Nutrient Acquisition Strategies Research Articles

Salt Tolerance Strategies of Nitraria tangutorum Bobr. and Elaeagnus angustifolia Linn. Determine the Inoculation Effects of Microorganisms in Saline Soil Conditions

Increasing salinization threatens the normal growth of halophytes in saline habitats, especially at the seedling stage. Soil beneficial microorganisms have the potential to promote salt tolerance of halophytes, but less attention has been paid to the various responses between different halophytes with microbial inoculations. Here we performed pot experiments to assess the responses of Nitraria tangutorum Bobr. and Elaeagnus angustifolia Linn. to arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) inoculation in saline soil conditions. The results showed that neither a single AMF inoculation nor a single PGPR inoculation promoted the growth of N. tangutorum. In contrast, co-inoculation not only promoted biomass accumulation but also promoted the absorption of P, K+, and Ca2+ in the roots, and the accumulation of N, Na+, K+, and Ca2+ in the leaves. Co-inoculation also increased the K+/Na+ ratio in the roots as well as the Ca2+/Na+ ratio in both roots and leaves of N. tangutorum. Na+ is an important inorganic osmolyte, essential for both efficient osmoregulation and biomass accumulation in N. tangutorum. PGPR inoculation alone could not promote the growth of E. angustifolia. AMF inoculation, solely or combined with PGPR, was beneficial to the absorption of K+ and Ca2+ in the roots, the accumulation of N and K+ in the leaves, the maintenance of the K+/Na+ ratio and Ca2+/Na+ ratio in the leaves, the selective transportation of K+ and Ca2+ from roots to leaves, and the accumulation of proline and glycine betaine in the leaves of E. angustifolia. Increased nutrient absorption, ion homeostasis, and K+ and Ca2+ selective transportation in AMF-inoculated E. angustifolia helped reduce the toxic effects of Na+ and the damage caused by osmotic stress in saline soil conditions. “Plant-microbe specificity” leads to the different responses of N. tangutorum and E. angustifolia seedlings to AMF and PGPR inoculation in saline soil conditions. The different salt tolerance strategies for osmoregulation, nutrient acquisition, ion homeostasis, and ion transportation determine the differential responses in N. tangutorum and E.angustifolia to AMF and PGPR inoculations under saline soil conditions.

Accumulation in nutrient acquisition strategies of arbuscular mycorrhizal fungi and plant roots in poor and heterogeneous soils of karst shrub ecosystems

BackgroundArbuscular mycorrhizal (AM) fungi and roots play important roles in plant nutrient acquisition, especially in nutrient poor and heterogeneous soils. However, whether an accumulation strategy of AM fungi and root exists in such soils of karst shrubland ecosystems remains unclear. Root traits related to nutrient acquisition (root biomass, AM colonisation, root acid phosphatase activity and N2 fixation) were measured in two N2-fixing plants (i.e. Albizia odoratissima (Linn. f.) Benth. and Cajanus cajan (Linn.) Millsp.) that were grown in heterogeneous or homogeneous nutrient (ammonium) soil with and without AM fungi inoculation.ResultsBoth of these plants had higher AM colonisation, root biomass and relative growth rate (RGR), but lower N2 fixation and root acid phosphatase activity in the rhizosphere in the heterogeneous soil environment, than that in the homogeneous soil environment. Plants grown in the AM fungi-inoculated heterogeneous soil environment had increased root biomass and root acid phosphatase activity compared with those grown in soil without inoculation. AM colonisation was negatively correlated with the N2 fixation rate of A. odoratissima, while it was not significantly correlated with the root phosphatase activity.ConclusionsOur results indicated that enhanced AM symbiosis and root biomass increased the absorptive surfaces for nutrient acquisition, highlighting the accumulation strategies of AM and root traits for plant nutrient acquisition in nutrient poor and heterogeneous soils of the karst shrubland ecosystem.

