Belowground Biomass Allocation Research Articles

Biomass allocation and seasonal non-structural carbohydrate dynamics do not explain the success of tall forbs in short alpine grassland

The majority of alpine plants are of small stature. Through their small size alpine plants are decoupled from the free atmospheric circulation and accumulate solar heat. However, a few alpine species do not follow that “rule” and protrude with their aboveground structures from the microclimatic shelter of the main canopy boundary layer. We aim at explaining the phenomenon of being tall by exploring the biomass production and carbon relations of four pairs of small and tall phylogenetically related taxa in alpine grassland. We compared species and stature-specific biomass allocation, shifts in non-structural carbohydrate (NSC) concentrations in different tissues throughout the season, and we used 13C labels to track carbon transfer from leaves to belowground structures. Small and tall herbs did not differ in their above- to belowground biomass allocation. The NSC composition (starch, fructan, simple sugars) and allocation did not show a stature-specific pattern, except for higher concentrations of simple sugars in tall species during their extended shoot growth. In relative terms, tall species had higher NSC pools in rhizomes, whereas small species had higher NSC pools in roots. Our findings do not place tall alpine forbs in an exceptional category in terms of biomass allocation and carbohydrate storage. The tall versus small stature of the examined herbs does not seem to be associated with specific adjustments in carbon relations. 13C pulse labelling revealed early C autonomy in young, unfolding leaves of the tall species, which are thus independent of the carbon reserves in the massive belowground organs.

Changes of Aboveground and Belowground Biomass Allocation in Four Dominant Grassland Species Across a Precipitation Gradient.

Climate change is predicted to affect plant growth, but also the allocation of biomass to aboveground and belowground plant parts. To date, studies have mostly focused on aboveground biomass, while belowground biomass and allocation patterns have received less attention. We investigated changes in biomass allocation along a controlled gradient of precipitation in an experiment with four plant species (Leymus chinensis, Stipa grandis, Artemisia frigida, and Potentilla acaulis) dominant in Inner Mongolia steppe. Results showed that aboveground biomass, belowground biomass and total biomass all increased with increasing growing season precipitation, as expected in this water-limited ecosystem. Biomass allocation patterns also changed along the precipitation gradient, but significant variation between species was apparent. Specifically, the belowground biomass: aboveground biomass ratio (i.e., B:A ratio) of S. grandis was not impacted by precipitation amount, while B:A ratios of the other three species changed in different ways along the gradient. Some of these differences in allocation strategies may be related to morphological differences, specifically, the presence of rhizomes or stolons, though no consistent patterns emerged. Isometric partitioning, i.e., constant allocation of biomass aboveground and belowground, seemed to occur for one species (S. grandis), but not for the three rhizome or stolon-forming ones. Indeed, for these species, the slope of the allometric regression between log-transformed belowground biomass and log-transformed aboveground biomass significantly differed from 1.0 and B:A ratios changed along the precipitation gradient. As changes in biomass allocation can affect ecosystem functioning and services, our results can be used as a basis for further studies into allocation patterns, especially in a context of environmental change.

Integrating Arctic Plant Functional Types in a Land Surface Model Using Above‐ and Belowground Field Observations

AbstractAccurate simulations of high‐latitude ecosystems are critical for confident Earth system model (ESM) projections of carbon cycle feedbacks to global climate change. Land surface model components of ESMs, including the E3SM Land Model (ELM), simulate vegetation growth and ecosystem responses to changing climate and atmospheric CO2 concentrations by grouping heterogeneous vegetation into like sets of plant functional types (PFTs). Many such models represent high‐latitude vegetation using only two PFTs (shrub and grass), thereby missing the diversity of vegetation growth forms and functional traits in the Arctic. Here, we use field observations of biomass and leaf traits across a gradient of plant communities on the Seward Peninsula in northwest Alaska to replace the original ELM configuration for the first time with nine Arctic‐specific PFTs. The newly developed PFTs include: (1) nonvascular mosses and lichens, (2) deciduous and evergreen shrubs of various height classes, including an alder PFT, (3) graminoids, and (4) forbs. Improvements relative to the original model configuration included greater belowground biomass allocation, persistent fine roots and rhizomes of nonwoody plants, and better representation of variability in total plant biomass across sites with varying plant communities and depth to bedrock. Simulations through 2100 using the RCP8.5 climate scenario and constant PFT fractional areas showed alder‐dominated plant communities gaining more biomass and lichen‐dominated communities gaining less biomass compared to default PFTs. Our results highlight how representing the diversity of arctic vegetation and confronting models with measurements from varied plant communities improves the representation of arctic vegetation in terrestrial ecosystem models.

