Atmospheric aerosol particles of biological origin are a very diverse group of biological materials and structures, including microorganisms, dispersal units, fragments and excretions of biological organisms. In recent years, the impact of biological aerosol particles on atmospheric processes has been studied with increasing intensity, and a wealth of new information and insights has been gained. This review outlines the current knowledge on major categories of primary biological aerosol particles (PBAP): bacteria and archaea, fungal spores and fragments, pollen, viruses, algae and cyanobacteria, biological crusts and lichens and others like plant or animal fragments and detritus. We give an overview of sampling methods and physical, chemical and biological techniques for PBAP analysis (cultivation, microscopy, DNA/RNA analysis, chemical tracers, optical and mass spectrometry, etc.). Moreover, we address and summarise the current understanding and open questions concerning the influence of PBAP on the atmosphere and climate, i.e. their optical properties and their ability to act as ice nuclei (IN) or cloud condensation nuclei (CCN). We suggest that the following research activities should be pursued in future studies of atmospheric biological aerosol particles: (1) develop efficient and reliable analytical techniques for the identification and quantification of PBAP; (2) apply advanced and standardised techniques to determine the abundance and diversity of PBAP and their seasonal variation at regional and global scales (atmospheric biogeography); (3) determine the emission rates, optical properties, IN and CCN activity of PBAP in field measurements and laboratory experiments; (4) use field and laboratory data to constrain numerical models of atmospheric transport, transformation and climate effects of PBAP. Keywords: primary biological atmospheric aerosol; climate; cloud condensation nuclei; biology; atmospheric ice nuclei (Published: 22 February 2012) Citation: Tellus B 2012, 64 , 15598, DOI: 10.3402/tellusb.v64i0.15598

https://www.tandfonline.com/doi/pdf/10.3402/tellusb.v64i0.15598

Primary biological aerosol particles in the atmosphere: a review

The potential benefits of herbivory to plants have been debated over the last decade. Several investigators claim that removal of or damage to the productive, absorptive, or reproductive tissue of plants by herbivores benefits some plant species by increasing their net primary productivity, seed production, or longevity, and that these changes increase plant fitness and result in the evolution of herbivore-plant mutualisms. Although more than 40 papers have been cited as presenting experimental evidence in support of these benefits and mutualisms, strong evidence is lacking. Increased plant biomass as a result of tissue removal has been found only under growth-chamber conditions and in cultivated crops. Although herbivores may benefit certain plants by reducing competition or removing senescent tissue, no convincing evidence supports the theory that herbivory benefits grazed plants.

Does herbivory benefit plants? A review of the evidence

The effects of meteorological factors on atmospheric bioaerosol concentrations--a review.

Bioaerosols in the Earth system: Climate, health, and ecosystem interactions

Understanding the mechanisms of population size regulation is of vital importance to both the pure and applied ecologist. Throughout the history of ecology one school of thought has maintained that populations of plants and animals are in some way regulated by "density-dependent factors"i.e. processes that either increase mortality or decrease fecundity as the density of the population increases (133). Thus there would be a densitydependent feedback that holds the population within certain limits. A second school of thought has maintained that "density-independent factors" (e.g. weather conditions or disturbance) are more important in determining population size. Whether populations are regulated by density-dependent or densityindependent factors has been the subject of intensive debate and controversy over the past twenty-five years, especially in the zoological literature (10,

The Ecological and Genetic Consequences of Density-Dependent Regulation in Plants

A suction trap has been made in which the spores entering a narrow orifice, directed into the wind, are impacted on a Vaseline-coated microscope slide moved across the orifice at 2 mm./hr. Estimates of spore content of the air can be made, with higher efficiency than by previous traps, at different times of day and thus be more closely correlated with variations in weather.

Wind-tunnel tests with spores of Lycopodium clavatum showed maximal and minimal efficiencies of 93.8 and 62.4% respectively, with a suction rate of 10.0 1./min., in the range of wind speeds from 1.5 to 9.3 m./sec.

