Silicon Dynamics During 2 Million Years of Soil Development in a Coastal Dune Chronosequence Under a Mediterranean Climate

Life at the conservative end of the leaf economics spectrum: intergeneric variation in the allocation of phosphorus to biochemical fractions in species of Banksia (Proteaceae) and Hakea (Proteaceae)

In severely phosphorus (P)-impoverished environments, plants have evolved to use P very efficiently. Yet, it is unclear how P allocation in leaves contributes to their photosynthetic P-use efficiency (PPUE) and position along the leaf economics spectrum (LES). We address this question in 10 species of Banksia and Hakea, two highly P-efficient Proteaceae genera. We characterised traits in leaves of Banksia and Hakea associated with the LES: leaf mass per area, light-saturated photosynthetic rates, P and nitrogen concentrations, and PPUE. We also determined leaf P partitioning to five biochemical fractions (lipid, nucleic acid, metabolite, inorganic and residual P) and their possible association with the LES. For both genera, PPUE was negatively correlated with fractional allocation of P to lipids, but positively correlated with that to metabolites. For Banksia only, PPUE was negatively correlated with residual P, highlighting a strategy contrasting to that of Hakea. Phosphorus-allocation patterns significantly explained PPUE but were not linked to the resource acquisition vs resource conservation gradient defined by the LES. We conclude that distinct P-allocation patterns enable species from different genera to achieve high PPUE and discuss the implications of different P investments. We surmise that different LES axes representing different ecological strategies coexist in extremely P-impoverished environments.

The preparation of paddy soil amendment using granite and marble waste: Performance and mechanisms

The wastes generated from the mining and processing of granite and marble stone are generally regarded as useless. However, these waste materials were used as the soil amendments for the first time. The functional groups, crystalline structure and micro-morphology of granite and marble wastes amendments (GMWA) were different from the original wastes demonstrated by X-ray diffractometer (XRD), Fourier transform infrared spectrometer (FT-IR) and Scanning electron microscope-energy dispersive spectrometer (SEM-EDS) analyses. With the addition of the amendments, the cation exchange capacity, electrical conductivity and nutrient availability of the soil increased, and the extractable heavy metals of the soil reduced significantly. Under the condition of the addition of 3% amendments, 7.0%, 99.9%, 99.7% and 70.5% of Cu, Pb, Zn and Cd in exchangeable fractions in soil were transformed to the more stable Fe-Mn oxides- or carbonates-bounded fractions. Tessier method and correlation analysis showed that the reduction of extractable metals in the acidic paddy soil can be attributed to the adsorption of available SiO₂, the co-precipitation induced by the elevated pH value, the complexation induced by Fe-Mn oxides and the cation exchange induced by mineral nutrients. This study provides a new strategy for resource recovery of waste stones and remediation of heavy metal-contaminated soil.

Why do plants silicify?

Despite seminal papers that stress the significance of silicon (Si) in plant biology and ecology, most studies focus on manipulations of Si supply and mitigation of stresses. The ecological significance of Si varies with different levels of biological organization, and remains hard to capture. We show that the costs of Si accumulation are greater than is currently acknowledged, and discuss potential links between Si and fitness components (growth, survival, reproduction), environment, and ecosystem functioning. We suggest that Si is more important in trait-based ecology than is currently recognized. Si potentially plays a significant role in many aspects of plant ecology, but knowledge gaps prevent us from understanding its possible contribution to the success of some clades and the expansion of specific biomes.

Bacteria common to rhizosphere communities of Asiatic bittersweet across a post-glacial landscape

Invasive plants such as Asiatic bittersweet (Celastrus orbiculatus Thunb.) are a significant problem for land managers as they impact plant species composition, disrupt nutrient dynamics and structure of native ecosystems, and are difficult to eradicate. As a result of the increasing abundance of Asiatic bittersweet across the eastern U.S., we have been investigating underlying factors potentially contributing to the success of this plant. Recently, ecologists have been investigating the role of plant-soil-microbe interactions contributing to plant invasion. This work has led to question: are there certain microbes (e.g., bacteria, fungi) contributing to the success of some invasive plants? We hypothesize that despite differences in geologic age of soils where Asiatic bittersweet has established in the Indiana Dunes National Park there are sufficient common factors that led to common bacterial taxa in their rhizosphere. The objectives were to determine differences and commonalities in the soil chemistry, plant community and bacterial communities of Asiatic bittersweet plants. To achieve these objectives, bittersweet plants were collected at thirteen locations in the national park from soils ranging in geologic age from 150 to over 14,500 years. Surrounding soil chemistry, plant cover and the 16S rRNA gene amplicon sequences of rhizosphere soil bacterial communities of these Asiatic bittersweet were compared. Asiatic bittersweet coverage of sampling sites ranged from 2 to 77% averaging 52 ± 2%. There were statistically significant differences (p < 0.05) in alpha diversity (Shannon, Faith’s PD and Pielou’s evenness) and beta diversity (Bray Curtis, Jaccard, unweighted Unifrac, weighted Unifrac) among the samples when grouped by soil age or habitat. Despite these differences in the bacterial communities from different soil ages and habitats, some bacterial taxa (e.g., Bacillus, Streptomyces, Sphingomonas and Rhizobiales) previously found in other studies to be beneficial to plant growth were found in every rhizosphere community sampled. These microbes provide insight into a possible contributing factor to the success of this invasive plant at the Indiana Dunes National Park, and a strategy for future work to reduce the impact of Asiatic bittersweet establishment and offer some new strategies to manage this nuisance species.

Silicon mobilisation by root-released carboxylates

Plants have evolved numerous strategies to acquire poorly available nutrients from soil, including the release of carboxylates from their roots. Silicon (Si) release from mineral dissolution increases in the presence of chelating substances, and recent evidence shows that leaf [Si] increases markedly in old phosphorus (P)-depleted soils, where many species exhibit carboxylate-releasing strategies, compared with younger P-richer soils. Here, we propose that root-released carboxylates, and more generally rhizosphere processes, play an overlooked role in plant Si accumulation by increasing soil Si mobilisation from minerals. We suggest that Si mobilisation is costly in terms of carbon but becomes cheaper if those costs are already met to acquire poorly available P. Uptake of the mobilised Si by roots will then depend on whether they express Si transporters.