Viminaria juncea does not vary its shoot phosphorus concentration and only marginally decreases its mycorrhizal colonization and cluster-root dry weight under a wide range of phosphorus supplies

Ecophysiological Performance of Proteaceae Species From Southern South America Growing on Substrates Derived From Young Volcanic Materials

Southern South American Proteaceae thrive on young volcanic substrates, which are extremely low in plant-available phosphorus (P). Most Proteaceae exhibit a nutrient-acquisition strategy based on the release of carboxylates from specialized roots, named cluster roots (CR). Some Proteaceae colonize young volcanic substrates which has been related to CR functioning. However, physiological functioning of other Proteaceae on recent volcanic substrates is unknown. We conducted an experiment with seedlings of five Proteaceae (Gevuina avellana, Embothrium coccineum, Lomatia hirsuta, L. ferruginea, and L. dentata) grown in three volcanic materials. Two of them are substrates with very low nutrient concentrations, collected from the most recent deposits of the volcanoes Choshuenco and Calbuco (Chile). The other volcanic material corresponds to a developed soil that exhibits a high nutrient availability. We assessed morphological responses (i.e., height, biomass, and CR formation), seed and leaf macronutrient and micronutrient concentrations and carboxylates exuded by roots. The results show that G. avellana was less affected by nutrient availability of the volcanic substrate, probably because it had a greater nutrient content in its seeds and produced large CR exuding carboxylates that supported their initial growth. Embothrium coccineum exhibited greater total plant height and leaf P concentration than Lomatia species. In general, in all species leaf macronutrient concentrations were reduced on nutrient-poor volcanic substrates, while leaf micronutrient concentrations were highly variable depending on species and volcanic material. We conclude that Proteaceae from temperate rainforests differ in their capacity to grow and acquire nutrients from young and nutrient-poor volcanic substrates. The greater seed nutrient content, low nutrient requirements (only for G. avellana) and ability to mobilize nutrients help explain why G. avellana and E. coccineum are better colonizers of recent volcanic substrates than Lomatia species.

Costs of acquiring phosphorus by vascular land plants: patterns and implications for plant coexistence

Content Summary 1420 I. Introduction 1421 II. Root adaptations that influence P acquisition 1422 III. Costs of P acquisition: general 1423 IV. Costs of P acquisition that are independent of soil P concentrations 1423 V. Costs of P acquisition that increase as soil P concentrations decline 1424 VI. Discussion and conclusions 1424 Acknowledgements 1425 References 1425 SUMMARY: We compare carbon (and hence energy) costs of the different modes of phosphorus (P) acquisition by vascular land plants. Phosphorus-acquisition modes are considered to be mechanisms of plants together with their root symbionts and structures such as cluster roots involved in mobilising or absorbing P. Phosphorus sources considered are soluble and insoluble inorganic and organic pools. Costs include operating the P-acquisition mechanisms, and resource requirements to construct and maintain them. For most modes, costs increase as the relevant soil P concentration declines. Costs can thus be divided into a component incurred irrespective of soil P concentration, and a component describing how quickly costs increase as the soil P concentration declines. Differences in sensitivity of costs to soil P concentration arise mainly from how economically mycorrhizal fungal hyphae or roots that explore the soil volume are constructed, and from costs of exudates that hydrolyse or mobilise insoluble P forms. In general, modes of acquisition requiring least carbon at high soil P concentrations experience a steeper increase in costs as soil P concentrations decline. The relationships between costs and concentrations suggest some reasons why different modes coexist, and why the mixture of acquisition modes differs between sites.

