Changes in the growth and reproduction of a clonal plant as a result of disruption of mycorrhizal network

In a clonal network, a mother plant is connected with daughter ramets. During network development, new ramets may encounter barriers that disrupt network integrity. As a result, resource allocation within a network is disturbed. In this study, the effect of network integrity disruption on the size of ramets and their sexual reproduction was investigated in mouse-ear hawkweed (Hieracium pilosella). Three types of networks were formed experimentally with unlimited resource allocation, with limited resource allocation between a mother plant and its daughter ramets and with limited resource allocation between all ramets. Networks were either supported by the presence of a mycorrhizal fungus or restricted by its absence. We found that the size of the mother and the effectiveness of sexual reproduction did not differ among network types. The length and dry mass of runners were higher in cases with limited resource exchange between a mother plant and its daughters. In the clonal plant network without any barriers to connection, a higher number of rosettes and lower dry mass of daughters were recorded. The mean number of daughter flowers did not differ among the network types. Mycorrhizal network is one of the most important factors for the sexual reproduction of clonal plants. With a reduced mycorrhizal network, plants invested in clonal growth.

Partitioning above and below ground interactions and their effects on juvenile Dacrycarpus dacrydioides (kahikatea) and Podocarpus totara (totara)

<p>Competitive and facilitative interactions play an important role in determining plant community structure and development. Historically, competitive interactions have been considered to be more prevalent in nature. However, in the past few decades strong facilitative interactions have been identified as being more important than competition in certain environments. Recent evidence has also suggested that interactions occurring in the above and below ground environments may be unevenly contributing to the net interaction effects between a target plant and nurses species. This study partitions the above and below ground interactions and determines their strength and directions in order to help better understand their relative importance to plant community dynamics. In Chapter 2 I develop species specific allometric models which aim to accurately estimate the total above- and below- ground biomass of individual D. dacrydioides and P. totara juveniles using measurements which are easily and non-destructively obtained in the field. The best model for each species is then used to construct total above and below ground biomass estimates for use in Chapter 3. Eight models using stem height, diameter, and volume either alone or in combination are examined for their predictive power and tested for their goodness of fit. Models using diameter alone are found to be less powerful in predicting total tree biomass, while models containing height either alone or in combination with diameter are more powerful. The absolute best model for predicting D. dacrydioides total biomass was BTOTAL = 0.0099(Height²)⁰˙⁸⁷⁴⁹, whereas the absolute best model for P. totara was BTOTAL = 0.2635((Height*Diameter)²)⁰˙⁵⁶⁹⁵. In Chapter 3 I use the Relative Interaction Index (RII) to determine the strength and direction of the net interactions affecting D. dacrydioides and P. totara juveniles. To partition the above ground interactions, I examined the effects of a conspecific or interspecific neighbour. I found that my two study species D. dacrydioides and P. totara showed different responses to the treatments that they received. D. dacrydioides showed net facilitation and gained biomass when it had access to the mycorrhizal network and a neighbour. Whereas, P. totara showed net neutral interactions and did not gain biomass. P. totara also showed net competition when it did not have access to the mycorrhizal network and was grown next to neighbours. The role of above ground interactions was found to be less important than below ground interactions, overall. In general, these results mean that D. dacrydioides juveniles should be expected to have higher growth, reproductive, and survival rates when grown next to nurse species in comparison to P. totara. Chapter 4 details the significance of this study for the restoration of Wairio wetland, and wetlands in general. Given the result in chapter 3 and the current restoration method at Wairio wetland, this study suggests that it may be worth exploring the benefit of planting new P. totara juveniles farther away from older woody species in order to avoid root competition.</p>

Partitioning above and below ground interactions and their effects on juvenile Dacrycarpus dacrydioides (kahikatea) and Podocarpus totara (totara)

<p>Competitive and facilitative interactions play an important role in determining plant community structure and development. Historically, competitive interactions have been considered to be more prevalent in nature. However, in the past few decades strong facilitative interactions have been identified as being more important than competition in certain environments. Recent evidence has also suggested that interactions occurring in the above and below ground environments may be unevenly contributing to the net interaction effects between a target plant and nurses species. This study partitions the above and below ground interactions and determines their strength and directions in order to help better understand their relative importance to plant community dynamics. In Chapter 2 I develop species specific allometric models which aim to accurately estimate the total above- and below- ground biomass of individual D. dacrydioides and P. totara juveniles using measurements which are easily and non-destructively obtained in the field. The best model for each species is then used to construct total above and below ground biomass estimates for use in Chapter 3. Eight models using stem height, diameter, and volume either alone or in combination are examined for their predictive power and tested for their goodness of fit. Models using diameter alone are found to be less powerful in predicting total tree biomass, while models containing height either alone or in combination with diameter are more powerful. The absolute best model for predicting D. dacrydioides total biomass was BTOTAL = 0.0099(Height²)⁰˙⁸⁷⁴⁹, whereas the absolute best model for P. totara was BTOTAL = 0.2635((Height*Diameter)²)⁰˙⁵⁶⁹⁵. In Chapter 3 I use the Relative Interaction Index (RII) to determine the strength and direction of the net interactions affecting D. dacrydioides and P. totara juveniles. To partition the above ground interactions, I examined the effects of a conspecific or interspecific neighbour. I found that my two study species D. dacrydioides and P. totara showed different responses to the treatments that they received. D. dacrydioides showed net facilitation and gained biomass when it had access to the mycorrhizal network and a neighbour. Whereas, P. totara showed net neutral interactions and did not gain biomass. P. totara also showed net competition when it did not have access to the mycorrhizal network and was grown next to neighbours. The role of above ground interactions was found to be less important than below ground interactions, overall. In general, these results mean that D. dacrydioides juveniles should be expected to have higher growth, reproductive, and survival rates when grown next to nurse species in comparison to P. totara. Chapter 4 details the significance of this study for the restoration of Wairio wetland, and wetlands in general. Given the result in chapter 3 and the current restoration method at Wairio wetland, this study suggests that it may be worth exploring the benefit of planting new P. totara juveniles farther away from older woody species in order to avoid root competition.</p>