Non-structural carbohydrates stored in belowground organs point to the diversity in Amaranthaceae

Amaranthaceae is a cosmopolitan and diverse family, with characteristics that enable plants to occupy habitats with harsh environmental conditions. The Brazilian Cerrado has numerous features that impose challenges to plant survival, such as seasonal drought and fires. Nearly one hundred species of Amaranthaceae occur in the Cerrado and many of them have thickened belowground systems that store non-structural carbohydrates. In this study, we analyze patterns in the adaptive strategies of Amaranthaceae species that occur in the Cerrado, by assessing the types of carbohydrates stored in the belowground systems and biomass allocation in light of photosynthetic characteristics reported in the literature. We analyzed species of Amaranthus (C4), Alternanthera (C3-C4), Froelichia (C4), Gomphrena (C4), and Pfaffia (C3). All the analyzed species had non-structural carbohydrate content higher than 20% of the dry mass. Sucrose was the main non-structural carbohydrate found in the belowground organs of Alternanthera tenella and Amaranthus viridis. Starch was detected only in Amaranthus viridis. All other species accumulate fructans; Pfaffia spp. have inulin-type fructans while Gomphrena and Froelichia have levan-type fructans. Two morphophysiological syndromes are characterized by the lowest or highest investment in belowground system mass and storage of fructans, being interpreted as generalist or specialist adaptive strategies. These two characteristics of such syndromes, together with the photosynthetic metabolisms are traits that reflect the diversity of the Amaranthaceae and their ability to occupy several habitats, including those marked by harsh conditions, such as the Cerrado.

Overgrazing-induced legacy effects may permit Leymus chinensis to cope with herbivory.

There is growing evidence that herbivory-induced legacy effects permit plants to cope with herbivory. However, herbivory-induced defense strategies in plants against grazing mammals have received little attention. To further understand the grazing-induced legacy effects on plants, we conducted a greenhouse experiment with Leymus chinensis experiencing different grazing histories. We focused on grazing-induced legacy effects on above-ground spatial avoidance and below-ground biomass allocation. Our results showed that L. chinensis collected from the continuous overgrazing plot (OG) exhibited higher performance under simulated grazing in terms of growth, cloning and colonizing ability than those collected from the 35-year no-grazing plot (NG). The enhanced adaptability of OG was attributed to increased above-ground spatial avoidance, which was mediated by larger leaf angle and shorter height (reduced vertical height and increased leaf angle contributed to the above-ground spatial avoidance at a lower herbivory stubble height, while reduced tiller natural height contributed to above-ground spatial avoidance at a higher herbivory stubble height). Contrary to our prediction, OG pre-allocated less biomass to the rhizome, which does not benefit the herbivory tolerance and avoidance of L. chinensis; however, this also may reflect a tolerance strategy where reduced allocation to rhizomes is associated with increased production of ramets.

Animal aggregations promote emergent aquatic plant production at the aquatic-terrestrial interface.

The roles mobile animals and abiotic processes play as vectors for resource transfers between ecosystems ("subsidies") are well studied, but the idea that resources from animals with limited mobility may be transported across boundaries through intermediate taxa remains unexplored. Aquatic plants ("macrophytes") are globally distributed and may mediate transfers of aquatic-derived nutrients from aggregations of aquatic animals to terrestrial ecosystems when consumed by terrestrial herbivores. We used mesocosms (94×44cm) to test whether aquatic animal-generated biogeochemical hotspots increase growth and nutrient content in macrophytes using the macrophyte Justicia americana and freshwater mussels. Justicia americana biomass production increased and belowground biomass allocation changed with increasing mussel density. At high mussel density, water-column phosphorus increased and carbon:phosphorus ratios in J. americana tissues decreased. We deployed motion-sensing cameras to explore herbivory on J. americana growing along the margins of the Kiamichi River, Oklahoma, and documented feeding by large mammals (Odocoileus virginianus, Sus scrofa, and Bos taurus). Thus, biogeochemical hotspots generated by aquatic animal aggregations can promote macrophyte production that subsequently is transferred to terrestrial animals. More broadly, this suggests that reductions in aquatic animal biomass may have bottom-up impacts that indirectly affect terrestrial ecosystems via plant-animal interactions bridging ecosystem boundaries.

