Root Biomass Allocation Research Articles

Root Biomass Allocation and Carbon Sequestration in Urban Landscaping Tree Species in South Korea

The quantification of urban tree biomass allocation has primarily relied on estimations using allometric equations (AEs) developed for nondestructive harvest methods. However, the lack of harvest-based AEs that account for belowground biomass, nutrient concentration, and annual growth rates poses challenges in accurately quantifying the greenhouse gas inventory for urban land uses. In this study, we aimed to develop AEs using a log-transformed linear model for eight urban landscaping tree species, taking into account belowground biomass. We purchased 117 urban landscaping trees from tree farms in South Korea and investigated their biomass fractions, carbon and nutrient concentrations, and annual growth rate using a destructive method. We also developed AEs for different tree compartments using diameter at breast height as an independent variable. The AEs obtained exhibited high suitability, as evidenced by their high R2 values (0.853–0.982 and 0.806–0.923 for aboveground and belowground biomass, respectively). The mean belowground biomass fraction across the different species was approximately 30%, suggesting that urban trees could allocate more belowground biomass than forest trees. Conversely, carbon and nitrogen concentrations varied significantly across species and compartments, and the mean annual carbon sequestration rate was 3.96 kg C year−1 tree−1. Therefore, the application of the AEs for urban trees may enhance the accuracy of the national greenhouse gas inventory for the settlement sector.

Deepening Root Inputs: Potential Soil Carbon Accrual From Breeding for Deeper Rooted Maize.

Breeding annual crops for enhanced root depth and biomass is considered a promising intervention to accrue soil organic carbon (SOC) in croplands, with benefits for climate change mitigation and soil health. In annual crops, genetic technology (seed) is replaced every year as part of a farmer's fixed costs, making breeding solutions to climate change more scalable and affordable than management approaches. However, mechanistic understanding and quantitative estimates of SOC accrual potentials from crops with enhanced root phenotypes are lacking. Maize is the highest acreage and yielding crop in the US, characterized by relatively low root biomass confined to the topsoil, making it a suitable candidate for improvement that could be rapidly scaled. We ran a 2-year field experiment to quantify the formation and composition (i.e., particulate (POM), coarse and fine mineral-associated organic matter (chaOM and MAOM, respectively) of new SOC to a depth of 90 cm from the decomposition of isotopically labeled maize roots and exudates. Additionally, we used the process-based MEMS 2 model to simulate the SOC accrual potential of maize root ideotypes enhanced to either shift root production to deeper depths or increase root biomass allocation, assuming no change in overall productivity. In our field experiment, maize root decomposition preferentially formed POM, with doubled efficiency below 50 cm, while root exudates preferentially formed MAOM. Modeling showed that shifting root inputs to deeper layer or increasing allocation to roots resulted in a deterministic increase in SOC, ranging from 0.05 to 0.15 Mg C ha-1 per year, which are at the low end of the range of published SOC per hectare annual accrual estimates from adoption of a variety of crop management practices. Our analysis indicates that for maize, breeding for increasing root inputs as a strategy for SOC accrual has limited impact on a per-hectare basis, although given that globally maize is produced on hundreds of millions of hectares each year, there is potential for this technology and its effect to scale. For maize-soy system that dominates US acres, changes in the overall cropping system are needed for sizable greenhouse gas reductions and SOC accrual. This study demonstrated a modeling and experimental framework to quantify and forecast SOC changes created by changing crop root inputs.

Soil water regime and nutrient availability modulate fine root distribution and biomass allocation in amazon forests with shallow water tables

Soil water regime and nutrient availability modulate fine root distribution and biomass allocation in amazon forests with shallow water tables

Morphological Traits and Biomass Allocation of Leymus secalinus along Habitat Gradient in a Floodplain Wetland of the Heihe River, China

