Jane Wishart

Spatial variability of soil total C and N and their stable isotopes in an upland Scottish grassland

As preparation for a below ground food web study, the spatial variability of three soil properties (total N, total C and pH) and two stable isotopes (δ13C and δ15N of whole soil) were quantified using geostatistical approaches in upland pastures under contrasting management regimes (grazed, fertilised and ungrazed, unfertilised) in Scotland. This is the first such study of upland, north maritime grasslands. The resulting patterns of variability suggest that to obtain statistically independent samples in this system, a sampling distance of ≥13.5 m is required. Additionally, temporal change (a decline of 1‰) was observed in whole soil δ15N for the grazed, fertilised plot. This may have been caused by new inputs of symbiotically-fixed atmospheric N2.

Stable isotope natural abundances of soil, plants and soil invertebrates in an upland pasture

Abstract In an exploratory study of below-ground trophic relations, natural abundances of the stable isotope pairs 13C/12C and 15N/14N (δ13C and δ15N) were measured on samples of plant shoots, whole soil and soil invertebrates taken in 1994 from two contrasting treatments of a pre-existing experiment: (1) continued grazing by sheep, with N:P:K fertiliser additions from 1990 onward; and (2) no added fertiliser, but sheep grazing removed entirely. Stepwise trophic increases were documented better by seasonal averages of δ13C and δ15N and by seasonal trends, composed of data collected on several occasions, than by instantaneous values. Seasonal changes in plant monocot vs dicot differences for shoot δ13C and δ15N were detected from patterns over several individual sampling dates; instantaneous samples were neither statistically significant nor qualitatively interpretable. Significant isotopic differences between treatments were evident in invertebrates only as seasonal averages or trends. Seasonal variations of δ13C and δ15N in earthworms and slugs may reflect previously unsuspected invertebrate behaviour. Whole soil δ13C was static through time and across treatments. Whole soil δ15N changed seasonally, an effect consistent with 15N/14N fractionation, e.g. during denitrification.

Mitochondrial DNA differences distinguishing Meloidogyne mayaguensis from the major species of tropical root-knot nematodes

- The mitochondrial DNA region between the COII and lRNA genes and the 63 base pair tandem repeat region have been used to differentiate and characterise Meloidogyne spp. In this study these regions have been amplified from M. mayaguensis, M. javanica, M. arenaria, M. incognita and M. hapla. Meloidogyne mayaguensis produces a unique product of 705 bp from the COII and lRNA region. Also, a product of 322 bp was produced from the 63 bp repeat region of M. mayaguensis unlike M. javanica, M. arenaria, and M. incognita that exhibit hypervariability in this region. Meloidogyne mayaguensis is a widely distributed root-knot nematode with the potential to cause great economic damage. These molecular diagnostics can be used for accurate identification of M. mayaguensis and can be used to monitor the occurrence and spread of this species, and to provide quarantine services tools to limit its dispersal.

Root traits for infertile soils

Crop production is often restricted by the availability of essential mineral elements. For example, the availability of N, P, K, and S limits low-input agriculture, the phytoavailability of Fe, Zn, and Cu limits crop production on alkaline and calcareous soils, and P, Mo, Mg, Ca, and K deficiencies, together with proton, Al and Mn toxicities, limit crop production on acid soils. Since essential mineral elements are acquired by the root system, the development of crop genotypes with root traits increasing their acquisition should increase yields on infertile soils. This paper examines root traits likely to improve the acquisition of these elements and observes that, although the efficient acquisition of a particular element requires a specific set of root traits, suites of traits can be identified that benefit the acquisition of a group of mineral elements. Elements can be divided into three Groups based on common trait requirements. Group 1 comprises N, S, K, B, and P. Group 2 comprises Fe, Zn, Cu, Mn, and Ni. Group 3 contains mineral elements that rarely affect crop production. It is argued that breeding for a limited number of distinct root ideotypes, addressing particular combinations of mineral imbalances, should be pursued.

Ribosomal intergenic spacer: a polymerase chain reaction diagnostic for Meloidogyne chitwoodi, M. fallax, and M. hapla.

ABSTRACT Polymerase chain reaction amplification of the intergenic spacer region between the 5S and 18S genes from Meloidogyne chitwoodi, M. fallax, and M. hapla enabled these three important temperate species to be differentiated. Length polymorphism was found between M. chitwoodi and M. fallax as a result of differing numbers of short repeats located between the 5S and 18S genes. The presence of the 5S gene within the rDNA cistrons was confirmed in the Meloidogyne spp. included in this study. The region between the 28S and 5S genes for M. chitwoodi and M. fallax was short and lacked variability in repeated sequences compared with the main tropical Meloidogyne spp. and M. hapla. Differences in the number of these repeats resulted in intraspecific length polymorphism for M.hapla.