A framework for fine‐root trait syndromes: syndrome coexistence may support phosphorus partitioning in tropical forests

Fine roots balance multiple essential plant functions that ultimately fuel plant productivity. The coordination of root functional traits is multidimensional, meaning that some traits are correlated while others can vary independently. This leads to a large variety of adaptive trait combinations and thus functional diversity in plant belowground morphology, anatomy, physiology and symbioses with soil biota. Within forest communities, co‐occurrence of such belowground trait combinations may be especially prevalent in tropical forests, not only due to their immense biodiversity but also because their soils are frequently weathered and limited in phosphorus. Phosphorus occurs in different forms (that differ in their mobility and accessibility) that may select for different trait combinations on relatively small spatial scales. While evidence accumulates of the myriad viable nutrient acquisition strategies on poor tropical soils, they are not well conceptualized. In this study, we outline criteria for the identification and investigation of fine‐root trait syndromes. We then apply these criteria to a case study of tropical tree species adapted to phosphorus‐poor soil and synthesize a range of traits. Five potentially coexisting syndromes are presented that are distinguished by root morphology, mycorrhizal association type, their interactions and implications for fine‐root functioning. We connect the functional variation of these species‐level syndromes in tropical communities to an established phosphorus partitioning hypothesis. The co‐occurrence of fine‐root trait syndromes could have implications for root sampling design, species coexistence, community structure and biogeochemical cycling.

Divergent responses of functional diversity to an elevational gradient for vascular plants, bryophytes and lichens

AbstractQuestionCold environments are stressful for vascular plants, and stress‐tolerant non‐vascular photoautotrophs, e.g. bryophytes and lichens, become relatively more important as competition from vascular plants decreases towards higher elevations. Under increasingly stressful climatic conditions, species assembly of vascular plants is commonly driven more by environmental filtering, and abiotic constraints may lead to increased similarity between species and thus low functional diversity. Because bryophytes and lichens are less constrained by harsh environments, environmental filtering may be less strong. Instead, reduced competition from vascular plants can potentially free up niche space for non‐vascular vegetation. Therefore, we hypothesized that functional diversity of vascular plants, bryophytes and lichens are likely to show contrasting responses to elevation.LocationFinse Alpine Research Centre, Southern Norway.MethodsWe utilized measurements of species abundance and functional traits of the three groups along a 500‐m elevational gradient in alpine southern Norway and calculated multi‐trait and single‐trait functional dispersion.ResultsFunctional diversity of vascular plants declined with elevation, indicating increased environmental filtering. By contrast, functional diversity of lichens and bryophytes increased along the same gradient, suggesting they are less exposed to environmental filtering, in line with our hypothesis. Instead, they likely benefit from the lower abundance of vascular plants at higher elevation.ConclusionsOur findings suggest that different photoautotroph groups vary in how they respond to the same environmental gradient, which may contribute to contrasting community assembly processes across groups. These divergent responses likely occur because non‐vascular vegetation differs from vascular plants in terms of nutrient acquisition and water economy strategies, meaning that they respond differently to the same factors. This highlights the need to explicitly consider bryophytes and lichens in community‐level studies whenever these groups are abundant.

Nutrient-acquisition strategy influences seed nutrient concentration and seed-to-seedling transition in ecological restoration in a regional dryland flora

Nutrient-acquisition strategy influences seed nutrient concentration and seed-to-seedling transition in ecological restoration in a regional dryland flora

Silicon mobilisation by root-released carboxylates.

Plants have evolved numerous strategies to acquire poorly available nutrients from soil, including the release of carboxylates from their roots. Silicon (Si) release from mineral dissolution increases in the presence of chelating substances, and recent evidence shows that leaf [Si] increases markedly in old phosphorus (P)-depleted soils, where many species exhibit carboxylate-releasing strategies, compared with younger P-richer soils. Here, we propose that root-released carboxylates, and more generally rhizosphere processes, play an overlooked role in plant Si accumulation by increasing soil Si mobilisation from minerals. We suggest that Si mobilisation is costly in terms of carbon but becomes cheaper if those costs are already met to acquire poorly available P. Uptake of the mobilised Si by roots will then depend on whether they express Si transporters.

