Breeding against mycorrhizal symbiosis:Modern cotton (Gossypium hirsutum L.) varieties perform more poorly than older varieties except at very high phosphorus supply levels

Cotton (Gossypium hirsutum L.) is an importantfiber cash crop,but its root traits related to phosphorus (P) acquisition,including mycorrhizal root traits,are poorly understood.Eight cotton varieties bred in northwestern China that were released between 1950 and 2013 were grown in pots with or without one arbuscular mycorrhizal fungal (AMF) species(Funneliformis mosseae) at three P supply levels (0,50 and 300 mg P as KH_(2)PO_(4)kg^(-1)).Eleven root traits were measured and calculated after 7 wk of growth.The more recent accessions had smaller root diameters,acquired less P and produced less biomass,indicating an (inadvertent) varietal selection for thinner roots that provided less cortical space for AMF,which then increased the need for a high P fertilizer level.At the two lower P levels,the mycorrhizal plants acquired more P and produced more biomass than non-mycorrhizal plants (3.2 vs.0.9 mg P per plant;1.8 vs.0.9 g biomass per plant at P_(0);14.5 vs.1.7 mg P per plant;and 4.7 vs.1.6 g biomass per plant at P_(50)).At the highest P level,the mycorrhizal plants acquired more P than non-mycorrhizal plants (18.8 vs.13.4 mg per P plant),but there was no difference in biomass (6.2 vs.6.3 g per plant).At the intermediate P level,root diameter was significantly positively correlated with shoot biomass,P concentration and the P content of mycorrhizal plants.The results of our study support the importance of the outsourcing model of P acquisition in the root economics space framework.Inadvertent varietal selection in the last decades,resulting in thinner roots and a lower benefit from AMF,has led to a lower productivity of cotton varieties at moderate P supply (i.e.,when mycorrhizal,the average biomass of older varieties 5.0 g per plant vs.biomass of newer varieties 4.4 g per plant),indicating the need to rethink cotton breeding efforts in order to achieve high yields without very high P input.One feasible way to solve the problem of inadvertent varietal selection for cotton is to be aware of the trade-offs between the root do-it-yourself strategy and the outsourcing towards AMF strategy,and to consider both morphological and mycorrhizal root traits when breeding cotton varieties.

Novel soil quality indicators for the evaluation of agricultural management practices:a biological perspective

Developments in soil biology and in methodsto characterize soil organic carbon can potentially delivernovel soil quality indicators that can help identifymanagement practices able to sustain soil productivityand environmental resilience. This work aimed atsynthesizing results regarding the suitability of a range ofsoil biological and biochemical properties as novel soilquality indicators for agricultural management. The soilproperties, selected through a published literature review,comprised different labile organic carbon fractions [hydrophilicdissolved organic carbon, dissolved organic carbon,permanganate oxidizable carbon (POXC), hot waterextractable carbon and particulate organic matter carbon],soil disease suppressiveness measured using a Pythium-Lepidium bioassay, nematode communities characterizedby amplicon sequencing and qPCR, and microbialcommunity level physiological profiling measured withMicroResp™. Prior studies tested the sensitivity of each ofthe novel indicators to tillage and organic matter additionin ten European long-term field experiments (LTEs) andassessed their relationships with pre-existing soil qualityindicators of soil functioning. Here, the results of theseprevious studies are brought together and interpretedrelative to each other and to the broader body of literatureon soil quality assessment. Reduced tillage increasedcarbon availability, disease suppressiveness, nematoderichness and diversity, the stability and maturity of thefood web, and microbial activity and functional diversity.Organic matter addition played a weaker role in enhancingsoil quality, possibly due to the range of composition of theorganic matter inputs used in the LTEs. POXC was theindicator that discriminated best between soil managementpractices, followed by nematode indices based on functionalcharacteristics. Structural equation modeling showsthat POXC has a central role in nutrient retention/supply,carbon sequestration, biodiversity conservation, erosion control and disease regulation/suppression. The novelindicators proposed here have great potential to improveexisting soil quality assessment schemes. Their feasibilityof application is discussed and needs for future research are outlined.

