Patterns of resource limitation of bacteria along a trophic gradient in Mediterranean inland waters

Abstract

The nature of the resource that limits heterotrophic bacteria, i.e. mineral nutrients or carbon (C), has consequences for biogeochemical cycles in aquatic ecosystems. Our aim was to identify the resource [C or phosphorus (P)] that mainly limits bacteria in a set of 31 Mediterranean inland water ecosystems spanning a wide trophic range. We followed an intersystem observational approach with three complementary perspectives, comparing the bacterial demand with the resource supply in terms of both the quantity (demand : supply ratio for C and P) and quality (C : P ratio of demand and supply), and assessing the relative strength of each resource in controlling bacterial production. The trophic gradient revealed a shift in the main limiting resource for bacteria, from C at the oligotrophic end (typically high-mountain, low-productivity lakes) to mainly P at the eutrophic end (typically nonmountain, high-productivity lakes). The patterns of resource limitation of bacteria found here may be related to the autotrophic nature of most of the studied ecosystems linked to a Mediterranean climate regime as representative of lakes with low inputs of allocthonous C. These patterns are consistent with the theoretical approaches and may potentially shape the contribution of this type of ecosystems to biogeochemical cycles.

Synergistic effects of UVR and simulated stratification on commensalistic phytoplankton–bacteria relationship in two optically contrasting oligotrophic Mediterranean lakes

“…Nevertheless, and in agreement with our hypothesis, photorepair mechanisms were insufficient to completely counteract UVR-induced damage, this being concordant with a sharp decrease in the UV-A : UV-B ratio (58 %) in the upper layers (subsurface conditions). Moreover, the increased HBP found after exposure of samples to higher PAR intensity in the upper layers is consistent with the previously reported stimulatory effect of PAR on HBP (Morán et al, 2001;Medina-Sánchez et al, 2002;Pakulski et al, 2007). Furthermore, a potential presence of aerobic anoxygenic phototrophic bacteria (Bertoni et al, 2011;Mašín et al, 2012;Ferrara et al, 2011) should not be ruled out in accounting for the increased HBP under high PAR in the low-UVR lake.…”

“…In this regard, it has been widely reported that greater exposure to UVR exerts an inhibitory effect on autotrophic and heterotrophic organisms (Häder et al, 2011), and that UV-B (280-315 nm), in particular, harms primary and bacterial production , enzymatic activity (Korbee et al, 2012), and cell viability , among other effects. However, it has been also reported Medina-Sánchez et al, 2002;) that UVR does not produce negative effects and it can even stimulate bacterial production and photosynthetic activity. These opposite effects may be attributable to the high acclimation capacity of organisms in high-UVR ecosystems Ruiz-González et al, 2013) or to differences in physical-chemical factors (e.g., temperature or nutrient content) among ecosystems (Harrison and Smith, 2009).…”

“…It has also been demonstrated that UVR exposure in the upper layers of the water column can increase the proportion of photosynthate released as exudates (Carrillo et al, 2008;Korbee al., 2012), which would stimulate the growth of UVR-resistant bacteria (Xenopoulos and Schindler, 2003) and give rise to a coupled phytoplankton-bacteria relationship in clear oligotrophic lakes . Coupling between phytoplankton and bacterioplankton has been defined as the capacity of the carbon (C) released by phytoplankton to support the bacterial carbon requirement (Morán et al, 2002) and will therefore differ depending on (i) the availability of alternative (allochthonous or autochthonous) carbon sources (Gasol et al, 2009) and (ii) the supply of inorganic nutrients (Medina-Sánchez et al, 2010;López-Sandoval et al, 2011). Although the bacterial dependence on C released by phytoplankton is a well-established paradigm in aquatic microbiology (Cole et al, 1988), it is currently under renewed debate.…”

Quantification of Carbon and Phosphorus Co-Limitation in Bacterioplankton: New Insights on an Old Topic

“…farming and cattle raising). Moreover, those ecosystems tend to be more autotrophic with greater eutrophy, as has been reported based on estimated BR:PP ratio values [32], probably related to the restricted terrestrial C input [36]. Likewise, the Mediterranean freshwater ecosystems undergo intense and irregular Saharan dust loads that constitute notable inputs of P [37]–[39] and of soil-derived organic components to these water bodies [39], [40].…”

“…Thus, studies performed in freshwater ecosystems involve arctic and alpine lakes [20], [29], tropical regions [26], [30], [31] or humic lakes [13], whereas inland waters of Mediterranean region have received less attention. Noticeably, the Mediterranean ecoregion shows a broad intersystem trophic gradient for inland waters, not only throughout the entire ecoregion, but also locally [32]. This has been promoted by traits such as scarceness of vegetation and developed soil on watersheds [33], the high frequency of extreme weather events [34], [35], and millennia of land use (i.e.…”