Abstract
BackgroundMacrophytes are key players in aquatic ecosystems diversity, but knowledge on variability of their functional traits, among and within species, is still limited. Remote sensing is a high-throughput, feasible option for characterizing plant traits at different scales, provided that reliable spectroscopy models are calibrated with congruous empirical data, but existing applications are biased towards terrestrial plants. We sampled leaves from six floating and emergent macrophyte species common in temperate areas, covering different phenological stages, seasons, and environmental conditions, and measured leaf reflectance (400–2500 nm) and leaf traits (dealing with photophysiology, pigments, and structure). We explored optimal spectral band combinations and established non-parametric reflectance-based models for selected traits, eventually showing how airborne hyperspectral data could capture spatial–temporal macrophyte variability.ResultsOur key finding is that structural—leaf dry matter content, leaf mass per area—and biochemical—chlorophyll-a content and chlorophylls to carotenoids ratio—traits can be surrogated by leaf reflectance with normalized error under 17% across macrophyte species. On the other hand, the performance of reflectance-based models for photophysiological traits substantively varies, depending on macrophyte species and target parameters.ConclusionsOur main results show the link between leaf reflectance and leaf economics (structure and biochemistry) for aquatic plants, thus envisioning a crucial role for remote sensing in enhancing the level of detail of macrophyte functional diversity analysis to intra-site and intra-species scales. At the same time, we highlighted some difficulties in establishing a general link between reflectance and photosynthetic performance under high environmental heterogeneity, potentially opening further investigation directions.
Highlights
Macrophytes are key players in aquatic ecosystems diversity, but knowledge on variability of their functional traits, among and within species, is still limited
Ludwigia hexapetala displayed Chl-a values slightly higher than native species (p < 0.05 from all pairwise post-hoc Dunn’s tests; Additional file 1: Fig. S1), while no significant difference across species was observed for Chl-b, and the lowest carotenoid content was found in N. nucifera and T. natans (p < 0.05 from all pairwise posthoc Dunn’s tests; Additional file 1: Fig. S1)
A strong level of segmentation at species level was shown for Chl/Car ratio (p < 0.001, Kruskal– Wallis One Way ANOVA): N. nucifera and T. natans exhibited the highest scores (p < 0.001 from pairwise post-hoc Dunn’s tests) and L. hexapetala, N. lutea, N. alba followed in decreasing Chl/Car (Additional file 1: Fig. S1)
Summary
Macrophytes are key players in aquatic ecosystems diversity, but knowledge on variability of their functional traits, among and within species, is still limited. Knowledge about ranges and interconnections of trait variability within aquatic plant communities (populations) is still relatively limited, probably due to the peculiar features of macrophytes and the environmental patchiness of their habitat [8]. Investigating spatial patterns of trait variability at local scales is a relatively recent topic [27,28,29,30] and some light has still to be shed on this level of heterogeneity in plant communities, with implications on productivity and connected processes [31]
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