CRITERIOS DE EVALUACIÓN

Zealand. Two year old plants of 12 native species were planted in 3 blocks and extracted 1, 2 (1 m

spacing) and 3 (1.5-2 m spacing) years after planting for analysis of biomass and root morphology.

Biomass for 1 and 2 years is for container-grown plants. Image from Phillips et al.(2008) and methodology as described in Marden et al. (2005).

The growth rate and below-ground morphology of New Zealand native species was variable. Of those studied, monocotyledons were faster growing and had higher root biomass than woody- dicotyledons of the same age (Marden and Phillips 2009). A. toetoe,P. tenax and C. secta had a dense mass of fine-fibrous roots, while C. australis formed a deep taproot (Marden et al. 2005, Marden and Phillips 2009). The native dicotyledons had less extensive but more substantially sized woody roots, which formed compact heart-rooted systems (Marden et al. 2005).

Figure 3.1 Changes in mean maximum root depth over a 5 year period for 12 New Zealand native plant species (from Marden et al. 2005 (Figure 2), with permission).

Rooting depth and spread varied considerably between native species. C. australis (cabbage tree)and P. regius (ribbonwood) were the deepest rooting species (Figure 3.1), while Pittosporum eugenioides (lemonwood) had the widest spreading roots (Figure 3.2). P. regius, P. eugenioides,

P. tenuifolium (kōhūhū), C. australis and C. robusta (karamu) were identified as the best performers in terms of quickly developing a root system with soil stabilising properties (Marden et al. 2005). These species were recommended for riparian planting where the bank height does not exceed 2 m. The toxicity of Coraderia arborea (tutu) to grazing stock limits its application to agricultural plantings (Marden et al. 2005). The roots of Myrsine australis (mapou), Knightia excelsa (rewarewa),

Pseudopanax arboreus (fivefinger), L. scoparium (mānuka) and S. tetraptera (kōwhai) were less extensive than other species (Figure 3.1, Figure 3.2). In other studies, differences between closely related species have been noted, for example mature L. scoparium can root to depths of 0.8 m

Figure 3.2 Changes in mean maximum root spread over a 5 year period for 12 New Zealand native plant species (from Marden et al. 2005 (Figure 4), with permission).

Other significant differences between root systems were also identified. The monocotyledons studied had 3-10 times longer structural root length than the native dicotyledons (Marden and Phillips 2009). Of the woody species, P. eugenioides, C. arborea and P. regius had the longest root length after 5 years, and L. scoparium and M. australis the least (Phillips et al. 2011a). In terms of root tensile strength S. tetraptera was the strongest and the fleshy roots of C. robusta the weakest (Phillips et al. 2011a). Root site occupancy modelling predicts P. regius and C. australis would stabilise soil the most effectively (Phillips et al. 2011a).

Section B:

Comparative investigation of native rhizosphere profiles

The below-ground morphology of New Zealand native plants are known to vary considerably. This section provides an overview of the literature involving comparative studies of native species root systems. In addition, the findings of a preliminary field investigation are presented. The rhizosphere soil profiles of six native species were described (i) to identify the extent of their root systems at the LUDF restoration site and compare this with the literature (Marden et al. 2005, Marden and Phillips 2009) and (ii) to identify variation in soil chemistry parameters that warrant further investigation.

3.5

Native rhizosphere soil profiles at the Lincoln University Dairy Farm field

study site

Soil pedology, soil physico-chemistry and root structure were compared in soil profiles beneath one of each of six native plant species (C. robusta, P. tenuifolium, K. ericoides, P. tenax, A. richardii and

C. australis)at the LUDF site. Plants had been established for 5 years at the time of this research. The LUDF site is on a Templeton silt loam soil (Hewitt 1998) (Typic halustept soil, Soil Survey Staff 2014). A further description of the soil properties and history of this site can be found in Chapter 4 and Chapter 6. Plants were selected in relatively open areas, in the centre of the plot, to minimise the influence of both the roots of other plants and variation of local soil conditions.

