Abstract Current approaches to project spatial biodiversity responses to climate change mainly focus on the direct effects of climate on species while regarding land use and land cover as constant or prescribed by global land‐use scenarios. However, local land‐use decisions are often affected by climate change and biodiversity on top of socioeconomic and policy drivers. To realistically understand and predict climate impacts on biodiversity, it is, therefore, necessary to integrate both direct and indirect effects (via climate‐driven land‐use change) of climate change on biodiversity. In this perspective paper, we outline how biodiversity models could be better integrated with regional, climate‐driven land‐use models. We initially provide a short, non‐exhaustive review of empirical and modelling approaches to land‐use and land‐cover change (LU) and biodiversity (BD) change at regional scales, which forms the base for our perspective about improved integration of LU and BD models. We consider a diversity of approaches, with a special emphasis on mechanistic models. We also look at current levels of integration and at model properties, such as scales, inputs and outputs, to further identify integration challenges and opportunities. We find that LU integration in BD models is more frequent than the other way around and has been achieved at different levels: from overlapping predictions to simultaneously coupled simulations (i.e. bidirectional effects). Of the integrated LU‐BD socio‐ecological models, some studies included climate change effects on LU, but the relative contribution of direct vs. indirect effects of climate change on BD remains a key research challenge. Important research avenues include concerted efforts in harmonizing spatial and temporal resolution, disentangling direct and indirect effects of climate change on biodiversity, explicitly accounting for bidirectional feedbacks, and ultimately feeding socio‐ecological systems back into climate predictions. These avenues can be navigated by matching models, plugins for format and resolution conversion, and increasing the land‐use forecast horizon with adequate uncertainty. Recent developments of coupled models show that such integration is achievable and can lead to novel insights into climate–land use–biodiversity relations. Read the free Plain Language Summary for this article on the Journal blog.

Submerged freshwater macrophytes are crucial for the functioning of lakes. Their growth and survival follow environmental conditions like light, temperature, and nutrient availability. Hence, the impending increase in water temperature as well as changes of nutrients and turbidity will lead to changes in macrophyte geographic and depth distribution: Herein, we assess these potential changes. We apply an eco‐physiological macrophyte growth model to simulate biomass growth and survival of virtual species defined by random trait combinations within expert‐derived trait ranges for oligotraphentic, mesotraphentic, and eutraphentic species groups in deep lakes in Bavaria, Germany, which cover clear, moderate, and turbid lake conditions. The emergent potential species richness is compared with empirically observed species richness to evaluate general predictions for current conditions. Thereafter, we apply the model to scenarios of temperature increase and of turbidity and nutrient change to assess potential changes in species richness and the influence of species' traits on being an environmental change ‘winner' or ‘loser'. We find a cross‐lake, hump‐shaped pattern of potential species richness along depth. This largely reflects observed patterns, although mismatches were also detected and might be explained by missing processes and environmental heterogeneity within the lake. Rising temperature leads to increased richness of potential species in all lake types, species groups, and depths. Turbidity and nutrient change effects depend on depth and lake type. ‘Loser species' under increased turbidity and nutrient level are light consumptive and sensible to disturbances, while ‘winner species' have a high biomass production. These findings show that the hump‐shaped depth distributions of submerged macrophyte diversity can emerge solely considering eco‐physiology. The differential responses to environmental changes imply that management measures must account for lake type because those responses can have opposite trends depending on lake depth and type.