Plant organ biomass allocation and morphological characteristics are important functional traits. The responses of plant root, stem, and leaf traits to heterogeneous habitats in floodplain wetlands are highly important for understanding the ecological adaptation strategies of riparian plants. However, the patterns of these responses remain unclear. In a floodplain wetland in the middle reaches of the Heihe River, we studied the responses of the root, stem, and leaf morphological traits and biomass allocation of Leymus secalinus to varying habitat conditions. We measured these traits in three sample plots, delineated based on distance from the riverbank: plot I (near the riparian zone, 50–150 m from the riverbank), plot II (middle riparian zone, 200–300 m from the riverbank), and plot III (far riparian zone, 350–450 m from the riverbank). The results showed that in plot I, L. secalinus tended to have slender roots and stems and small leaves, with a biomass allocation strategy that maximized the root–shoot ratio (RSR). In plot II, L. secalinus had thick stems and moderate leaf and root patterns, and the RSR values were between those of plot I and plot III. In plot III, L. secalinus had thin and short stems and large leaves; furthermore, among the root morphological structures, plot III had the shortest Rhizome length (RL) and longest Rhizome diameter (RD), and the RSR was the lowest. Moreover, there was a significant correlation between organ biomass and leaf thickness, stem length, RD, and RL in the three habitats (p < 0.05). By balancing the biomass allocation among organs, wetland plants in floodplains balance changes in root, stem, and leaf morphological characteristics to improve their environmental adaptation.

Effects of Drought Stress on Leaf Functional Traits and Biomass Characteristics of Atriplex canescens.

Drought is a critical factor constraining plant growth in arid regions. However, the performance and adaptive mechanism of Atriplex canescens (A. canescens) under drought stress remain unclear. Hence, a three-year experiment with three drought gradients was performed in a common garden, and the leaf functional traits, biomass and biomass partitioning patterns of A. canescens were investigated. The results showed that drought stress had significant effects on A. canescens leaf functional traits. A. canescens maintained the content of malondialdehyde (MDA) and the activity of superoxide dismutase (SOD), but the peroxidase (POD) and catalase (CAT) activity decreased, and the content of proline (Pro) and soluble sugar (SS) increased only under heavy drought stress. Under drought stress, the leaves became smaller but denser, the specific leaf area (SLA) decreased, but the dry matter content (LDMC) maintained stability. Total biomass decreased 60% to 1758 g under heavy drought stress and the seed and leaf biomass was only 10% and 20% of non-stress group, but there had no significant difference on root biomass. More biomass was allocated to root under drought stress. The root biomass allocation ratio was doubled from 9.62% to 19.81% under heavy drought, and the root/shoot ratio (R/S) increased from 0.11 to 0.25. The MDA was significantly and negatively correlated with biomass, while the SPAD was significantly and positively correlated with total and aboveground organs biomass. The POD, CAT, Pro and SS had significant correlations with root and seed allocation ratio. The leaf morphological traits related to leaf shape and weight had significant correlations with total and aboveground biomass and biomass allocation. Our study demonstrated that under drought stress, A. canescens made tradeoffs between growth potential and drought tolerance and evolved with a conservative strategy. These findings provide more information for an in-depth understanding of the adaption strategies of A. canescens to drought stress and provide potential guidance for planting and sustainable management of A. canescens in arid and semi-arid regions.

Belowground plant competition: uncoupling root response strategies of peas.

Belowground plant competition has been shown to induce varying responses, from increases to decreases in root biomass allocation or in directional root placement. Such inconsistencies could result from the fact that root allocation and directional growth were seldom studied together, even though they might represent different strategies. Moreover, variations in belowground responses might be due to different size hierarchies between plants, but this hypothesis has not been studied previously. In a greenhouse rhizobox experiment, we examined the way both root allocation and directional root placement of Pisum sativum are affected by the size and density of Festuca glauca neighbours, and by nutrient distribution. We found that root allocation of P. sativum increased with the density and size of F. glauca. By contrast, directional root placement was unaffected by neighbour size and increased either towards or away from neighbours when nutrients were patchily or uniformly distributed, respectively. These results demonstrate that directional root placement under competition is contingent on the distribution of soil resources. Interestingly, our results suggest that root allocation and directional placement might be uncoupled strategies that simultaneously provide stress tolerance and spatial responsiveness to neighbours, thus highlighting the importance of measuring both when studying belowground plant competition.

Ecosystem engineers can regulate resource allocation strategies in associated plant species.

