Drought mildly reduces plant dominance in a temperate prairie ecosystem across years

1. Shifts in dominance and species reordering can occur in response to global change. However, it is not clear how altered precipitation and disturbance regimes interact to affect species composition and dominance.
2. We explored community‐level diversity and compositional similarity responses, both across and within years, to a manipulated precipitation gradient and annual clipping in a mixed‐grass prairie in Oklahoma, USA. We imposed seven precipitation treatments (five water exclusion levels [?20%, ?40%, ?60%, ?80%, and ?100%], water addition [+50%], and control [0% change in precipitation]) year‐round from 2016 to 2018 using fixed interception shelters. These treatments were crossed with annual clipping to mimic hay harvest.
3. We found that community‐level responses were influenced by precipitation across time. For instance, plant evenness was enhanced by extreme drought treatments, while plant richness was marginally promoted under increased precipitation.
4. Clipping promoted species gain resulting in greater richness within each experimental year. Across years, clipping effects further reduced the precipitation effects on community‐level responses (richness and evenness) at both extreme drought and added precipitation treatments.
5. Synthesis: Our results highlight the importance of studying interactive drivers of change both within versus across time. For instance, clipping attenuated community‐level responses to a gradient in precipitation, suggesting that management could buffer community‐level responses to drought. However, precipitation effects were mild and likely to accentuate over time to produce further community change.

     

EVIDENCE FOR A MOSAIC HYBRID ZONE IN THE GRASS SHRIMP PALAEMONETES KADIAKENSIS (PALAEMONIDAE) AS REVEALED BY MULTIPLE GENETIC MARKERS

Molecular techniques provide powerful tools for studying the geographic structure of hybrid zones and the dynamics of gene exchange between incipient species. We examined allozyme variation at five loci (PGM, GPI, MDH-1, MDH-2, and LDH) for 27 populations of Palaemonetes kadiakensis from the central, coastal, and eastern regions of Texas. Central Texas populations of P. kadiakensis exhibited highly significant linkage disequilibrium and departures from Hardy-Weinberg genotype proportions. In populations with linkage disequilibrium, allelic differences at GPI defined two types of P. kadiakensis, designated A and B. Both types existed in central Texas with little or no evidence of interbreeding, whereas the populations from all other localities showed complete introgression of type B alleles into the type A gene pool. We also examined ribosomal DNA (rDNA) and mitochondrial DNA (mtDNA) variation in a subset of populations, chosen to cover a range of geographic locations and levels of linkage disequilibrium. Two groups of mtDNA haplotypes and two restriction fragment patterns for the rDNA corresponded to allozyme type A and B individuals in populations exhibiting linkage disequilibrium. In populations with ongoing hybridization, all hybrid animals (N= 15) exhibited type A mtDNA. Exhibition of type A mtDNA indicated that type A females had mated successfully with type B males, but type B females had not mated successfully with type A males. Genotype distributions suggest reduced reproduction by hybrid offspring in central Texas populations. These patterns are consistent with a mosaic model of hybrid zone dynamics.     

The inheritance of seed peroxidases of wheat and rye: further data

Summary Further data on the inheritance of seed peroxidases of hexaploid wheat (Triticum aestivum L.) and rye (Secale cereale L.) have been obtained from the genetic analysis of several progenies of both species. Additional data on the inheritance and the chromosomal location and linkage have been obtained for peroxidases of wheat embryo and rye endosperm. The general presence of null alleles in peroxidase loci has been confirmed in both species. In addition to simple monogenic inheritance, epistatic segregations have been observed in both species. These epistatic segregations again suggest the presence of regulatory genes controlling the expression of individual peroxidases in both species and also the existence of several duplicate homoeologous genes in wheat. Known linkage relationships have been confirmed and new ones are indicated. Loci for embryo wheat peroxidases seem to be in chromosomes of the homoeology group 3. The rye endosperm ones should be in chromosome 7R, although it is hypothesized that a duplication of gene EPer1 is located in chromosomes 4R and 7R.     

高等植物花粉母细胞内肌动蛋白的聚丙烯酰胺凝胶电泳分析

采用聚丙烯酰胺凝胶电泳技术分析了黑麦、蚕豆和百合花粉母细胞内肌动蛋白的存在与动态,结果表明高等植物的花粉母细胞在细胞融合期内的确存在一定量的肌动蛋白,并且,这种蛋白在早偶线期时出现,到四分体时期后消失。文章讨论了肌动蛋白的存在及其与细胞融合现象的联系。     

Association of four isozyme loci with a reciprocal translocation between 1R/4R chromosomes in cultivated rye (Secale cereale L.)