IntroductionSubmerged macrophytes provide a broad range of ecosystem services in lakes (Thomaz, 2021). They create habitat for many other species and change the lake environment by binding nutrients or stabilising the sediment. Most importantly, the eco-physiological processes controlling their growth and survival are strongly affected by environmental conditions, as they depend on light availability, nutrient availability, and temperature. However, the accelerating global biodiversity loss, especially of submerged macrophytes, is well documented (Körner, 2002; Phillips et al., 2016; Sand‐Jensen et al., 2000; Zhang et al., 2017) despite evidence of increasing species richness in some lakes (Murphy et al., 2018). The main influencing factors on the change of species richness seem to be global climate and regional land-use changes (Hofstra et al., 2020; Zhang et al., 2017) resulting in changes of light availability (due to changes in water turbidity), nutrient availability, or water temperature. The ways in which climate change influences water temperature, nutrients, and turbidity in lakes are highly complex including direct and indirect effects (Lind et al., 2022). For example, lake water temperature rises due to climate change which can also have indirect impacts on turbidity and nutrients in lakes, as higher temperature can promote algae growth (lower light availability). Therefore, nutrients and turbidity seem to co-vary, while temperature could change independently. However, nutrient content and turbidity can also be influenced by land-use practices (e.g. content and timing of fertiliser on fields), and wastewater treatment management. Overall, the direction and impact of future climate change on submerged macrophytes seems to be more obvious than changes in land use.All these stressors have an effect on the eco-physiological processes of macrophytes (Cao & Ruan, 2015; Reitsema et al., 2018). Hence, changes in these stressors likely affect the geographical distribution of individual species and of species richness of submerged macrophytes. Because of their response to their physio-chemical, geomorphological, hydrological, and biotic surroundings (O’Hare et al., 2018), species can be differentiated into oligo-, meso-, and eutraphentic species by their preference for nutrient conditions (Melzer, 1999). The presence of distinct species can then be an indicator of the water quality and ecological state of the lake (Schaumburg et al., 2004). However, studies on macrophyte species richness distribution remain largely based on observational and correlative studies, while there is a need to understand how simultaneous stressors combine and may result in synergistic effects on biodiversity (Lind et al., 2022). Therefore, it is paramount to assess these potential effects on macrophytes.Process-based models based on first principles and known ecophysiology are better suited to assess biodiversity response from changing conditions than correlative models (Cabral et al., 2017; Dormann et al., 2012; Higgins et al., 2020; Schouten et al., 2020). To predict the potential distribution of species based on environmental factors, process-based models incorporating critical eco-physiological processes are necessary. The application of process-based models describing the growth of submerged macrophytes have a long tradition, already stemming as early as the late 1980s (Best et al., 2001; Collins & Wlosinski, 1989; Herb & Stefan, 2003; Hootsmans, 1994; Scheffer et al., 1993; Wortelboer, 1990). The majority of those models were developed to answer different study questions, however, like the effect of macrophytes on algal blooms (Asaeda & Van Bon, 1997), the effect of varying light regimes (Herb & Stefan, 2003), or their impact on water quality (Sachse et al., 2014). Furthermore, most models were only used and calibrated for one or a few species (Gao et al., 2017; van Nes et al., 2003) and under very specific environmental conditions. None of these models was used to study the macroecological distribution patterns of macrophytes or its response to environmental change. Among the reasons for the delay in applying any of these models to multiple species and under different environmental conditions is the lack of computationally efficient models and empirical data to constrain both eco-physiological and environmental parameters. Hence, applying eco-physiological models to assess the species and richness distribution in both current and future conditions deserves further attention for this neglected group of species.Macrophytes are still underrepresented in trait-based research and in environmental change assessments (Dalla Vecchia et al., 2020; Iversen et al., 2022). Consequently, the determination of a broad range of eco-physiological parameters has yet to be established for most macrophytes. In the case of low trait-based information, applying eco-physiological models to a virtual species pool remains the best alternative to assess impacts of environmental change on macrophytes (Cabral et al., 2017; Dormann et al., 2012). As computational power and methods are evolving (Peréz-Sánchez et al., 2015), experiments with a broad range of randomly selected species within defined functional types can be a way of determining trait combinations (potential species) that allow species to survive and reproduce, as already done for terrestrial plants (Webb et al., 2010; Zakharova et al., 2019). In such applications, the process-based model acts as a performance filter, with the surviving virtual species representing those trait combinations able to cope with the environmental conditions given the considered mechanisms. However, this approach was not yet used for macrophytes.In this study, we tackle two main objectives. First, we address the potential species richness of oligotraphentic, mesotraphentic, and eutraphentic submerged macrophytes under recent environmental conditions. We ask: How many observed and potential species of the species pool can grow in clear, intermediate, and turbid lakes (Q1.1)? Do the potential species richness patterns across the depth follow the observed distribution in all lake types (Q1.2)? Second, we assess scenarios of water temperature increase and water quality change (increase or decrease in both nutrients and turbidity). Here, we ask: In which depth and lake types do we lose or gain oligo-, meso-, and eutraphentic species (Q2.1)? Is this change dependent on eco-physiological traits (Q2.2)?To answer questions Q1.1 and Q1.2, we run random species parameter combinations within the three defined parameter spaces of oligotraphentic, mesotraphentic, and eutraphentic species and analyse the resulting distribution patterns of the growing species by comparing them with the corresponding observed pattern. We expect to find the highest species richness in moderately nutrient rich lakes (Q1.1) (Lewerentz & Cabral, 2021). We hypothesise to find hump-shaped patterns (Q1.2) of species richness along depths (Lewerentz et al., 2021). In general, we hypothesise that we see a higher potential species richness than observed species richness because limiting processes like herbivory have not been modelled (Q1.1 and Q1.2). To answer question Q2.1 and Q2.2, we run scenarios of water temperature increase and scenarios of water quality change for the recent potential species pool. We hypothesise that the studied lakes will lose species under increased turbidity and nutrient conditions but gain species under decreased turbidity and nutrient conditions and under increased water temperature (Q2.1) (Lewerentz & Cabral, 2021). To answer question Q2.2, we determine the plant traits that significantly influence if a species will win or lose habitat within two selected scenarios of turbidity and nutrient decrease or increase. We hypothesise that under increased conditions, high biomass production is the main advantage, as species can grow at high rates even under limited conditions.