Responses of biomass allocation to multi-factor global change: A global synthesis

Knowledge of plant aboveground and belowground biomass (AGB and BGB) allocation is fundamental for our understanding of terrestrial carbon sequestration in a changing climate. However, how multiple global change factors interactively affect biomass allocation in terrestrial ecosystems remains unclear. We used meta-analysis to synthesize main and interactive effects of global change factors on AGB, BGB, and root/shoot based on 129 multiple-factor studies. Elevated CO2 (E), nitrogen addition (N), warming (W), irrigation (I) and their combinations (EN, EW, NW, ENW, IE, IN, IW, IEN, INW and IENW) significantly increased AGB. However only half of the treatments (i.e., E, N, W, EN, EW, NW, IE and IW) stimulated BGB, leading to significant declines of root/shoot in treatments with I and/or N. Drought (D) significantly decreased both total biomass (14%) and AGB (47%), but increased root/shoot by 21% as well as DE and DW. Additive interactions between global change factors exhibited a predominance on both plant biomass (69.0%) and biomass allocation (64.8%). The proportion of synergistic interaction in AGB’s responses to multiple global change factors was greater relative to that in BGB. Response correlation between AGB and root/shoot was observed in woody plants, while, in herbaceous ones, we found the correlation between BGB and root/shoot. Our findings highlight the importance of the interactive effects among global change factors on biomass allocation. Incorporating these interactions into global vegetation models may improve predictions of future global carbon storage and could inform sustainable strategies for grassland and plantation management in a future climate.

Lineage and latitudinal variation in Phragmites australis tolerance to herbivory: implications for invasion success

Herbivores play a critical role in plant invasions either by facilitating or inhibiting species establishment and spread. However, relatively few studies with invasive plant species have focused on the role of plant tolerance and how it varies geographically to influence invasion success. We conducted a common garden study using two lineages (native and invasive) of the grass Phragmites australis that are prevalent in North American wetlands. Using 31 populations collected across a broad geographic range, we tested five predictions: 1) the invasive lineage is more tolerant to simulated folivory than the native lineage, 2) tolerance to herbivory decreases with increasing latitude of origin of the populations, 3) estimates of tolerance are correlated with putative tolerance traits and plasticity in those traits, 4) a tradeoff exists between tolerance and resistance to herbivory and 5) tolerance has a fitness cost. Response to folivory varied substantially among populations of P. australis, ranging from intolerance to overcompensation. Our model selection procedure deemed lineage to be an important predictor of tolerance but, contrary to our prediction, the native lineage was 19% more tolerant to folivory than the invasive lineage. Tolerance for both lineages exhibited a u‐shaped relationship with latitude. A tolerance–resistance tradeoff was evident within the invasive but not the native lineage. Also, tolerance was positively correlated with belowground biomass allocation, leaf silica concentrations, specific leaf area and plasticity in stem density, and negatively correlated with the relative growth rate of the population and plasticity in putative resistance traits. Lastly, although we did not detect costs of tolerance, our results highlight that fast growth rates can maintain high fitness in the presence of herbivory. Herbivory and plant defense strategies for P. australis lineages in North America exhibit complex biogeographic patterns that cause substantial heterogeneity in enemy release and biotic resistance and, consequently, invasion success.

Jena Soil Model (JSM v1.0; revision 1934): a microbial soil organic carbon model integrated with nitrogen and phosphorus processes

Abstract. Plant–soil interactions, such as the coupling of plants' below-ground biomass allocation with soil organic matter (SOM) decomposition, nutrient release and plant uptake, are essential to understand the response of carbon (C) cycling to global changes. However, these processes are poorly represented in the current terrestrial biosphere models owing to the simple first-order approach of SOM cycling and the ignorance of variations within a soil profile. While the emerging microbially explicit soil organic C models can better describe C formation and turnover, at present, they lack a full coupling to the nitrogen (N) and phosphorus (P) cycles with the soil profile. Here we present a new SOM model – the Jena Soil Model (JSM) – which is microbially explicit, vertically resolved and integrated with the N and P cycles. To account for the effects of nutrient availability and litter quality on decomposition, JSM includes the representation of enzyme allocation to different depolymerisation sources based on the microbial adaptation approach as well as of nutrient acquisition competition based on the equilibrium chemistry approximation approach. Herein, we present the model structure and basic features of model performance in a beech forest in Germany. The model reproduced the main SOM stocks and microbial biomass as well as their vertical patterns in the soil profile. We further tested the sensitivity of the model to parameterisation and showed that JSM is generally sensitive to changes in microbial stoichiometry and processes.