Balancing the biomass requirements of different functions for the purpose of population reproduction and persistence can be challenging for alpine plants due to extreme environmental stresses from both above- and below-ground sources. The presence of ecosystem engineers in alpine ecosystems effectively alleviates microenvironmental stresses, hence promoting the survival and growth of other less stress-tolerant species. However, the influence of ecosystem engineers on plant resource allocation strategies remains highly unexplored. In this study, we compared resource allocation strategies, including biomass accumulation, reproductive effort (RE), root fraction (RF), as well as relationships between different functions, among four alpine plant species belonging to Gentianaceae across bare ground, tussock grass-, cushion-, and shrub-engineered microhabitats. Shrub-engineered microhabitats exerted the strongest effects on regulating plant resource allocation patterns, followed by tussock grass- and cushion-engineered microhabitats. Additionally, apart from microhabitats, population background and plant life history also significantly influenced resource allocation strategies. Generally, plants established within engineered microhabitats exhibited higher biomass accumulation, as well as increased flower, leaf and stem production. Furthermore, individuals within engineered microhabitats commonly displayed lower RF, indicating a greater allocation of resources to above-ground functions while reducing allocation to root development. RE of annual plants was significantly higher than that of perennial plants. However, individuals of annual plants within engineered microhabitats showed lower RE compared to their counterparts in bare ground habitats; whereas perennial species demonstrated similar RE between microhabitat types. Moreover, RE was generally independent of plant size in bare-ground habitats but exhibited size-dependency in certain populations for some species within specific engineered microhabitat types. However, size-dependency did exist for absolute reproductive and root biomass allocation in most of the cases examined here. No trade-offs were observed between flower mass and flower number, nor between leaf mass and leaf number. The capacity of ecosystem engineers to regulate resource allocation strategies in associated plants was confirmed. However, the resource allocation patterns resulted synergistically from the ecosystem engineering effects, population environmental backgrounds, and plant life history strategies. In general, such regulations can improve individual survival and reproductive potential, potentially promoting population persistence in challenging alpine environments.

Effects of Salt Stress on Salt-Repellent and Salt-Secreting Characteristics of Two Apple Rootstocks.

The effects of NaCl-induced salinity on biomass allocation, anatomical characteristics of leaves, ion accumulation, salt repellency, and salt secretion ability were investigated in two apple rootstock cultivars (Malus halliana '9-1-6' and Malus baccata), which revealed the physiological adaptive mechanisms of M. halliana '9-1-6' in response to salt stress factors. This experiment was conducted in a greenhouse using a nutrient solution pot. Salt stress was simulated by treating the plants with a 100 mM NaCl solution, while 1/2 Hoagland nutrient solution was used as a control (CK) instead of the NaCl solution. The results showed that the two rootstocks responded to salt environments by increasing the proportion of root biomass allocation. According to the stress susceptibility index, '9-1-6' exhibits a lower salt sensitivity index and a higher salt tolerance index. The thickness of the leaf, upper and lower epidermis, palisade tissue, and mesophyll tissue compactness (CTR) of the two rootstocks were significantly decreased, while the thickness of sponge tissue and mesophyll tissue looseness (SR) were significantly increased, and the range of '9-1-6' was smaller than that of M. baccata. With an extension of stress time, the accumulation of Na+ increased significantly, and the accumulation of K+ decreased gradually. The stem and leaves of '9-1-6' showed a lower accumulation of Na+ and a higher accumulation of K+, and the roots displayed a higher ability to reject Na+, as well as young and old leaves showed a stronger ability to secrete Na+. In conclusion, within a certain salt concentration range, the '9-1-6' root part can maintain lower salt sensitivity and a higher root-to-shoot ratio by increasing the proportion of root biomass allocation; the aerial part responds to salt stress through thicker leaves and a complete double-layer fence structure; the roots and stem bases can effectively reduce the transportation of Na+ to the aerial parts, as well as effectively secrete Na+ from the aerial parts through young and old leaves, thereby maintaining a higher K+/Na+ ratio in the aerial parts, showing a strong salt tolerance.