Interactive effects of light, CO2 and temperature on growth and resource partitioning by the mixotrophic dinoflagellate, Karlodinium veneficum.

There is little information on the impacts of climate change on resource partitioning for mixotrophic phytoplankton. Here, we investigated the hypothesis that light interacts with temperature and CO2 to affect changes in growth and cellular carbon and nitrogen content of the mixotrophic dinoflagellate, Karlodinium veneficum, with increasing cellular carbon and nitrogen content under low light conditions and increased growth under high light conditions. Using a multifactorial design, the interactive effects of light, temperature and CO2 were investigated on K. veneficum at ambient temperature and CO2 levels (25°C, 375 ppm), high temperature (30°C, 375 ppm CO2), high CO2 (30°C, 750 ppm CO2), or a combination of both high temperature and CO2 (30°C, 750 ppm CO2) at low light intensities (LL: 70 μmol photons m-2 s-2) and light-saturated conditions (HL: 140 μmol photons m-2 s-2). Results revealed significant interactions between light and temperature for all parameters. Growth rates were not significantly different among LL treatments, but increased significantly with temperature or a combination of elevated temperature and CO2 under HL compared to ambient conditions. Particulate carbon and nitrogen content increased in response to temperature or a combination of elevated temperature and CO2 under LL conditions, but significantly decreased in HL cultures exposed to elevated temperature and/or CO2 compared to ambient conditions at HL. Significant increases in C:N ratios were observed only in the combined treatment under LL, suggesting a synergistic effect of temperature and CO2 on carbon assimilation, while increases in C:N under HL were driven only by an increase in CO2. Results indicate light-driven variations in growth and nutrient acquisition strategies for K. veneficum that may benefit this species under anticipated climate change conditions (elevated light, temperature and pCO2) while also affecting trophic transfer efficiency during blooms of this species.

Nutrient sources for offspring formation: diet–mother and mother–offspring isotope discrimination in domesticated gallinaceous birds

ABSTRACT Stable isotope techniques can be used to assess nutrient acquisition and allocation strategies used to produce offspring. Before stable isotope techniques can be employed, researchers need reliable isotope discrimination values. In this context, isotope discrimination compares the difference in the isotope ratio between the maternal–offspring tissue that occurs during nutrient transfer prior to egg laying. Currently, isotope discrimination values are unknown between the maternal blood constituents – that reflect different temporal scales of integration – and downy feathers of their offspring. In this study, we experimentally derive isotope discrimination relationships between maternal diet–blood constituents for egg laying, and between maternal blood constituents–down feathers of offspring in an experiment with 3 types of domesticated gallinaceous birds raised on known diets. Our experiment is the first to report isotope discrimination values for maternal blood constituents–down of offspring in avian taxa and provides a new sampling technique that is less invasive than previously available as collecting down does not require sampling viable eggs or individuals. Future researchers can use these results to assist in identifying nutrient sources used by adult birds to produce young.

Mycorrhizal roots slow the decay of belowground litters in a temperate hardwood forest.

There is increasing evidence that plant roots and mycorrhizal fungi, whether living or dead, play a central role in soil carbon (C) cycling. Root-mycorrhizal-microbial interactions can both suppress and enhance litter decay, with the net result dependent upon belowground nutrient acquisition strategies and soil nutrient availability. We measured the net effect of living roots and mycorrhizal fungi on the decay of dead roots and fungal hyphae in a hardwood forest dominated by either sugar maple (Acer saccharum) or white oak (Quercus alba) trees. Root and fungal litter were allowed to decompose within root-ingrowth bags and root-exclusion cores. In conjunction with root effects on decay, we assessed foraging responses and root induced changes in soil moisture, nitrogen (N) availability and enzyme activity. After 1 year, maple root production increased, and mycorrhizal fungal colonization decreased in the presence of decaying litter. In addition, we found that actively foraging roots suppressed the decay of root litter (-14%) more than fungal litter (-3%), and suppression of root decay was stronger for oak (-20%) than maple roots (-8%). Suppressive effects of oak roots on decay were greatest when roots also reduced soil N availability, which corresponded with reductions in hydrolytic enzyme activity and enhanced oxidative enzyme activities. These findings further our understanding of context-dependent drivers of root-mycorrhizal-microbial interactions and demonstrate that such interactions can play an underappreciated role in soil organic matter accumulation and turnover in temperate forests.

