Root Carbon Research Articles

The effects of plastic-film mulch on the grain yield and root biomass of maize vary with cultivar in a cold semiarid environment

Plastic-film mulch is an agricultural technology widely used for maize (Zea mays L.) production in northern China, but the effects of the interaction between cultivar and plastic-film mulch on the grain yield and biomass production have not been studied. Five maize hybrids, Jinsui 4; Jixiang 1; Pingyu 8; Xianyu 335 and Yuyuan 5, were assessed in 2014 and 2015 in plastic-film mulched and non-mulched ridge-furrow plots in a cold semiarid environment. In 2014, the grain yield of the five cultivars varied from 685 to 898gm−2 with no mulch, and from 966 to 1228gm−2 under mulch. In 2015 (drier and warmer than in 2014), the grain yield varied from 179 to 353gm−2 without mulch, and from 548 to 1021gm−2 with mulch. By incorporating the variation in grain yield over cultivars, mulch treatments and cropping years, Jixiang 1 was the highest yielding cultivar: in 2014 the grain yield reached 898gm−2 under no mulch, compared to 1228gm−2 under mulch, while in 2015 the grain yield was 329gm−2 under no mulch compared to 1021gm−2 under mulch. Cultivar and mulch independently affected the aboveground biomass and harvest index of maize. Jixiang 1 attained high yields as a result of average aboveground biomass, but high harvest index. Differences in maize water use efficiency (grain yield per unit of evapotranspiration) as affected by mulch and cultivar paralleled those of grain yield due to minor effects of mulch and cultivar on growing-season evapotranspiration. The effects of plastic-film mulch on maize root biomass in the upper 0.6m soil profile and root/shoot ratio varied with cultivar. Averaging years and mulch treatments, Jixiang 1 had the smallest root biomass in the upper 0.6m soil layer and Jixiang 1 and Jinsui 4 had smaller root/shoot ratios than the other three cultivars. We conclude that the effects of plastic-film mulch on the grain yield, root biomass and root/shoot ratio varied significantly with cultivar. A moderate aboveground biomass and high harvest index may give satisfactory grain yield in plastic-film mulched or non-mulched fields in hydrothermally-limited areas. A wide variation of root/shoot ratio with maize cultivar and cropping year indicated that using a fixed root/shoot ratio to estimate the root carbon input to the soil would induce large uncertainty.

Seasonal variations in carbon, nitrogen and phosphorus concentrations and C:N:P stoichiometry in different organs of a Larix principis-rupprechtii Mayr. plantation in the Qinling Mountains, China.

Understanding how concentrations of elements and their stoichiometry change with plant growth and age is critical for predicting plant community responses to environmental change. We used long-term field experiments to explore how the leaf, stem and root carbon (C), nitrogen (N) and phosphorous (P) concentrations and their stoichiometry changed with growth and stand age in a L. principis-rupprechtii Mayr. plantation from 2012–2015 in the Qinling Mountains, China. Our results showed that the C, N and P concentrations and stoichiometric ratios in different tissues of larch stands were affected by stand age, organ type and sampling month and displayed multiple correlations with increased stand age in different growing seasons. Generally, leaf C and N concentrations were greatest in the fast-growing season, but leaf P concentrations were greatest in the early growing season. However, no clear seasonal tendencies in the stem and root C, N and P concentrations were observed with growth. In contrast to N and P, few differences were found in organ-specific C concentrations. Leaf N:P was greatest in the fast-growing season, while C:N and C:P were greatest in the late-growing season. No clear variations were observed in stem and root C:N, C:P and N:P throughout the entire growing season, but leaf N:P was less than 14, suggesting that the growth of larch stands was limited by N in our study region. Compared to global plant element concentrations and stoichiometry, the leaves of larch stands had higher C, P, C:N and C:P but lower N and N:P, and the roots had greater P and C:N but lower N, C:P and N:P. Our study provides baseline information for describing the changes in nutritional elements with plant growth, which will facilitates plantation forest management and restoration, and makes a valuable contribution to the global data pool on leaf nutrition and stoichiometry.

