular mycorrhizal fungi

PREMISE

While many studies have measured the aboveground responses of plants to mycorrhizal fungi at a single time point, little is known about how plants respond belowground or across time to mycorrhizal symbiosis. By measuring belowground responses and growth over time in many plant species, we create a more complete picture of how mycorrhizal fungi benefit their hosts.

METHODS

We grew 26 prairie plant species with and without mycorrhizal fungi and measured 14 functional traits to assess above- and belowground tissue quality and quantity responses and changes in resource allocation. We used function-valued trait (FVT) modeling to characterize changes in species growth rate when colonized.

RESULTS

While aboveground biomass responses were positive, the response of traits belowground were much more variable. Changes in aboveground biomass accounted for 60.8% of the variation in mycorrhizal responses, supporting the use of aboveground biomass response as the primary response trait. Responses belowground were not associated with aboveground responses and accounted for 18.3% of the variation. Growth responses over time were highly variable across species. Interestingly, none of the measured responses were phylogenetically conserved.

CONCLUSIONS

Mycorrhizal fungi increase plant growth in most scenarios, but the effects of these fungi belowground and across time are more complicated. This study highlights how differences in plant allocation priorities might affect how they utilize the benefits from mycorrhizal fungi. Identifying and characterizing these differences is a key step to understanding the effects of mycorrhizal mutualisms on whole plant physiology.

Responses of non-native and native plant species to fluctuations of water availability in a greenhouse experiment

Water availability strongly influences the survival, growth, and reproduction of most terrestrial plant species. Experimental evidence has well documented the effect of changes in total amount of water availability on non-native vs. native plants. However, little is known about how fluctuations in water availability affect these two groups, although more extreme fluctuations in water availability increasingly occur with prolonged drought and extreme precipitation events. Here, we grew seven non-native and seven native plant species individually in the greenhouse. Then, we exposed them to four watering treatments, each treatment with the same total amount of water, but with different divisions: W1 (added water 16 times with 125 mL per time), W2 (8 times, 250 mL per time), W3 (4 times, 500 mL per time), and W4 (2 times, 1000 mL per time). We found that both non-native and native plants produced the most biomass under medium frequency/magnitude watering treatments (W2 and W3). Interestingly, non-native plants produced 34% more biomass with the infrequent, substantial watering treatment (W4) than with frequent, minor watering treatment (W1), whereas native plants showed opposite patterns, producing 26% more biomass with W1 than with W4. Differences in the ratio of root to shoot under few/large and many/small watering treatments of non-native vs. native species probably contributed to their different responses in biomass production. Our results advance the current understanding of the effect of water availability on non-native plants, which are affected not only by changes in amount of water availability but also by fluctuations in water availability. Furthermore, our results indicate that an increased few/large precipitation pattern expected under climate change conditions might further promote non-native plant invasions. Future field experiments with multiple phylogenetically controlled pairs of non-native and native species will be required to enhance our understanding of how water availability fluctuations impact on non-native invasions.

Changes in above- versus belowground biomass distribution in permafrost regions in response to climate warming

Permafrost regions contain approximately half of the carbon stored in land ecosystems and have warmed at least twice as much as any other biome. This warming has influenced vegetation activity, leading to changes in plant composition, physiology, and biomass storage in aboveground and belowground components, ultimately impacting ecosystem carbon balance. Yet, little is known about the causes and magnitude of long-term changes in the above- to belowground biomass ratio of plants (η). Here, we analyzed η values using 3,013 plots and 26,337 species-specific measurements across eight sites on the Tibetan Plateau from 1995 to 2021. Our analysis revealed distinct temporal trends in η for three vegetation types: a 17% increase in alpine wetlands, and a decrease of 26% and 48% in alpine meadows and alpine steppes, respectively. These trends were primarily driven by temperature-induced growth preferences rather than shifts in plant species composition. Our findings indicate that in wetter ecosystems, climate warming promotes aboveground plant growth, while in drier ecosystems, such as alpine meadows and alpine steppes, plants allocate more biomass belowground. Furthermore, we observed a threefold strengthening of the warming effect on η over the past 27 y. Soil moisture was found to modulate the sensitivity of η to soil temperature in alpine meadows and alpine steppes, but not in alpine wetlands. Our results contribute to a better understanding of the processes driving the response of biomass distribution to climate warming, which is crucial for predicting the future carbon trajectory of permafrost ecosystems and climate feedback.

Differences in growth and competition between plants of a naturalized and an invasive population of Bunias orientalis

The global shift of species' distributions has led to high numbers of noninvasive naturalized plants and the accumulation of invasive species within ecosystems. Competition between species may influence population dynamics, but little is known about the impacts of competition between conspecifics of naturalized and invasive populations. We investigated several plant traits at initial growth and regrowth following artificial defoliation in intra and interpopulation competition. Therefore, we used plants of Bunias orientalis from one noninvasive naturalized and one invasive population grown alone or in competition of two or three. Plants from the naturalized population were expected to be less competitive than plants from the invasive population, reflecting their differential impact in the introduced range. Independent of status, intrapopulation competition was expected to have less negative impacts on plants than interpopulation competition. Our results show that competition impacted mostly growth- rather than physiology-related traits. The relative magnitude of intra and interpopulation competition differed among plant traits at the first and second harvest. Plants of the invasive population outperformed the naturalized population by allocating relatively more resources to the aboveground biomass and producing more and longer leaves particularly when grown in competition against two plants. Moreover, plants of the invasive population were more competitive, which may influence their successful establishment and range expansion in the introduced range, but growth patterns differed after artificial defoliation. Although evolution of intrapopulation competition in naturalized and invasive ranges may be expected, interpopulation competition seems to adversely impact the performance of the naturalized plant population of B. orientalis studied here. Apart from the status (naturalized vs. invasive), other factors may have had an influence on plant performance. Thus, further research is needed with more naturalized and invasive populations to test the generality of our findings and to isolate the specific mechanisms driving differences in competitiveness.

Nitrogen addition regulates the effects of variation in precipitation patterns on plant biomass formation and allocation in a Leymus chinensis grassland of northeast China

Global warming is predicted to change precipitation amount and reduce precipitation frequency, which may alter grassland primary productivity and biomass allocation, especially when interact with other global change factors, such as nitrogen deposition. The interactive effects of changes in precipitation amount and nitrogen addition on productivity and biomass allocation are extensively studied; however, how these effects may be regulated by the predicted reduction in precipitation frequency remain largely unknown. Using a mesocosm experiment, we investigated responses of primary productivity and biomass allocation to the manipulated changes in precipitation amount (PA: 150 mm, 300 mm, 450 mm), precipitation frequency (PF: medium and low), and nitrogen addition (NA: 0 and 10 g N m-2 yr-1) in a Leymus chinensis grassland. We detected significant effects of the PA, PF and NA treatments on both aboveground biomass (AGB) and belowground biomass (BGB); but the interactive effects were only significant between the PA and NA on AGB. Both AGB and BGB increased with an increment in precipitation amount and nitrogen addition; the reduction in PF decreased AGB, but increased BGB. The reduced PF treatment induced an enhancement in the variation of soil moisture, which subsequently affected photosynthesis and biomass formation. Overall, there were mismatches in the above- and belowground biomass responses to changes in precipitation regime. Our results suggest the predicted changes in precipitation regime, including precipitation amount and frequency, is likely to alter primary productivity and biomass allocation, especially when interact with nitrogen deposition. Therefore, predicting the influence of global changes on grassland structure and functions requires the consideration of interactions among multiple global change factors.