Biogeomorphological evolution of rocky hillslopes driven by roots in campos rupestres, Brazil

The campos rupestres (rocky grassland) comprise an old-growth seasonally dry herbaceous ecosystem on mountaintops in central and eastern Brazil and in disjoint areas with sparse shrubs with high plant diversity and endemism. This ecosystem consists of sharp-edged quartzite landforms and rocky hillslopes with boulders, blocks, and sparse soil cover. The slopes in these environments have traditionally been viewed as a product of mechanical rock breakdown controlled by structural and lithological features of rocky hillslopes. In addition to the lithological effects on slope evolution, plant cover plays a pivotal role in the geomorphological process. We explored process–form relationships between plant cover and quartzite rocky hillslopes of campos rupestres, considering the functioning of root traits of rock dwelling endemic species of Velloziaceae. Velloziaceae is an iconic plant family in campos rupestres, and several species colonize quartzite rock with different biogeomorphic effects at different scales. We present a conceptual model of the evolution of quartzite hillslopes based on the arenization process driven by roots expressing a specialized nutrient-acquisition strategy: vellozioid roots. Our results show that at the outcrop scale, roots respond to previous lithological characteristics such as joints and fractures that allow root establishment, followed by the release of large quantities of carboxylates that lead to rock dissolution. The microscopic pattern of bioweathering is associated with enlargement of the quartzite secondary porosity through the formation of root microcracks. Roots that are about 100 μm thick form root mats that surround the grains and produce inter-mineral and intra-mineral porosity systems facilitating percolation of water and organic solutes increasing the weathering. This results in arenization of quartzite by grain-by-grain dissolution and reduces the rock strength, which leads to the formation of quartzite hillslopes, driven by a nutrient-acquisition strategy of vellozioid roots. The described biogeomorphic process determines trajectories of the development of landforms through time, slope-sediment production, slope morphology by the production of boulders and block fields, and sand patches that are reworked by surface runoff along the slope. The hillslopes and landforms that develop in campos rupestres are therefore products of self-reinforcing processes involving nutrient acquisition from bedrock by plants and denudation processes. Also, these positive feedbacks characterize the Velloziaceae species as ecosystem engineers.

Crop Domestication, Root Trait Syndromes, and Soil Nutrient Acquisition in Organic Agroecosystems: A Systematic Review

Selecting crops that express certain reproductive, leaf, and root traits has formed detectable, albeit diverse, crop domestication syndromes. However, scientific and informal on-farm research has primarily focused on understanding and managing linkages between only certain domestication traits and yield. There is strong evidence suggesting that functional traits can be used to hypothesize and detect trade-offs, constraints, and synergies among crop yield and other aspects of crop biology and agroecosystem function. Comparisons in the functional traits of crops vs. wild plants has emerged as a critical avenue that has helped inform a better understanding of how plant domestication has reshaped relationships among yield and traits. For instance, recent research has shown domestication has led important economic crops to express extreme functional trait values among plants globally, with potentially major implications for yield stability, nutrient acquisition strategies, and the success of ecological nutrient management. Here, we present an evidence synthesis of domestication effects on crop root functional traits, and their hypothesized impact on nutrient acquisition strategies in organic and low input agroecosystems. Drawing on global trait databases and published datasets, we show detectable shifts in root trait strategies with domestication. Relationships between domestication syndromes in root traits and nutrient acquisition strategies in low input systems underscores the need for a shift in breeding paradigms for organic agriculture. This is increasingly important given efforts to achieve Sustainable Development Goal (SDG) targets of Zero Hunger via resilient agriculture practices such as ecological nutrient management and maintenance of genetic diversity.