Biomass allocation and productivity-richness relationship across four grassland types at the Qinghai Plateau.

Aboveground biomass (AGB) and belowground biomass (BGB) allocation and productivity–richness relationship are controversial. Here, we assessed AGB and BGB allocation and the productivity–richness relationship at community level across four grassland types based on the biomass data collected from 80 sites across the Qinghai Plateau during 2011–2012. The reduced major axis regression and general linear models were used and showed that (a) the median values of AGB were significantly higher in alpine meadow than in other three grassland types; the ratio of root to shoot (R/S) was significantly higher in desert grassland (36.06) than intemperate grassland (16.60), alpine meadow (13.35), and meadow steppe (19.46). The temperate grassland had deeper root distribution than the other three grasslands, with about 91.45% roots distributed in the top 30 cm soil layer. (b) The slopes between log AGB and log BGB in the temperate grassland and meadow steppe were 1.09 and 1, respectively, whereas that in the desert grassland was 1.12, which was significantly different from the isometric allocation relationship. A competitive relationship between AGB and BGB was observed in the alpine meadow with a slope of −1.83, indicating a trade‐off between AGB and BGB in the alpine meadow. (c) A positive productivity–richness relationship existed across the four grassland types, suggesting that the positive productivity–richness relationship might not be affected by the environmental factors at the plant location. Our results provide a new insight for biomass allocation and biodiversity–ecosystem functioning research.

Jointed cactus Opuntia aurantiaca modifies soil nutrient concentrations, grass species assemblage and biomass yield in a savanna rangeland

Biological invasions are currently recognized as a major threat to biodiversity and ecosystem function worldwide, but invasion studies in savanna rangelands are limited. Therefore, we studied the soil properties and grass species abundance, diversity and biomass yield in Opuntia aurantiaca uninvaded, recently-invaded (<30 years ago) and historically-invaded (>30 years) sites in a savanna rangeland, Zimbabwe. Soil nutrient concentrations significantly differed between sites, with nutrient-rich soils in Opuntia-invaded sites. The soil nutrient content in invaded sites was greater by a factor of up to 7 for N, 44 for P and 3.4 for Ca. However, soil pH did not differ between sites (p > 0.05), with slightly acidic soils in all sites. Grass species abundance declined while species evenness increased with time since Opuntia invasion. Further, grass species height and biomass yield in the uninvaded sites were greater than those in the recently-invaded and historically-invaded sites. We also observed a shift in above and belowground biomass allocation in grass species suggesting shifts in plastic allocations with invasion. Overall, redundancy analysis showed a significant negative effect of O. aurantiaca density on the abundance, species richness, species diversity and biomass yield of grass species. In contrast, species evenness and dominance were positively correlated with O. aurantiaca density. In conclusion, despite the positive effects of invasion on soil nutrient concentrations, the findings are worrisome as grass abundance, height and biomass yield are negatively affected. Consequently, rangeland productivity might also be curtailed, indicating the need to manage and eradicate O. aurantiaca given a considerable amount of comparable rangeland that can be affected.

Precipitation and nitrogen addition enhance biomass allocation to aboveground in an alpine steppe.

There are two important allocation hypotheses in plant biomass allocation: allometric and isometric. We tested these two hypotheses in an alpine steppe using plant biomass allocation under nitrogen (N) addition and precipitation (Precip) changes at a community level. An in situ field manipulation experiment was conducted to examine the two hypotheses and the responses of the biomass to N addition (10 g N m−2 y−1) and altered Precip (±50% precipitation) in an alpine steppe on the Qinghai–Tibetan Plateau from 2013 to 2016. We found that the plant community biomass differed in its response to N addition and reduced Precip such that N addition significantly increased aboveground biomass (AGB), while reduced Precip significantly decreased AGB from 2014 to 2016. Moreover, reduced Precip enhanced deep soil belowground biomass (BGB). In the natural alpine steppe, the allocation between AGB and BGB was consistent with the isometric hypotheses. In contrast, N addition or altered Precip enhanced biomass allocation to aboveground, thus leading to allometric growth. More importantly, reduced Precip enhanced biomass allocation into deep soil. Our study provides insight into the responses of alpine steppes to global climate change by linking AGB and BGB allocation.

