Below-ground Biomass Partitioning Research Articles

Genotypic stability in root system architecture and aboveground biomass revealed diverse adaptability of peanut (Arachis hypogaea L.) to moderate water deficit

AbstractMany crop species, including cultivated peanut (Arachis hypogaea L.), modify their above‐ and below‐ground growth to cope with water deficit stress. This acclimation to water deficit often triggers a biomass partitioning shift—allocating more biomass to the roots, to increase the accessibility of roots to water resources. However, additional carbon partitioning to roots may not always translate into increased water use and maintenance of aboveground biomass (ABM) and yield. Therefore, selecting an efficient root system architecture (RSA) should aim to sustain a high ABM production under a water deficit scenario. To better understand the associations of above and belowground biomass partitioning under moderate water deficit, this study evaluated the genotypic stability of 40 peanut genotypes in ABM and RSA in greenhouse experiments and further assessed genotypic differences in 4 site‐year field experiments. Our results suggested that higher ABM‐producing genotypes generally had high plasticity when subjected to water deficit whereas the low ABM‐producing genotypes had relatively high stability. Hierarchical clustering analysis further revealed that genotypes with a high root‐to‐shoot ratio potentially had increased genotypic stability in ABM underwater deficit. Interestingly, genotypes that maintained the highest ABM underwater deficit did not have the highest total root biomass and length. Instead, these genotypes had the highest root length in the top layer of soil (0–0.3 m) and relatively fewer roots in the deeper layer of soil (0.3–1 m). Greenhouse‐screened stable genotypes exhibited minimal yield reduction when subjected to mid‐season water deficit in some of the field validation experiments, but it also happened to some plastic genotypes, indicating that further validation of controlled environment screenings for genotypic water‐deficit tolerance in the field is necessary.

Breeding crops for enhanced roots to mitigate against climate change without compromising yield

Boosting soil carbon by adding it to the soil, is among climate mitigation strategies. In a viewpoint more than a decade ago, Kell (2011) proposed plant breeding as a tool to develop varieties with larger underground biomass as a method to store carbon in the soil and reverse the trends of increasing atmospheric CO2 concentrations. To this date, the only evidence showing breeding for root traits is in rice. Wheat is well suited to serve this purpose because it is an important crop for food security and is the crop with highest cultivated area in the world. In this study, we developed breeding populations by crossing ‘Penny’ (a donor parent with large root) and ‘Yecora’ (a small root cultivar). Aboveground and belowground biomass partitioning, carbon content, and grain weight were studied in soil under controlled environment. Selection candidates differed significantly for all traits except carbon content. Broad-sense heritability for shoot biomass was 0.75 and for all other traits were equal or above 0.94. The root biomass ranged 0.43–7.72 g, averaging 2.13 g. A considerable range of root/shoot ratio was observed the selection candidates from 0.029 to 0.341, averaging 0.10. Based on LSD test, 13 out of 23 progenies tested in the replicated experiment, had significantly greater root biomass than ‘Yecora’. Among those, there were lines that produced equal or greater grain weight than “Yecora”. BC2 129, for example, showed 8.6-folds greater root biomass compared with ‘Yecora’ yet produced grain weight with no significant difference with that of ‘Yecora’. Similarly, BC2 147, BC2 165, BC2 137, showed 3.1-folds, 2.4-folds, 2.3-folds, respectively, greater root biomass but similar grain weights compared with ‘Yecora’. These lines showed significantly greater root/shoot ratios. Roots collected at physiological maturity showed 40.2%, on average, carbon content per dry biomass. This study showed that given one cycle of breeding involving a donor germplasm from genebank wheat root system can be manipulated to develop germplasm for grain production and simultaneously mitigating climate change by allocating more carbon in soil.

Biomass, Carbon and Nitrogen Partitioning and Water Use Efficiency Differences of Five Types of Alpine Grasslands in the Northern Tibetan Plateau.