Root and mycorrhizal strategies for nutrient acquisition in forests under nitrogen deposition: A meta-analysis

Global increase in nitrogen (N) deposition influences the belowground allocation of plant photosynthates and the formation of roots and rhizosphere-associated symbionts as well as soil nutrient availability, thereby affecting the nutrient acquisition by trees. Trees obtain nutrients primarily through fine root growth or mycorrhizal symbioses. These two mechanisms have an antagonistic relationship, but how they are modified by N deposition remains unknown. Arbuscular mycorrhizae (AM) and ectomycorrhizae (EM) are the two dominant types of mycorrhizal fungi that form symbioses with the roots of most trees. However, the divergent adaptive mechanisms and nutrient acquisition strategies of trees with a symbiotic relationship with AM (AM trees) or with EM (EM trees) in response to N deposition are unclear. To clarify these points, we conducted a meta-analysis of 116 studies on global forest ecosystems. Following prolonged (>2 years) or high-load (>140 kg ha−1 y−1) N addition, both AM and EM trees decrease the amount of energy allocated to mycorrhizal symbioses and increasingly rely on fine roots to obtain nutrients. The faster growth of AM trees than of EM trees under N deposition is partly attributed to their divergent nutrient acquisition strategies: the fine root biomass and length decreased significantly in EM trees (−13% and −17%, respectively), but not in AM trees. Furthermore, the acid phosphatase activity increased more for the AM trees than for the EM trees (28% and 4%, respectively), indicative of a greater abundance of available P for the AM trees than for the EM trees after N addition. Consequently, AM trees have advantages in terms of root morphology and phosphatase activity over EM trees, suggesting they are better adapted to high N deposition.

Differential responses of N benefit mediated by root exudate inputs to N addition between two subalpine forests

Root C investment to exchange for the nutrient is a critical nutrient acquisition strategy in regulating soil biogeochemical processes and maintaining the stability of forest structure and functions. However, the response patterns of root C cost-nutrient benefit strategies to N deposition in forests with different initial soil N availability are poorly understood. In this study, root exudation rates were measured by in situ collection during the growing season in two coniferous plantations (i.e., Pinus armandii and Picea asperata plantations with relatively lower and higher initial soil N availability, respectively) to assess whether two plantations differed in root C cost under N addition (25 kg N ha−1 a−1). Simultaneously, the differences in enzyme activity and related soil N mineralization rate between the rhizosphere and bulk soils were quantified to assess whether two plantations differed in N acquisition capacities under N addition. The results showed that N addition to some extent mitigated N-limitation by improving soil N availability, reducing root exudation rate per root biomass and rhizosphere effect of N mineralization by 36.43% and 38.13% in the P. armandii plantation, implying that plant nutrient acquisition strategy shifts from “high C cost-N benefit” to “low C cost-N benefit” strategy. In contrast, in the P. asperata plantation with relatively high initial soil N availability, N addition had little effect on root exudate inputs and related N mineralization capacity, i.e., plant root C cost-nutrient acquisition strategy was independent of N addition in the P. asperata plantation. Collectively, the results suggest that the response patterns of root C cost-N acquisition strategies to N addition between different tree species closely depend on soil N availability, which was more sensitive in forests with lower soil N availability. As a result, variable tradeoffs between root C investment and N acquisition provide new insight into the understanding of rhizosphere nutrient cycling for stability and productivity of forest ecosystem under environmental changes.

Nutrient Acquisition and Attachment Strategies in Basal Lineages: A Tough Nut to Crack in the Evolutionary Puzzle of Apicomplexa.