Effects of nutrient pulses on exotic species shift from positive to neutral with decreasing water availability

Temporal fluctuation in nutrient availability generally promotes the growth of exotic plant species and has been recognized as an important driver of exotic plant invasions. However, little is known about how the impact of fluctuating nutrients on exotic species is dependent on the availability of other resources, although most ecosystems are experiencing dramatic variations in a wide variety of resources due to global change and human disturbance. Here, we explored how water availability mediates the effect of nutrient pulses on the growth of six exotic and six native plant species. We subjected individual plants of exotic and native species to well watered or water stressed conditions. For each level of water availability, we added equivalent amounts of nutrients at a constant rate, as a single large pulse, or in multiple small pulses. Under well watered conditions, nutrient pulses promoted exotic plant growth relative to nutrients supplied constantly, while they had no significant effect on natives. In contrast, under water stressed conditions, water deficiency inhibited the growth of all exotic and native species. More importantly, nutrient pulses did not increase plant growth relative to nutrients supplied constantly and these phenomena were observed for both exotic and native species. Taken together, our study shows that the impact of fluctuating nutrient availability on the growth of exotic plant species strongly depends on the variation of other resources, and that the positive effect of nutrient pulses under well watered conditions disappears under water stressed conditions. Our findings suggest that the variation in multiple resources may have complex feedback on exotic plant invasions and, therefore, it is critical to encompass multiple resources for the evaluation of fluctuating resource availability effects on exotic plant species. This will allow us to project the invasive trajectory of exotic plant species more accurately under future global change and human disturbance.

Decadal soil warming decreased vascular plant above and belowground production in a subarctic grassland by inducing nitrogen limitation

Below and aboveground vegetation dynamics are crucial in understanding how climate warming may affect terrestrial ecosystem carbon cycling. In contrast to aboveground biomass, the response of belowground biomass to long-term warming has been poorly studied. Here, we characterized the impacts of decadal geothermal warming at two levels (on average +3.3°C and +7.9°C) on below and aboveground plant biomass stocks and production in a subarctic grassland. Soil warming did not change standing root biomass and even decreased fine root production and reduced aboveground biomass and production. Decadal soil warming also did not significantly alter the root-shoot ratio. The linear stepwise regression model suggested that following 10 yr of soil warming, temperature was no longer the direct driver of these responses, but losses of soil N were. Soil N losses, due to warming-induced decreases in organic matter and water retention capacity, were identified as key driver of the decreased above and belowground production. The reduction in fine root production was accompanied by thinner roots with increased specific root area. These results indicate that after a decade of soil warming, plant productivity in the studied subarctic grassland was affected by soil warming mainly by the reduction in soil N.

Climate factors affect forest biomass allocation by altering soil nutrient availability and leaf traits

Biomass in forests sequesters substantial amounts of carbon; although the contribution of aboveground biomass has been extensively studied, the contribution of belowground biomass remains understudied. Investigating the forest biomass allocation is crucial for understanding the impacts of global change on carbon allocation and cycling. Moreover, the question of how climate factors affect biomass allocation in natural and planted forests remains unresolved. Here, we addressed this question by collecting data from 384 planted forests and 541 natural forests in China. We evaluated the direct and indirect effects of climate factors on the belowground biomass proportion (BGBP). The average BGBP was 31.09% in natural forests and was significantly higher (38.75%) in planted forests. Furthermore, we observed a significant decrease in BGBP with increasing temperature and precipitation. Climate factors, particularly those affecting soil factors, such as pH, strongly affected the BGBP in natural and planted forests. Based on our results, we propose that future studies should consider the effects of forest type (natural or planted) and soil factors on BGBP.

Colchicine-Induced Polyploidy in Leguminous Crops Enhances Morpho-Physiological Characteristics for Drought Stress Tolerance

Legumes play a significant role in the alleviation of food insecurity, maintaining soil fertility, and achieving sustainable crop production under adverse environmental conditions. The increased demand in legume production contemplates that attention on the genetic improvement of these crops through various means such as genetic engineering and mutation breeding should take a centre stage in global agriculture. Therefore, this paper provides a succinct analysis of the currently available literature on morphological and physiological traits in polyploidised leguminous plants to counter the adverse effects of drought stress. The effects of colchicine on various morphological and physiological traits of polyploidised legumes compared to their diploid counterparts were examined. Numerous reports revealed variations in these traits, such as improved root and shoot growth, plant biomass, chloroplastidic content, protein, RNA, and DNA. The differences observed were also associated with the strong relationship between plant ploidy induction and colchicine application. Furthermore, the analysis indicated that polyploidisation remains dose-dependent and may be achievable within a shorter space of time as this antimitotic chemical interferes with chromosome separations in somatic plant cells. The efficiency of this process also depends on the advancement of treatment conditions (in vitro, in vivo, or ex vitro) and the successful regeneration of polyploidised plants for adaptation under drought stress conditions. As such, the improvement in metabolite profile and other essential growth characteristics serves as a clear indication that induced polyploidy needs to be further explored to confer resilience to environmental stress and improve crop yield under drought stress conditions in leguminous plants.

Precipitation Dominates the Allocation Strategy of Above- and Belowground Biomass in Plants on Macro Scales

The allocation of biomass reflects a plant's resource utilization strategy and is significantly influenced by climatic factors. However, it remains unclear how climate factors affect the aboveground and belowground biomass allocation patterns on macro scales. To address this, a study was conducted using aboveground and belowground biomass data for 486 species across 294 sites in China, investigating the effects of climate change on biomass allocation patterns. The results show that the proportion of belowground biomass in the total biomass (BGBP) or root-to-shoot ratio (R/S) in the northwest region of China is significantly higher than that in the southeast region. Significant differences (p < 0.05) were found in BGBP or R/S among different types of plants (trees, shrubs, and herbs plants), with values for herb plants being significantly higher than shrubs and tree species. On macro scales, precipitation and soil nutrient factors (i.e., soil nitrogen and phosphorus content) are positively correlated with BGBP or R/S, while temperature and functional traits are negatively correlated. Climate factors contribute more to driving plant biomass allocation strategies than soil and functional trait factors. Climate factors determine BGBP by changing other functional traits of plants. However, climate factors influence R/S mainly by affecting the availability of soil nutrients. The results quantify the productivity and carbon sequestration capacity of terrestrial ecosystems and provide important theoretical guidance for the management of forests, shrubs, and herbaceous plants.