Summary The progeny of four crosses between a structural heterozygote for a reciprocal translocation and a homozygote for the standard chromosome arrangement were analyzed in rye (Secale cereale L. cv Ailés) for the electrophoretic patterns of eight different leaf and endosperm isozymes and also for the meiotic configuration at metaphase I. The Pgi-1, 6-Pgd-2 and Mdh-1 loci are linked to each other and also to the reciprocal translocation. These loci have been located on chromosome 1R. The Mdh-1 locus is located in the interstitial segment of chromosome 1R, between the centromere and the breakpoint. The Pgm-1 locus has been located on chromosome arm 4RS and is linked to Pgi-1, 6-Pgd-2, Mdh-1 and the reciprocal translocation. The estimated distance between the Pgm-1 locus and the centromere is 14.98 ± 2.27 cM. Therefore, the reciprocal translocation involves the 1R and 4R chromosomes. Other linked loci detected have been Mdh-2b and Est-2 (7.40 ± 2.90 cM) and Got-3 and Est-2 (5.62 ± 3.07 cM). These three last loci are located on chromosome 3R and their order most probably is Mdh-2b — Est-2 — Got-3.     

Host Status of Five Weed Species and Their Effects on Pratylenchus zeae Infestation of Maize

The host suitability of five of the most common weed species occurring in maize (Zea mays L.) fields in South Africa to Pratylenchus zeae was tested. Based on the number of nematodes per root unit, mealie crotalaria (Crotalaria sphaerocarpa) was a good host; goose grass (Eleusine indica), common pigweed (Amaranthus hybridus), and thorn apple (Datura stramonium) were moderate hosts; and khaki weed (Tagetes minuta) was a poor host. Only the root residues of khaki weed suppressed the P. zeae infestation of subsequently grown maize. When goose grass, khaki weed, and mealie crotalaria were grown in association with maize in soil infested with P. zeae, goose grass and khaki weed severely suppressed maize root development; this resulted in a low number of nematodes per maize root system and a high number of nematodes per maize root unit. Mealie crotalaria did not restrict maize root growth and did not affect nematode densities per maize root system or maize root unit. Special attention should be given to the control of mealie crotalaria, which is a good host for P. zeae, and goose grass, which, in addition to its ability to compete with maize, is also a suitable host for P. zeae.     

Spatial arrangement of tiller replacement in Agropyron desertorum following grazing

Summary The spatial arrangement of tiller replacement was assessed on grazed and ungrazed tussocks of Agropyron desertorum (Fisch. ex Link) Schult. for three annual cycles. Frequency distributions of the number of replacement tillers per single progenitor were also determined. Tiller replacement was usually greater on the perimeter of tussocks than within the core, with or without grazing. Replacement was inversely related to grazing intensity, both on the perimeter and within the core of tussocks. Heights of replacement tillers on the perimeter or within the core seldom differed. Furthermore, grazing seldom affected the number of replacement tillers per progenitor. Greater tillering on the perimeter than within the core indicates that the tussocks were expanding. Apparently, grazing neither enhances tussock expansion and subsequent disintegration, nor does it necessarily lead to patches of tillers (multiple tillering per progenitor) within tussocks of A. desertorum.     

Plant-bacteria interactions with special emphasis on the kallar grass association

Kallar grass is a highly salt-tolerant grass grown as a pioneer plant on alkaline, salt-affected soils in Pakistan. Nitrogen-fixing bacteria and kallar grass were found to be in close association, which was even root-zone specific: rhizoplane and endorhizosphere were colonized by two different populations. Among theAzospirillum isolates originating from the root surface, some were of a new species, now namedA. halopraeferens. To study plant-bacterium interactions, this natural kallar grass association was chosen. The possible role of bacterial chemotaxis and oxygen tolerance are discussed.     

Chloris gayana (Rhodes grass), a better host for the mas production ofGlomus fasciculatum inoculum

Seven different hosts,Panicum maximum, Chrysopogon fulvis, Themeda triandra, Chloris gayana, Brachiaria brizantha, Paspalum scrobiculatum andEleusine coracana were screened in order to select a better host for mass multiplication ofGlomus fasciculatum inoculum. Of these,Chloris gayana (Rhodes grass) was found to be the best host on the basis of root colonization and spore production and of the infective propagules of the potball.