Lianas Significantly Reduce Aboveground and Belowground Carbon Storage: A Virtual Removal Experiment

Lianas are structural parasites of trees that cause a reduction in tree growth and an increase in tree mortality. Thereby, lianas negatively impact forest carbon storage as evidenced by liana removal experiments. In this proof-of-concept study, we calibrated the Ecosystem Demography model (ED2) using 3 years of observations of net aboveground biomass (AGB) changes in control and removal plots of a liana removal experiment on Gigante Peninsula, Panama. After calibration, the model could accurately reproduce the observations of net biomass changes, the discrepancies between treatments, as well as the observed components of those changes (mortality, productivity, and growth). Simulations revealed that the long-term total (i.e., above- and belowground) carbon storage was enhanced in liana removal plots (+1.2 kgC m–2 after 3 years, +1.8 kgC m–2 after 10 years, as compared to the control plots). This difference was driven by a sharp increase in biomass of early successional trees and the slow decomposition of liana woody tissues in the removal plots. Moreover, liana removal significantly reduced the simulated heterotrophic respiration (−24%), which resulted in an average increase in net ecosystem productivity (NEP) from 0.009 to 0.075 kgC m–2 yr–1 for 10 years after liana removal. Based on the ED2 model outputs, lianas reduced gross and net primary productivity of trees by 40% and 53%, respectively, mainly through competition for light. Finally, model simulations suggested a profound impact of the liana removal on the soil carbon dynamics: the simulated metabolic litter carbon pool was systematically larger in control plots (+51% on average) as a result of higher mortality rates and faster leaf and root turnover rates. By overcoming the challenge of including lianas and depicting their effect on forest ecosystems, the calibrated version of the liana plant functional type (PFT) as incorporated in ED2 can predict the impact of liana removal at large-scale and its potential effect on long-term ecosystem carbon storage.

No Effect of Selective Maturation on Fruit Traits for a Bird-Dispersed Species, Sambucus racemosa

Selective abortion, also called selective maturation, is a phenomenon wherein maternal plants selectively mature ovules that have the potential to grow into higher-quality fruits, such as those that contain more seeds. We hypothesized that the effects of selective maturation on fruit traits could be influenced by the dispersal mechanism. However, to date, limited studies have been conducted on selective maturation in bird-dispersed fruits. Unlike self- or wind-dispersed species, bird-dispersed species would not selectively mature fruits that contain more seeds because they are not preferred by birds. Here, we investigated the effect of selective abortion on the fruit traits of a bird-dispersed species, elderberry (Sambucus racemosa L. subsp. kamtschatica). We performed a flower-removal experiment. Half of the inflorescences on each individual tree were removed for the treatment group, whereas the control group was not manipulated. We found that the flower-removed trees showed higher fruit sets, suggesting the existence of resource limitation. The number of seeds per fruit did not increase by the experimental treatment. Additionally, the control individuals did not produce larger fruits. The lack of effects on fruit traits supported our hypothesis that the effect of selective maturation on fruit traits may differ among species with different dispersal mechanisms.

Distribution Characteristics of Inorganic Solids in Biochemical Treatment System

This paper studies the accumulation mechanism of different types of inorganic solids in activated sludge system by taking two main kinds of inorganic solids-chemical sludge and sediment as the research object. In the chemical phosphorus removal experiment, self-made calcium silicate hydrate was used as the chemical phosphorus removal agent and added to the end of the biochemical system of domestic sewage for phosphorus removal experiment, while the fine sediment was simulated by quartz sand of 26, 73, 106, 165 and 210 μm respectively, and a complete mixture model of inorganic solid accumulation was established as Xiss = Ciss, inf × (SRT/HRT + 1) × (1 – e–t/SRT). The results showed that the self-made hydrated calcium silicate had good phosphorus removal effect, and the TP of domestic sewage could be removed from 7 mg/L to 0.5 mg/L. The chemical sludge accumulation in the phosphorus removal process conforms to the complete mixing model, and the relative errors of measured and predicted values of MLVSS/MLSS and MLISS were 1% and 3%, respec- tively. The sediment accumulation process does not conform to the completely mixed model. The relative error of MLVSS/MLSS is between 56% and 77%, and that of MLISS is between –45% and –80%. The accumulation forms of inorganic solids in different forms of activated sludge systems are also different. Chemical sludge is mainly suspended in the mixture, reducing the proportion of MLVSS/MLSS. In activated sludge system, sediment is accumulated in various forms such as suspension and deposition.

Active support of mistletoe to the host tree with carbon assimilation under source-limitation – results from a 13C labelling experiment

<p>Pine Mistletoe (<em>Viscum album ssp. austriacum</em>) is a hemi-parasite shrub species, whose survival and development rely on water and mineral resources obtained through the xylem sap from the host tree. Mistletoe can produce photosynthates in its green organs on its own. On the other side, as they are connected to the phloem of the host tree, they may also be able to retrieve  carbon assimilates from their host and/or vice versa. However, the dynamics and the steering factors of this relationship remains unclear. We conducted <sup>13</sup>C- labelling experiments with mature Scots pine (<em>Pinus sylvestris</em>) infected by mistletoes in a long-term (15 years) irrigation experiment in Switzerland (Pfynwald, Valais) to investigate the transport of carbon assimilates and nutrients between the host and the parasite under different soil moisture (600 mm vs 1200 mm of precipitation per year). Three irrigated and three control (natural xeric) pine trees infected by mistletoes were <sup>13</sup>C labelled for 4 hours. During the <sup>13</sup>C labelling of the trees, the following two experiments were carried out. <br>    1) Wrapping experiment: 3-4 clusters of mistletoes on the labelled trees were wrapped with aluminium foil and enclosed in plastic bags to prevent mistletoe photosynthesis using <sup>13</sup>C-enriched CO<sub>2</sub> and to investigate a potential host-mistletoe carbon transfer.<br>    2) Girdling and removal experiment: The phloem of 12 host tree branches (6 control & 6 irrigated) infected by mistletoes was manually removed (ca. 2 cm in width, basipetally of the mistletoes) to stop the downward transport of photosynthates from the girdled branches. Additionally, host needles or mistletoes were removed from the girdled branches to investigate the respective contribution of photosynthesis by the host needles vs. mistletoes to the host branch carbon balance.<br>     In the wrapping experiment, wrapped and unwrapped mistletoe leaves and stems were harvested at 10 times points over 6 months. In the girdling and removal experiment, needles, twigs (i.e. xylem and phloem) and mistletoe leaves were harvested at 7 time points over 14 days. In both experiment, bulk organic matter of each tissue was analysed to trace the <sup>13</sup>C signal.<br>     We found that there was no <sup>13</sup>C signal in the wrapped mistletoe leaves, indicating that there was no C-transfer from the host to the mistletoes via the phloem sap. Mistletoe removal from girdled branches decreased <sup>13</sup>C-labelled carbon assimilates in host xylem and phloem. Meanwhile, when needles were completely removed from the girdled branches, host xylem and phloem were still able to acquire <sup>13</sup>C from the mistletoes. These results suggest that mistletoes can support the host with carbon resources, which might be especially important when the host is C resource limited.<br>Our study provides new insights into the relationship between the hemi-parasite and its host tree. Mistletoes may play a role as C source providers to support the host and maintain a symbiotic relationship to survive. </p>