Nitrogen and phosphorus availability alters tree‐grass competition intensity in savannas

Abstract Plant essential macronutrients like nitrogen (N) and phosphorus (P) can limit savanna tree growth and are important determinants of savanna vegetation dynamics, along with rainfall, fire and herbivory. How nitrogen and phosphorus shape tree‐grass competition and their coexistence remain unclear, hindering our ability to predict how savannas may respond to altered nutrient cycling. Here, we evaluate (1) if trees and grasses respond differently to N versus P availability, or (2) if grasses are more competitive in low nutrient environments while trees are more competitive in high nutrient environments. To do this, we grew saplings of 6 tree and 1 grass species from the Kruger National Park, South Africa, for 16 weeks under fully factorial nutrient and competition treatments (with/without competitors, low/high rate of N supply and low/high rate of P supply) under a watering regime designed to mimic wet season rainfall in a mesic savanna. Trees and grasses foraged most aggressively for nitrogen and allocated biomass differently depending on nitrogen availability. Overall, tree growth decreased in competition with grass, even in high nutrient environments where they grew faster. Grasses were always better below‐ground competitors, utilising aggressive nutrient foraging strategies, including high root phosphatase activity in response to nitrogen and large root biomass allocation. Synthesis. In low nutrient environments (e.g. on nutrient‐poor sandy soils), nutrients may limit tree growth. Nutrient rich environments enable tree growth, but grasses continue to compete effectively with trees. Understanding what this means for ecosystem responses to nutrient availability is not trivial, especially in the context of fire and herbivory. However, it is clear that soil nutrients likely affect tree and grass growth and competition in savannas, which suggests that future changes in nutrient cycling, such as N deposition, may have important effects on savanna vegetation.

Nutrient Dynamics in a Coupled Terrestrial Biosphere and Land Model (ELM‐FATES‐CNP)

AbstractWe present a representation of nitrogen and phosphorus cycling in the Functionally Assembled Terrestrial Ecosystem Simulator, a demographic vegetation model within the Energy Exascale Earth System land model. This representation is modular, and designed to allow testing of multiple hypothetical approaches for carbon‐nutrient coupling in plants. Novel model hypotheses introduced in this work include, (a) the controls on plant acquisition of aqueous mineralized nutrients in the soil and (b) fairly straight forward methods of allocating nutrients to specific plant organs and their losses through live plant turnover as well as litter fluxes generated through plant mortality. This combines the new with pre‐existing hypotheses (such as nitrogen fixation and soil decomposition) into a system that can accommodate plant‐soil dynamics for a large number of size‐ and functional‐type‐resolved plant cohorts within a time‐since‐disturbance‐resolved ecosystem. Root uptake of nutrients is governed by fine root biomass, and plants vary in their fine root biomass allocation in order to balance carbon and nutrient limitations to growth. We test the sensitivity of the model to a wide range of parameter variations and structural representations, and in the context of observations at Barro Colorado Island, Panama. A key model prediction is that plants in the high‐light‐availability canopy positions allocate more carbon to fine roots than plants in low‐light understory environments, given the widely different carbon versus nutrient constraints of these two niches within a given ecosystem. This model provides a basis for exploring carbon‐nutrient coupling with vegetation demography within Earth system models.

Bornean tropical forests recovering from logging at risk of regeneration failure.

Active restoration through silvicultural treatments (enrichment planting, cutting climbers and liberation thinning) is considered an important intervention in logged forests. However, its ability to enhance regeneration is key for long-term recovery of logged forests, which remains poorly understood, particularly for the production and survival of seedlings in subsequent generations. To understand the long-term impacts of logging and restoration we tracked the diversity, survival and traits of seedlings that germinated immediately after a mast fruiting in North Borneo in unlogged and logged forests 30-35 years after logging. We monitored 5119 seedlings from germination for ~1.5 years across a mixed landscape of unlogged forests (ULs), naturally regenerating logged forests (NR) and actively restored logged forests via rehabilitative silvicultural treatments (AR), 15-27 years after restoration. We measured 14 leaf, root and biomass allocation traits on 399 seedlings from 15 species. Soon after fruiting, UL and AR forests had higher seedling densities than NR forest, but survival was the lowest in AR forests in the first 6 months. Community composition differed among forest types; AR and NR forests had lower species richness and lower evenness than UL forests by 5-6 months post-mast but did not differ between them. Differences in community composition altered community-weighted mean trait values across forest types, with higher root biomass allocation in NR relative to UL forest. Traits influenced mortality ~3 months post-mast, with more acquisitive traits and relative aboveground investment favoured in AR forests relative to UL forests. Our findings of reduced seedling survival and diversity suggest long time lags in post-logging recruitment, particularly for some taxa. Active restoration of logged forests recovers initial seedling production, but elevated mortality in AR forests lowers the efficacy of active restoration to enhance recruitment or diversity of seedling communities. This suggests current active restoration practices may fail to overcome barriers to regeneration in logged forests, which may drive long-term changes in future forest plant communities.

