Altering Neighborhood Relatedness and Species Composition Affects Interior Douglas-Fir Size and Morphological Traits With Context-Dependent Responses

Amanda K Asay,Susan A Dudley,Suzanne W Simard

doi:10.3389/fevo.2020.578524

Amanda K Asay, Susan A Dudley + Show 1 more

Open Access

https://doi.org/10.3389/fevo.2020.578524

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Abstract

Trees often exist in a complex ecological system with many biological interactions. Here we examine kin interactions of Pseudotsuga menziesii var. glauca (interior Douglas-fir) both in the context of pure kin stands, in accordance with established plant kin selection and recognition studies, but also in combination with inter and intraspecific neighbors in order to observe how interactions may differ in a more complex system. Seedlings grown with kin neighbors (i.e. in stands that contained only kin) were significantly larger (biomass, height and root length) than those grown with any type of unrelated neighbor. However, of those with an unrelated neighbor, performance was better if that neighbor was interspecific (lodgepole pine rather than a stranger, or non-kin, Douglas-fir neighbor). Interestingly when Douglas-fir was grown in mixed stands, the four growth and four morphological traits of the seedlings examined paralleled neither pure stranger nor pure kin stands. This suggests that a mixed stand environment yielded cues that were uniquely different than either type of pure stand and that these seedlings are able to integrate that information and respond in a different way; for example, with increased early mycorrhizal fungal colonization. The morphological traits fine: coarse root allocation and slenderness (height relative to diameter) closely paralleled the seeding-size results, with the greatest values in pure kin stands. Whereas, fine root: needle allocation showed a kin response of less fine root allocation relative to needle mass compared to strangers, but kin seedlings had more fine root allocation when grown with a pine compared to a stranger Douglas-fir neighbor. We have demonstrated that the kin response in Douglas-fir is influenced by the complexity of the environment in which it grows, and this has significant effects on growth, morphology and mycorrhizal fungal colonization that may affect the success and resiliency of regeneration.

Highlights

In Douglas-fir forests of interior British Columbia, an individual of Pseudotsuga menziesii var. glauca [interior Douglas-fir (Fdi); hereafter referred to as Douglas-fir] interacts with a complex arrangement of neighbors that can include other Douglasfir individuals that are conspecifics of either kin or stranger relation, different tree species, or many other plant species present in the environment
Kin recognition and kin selection studies often isolate a species from others it may naturally co-occur with and kin are compared with strangers grown separately in pairs or groups (Cheplick and Kane, 2004; Dudley and File, 2007; Murphy and Dudley, 2009; Biedrzycki and Bais, 2010; Biedrzycki et al, 2010; Bhatt et al, 2011; File et al, 2012b; Asay, 2013; Gorzelak, 2017; Pickles et al, 2017)
In contrasts that included interspecific comparisons (Table 1; Planned Contrasts–inter- vs. intraspecific neighbor, pine seedlings (Pine) presence and Number of pines), there were no significant differences in colonization

Summary

Introduction

In Douglas-fir forests of interior British Columbia, an individual of Pseudotsuga menziesii var. glauca [interior Douglas-fir (Fdi); hereafter referred to as Douglas-fir] interacts with a complex arrangement of neighbors that can include other Douglasfir individuals that are conspecifics of either kin or stranger relation, different tree species, or many other plant species present in the environment. Seedling growth is commonly affected by the presence and density of neighboring plants (Harper, 1977; Goldberg and Werner, 1983) through their influences on light, water and nutrient availability (Murison, 1960; Williams et al, 1999; Restaino et al, 2016). They can affect the microclimate, mutualists such as mycorrhizal fungi, and the cues they provide. In nature, trees such as Douglas-fir often interact with kin and strangers simultaneously, and with different species, which creates a more complex environment

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