A deeper look at the relationship between root carbon pools and the vertical distribution of the soil carbon pool

Abstract. Plant root material makes a substantial contribution to the soil organic carbon (C) pool, but this contribution is disproportionate below 20 cm where 30 % of root mass and 50 % of soil organic C is found. Root carbon inputs changed drastically when native perennial plant systems were shifted to cultivated annual plant systems. We used the reconstruction of a native prairie and a continuous maize field to examine both the relationship between root carbon and soil carbon and the fundamental rooting system differences between the vegetation under which the soils developed versus the vegetation under which the soils continue to change. In all treatments we found that root C : N ratios increased with depth, and this plays a role in why an unexpectedly large proportion of soil organic C is found below 20 cm. Measured root C : N ratios and turnover times along with modeled root turnover dynamics showed that in the historical shift from prairie to maize, a large, structural-tissue-dominated root C pool with slow turnover concentrated at shallow depths was replaced by a small, nonstructural-tissue-dominated root C pool with fast turnover evenly distributed in the soil profile. These differences in rooting systems suggest that while prairie roots contribute more C to the soil than maize at shallow depths, maize may contribute more C to soil C stocks than prairies at deeper depths.

Soil C and N statuses determine the effect of maize inoculation by plant growth-promoting rhizobacteria on nitrifying and denitrifying communities

Maize inoculation by Azospirillum stimulates root growth, along with soil nitrogen (N) uptake and root carbon (C) exudation, thus increasing N use efficiency. However, inoculation effects on soil N-cycling microbial communities have been overlooked. We hypothesized that inoculation would (i) increase roots-nitrifiers competition for ammonium, and thus decrease nitrifier abundance; and (ii) increase roots-denitrifiers competition for nitrate and C supply to denitrifiers by root exudation, and thus limit or benefit denitrifiers depending on the resource (N or C) mostly limiting these microorganisms. We quantified (de)nitrifiers abundance and activity in the rhizosphere of inoculated and non-inoculated maize on 4 sites over 2 years, and ancillary soil variables. Inoculation effects on nitrification and nitrifiers (AOA, AOB) were not consistent between the three sampling dates. Inoculation influenced denitrifiers abundance (nirK, nirS) differently among sites. In sites with high C limitation for denitrifiers (i.e. limitation of denitrification by C > 66%), inoculation increased nirS-denitrifier abundance (up to 56%) and gross N2O production (up to 84%), likely due to increased root C exudation. Conversely, in sites with low C limitation (<47%), inoculation decreased nirS-denitrifier abundance (down to −23%) and gross N2O production (down to −18%) likely due to an increased roots-denitrifiers competition for nitrate.

Economic trade-offs of hydrophytes and neighbouring terrestrial herbaceous plants based on plant functional traits

This study aims to compare variation and co-variation of leaf, stem and root economic traits between hydrophytes and sympatric terrestrial plants, and further to explore the ecological strategies of the aquatic plants. We collected data for 145 species from 38 sites in Shaanxi Province, including 60 aquatic species and 85 terrestrial species (112 genera and 48 families). Fifteen plant economic traits of these species were measured, including specific leaf area, dry matter content and C, N, P stoichiometry in leaves, stems and roots. Multivariate analysis was employed to uncover the differences in economic trade-offs between aquatic and terrestrial plants. The results indicated that: (1) Hydrophytes exhibited much higher specific leaf area and lower mean leaf dry matter content, stem dry matter content, root dry matter content, stem carbon content and root carbon content compared with that of terrestrial plants in order to adapt to the aquatic environment, that is, there were differences in mean traits about the economic trade-offs faced by hydrophytes and terrestrial plants. (2) The leaf economic spectrum of aquatic plants in this region coincided with the worldwide leaf economics spectrum, while hydrophytes are located at the extreme of thin leaves which is conducive to rapid acquisition of resources. (3) Aquatic and terrestrial species can be discriminated by few functional traits related to resource acquisition and support tissues. (4) Aquatic and terrestrial plants differed in bivariate correlations between certain economic traits (standardized major axis analysis), indicating differences in plant strategies.

