The impact of land use and climate change on surface runoff and groundwater in Cimanuk watershed,Indonesia

Limnology - The Cimanuk River with a total watershed area of 4010.8 km2 flowing from the Garut Regency to Indramayu Delta is the longest in West Java Province. However, the cumulative...     

Response of different forms of propagules of Rhizoctonia solani AG2-1 (ZG5) exposed to the volatiles produced in soil amended with green manures

The sensitivity of different forms of propagules of Rhizoctonia solani anastomosis group (AG)2‐1/zymogram group (ZG)5 to volatile compounds produced in soil amended with green manure will influence the efficacy of green manures used to manage the disease. In laboratory experiments, we determined the impact of volatiles arising from residues of five species of Brassicaceae, and Avena sativa (oat), a non‐Brassicaceae species, and volatiles of pure allyl isothiocyanate (AITC) or 2‐phenylethyl isothiocyanate (2‐PEITC) in either their soluble or vapour phase on the hyphal growth of R. solani arising from different propagules. The brassicaceous species were Brassica napus var. Karoo, B. napus B1, B. napus B2, B. nigra and Diplotaxis tenuifolia (a brassicaceous weed). Colony growth and hyphal density on water agar were measured up to 7 days. The amendment of a sandy soil with green manures at a high (100 g kg^?1, 10%) concentration generally suppressed the growth of the pathogen, but at a low (10 g kg^?1, 1%) concentration, the amendment had little effect on the radial fungal growth of the pathogen but increased the density of hyphae through more branching. The inhibition by volatiles from the residues of Brassicaceae species at 10% concentration was stronger (82–86%) than that by volatiles from oat (64%) amendment at the same rate. Hyphae arising from sclerotia and precolonised ryegrass seed were less sensitive than hyphae growing out of potato dextrose agar plugs. This indicates that thick‐pigmented cell walls may have protected the fungus from these unfavourable conditions. Pure AITC and 2‐PEITC in the range of 0.5–2.0 mM inhibited the growth of R. solani from all forms of propagules, but hyphae originating from agar plugs were the most vulnerable compared with the two others. Thus, hyphae arising from the medulla of the sclerotia may be relatively tolerant to volatile compounds emanating from decomposing Brassica green manure amendments in the field and in vitro inhibition of the vegetative growth of the pathogen may not reflect its response to the amendments in the field.     

Butterfly species and traits associated with selectively logged forest in Borneo

Logging can significantly change the structure of rainforest communities. To better understand how logging drives this change, butterflies and environmental variables were assessed within both unlogged and logged forest in Indonesian Borneo. In the whole dataset, we found local environmental variables and geographic distance combined captured 53.1% of the variation in butterfly community composition; 29.6% was associated with measured local environmental variables, 13.6% with geographic distance between sites, and 9.9% with covariation between geographic distance and environmental variables. The primary axis of variation in butterfly community composition represented a disturbance gradient from unlogged to logged forest. Subsequent axes represented gradients influenced by variables such as canopy cover and total tree density. There were significant associations between environmental variables and geographic range and larval host plant use of species. Specifically, butterflies using trees as larval host plants and those with distributions limited to Borneo were more likely to be present in unlogged forest. By contrast, species that tended to be more abundant in logged forest were those with widespread distributions and those using lianas and grasses as larval host plants. The results of this study highlight the importance of environmental variables and disturbance, e.g., selective logging, in structuring rainforest community diversity. Moreover, they confirm how species traits, such as larval food use and geographic distributions can determine patterns of species abundance following environmental change.     

Saprophytic and pathogenic behaviour of R. solani AG2-1 (ZG-5) in a soil amended with Diplotaxis tenuifolia or Brassica nigra manures and incubated at different temperatures and soil water content

The Brassicaceae species Diplotaxis tenuifolia and Brassica nigra contain high concentrations of glucosinolates, the precursors of isothiocyanates (ITCs) that can have biofumigation effects in amended soils. In a laboratory experiment, incorporation of these plants as green manures into soil was expected to suppress Rhizoctonia solani AG2-1 (ZG5), the causal agent of damping-off in canola (Brassica napus). The manures were incorporated at 1 (1% w/w) or 5 (5% w/w) g fresh material per 100 g dry soil and incubated for 6 months at 10, 20, or 30°C and at soil water contents of 10%, 40%, or 70% of water holding capacity. R. solani survived for up to 6 months as a saprophyte in un-amended soil at all soil water contents and at 10 and 20°C. A temperature of 30°C suppressed R. solani below the level of detection in all treatments after one week. At 1% concentration, the green manures increased the colonisation of the soil by R. solani, which caused severe damping-off of canola subsequently sown in this soil treatment. Soil amendments at 1% temporarily increased soil microbial activity. The addition of B. nigra or D. tenuifolia green manure at 5% concentration suppressed the saprophytic growth of R. solani incubated at 10 or 20°C over all soil water contents and significantly increased the microbial activity at all soil temperatures and water contents. Canola sown into these pots did not succumb to damping-off. The efficiency of hydrolysis of glucosinolates in the 5% treatment in the first week of incubation ranged from 1.6% for 2-propenyl ITC, extracted from soil containing tissues of B. nigra, to 3.4% for 3-butenyl ITC extracted from soil containing tissues of D. tenuifolia. 2-propenyl ITC could not be detected after 7 d of incubation. In the longer term (weeks to months), the increase of microbial activity, caused by adding green manures at 5%, or volatiles from the green manures, most likely played a dominant role in suppressing R. solani. The impact of ITCs, if any, appears to be short-term (days). Responsible Editor: Peter A. H. Bakker