Decreasing Defoliation Frequency Enhances Bromus valdivianus Phil. Growth under Low Soil Water Levels and Interspecific Competition

Javier García-Favre,Yongmei Zhang,Peter D Kemp,Daniel J Donaghy,Lydia M Cranston,Ignacio F López

doi:10.3390/agronomy11071333

Javier García-Favre, Yongmei Zhang + Show 4 more

Open Access

https://doi.org/10.3390/agronomy11071333

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Abstract

Bromus valdivianus Phil. (Bv) is a water stress-tolerant species, but its competitiveness in a diverse pasture may depend on defoliation management and soil moisture levels. This glasshouse study examined the effect of three defoliation frequencies, based on accumulated growing degree days (AGDD) (250, 500, and 1000 AGDD), and two soil water levels (80–85% of field capacity (FC) and 20–25% FC) on Bv growth as monoculture and as a mixture with Lolium perenne L. (Lp). The treatments were applied in a completely randomised block design with four blocks. The above-ground biomass of Bv was lower in the mixture than in the monoculture (p ≤ 0.001). The Bv plants in the mixture defoliated more infrequently (1000 AGDD) showed an increase in root biomass under 20–25% FC compared to 80–85% FC, with no differences measured between soil water levels in the monoculture. Total root length was highest in the mixture with the combination of infrequent defoliation and 20–25% FC. Conversely, frequent defoliation treatments resulted in reduced water-soluble carbohydrate reserves in the tiller bases of plants (p ≤ 0.001), as they allocated assimilates mainly to foliage growth. These results provide evidence that B. valdivianus can increase its competitiveness relative to Lp through the enhancement of the root growth and the energy reserve in the tiller base under drought conditions and infrequent defoliation in a mixture.

Highlights

Natural grasslands and anthropogenic pastures cover 31–43% of Earth’s terrestrial habitats [1]
In New Zealand, the pastoral systems rely mainly on Lolium perenne L. (Lp) and Trifolium repens L. mixed pastures. Management practices for this simple mixture are well understood by farmers in New Zealand, Hooper et al [3] have reported that enhancing pasture diversity improves herbage mass production
Leaf weight and specific leaf area (SLA) per tiller of Bromus valdivianus Phil. (Bv) increased under the most frequent defoliation (p ≤ 0.01), while accumulated leaf length per tiller showed the lowest value at this defoliation frequency (Table 1)

Summary

Introduction

Natural grasslands and anthropogenic pastures cover 31–43% of Earth’s terrestrial habitats [1]. A greater herbage mass production of mixed pastures is based on the plant functional diversity of the ecosystem [4,5], that is, how the ecosystem functionality and stability are modified by species richness and species traits [6]. Morphological plant traits, such as root depth and specific leaf area (SLA) indicate how a plant behaves and, how it interacts in the ecosystem (i.e., competes) with neighbours [7]. Plants with slow traits invest more resources to acquire a deep and coarse root system to maintain a minimum of water uptake, even during extreme droughts [9], which confers a dehydration tolerance strategy to the species [10]

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