Apicomplexa are unicellular eukaryotes that parasitise a wide spectrum of invertebrates and vertebrates, including humans. In their hosts, they occupy a variety of niches, from extracellular cavities (intestine, coelom) to epicellular and intracellular locations, depending on the species and/or developmental stages. During their evolution, Apicomplexa thus developed an exceptionally wide range of unique features to reach these diversified parasitic niches and to survive there, at least long enough to ensure their own transmission or that of their progeny. This review summarises the current state of knowledge on the attachment/invasive and nutrient uptake strategies displayed by apicomplexan parasites, focusing on trophozoite stages of their so far poorly studied basal representatives, which mostly parasitise invertebrate hosts. We describe their most important morphofunctional features, and where applicable, discuss existing major similarities and/or differences in the corresponding mechanisms, incomparably better described at the molecular level in the more advanced Apicomplexa species, of medical and veterinary significance, which mainly occupy intracellular niches in vertebrate hosts.

Differential effects of nitrogen vs. phosphorus limitation on terrestrial carbon storage in two subtropical forests: A Bayesian approach

Nitrogen (N) and phosphorus (P) have been demonstrated to limit terrestrial carbon (C) storage in terrestrial ecosystems. However, the reliable indicator to infer N and P limitation are still lacking, especially in subtropical forests. Here we used a terrestrial ecosystem (TECO) model framework in combination with a Bayesian approach to evaluate effects of nutrient limitation from added N/P processes and data sets on C storage capacities in two subtropical forests (Tiantong and Qianyanzhou [QYZ]). Three of the six simulation experiments were developed with assimilating data (TECO C model with C data [C-C], TECO C-N coupling model with C and N data [CN-CN], and TECO C-N-P model with C, N, and P data [CNP-CNP]), and the other three ones were simulated without assimilating data (C-only, CN-only, and CNP-only). We found that P dominantly constrained C storage capacities in Tiantong (42%) whereas N limitation decreased C storage projections in QYZ (44%). Our analysis indicated that the stoichiometry of wood biomass and soil microbe (e.g., N:P ratio) were more sensitive indicators of N or P limitation than that of other pools. Furthermore, effects of P-induced limitation were mainly on root biomass by additional P data and on both metabolic litter and soil organic carbon (SOC) by added P processes. N-induced effects were mainly from added N data that limited plant non-photosynthetic tissues (e.g., woody biomass and litter). The different effects of N and P modules on C storage projections reflected the diverse nutrient acquisition strategies associated with stand ages and plant species under nutrient stressed environment. These findings suggest that the interaction between plants and microorganisms regulate effects of nutrient availability on ecosystem C storage, and stoichiometric flexibility of N and P in plant and soil C pools could improve the representation of N and P limitation in terrestrial ecosystem models.

Calcicole-calcifuge plant strategies limit restoration potential in a regional semi-arid flora.

AimTo examine calcicole and calcifuge plant strategies, as well as nutrient‐acquisition strategies, as drivers of the distribution of species in response to edaphic factors, and the degree to which these strategies may act as filters to species establishment in ecological restoration on heavily altered or reconstructed substrates.LocationAn 82,000‐ha area within a major mining province in the Mid‐West region of Western Australia, harboring vegetation communities ranging from species‐poor halophytic scrub on saline flats to dense biodiverse shrubland on the skeletal soils of ancient Banded Ironstone Formations (BIF).MethodsUnivariate and multivariate analyses were employed to examine how variation in soil chemistry and landscape position (undulating plains, slopes, and BIF crests and ridges) influenced patterns of floristic diversity, calcifuge plant strategies, and nutrient‐acquisition strategies in 538 plant species from 830 relevés.ResultsLandscape position was the strongest driver of species richness and vegetation functional composition. Soils became increasingly acidic and P‐impoverished along an increasing elevational gradient. Vegetation from different landscape positions was not compositionally dissimilar, but vegetation of BIF crests and ridges was up to twice as biodiverse as vegetation from adjacent lower‐relief areas and harbored higher proportions of calcifuge species and species with mycorrhizal associations.Main conclusionsTopographic and edaphic complexity of BIF landforms in an otherwise relatively homogenous landscape has likely facilitated species accumulation over long time periods. They represent musea of regional floristic biodiversity, excluding only species that cannot establish or are inferior competitors in heavily weathered, acidic, skeletal, and nutrient‐impoverished soils. Plant strategies likely represent a major filter in establishing biodiverse, representative vegetation on postmining landforms in geologically ancient regions.