Increase of forest carbon biomass due to community forestry management in Nepal

Community forest management helps in mitigating deforestation and forest degradation by addressing the negative aspects of rural livelihoods such as poverty and social exclusion. It is important in regulating global climate by encouraging sequestration of carbon in shoots, roots and soils. We studied the status of community forest management, forest resource harvest and carbon stocks in two community forests of the mid hill region of central and western Nepal. The study was based on primary and secondary data collected through carbon stock measurement from field visits and allometric equations, household surveys, focus group discussions, key informant interviews, and review of past studies. Socioeconomic variables such as gender, age group, livestock and landholding status were related to resource utilization, conservation, and management of community forest. Forest resources such as timber, firewood, fodder and leaf litter were harvested in sustainable ways. People were involved in forest thinning, co-management meetings, guarding and planting trees for forest conservation and management. Density and carbon stock of trees increased gradually in comparison to a previous study. We recommend further research on other community forests for more accurate and better results.

Decoupled leaf and root carbon economics is a key component in the ecological diversity and evolutionary divergence of deciduous and evergreen lineages of genus Rhododendron.

We explored trait-trait and trait-climate relationships for 27 Rhododendron species while accounting for phylogenetic relationships and within-species variation to investigate whether leaf and root traits are coordinated across environments and over evolutionary time, as part of a whole-plant economics spectrum. We examined specific leaf area (SLA) and four root traits: specific root length (SRL), specific root tip abundance (SRTA), first order diameter, and link average length, for plants growing in a cold, seasonal climate (Kirtland, Ohio) and a warmer, less seasonal climate (Federal Way, Washington) in the United States. We estimated a phylogeny and species' climate of origin, determined phylogenetic signal on mean traits and within-species variation, and used phylogenetically informed analysis to compare trait-trait and trait-climate relationships for deciduous and evergreen lineages. Mean SLA and within-species variation in SRL were more similar between close relatives than expected by chance. SLA and root traits differed according to climate of origin and across growth environments, though SLA differed within- and among-species less than roots. A negative SRL-SRTA correlation indicates investment in foraging scale vs. precision as a fundamental trade-off defining the root economic spectrum. Also, the deciduous clade exhibited a strong negative relationship between SLA and SRL, while evergreen clades showed a weaker positive or no relationship. Our work suggests that natural selection has shaped relationships between above- and belowground traits in genus Rhododendron and that leaf and root traits may evolve independently. Morphological decoupling may help explain habitat diversity among Rhododendron species, as well as the changes accompanying the divergence of deciduous and evergreen lineages.

Soil organic carbon changes after deforestation and agrosystem establishment in Amazonia: An assessment by diachronic approach

Abstract Deforestation and agrosystem establishment can alter soil organic carbon (SOC) stocks, leading to greenhouse gases emissions and fertility losses, however SOC response has great variability. In the humid tropics like the Amazonia biome, carbon inputs from agrosystems are rarely quantified and described, despite their major contribution to the SOC dynamics after deforestation. We assessed SOC dynamics with repeated measurements in the layer 0–30 cm until five years after deforestation in a diachronic site in French Guiana, cleared with a fire-free method associated to large woody debris inputs. Three agrosystems were studied: one year maize/soybean rotation with disk tillage (DT) and without tillage (NT), and a mowed grassland (G). Aboveground carbon inputs from agrosystems were measured. In addition to SOC stocks assessment, we measured roots carbon stocks, and performed δ 13 C measurements in grassland soil. We found a transient SOC stock increase until 1.5 years after deforestation because of large woody debris inputs from deforestation method, but these C inputs were rapidly mineralized and poorly contributed to SOC stocks 5 years after deforestation. SOC stocks in grassland did not differ from forest despite large hay exports. Thanks to large root-derived carbon inputs, C4-SOC stock in grassland was 10.4 t ha −1 5 years after deforestation (18.7% of the SOC stock). In annual crops, 5 years after deforestation, SOC stocks decreased on average by 18.6% compared to forest. SOC stocks did not differ according to soil tillage since aboveground carbon inputs were similar in DT and NT systems. Lower SOC stocks in annual crops compared to grassland is explained by lower carbon restitutions and by higher mineralization rate of organic matter.

