Effects of compost, cover crops, and local conditions on degradation of two agricultural mulches in soil

Biobased and biodegradable mulches (BDM) are a potentially sustainable alternative to polyethylene plastic mulch because they can be tilled into the soil at the end of the growing season. However, their degradation rate in the soil is uncertain, limiting their on-farm adoption. The objective of this study was to determine whether organic soil management practices could be leveraged to speed degradation of two potentially BDM across two diverse agroecoregions [Lincoln (LNK) and Scottsbluff (SBF), NE, USA]. Management treatments included compost, compost extract, cover crops, all three of these practices combined and a control. The two mulch types studied were a nonwoven polylactic acid fabric with embedded wood particles (PLA), and a starch-polyester mulch film (BLK). Mulches were applied in spring 2017 for vegetable production and removed in fall after harvest. Recovered mulch was sectioned into squares 10 cm2 and buried in mesh bags for 22 months. Mulch degradation, and soil chemical, physical and biological properties were measured at four times over 2 years. Management treatments applied seasonally across 2 years led to expected changes in soil properties, yet they had no effect on mulch degradation. Instead, mulch degradation was driven by the interaction of location and mulch type. The BLK mulch had degraded by 98% at LNK after 12 months, but only by half after 22 months at SBF. Degradation of PLA after 22 months was similar between locations with 29 ± 4% mulch mass remaining at SBF and 33 ± 4% remaining at LNK. Climate and soil characteristics at each location were strong determinants of mulch degradation. Specifically, soils at LNK were finer textured, lower in pH, higher in soil water content, organic matter and nitrates, and with greater bacterial abundance compared to SBF. The strong location by mulch type interaction observed could inform the development of regionally specific predictive models of degradation.

In-Stream Variability of Litter Breakdown and Consequences on Environmental Monitoring

Energy derived from leaf litter decomposition fuels food webs in forested streams. However, the natural spatial variability of the decomposition rate of leaf litter and the relative contributions of its drivers are poorly known at the local scale. This study aims to determine the natural in-stream variability of leaf litter decomposition rates in successive riffles and to quantify the factors involved in this key ecosystem process at the local scale. Experiments were conducted on six successive riffles in nine streams in north-western France to monitor the decomposition rate in fine (microbial decomposition, kf) and coarse (total decomposition, kc) mesh bags. We recorded 30 ± 2% (mean ± S.E.) variation in kc among riffles and 43 ± 4% among streams. kf variability was 15 ± 1% among riffles and 20 ± 3% among streams. However, in-stream variability was higher than between-stream variability in four of the nine streams. Streambed roughness was negatively related to decomposition and was the most important factor for both total and microbial decomposition. Our study shows that the natural variability of the decomposition rate resulting from the local morphological conditions of habitats could be very important and should be taken into consideration in studies using leaf litter assays as a bio-indicator of anthropogenic impacts in streams.

Nectar secretion of Callistemon citrinus (Curtis) Skeels, Myrtaceae: Potential for honey production

The honey production capacity of bee flora is used to estimate the optimum colony carrying capacity of given area that helps to harvest the best honey yield. The research was conducted to quantify the nectar secretion pattern, the effect of temperature and humidity on dynamics of nectar secretion, and honey production capacity of Callistemon citrinus. One day before nectar collection, five inflorescences were enclosed with mesh bags on different branches of the tree. From these, twenty flowers were randomly selected per tree for the measurement of nectar volume. Additionally, nectar volume and concentration, temperature, and air humidity were measured with an interval of one hour. One way ANOVA and linear regression were used for data analysis. The average amount of nectar and its concentration were different significantly within the time of the day. Nectar amount was correlated positively with humidity while concentration was negatively correlated with temperature. The average nectar volume (µl) per flower in 24 hours, sugar amount per tree (kg), honey yield per individual tree (kg) and honey production capacity of Callistemon citrinus per hectare were 10.9+0.4, 0.65, 0.79, and 1264 kg (46-3808 kg), respectively. The real expected honey yield was 632 kg ha-1. Total financial return was estimated to be $4424 based on a value of $7 kg-1 of Callistemon citrinus honey. Therefore, the multiplication and plantation of this plant are suggested for honey production.