Phosphorus- and nitrogen-acquisition strategies in two Bossiaea species (Fabaceae) along retrogressive soil chronosequences in south-western Australia

During long-term ecosystem development and its associated decline in soil phosphorus (P) availability, the abundance of mycorrhizal plant species declines at the expense of non-mycorrhizal species with root specialisations for P-acquisition, such as massive exudation of carboxylates. Leaf manganese (Mn) concentration has been suggested as a proxy for such a strategy, Mn concentration being higher in non-mycorrhizal plants that release carboxylates than in mycorrhizal plants. Shifts in nitrogen (N)-acquisition strategies also occur; nodulation in legumes is expected at low N availability, when sufficient P is available. We investigated whether two congeneric legume species (Bossiaea linophylla and Bossiaea eriocarpa) occurring along two long-term chronosequences on the south-western Australian coast and grown in a glasshouse at varying N and P supply exhibited plasticity in nutrient-acquisition strategies. We hypothesised that the shifts in nutrient limitation and nutrient-acquisition strategies at the community level would also be found at the species level. Leaf N: P ratios and the responses to nutrient availability suggested that growth of both species exhibited P-limitation in all treatments, due to the very high leaf [N] of legumes afforded by symbiotic N-fixation. Mycorrhizal colonisation was not greater at higher P supply, and root exudation of carboxylates was not stimulated at low P supply; both were unrelated to leaf [Mn]. However, nodule production declined with increasing N supply. We conclude that intraspecific variation in nutrient-acquisition and use is low in these species, and that the variation at the community level, observed in previous studies, is likely driven by high-species turnover.

Molecular cloning and functional analysis of two phosphate transporter genes from Rhizopogon luteolus and Leucocortinarius bulbiger, two ectomycorrhizal fungi of Pinus tabulaeformis

Inorganic phosphorus (Pi) is essential for plant growth, and phosphate (P) deficiency is a primary limiting factor in Pinus tabulaeformis development in northern China. P acquisition in mycorrhizal plants is highly dependent on the activities of phosphate transporters of their root-associated fungi. In the current study, two phosphate transporter genes, RlPT and LbPT, were isolated from Rhizopogon luteolus and Leucocortinarius bulbiger, respectively, two ectomycorrhizal fungi forming symbiotic interactions with the P. tabulaeformis. Phylogenetic analysis suggested that the sequence of the phosphate transporter of L. bulbiger is most closely related to a phosphate transporter of Hebeloma cylindrosporum, whereas the phosphate transporter of R. luteolus is most closely related to that of Piloderma croceum. The subcellular localization indicated that RlPT and LbPT were expressed in the plasma membrane. The complementation assay in yeast indicated that both RlPT and LbPT partially compensated for the absence of phosphate transporter activity in the MB192 yeast strain, with a K m value of 57.90 μmol/L Pi for RlPT and 35.87 μmol/L Pi for LbPT. qPCR analysis revealed that RlPT and LbPT were significantly up-regulated at lower P availability, which may enhance P uptake and transport under Pi starvation. Our results suggest that RlPT and LbPT presumably play a key role in Pi acquisition by P. tabulaeformis via ectomycorrhizal fungi.

Different mechanisms drive the performance of native and invasive woody species in response to leaf phosphorus supply during periods of drought stress and recovery

The effects of drought stress and leaf phosphorus (Pi) supply on photosynthetic metabolism in woody tropical species are not known, and given the recent global environmental change models that forecast lower precipitation rates and periods of prolonged drought in tropical areas, this type of study is increasingly important. The effects of controlled drought stress and Pi supply on potted young plants of two woody species, Anadenanthera colubrina (native) and Prosopis juliflora (invasive), were determined by analyzing leaf photosynthetic metabolism, biochemical properties and water potential. In the maximum stress, both species showed higher leaf water potential (Ψl) in the treatment drought +Pi when compared with the respective control -Pi. The native species showed higher gas exchange under drought +Pi than under drought -Pi conditions, while the invasive species showed the same values between drought +Pi and -Pi. Drought affected the photochemical part of photosynthetic machinery more in the invasive species than in the native species. The invasive species showed higher leaf amino acid content and a lower leaf total protein content in both Pi treatments with drought. The two species showed different responses to the leaf Pi supply under water stress for several variables measured. In addition, the strong resilience of leaf gas exchange in the invasive species compared to the native species during the recovery period may be the result of higher efficiency of Pi use. The implications of this behavior for the success of this invasive species in semiarid environments are discussed.