Juliano Sarmento Cabral1, Alma Mendoza-Ponce2,3, André Pinto da Silva4,5, Johannes Oberpriller6, Anne Mimet7, Julia Kieslinger8, Thomas Berger9, Jana Blechschmidt1, Maximilian Brönner8, Alice Classen10, Stefan Fallert1, Florian Hartig6, Christian Hof7, Markus Hoffmann11, Thomas Knoke12, Andreas Krause13, Anne Lewerentz1, Perdita Pohle8, Uta Raeder11, Anja Rammig13, Sarah Redlich10, Sven Rubanschi7, Christian Stetter14, Wolfgang Weisser7, Daniel Vedder1,15,16,17 , Peter H. Verburg18, Damaris Zurell191 Ecosystem Modelling, Center for Computational and Theoretical Biology (CCTB), University of Würzburg, Klara-Oppenheimer-Weg 32, 37074, Würzburg, Germany2 Research Program on Climate Change, Universidad Nacional Autónoma de México, Mexico City, Mexico3 International Institute for Applied Systems Analysis, Laxenburg, Austria4 Department of Ecology and Genetics, Animal Ecology, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden5 Centre for Ecology, Evolution and Environmental Changes (cE3c), Faculdade de Ciências, Universidade de Lisboa, Lisbon, Portugal6 Theoretical Ecology Lab, University of Regensburg, Universitätsstraße 31, 93053 Regensburg, Germany7 Technical University of Munich, Terrestrial Ecology Research Group, Department of Life Science Systems, School of Life Sciences, 84354 Freising, Germany8 Institute of Geography, Friedrich-Alexander University Erlangen-Nuernberg, Wetterkreuz 15, 91058 Erlangen, Germany9 Land-Use Economics in the Tropics and Subtropics, Hans-Ruthenberg Institute, Hohenheim University, Hohenheim, Germany10 Department of Animal Ecology and Tropical Biology, Biocentre, University of Würzburg, Am Hubland, 97074 Würzburg, Germany11 Technical University of Munich, Limnologische Station Iffeldorf, Chair of Aquatic Systems Biology, Department of Life Science Systems, School of Life Science,Hofmark 1-3, 82393 Iffeldorf, Germany12 Technical University of Munich, Institute of Forest Management, Department of Life Science Systems, School of Life Sciences, 58354 Freising, Germany13 Technical University of Munich, Land Surface-Atmosphere Interactions, Department of Life Science Systems, School of Life Sciences, 85354 Freising, Germany14 Agricultural Production and Resource Economics, School of Life Sciences, Technical University of Munich, 84354 Freising, Germany15 Helmholtz Center for Environmental Research - UFZ, Department of Ecosystem Services, Permoserstr. 15, 04318 Leipzig, Germany16 Institute of Biodiversity, Friedrich Schiller University Jena, Dornburger Straße 159, 07743 Jena, Germany17 German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Puschstr. 4, 04103 Leipzig, Germany18 Institute for Environmental Studies, VU University Amsterdam, De Boelelaan 1111, 1081 HV Amsterdam, The Netherlands19 Ecology & Macroecology, Inst. for Biochemistry and Biology, University of Potsdam, Am Neuen Palais 10, 14469 Potsdam, GermanyArticle type: review/perspective

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 (D max) is influenced by light quality, light quantity, and layering depth, whereas the respective maximum alpha richness within the depth gradient (R max) 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 R max and D max 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.

