Diversity of Benthic Organisms on Artificial Reef Structure

One of the methods of a marine rehabilitation program to accelerate the recovery of damaged coral reefs is to make artificial reefs as a new coral growth substrate. Interestingly, many benthic invertebrates overgrowth the artificial reef structures. The purpose of this study was to investigate the benthic organisms encrusting the artificial reefs including the cement and iron substrates. In June 2018, 10 artificial reef structures were deployed in 7-8m depth around Putri Island, Belinyu, Bangka Regency. The artificial reef structures were made in the form of an iron frame with a cement concrete weight. Colonization of sessile benthic organisms is generally marine invertebrates; Scleractinia corals, sponges, bivalves, hydrozoa, bryozoa, soft corals, gastropoda, crinoid, ascidian, and gorgonian. Natural recruited coral Pocillopora sp. was found in all artificial reef structures with colony sizes 3-8cm and surprisingly only coral pocillopora found adhered in iron frames and sinkers. The other benthic organisms are sponge, crinoid, and bryozoa with the number of densities are 2 organism/m2. Meanwhile, the lowest benthic density are groups of Mollusc and Ascidian with organism/m2. The type of succession that occurs in this research was likely a primary succession. The preference of benthic organisms among reefs appeared to be related to the proximity of natural hard-bottom habitat and type of iron and coating materials.

The Abundance of the nifH Gene Became Higher and the nifH-Containing Diazotrophic Bacterial Communities Changed During Primary Succession in the Hailuogou Glacier Chronosequence, China

Primary successional ecosystems and the related soil development are often N limited. To date, N2-fixing communities during primary succession in alpine ecosystems have remained underexplored. In this study, we applied quantitative PCR (qPCR) quantitation and targeted amplicon sequencing of nifH in the Hailuogou Glacier foreland to investigate the succession of N2-fixing communities in five sites along a 62-year chronosequence. The abundance of the nifH gene increased along the primary succession in the chronosequence and correlated positively with pH, acetylene reduction activity, and water, organic C, total and available N, and available P contents. The increases in alpha diversity along the chronosequence may have been partly due to less competition for resources. In contrast to the clear separation based on soil properties, the changes in the diazotrophic community composition lacked a clear trend and were associated mostly with changes in soil available K and organic C contents. The changes among differentially abundant genera were possibly due to the changes in plant coverage and species composition. The whole primary succession of the diazotrophic communities was consistent with stochastic community assembly, which is indicative of low competitive pressure.

Dynamics of nitrogen and phosphorus accumulation and their stoichiometry along a chronosequence of forest primary succession in the Hailuogou Glacier retreat area, eastern Tibetan Plateau

As the two limiting nutrients for plants in most terrestrial ecosystems, nitrogen (N) and phosphorus (P) are essential for the development of succession forests. Vegetation N:P stoichiometry is a useful tool for detecting nutrient limitation. In the present work, chronosequence analysis was employed to research N and P accumulation dynamics and their stoichiometry during forest primary succession in a glacier retreat area on the Tibetan Plateau. Our results showed that: (1) total ecosystem N and P pools increased from 97 kg hm−2 to 7186 kg hm−2 and 25 kg hm−2 to 487 kg hm−2, respectively, with increasing glacier retreat year; (2) the proportion of the organic soil N pool to total ecosystem N sharply increased with increasing glacier retreat year, but the proportion of the organic soil and the vegetation P pools to the total ecosystem P was equivalent after 125 y of recession; (3) the N:P ratio for tree leaves ranged from 10.1 to 14.3, whereas the N:P ratio for total vegetation decreased form 13.3 to 8.4 and remained constant after 35 y of recession, and the N:P ratio for organic soil increased from 0.2 to 23.1 with increasing glacier retreat. These results suggested that organic soil N increased with increasing years of glacier retreat, which may be the main sink for atmospheric N, whereas increased P accumulation in vegetation after 125 y of recession suggested that much of the soil P was transformed into the biomass P pool. As the N:P ratio for vegetation maintained a low level for 35–125 y of recession, we suggested that N might be the main limiting element for plant growth in the development of this ecosystem.

Plant and Soil Development Cooperatively Shaped the Composition of the phoD-Harboring Bacterial Community along the Primary Succession in the Hailuogou Glacier Chronosequence

ABSTRACT Microbes that produce phosphatases play an important role in the cycling of phosphorus (P), a key nutrient in soil development. We studied the development, compositional turnover, and environmental drivers of microbial communities carrying the phosphatase-encoding phoD gene (here called phoD communities) in the course of primary succession in the Hailuogou glacier chronosequence. We selected the pioneer species Populus purdomii Rehder as a model plant to study the communities in rhizosphere and bulk soils along the chronosequence. The bulk and rhizosphere soils hosted distinct phoD communities. Changes in the taxa Pseudomonas and Pleomorphomonas in the rhizosphere and Bradyrhizobium, Cupriavidus, and Pleomorphomonas in the bulk soil were associated with soil development. The plant development and soil property changes along the chronosequence were accompanied with changes in the phoD communities. Soil pH, soil organic carbon, and total nitrogen contents that are directly related to the plant development and litter input differences along the chronosequence were the main factors related to changes in community compositions. The community similarity decreased along the chronosequence, and the distance decay rate was higher in the bulk soil than in the rhizosphere. In summary, both in the rhizosphere and in bulk soils the phoD community succession was shaped by plant and soil development-related factors along the primary succession in the Hailuogou glacier chronosequence. IMPORTANCE Phosphorus was the key limiting nutrient for soil development during primary succession that occurred in alpine and high-latitude ecosystems with cold and humid climates. The interactions of functional microbiota involved in phosphorus cycling in the rhizosphere under different soil developmental stages along primary succession are still rarely examined. We selected the pioneer species Populus purdomii as a model plant to study the phoD-harboring bacterial communities in rhizosphere and bulk soils along a mountain glacier chronosequence. Our results showed that the bulk soils and rhizosphere host distinct phoD communities and diversity that differentially varied along the chronosequence, describing in detail the development and compositional turnover of the phoD community in the course of primary succession and determining the main environmental factors driving the development.