Carbon Storage in Different Compartments in Eucalyptus Stands and Native Cerrado Vegetation

This study evaluated Carbon (C) storage in different compartments in eucalyptus stands and native Cerrado vegetation. To determine C above ground, an inventory was carried out in the areas where diameter at breast height (DBH), diameter at base height (Db), and total tree height (H) were measured. In the stands, the rigorous cubage was made by the direct method, and in the native vegetation, it was determined by the indirect method through an allometric equation. Roots were collected by direct method using circular monoliths to a depth of 60 cm and determined by the volume of the cylinder. Samples were collected up to 100 cm deep to estimate C stock in the soil. All samples collected directly had C determined using the CHNS elemental analyzer. Gas samples were collected using a manually closed chamber, and the gas concentration was determined by gas chromatography. The results indicate high C storage in the studied areas > 183.99 Mg ha^-1, could contribute to CO₂ mitigation > 674.17 Mg ha^-1. In addition to low emissions (<1 kg ha^-1 yr^-1) for the three evaluated areas, with no statistical difference in relation to the Global Warming Potential. Concerning the native cerrado vegetation conversion, the "4-year-old eucalyptus stand" seemed to restore the original soil carbon stocks in the first-meter depth, regardless of some losses that might have occurred right after establishment. Conversely, a significant loss of carbon in the soil was observed due to the alternative setting, where similar natural land was converted into agriculture, mostly soybean, and then, years later, turned into the "6-year-old eucalyptus stand" (28.43 Mg ha^-1). Under this study, these mixed series of C baselines in landscape transitions have reflected on unlike C dynamics outcomes, whereas at the bottom line, total C stocks were higher in the younger forest (4-year-old stand). Therefore, our finding indicates that we should be thoughtful regarding upscaling carbon emissions and sequestration from small-scale measurements to regional scales.

On the Possible Trade-Off between Shoot and Root Biomass in Wheat

Numerous studies have shown that under a limited water supply, a larger root biomass is associated with an increased above-ground biomass. Root biomass, while genetically controlled, is also greatly affected by the environment with varying plasticity levels. In this context, understanding the relationship between the biomass of shoots and roots appears prudent. In this study, we analyze this relationship in a large dataset collected from multiple experiments conducted up to different growth stages in bread wheat (Triticum aestivum L.) and its wild relatives. Four bread wheat mapping populations as well as wild and domesticated members of the Triticeae tribe were evaluated for the root and shoot biomass allocation patterns. In the analyzed dataset the root and shoot biomasses were directly related to each other, and to the heading date, and the correlation values increased in proportion to the length of an experiment. On average, 84.1% of the observed variation was explained by a positive correlation between shoot and root biomass. Scatter plots generated from 6353 data points from numerous experiments with different wheats suggest that at some point, further increases in root biomass negatively impact the shoot biomass. Based on these results, a preliminary study with different water availability scenarios and growth conditions was designed with two cultivars, Pavon 76 and Yecora Rojo. The duration of drought and water level significantly affected the root/shoot biomass allocation patterns. However, the responses of the two cultivars were quite different, suggesting that the point of diminishing returns in increasing root biomass may be different for different wheats, reinforcing the need to breed wheats for specific environmental challenges.

Effects of tomato inoculation with the entomopathogenic fungus Metarhizium brunneum on spider mite resistance and the rhizosphere microbial community

Entomopathogenic fungi have been well exploited as biocontrol agents that can kill insects through direct contact. However, recent research has shown that they can also play an important role as plant endophytes, stimulating plant growth, and indirectly suppressing pest populations. In this study, we examined the indirect, plant-mediated, effects of a strain of entomopathogenic fungus, Metarhizium brunneum on plant growth and population growth of two-spotted spider mites (Tetranychus urticae) in tomato, using different inoculation methods (seed treatment, soil drenching and a combination of both). Furthermore, we investigated changes in tomato leaf metabolites (sugars and phenolics), and rhizosphere microbial communities in response to M. brunneum inoculation and spider mite feeding. A significant reduction in spider mite population growth was observed in response to M. brunneum inoculation. The reduction was strongest when the inoculum was supplied both as seed treatment and soil drench. This combination treatment also yielded the highest shoot and root biomass in both spider mite-infested and non-infested plants, while spider mite infestation increased shoot but reduced root biomass. Fungal treatments did not consistently affect leaf chlorogenic acid and rutin concentrations, but M. brunneum inoculation via a combination of seed treatment and soil drenching reinforced chlorogenic acid (CGA) induction in response to spider mites and under these conditions the strongest spider mite resistance was observed. However, it is unclear whether the M. brunneum-induced increase in CGA contributed to the observed spider mite resistance, as no general association between CGA levels and spider mite resistance was observed. Spider mite infestation resulted in up to two-fold increase in leaf sucrose concentrations and a three to five-fold increase in glucose and fructose concentrations, but these concentrations were not affected by fungal inoculation. Metarhizium, especially when applied as soil drench, impacted the fungal community composition but not the bacterial community composition which was only affected by the presence of spider mites. Our results suggest that in addition to directly killing spider mites, M. brunneum can indirectly suppress spider mite populations on tomato, although the underlying mechanism has not yet been resolved, and can also affect the composition of the soil microbial community.

Effects of experimental nitrogen deposition on soil organic carbon storage in Southern California drylands

Atmospheric nitrogen (N) deposition is enriching soils with N across biomes. Soil N enrichment can increase plant productivity and affect microbial activity, thereby increasing soil organic carbon (SOC), but such responses vary across biomes. Drylands cover ~45% of Earth's land area and store ~33% of global SOC contained in the top 1 m of soil. Nitrogen fertilization could, therefore, disproportionately impact carbon (C) cycling, yet whether dryland SOC storage increases with N remains unclear. To understand how N enrichment may change SOC storage, we separated SOC into plant-derived, particulate organic C (POC), and largely microbially derived, mineral-associated organic C (MAOC) at four N deposition experimental sites in Southern California. Theory suggests that N enrichment increases the efficiency by which microbes build MAOC (C stabilization efficiency) if soil pH stays constant. But if soils acidify, a common response to N enrichment, then microbial biomass and enzymatic organic matter decay may decrease, increasing POC but not MAOC. We found that N enrichment had no effect on C fractions except for a decrease in MAOC at one site. Specifically, despite reported increases in plant biomass in three sites and decreases in microbial biomass and extracellular enzyme activities in two sites that acidified, POC did not increase. Furthermore, microbial C use and stabilization efficiency increased in a non-acidified site, but without increasing MAOC. Instead, MAOC decreased by 16% at one of the sites that acidified, likely because it lost 47% of the exchangeable calcium (Ca) relative to controls. Indeed, MAOC was strongly and positively affected by Ca, which directly and, through its positive effect on microbial biomass, explained 58% of variation in MAOC. Long-term effects of N fertilization on dryland SOC storage appear abiotic in nature, such that drylands where Ca-stabilization of SOC is prevalent and soils acidify, are most at risk for significant C loss.