Twenty-four aquatic neophytes have been introduced to Germany so far and at least 16 non-native species established stable populations in northern and north-western Germany. Invasive aquatic neophytes can cause serious ecological and economic problems in lakes and other freshwater ecosystems. In the presented study, a species distribution model was used to identify possible habitats for neophytes in Bavaria (Southern Germany) and to predict which Bavarian lakes might become suitable habitats for neophytes due to climate change. A total of 55 Bavarian lakes were fitted with high-resolution temperature loggers as part of this monitoring programme. Furthermore, the physical and chemical properties of the lakes were determined and verified in regular intervals. The presence or absence of the native thermophilic macrophyte Najas marina L. was used as an indicator to determine whether a lake was a suitable habitat for neophytes. The results revealed that the spread of neophytes in Bavaria is mainly limited by spring and summer water temperature. In contrast, nutrient concentrations in the water showed no significant influence. Suitable lakes reached temperatures of at least 15 °C for 2 months during spring and at least 20 °C for 2 months during summer. By comparison, the water temperatures in lakes classified as not suitable for neophytes were 2–5 °C lower. The computed predictions for the estimated temperature increase of 1.4 °C, for the period between 2021 and 2050, indicate that up to 70 % of Bavarian lakes might become suitable habitats for neophytes.

The presented study was conducted to determine which environmental factors and conditions can affect the regenerative capacity and survivability of Elodea nuttallii [o1] and therefore the efficiency of mechanical management methods like cutting and harvesting. The influence of water temperature, light intensity and nutrient concentration in the sediment on the survivability and regenerative capacity of the invasive species E. nuttallii was determined in three laboratory and one field experiments. E. nuttallii fragments with one to four nodes were stored in aquaria under constant temperature and/or light conditions. To examine the influence of water temperature, four aquaria were kept at a constant water temperature of either 15°C or 20°C. The influence of light intensity was studied by shading the aquaria with different types of mesh. The fragments were stored at constant light intensities of 215, 161, 86 and 31 µmol photons m–2 s–1. Fragments in aquaria filled with sediment with 20 µg P2O5-P g–1 soil, 150 µg P2O5-P g–1 soil or without sediment were studied to determine the influence of the sediment. The results of the laboratory experiments showed how the mechanical management methods are most efficient during periods with low water temperatures, high turbidity or low global irradiation and nutrient poor waters. The field experiment was designed to study the influence of the nutrient compositions in the sediment on the growth and regenerative capacity of rooted E. nuttallii. E. nuttallii fragments were planted in compartments treated with PO43-- and/or NH4+-fertiliser and were trimmed after six weeks. The experiment revealed that the growth before a harvest and the growth after a harvest (regenerative capacity) differ significantly, depending on the nutrient composition in the substrate. An increase of the PO43- concentration in the sediment, for example, reduced the growth of E. nuttallii before the harvest, but increased the growth after the harvest. A treatment with PO43-- and NH4+-fertiliser had an opposite effect on growth and regenerative capacity. The study proved that the environmental conditions have a significant influence on the efficiency of mechanical management methods.

Die invasive Ausbreitung von heimischen und neophytischen Wasserpflanzen ist eine Hauptursache fur den Verlust an Biodiversitat in Seen und hat eine empfindliche Storung der komplexen Lebensgemeinschaften des Litorals zur Folge. In der vorliegenden Arbeit wurde anhand der beiden Modellarten Elodea nuttallii und Najas marina ssp. intermedia untersucht welche Umweltfaktoren die Ausbreitung invasiver Pflanzen beeinflussen, um ein besseres Verstandnis von Invasionsprozessen in aquatischen Okosystemen zu bekommen und Anpassungsstrategien zu entwickeln.