Tropical fruit production depends on wild insect communities: bees and lychees in Thailand

The importance of wild insects as pollinators of tropical tree crops has rarely been tested. Across 18 small-scale lychee orchards in northern Thailand, we evaluated the roles of different wild insects as pollinators and predators of pests in fruit production. Quantitative assessments showed that bees (Family Apidae) were strongly dominant (83%) among insect flower visitors, comprising four species in tribes Apini and four in Meliponini. Experimental manipulations of inflorescences showed that fruit production in these orchards was: (1) dependent on flower visits by wild insects because enclosure of inflorescences in mesh bags decreased fruit set (to one-fifth) and (2) not greatly limited by pollinator deficiencies, because hand pollination of unbagged flowers did not enhance fruit set. Pollination success, as indicated by the proportion of unmanipulated flowers setting fruit, correlated positively across orchards with the abundance of large-bodied Apidae (>7 mm; most were Apis species) and of Apini, and negatively with abundance of small-bodied Apidae and of all Meliponini, despite the latter being the commonest flower visitors. We conclude that larger-bodied bees are most likely to travel sufficiently far to import genetically diverse pollen, in this landscape-scale mosaic where non-orchard habitats (both agriculture and treed patches) were sufficient to sustain wild pollinators.

Extramatrical Mycelium and Ectomycorrhizal Community Composition of Quercus pubescens in a Sub-Mediterranean Stress-Prone Environment

Temporal studies that would offer insight into resilience of ectomycorrhizal (ECM) communities in stress prone climates are scarce despite their role in tree nutrition and water supply. Our study characterized the vitality, community composition, diversity, and function of Quercus pubescens Willd. ECM fungi in the Sub-Mediterranean stress-prone environment for 2 consecutive years (June 2016–May 2018) and related the investigated measures to environmental parameters. ECM community was assessed for species actively associating with root tips and exploring the soil volume through the assessment of mycelial ingrowth into sand-filled mesh bags. The investigated period was characterized by a drier than average summer combined with wildfire in 2016 followed by another dry summer in 2017. The vital to non-vital ECM root tip ratio decreased below one in August 2016 and remained low until January 2018. This was ascribed to a series of stress events that occurred at the site including sequential droughts and wildfire. The most abundant ECM lineages on root tips were Tomentella and other Thelephoraceae, Sebacina, and Cenococcum while in mesh bags the most abundant were Tomentella, Sebacina, Pseudotomentella, Pyronemataceae, Inocybe, Cortinarius, Agaricales, and Boletales lineages. High intra-site variability was observed, with ECM communities directly associated with root tips and exploring the soil volume varying significantly among the plots. Community composition was stable over time, while species richness varied with mean air and soil temperature, relative air humidity, and solar radiation. The most abundant exploration type observed at this site was short distance, which was associated with precipitation along with long distance exploration type. The medium distance exploration type was temporally variable and responded to soil temperature and relative air humidity reflecting seasonality at the site. The presented results indicate complex relationships between environmental parameters, abiotic stress, and ECM fungi.

Biochar effects on germination and radicle extension in temperate tree seedlings under field conditions

Pyrolyzed organic matter, or biochar, generally increases the growth of established plants; in some cases, biochar also promotes seed germination in agricultural species, but comparable effects on tree species have received little attention. Potential biochar effects on seed germination and early seedling development were examined in a field experiment involving 14 species of temperate forest trees. Replicated sets of seeds with and without biochar (at 5 t·ha–1) were placed in mesh bags beneath leaf litter near the time of autumnal leaf fall and retrieved the following spring. Pooled analyses show a positive but small average effect of biochar on germination. Effects on seedling radicle extension growth were more pronounced, with more than a doubling in growth observed overall and large increases observed in some species, including both conifers (e.g., Picea mariana (Mill.) Britton, Sterns & Poggenb. and Pinus resinosa Sol. ex Aiton) and angiosperms (Betula papyrifera Marsh., Prunus virginiana L., and Ulmus americana L.). Species varied in responses, but differences were not related to fire or shade tolerance. The results indicate that biochar can substantially enhance early seedling development in temperate trees; likely mechanisms involve “priming” effects resulting from increased pH and potassium availability or sorption of germination-inhibiting phenolics in the litter layer.

Organic Matter Decomposition and Ecosystem Metabolism as Tools to Assess the Functional Integrity of Streams and Rivers–A Systematic Review

Streams and rivers provide important services to humans, and therefore, their ecological integrity should be a societal goal. Although ecological integrity encompasses structural and functional integrity, stream bioassessment rarely considers ecosystem functioning. Organic matter decomposition and ecosystem metabolism are prime candidate indicators of stream functional integrity, and here we review each of these functions, the methods used for their determination, and their strengths and limitations for bioassessment. We also provide a systematic review of studies that have addressed organic matter decomposition (88 studies) and ecosystem metabolism (50 studies) for stream bioassessment since the year 2000. Most studies were conducted in temperate regions. Bioassessment based on organic matter decomposition mostly used leaf litter in coarse-mesh bags, but fine-mesh bags were also common, and cotton strips and wood were frequent in New Zealand. Ecosystem metabolism was most often based on the open-channel method and used a single-station approach. Organic matter decomposition and ecosystem metabolism performed well at detecting environmental change (≈75% studies), with performances varying between 50 and 100% depending on the type of environmental change; both functions were sensitive to restoration practices in 100% of the studies examined. Finally, we provide examples where functional tools are used to complement the assessments of stream ecological integrity. With this review, we hope to facilitate the widespread incorporation of ecosystem processes into bioassessment programs with the broader aim of more effectively managing stream and river ecosystems.

