Effects of pollen leaching and microbial degradation on organic carbon and nutrient availability in lake water

Abstract

Nutrient fluxes across terrestrial-aquatic boundaries and their subsequent integration into lake nutrient cycles are currently a major topic of aquatic research. Although pollen represents a good substrate for microorganisms, it has been neglected as a terrestrial source of organic matter in lakes. In laboratory experiments, we incubated pollen grains of Pinus sylvestris in water of lakes with different trophy and pH to estimate effects of pollen input and its subsequent microbial degradation on nutrient dynamics. In this ex situ experiment, we measured concentrations of organic carbon, phosphorus and nitrogen in the surrounding water as well as microbial dynamics (bacteria and fungal sporangia) at well-controlled conditions. Besides leaching, chemical and microbial decomposition of pollen was strongest within the first week of incubation. This led to a marked increase of soluble reactive phosphorus and total dissolved nitrogen (up to 0.04 and 1.5 mg L -1 , respectively, after 5 days of incubation) in the ambient water. In parallel, pollen grains were rapidly colonized by heterotrophic bacteria and aquatic fungi. Leaching and microbial degradation of pollen accounted for C80, C40, C50% for organic C, N and P, respectively, and did not significantly differ among water samples from the studied lakes. Thus, pollen introduces high amounts of bio-available terrestrial organic matter and nutrients into surface waters within a short time. A rough calculation on P input into oligotrophic Lake Stechlin indicates that pollen plays an important ecological role in nutrient cycling of temperate lakes. This requires further attention in aquatic ecology.

Contrasting dynamics in activity and community composition of free-living and particle-associated bacteria in spring

“…Nevertheless, because both fractions seem to be significantly different, the separation into FL and PA Bacteria achieves a much better correlation between changes in BCC and given environmental variables (e.g. Allgaier & Grossart 2006, Rösel et al 2012b.The second maximum in bacterial activities in the present study was not related to phytoplankton but to increased nutrient and DOC concentrations following a massive input of pine pollen into Lake Stechlin in June (Rösel et al 2012a). These distinct changes in lake chemistry also have a strong effect on the BCC of both PA and FL fractions.…”

“…It is an oligotrophic dimictic hard-water lake with a maximum depth of 69.5 m and a lake surface of 4.25 km 2 . Basic limnological and chemical variables of this well-studied lake have been previously described (Allgaier & Grossart 2006, Rösel et al 2012a. Lake Stechlin was sampled between the end of February and the beginning of July 2008 at least 2 or 3 times per week at the sampling site in the southern bight of the lake (max.…”

“…Thereby, a substantial fraction of the PP is rapidly channelled through the microbial loop during and after such bloom events (Weisse et al 1990) because increased concentrations of dissolved organic carbon (DOC) are released into the surrounding water either by algal exudation or microbial breakdown of the phytoplankton bloom (Bunte & Simon 1999). Furthermore, pollen fall in spring or early summer leads to increased bacterial growth (Doskey & Ugoagwu 1989, Graham et al 2006, Rösel et al 2012a), but little is known of related changes in natural BCC.When assessing bacteria-phytoplankton interactions in the lab, Grossart et al (2005) demonstrated that the dynamics of particle-associated (PA) and free-living (FL) bacteria communities greatly differ from each other. Hence, it is surprising that only a few studies , Allgaier & Grossart 2006, Parveen et al 2011, Rösel et al 2012b) have differentiated between PA and FL bacterial fractions in natural ecosystems to better elucidate seasonal changes in BCC.…”

Carbon transfer from dissolved organic carbon to the cladoceranBosmina: a mesocosm study

“…Besides, microbial food for zooplankton consists of additional heterotrophic microbes in addition to bacteria, e.g. fungi and bactivorous protists (Sherr and Sherr, 1994;Rösel et al, 2012). Their ability of HUFA synthesis was previously reported (Hauvermale et al, 2006;Chu et al, 2008).…”

“…Firstly, the inclusion of heterotrophic fungi, which can be supported by extra organic carbon, e.g. t-DOC (Rösel et al, 2012). Second, the presence of mixotrophic and heterotrophic protists by grazing on bacteria or osmosis as well as osmotrophic algae, which are able to assimilate DOC and synthesize HUFA (Jones, 2000;Tittel et al, 2009).…”