Doctor Rocky Putra


Graduated PhD 2023

Thesis Title

The functional role of silicon in legumes: from root nodulation to community-level responses

Research Project

Silicon is ubiquitous in the soil and is a beneficial element that often promotes plant performance, most notably under stressful conditions. Moreover, soil is also home for a myriad of microbes and terrestrial plants (roots). Soil therefore provides an excellent ecological platform to better understand tripartite interactions between silicon, roots and their associated microbes.

A distinct plant functional group, the legumes (Fabaceae) forms an intimate relationship with nitrogen-fixing bacteria (collectively known as rhizobia) inside the root nodules. However, the extent to which silicon affects this relationship is largely overlooked. Starting from these ecological and evolutionary perspectives, in my PhD project, I am investigating the functional role of silicon in nitrogen-fixing legumes, particularly in the context of legume-rhizobium symbioses.

A preliminary result showed that silicon supplementation significantly increased potential nitrogen fixation in three different genotypes of the model legume Medicago truncatula inoculated with the model rhizobium Ensifer meliloti strain SM1021. Further experiments will be conducted to better understand the intraspecific responses of the model legume species to silicon in various ecological contexts. Therefore, I am now focused on understanding:

  1. The context-dependency of these tripartite interactions, e.g. whether the magnitude of plant symbiotic traits is dependent on variation at rhizobial levels and the presence of an external stressor, such as insect herbivory.
  2. The underlying biochemical mechanisms, e.g. whether silicon supplementation alters the root and/or nodule isoflavonoids and flavonoids which are critical signals for symbioses, plant growth and defence in nitrogen-fixing legumes.
  3. Community-wide consequences of silicon supplementation in a field setting, focusing on the extent to which silicon alters cumulative crop yield, forage quality, invertebrate and microbial communities and soil chemistry in lucerne Medicago sativa in collaboration with the Australian Steel Mill Services (ASMS).

Given the growing importance of legumes at a global scale, silicon could play a vital role in improving legume health and productivity with manifold environmental benefits.


Cibils-Stewart X, Putra R, Islam T, Fanna DJ, Wuhrer R, Mace WJ, Hartley SE, Popay AJ, Johnson SN, (2023) 'Silicon and Epichloë-endophyte defences in a model temperate grass diminish feeding efficiency and immunity of an insect folivore', Functional Ecology, vol.37, no.12, pp 3177-3192

Putra R, Waterman JM, Mathesius U, Wojtalewicz D, Powell JR, Hartley SE, Johnson SN, (2022) 'Benefits of silicon-enhanced root nodulation in a model legume are contingent upon rhizobial efficacy', Plant and Soil, vol.477, pp 201–217

Putra R, Vandegeer RK, Karan S, Powell JR, Hartley SE, Johnson SN, (2021) 'Silicon enrichment alters functional traits in legumes depending on plant genotype and symbiosis with nitrogen-fixing bacteria', Functional Ecology, vol.35, no.12, pp 2856-2869

Paul SC, Putra R, Mueller C, (2020) 'Early life starvation has stronger intra-generational than transgenerational effects on key life-history traits and consumption measures in a sawfly', Plos One, vol.14, no.12, Article no.e0226519

Putra R, Powell JR, Hartley SE, Johnson SN, (2020) 'Is it time to include legumes in plant silicon research?', Functional Ecology, vol.34, pp 1142– 1157 (opens in a new window)

Tyc O, Putra R, Gols R, Harvey JA, Garbeva P, (2020) 'The ecological role of bacterial seed endophytes associated with wild cabbage in the United Kingdom', Microbiologyopen, vol.9, no.1, e00954 doi:10.1002/mbo3.954


Associate Professor Scott N. Johnson, Professor Jeff R. Powell and Professor Susan E. Hartley (The University of Sheffield)