Inventive nesting behaviour in the keyhole wasp Pachodynerus nasidens Latreille (Hymenoptera: Vespidae) in Australia, and the risk to aviation safety

The keyhole wasp (Pachodynerus nasidens Latreille 1812), a mud-nesting wasp native to South and Central America and the Caribbean, is a relatively recent (2010) arrival in Australia. In its native range it is known to use man-made cavities to construct nests. A series of serious safety incidents Brisbane Airport related to the obstruction of vital airspeed measuring pitot probes on aircraft possibly caused by mud-nesting wasps, prompted an assessment of risk. An experiment was designed to determine the species responsible, the types of aircraft most affected, the seasonal pattern of potential risk and the spatial distribution of risk on the airport. A series of replica pitot probes were constructed using 3D-printing technology, representing aircraft with high numbers of movements (landings and take-offs), and mounted at four locations at the airport. Probes were monitored for 39 months. Probes blocked by mud nesting wasps were retrieved and incubated in mesh bags. Emerging wasps were identified to species. Results show that all nests in probes were made by P. nasidens, and peak nesting occurs in the summer months. Nesting success (as proportion of nests with live adult emergents) was optimal between 24 and 31°C and that probes with apertures of more than 3 mm diameter are preferred. Not all areas on the airport are affected equally, with the majority of nests constructed in one area. The proportion of grassed areas within 1000 m of probes was a significant predictor of nesting, and probe volume may determine the sex of emerging wasps.

The Effect of Leaching Fraction-Based Irrigation on Fertilizer Longevity and Leachate Nutrient Content in a Greenhouse Environment

An experiment was conducted to evaluate the effects of leaching fraction (LF) on the longevity of controlled-release fertilizer (CRF) and leachate nutrient content in a pine bark substrate. The effect of LF-based irrigation was evaluated under six target LFs of 0.05, 0.15, 0.25, 0.35, 0.45, and 0.55. The 2.72 L nursery pots were filled with 100% pine bark substrate amended with dolomitic lime at a rate of 2.97 kg/m3 and Harrell’s 16-6-13 POLYON® applied at a rate of 6 g per container. Fertilizer was encased in vinyl-coated fiberglass mesh bags and subdressed 2.5 cm under the substrate surface for recovery at the end of 10 weeks. The total amount of nutrients leached from the container was greater at higher LFs, with twice as much inorganic nitrogen leached at a LF of 0.55 than a 0.15 LF. The amount of dissolved nutrients left in the substrate decreased as the LF treatments increased. There were 29.6% more inorganic nitrogen and 37.7% more phosphorus left in the substrate irrigated with a 0.15 LF as compared to a 0.55 LF. This suggests that at lower LFs, more dissolved nutrients may be available for plant uptake. No differences were seen in the amount of nutrients lost from the CRF or remaining in the prills. Results indicate that reducing the LF did not influence the longevity of POLYON® CRF in a pine bark substrate, but that a lower LF may be useful in reducing nutrient runoff into the environment. Targeting a lower LF also resulted in a larger pool of plant-available nutrients, allowing nursery producers to potentially reduce fertilizer rates.

Spat efficiency in the pearl oyster Pinctada radiata (Leach, 1814) in the surface and bottom water at Karantina Island

The present study was carried out to determine the spat efficiency in the pearl oyster (Pinctada radiata, Leach, 1814) in surface and bottom water at Karantina Island (Izmir/Turkey). Polyethylene mesh bags were used as collectors. An annual average of 175.16 ± 11.32 spat m−2 was obtained from PSC (placed surface collectors) and 82.65 ±3.89 spat m−2 was obtained from PBC (placed bottom collectors). The largest number of new spat attachments occurred in August, both on PSC and PBC: 44 ± 3.46 and 26 ± 2.88 spats were found respectively in the outer and inner mesh bags of PSC, and 33 ±5.77 and 48 ± 6.92 spats were found respectively in the outer and inner mesh bags of PBC. New spat attachments (≥ 10 mm) continued throughout the study period, except April and May. Adult pearl oysters (≥ 50 mm) were found in May. There was a significant difference between PSC and PBC in the total number of spat attachments, the monthly spat attachments and the first spat attachments (p < 0.05). The total number of new spat attachments was positively correlated with temperature and chlorophyll a for both depths (p<0.05).