Using stable isotopes to explore root-microbe-mineral interactions in soil

The few millimeters of soil surrounding a plant's roots, the 'rhizosphere', are a nexus of biological activity, and inhabited by microorganisms that are critically important to both plant health and soil carbon (C) transformation and stabilization. Advancing our understanding of plant-microbe interactions and the soil carbon cycle requires disentangling the complex relationships among roots, soil microbes, mycorrhizae, and soil mineral surfaces. Yet in wildland systems, many important mechanistic rhizosphere questions remain unanswered. For example, most root C is decomposed to CO2, but of the remainder, what microbial transformations lead to the opportunity to become stabilized? How do plant species and microbial functionality regulate flows of C and nutrients, and how much do these vary over space and time? Transfer of root carbon to bacterial and fungal cell biomass may be a particularly important activity that precedes C stabilization on mineral surfaces, but the steps involved in this process remain ambiguous. In the past decade, multiple 'isotope-enabled' approaches have been developed that allow us to see and measure these complex rhizosphere interactions with high spatial, chemical, and molecular resolution. Here we present illustrative examples of these approaches as applied in non-cultivated soil systems.

Root cortical senescence decreases root respiration, nutrient content and radial water and nutrient transport in barley.

The functional implications of root cortical senescence (RCS) are poorly understood. We tested the hypotheses that RCS in barley (1) reduces the respiration and nutrient content of root tissue; (2) decreases radial water and nutrient transport; and (3) is accompanied by increased suberization to protect the stele. Genetic variation for RCS exists between modern germplasm and landraces. Nitrogen and phosphorus deficiency increased the rate of RCS. Maximal RCS, defined as the disappearance of the entire root cortex, reduced root nitrogen content by 66%, phosphorus content by 63% and respiration by 87% compared with root segments with no RCS. Roots with maximal RCS had 90, 92 and 84% less radial water, nitrate and phosphorus transport, respectively, compared with segments with no RCS. The onset of RCS coincided with 30% greater aliphatic suberin in the endodermis. These results support the hypothesis that RCS reduces root carbon and nutrient costs and may therefore have adaptive significance for soil resource acquisition. By reducing root respiration and nutrient content, RCS could permit greater root growth, soil resource acquisition and resource allocation to other plant processes. RCS merits investigation as a trait for improving the performance of barley, wheat, triticale and rye under edaphic stress.

Responses of root exudation and nutrient cycling to grazing intensities and recovery practices in an alpine meadow: An implication for pasture management

The rhizosphere priming effect is caused by root carbon (C) exudation into the rhizosphere; the role of this effect in nutrient cycling and ecosystem recovery of natural grasslands as affected by different grazing intensities is still unknown. The objective of the present study was to investigate the relationships among root C exudation, rhizospheric microbial activity, and their influences on plant nutrient uptake during grazing and recovery periods. Field experiments were conducted in the Hongyuan Alpine Meadow to measure root exudation rate and nutrient cycling processes of the dominant species Elymus nutans. Three grazing intensities (an ungrazed control, moderate grazing and heavy grazing) were introduced for two months, following which all treatments received a recovery practice (no grazing for 21 days). Heavy grazing significantly decreased root exudation rate, soil nitrogen (N) mineralization rate, β-1,4-glucosidase (BG) activity, and foliar C concentration, while moderate grazing had no influence on these parameters compared to the control. After the 21 days of recovery, all these parameters, except N mineralization rate and foliar C concentrations in the heavy grazing treatment, returned to similar levels as in the control, whereas root exudation rate and BG activity rose to even higher levels. Meanwhile, moderate grazing significantly promoted root exudation rate, soil inorganic N concentration, net soil N mineralization rate, and β-N-acetylglucosaminidase (NAG) activity during the recovery stage as compared to the control. Foliar quality was also improved by the recovery practice, indicating that the high availability of N and P is a consequence of the positive root–microbe feedback and will ultimately benefit grazers. The flush of labile C released to the rhizosphere by grazed plants stimulated extracellular enzyme activities, enhanced soil N mineralization, and increased plant nutrient uptake. These results imply that reasonable (i.e. moderate) grazing followed by a recovery practice can effectively restore and strengthen grassland vegetation, and contribute to the sustainable use of alpine meadows such as Hongyuan.