Growth experiments with macrophytes revealed anomalies in the growth and development of Najas intermedia. Further analyses showed that these anomalies were caused by differences between the male and female plants. To examine the gender-related differences, the results of two field experiments and a phenological monitoring programme were analysed. The field experiments were conducted in four different lakes in Southern Germany. Over the course of 2 years, eight different sediments were used to research the interaction between the gender and the growth of N. intermedia plants. The phenological monitoring programme, on the other hand, was focused on the development of three different populations of N. intermedia in three Southern German lakes. The results of the experiments revealed significant differences in the gender-related development: Depending on the environmental conditions, male plants grew between 20 and 40% faster than female plants. Additionally, the male plants developed flowers earlier in the vegetation period and died before the female plants. As a result, male and female plants coexisted in the same lake only for a short period of time. This might be a strategy to reduce the competitive pressure between the genders and to gain an advantage over rival species.

Najas marina ssp. intermedia (Wolfg. ex Gorski) Casper (Najas intermedia) is a thermophile macrophyte species native to Central Europe, which started mass spreading across Southern Germany about 10 years ago, almost reaching the intensity of the invasive neophyte Elodea nuttallii. As part of a study to examine the spread of N. intermedia with regard to climate change, predominant populations of N. intermedia were continuously monitored. The observations revealed that some areas and lakes remained free of N. intermedia, although water temperatures and light conditions were similar to locations with predominant populations of N. intermedia. As a result, growth experiments were conducted to show that the properties of the lake sediment can affect the growth of N. intermedia.Four lakes without populations of N. intermedia and with different environmental conditions were chosen as experimental sites. During the experiments eight different sediments from four different lakes were used. Five sediments were collected from sites with extensive or predominant Najas populations, three sediments originated from locations with no or minor amounts of N. intermedia. The experiments revealed that the sediment from different lakes as well as from different locations within the same lake significantly differs in nutrient concentration and density and that those differences can affect the growth of N. intermedia. Plants growing in nutrient-rich sediment (SRP: 15 mg 100 g(-1) soil, Total-P: 50 mg 100 g(-1) soil) reached with 43.1 (+/- 6.9) mm day(-1), compared to 6.9 (+/- 2.0) mm day(-1) in sediment with lower nutrient concentrations (SRP: 2 mg 100 g(-1) soil, Total-P: 10 mg 100 g(-1) soil), higher growth rates and were less affected by the density of the sediment. The density of the sediment, on the other hand, played a significant role under conditions with low nutrient concentrations, respectively when sediments with similar nutrient concentrations were compared. For example, a comparison of sediments with a soluble phosphor concentration of 2 mg 100 g(-1) soil and a total phosphor concentration of 10 mg 100 g(-1) soil showed that plants growing in sediment with 75.7% particles > 0.063 mm reached twice the growth rates (6.9 +/- 2.0 mm day(-1)) than plant growing in sediment with only 47% particles >0.063 mm (1.7 +/- 0.6 mm day(-1)). Nutrient-poor sediment (SRP: <1 mg 100 g(-1) soil, Total-P: <1 mg 100 g(-1) soil), inhibited the growth of N. intermedia (0.8 +/- 0.2 mm day(-1)). The significantly different growth rates of N. intermedia show that the lake sediment, respectively the nutrient concentration and density must be included in assessments and models regarding the growth and spread of N. intermedia. (c) 2012 Elsevier GmbH. All rights reserved.

The use of jute matting in managing the invasive aquatic macrophyte species Elodea nuttallii (Planch.) H. St. John and Najas marina ssp. intermedia (Wolfg. ex Gorski) Casper (Najas intermedia) was studied in laboratory experiments and field trials. Four German lakes with predominant population of Najas intermedia or Elodea nuttalli were chosen for the experiment and areas between 150 and 300 m² were covered with jute textile. The effect of the matting on the growth of invasive and non-invasive macrophytes was determined through comparison with control transects. Biodegradable jute matting successfully suppressed the invasive macrophyte Najas intermedia and significantly reduced the growth of Elodea nuttalli in lakes. The results indicate that the capability of the matting to inhibit the growth of Elodea nuttallii and Najas intermedia depends on the mesh size of the jute weaving and that environmental conditions can affect its efficiency. Various indigenous species like Charales or Potamogeton pusillus L. were able to grow through the jute fabric and populate the treated areas. Until the end of the vegetation period, none of the invasive species were able to penetrate the covering and establish a stable population; in fact, in the subsequent year the jute matting affected only the spread of Najas intermedia. Jute matting proved to be an easy-to-use and cheap method to control the growth of Elodea nuttallii and Najas intermedia.