Utilization of Indole Acetic Acid with Leucadendron rubrum and Rhododendron pulchrum for the Phytoremediation of Heavy Metals in the Artificial Soil Made of Municipal Sewage Sludge

The development of phytoremediation by garden plants is an effective way to deal with the dilemma of municipal sewage sludge disposal. In this study, two ornamental plants were used as phytoremediation plants to rehabilitate heavy-metal-contaminated municipal sewage sludge in field experiments, and the role of exogenous phytohormone IAA was also tested. Ornamental plants Loropetalum chinense var. rubrum (L. rubrum) and Rhododendron pulchrum (R. pulchrum) adapted well to the artificial soil made of municipal sewage sludge, and the concentrations of Cu, Zn, Pb, and Ni were decreased by 7.29, 261, 20.2, and 11.9 mg kg−1, respectively, in the soil planted with L. rubrum, and 7.60, 308, 50.1, and 17.7 mg kg−1, respectively, in the soil planted with R. pulchrum, accounted for 11−37% of the total amounts and reached significant levels (p < 0.05), except Cd. The concentration of Pb in all parts of the two ornamental plants was increased, as well as most heavy metals in L. rubrum root. As a result, three months after transplant, the phyto-extraction amounts in L. rubrum were 397, 10.9, and 1330 μg for Ni, Cd, and Pb, respectively, increased by 233% to 279%. The phyto-extraction amount in R. pulchrum were 1510, 250, and 237 μg for Zn, Pb, and Cu, respectively, increased by 143% to 193%. These results indicated a potential to remediate heavy metals of the two ornamental plants, especially L. rubrum. The results of correlation analysis implied that the interaction of heavy metals in the plant itself played an important role in the uptake of heavy metals. This seemed to explain why applying IAA in the experiment had little effect on plant growth and phytoremediation of heavy metals. This study provided a green and feasible idea for the proper disposal of municipal sewage sludge.

Drought affects the performance of native oak seedlings more strongly than competition with invasive crested wattle seedlings

Two of the most important processes threatening vulnerable plant species are competitive displacement by invasive alien species and water stress due to global warming. Quercus lusitanica, an oak shrub species with remarkable conservation interest, could be threatened by the expansion of the invasive alien tree Paraserianthes lophantha. However, it is unclear how competition would interact with predicted reductions in water availability due to global climate change. We set up a full factorial experiment to examine the direct interspecific competition between P. lophantha and Q. lusitanica seedlings under control and water-limited conditions. We measured seed biomass, germination, seedling emergence, leaf relative growth rate, biomass, root/shoot ratio, predawn shoot water potential and mortality to assess the individual and combined effects of water stress and interspecific competition on both species. Our results indicate that, at seedling stage, both species experience competitive effects and responses. However, water stress exhibited a stronger overall effect than competition. Although both species responded strongly to water stress, the invasive P. lophantha exhibited significantly less drought stress than the native Q. lusitanica based on predawn shoot water potential measurements. The findings of this study suggest that the competition with invasive P. lophantha in the short term must not be dismissed, but that the long-term conservation of the native shrub Q. lusitanica could be compromised by increased drought as a result of global change. Our work sheds light on the combined effects of biological invasions and climate change that can negatively affect vulnerable plant species.

Root exudate composition reflects drought severity gradient in blue grama (Bouteloua gracilis)

Plant survival during environmental stress greatly affects ecosystem carbon (C) cycling, and plant–microbe interactions are central to plant stress survival. The release of C-rich root exudates is a key mechanism plants use to manage their microbiome, attracting beneficial microbes and/or suppressing harmful microbes to help plants withstand environmental stress. However, a critical knowledge gap is how plants alter root exudate concentration and composition under varying stress levels. In a greenhouse study, we imposed three drought treatments (control, mild, severe) on blue grama (Bouteloua gracilis Kunth Lag. Ex Griffiths), and measured plant physiology and root exudate concentration and composition using GC–MS, NMR, and FTICR. With increasing drought severity, root exudate total C and organic C increased concurrently with declining predawn leaf water potential and photosynthesis. Root exudate composition mirrored the physiological gradient of drought severity treatments. Specific compounds that are known to alter plant drought responses and the rhizosphere microbiome mirrored the drought severity-induced root exudate compositional gradient. Despite reducing C uptake, these plants actively invested C to root exudates with increasing drought severity. Patterns of plant physiology and root exudate concentration and composition co-varied along a gradient of drought severity.

Balanced below- and above-ground growth improved yield and water productivity by cultivar renewal for winter wheat

Breeding cultivars that can maintain high production and water productivity (WP) under various growing conditions would be important for mitigating freshwater shortage problems. Experiments were carried out to assess the changes in yield and WP of different cultivars by breeding and traits related to the changes using tubes with 1.05 m depth and 19.2 cm inner diameter buried in the field located in the North China Plain. Six winter wheat cultivars released from the 1970s to 2010s were assessed under three water levels for three seasons. The results indicated that yield was on average improved by 19.9% and WP by 21.5% under the three water levels for the three seasons for the cultivar released in the 2010s as compared with that released in the 1970s. The performance of the six cultivars was relatively stable across the experimental duration. The improvement in yield was mainly attributed to the maintenance of higher photosynthetic capacity during the reproductive growth stage and greater above-ground biomass accumulation. These improvements were larger under wet conditions than that under dry conditions, indicating that the yield potential was increased by cultivar renewal. Traits related to yield and WP improvements included the increased harvest index and reduced root: shoot ratio. New cultivars reduced the redundancy in root proliferation in the topsoil layer, which did not compromise the efficient utilization of soil moisture but reduced the metabolic input in root growth. Balanced above- and below-ground growth resulted in a significant improvement in root efficiency at grain yield level up to 40% from the cultivars released in the 1970s to those recently released. The results from this study indicated that the improved efficiency in both the above- and below-parts played important roles in enhancing crop production and resource use efficiency.

The relationship between tree size and tree water-use: is competition for water size-symmetric or size-asymmetric?

Relationships between tree size and water use indicate how soil water is partitioned between differently sized individuals, and hence competition for water. These relationships are rarely examined, let alone whether there is consistency in shape across populations. Competition for water among plants is often assumed to be size-symmetric, i.e., exponents (b1) of power functions (water use ∝ biomassb1) equal to 1, with all sizes using the same amount of water proportionally to their size. We tested the hypothesis that b1 actually varies greatly, and based on allometric theory, that b1 is only centered around 1 when size is quantified as basal area or sapwood area (not diameter). We also examined whether b1 varies spatially and temporally in relation to stand structure (height and density) and climate. Tree water use ∝ sizeb1 power functions were fitted for 80 species and 103 sites using the global SAPFLUXNET database. The b1 were centered around 1 when tree size was given as basal area or sapwood area, but not as diameter. The 95% confidence intervals of b1 included the theoretical predictions for the scaling of plant vascular networks. b1 changed through time within a given stand for the species with the longest time series, such that larger trees gained an advantage during warmer and wetter conditions. Spatial comparisons across the entire dataset showed that b1 correlated only weakly (R2 < 12%) with stand structure or climate, suggesting that inter-specific variability in b1 and hence the symmetry of competition for water may be largely related to inter-specific differences in tree architecture or physiology rather than to climate or stand structure. In conclusion, size-symmetric competition for water (b1 ≈ 1) may only be assumed when size is quantified as basal area or sapwood area, and when describing a general pattern across forest types and species. There is substantial deviation in b1 between individual stands and species.

