Functional traits of individual varieties as determinants of growth and nitrogen use patterns in mixed stands of willow (Salix spp.)

Martin Weih,Nils-Erik Nordh,Stefano Manzoni,Stefanie Hoeber

doi:10.1016/j.foreco.2020.118605

Martin Weih, Nils-Erik Nordh + Show 2 more

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https://doi.org/10.1016/j.foreco.2020.118605

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Abstract

Short rotation plantations of willows (Salix spp.) have high biomass production potential in many parts of the world, and may frequently support ecosystem services related to nutrient cycling. A plantation management enhancing favorable environmental impacts that are conducive to maintaining ecosystem services is a main challenge in establishing sustainable biomass production systems. There is evidence supporting the hypothesis that biomass production and nutrient cycling can be increased by supporting ecosystem niche differentiation (complementarity) through enhancing the number of plant species or varieties grown in the stand. However, the specific trait values of the individual components (e.g., varieties) in a mixed community could also be more important than the community diversity per se. We assessed, at community level, the plant trait profiles related to growth and nitrogen (N) use for four different Salix varieties that were taxonomically distinct at species or genotype level (‘Björn’, ‘Jorr’, ‘Loden’, ‘Tora’) and field-grown in unfertilized plots of pure and mixed communities during one cutting cycle in Central Sweden. The aims were to use elements of functional growth analysis for exploring the mechanistic relationships between various traits related to growth and N use at stand level in our pure and mixed willow communities; and to address two hypotheses related to (i) the effect of diversity level on above-ground traits linked to growth, N uptake efficiency, N productivity and N conservation; and (ii) the influence of individual variety identities on the growth and N use traits observed in a mixture. Diversity level had no significant effect on the traits assessed here, and we thus found no evidence in support of our hypothesis that traits linked to growth, N uptake and use are significantly affected by the diversity level per se. In most but not all cases, the admixing effects on trait values were explained by the effects of the individual variety characteristics assessed in monocultures in combination with their relative share in the respective mixtures. The absence or presence of individual varieties strongly affected community-averaged (stand level) trait values. Therefore, the design of desirable variety mixtures is suggested that combine, for example, the high nutrient conversion efficiency that certain varieties achieve in mixed stands with the specific nutrient acquisition characteristics of other varieties.

Highlights

Managed plantations of willows are grown on agricultural land especially in temperate and arctic zones of the northern hemisphere (Dickmann and Kuzovkina, 2014)
Assuming that community components differ in their functional traits assessed both at high and low levels of organization, we explored the following hypotheses: (H1) Growth and N use traits are significantly affected by the diversity level, especially for traits at high level of or ganization for which the effects of trait plasticity are compounded. (H2) The presence or absence of individual varieties in a mixture sig nificantly affects the growth and N use traits observed in a mixture; as a consequence, there are variety traits for which the mean values ob served in a mixture are different from the weighted average values calculated from community components grown in pure cultures
Considering only the plots with the pure cultures (n = 3), annual shoot growth and relative shoot biomass annual increment (RSB) were similar between the varieties; significant variation between the varieties was found with respect to some traits, mainly those at a lower level of organization and linked to biomass allocation and N use (Table 2)

Summary

Introduction

Managed plantations of willows (genus Salix, family Salicaceae) are grown on agricultural land especially in temperate and arctic zones of the northern hemisphere (Dickmann and Kuzovkina, 2014). An important issue in sustainable land use for biomass production is the goal to reduce the depletion of nutrient resources (Higman et al, 2005; Ra et al, 2012); whilst at the same time, the efficient uptake and use of mineral nu trients, in particular nitrogen (N), is a critical management factor in willow production. Higher productivity accomplished by greater nutrient (e.g., N) supply is frequently associated with the use of synthetic fertilizers. According to life cycle assessment, the production and use of synthetic fertilizers contributes most of all management actions to the energy use in willow plantations (Hammar et al, 2017) and increases the Nomenclature

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