Rootstock effect on irrigated grapevine yield under arid climate conditions are explained by changes in traits related to light absorption of the scion

The purpose of this study was to investigate the mechanisms underlying the effect of rootstocks on table grapevines grown under irrigated conditions in the arid North macro-zone of Chile.Grapevine cv. Red Globe grafted onto three rootstocks (Harmony, Saint George and Salt Creek) were studied Structural and physiological parameters were monitored at different phenological stages under optimal production conditions.An outstanding yield increment brought about by the rootstocks Harmony and Salt Creek was correlated with increased individual leaf and specific leaf area, pruning weight (proxy for total leaf area), photosynthesis per unit leaf mass, sugar in leaves and root carbon reserves. In addition, these high yielding rootstocks induced higher contents of light-harvesting chlorophyll a/b protein of photosystem II and total chlorophyll in the leaves of the scion. No correlations of yield with traits involved in water use (relative water content or instantaneous water use efficiency) were observed.The effects of rootstocks on the light capture capacity of the scion directly affected carbon assimilation and storage and, accordingly, yield. Therefore, the identified traits are valuable targets for screening and selecting yield efficient rootstocks for irrigated table grape production in arid zones.

SPATIAL AND VERTICAL DISTRIBUTION OF LITTER AND BELOWGROUND CARBON IN A BRAZILIAN CERRADO VEGETATION

ABSTRACT Forest ecosystems contribute significantly to store greenhouse gases. This paper aimed to investigate the spatial and vertical distribution of litter, roots, and soil carbon. We obtained biomass and carbon of compartments (litter, roots, and soil) in a vegetation from Cerrado biome, state of Minas Gerais, Brazil. The materials were collected in 7 0.5 m² sub-plots randomly allocated in the vegetation. Root and soil samples were taken from five soil layers across the 0-100 cm depth. Roots were classified into three diameter classes: fine (&lt;5 mm), medium (5-10 mm), and coarse (&gt;10 mm) roots. The carbon stock was mapped through geostatistical analysis. The results indicated averages of soil carbon stock of 208.5 Mg.ha-1 (94.6% of the total carbon), root carbon of 6.8 Mg.ha-1 (3.1%), and litter of 5 Mg.ha-1 (2.3%). The root carbon was majority stored in coarse roots (83%), followed by fine (10%), and medium roots (7%). The largest portion of fine roots concentrated in the 0-10 cm soil depth, whereas medium and coarse roots were majority in the 10-20 cm depth. The largest portion of soil (53%) and root (85%) carbon were stored in superficial soil layers (above 40 cm). As conclusion, the carbon spatial distribution follows a reasonable trend among the compartments. There is a vertical relation of which the deeper the soil layer, the lower the soil and root carbon stock. Excepting the shallowest layer, coarse roots held the largest portion of carbon across the evaluated soil layers.

Emoval of malachite green dye from aqueous solutions by diasporic Greek raw bauxite

Raw bauxite from Klisoura mine (Prefecture of Fokida, Greece) containing 72 wt.% diaspore, 16 wt.% hematite, 6 wt.% quartz, 4 wt.% anatase and 2 wt.% calcite, has been used for the removal of malachite green dye from aqueous solutions. The batch type experiments were conducted with 10 ml of solution, at pH = pHZPC = 6.7 and contact time 1 h. The initial concentration of malachite green dye was 10 mg/l, the bauxite quantity was 0.02 g, 0.04 g, 0.06 g, 0.1 g and 0.2 g. The highest adsorption capacity achieved was 4.5 mg/g (90% removal) using 0.02 g bauxite. The removal capacity of raw bauxite is comparable to other non-conventional adsorbents, such as neem sawdust, sugar cane dust and cane root carbon.