Effects of AMF on plant nutrition and growth depend on substrate gravel content and patchiness in the karst species Bidens pilosa L

Karst ecosystems represent a typical heterogeneous habitat, and it is ubiquitous with varying interactive patches of rock and soil associated with differential weathering patterns of carbonate rocks. Arbuscular mycorrhizae fungi (AMF) play an important role in regulating plant growth and nutrition in heterogeneous karst habitats. However, it remains unclear how AMF affects the growth and nutrition of plants in heterogeneous karst soil with varying patches and weathering gravel. A heterogeneous experiment with Bidens pilosa L. was conducted in a grid microcosm through patching karst soil with different gravel contents. The experimental treatments included the AMF treatments inoculated with (M⁺) or without (M^-) fungus Glomus etunicatum; the substrate patchiness treatments involved different sizes of the homogeneous patch (Homo), the heterogeneous large patch (Hetl), and the heterogeneous small patch (Hets); the substrate gravel treatments in the inner patch involved the free gravel (FG), the low gravel (LG) 20% in 80% soil, and the high gravel (HG) 40% in 60% soil. Plant traits related to growth and nutrients were analyzed by comparing substrate gravel content and patch size. The results showed that AMF was more beneficial in increasing the aboveground biomass of B. pilosa under the LG and HG substrates with a higher root mycorrhizal colonization rate than under the FG substrate with a lower root mycorrhizal colonization rate. AMF enhanced higher growth and nutrients for B. pilosa under the LG and HG substrates than under the FG substrate and under the Hets than under the Hetl. Moreover, AMF alleviated the limited supply of N for B. pilosa under all heterogeneous treatments. Furthermore, the response ratio LnRR of B. pilosa presented that the substrate gravel promoted the highest growth, N and P absorption than the substrate patchiness with M⁺ treatment, and the gravel content had a more effect on plant growth and nutrition as compared to the patch size. Overall, this study suggests that plant growth and nutrition regulated by AMF mainly depend on the substrate gravel content rather than the spatial patchiness in the heterogeneous karst habitat.

Root tragedy of the commons: Revisiting the mechanisms of a misunderstood theory

Fine root density in the soil is a plant functional trait of paramount importance for plant ecology and agriculture. Fine root proliferation by plants involves complex plant strategies that may depend on various abiotic and biotic factors. Concretely, the root tragedy of the commons (RToC) is a behavioral strategy predicted by game theory models in which interacting plants forage for soil resources inefficiently. Generally, researchers assume that the RToC is a proactive competition strategy directly induced by the non-self roots. In this opinion, I recall Hardin's original definition of the tragedy of the commons to challenge this notion. I argue that the RToC is a suboptimal phenotypically plastic response of the plants based on the soil resource information exclusively, and I discuss how this alternative perspective carries important implications for the design of experiments investigating the physiological mechanisms underlying observable plant root responses.

Rates and drivers of aboveground carbon accumulation in global monoculture plantation forests

Restoring forest cover is a key action for mitigating climate change. Although monoculture plantations dominate existing commitments to restore forest cover, we lack a synthetic view of how carbon accumulates in these systems. Here, we assemble a global database of 4756 field-plot measurements from monoculture plantations across all forested continents. With these data, we model carbon accumulation in aboveground live tree biomass and examine the biological, environmental, and human drivers that influence this growth. Our results identify four-fold variation in carbon accumulation rates across tree genera, plant functional types, and biomes, as well as the key mediators (e.g., genus of tree, endemism of species, prior land use) of variation in these rates. Our nonlinear growth models advance our understanding of carbon accumulation in forests relative to mean annual rates, particularly during the next few decades that are critical for mitigating climate change.

Tree planting is a promising yet controversial natural climate solution. Here the authors perform a global analysis of aboveground C accumulation in tree monocultures, identifying key predictors such as prior land use, taxonomic identity, and plant traits.

Allometric Equations for the Biomass Estimation of Calophyllum inophyllum L. in Java, Indonesia

Reliable data on CO2 quantification is increasingly important to quantify the climate benefits of forest landscape restoration and international commitments, such as the Warsaw REDD+ Framework and Nationally Determined Contributions under the Paris Agreement. Calophyllum inophyllum L. (nyamplung as a local name or tamanu tree for the commercial name) is an increasingly popular tree species in forest landscape restoration and bioenergy production for a variety of reasons. In this paper, we present allometric equations for aboveground biomass (AGB), belowground biomass (BGB), and total above- and belowground biomass (TABGB) predictions of C. inophyllum L. Data collection was carried out twice (2017 and 2021) from 40 trees in Java, Indonesia. Allometric equations using the natural logarithm of diameter at breast height (lnDBH) and ln height (lnH) for biomass prediction qualified the model’s fit with statistical significance at 95% of the confidence interval for AGB, BGB, and TABGB predictions. The results showed that the linear models using both lnDBH and lnH were well fit and accurate. However, the model with lnDBH is more precise than the model using lnH. Using lnDBH as a predictor, the R2 values were 0.923, 0.945, and 0.932, and MAPE were 24.7, 37.0, and 25.8 for AGB, BGB, and TABGB, respectively. Using lnH as a predictor, the R2 values were 0.887, 0.918, and 0.898 and MAPE were 37.4, 49.0, and 39.8 for AGB, BGB, and TABGB, respectively. Consequently, the driven allometric equations can help accurate biomass quantification for carbon-trading schemes of C. inophyllum L.

Path Coefficient and Principal Component Analyses for Biomass Allocation, Drought Tolerance and Carbon Sequestration Potential in Wheat

Increased root biomass allocation could serve as a proxy trait for selecting crop ideotypes with drought tolerance and carbon sequestration potential in agricultural soils. The objective of this study was to assess the magnitude of the relationship between root biomass and yield components and to identify influential traits so as to optimise genotype selection for enhanced biomass allocation, drought tolerance and carbon sequestration potential in bread wheat (Triticum aestivum L.). One-hundred wheat genotypes consisting of 10 parents and 90 derived F2 families were evaluated under drought-stressed and non-stressed conditions at two different sites. Data were collected for days to heading (DTH), days to maturity (DTM), plant height, productive tiller number (TN), spike length, spikelets per spike (SPS), kernels per spike (KPS), thousand kernel weight (TKW), shoot biomass, root biomass, total plant biomass (PB), root-to-shoot ratio (RS) and grain yield. There was significant (p < 0.05) genetic variation in most assessed traits, TN and RS being exceptions. Root biomass had significant positive correlations with grain yield under drought-stressed (r = 0.28) and non-stressed (r = 0.41) conditions, but a non-significant correlation was recorded for RS and grain yield. Notably, both root biomass and shoot biomass had significant positive correlations under both water regimes, revealing the potential of increasing both traits with minimal biomass trade-offs. The highest positive direct effects on grain yield were found for KPS and PB under both water regimes. The present study demonstrated that selection based on KPS and PB rather than RS will be more effective in ideotype selection of segregating populations for drought tolerance and carbon sequestration potential.

Phenotypic differentiation and diversifying selection in populations of Eruca sativa along an aridity gradient

Background

The aridity gradient in the eastern Mediterranean offers an opportunity to investigate intra-specific genetic differentiation and local adaptation in plant populations. Here we used genetic (F_ST) and quantitative trait (P_ST) differentiation to assess local adaptation among three natural populations of Eruca sativa (Brassicaceae) distributed along a climatic range representing desert, semi-arid and Mediterranean habitats.