Urban Dominant Trees Followed the Optimal Partitioning Theory and Increased Root Biomass Allocation and Nutrient Uptake under Elevated Nitrogen Deposition

Nitrogen (N) is one of the limiting nutrients for plant growth and metabolism in terrestrial ecosystems. Numerous studies have explored the effects of N addition on the eco-physiological traits and biomass production of plants, but the underlying mechanism of how N deposition influences biomass allocation patterns remains controversial, especially for urban greening trees. A greenhouse experiment was conducted for 7 months, using two dominant tree species of urban streets in North China, including the coniferous tree species Pinus tabuliformis and the broadleaved tree Fraxinus chinensis, under three levels of N addition: ambient, low N addition, and high N addition (0, 3.5, and 10.5 gN m−2 year−1). The plant growth, biomass distribution, functional traits, and soil nutrient properties of the two trees were determined. Overall, N addition had positive effects on the aboveground and belowground biomass of P. tabuliformis, which also shifted its functional traits to an acquisitive strategy, while F. chinensis only increased root biomass distribution and fast traits as N increased. Furthermore, N supply increased the soil N and phosphorus availability of both trees and improved their root nutrient uptake capacity, resulting in an increase in their root–shoot ratio. Optimal partitioning theory could better explain why trees would invest more resources in roots, changing root structure and nutrient uptake, thus increasing root biomass allocation to adapt to a resource-poor environment. These findings highlight the importance of plant functional traits in driving the responses of biomass allocation to environmental changes for urban greening dominant tree species and could help to come up with new tree growth strategies in silvicultural practice for urban green space.

Do winter and summer cohorts of the invasive weed Parthenium hysterophorus differ in seed germination and seedling growth?

AbstractThe highly invasive weed Parthenium hysterophorus flowers during both hot, humid summers and cold, dry winters in Nepal, yet it remains unknown if there are differences in seed germination and seedling growth during these contrasting seasons. We analysed seed germination and seedling growth of summer and winter cohorts of P. hysterophorus in Kathmandu Valley. Seeds were germinated at low (25/15°C) and high (30/20°C) temperatures, 12/12 h photoperiod and complete dark, and at different levels of water stress. Seedlings were grown in a greenhouse to determine biomass allocation and relative growth rate (RGR). Winter seeds had higher seed biomass than summer seeds, and both seed types germinated under complete dark and 12/12 h photoperiod. Summer seeds germinated at significantly lower rates and percentage than winter seeds at the low temperature, but this difference in germination was not present when summer and winter seeds were incubated at the high temperature. Winter seeds had higher germination (percentage and rate) and took a longer time to reach maximum germination than summer seeds at different levels of water stress. Seedling emergence of both seed types declined with increasing soil depth. Seedling RGRs were nearly equal (summer: 73 mg g−1 day−1, winter: 77 mg g−1 day−1). Biomass allocation to stem and leaves were similar in both cohorts but root biomass allocation was higher in the winter than in the summer cohort. Overall, the maternal environmental effect was moderate on seed germination, and weak on seedling growth. Lack of a pronounced difference in the germination and seedling growth of summer and winter cohorts of P. hysterophorus suggests a wide environmental tolerance of the species, and this could be one of the reasons for the species' ability to invade diverse climatic and geographic regions globally.

Persistence of Root Exudates of Sorghum bicolor and Solidago canadensis: Impacts on Invasive and Native Species.