Above-ground grazing affects floristic composition and modifies soil trophic interactions

Abstract There are few data on the functional inter-relationships between above- and below-ground components of soil ecosystems. Here, we report changes in below-ground soil invertebrate trophic relationships (manifested as alterations in stable isotope natural abundances, δ 13 C and δ 15 N) that arose in association with the removal of sheep grazing and from the resulting changes in above-ground floristic composition. Consequent to grazing removal, Lolium perenne L. (perennial rye-grass) was replaced as the dominant plant species in ungrazed treatments by Ranunculus repens L. (creeping buttercup), a species with more 13 C-enriched foliage. Consequently, all invertebrate functional groups studied, but not whole soil, were more 13 C-enriched in ungrazed treatments. Earthworms (detritivore) from grazed treatments were significantly 15 N-enriched compared with earthworms from ungrazed treatments. In contrast, slug (herbivore) δ 15 N exhibited no treatment effect. Reasons for this are unclear but may be related to the effects of above-ground grazing on the composition of below-ground microbial/microfaunal communities. Omnivores/carnivores (beetles and spiders), were more 15 N-enriched than primary producers in the grazed than in the ungrazed treatments (6 vs. 4‰) suggesting a longer below-ground foodchain in the grazed plots. The cessation of fertilizer application had no comparable effects on below-ground trophic relationships.

Field phenotyping of potato to assess root and shoot characteristics associated with drought tolerance

AimsPotatoes are a globally important source of food whose production requires large inputs of fertiliser and water. Recent research has highlighted the importance of the root system in acquiring resources. Here measurements, previously generated by field phenotyping, tested the effect of root size on maintenance of yield under drought (drought tolerance).MethodsTwelve potato genotypes, including genotypes with extremes of root size, were grown to maturity in the field under a rain shelter and either irrigated or subjected to drought. Soil moisture, canopy growth, carbon isotope discrimination and final yields were measured. Destructively harvested field phenotype data were used as explanatory variables in a general linear model (GLM) to investigate yield under conditions of drought or irrigation.ResultsDrought severely affected the small rooted genotype Pentland Dell but not the large rooted genotype Cara. More plantlets, longer and more numerous stolons and stolon roots were associated with drought tolerance. Previously measured carbon isotope discrimination did not correlate with the effect of drought.ConclusionsThese data suggest that in-field phenotyping can be used to identify useful characteristics when known genotypes are subjected to an environmental stress. Stolon root traits were associated with drought tolerance in potato and could be used to select genotypes with resilience to drought.

Pasteuria penetrans and P. nishizawae attachment to Meloidogyne chitwoodi , M. fallax and M. hapla

This is the first report of endospores of Pasteuria penetrans and P. nishizawae isolates binding to juveniles of Meloidogyne chitwoodi and M. fallax. The patterns of endospore attachment to M. chitwoodi and M. fallax compared with the related M. hapla suggest that there are differences amongst these three temperate root-knot nematode species. Intraspecific variability in attachment of P. penetrans to juveniles of M. chitwoodi was demonstrated.

Flower choices by raspberry beetles : cues for feeding and oviposition

Raspberry beetles, Byturus tomentosus, use raspberry as the host plant for feeding, mating and oviposition; the larvae are a major pest on the fruit. This study seeks reasons for their choices between flowers of different cultivars. Beetles showed consistent diurnal movements between different cultivars of raspberry, which were linked to differential behavioural patterns; they fed predominantly on Glen Clova canes in the morning and moved to Glen Prosen later in the day where oviposition behaviour was commoner and substantially more effective. Hence two closely similar cultivars of the same plant species received very different levels of flower damage (from adult feeding) and of fruit damage (from larval infestation). These patterns were linked to subtle differences in cues from the host plant; Glen Clova produces unusually copious nectar which may limit oviposition opportunities because of osmotic threats to eggs and larvae, whereas Glen Prosen has drier flowers for egg laying and apparently emits a short-lived volatile cue that principally attracts female beetles. Selective breeding of the host plant has therefore had unexpected side-effects on interactions with a major pest species, mediated by the behaviour of the insect, and perhaps accentuating natural behavioural preferences that serve to reduce competition between adult and larval stadia. Copyright 1998 The Association for the Study of Animal Behaviour.

Juvenile root vigour improves phosphorus use efficiency of potato

AimsPotato (Solanum tuberosum L.) has a large phosphorus (P)-fertiliser requirement. This is thought to be due to its inability to acquire P effectively from the soil. This work tested the hypothesis that early proliferation of its root system would enhance P acquisition, accelerate canopy development, and enable greater yields.MethodsSix years of field experiments characterised the relationships between (1) leaf P concentration ([P]leaf), tuber yield, and tuber P concentration ([P]tuber) among 27 Tuberosum, 35 Phureja and 4 Diploid Hybrid genotypes and (2) juvenile root vigour, P acquisition and tuber yield among eight Tuberosum genotypes selected for contrasting responses to P-fertiliser.ResultsSubstantial genetic variation was observed in tuber yield, [P]leaf and [P]tuber. There was a strong positive relationship between tuber yields and P acquisition among genotypes, whether grown with or without P-fertiliser. Juvenile root vigour was correlated with accelerated canopy development and both greater P acquisition and tuber biomass accumulation early in the season. However, the latter relationships became weaker during the season.ConclusionsIncreased juvenile root vigour accelerated P acquisition and initial canopy cover and, thereby, increased tuber yields. Juvenile root vigour is a heritable trait and can be selected to improve P-fertiliser use efficiency of potato.