Javier Gulías

Arbuscular mycorrhizal symbiosis with Arundo donax decreases root respiration and increases both photosynthesis and plant biomass accumulation

The effect of arbuscular mycorrhiza (AM) symbiosis on plant growth is associated with the balance between costs and benefits. A feedback regulation loop has been described in which the higher carbohydrate cost to plants for AM symbiosis is compensated by increases in their photosynthetic rates. Nevertheless, plant carbon balance depends both on photosynthetic carbon uptake and respiratory carbon consumption. The hypothesis behind this research was that the role of respiration in plant growth under AM symbiosis may be as important as that of photosynthesis. This hypothesis was tested in Arundo donax L. plantlets inoculated with Rhizophagus irregularis and Funneliformis mosseae. We tested the effects of AM inoculation on both photosynthetic capacity and in vivo leaf and root respiration. Additionally, analyses of the primary metabolism and ion content were performed in both leaves and roots. AM inoculation increased photosynthesis through increased CO2 diffusion and electron transport in the chloroplast. Moreover, respiration decreased only in AM roots via the cytochrome oxidase pathway (COP) as measured by the oxygen isotope technique. This decline in the COP can be related to the reduced respiratory metabolism and substrates (sugars and tricarboxylic acid cycle intermediates) observed in roots.

Dry matter allocation in Medicago arborea and Medicago citrina in response to drought and defoliation

Abstract. Soil water availability is one of the main factors determining plant growth and forage production. The effects of soil water deficit on the development of two woody Mediterranean Medicago species, M. arborea and M. citrina were studied. A field experiment was carried out in the University of the Balearic Islands (Spain), under irrigated and drought conditions on both non-defoliated plants (NDP) and defoliated plants (DP). Under drought, all studied parameters for NDP were affected by water stress in summer, though there were no significant differences between species for shoot biomass (B). However, M. citrina maintained significantly higher leaf biomass than M. arborea, which represents a great part of B. On the contrary, M. arborea plants suffered total leaf senescence in summer, and B was totally composed of woody parts. For DP, spring–autumn was a favourable period for plant growth and development, under both water regimes. In well irrigated M. citrina plants, and compared with M. arborea, the capacity of regrowth was higher, and leaf area was similar for NDP and for DP. During summer, the regrowth was sensitive to the extreme temperatures. In drought conditions, the capacity of regrowth was relatively favoured in spring but completely inhibited in summer for both species.

Possible link between photosynthesis and leaf modulus of elasticity among vascular plants: a new player in leaf traits relationships?

A compromise between carbon assimilation and structure investment at the leaf level is broadly accepted, yet the relationship between net assimilation per area (An ) and leaf mass per area has been elusive. We propose bulk modulus of elasticity (ε) as a suitable parameter to reflect both leaf structure and function, and an inverse relationship between ε and An and mesophyll conductance (gm ) is postulated. Using data for An , gm and ε from previous studies and new measurements on a set of 20 species covering all major growth forms, a negative relationship between An or gm and ε was observed. High ε was also related to low leaf capacitance and higher diffusive limitations to photosynthesis. In conclusion, ε emerges as a key trait linked with photosynthetic capacity across vascular plants, and its relationship with gm suggests the existence of a common mechanistic basis, probably involving a key role of cell walls.