Nitrogen Nutrition Promotes Rhizome Bud Outgrowth via Regulation of Cytokinin Biosynthesis Genes and an Oryza longistaminata Ortholog of FINE CULM 1.

Oryza longistaminata, a wild rice, can propagate vegetatively via rhizome formation and, thereby, expand its territory through horizontal growth of branched rhizomes. The structural features of rhizomes are similar to those of aerial stems; however, the physiological roles of the two organs are different. Nitrogen nutrition is presumed to be linked to the vegetative propagation activity of rhizomes, but the regulation of rhizome growth in response to nitrogen nutrition and the underlying biological processes have not been well characterized. In this study, we analyzed rhizome axillary bud growth in response to nitrogen nutrition and examined the involvement of cytokinin-mediated regulation in the promotion of bud outgrowth in O. longistaminata. Our results showed that nitrogen nutrition sufficiency promoted rhizome bud outgrowth to form secondary rhizomes. In early stages of the response to nitrogen application, glutamine accumulated rapidly, two cytokinin biosynthesis genes, isopentenyltransferase, and CYP735A, were up-regulated with accompanying cytokinin accumulation, and expression of an ortholog of FINE CULM1, a negative regulator of axillary bud outgrowth, was severely repressed in rhizomes. These results suggest that, despite differences in physiological roles of these organs, the nitrogen-dependent outgrowth of rhizome axillary buds in O. longistaminata is regulated by a mechanism similar to that of shoot axillary buds in O. sativa. Our findings provide a clue for understanding how branched rhizome growth is regulated to enhance nutrient acquisition strategies.

Association of putatively adaptive genetic variation with climatic variables differs between a parasite and its host.

Parasitism is a pervasive phenomenon in nature with the relationship between species driving evolution in both parasite and host. Due to their host‐dependent lifestyle, parasites may adapt to the abiotic environment in ways that differ from their hosts or from free‐living relatives; yet rarely has this been assessed. Here, we test two competing hypotheses related to whether putatively adaptive genetic variation in a specialist mistletoe associates with the same, or different, climatic variables as its host species. We sampled 11 populations of the specialist mistletoe Amyema gibberula var. tatei (n = 154) and 10 populations of its associated host Hakea recurva subsp. recurva (n = 160). Reduced‐representation sequencing was used to obtain genome‐wide markers and putatively adaptive variation detected using genome scan methods. Climate associations were identified using generalized dissimilarity modelling, and these were mapped geographically to visualize the spatial patterns of genetic composition. Our results supported the hypothesis of parasites and host species responding differently to climatic variables. Temperature was relatively more important in predicting allelic turnover in the specialist mistletoe while precipitation was more important for the host. This suggests that parasitic plants and host species may respond differently to selective pressures, potentially as a result of differing nutrient acquisition strategies. Specifically, mistletoes acquire water from hosts (rather than the abiotic environment), which may provide a buffer to precipitation as a selective pressure. This work deepens and complements the physiological and other ecological studies of adaptation and provides a window into the evolutionary processes that underlie previously observed phenomena. Applying these methods to a comparative study in a host–parasite system has also highlighted factors that affect the study of selection pressure on nonmodel organisms, such as differing adaptation rates and lack of reference genomes.

