Contrasting time-scale effects of land-use legacy on species richness,diversity and composition in Mediterranean scrubland communities

Context

It is known that land-use and land-cover (LULC) changes affect plant community assembly for decades. However, both the short- and the long-term effects of contrasting LULC change pathways on this assembly are seldom explored.

Objectives

To assess how LULC change pathways affect woody plant community parameters (i.e. species richness, diversity and evenness) and species’ presence and abundance, compared with environmental factors and neutral processes.

Methods

The study was performed in Mediterranean limestone scrublands in NE Spain. Cover of each woody species was recorded in 150 scrubland plots belonging to five LULC change pathways along the past century, identified using land-cover maps and fieldwork. For each plot, total woody and herbaceous vegetation cover, local environmental variables and geographical position were recorded. Effects of these pathways and factors on plant community parameters and on species presence and abundance were assessed, considering spatial effects potentially associated to neutral processes.

Results

Species richness and diversity were associated with LULC change pathways and elevation, while evenness was only associated with this last. Pathways and environmental variables explained similar variance in both species’ presence and cover. In general, while community parameters were affected by recent-past (1956) use, species presence and abundance were associated with far-past (pre-1900) cropping. No relevant spatial effect was detected for any studied factor.

Conclusions

Historical LULC changes and current environmental factors drive local-scale community assembly in Mediterranean scrublands to an equal extent, while contrasting time-scale effects are found at community and species level. Neutral, dispersal-based processes are found to be non-relevant.

     

Combining endophytic fungi and bacteria for the biocontrol of Radopholus similis (Cobb) Thorne and for effects on plant growth

Eight endophytic fungal and bacterial isolates with antagonistic activity against Radopholus similis were evaluated in vivo for their individual and combined effects on biocontrol of R. similis and on the growth of “Grand Naine” cultivar banana plantlets in the greenhouse. Penetration efficiency (PE) of R. similis was between 3 and 21% in 29 biological agents (BAs) treatments, less than the 29% of the nematode-alone control (p ≤ 0.0001); 24 of the BAs treatments did not differ from the PE of 5% for a nematicide control. Twenty nine BAs treatments exhibited antagonistic activity against nematodes which reduced final population levels between 18 and 93%, relative to those on nematode-alone control plants (p ≤ 0.0001), and 14 BAs treatments were statistically similar to the nematicide treatment (88% reduction). Twenty four BAs treatments had increments of plant root biomass ranging from 20 to 58%, greater than the control plants; 37% of the treatments with single and combined BAs inoculations had root length increments ranging from 29 to 54% compared with control and chemical treatment. The nematicide, Terbufos 10GR, did not affect plant growth.     

Characterization of resistance to the wheat stem sawfly in spring wheat landrace accessions from targeted geographic regions of the world

Plant landraces have long been recognized as potential gene pools for biotic and abiotic stress-related genes. This research used spring wheat landrace accessions to identify new sources of resistance to the wheat stem sawfly (WSS) (Cephus cinctus Norton), an important insect pest of wheat in the northern Great Plains of North America. Screening efforts targeted 1409 accessions from six geographical areas of the world where other species of grain sawflies are endemic or where a high frequency of accessions possesses the resistance characteristic of solid stems. Resistance was observed in approximately 14% of accessions. Half of the lines displayed both antixenosis and antibiosis types of resistance. Among the resistant accessions, 41% had solid or semi-solid stems. Molecular genetic screening for haplotypes at the solid stem QTL, Qss.msub.3BL, showed that 15% of lines shared the haplotype derived from ‘S-615’, the original donor of the solid stem trait to North American germplasm. Other haplotypes associated with solid stems were also observed. Haplotype diversity was greater in the center of origin of wheat. Evaluation of a representative set of resistant landrace accessions in replicated field trials at four locations over a three year period identified accessions with potential genes for reduced WSS infestation, increased WSS mortality, and increased indirect defense via parasitoids. Exploitation of distinct types of plant defense will expand the genetic diversity for WSS resistance currently present in elite breeding lines.     

Pulmonary thromboembolism associated with Blastomyces dermatitidis in a dog

An 8-year-old, male castrated golden retriever presented for cough and increased respiratory effort. Radiographs revealed an alveolar pattern in the right caudal lung lobe and an opacity at the carina suspected to be enlarged tracheobronchial lymph nodes. The disease progressed to involve the right middle lung lobe. Cytopathology of a fine-needle aspirate and bronchoalveolar lavage fluid were nondiagnostic. Surgical removal of the right caudal lung lobe and biopsy of the perihilar lymph nodes revealed pulmonary thromboembolism and reactive lymph nodes. The dog died several days postoperatively, and necropsy revealed diffuse pulmonary thromboembolism. Additionally, Blastomyces dermatitis organisms were identified in a pyogranulomatous mass surrounding the trachea near the carina. In an extensive literature search, no reports of pulmonary thromboembolism associated with blastomycosis were identified. It is suspected that the inflammation secondary to blastomycosis caused the thromboembolism.     

Spatial Variability of Agricultural Soil Fertility Parameters in a Gleyic Podzol of Belgium

Precise information about the spatial variability of soil nutrients is essential in developing site-specific management, e.g., variable rate application of nutrients. In this study 5 fields (4 grassland, 1 arable land) on a Gleyic Podzol, each of about 1 ha, were sampled according to a 20 m×20 m grid. On these samples pH, carbon content and nutrient status (P, K, Ca, Mg, and Na) were measured. The variogram analysis of the different soil fertility parameters revealed quite different ranges for these parameters. Carbon content, pH and calcium have high ranges, between 110 and 170 m. On the other hand, ranges for potassium and sodium are much smaller, 60 m and 30 m respectively. For the elements potassium and sodium, high coefficients of variation are found, especially on the grassland fields. These differences in ranges of spatial relationship indicate that the sampling strategy for estimating variability of soil fertility, should be adopted to the different selected soil parameters and the soil use.