(1) Background: Grassland covers most areas of the northern Tibetan Plateau along with important global terrestrial carbon (C) and nitrogen (N) pools, so there is a need to better understand the different alpine grassland growth associated with ecosystem C, N storage and water use efficiency (WUE). (2) Methods: The plant biomass and C, N concentrations, stocks and vegetation WUE of five kinds of alpine grassland types were investigated in northern Tibetan Plateau. (3) Results: The results showed that there were significant differences among five types of alpine grasslands in aboveground biomass (AGB), belowground biomass (BGB), total biomass (TB) and root:shoot (R/S) ratio while the highest value of different indices was shown in alpine meadow type (AM). The AGB and BGB partitioning results significantly satisfied the allometric biomass partitioning theory. The C, N concentrations and C/N of the vegetation in AGB and BGB showed significant grassland type differences. The highest C, N stocks of BGB were in AM which was almost six or seven times more than the C, N stocks of AGB in alpine desert type (AD). There were significant differences in δ13C and intrinsic water use efficiency (WUEi) under five alpine grassland types while the highest mean values of foliar δ13C and WUEi were in AD. Significant negative correlations were found between WUEi and C, N concentrations, C/N of AGB and soil water content (SWC) while the correlation with BGB C/N was not significant. For AGB, BGB, TB and R/S, there were positive correlations with C, N concentrations of AGB, BGB and SWC while it had significant negative correlations with C/N of BGB. (4) Conclusions: With regard to its types, it is suggested that the AM or AS may be an actively growing grassland type in the northern Tibetan Plateau.

Shrubland biomass and root-shoot allocation along a climate gradient in China

Background – Shrublands are receiving increasing attention because of climate change. However, knowledge about biomass allocation of shrublands at the community level and how this is regulated by climate is of limited availability but critical for accurately estimating carbon stocks and predicting global carbon cycles. Methods – We sampled 50 typical shrublands along a climate gradient in China and investigated the biomass allocation of shrubland at the community level and the effect of climate on biomass allocation. Shrub biomass was estimated using species-specific allometric relationships and the biomass of understory herbs was collected by excavating the whole plant. Regression analysis was used to examine the relationships between the biomass and the climate factors. RMA were conducted to establish the allometric relationships between the root and the shoot biomass at the community level.Key results – Shoot, root, and total biomass of shrub communities across different sites were estimated with median values of 206.5, 145.8, and 344.5 g/m2, respectively. Shoot, root, and total biomass of herb communities were estimated at 68.2, 58.9, and 117.2 g/m2, respectively. The median value of the R/S ratio of shrub communities was 0.58 and that of herb communities was 0.84. The R/S ratio of the shrub community showed a negative relationship with mean annual temperature and mean annual precipitation and a positive relationship with total annual sunshine and the aridity index. The R/S ratio of the herb community however showed a weak relationship with climate factors. Shoot biomass of the shrub community was nearly proportional to root biomass with a scaling exponent of 1.17, whereas shoot biomass of the herb community was disproportional to root biomass with a scaling exponent of 2.1.Conclusions – In shrublands, root biomass was more affected than shoot biomass by climate factors and this is related to water availability as a result of biomass allocation change of the shrub community. The understory herb community was less affected by climate due to the modification of the overstory–understory interaction to the climate-induced biomass allocation pattern. Shoot biomass of shrubs scales isometrically with root biomass at the community level, which supports the isometric theory of above-ground and below-ground biomass partitioning.

Altitudinal pattern of shrub biomass allocation in Southwest China.

Shrubs play an important role in the global carbon cycle and are particularly sensitive to climate change. However, the altitudinal pattern of biomass allocation in mountainous shrubs and its responses to climate change are still unclear. In this study, biomass accumulation and allocation of the shrub community and their relationships with climatic factors were investigated in 331 sampling sites along an extensive altitudinal gradient (311–4911 m) in Southwest China. The results showed that the above-ground biomass (AGB) and the total biomass (TB) of the shrub community decreased quadratically (R2 = 0.107) and linearly (R2 = 0.024) from 9.86 to 0.15 kg·m-2 and 15.61 to 0.26 kg·m-2 with increasing altitude, respectively. However, the below-ground biomass (BGB) and TB of the herb layer increased quadratically with increasing altitudes (R2 = 0.136 and 0.122, respectively. P<0.001). The root/shoot ratio (R/S) of the community and its component synusiae increased gradually with increasing altitudes (P<0.001). The standardized major axis (SMA) indicated an isometric relationship between AGB and BGB for the whole shrub community, but allometric relationships were found for the shrub and herb layer. Redundancy analysis and Pearson correlation analysis showed that the biomass and R/S were significantly correlated with mean annual temperature (MAT), mean annual precipitation (MAP) and reconnaissance drought index (RDI). These findings indicate that shrub biomass allocation is strongly affected by the altitude, MAT and MAP and support the isometric relationship of AGB and BGB partitioning at the community level on mountainous shrub biomes.