An automatic volumetric spore trap

The use of a power-operated suction trap, in which spores are impacted on the sticky surface of a slowly moving slide, made it possible to estimate accurately the concentration of different kinds of spore in the air at any given time. In an open field at 2 m. above ground the catches often consisted predominantly of small hyaline spores, of types rarely caught by other kinds of trap. Changes in the types of spore caught at different times of day showed that some species have well-defined diurnal periodicity; the catches also reflect changes in weather. In dry weather, pollen grains and spores of such fungi as Cladosporium, Erysiphe, Alternaria , smuts and rusts, are the main components of the air spora; they are most abundant in the afternoon and least in the early morning. Phytophthora infestans and Polythrincium trifolii also occur, but reach their maximum concentration before noon. Prolonged rain removes most of these spores, and for a time there are few in the air. Within a few hours of the start of rain, the typical dry-air spora is replaced by hyaline spores ; few of these can be identified, but they include splash-dispersed types, ascospores and basidiospores. Except after rain this damp-air spora occurs in quantity only at night when dew is formed, and the greatest concentration is reached between midnight and dawn. Basidiospores were at times the dominant type of spore. Hyaline forms, often mainly Sporobolomyces sp., rapidly reached large numbers in the early hours of the morning, particularly when there was heavy dew, and then disappeared almost completely. Coloured basidiospores mainly from the Agaricales were also commonest at night, but their occurrence depended less on weather than the hyaline forms and their diurnal periodicity was less pronounced.

Changes in atmospheric spore content: Diurnal periodicity and the effects of weather

SUMMARY: The air over an arable field at Rothamsted Experimental Station, Harpenden, was sampled from 1 June to 25 October 1952 at 2 m. above ground with an automatic volumetric spore trap. Each day's slide was scanned and all the spores counted on an area representing a sample volume of 41 1. of air. Spores were classified in 20 morphological groups and a miscellaneous one. Seasonal periodicities are presented as 6-day running means of the daily average number of spores/m.3 air, and then related to meteorological data. Cladosporium conidia accounted for 46% of the total catch; hyaline basidiospores (chiefly Sporobolomyces) for 31%; and pollen only 1%. The relative frequency of various spore types differs from that recorded by earlier workers because the suction trap catches spores of all sizes with almost equal efficiency and is little influenced by external conditions. The results which should be representative of large rural areas of central and south England show that the major changes of spore concentration depend on the weather and the phenology of the local vegetation and its associated fungal flora. During 24 days in late June and July comparable estimates of spore concentration were made with another trap 24 m. above ground. The spore concentration of the twelve commonest groups at 24 m. totalled 82% of that at 2 m.

The summer air-spora at Rothamsted in 1952.

SUMMARY: Large transient increases in the concentration of some dry airborne spores coincident with the start of rain suggested that the first raindrops to wet surfaces might disperse spores other than in splash droplets or by wetting fructifications. Experimental collisions between glass beads or water drops and spore-bearing surfaces showed that both rapid air movement in advance of radially spreading splashes and vibration can suspend spores in air. Removal by air movement is most effective when large drops collide with surfaces carrying spores that are loose or raised above the surface.

Dry Liberation of Fungus Spores by Raindrops

Temperature and relative humidity of air within and above potato crops were recorded throughout the growing seasons of 1951-8, with wet- and dry-bulb mercury-in-steel thermographs. Diurnal periodicity curves of successive weeks showed that conditions within the crop changed, relative to those above, as the crop grew. When much bare ground was exposed, the air within the crop was warmer and less humid at midday than at 4 ft. above ground, particularly in dry and sunny weather. The growth of the foliage and the amount of sunshine and rain determined how quickly this pattern was replaced by one with smaller temperature differences and crop humidity slightly in excess of that above it, at all times of day. Rain on crops with dense foliage almost completely eliminated temperature differences and gave relative humidities over 90% that persisted in the crop for a larger proportion of each day than in the screen. Finally, as the disease defoliated the crop and again exposed the soil, the relationship partly reverted to that early in the season.



Above the crops, curves of the number of hours per day with relative humidity not less than 90%, rose and fell with the passing of wet spells. At first this was also true within crops, but when foliage was dense the rise in relative humidity after rain often persisted through intervals of dry weather. Such conditions usually preceded the appearance of potato blight in epidemic proportions by 1–3 weeks. It is difficult to account for the regularity of blight outbreaks by seasonal climatic changes, and although many factors are probably involved, changes in ecoclimate seem important. When knowledge about the response of Phytophthora infestans is related to the meteorological observations and to the dates of blight outbreak, the growth of potato crops seems often to be self-destructive, because it progressively modifies the immediate environment to favour the spread of the crop's most destructive pathogen.

J. M. Hirst

Papers

An automatic volumetric spore trap

Changes in atmospheric spore content: Diurnal periodicity and the effects of weather

The summer air-spora at Rothamsted in 1952.

Dry Liberation of Fungus Spores by Raindrops

The epidemiology of phytophthora infestans.: ii. the source of inoculum