Depth diversity gradients of macrophytes: Shape, drivers, and recent shifts

Abstract

Investigating diversity gradients helps to understand biodiversity drivers and threats. However, one diversity gradient is rarely assessed, namely how plant species distribute along the depth gradient of lakes. Here, we provide the first comprehensive characterization of depth diversity gradient (DDG) of alpha, beta, and gamma species richness of submerged macrophytes across multiple lakes. We characterize the DDG for additive richness components (alpha, beta, gamma), assess environmental drivers, and address temporal change over recent years. We take advantage of yet the largest dataset of macrophyte occurrence along lake depth (274 depth transects across 28 deep lakes) as well as of physiochemical measurements (12 deep lakes from 2006 to 2017 across Bavaria), provided publicly online by the Bavarian State Office for the Environment. We found a high variability in DDG shapes across the study lakes. The DDGs for alpha and gamma richness are predominantly hump‐shaped, while beta richness shows a decreasing DDG. Generalized additive mixed‐effect models indicate that the depth of the maximum richness (Dmax) is influenced by light quality, light quantity, and layering depth, whereas the respective maximum alpha richness within the depth gradient (Rmax) is significantly influenced by lake area only. Most observed DDGs seem generally stable over recent years. However, for single lakes we found significant linear trends for Rmax and Dmax going into different directions. The observed hump‐shaped DDGs agree with three competing hypotheses: the mid‐domain effect, the mean–disturbance hypothesis, and the mean–productivity hypothesis. The DDG amplitude seems driven by lake area (thus following known species–area relationships), whereas skewness depends on physiochemical factors, mainly water transparency and layering depth. Our results provide insights for conservation strategies and for mechanistic frameworks to disentangle competing explanatory hypotheses for the DDG.

Synergistic effects between global warming and water quality change on modelled macrophyte species richness

“…Single scale and single dimension are not appropriate to depict the patterns of species richness (Mirochnitchenko et al 2021). In line with other studies (Mellin et al 2010, Ruiz‐Benito et al 2012, Toledo et al 2012, Lewerentz et al 2021), we see that the multidimensionality of environmental gradients across lake types are worth disentangling to understand species richness patterns.…”

“…Our results show for the first time that the empirically observed hump‐shaped pattern of species richness along depth (Lewerentz et al 2021) already emerge solely from eco‐physiological processes (Fig. 2a, b).…”

“…We expect to find the highest species richness in moderately nutrient rich lakes (Q1.1) (Lewerentz and Cabral 2021). We hypothesise to find hump‐shaped patterns (Q1.2) of species richness along depth gradients (Lewerentz et al 2021). Moreover, we expect a higher potential than observed species richness because limiting processes like herbivory have not been modelled (Q1.1 and Q1.2).…”

Water Availability and Proximity to Natural Areas Influence Terrestrial Plant and Macroinvertebrate Communities in Urban Stormwater Infrastructures

“…Surprisingly, obligate wetland species richness (OBL) did not differ between wet basins and ponds, even though the area permanently submerged in ponds is much greater. Stormwater infrastructures in urban areas may not be appropriate for attracting a high richness of OBL species because of urban pressures, such as high turbidity and nutrient concentration, or the high pond water levels that leaves little space for the establishment of wetland plants (Akasaka et al 2010;Lewerentz et al 2021;Mackintosh et al 2015). However, a higher proportion of OBL was found in ponds compared to wet basins, certainly due to the permanent presence of water, favorable to the establishment of these species while limiting others.…”

Water depth modulates the species richness–biomass relationship in submerged macrophytes

“…With the increasing water depth, the absorption and scattering of light in water increases (Middelboe and Markager, 1997), creating stronger light-limited conditions. Previous studies have revealed that increasing the water depth negatively affects species richness (Fu et al, 2014a;Ye et al, 2018;Lewerentz et al, 2021;Ma et al, 2021). Additionally, some studies have shown that the relationship between community biomass and water depth is unimodal or is either negative or positive (Fu et al, 2014a;Dong et al, 2014;Bolpagni et al, 2016;Ye et al, 2018;Wang et al, 2022a).…”