Common mycorrhizal networks of European Beech trees drive belowground allocation and distribution of plant-derived C in soil

&lt;p&gt;Mycorrhizal fungi are an important partner of almost all land plants, who trade soil nutrients, such as Phosphorus or Nitrogen, for photosynthetic Carbon (C). Moreover, mycorrhizal fungi connect multiple plants with their mycelium in so called Common Mycorrhizal Networks (CMNs). CMNs formed by ectomycorrhizal (EM) fungi are an inherent part of boreal and temperate forests, often termed the &amp;#8216;wood-wide web&amp;#8217;. However, the role of these networks for plant belowground C allocation and distribution is not well known.&lt;/p&gt;&lt;p&gt;Here, we examined how plant photosynthates are distributed within EM mycelium networks connecting pairs of young beech trees, addressing the following questions: (1) Is the total belowground C allocation of plant photosynthates influenced by the size of the mycorrhizal network and its access to resources? (2) Is the belowground C distribution within a CMN altered if trees have unequal access to C from photosynthesis? (3) Do CMNs amplify or alleviate competition for nutrients between connected trees?&lt;/p&gt;&lt;p&gt;We planted young beech trees in pots in a special two-plant box set-up which allows to control the establishment of mycorrhizal networks between them. For this, two plant pots, penetrable by fungal hyphae but not by roots, were placed inside of plastic boxes and the interstitial space was filled with quartz sand. In addition, a hyphal-exclusive N source consisting of &lt;sup&gt;15&lt;/sup&gt;N labeled peat (&amp;#8216;peat bag&amp;#8217;), was buried within each plant pot. Two treatments were applied in a fully factorial design: 1) Allowing/preventing the establishment of a CMN between the pots (some pots were turned around at a regular interval to prevent the establishment of CMNs) and 2) inequality of access to photoassimilated C (in part of the boxes one of the two plants was shaded). In a &lt;sup&gt;13&lt;/sup&gt;C-CO&lt;sub&gt;2&lt;/sub&gt; labeling approach, we traced &lt;sup&gt;13&lt;/sup&gt;C assimilated by one plant of each tree pair into belowground pools of both plants by isotope ratio mass spectrometry (EA-IRMS) and &lt;sup&gt;13&lt;/sup&gt;C phospholipid fatty acid (PLFAs) analysis (GC-IRMS). At the same time, we investigated plant uptake of &lt;sup&gt;15&lt;/sup&gt;N via mycorrhiza by EA-IRMS.&lt;/p&gt;&lt;p&gt;Our results demonstrate that plants relied mostly on their fungal partners to acquire nutrients (63% of plant N was derived from mycorrhiza-exclusive peat bags), and also directed the majority of the C allocated belowground to their mycorrhizal partners. The presence of a larger mycorrhizal network connecting to another plant and an additional N source almost doubled photosynthetic CO&lt;sub&gt;2&lt;/sub&gt; assimilation and belowground C allocation by plants. Fungi translocated carbon via hyphal linkages preferentially into mycorrhiza-exclusive nutrient patches, even when they were located within the realm of a neighboring plant and this necessitates to cross a nutrient-poor zone of sand. Shading did not affect the belowground distribution of C.&lt;/p&gt;&lt;p&gt;We conclude that belowground ectomycorrhizal networks represent a significant sink strength for plant photosynthates and may thus be a major driver of C sequestration in beech forest soils. The belowground distribution of C via fungal networks is mainly related to the distribution of nutrient-rich patches in the soil and less to differences in the photosynthetic capacity of the host plants.&lt;/p&gt;

Mycorrhiza induced resistance (MIR): a defence developed through synergistic engagement of phytohormones, metabolites and rhizosphere

Plants get phosphorus, water and other soil nutrients at the cost of sugar through mycorrhizal symbiotic association. A common mycorrhizal network (CMN) – a dense network of mycorrhizal hyphae – provides a passage for exchange of chemicals and signals between the plants sharing CMN. Mycorrhisation impact plants at hormonal, physiological and metabolic level and successful symbiosis also regulates ecology of the plant rhizosphere. Apart from nutritional benefits, mycorrhisation provides an induced resistance to the plants known as mycorrhiza induced resistance (MIR). MIR is effective against soil as well as foliar pathogens and pest insects. In this review, molecular mechanisms underlying MIR such as role of phytohormones, their cross talk and priming effect are discussed. Evidence of MIR against economically important pathogens and pest insects in different plants is summarised. Mycorrhiza induces many plant secondary metabolites, many of which have a role in plant defence. Involvement of these secondary metabolites in mycorrhisation and their putative role in MIR are further reviewed. Controversies about MIR are also briefly discussed in order to provide insights on the scope for research about MIR. We have further extended our review with an open ended discussion about the possibilities for transgenerational MIR.