Effects of soil flooding, sunlight and herbivory on seedlings of Annona glabra and Pachira aquatica in a tropical swamp

Wetland seedlings, in addition to dealing with the effects of flooding, must gain access to sunlight and avoid herbivore damage in order to establish. Understanding the effects of environmental factors on seedling growth and how plants modify their functional traits in response to them, is a challenge of wetland ecology. We evaluated the effects of different conditions of soil flooding (flooded and mesic), sunlight (closed and no canopy) and herbivory (presence and absence) on the survival, growth, and morphological traits of Annona glabra and Pachira aquatica seedlings, two dominant woody species of Neotropical swamps. We had eight experimental treatments with five replicates each. Our results showed that the survival of both species was high and was not affected by soil flooding, sunlight and herbivory. However, these factors affected plant growth rates. In general, the highest growth rates were observed in the treatment with high sunlight, mesic soil and herbivore exclusion. Both species displayed higher leaf biomass allocation under closed than under no canopy. Furthermore, under closed canopy conditions both species produced relatively more slender and taller stems, which may allow them to intercept light more efficiently. Also, both species showed low belowground biomass allocation in flooded soils, probably as a consequence of a high anoxic condition. Our results confirmed that soil flooding, sunlight and herbivory are important factors that influence the growth patterns of A. glabra and P. aquatica seedlings, but they do not affect seedling survival. This information may help resource managers to identify high-quality sites that deserve to be protected. Also, the knowledge on species responses to different environmental conditions may be useful in restoration programs for tropical swamp forests.

Root density distribution and biomass allocation of co-occurring woody plants on contrasting soils in a subtropical savanna parkland

Root niche partitioning among trees/shrubs and grasses facilitates their coexistence in savannas, but little is known regarding root distribution patterns of co-occurring woody plants, and how they might differ on contrasting soils. We quantified root distributions of co-occurring shrubs to 2 m on argillic and non-argillic soils. Root biomass in the two shrub communities was 3- to 5- fold greater than that in the grassland community. Prosopis glandulosa, the dominant overstory species was deep-rooted, while the dominant understory shrub, Zanthoxylum fagara, was shallow-rooted (47% vs. 25% of root density at depths >0.4 m). Shrubs on argillic soils had less aboveground and greater belowground mass than those on non-argillic soils. Root biomass and density on argillic soils was elevated at shallow (< 0.4 m) depths, whereas root density of the same species on non-argillic soils were skewed to depths >0.4 m. Root density decreased exponentially with increasing distance from woody patch perimeters. Belowground biomass (carbon) pools increased markedly with grassland-to-shrubland state change. The presence/absence of a restrictive barrier had substantial effects on root distributions and above- vs. belowground biomass allocation. Differences in root distribution patterns of co-occurring woody species would facilitate their co-existence.

Divergent responses to water and nitrogen addition of three perennial bunchgrass species from variously degraded typical steppe in Inner Mongolia

Water and nitrogen (N) availability to plants are spatially and temporally variable in arid and semi-arid grasslands. We aimed to investigate the eco-physiological responses of three bunchgrass species to water and N addition along a gradient of habitat degradation in the Inner Mongolian typical grasslands. The effects of water and N addition on aboveground and belowground growth and biomass allocation and water- and nitrogen-use efficiency (WUE and NUE) of Stipa grandis, Agropyron cristatum and Cleistogenes squarrosa from non-degraded, moderately-degraded and heavily-degraded grasslands, respectively, were compared. Stipa grandis had higher specific root length and WUE than C. squarrosa, while C. squarrosa had higher NUE than S. grandis in water- and N-limited conditions. Responses of A. cristatum were intermediate between those of S. grandis and C. squarrosa. Water and N addition did not have a significant effect on growth and biomass allocation of S. grandis, but it increased growth and leaf biomass allocation of A. cristatum and growth and stem biomass allocation of C. squarrosa. The three species differ in WUE, NUE, biomass allocation and responses to water and N addition, and these differences are adaptive to their respective habitats. The degraded grasslands can be restored by an increase in water and N availability such as is expected to occur via climatic change, but S. grandis will not benefit from the increases.