Root exudates of the invasive Solidago canadensis and the cereal crop Sorghum bicolor (L.) Moench cv. 'Hybridsorgo' were tested for allelopathic interactions against native and invasive plant species in a controlled environment. After the surface was sterilized, the seeds of two invasive species (Bromus sterilis and Veronica persica) and two native species (Youngia japonica and Rumex acetosa) were germinated and transplanted into the soil (1:1 mixture of coco peat and sand) that had been conditioned for one month by the cultivation of Solidago canadensis and Sorghum bicolor, both in combination or as unplanted controls. After an additional eight weeks of growth, morphometric measurements of the shoot and root, including foliar characteristics and above- and below-ground biomass accumulation, were performed. The results revealed significant inhibitory effects of root exudates released by Sorghum bicolor and Solidago canadensis on native species' productivity and physiology. The invasive species exhibited variable growth responses, with Veronica persica showing reduced shoot and root expansion, but Bromus sterilis revealed increased shoot and root biomass allocation and nutrition under the exudate treatments. Exudates from Solidago canadensis and Sorghum bicolor together showed synergistic negative effects on native species, while they promoted growth and nutrition in Veronica persica. Taken together, the differential species responses indicate that the tested native species were more sensitive to the allelopathic compounds than the invasive species, which is in line with the theory of novel weapons. The legacy effects of root exudates of both Sorghum bicolor and Solidago canadensis could promote invasive establishment through imposing allelochemical interference competition against native plant species. Understanding the specific allelopathic mechanisms may help with the development of integrated strategies for managing invasive species.

Ozone enrichment and drought stress have more negative effects on invasive leguminous woody species than co-occurring native species

Ozone (O3) enrichment and drought stress are common phenomenon of global climate change. However, it remains unknown to what extent these factors might affect leguminous woody plant species invasion. In an open-top chamber (OTC) experiment, we grew four congeneric pairs of invasive and native woody plant species under two levels of O3 concentrations (ambient vs. elevated) and water conditions (dry vs. wet). We studied the effects of O3 enrichment and drought stress on the biomass, biomass allocation and leaf number of these four pairs of invasive vs. native woody species that are common in temperate forests. The results showed that O3 enrichment and drought stress alone reduced the total biomass of invasive woody species significantly greater than those of co-occurring native species. Moreover, O3 enrichment reduced the root biomass allocation of invasive species significantly more than that of native species. Under elevated O3 environments, the ratio of damaged leaves to total leaves for invasive species was 22.6% and 33.9%, and for native species was 13.9% and 24.4%, under dry and wet conditions, respectively. Results suggested that negative effects of O3 enrichment on plants was alleviated under drought conditions, and such negative effects on invasions of woody plant species were both detected from biomass allocation and visible foliar injury perspectives. Our study demonstrated that elevated O3 and drought stress have stronger adverse effects on invasive woody species than that co-occurring native species. The invasive woody plant species may be facilitated for invasion to the areas with lower O3 concentration or higher precipitation.

Effects of Tree Competition on Biomass Allocation of Stump and Coarse Roots of Larix olgensis of Different Site Classes

Site class is a quantitative indicator used to evaluate site quality. It reflects site conditions, mainly climate, the suitability of soil for tree species and soil fertility. Despite the economic and ecological importance of tree competition and site class in sustainable forest management, there has been little research on its impact on the stump and coarse root biomass allocation within plantations. The stump and coarse roots were divided into five components ((stump disc (SD), stump knot (SK), coarse roots (>10 cm in diameter) (CR1), medium coarse roots (5–10 cm) (CR2) and fine coarse roots (2–5 cm) (CR3)), and the biomass of each component was obtained via the weighing method. It was found that the biomass of SD, CR1, CR2 and CR3 was mainly affected by competition (p ≤ 0.01). In the three site classes, the biomass of CR3 increased significantly with the increase in the competition index (CI) (p < 0.01); the biomass of CR1 decreased gradually. In site V, the biomass of SK, sapwood and heartwood increased significantly with the increase in CI. The results show that competition affects the allocation of stump and coarse root biomass mainly by changing the coarse root biomass. The development of stump knots is greatly influenced by site class. This study provides a reference for solving the competition mechanism underlying larch wood forest development, which will in turn promote more effective utilization of larch wood forests. This study also provides a scientific basis for accurately estimating the belowground biomass and carbon storage of artificial plantation forests.

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.

Changes in mass allocation play a more prominent role than morphology in resource acquisition of the rhizomatous Leymus chinensis under drought stress.