Geostatistical modelling and mapping of nematode-based soil ecological quality indices in a polluted nature reserve

Nematodes are indicators of soil quality and soil health.Knowledge of the relationships between nematode-based soil quality indices and environmental properties is beneficial for assessing environmental threats on soil biota.This study evaluated the spatial distribution of nematode-based soil quality indices in a 23-ha heavy metal-polluted nature reserve using geostatistical methods.We expected that a selection of abiotic soil properties(pH and moisture,clay,organic matter,cadmium(Cd),and zinc(Zn)contents)could explain a significant portion of the spatial variation of the indices and that regression kriging could more accurately model their spatial distribution than ordinary kriging.A stratified simple random sampling scheme was used to select 80 locations where soil samples were taken to extract nematodes and derive the indices.The area had a distinct gradient in soil properties with Cd and Zn content ranging from 0.07 to 68.9 and 5.3 to 1329 mg kg^(-1),respectively.Linear regression models were fitted to describe the relationships between the indices and soil properties.By also modelling the spatial correlation structure of regression residuals using spherical semivariograms,regression kriging was used to produce maps of the indices.The regression models explained between 21% and 44% of the total original variance in the indices.Soil pH was a significant explanatory variable in almost all cases,while heavy metal conent had a remarkably low effect.In some cases,the regression residuals had spatial structure.Independent validation indicated that in all cases,regression kriging performed slightly better because of having lower values of the root mean square prediction error and a mean prediction error closer to zero than ordinary kriging.This study showed the importance of soil properties in explaining the spatial distribution of biological soil quality indices in ecological risk assessment.

A trade-off between space exploration and mobilization of organic phosphorus through associated microbiomes enables niche differentiation of arbuscular mycorrhizal fungi on the same root

Ecology seeks to explain species coexistence,but experimental tests of mechanisms for coexistence are difficult to conduct.We synthesized an arbuscular mycorrhizal(AM)fungal community with three fungal species that differed in their capacity of foraging for orthophosphate(P)due to differences in soil exploration.We tested whether AM fungal species-specific hyphosphere bacterial assemblages recruited by hyphal exudates enabled differentiation among the fungi in the capacity of mobilizing soil organic P(P_(o)).We found that the less efficient space explorer,Gigaspora margarita,obtained less ^(13)C from the plant,whereas it had higher efficiencies in P_(o)mobilization and alkaline phosphatase(Al Pase)production per unit C than the two efficient space explorers,Rhizophagusintraradices and Funneliformis mosseae.Each AM fungus was associated with a distinct alp gene harboring bacterial assemblage,and the alp gene abundance and P_(o)preference of the microbiome associated with the less efficient space explorer were higher than those of the two other species.We conclude that the traits of AM fungal associated bacterial consortia cause niche differentiation.The trade-off between foraging ability and the ability to recruit effective P_(o)mobilizing microbiomes is a mechanism that allows co-existence of AM fungal species in a single plant root and surrounding soil habitat.

Net ecosystem carbon exchange for Bermuda grass growing in mesocosms as affected by irrigation frequency

Intensification of grazed grasslands following conversion from dryland to irrigated farming has the potential to alter ecosystem carbon(C)cycling and affect components of carbon dioxide(CO_(2))exchange that could lead to either net accumulation or loss of soil C.While there are many studies on the effect of water availability on biomass production and soil C stocks,much less is known about the effect of the frequency of water inputs on the components of CO_(2)exchange.We grew Bermuda grass(Cynodon dactylon L.)in mesocosms under irrigation frequencies of every day(I_(1) treatment,30 d),every two days(I_(2) treatment,12 d),every three days(I_(3) treatment,30 d),and every six days(I_(6) treatment,18 d,after I_(2) treatment).Rates of CO_(2)exchange for estimating net ecosystem CO_(2)exchange(F_(N)),ecosystem respiration(R_(E)),and soil respiration(R_(S))were measured,and gross C uptake by plants(F_(G))and respiration from leaves(R_(L))were calculated during two periods,1–12 and 13–30 d,of the 30-d experiment.During the first 12 d,there were no significant differences in cumulative F_(N)(mean±standard deviation,61±30 g C m^(-2),n=4).During the subsequent 18 d,cumulative F_(N) decreased with decreasing irrigation frequency and increasing cumulative soil water deficit(W),with values of 70±22,60±16,and 18±12 g C m^(-2) for the I_(1),I_(3),and I_(6) treatments,respectively.There were similar decreases in F_(G),R_(E),and R_(L) with increasing W,but differences in R_(S) were not significant.Use of the C_(4) grass growing in a C_(3)-derived soil enabled partitioning of R_(S) into its autotrophic(R_(A))and heterotrophic(R_(H))components using a^(13)C natural abundance isotopic technique at the end of the experiment when differences in cumulative W between the treatments were the greatest.The values of R_(H) and its percentage contributions to R_(S)(43%±8%,42%±8%,and 8%±5%for the I_(1),I_(3),and I_(6) treatments,respectively)suggested that R_(H) remained unaffected across a wide range of W and then decreased under extreme W.There were no significant differences in aboveground biomass between the treatments.Nitrous oxide(N_(2)O)emission was measured to determine if there was a trade-off effect between irrigation frequency and increasing W on net greenhouse gas emission,but no significant differences were found between the treatments.These findings suggest that over short periods in well-drained soil,irrigation frequency could be managed to manipulate soil water deficit in order to reduce net belowground respiratory C losses,particularly those from the microbial decomposition of soil organic matter,with no significant effect on biomass production and N_(2)O emission.