Above- and below-ground carbon accumulation and biomass allocation in poplar short rotation plantations under Mediterranean conditions

Beside the production of biomass, short rotation coppice (SRC) poplar plantations can also contribute to carbon sequestration in the soil through their below-ground biomass. The present study evaluated the allocation of above and below-ground biomass at the end of the first rotation of four SRC plantations under Mediterranean conditions. The genotypes evaluated are commonly used for biomass plantations, i.e. genotypes ‘AF2’ and ‘I-214’ (Populus × canadensis Mönch), and ‘Monviso’ (P. × generosa Henry × P. nigra L.). No significant differences among genotypes were found with regard to below-ground biomass yield. The root:shoot ratio decreased in line with the growth in shoot basal diameter, with values ranging from 0.15 to 0.26. The accumulation of carbon in the below-ground fraction of the biomass ranged from 0.86 to 0.91 Mg C ha−1 yr−1, whereas the above-ground carbon accumulation ranged from 3.89 to 6.48 Mg C ha−1 yr−1. A general as well as a genotype-specific allometric model allowed to accurately predict the below-ground biomass yield using shoot basal diameter as the predictor variable. Both models provide an important tool to quantify the carbon accumulated in the below-ground fraction of the biomass.

Minimum Fe requirement and toxic tissue concentration of Fe in Phragmites australis: A tool for alleviating Fe-deficiency in constructed wetlands

In constructed wetlands (CWs) with forced aeration and vertical flow, plants can suffer from iron (Fe) deficiency due to Fe immobilization in the gravel substrate as a consequence of the oxic condition. The common reed (Phragmites australis) is the most commonly used plant species in CWs and frequently displays Fe-deficiency symptoms particularly in new-established systems. The aim of this study was therefore to study the Fe-nutrition of P. australis in order to gain knowledge on how Fe-deficiency in P. australis can be alleviated. For this purpose, we grew two genetically distinct phylogeographic groups of P. australis hydroponically with seven different Fe concentrations (0, 0.1, 0.2, 0.5, 1.0, 5.0 and 20.0 mg Fe-EDDHA ([iron (3+) ethylenediamine di (o-hydroxyphenylacetic) acid]) L−1) in a phytotron. Both groups responded strongly to the increasing Fe supply. The belowground biomass allocation ratio, light-saturated photosynthesis rates, chlorophyll content and leaf Fe tissue concentration all significantly increased with increasing Fe availability. Phragmites australis in the 0 mg Fe-EDDHA L−1 treatment suffered strongly from Fe deficiency, and plants in the high 20.0 mg Fe-EDDHA L−1 treatment also had reduced growth and Fe toxicity symptoms. The ‘critical deficiency concentration’ of Fe in leaves of juvenile P. australis was 40–50 mg kg−1 DM, and the ‘critical toxicity concentration’ of Fe in leaves of juvenile P. australis were approximately 150 mg kg−1 DM. Overall the two genetically distinct P. australis groups differed in their ecophysiological traits, and the two groups also responded differently to the different Fe-supply rates which may be the result of adaptations obtained in their native growth habitats. We suggest that the Fe-deficiency in CW systems with unsaturated vertical flow and/or forced aeration can be alleviated by application of a foliar spray containing chelated iron. However, the application rate and frequency should be further studied.

Complementarity of three distinctive phytoremediation crops for multiple-trace element contaminated soil