Plants can respond to drought by changing their relative investments in the biomass and morphology of each organ. The aims of this study were to quantify the relative contribution of changes in morphology vs. allocation and determine how they affect each other. These results should help us understand the mechanisms that plants use to respond to drought events. In a glasshouse experiment, we applied a drought treatment (well-watered vs. drought) at early and late stages of plant growth, leading to four treatment combinations (well-watered in both early and late periods, WW; drought in the early period and well-watered in the late period, DW; well-watered in the early period and drought in the late period, WD; drought in both early and late periods, DD). We used the variance partitioning method to compare the contribution of organ (leaf and root) biomass allocation and morphology to the leaf area ratio, root length ratio and root area ratio, for the rhizomatous grass Leymus chinensis (Trin.) Tzvelev. Compared with the continuously well-watered treatment, the leaf area ratio, root length ratio and root area ratio showed increasing trends under various drought treatments. The contribution of leaf mass allocation to leaf area ratio differed among the drought treatments and was 2.1- to 5.3-fold greater than leaf morphology, and the contribution of root mass allocation to root length ratio was ~2-fold greater than that of root morphology. In contrast, root morphology contributed more to the root area ratio than biomass allocation under drought in both the early and late periods. There was a negative correlation between the ratio of leaf mass fraction to root mass fraction and the ratio of specific leaf area to specific root length (or specific root area). This study suggested that organ biomass allocation drove a larger proportion of variation than morphological traits for the absorption of resources in this rhizomatous grass. These findings should help us understand the adaptive mechanisms of plants when they are confronted with drought stress.

Effects of benthic fish and light regimes on water quality and the growth of Vallisneria natans with two sediment types.

In shal low eutrophic lakes, submersed macrophytes are essential for maintaining a clear water state and they are significantly affected by benthic fish disturbance, light availability, and sediment types. We conducted a mesocosm experiment with benthic fish (Misgurnus anguillicaudatus), two light regimes, and submerged macrophyte (Vallisneria natans) growing in two sediment types to investigate the ecological effects of benthic fish and light regimes on water quality and the growth of submersed macrophyte. Our findings indicated that the benthic fish increased the concentrations of total nitrogen, total phosphorus, and total dissolved phosphorus in the overlying water. The effects of benthic fish on ammonia-nitrogen (NH4+-N) and chlorophyll a (Chl-a) contents were related to light regimes. Fish disturbance indirectly promoted the growth of macrophytes growing in sand by increasing NH4+-N content in overlying water. However, the increasing Chl-a content stimulated by fish disturbance and high light regime reduced the growth of submersed macrophytes growing in clay due to shading. Macrophytes with different sediments had different strategies coping with light. Plants growing in sand responded to low light mainly by adjusting the leaf and root biomass allocation, whereas plants growing in clay responded to low light by physiologically adjusting the soluble carbohydrate content. The findings of this study might help restore lake vegetation to some degree, and using nutrient-poor sediment might be an appropriate method to avoid the detrimental effects of fish-mediated disturbances on the growth of submerged macrophytes.

Overcompensation of ecosystem productivity following sustained extreme drought in a semiarid grassland.

Drought events are projected to be more extreme and frequent in the future and have profound influences on the structure and functions of terrestrial ecosystems. Thus, better understanding the mechanisms of recovery is critical for predicting the future dynamics of terrestrial ecosystems. We performed a 7-year field precipitation experiment to examine recovery of a grassland ecosystem from different magnitudes of sustained drought, from slight to extreme. The ecosystem was exposed to precipitation treatments in the first 3 years (2010-2012) and recovered during the last 4 years (2013-2016) without precipitation treatments. Overall, large reductions of aboveground net primary productivity (ANPP, -43.3%) and perennial forb biomass (-83.1%) were observed in the third year (2012) of extreme drought only. Nevertheless, ANPP fully recovered within 1 year after the drought treatments were terminated, and the rapid recovery was mainly due to increased soil total nitrogen and root biomass allocation after drought. Surprisingly, large increases of ANPP under the extreme drought treatment occurred during the recovery periods from 2013 to 2015 (+74.1, +88.5, and +119.8 g m-2 year-1 ) compared to the control. The overcompensation offset the extreme drought-induced reduction of ANPP in the treatment years and was primarily ascribed to the enhanced biomass of perennial grasses (PG). Higher resistance to drought and fast resource acquisition strategy might drive the rapid recovery and expansion of PG. Our findings revealed the rapid recovery of grasslands and the critical role of community overcompensation in maintaining grassland ecosystem function and stability under future climate change scenarios.