Storage of Miscanthus-derived carbon in rhizomes, roots, and soil

Compared with annual crops, dedicated perennial bioenergy crops are ascribed additional benefits in terms of reduced greenhouse gas emissions; these benefits include increased carbon (C) storage in soil. We measured Miscanthus-derived C in rhizomes, roots, and 0–100 cm soil beneath three 16-yr-old stands established on sandy soils at two experimental sites in Denmark. Miscanthus C in soil was estimated from changes in the natural abundance of 13C. In the 0–20 cm depth, soil C derived from Miscanthus made up to 15–18% of the soil total C. In the 20–50 cm and 50–100 cm depth, Miscanthus C accounted for less than 7% and 5% of the soil total C, respectively. After 16 yr, the total quantity of Miscanthus C in 0–20 cm ranged from 11.9 to 18.2 Mg C ha−1, of which 23–34% was in rhizomes and roots, substantiating their crucial contribution to soil C storage. Future studies should prioritize the seasonal and annual dynamics of C stored in rhizomes and roots, and the fate of these C pools following termination of Miscanthus stands.

The responses of soil, litter and root carbon stocks to the conversion of forest regrowth to crop and tree production systems used by smallholder farmers in eastern Amazonia

AbstractThe impact of substituting forests for smallholder agricultural production systems on soil carbon (C) stocks is not well understood in Brazilian Amazonia. Most surveys of soil C stocks are restricted to the top 30 cm of soil and do not include measurements of litter and root stocks. Here, we quantify the stocks of C in soil (0–100 cm depth), aboveground litter and coarse roots of traditional (slash‐and‐burn) and alternative (Schizolobium amazonicum‐planted forest and silvopastoral system) smallholder agricultural systems, which were compared with a reference area (forest regrowth) in the eastern Amazonia. The soil C stocks in the 0–100 cm layer were larger in the forest regrowth treatment (156.8 ± 15.5 Mg/ha) than in the other treatments (S. amazonicum = 85.3 ± 6.5, silvopastoral = 108.0 ± 4.4 Mg/ha) but did not differ from the soil C stock in the slash‐and‐burn treatment (127.2 ± 6.1 Mg/ha). The soil C stocks at the 0–30 cm layer, which represented 33–50% of the total C of the 0–100 cm layer, did not differ among the treatments. The litter C stocks were ranked in the following order: silvopastoral &gt; forest regrowth &gt; S. amazonicum &gt; slash‐and‐burn. The forest regrowth treatment had a greater coarse root C stock (0.84 ± 0.10 Mg/ha) than the other treatments (silvopastoral = 0.28 ± 0.03, S. amazonicum = 0.18 ± 0.03, slash‐and‐burn = 0.27 ± 0.04 Mg/ha). Soil, litter and root C stocks were negatively impacted by the conversion of forest regrowth to cultivation systems.

Effects of increasing root carbon investment on the mortality and resprouting of Haloxylon ammodendron seedlings under drought.

Tree mortality induced by drought is one of the most complex processes in ecology. Although two mechanisms associated with water and carbon balance are proposed to explain tree mortality, outstanding problems still exist. Here, in order to test how the root system benefits survival and resprouting of Haloxylon ammodendron seedlings, we examined the various water- and carbon-related physiological indicators (shoot water potential, photosynthesis, dark respiration, hydraulic conductance and non-structural carbohydrates [NSC]) of H. ammodendron seedlings, which were grown in drought and control conditions throughout a grow season in greenhouse. The survival time of the seedling root system (died 70 days after drought) doubled the survival time of the shoot (died at 35 days). Difference in survival time between shoot and root resulted from sustained root respiration supported by increased NSC in roots under drought. Furthermore, investment into the root contributed to resprouting following drought. Based on these results, a death criterion is proposed for this species. The time sequence of major events indicated that drought shifted carbon allocation between shoot and root and altered the flux among different sinks (growth, respiration or storage). The interaction of water and carbon processes determined death or survival of droughted H. ammodendron seedlings. These findings revealed that the 'root protection' strategy is critical in determining survival and resprouting of this species, and provided insights into the effects of carbon and water dynamics on tree mortality.