Intercropping enables a sustainable intensification of agriculture

Intercropping is the cultivation of more than one crop species on a single parcel of land. Intercropping seeks toexploit species complementarities to capture more of the available light, water and nutrient resources, and thusincrease combined crop yield[1]. Intercropping is well known in China, where smallholder farmers practice a greatdiversity of species combinations to increase their yields[2]. Figure 1 illustrates intercropping as done by a farmer inGansu Province, China, who chose to combine wheat, soybean and maize. This three-way combination offersseveral species complementarities. First, the growing period of wheat ends earlier than that of soybean and maize,so the soybean and maize can use all the light, water and nutrient resources of the land after wheat harvest. With thewheat covering only around half of the area, the plants will still produce about 70% of the normal yield for wheatgrown as a sole crop, because the wheat has virtually no competition for resources early on, resulting in greatercapture of light, water and nutrient resources in the intercrop than in a sole crop[3]. Furthermore, soybean and maizehave a complementarity for nitrogen acquisition, with maize requiring nitrogen from soil, but soybean being able to fixit from the air. Therefore, this combination can reduce fertilizer requirements.

A conceptual framework and an empirical test of complementarity and facilitation with respect to phosphorus uptake by plant species mixtures

Plant species have different traits for mobilizing sparingly soluble phosphorus (P) resources,which could potentially lead to overyielding in P uptake by plant species mixtures compared to monocultures due to higher P uptake as a result of resource (P) partitioning and facilitation.However,there is circumstantial evidence at best for overyielding as a result of these mechanisms.Overyielding (the outcome) is easily confused with underlying mechanisms because of unclear definitions.We aimed to define a conceptual framework to separate outcome from underlying mechanisms and test it for facilitation and complementarity with respect to P acquisition by three plant species combinations grown on four soils.Our conceptual framework describes both mechanisms of complementarity and facilitation and outcomes (overyielding of mixtures or no overyielding) depending on the competitive ability of the species to uptake the mobilized P.Millet/chickpea mixtures were grown in pots on two calcareous soils mixed with calcium-bound P (CaP) and phytate P (PhyP).Cabbage/faba bean mixtures were grown on both acid and neutral soils mixed with P-coated iron (hydr)oxide (FeP) and PhyP.Wheat/maize mixtures were grown on all four soils.Rhizosphere carboxylate concentration and acid phosphatase activity (mechanisms) as well as plant P uptake and biomass (outcome) were determined for monocultures rhizosphere and species mixtures.Facilitation of P uptake occurred in millet/chickpea mixtures on one calcareous soil.We found no indications for P acquisition from different P sources,neither in millet/chickpea,nor in cabbage/faba bean mixtures.Cabbage and faba bean on the neutral soil differed in rhizosphere acid phosphatase activity and carboxylate concentration,but showed no overyielding.Wheat and maize,with similar root exudates,showed overyielding (the observed P uptake being 22%higher than the expected P uptake) on one calcareous soil.We concluded that although differences in plant physiological traits (root exudates) provide necessary conditions for complementarity and facilitation with respect to P uptake from different P sources,they do not necessarily result in increased P uptake by species mixtures,because of the relative competitive ability of the mixed species.