Results

Amplified fragment length polymorphism (AFLP) analysis revealed high genetic diversity in each population, but low genetic differentiation between populations and relatively high gene flow. Further phenotypic evaluation in a common garden experiment (conduced in a Mediterranean habitat) showed clear differences in phenological traits among populations (day of flowering and duration of the reproductive stage), shoot and root biomass, as well as fitness-related traits (total number of fruits and total seed weight). F_ST–P_ST comparison showed that P_ST values of the phenological traits, as well as below- and above-ground biomass and fitness-related traits, were higher than the F_ST values.

Conclusions

Overall, our results support the identification of genotypic and phenotypic differentiation among populations of E. sativa. Furthermore, the F_ST–P_ST comparison supports the hypothesis that these were subjected to past diversifying selection. Thus, the results clearly demonstrate adaptive divergence among populations along an aridity gradient, emphasize the ecological value of early flowering time in arid habitats, and contribute to our understanding of the possible impact of climate change on evolutionary processes in plant populations.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12862-022-01996-w.

Small Semi-Fossorial Herbivores Affect the Allocation of Above- and Below-Ground Plant Biomass in Alpine Meadows

Small semi-fossorial herbivores can affect plant aboveground biomass (AGB) in grasslands and possibly alter the allocation of AGB and belowground biomass (BGB). In this study, plateau pika (Ochotona curzoniae) was used to investigate such effects at three alpine meadow sites on the Eastern Tibetan Plateau, where pairs of disturbed vs. undisturbed plots were randomly selected and sampled. We also explored the relationships between soil properties and BGB/AGB across the plots in the presence and absence of plateau pikas, respectively. We found that BGB and BGB/AGB were 11.40 and 8.20% lower in the presence of plateau pikas than in their absence, respectively. We also found that the BGB/AGB was positively related to soil moisture and soil total nitrogen (STN) in the absence of plateau pikas. In contrast, BGB/AGB was positively related to STN, soil organic carbon (SOC), soil carbon/nitrogen (C/N), and soil total phosphorus in the presence of plateau pikas. These factors indicated plateau pika disturbance increased AGB allocation. The relationship between AGB and BGB of alpine meadow plants to soil variables was also different between sites with and without plateau pika disturbance. In conclusion, small semi-fossorial herbivore disturbance is likely to alter grassland carbon stock and should be well controlled for sustainable conservation and management of alpine meadows on the Tibetan Plateau.

Effects of Different Soils on the Biomass and Photosynthesis of Rumex nepalensis in Subalpine Region of Southwestern China

The performance of Rumex nepalensis, an important medicinal herb, varies significantly among subalpine grasslands, shrublands and forest ecosystems in southwestern China. Plant–soil feedback is receiving increasing interest as an important driver influencing plant growth and population dynamics. However, the feedback effects of soils from different ecosystems on R. nepalensis remain poorly understood. A greenhouse experiment was carried out to identify the effects of different soil sources on the photosynthesis and biomass of R. nepalensis. R. nepalensis was grown in soils collected from the rooting zones of R. nepalensis (a grassland soil, RS treatment), Hippophae rhamnoides (a shrub soil, HS treatment), and Picea asperata (a forest soil, PS treatment). The chlorophyll contents, net photosynthetic rates, and biomasses of R. nepalensis differed significantly among the three soils and followed the order of RS > HS > PS. After soil sterilization, these plant parameters followed the order of RS > PS > HS. The total biomass was 16.5 times higher in sterilized PS than in unsterilized PS, indicating that the existence of soil microbes in P. asperata forest ecosystems could strongly inhibit R. nepalensis growth. The root to shoot biomass ratio of R. nepalensis was the highest in the sterilized PS but the lowest in the unsterilized PS, which showed that soil microbes in PS could change the biomass allocation. Constrained redundancy analysis and path analysis suggested that soil microbes could impact the growth of R. nepalensis via the activities of soil extracellular enzymes (e.g., β-1,4-N-acetylglucosaminidase (NAG)) in live soils. The soil total soluble nitrogen concentration might be the main soil factor regulating R. nepalensis performance in sterilized soils. Our findings underline the importance of the soil microbes and nitrogen to R. nepalensis performance in natural ecosystems and will help to better predict plant population dynamics.

Cadmium phytoremediation potential of Deenanath grass (Pennisetum pedicellatum) and the assessment of bacterial communities in the rhizospheric soil

Phytoremediation technology is gaining excessive consideration as a promising method for heavy metal remediation from contaminated soil. In the present research study, a greenhouse trial was performed to assess the proficiency of Pennisetum pedicellatum as a potential plant species for the remediation of cadmium from the soil. Four sets of treatments i.e., (T_o) control, (T₁) 25 ppm, (T₂) 50 ppm, and (T₃) 100 ppm were studied till 60 days. Soil and plant samples were collected at a regular interval of 15 days after the seed sowing and analysed for different physicochemical properties and Cd concentrations from each treatment. The cadmium uptake was studied in the roots and shoots independently to examine the cadmium accumulation in P. pedicellatum. The present study showed that P. pedicellatum accumulated cadmium mostly in their roots compared to the shoots resulting in the accumulation of Cd from the soil. The finding indicates that P. pedicellatum is a virtuous plant species to restore cadmium-contaminated soil. It effectively banished 83% of Cd from the 100 ppm spiked soil at the end of 60 days. The microbial characterization of rhizospheric soil was also done using serial dilution and spread plate procedures to determine the presence of bacterial species in the rhizospheric soil. Seven bacterial strains were isolated from the soil and were further assessed for their biochemical, molecular, and phylogenic characteristics. The 16S rRNA sequencing analysis confirmed the presence of different bacterial species such as Alcaligenes sp., Bacillus drentensis, Bacillus subtilis, Bacillus foraminis, Bacillus wudalianchiensis, Bacillus amyloliquefaciens, and Planococcus ruber. This study concluded that phytoremediation using P. pedicellatum is a fascinating and compelling green technology for the remediation of cadmium from soil.

Differential Responses of Plant Primary Productivity to Nutrient Addition in Natural and Restored Alpine Grasslands in the Qinghai Lake Basin

Climate, land-use changes, and nitrogen (N) deposition strongly impact plant primary productivity, particularly in alpine grassland ecosystems. In this study, the differential responses of plant community primary productivity to N and phosphorus (P) nutrient application were investigated in the natural (NG) and "Grain for Green" restored (RG) alpine grasslands by a continuous 3-year experiment in the Qinghai Lake Basin. N addition only significantly promoted plant aboveground biomass (AGB) by 42% and had no significant effect on belowground biomass (BGB) and total biomass (TB) in NG. In comparison with NG, N addition elevated AGB and BGB concurrently in RG by 138% and 24%, respectively, which further significantly increased TB by 41% in RG. Meanwhile, N addition significantly decreased BGB and the AGB ratio (R/S) both in NG and RG. Compared with N addition, P addition did not perform an evident effect on plant biomass parameters. Additionally, AGB was merely negatively influenced by growing season temperatures (GST) under the N addition treatment in NG. AGB was negatively associated with GST but positively related to growing season precipitation (GSP) in RG. By contrast, changes in the R/S ratio in RG were positively correlated with GST and negatively related to GSP. In sum, the results revealed that plant community biomass exhibited convergent (AGB and R/S) and divergent (BGB and TB) responses to N addition between NG and RG. In addition, the outcomes suggested that climate warming would enhance plant biomass allocation to belowground under ongoing N deposition, and indicated the significance of precipitation for plant growth and AGB accumulation in this restored alpine grassland ecosystem.