Trace element (TE) contaminated land represents an important risk to the environment and to human health worldwide. These soils usually contain a variety of TEs which can be a challenge for plant-based remediation options. As individual plant species often possess a limited range of TE remediation abilities, functional complementarity principles could be of value for remediation of soil contaminated by multiple TEs using assemblages of species. Monocultures and polycultures of Festuca arundinacea, Medicago sativa and Salix miyabeana were grown for 4months in aged-polluted soil contaminated by Ag, As, Cd, Cr, Cu, Pb, Se and Zn. Above and belowground biomass yields, root surface area (RSA) and TE tissue concentrations were recorded. In monoculture, the greatest aboveground biomass was produced by S. miyabeana (S), the greatest belowground biomass was from M. sativa (M) and F. arundinacea (F) produced the highest RSA. The polycultures of F+M, F+S and F+M+S produced among the highest values across all three traits. F. arundinacea monoculture and its combination with S. miyabeana (F+S) accumulated the highest amounts of total TEs in belowground tissues, whereas the most effective combination (or monoculture) for aboveground extraction yields varied depending on the TE considered. The crops demonstrated complementarity in their biomass allocation patterns as well as facilitative interactions. When considering contamination with a particular TE, the best phytomanagement approach could include a specific monoculture option; however, when above and belowground biomass allocation patterns, TE-remediation abilities as well as nitrogen accessibility are considered, co-cropping all three species (F+M+S) was the most robust scenario for remediation of multiple-TE contaminated land. By more effectively addressing a diversity of TE, species assemblage approaches could represent an important advancement towards enabling the use of plants to address contaminated-land issues worldwide.

Patterns of biomass allocation in Haloxylon persicum woodlands and their understory herbaceous layer along a groundwater depth gradient

To investigate above- and belowground biomass allocation patterns and the relationship of root distribution between different functional groups (shrubs vs. herbs) along a groundwater depth gradient, an experiment was carried out in a Haloxylon persicum woodland. Four sites were selected along the groundwater depth gradient. At each site, five sample plots (20×20m) and 15 subplots (1×1m) were established for a vegetation inventory of Haloxylon persicum and the herbaceous layer. The vegetation inventory included plant density, canopy coverage, height, and basal stem diameter of H. persicum. Allometric equations were established for H. persicum based on the biomass of 22 excavated trees, which were then applied to inventory data to provide stand estimates of aboveground biomass (AGB), belowground biomass (BGB), and total biomass (TB) of H. persicum. The AGB of the herbaceous layer was measured in subplots (1×1m) and BGB was excavated and measured to a depth of 100cm at 10-cm intervals. Our results indicated that the BGB-to-AGB ratio at the community level in the herbaceous layer increased notably along the gradient of declining groundwater depth. The depth of the soil horizon that contained 65% of the root surface area and 85% of the root biomass was shallower (0–2.5m) in the deep end of the groundwater depth gradient than in the shallow end (0–3m) of the gradient. H. persicum adjusted root distribution to capture water in the upper soil layers in response to the decline in groundwater depth. However, this adjustment was not sufficient to compensate for the decline in the water table: the BGB-to-AGB ratio showed no significant increase as AGB declined. On the contrary, herbaceous plants seemed better adapted to changes in the water table by effectively adjusting their BGB-to-AGB ratio. Use of BGB-to-AGB ratios that are specific to groundwater tables will significantly improve our estimates of BGB carbon stocks in these woodlands. Considering the scarcity of information on biomass stocks and partitioning in desert woodlands, our results might be applicable to other desert regions in Central Asia dominated by H. persicum.

Effects of soil compaction on seedling morphology, growth, and architecture of chestnut-leaved oak (Quercus castaneifolia)

Abstract: Soil compaction following traffic by heavy-timber harvesting machinery usually causes an increase in soil strength, that is a stress factor negatively affecting the growth of newly germinated seedlings. This study used a soil strength experiment carried out in a greenhouse to test the hypotheses that increasing soil strength would adversely affect seedling morphology and alter seedling architecture by changing biomass allocation patterns. We explored the effects of soil compaction in a loam to clay-loam textured soil with optimal conditions of water on a continuous scale (0.2-1.0 MPa penetration resistance) on growth responses of the deciduous Quercus castaneifolia (C.A.Mey). Both above- and below-ground seedling characteristics, including size and biomass, were negatively affected by soil compaction. At the highest intensity of compaction, size and growth were reduced by 50% compared to controls; negative effects were typically more severe on below-ground (i.e., the length and biomass of the root system) than on above-ground responses. Increasing soil strength did not change above- and below-ground biomass allocation patterns (i.e., root mass ratio, root:shoot ratio, specific root length), resulting in unchanged seedling architecture. Strong adverse effects were already evident in the low-intensity compaction treatment and no critical soil strength threshold was observed. We conclude that root and height growth in Q. castaneifolia seedlings is limited by any increase of soil strength, though no evidence for the disruption of a functional equilibrium between above- and below-ground plant portions was found up to soil strengths of 1.0 MPa, at least under optimal water supply.