The Influence of Three Years of Supplemental Nitrogen on Above- and Belowground Biomass Partitioning in a Decade-Old Miscanthus × giganteus in the Lower Silesian Voivodeship (Poland)

Because of the different opinions regarding nitrogen (N) requirements for Miscanthus × giganteus biomass production, we conducted an experiment with a set dose of nitrogen. The objective of this study was to examine the effects of nitrogen fertilization on the biomass yield, water content, and morphological features of rhizomes and aboveground plant parts in various terms during a growing season over the course of three years (2014–2016) in Lower Silesia (Wroclaw, Poland). The nitrogen fertilization (dose 60 kg/ha and control) significantly affected the number of shoots (p = 0.0018), the water concentration of rhizomes (p = 0.0004) and stems (p = 0.0218), the dry matter yield of leaves (p = 0.0000), and the nitrogen uptake (p = 0.0000). Nitrogen fertilization significantly affected the nitrogen uptake in all plant parts (p = 0.0000). Although low levels of nitrogen appeared to be important in maintaining the maximum growth potentials of mature Miscanthus × giganteus, the small reductions in the above- and belowground biomass production are unlikely to outweigh the environmental costs of applying nitrogen. More studies should use the protocols for the above- and belowground yield determination described in this paper in order to create site- and year-specific fertilizer regimes that are optimized for quality and yield for autumn (green) and spring (delayed) harvests.

Ecological biomass allocation strategies in plant species with different life forms in a cold desert, China

Biomass allocation patterns among plant species are related to their adaptive ecological strategies. Ephemeral, ephemeroid and annual plant life forms represent three typical growth strategies of plants that grow in autumn and early spring in the cold deserts of China. These plants play an important role in reducing wind velocity in the desert areas. However, despite numerous studies, the strategies of biomass allocation among plant species with these three life forms remain contentious. In this study, we conducted a preliminary quadrat study during 2014–2016 in the southern part of the Gurbantunggut Desert, China, to investigate the allocation patterns of above-ground biomass (AGB) and below-ground biomass (BGB) at the individual level in 17 ephemeral, 3 ephemeroid and 4 annual plant species. Since ephemeral plants can germinate in autumn, we also compared biomass allocation patterns between plants that germinated in autumn 2015 and spring 2016 for 4 common ephemeral species. The healthy mature individual plants of each species were sampled and the AGB, BGB, total biomass (TB), leaf mass ratio (LMR) and root/shoot ratio (R/S) were calculated for 201 sample quadrats in the study area. We also studied the relationships between AGB and BGB of plants with the three different life forms (ephemeral, ephemeroid and annual). The mean AGB values of ephemeral, ephemeroid and annual plants were 0.806, 3.759 and 1.546 g/plant, respectively, and the mean BGB values were 0.106, 4.996 and 0.166 g/plant, respectively. The mean R/S value was significantly higher in ephemeroid plants (1.675) than in ephemeral (0.154) and annual (0.147) plants. The mean LMR was the highest in annual plants, followed by ephemeroid plants and ephemeral plants, reflecting the fact that annual plants allocate more biomass to leaves, associated with their longer life span. Biomass of ephemeral plants that germinated in autumn was significantly higher than those of corresponding plants that germinated in spring in terms of AGB, BGB and TB. However, the R/S value was similar in plants that germinated in autumn and spring. The slope of regression relationship between AGB and BGB differed significantly among the three plant life forms. These results support different biomass allocation hypotheses. Specifically, at the individual level, the AGB and BGB partitioning supports the allometric hypothesis for ephemeroid and annual plants and the isometric hypothesis for ephemeral plants.

INCREASED CARBON LOSS VIA ROOT RESPIRATION AND IMPAIRED ROOT MORPHOLOGY UNDER FREE-AIR OZONE ENRICHMENT ADVERSELY AFFECT RICE (ORYZA SATIVA L.) PRODUCTION

SUMMARYThe increasing tropospheric ozone concentration [O3] strongly affects plant growth. However, the response of belowground processes in rice (Oryza sativa L.) systems to higher O3 is not well understood. The grain production, belowground biomass partitioning, root morphology and activity of rice (cv. Shanyou 63) were investigated in a free-air O3 enrichment platform at four key growth stages. Elevated O3 (EO3, 50% above the ambient O3) significantly decreased the grain yield and total biomass at the grain milky mature stage, root biomass at the tillering stage and root to shoot ratios (RRS) at the flowering and grain filling stages. The effects of EO3 on root morphology and activity varied among rice growth stage. EO3 significantly decreased root length, density, area, diameter and volume at the flowering stage, but EO3 significantly decreased various root morphological indices at the tillering, grain filling and milky mature stages. EO3 significantly increased the specific root respiration rate (root activity) and root respiration rate (autotrophic respiration) at grain filling and milky mature stages. Higher root autotrophic respiration and lower RRS in response to EO3 would reduce allocation of assimilated carbon to root growth, adversely affecting rice productivity. Our findings are critical for understanding the O3-induced impairment of belowground processes and carbon cycling in rice cropping systems and breeding of O3-tolerant cultivars under higher [O3] scenarios.