Fungal diversity notes 253-366:taxonomic and phylogenetic contributions to fungal taxa

Notes on 113 fungal taxa are compiled in this paper,including 11 new genera,89 new species,one new subspecies,three new combinations and seven reference specimens.Awide geographic and taxonomic range of fungal taxa are detailed.In the Ascomycota the new genera Angustospora(Testudinaceae),Camporesia(Xylariaceae),Clematidis,Crassiparies(Pleosporales genera incertae sedis),Farasanispora,Longiostiolum(Pleosporales genera incertae sedis),Multilocularia(Parabambusicolaceae),Neophaeocryptopus(Dothideaceae),Parameliola(Pleosporales genera incertae sedis),and Towyspora(Lentitheciaceae)are introduced.Newly introduced species are Angustospora nilensis,Aniptodera aquibella,Annulohypoxylon albidiscum,Astrocystis thailandica,Camporesia sambuci,Clematidis italica,Colletotrichum menispermi,C.quinquefoliae,Comoclathris pimpinellae,Crassiparies quadrisporus,Cytospora salicicola,Diatrype thailandica,Dothiorella rhamni,Durotheca macrostroma,Farasanispora avicenniae,Halorosellinia rhizophorae,Humicola koreana,Hypoxylon lilloi,Kirschsteiniothelia tectonae,Lindgomyces okinawaensis,Longiostiolum tectonae,Lophiostoma pseudoarmatisporum,Moelleriella phukhiaoensis,M.pongdueatensis,Mucoharknessia anthoxanthi,Multilocularia bambusae,Multiseptospora thysanolaenae,Neophaeocryptopus cytisi,Ocellularia arachchigei,O.ratnapurensis,Ochronectria thailandica,Ophiocordyceps karstii,Parameliola acaciae,P.dimocarpi,Parastagonospora cumpignensis,Pseudodidymosphaeria phlei,Polyplosphaeria thailandica,Pseudolachnella brevifusiformis,Psiloglonium macrosporum,Rhabdodiscus albodenticulatus,Rosellinia chiangmaiensis,Saccothecium rubi,Seimatosporium pseudocornii,S.pseudorosae,Sigarispora ononidis and Towyspora aestuari.New combinations are provided for Eutiarosporella dactylidis(sexual morph described and illus trated)and Pseudocamarosporium pini.Descriptions,illustrations and/or reference specimens are designated for Aposphaeria corallinolutea,Cryptovalsa ampelina,Dothiorella vidmadera,Ophiocordyceps formosana,Petrakia echinata,Phragmoporthe conformis and Pseudocamarosporium pini.The new species of Basidiomycota are Agaricus coccyginus,A.luteofibrillosus,Amanita atrobrunnea,A.digitosa,A.gleocystidiosa,A.pyriformis,A.strobilipes,Bondarzewia tibetica,Cortinarius albosericeus,C.badioflavidus,C.dentigratus,C.duboisensis,C.fragrantissimus,C.roseobasilis,C.vinaceobrunneus,C.vinaceogrisescens,C.wahkiacus,Cyanoboletus hymenoglutinosus,Fomitiporia atlantica,F.subtilissima,Ganoderma wuzhishanensis,Inonotus shoreicola,Lactifluus armeniacus,L.ramipilosus,Leccinum indoaurantiacum,Musumecia alpina,M.sardoa,Russula amethystina subp.tengii and R.wangii are introduced.Descriptions,illustrations,notes and/or reference specimens are designated for Clarkeinda trachodes,Dentocorticium ussuricum,Galzinia longibasidia,Lentinus stuppeus and Leptocorticium tenellum.The other new genera,species new combinations are Anaeromyces robustus,Neocallimastix californiae and Piromyces finnis from Neocallimastigomycota,Phytophthora estuarina,P.rhizophorae,Salispina,S.intermedia,S.lobata and S.spinosa from Oomycota,and Absidia stercoraria,Gongronella orasabula,Mortierella calciphila,Mucor caatinguensis,M.koreanus,M.merdicola and Rhizopus koreanus in Zygomycota.