Plant carbon investment in fine roots and arbuscular mycorrhizal fungi: A cross-biome study on nutrient acquisition strategies

Comparing the belowground allocation of assimilated carbon (C) to roots and mycorrhizal fungi across biomes can reveal specific plant nutrient acquisition strategies in ecosystems and allows to predict consequences of environmental changes. Three natural ecosystems (arid shrubland, coastal matorral, humid-temperate forest) distinct in annual precipitation and vegetation cover and compositions were selected to conduct a 13CO2 pulse labeling of natural woody vegetation to chase the allocation of assimilated C to arbuscular mycorrhizal (AM) fungi and fine roots. Further, nitrogen (N) and phosphorus (P) availability, root traits, root colonization, and the extraradical AM fungal mycelium (PLFA and NLFA 16:1ω5c) were analyzed to evaluate the efficiency of nutrient acquisition strategies. AM fungal colonization decreased with increasing aridity by up to 55% intraradical and by up to 90% extraradical. High root tissue densities – indicating longevity of roots – and low specific root lengths – indicating a low nutrient uptake capacity – pointed to a slow and resource conservative acquisition strategy of plants in the arid shrubland. Plants in the matorral, on the contrary, had lower root tissue densities but higher specific root lengths and higher root N contents, pointing to a fast nutrient acquisition strategy. The expression of abundant acquisitive fine roots of plants in the matorral, however, comes at the cost of larger C investment, shown by high 13C incorporation into root tissue. High root tissue densities and greater root diameter indicated that plants in the humid-temperate forest followed a resource-conservative strategy and outsource their nutrient acquisition to AM fungi. This outsourcing provides an efficient pathway to compensate a low uptake capacity of thick and dense roots. These ecosystem-specific acquisition strategies and distinct mutualism with AM fungi across the biomes will likely affect the sensitivity of plants to abiotic and biotic stressors and, thus, ecosystem responses to future climatic and environmental changes.

Response of root nutrient resorption strategies to rhizosphere soil microbial nutrient utilization along Robinia pseudoacacia plantation chronosequence

Understanding root nutrient resorption strategies and their drivers is essential to explore plant nutrient acquisition strategies in restored ecosystems. However, the interaction between root nutrient resorption and the nutrient utilization of rhizosphere soil microorganisms in restored ecosystems has yet to be determined. In this study, we investigated plant fine roots and rhizosphere soils in Robinia pseudoacacia plantations at four stages of forest succession (14, 20, 30, and 45 years of age) on the Loess Plateau in China. We studied the characteristics of root nitrogen and phosphorus resorption efficiencies (NRE and PRE) at different recovery stages and analyzed the relationships among nutrient resorption and rhizosphere soil variables (nutrients and microbial communities). We detected a tendency of an initial reduction and subsequent increase in root NRE and PRE with stand age (the lowest value at 30-y sites), whereas the nutrient contents of rhizosphere soil increased with stand age, and soil available nutrients initially increased and then declined. The diversity of rhizosphere soil microorganisms also showed an initial increase and subsequent decline. Proteobacteria were considered to be at an advantage during the nutrient-rich stage of restoration (30-y sites), whereas Acidobacteria were found to be dominant during the low-nutrient restoration stage (14-y sites). Furthermore, the microbial nutrient utilization ratios of soil microbial biomass carbon: soil organic carbon, microbial biomass nitrogen: soil total nitrogen, and microbial biomass phosphorus: soil total phosphorus also showed an initial increase and then decreased (with peaks at the 30-y sites). Redundancy analysis indicated that the nutrient contents of rhizosphere soil were significantly related to microbial communities and correlation analysis revealed that microbial nutrient-use efficiencies were significantly related to rhizosphere soil nutrient contents and the dominant microbial communities. We also detected a significant negative correlation between root nutrient resorption and microbial nutrient utilization. Partial least squares path modeling revealed that forest restoration influences the contents of nutrients in rhizosphere soil and the composition of microbial communities, whereas microbial biomass and nutrient utilization efficiency were shown to have a negative effect on root resorption efficiency. Based on our findings, we propose that the highly conservative nutrient utilization strategies of the rhizosphere soil microbial community may negatively drive root nutrient resorption strategies during the succession of R. pseudoacacia.