Ecologically driven selection of nonstructural carbohydrate storage in oak trees

Leaf habit is a major axis of plant diversity that has consequences for carbon balance since the leaf is the primary site of photosynthesis. Nonstructural carbohydrates (NSCs) produced by photosynthesis can be allocated to storage and serve as a resiliency mechanism to future abiotic and biotic stress. However, how leaf habit affects NSC storage in an evolutionary context has not been shown. Using a comparative physiological framework and an analysis of evolutionary model fitting, we examined if variation in NSC storage is explained by leaf habit. We measured sugar and starch concentrations in 51 oak species (Quercus spp.) growing in a common garden and representing multiple evolutions of three different leaf habits (deciduous, brevideciduous and evergreen). The best fitting evolutionary models indicated that deciduous oak species are evolving towards higher NSC concentrations than their brevideciduous and evergreen relatives. Notably, this was observed for starch (the primary storage molecule) in the stem (a long-term C storage organ). Overall, our work provides insight into the evolutionary drivers of NSC storage and suggests that a deciduous strategy may confer an advantage against stress associated with a changing world. Future work should examine additional clades to further corroborate this idea.

Seasonal dynamics of non-structural carbon pools and their relationship to growth in two boreal conifer tree species

In an attempt to comprehensively study the dynamics of non-structural carbon compounds (NCCs), we measured the seasonal changes of soluble sugars, starch, lipids and sugar alcohols in the leaves, branches, stem and roots of the fast-growing Pinus contorta (Loudon) (pine) and slow-growing Picea glauca (Moench) Voss (spruce) trees growing in a boreal climate. In addition to measuring the seasonal concentrations of these compounds, the relative contribution of these compounds to the total NCC pool within the organs of trees (~8 m tall) was estimated and compared across different phenological and growth stages. Both species showed large seasonal shifts from starch to sugars from spring to fall in nearly all organs and tissues; most likely an adaptation to the cold winters. For both species, the total fluctuation of sugar + starch across the year (i.e., the difference between the minimum and maximum observed across collection times) was estimated to be between 1.6 and 1.8 kg for all NCCs. The fluctuation, however, was 1.40 times greater than the minimum reserves in pine, while only 0.72 times the minimum reserves in spruce. By tissue type, NCC fluctuations were greatest in the roots of both species. Roots showed a large build-up of reserves in late spring, but these reserves were depleted over summer and fall. Storage reserves in needles and branches declined over the summer, and this decline may be linked to the sink strength of the stem during diameter growth. Some notable highlights of this holistic study: a late winter build-up of sugars in the stem xylem of both species, but especially spruce; and an increase in sugar alcohols in the bark of spruce in very late winter, which could indicate mobilization to support early growth in spring and high lipid reserves in the bark of pine, which appeared not to be impacted by seasonal changes between summer and winter. Collectively, these observations point toward a more conservative NCC reserve strategy in spruce compared with pine, which is consistent with its stress tolerance and greater longevity.

Urbanization minimizes the effects of plant traits on soil provisioned ecosystem services across climatic regions

An increasingly urbanized world is one of the most prominent examples of global environmental change. Across the globe, urban parks are designed and managed in a similar way, resulting in visually pleasing expansions of lawn interspersed with individually planted trees of varying appearances and functional traits. These large urban greenspaces have the capacity to provide various ecosystem services, including those associated with soil physicochemical properties. Our aim was to explore whether soil properties in urban parks diverge underneath vegetation producing labile or recalcitrant litter, and whether the impact is affected by climatic zone (from a boreal to temperate to tropical city). We also compared these properties to those in (semi)natural forests outside the cities to assess the influence of urbanization on plant-trait effects. We showed that vegetation type affected percentage soil organic matter (OM), total carbon (C) and total nitrogen (N), but inconsistently across climatic zones. Plant-trait effects were particularly weak in old parks in the boreal and temperate zones, whereas in young parks in these zones, soils underneath the two tree types accumulated significantly more OM, C and N compared to lawns. Within climatic zones, anthropogenic drivers dominated natural ones, with consistently lower values of organic-matter-related soil properties under trees producing labile or recalcitrant litter in parks compared to forests. The dominating effect of urbanization is also reflected in its ability to homogenize soil properties in parks across the three cities, especially in lawn soils and soils under trees irrespective of functional trait. Our study demonstrates that soil functions that relate to carbon and nitrogen dynamics-even in old urban greenspaces where plant-soil interactions have a long history-clearly diverged from those in natural ecosystems, implying a long-lasting influence of anthropogenic drivers on soil ecosystem services.

The global distribution and environmental drivers of aboveground versus belowground plant biomass

A poor understanding of the fraction of global plant biomass occurring belowground as roots limits our understanding of present and future ecosystem function and carbon pools. Here we create a database of root-mass fractions (RMFs), an index of plant below- versus aboveground biomass distributions, and generate quantitative, spatially explicit global maps of RMFs in trees, shrubs and grasses. Our analyses reveal large gradients in RMFs both across and within vegetation types that can be attributed to resource availability. High RMFs occur in cold and dry ecosystems, while low RMFs dominate in warm and wet regions. Across all vegetation types, the directional effect of temperature on RMFs depends on water availability, suggesting feedbacks between heat, water and nutrient supply. By integrating our RMF maps with existing aboveground plant biomass information, we estimate that in forests, shrublands and grasslands, respectively, 22%, 47% and 67% of plant biomass exists belowground, with a total global belowground fraction of 24% (20-28%), that is, 113 (90-135) Gt carbon. By documenting the environmental correlates of root biomass allocation, our results can inform model projections of global vegetation dynamics under current and future climate scenarios.

Canopy Density and Roughness Differentiate Resistance of a Tropical Dry Forest to Major Hurricane Damage

Tropical dry forest is vulnerable to increased climate variability with more frequent and severe storms. Studies of hurricane impact on tropical dry forest often focused on individual tree traits. How trees in tropical dry forests work together to combat wind damage is still unclear. To address this, we integrated ground-observed ecosystem structure from National Ecological Observation Network (NEON) with airborne-LiDAR images and analyzed resistance in forest structure of Guánica dry forest in Puerto Rico to major hurricanes in 2017 at the forest-stand level. Using each plot instead of the individual tree as the base unit, we regressed mean changes in stem height and fractions of lost or damaged stems at 15 plots on mean stem diameter, mean and standard deviation of stem height, stem density, and topography. Meanwhile, using the LiDAR-derived canopy heights, we compared the changes in canopy height before and after the hurricanes and regressed spatially the canopy height change on prior-hurricane tree cover, canopy height, and rugosity. We found that the damage was small in places with high stem density or high tree cover. Ground-observed damage in terms of height reduction significantly increased with the standard deviation of stem height, an index of roughness, but decreased with the mean stem diameter of the plots. LiDAR-detected damage in terms of reduction in canopy height was also found to decrease with tree cover and mean canopy height when the canopy height was small or moderate but increase with the rugosity. The fraction of lost stems significantly decreased with the stem density, and the fraction of damaged stems significantly increased with the roughness and the plot elevation. The collective parameters of forest stand quantified from ground-observation and LiDAR, such as stem density, tree cover, and canopy roughness or rugosity, highlighted mutual supports of trees and played important roles in resisting damages to the tropical dry forest during major hurricanes.