Above- and Belowground Biomass Allocation in Shrub Biomes across the Northeast Tibetan Plateau.

Biomass partitioning has been explored across various biomes. However, the strategies of allocation in plants still remain contentious. This study investigated allocation patterns of above- and belowground biomass at the community level, using biomass survey from the Tibetan Plateau. We explored above- and belowground biomass by conducting three consecutive sampling campaigns across shrub biomes on the northeast Tibetan Plateau during 2011–2013. We then documented the above-ground biomass (AGB), below-ground biomass (BGB) and root: shoot ratio (R/S) and the relationships between R/S and environment factors using data from 201 plots surveyed from 67 sites. We further examined relationships between above-ground and below-ground biomass across various shrub types. Our results indicated that the median values of AGB, BGB, and R/S in Tibetan shrub were 1102.55, 874.91 g m-2, and 0.85, respectively. R/S showed significant trend with mean annual precipitation (MAP), while decreased with mean annual temperature (MAT). Reduced major axis analysis indicated that the slope of the log-log relationship between above- and belowground biomass revealed a significant difference from 1.0 over space, supporting the optimal hypothesis. Interestingly, the slopes of the allometric relationship between log AGB and log BGB differed significantly between alpine and desert shrub. Our findings supported the optimal theory of above- and belowground biomass partitioning in Tibetan shrub, while the isometric hypothesis for alpine shrub at the community level.

Above- and below-ground biomass partitioning and fine root morphology in juvenile Sitka spruce clones in monoclonal and polyclonal mixtures

Six juvenile Sitka spruce (Picea sitchensis (Bong.) Carr) clones were grown in monoclonal (pure) and polyclonal mixtures (mixed) in a field experiment to assess effects of clonal diversity on above- and below-ground growth, biomass partitioning and fine root morphology. Shoot height and root collar diameter were measured twice annually and after the second year 48 clones were destructively harvested. Fine roots were divided into 10 diameter classes, for each of which morphological characteristics were calculated from digitized images. Competitive interactions arising from deployment type were found to significantly increase fine root surface area in mixed plots and fine root length in pure plots for two fine root diameter classes for some clones. Competitive interactions were also found to significantly alter relationships between above- and below-ground variables and reduce the strength and significance of relationships among root traits in mixed plots. Significant inter-clonal variation for many above- and below-ground parameters was also observed. The two most productive clones, in terms of height and diameter growth, differed significantly in biomass partitioning suggesting that a high degree of variation occurs among Sitka spruce clones, which may affect stand productivity and uniformity.

Comparing fast- and slow-growing provenances of Picea koraiensis in biomass, carbon parameters and their relationships with growth

Tree genetic selection programs are primarily focused on improving stem volume plantation productivity. Due to changes in climate and emergence of carbon (C) market, plantations are also being credited for total biomass productivity and C sequestration. Does growth selection adversely affect total above- and belowground biomass and C sequestration? We investigated this by comparing two fast-growing provenances (LS and CH) to a slow-growing provenance (KT) from a 31-year-old Picea koraiensis experiment. Results showed that (1) the fast-growing provenances could enhance both above- and belowground biomass productivity and carbon sequestration. On average, trees of LS and CH provenances produced 16.1% and 31.8% more biomass and had 17.2% and 31.8% more C stock, respectively, than KT provenance, although these differences were statistically non-significant (P<0.10). The fast-growing provenances displayed a comparable to or even slightly higher C concentration than KT provenance; (2) growth selection influenced biomass and C partitioning. Compared to KT, the CH and LS allocated relatively more to stem wood but less to the needles and branches aboveground and partitioned more to the stump and coarse roots but less to the fine and medium size roots belowground. The fast-growing provenances had a very similar or lower above- to belowground biomass partitioning slope. Thus, the superiority of the aboveground growth of LS and CH was not achieved at the expense of belowground compartments; and (3) the best function to predict biomass and C content was ‘a(DBH2H)b’. Fitting provenance-specific relationship parameter (a or b) improved prediction precision. This was particularly true for b and for the biomass of branches, aboveground and whole tree. Overall our results suggest the possibility of improving biomass productivity and C sequestration via planting growth-improved seed sources. Implications to tree improvement are discussed.