Forest burning affects quality and quantity of soil organic matter

Fire alters ecosystem carbon cycling and generates pyrogenic matter such as charcoal, which can be incorporated into soils. The incorporation and cycling of charcoal in soils is a potential carbon sink, but studies investigating charcoal and carbon dynamics in soils are still lacking. We investigated soil carbon, charcoal and nitrogen dynamics in the top 20cm of a sandy soil within a eucalypt forest in eastern Australia at three sites representing a chronosequence from 3months to 14years post-fire. In the short-term, fire removed litter, but resulted in an increase in both the charcoal and non-charcoal SOC content of the soils, which we attribute to above-ground charcoal generation and its incorporation into the soil profile, as well as below-ground root mortality. On a decadal timeframe, charcoal was preferentially retained in the sandy soil, in which other stabilisation mechanisms are limited, so that the influx of dead root carbon had no remnant effects. The incorporation and retention of charcoal in the soil profile is highly important to carbon cycling in such sandy soils with high fire frequency. It is highly likely that these effects are not limited to the upper 20cm of soil and future studies should investigate deep soil charcoal cycling.

Differences in interactions of aboveground and belowground herbivores on the invasive plant Alternanthera philoxeroides and native host A. sessilis

Plant invasions may result in novel plant-herbivore interactions. However, we know little about whether and how invasive plants can mediate native above- and belowground herbivore interactions. In this study, we conducted greenhouse experiments to examine the interaction between a native defoliating beetle, Cassida piperata, and a native root-knot nematode, Meloidogyne incognita, on the invasive alligator weed, Alternanthera philoxeroides. We also included their native host A. sessilis in the experiments to examine whether the patterns of above- and belowground herbivore interaction vary with host plants (invasive vs. native). We analyzed total carbon and nitrogen in leaves and roots attacked by M. incognita and C. piperata. M. incognita slightly negatively affected feeding by C. piperata on A. philoxeroides, and the leaf area damaged decreased as the number of M. incognita increased. M. incognita had a negative impact on total leaf nitrogen, but had no impact on total leaf carbon. M. incognita egg production on A. philoxeroides roots decreased as the amount of damage caused by C. piperata increased. Herbivory by C. piperata did not affect total root carbon or nitrogen. M. incognita and C. piperata did not affect each other on the native plant A. sessilis. These results suggest that invasive plants can mediate native above- and belowground herbivore interactions. The knowledge of how invasive plants affect those interactions is crucial for better understanding the impacts of biological invasions on native above- and belowground organisms.

Host phenology and potential saprotrophism of ectomycorrhizal fungi in the boreal forest

Summary Phenology‐induced changes in carbon assimilation by trees may affect carbon stored in fine roots and as a consequence, alter carbon allocated to ectomycorrhizal fungi. Two competing models exist to explain carbon mobilization by ectomycorrhizal fungi. Under the ‘saprotrophy model’, decreased allocation of carbon may induce saprotrophic behaviour in ectomycorrhizal fungi, resulting in the decomposition of organic matter to mobilize carbon. Alternatively, under the ‘nutrient acquisition model’, decomposition may instead be driven by the acquisition of nutrients locked within soil organic matter compounds, with carbon mobilization a secondary process. We tested whether phenology‐induced shifts in carbon reserves of fine roots of aspen (Populus tremuloides) affect potential activity of four carbon‐compound degrading enzymes, β‐glucuronidase, β‐glucosidase, N‐acetylglucosaminidase and laccase, by ectomycorrhizal fungi. Ectomycorrhizal roots from mature aspen were collected across eight stands in north‐eastern Alberta, Canada, and analysed during tree dormancy, leaf flush, full leaf expansion and leaf abscission. We predicted potential extracellular enzyme activity to be highest when root carbon reserves were lowest, should host phenology induce saprotrophism. Further, we anticipated enzyme activity to be mediated by invertase, a plant‐derived enzyme which makes carbon available to fungal symbionts in the plant–fungus interface. Root carbon reserves were positively correlated with invertase, suggesting phenology may affect carbon allocation to ectomycorrhizal fungi. However, of the four enzymes, host phenology had the largest effect on β‐glucuronidase, but activity of this enzyme was not correlated with root carbon reserves or invertase. Low‐biomass ectomycorrhizas had greater potential laccase activity than high‐biomass ectomycorrhizas, highlighting discrete functional traits in fungi for litter decomposition. Our results suggest that the decomposition of organic matter may be driven by foraging by fungi for nutrients locked within organic compounds rather than for mobilizing carbon. Furthermore, the potential ability to degrade lignin was more common in low‐biomass ectomycorrhizas when compared to high‐biomass ectomycorrhizas. A Lay Summary is available for this article.