3.5.1

Soil investigation

Soil pits were excavated by hand in October 2013 to a depth of 0.9-1.0 m, directly adjacent to the centre of each individual plant (to reach the vertical extent of roots). Branches and leaves of the plants were cut away on one side to position the exposed soil profile below the stem or centre of the plant. Pits were 1.0-1.5 m wide across the principal face, extended in order to reveal the lateral extent of roots (in the case of C. australis roots extended further than the pit, 1.5 m wide). The sides of the pits were of approximately 0.5 m breadth to allow access. Soil was carefully removed from around the roots leaving them intact protruding from the pit wall to facilitate accurate description of root size and distribution. Horizon depths, root size and density and other morphological features were described using standard methodology (Milne et al. 1995) on the principal wall (rhizosphere wall) and an adjoining, side wall (chosen for least influence of surrounding plants). The adjoining wall was described for comparison to the rhizosphere profile.

Soil samples were collected from directly below the centre of the principal face, at 0.15, 0.3, 0.45, 0.6 and 0.9 m depth, for physico-chemical analysis. Soil samples were immediately sieved (4 mm) and then stored in a fridge until analysis the following day. A subsample of soil was dried at 105 °C to determine gravimetric soil moisture content. A 4 g subsample of moist soil was shaken with 40 mL of 2 M potassium chloride (KCl) for 1 hour, centrifuged at 2000 rpm for 10 minutes and then filtered (Whatman No. 41) (Blakemore et al. 1987). The KCl extracts were frozen until they could be analysed by Flow Injection Analyser (FIA) (FOSS FIAstar 5000 triple channel with SoFIA software version 1.30; Foss Tecator, Hoganas, Sweden) for ammonium-N (NH4+-N) and nitrate-N (NO3−-N). The remaining soil

was air dried (35 °C for 48 hours), ground and sieved (2 mm) for subsequent analysis. Soil pH was measured in suspension with water (10 g of air-dried soil to 25 mL of water) (S20 SevenEasyTM _pH;

3.5.2

Rhizosphere profile descriptions

A comparative description of findings is presented here, as replication with statistical analysis was not possible. A full pedological description of the rhizosphere profiles (and adjacent walls for comparison) can be found in Table A.1. (see Plate A.1 for associated photographs). Figure 3.3 provides a comparison of profile coverage by roots of different size classes. The rooting profiles show a large amount of variation between native species (Plate 3.14, Plate 3.15, Plate A.1), consistent with the findings of Marden et al. (2005) and Marden and Phillips (2009) for plants of similar age.

Description and comparison of root structure

C. australis had a substantial (70-90 mm diameter) taproot-like structure to a depth of 0.8 m (Plate 3.15a, Figure 3.3). Lateral fine roots extended horizontally from the taproot in the upper 0.4 m of soil and diagonally from 0.4-0.6 m to a depth of 1.0 m. C. australis was the only species to develop a substantial amount of roots below the Ah horizon. The vertical and lateral extent of roots was greater than previously recorded for C. australis of this age(Czernin and Phillips 2005, Marden et al. 2005). Soil under C. australis was noticeably softer than under the other species.

The fibrous root systems of P. tenax and A. richardii were extensive (Plate 3.15b and c, Figure 3.3) and consistent in extent with minimal previous description for young plants (McGruddy 2006, Marden and Phillips 2009). The soil profile was more extensively covered by roots (<6 mm) under

A. richardii than P. tenax, however the roots of A. richardii were largely confined to the top 0.3 m of soil (P. tenax to 0.4 m). Both species had a few very fine roots extending vertically to almost 1.0 m. Notably, two types of roots were present in P. tenax, a many branched network of orange roots in the upper soil profile and additional straight, transparent, water-filled roots descending vertically (Atkinson (1922) gave a similar description).