The effects of physiological integration on biomass partitioning in plant modules: an experimental study with the stoloniferous herb Glechoma hederacea

Morphological and physiological plasticity are crucial attributes enabling plants to acquire resources from heterogeneous habitats. Although physiological integration can modify biomass partitioning in modules, especially when connected modules experience different conditions, its ecological importance has been largely overlooked. This experiment examined its effects on above- and belowground biomass partitioning by modules in the stoloniferous herb Glechoma hederacea. We studied how biomass allocation to roots by younger ramets was affected by connection to older ramets, and by nutrient conditions. A lower proportion of biomass was allocated to roots by younger ramets growing under low nutrient (LN) conditions when connected to older ramets in high nutrient (HN) conditions than when they were isolated, demonstrating localised modification of biomass partitioning due to physiological integration. The proportion of biomass allocated to roots by younger ramets was also lower when connected to older ramets in HN conditions than when connected to older ramets in LN conditions. Thus, the effect of integration on biomass partitioning depended on the nutrient conditions experienced by connected ramets. Such changes in biomass partitioning would result in more extensive stolon growth, and greater lateral displacement of new ramets. Understanding the ecological implications of phenotypic plasticity in plants will require further examination of the effects of physiological integration when connected modules experience contrasting growing conditions. This study demonstrates that such integration affects the biomass allocation strategy of connected ramets, enhancing resource acquisition in heterogeneous habitats. The widespread success of clonality in many communities is likely to be strongly promoted by this characteristic.

Erratum to: Do chronic aboveground O3 exposure and belowground pathogen stress affect growth and belowground biomass partitioning of juvenile beech trees (Fagus sylvatica L.)?

Erratum to: Do chronic aboveground O3 exposure and belowground pathogen stress affect growth and belowground biomass partitioning of juvenile beech trees (Fagus sylvatica L.)?

Do chronic aboveground O3 exposure and belowground pathogen stress affect growth and belowground biomass partitioning of juvenile beech trees (Fagus sylvatica L.)?

The impact of chronic free air ozone (O3) exposure and belowground pathogen stress on growth and total biomass development of young beech trees (Fagus sylvatica L.) was investigated in a lysimeter study. Plants were growing during four years under ambient or elevated atmospheric O3 concentrations. Additionally, in the last vegetation period the root rot pathogen Phytophthora citricola was introduced to study the interaction of ozone exposure and pathogen stress in the soil-plant system. A complete harvest at the end of the experiment enabled for the first time the assessment of fine and coarse root biomass of individual trees with a high vertical resolution down to two meter depth. Plant growth was significantly reduced by elevated ozone but not affected by P. citricola. Biomass partitioning between fine and coarse roots as well as vertical root distribution were significantly affected by both factors, whereas changes in root/shoot biomass ratio were not observed.

Effects of herbivory on above- and below-ground biomass partitioning in two arid-zone dwarf shrubs

Biomass partitioning by arid-zone dwarf shrubs between above- and below-ground fractions could be influenced by plant adaptations to herbivory. The response of potted Indigofera spinosa and I. cliffordiana to heavy and moderate top defoliations, compared to non-defoliated controls, was investigated. Relative growth rates of plants (Weeks 1–8), number of lateral shoots (Weeks 5–13), total number of leaves and leaf area (at Week 13), clipped biomass (CB) at Weeks 8 and 11 as well as residual biomass (RB), total above-ground biomass (TAGB) (i.e. the sums of CB and RB) and total root biomass (TRB) by treatments at Week 13 were greater in I. cliffordiana than in I. spinosa. Clipping reduced the shoot-root ratio (S:R) in I. cliffordiana but not in I. spinosa. For I. spinosa, plants defoliated at moderate intensities produced more root biomass (22.9%) than at heavy regimes (17.6%) or the controls (12.9%). In I. cliffordiana, below-ground biomass as a fraction of the combined biomass was less in control plants (16.5%), compared to moderate (18.2%) and heavy defoliation treatments (26.5%). The two dwarf shrub species compensated at different intensities for above- and below-ground biomass: I. spinosa at moderate defoliations and I. cliffordiana at heavy defoliations.

Global allocation rules for patterns of biomass partitioning in seed plants.

A general allometric model has been derived to predict intraspecific and interspecific scaling relationships among seed plant leaf, stem, and root biomass. Analysis of a large compendium of standing organ biomass sampled across a broad sampling of taxa inhabiting diverse ecological habitats supports the relations predicted by the model and defines the boundary conditions for above- and below-ground biomass partitioning. These canonical biomass relations are insensitive to phyletic affiliation (conifers versus angiosperms) and variation in averaged local environmental conditions. The model thus identifies and defines the limits that have guided the diversification of seed plant biomass allocation strategies.