Abstract
BackgroundThe importance of intraspecific trait variation (ITV) is increasingly acknowledged among plant ecologists. However, our understanding of what drives ITV between individual plants (ITVBI) at the population level is still limited. Contrasting theoretical hypotheses state that ITVBI can be either suppressed (stress-reduced plasticity hypothesis) or enhanced (stress-induced variability hypothesis) under high abiotic stress. Similarly, other hypotheses predict either suppressed (niche packing hypothesis) or enhanced ITVBI (individual variation hypothesis) under high niche packing in species rich communities. In this study we assess the relative effects of both abiotic and biotic niche effects on ITVBI of four functional traits (leaf area, specific leaf area, plant height and seed mass), for three herbaceous plant species across a 2300 km long gradient in Europe. The study species were the slow colonizing Anemone nemorosa, a species with intermediate colonization rates, Milium effusum, and the fast colonizing, non-native Impatiens glandulifera.ResultsClimatic stress consistently increased ITVBI across species and traits. Soil nutrient stress, on the other hand, reduced ITVBI for A. nemorosa and I. glandulifera, but had a reversed effect for M. effusum. We furthermore observed a reversed effect of high niche packing on ITVBI for the fast colonizing non-native I. glandulifera (increased ITVBI), as compared to the slow colonizing native A. nemorosa and M. effusum (reduced ITVBI). Additionally, ITVBI in the fast colonizing species tended to be highest for the vegetative traits plant height and leaf area, but lowest for the measured generative trait seed mass.ConclusionsThis study shows that stress can both reduce and increase ITVBI, seemingly supporting both the stress-reduced plasticity and stress-induced variability hypotheses. Similarly, niche packing effects on ITVBI supported both the niche packing hypothesis and the individual variation hypothesis. These results clearly illustrates the importance of simultaneously evaluating both abiotic and biotic factors on ITVBI. This study adds to the growing realization that within-population trait variation should not be ignored and can provide valuable ecological insights.
Highlights
The importance of intraspecific trait variation (ITV) is increasingly acknowledged among plant ecologists
When comparing the between individual intraspecific trait variation (ITVBI) (CV) for the different traits across species, it was not consistently the same study species exhibiting the highest ITVBI, with the highest mean variability in plant height and leaf area for I. glandulifera, the highest mean variability in specific leaf area (SLA) for M. effusum and the highest mean variability in seed mass for A. nemorosa (Table 1). ITVBI was positively correlated among all traits for A. nemorosa, except between SLA and leaf area and between SLA and seed mass
For M. effusum positive correlations only occurred between seed mass, SLA and leaf area ITVBI, while for I. glandulifera, only leaf area ITVBI correlated positively with all other traits (Additional file 4)
Summary
The importance of intraspecific trait variation (ITV) is increasingly acknowledged among plant ecologists. Many plant species occur over relatively broad spatial scales and are exposed to strong abiotic and biotic gradients. This suggests that species exhibit large variation in their functional trait attributes across these gradients, caused by adaptation by natural selection or/and phenotypic plasticity [4]. Since functional traits and their intraspecific variability are closely linked to plant community dynamics [10,11,12], ecosystem functions such as litter decomposition [13,14,15], ecosystem services such as disease risk reduction [15] and species responses to climate change [16,17,18], it is important to understand which factors drive ITV in plant species [4, 19]
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