Novel QTL Associated with Shoot Branching Identified in Doubled Haploid Rice (Oryza sativa L.) under Low Nitrogen Cultivation

Shoot branching is considered as an important trait for the architecture of plants and contributes to their growth and productivity. In cereal crops, such as rice, shoot branching is controlled by many factors, including phytohormones signaling networks, operating either in synergy or antagonizing each other. In rice, shoot branching indicates the ability to produce more tillers that are essential for achieving high productivity and yield potential. In the present study, we evaluated the growth and development, and yield components of a doubled haploid population derived from a cross between 93-11 (P1, indica) and Milyang352 (P2, japonica), grown under normal nitrogen and low nitrogen cultivation open field conditions. The results of the phenotypic evaluation indicated that parental lines 93-11 (P1, a high tillering indica cultivar) and Milyang352 (P2, a low tillering japonica cultivar) showed distinctive phenotypic responses, also reflected in their derived population. In addition, the linkage mapping and quantitative trait locus (QTL) analysis detected three QTLs associated with tiller number on chromosome 2 (qTNN2-1, 130 cM, logarithm of the odds (LOD) 4.14, PVE 14.5%; and qTNL2-1, 134 cM, LOD: 6.05, PVE: 20.5%) and chromosome 4 (qTN4-1, 134 cM, LOD 3.92, PVE 14.5%), with qTNL2-1 having the highest phenotypic variation explained, and the only QTL associated with tiller number under low nitrogen cultivation conditions, using Kompetitive Allele-Specific PCR (KASP) and Fluidigm markers. The additive effect (1.81) of qTNL2-1 indicates that the allele from 93-11 (P1) contributed to the observed phenotypic variation for tiller number under low nitrogen cultivation. The breakthrough is that the majority of the candidate genes harbored by the QTLs qTNL2-1 and qTNN4-1 (here associated with the control of shoot branching under low and normal nitrogen cultivation, respectively), were also proposed to be involved in plant stress signaling or response mechanisms, with regard to their annotations and previous reports. Therefore, put together, these results would suggest that a possible crosstalk exists between the control of plant growth and development and the stress response in rice.

Biomass Functions and Carbon Content Variabilities of Natural and Planted Pinus koraiensis in Northeast China

The population of natural Korean pine (Pinus koraiensis) in northeast China has sharply declined due to massive utilization for its high-quality timber, while this is vice versa for Korean pine plantations after various intensive afforestation schemes applied by China’s central authority. Hence, more comprehensive models are needed to appropriately understand the allometric relationship variations between the two origins. In this study, we destructively sampled Pinus koraiensis from several natural and plantation sites in northeast China to investigate the origin’s effect on biomass equations. Nonlinear seemingly unrelated regression with weighted functions was used to present the additivity property and homogenize the model residuals in our two newly developed origin-free (population average) and origin-based (dummy variable) biomass functions. Variations in biomass allocations, carbon content, and root-to-shoot ratio between the samples obtained from plantations and natural stands were also investigated. The results showed that (1) involving the origin’s effect in dummy variable models brought significant improvement in model performances compared to the population average models; (2) incorporating tree total height (H) as an additional predictor to diameter at breast height (D) consistently increase the models’ accuracy compared to using D only as of the sole predictors for both model systems; (3) stems accounted for the highest partitioning proportions and foliage had the highest carbon content among all biomass components; (4) the root-to-shoot ratio ranged from 0.18–0.35, with plantations (0.28 ± 0.04) had slightly higher average value (±SD) compared to natural forests (0.25 ± 0.03). Our origin-based models can deliver more accurate individual tree biomass estimations for Pinus koraiensis, particularly for the National Forest Inventory of China.

An Evaluation of Eight Machine Learning Regression Algorithms for Forest Aboveground Biomass Estimation from Multiple Satellite Data Products

This study provided a comprehensive evaluation of eight machine learning regression algorithms for forest aboveground biomass (AGB) estimation from satellite data based on leaf area index, canopy height, net primary production, and tree cover data, as well as climatic and topographical data. Some of these algorithms have not been commonly used for forest AGB estimation such as the extremely randomized trees, stochastic gradient boosting, and categorical boosting (CatBoost) regression. For each algorithm, its hyperparameters were optimized using grid search with cross-validation, and the optimal AGB model was developed using the training dataset (80%) and AGB was predicted on the test dataset (20%). Performance metrics, feature importance as well as overestimation and underestimation were considered as indicators for evaluating the performance of an algorithm. To reduce the impacts of the random training-test data split and sampling method on the performance, the above procedures were repeated 50 times for each algorithm under the random sampling, the stratified sampling, and separate modeling scenarios. The results showed that five tree-based ensemble algorithms performed better than the three nonensemble algorithms (multivariate adaptive regression splines, support vector regression, and multilayer perceptron), and the CatBoost algorithm outperformed the other algorithms for AGB estimation. Compared with the random sampling scenario, the stratified sampling scenario and separate modeling did not significantly improve the AGB estimates, but modeling AGB for each forest type separately provided stable results in terms of the contributions of the predictor variables to the AGB estimates. All the algorithms showed forest AGB were underestimated when the AGB values were larger than 210 Mg/ha and overestimated when the AGB values were less than 120 Mg/ha. This study highlighted the capability of ensemble algorithms to improve AGB estimates and the necessity of improving AGB estimates for high and low AGB levels in future studies.

Home climate and habitat drive ecotypic stress response differences in an invasive grass

Invasive plants and agricultural weeds are a ubiquitous and ever-expanding threat to biosecurity, biodiversity and ecosystem services. Many of these species are known to succeed through rapid adaptation to biotic and abiotic stress regimes, often in highly disturbed systems. Given the current state of evidence for selection of weedy genotypes via primary physiological stresses like drought, flooding, heat, cold and nutrient deficiency, we posit that adaptation to land management regimes which comprise suites of these stresses can also be expected. To establish this link, we tested adaptation to water and nutrient stresses in five non-agricultural and five agricultural populations of the invader Johnsongrass (Sorghum halepense) sampled across a broad range of climates in the USA. We subjected seedlings from each population to factorial drought and nutrient stresses in a common garden greenhouse experiment. Agricultural and non-agricultural ecotypes did not respond differently to experimentally applied stresses. However, non-agricultural populations from more drought-prone and nutrient-poor locations outperformed their agricultural counterparts in shoot allocation and chlorophyll production, respectively. We also found evidence for root allocation adaptation to hotter climates, in line with other C4 grasses, while greater adaptation to drought treatment was associated with soil organic carbon (SOC)-rich habitats. These findings imply that adaptation to land-use types can interact with other macrohabitat parameters, which will be fluctuating in a changing climate and resource-needy world. We see that invasive plants are poised to take on novel habitats within their introduced ranges, leading to complications in the prevention and management of their spread.