Influence of the exclusion distance among trees on gap fraction and foliage clumping index of forest plantations

Key message

A hypergeometric model is proposed explicitly instead of two previous stochastic models (the Poisson model and Neyman-A model) to describe the topological relationship of trees and the influence of the exclusion distance on gap fraction and clumping index of forest plantation canopies.

Abstract

Gap fraction (GF) and clumping index (CI) play key roles in plant light interception, and therefore they have strong impacts on plant growth and canopy radiative transfer processes. Trees are usually assumed to be randomly distributed in natural forests in many previous studies. However, few studies have shown how trees are distributed in forest plantations and how these distribution patterns affect GF and CI in these forests. In this paper, a simple and general distance factor defined as relative allowable shortest distance between centers of two adjacent crowns divided by the mean diameter of the crowns (RASD) is proposed to describe quantitatively the degree of mutual exclusion among trees in forest plantations of various tree distribution patterns. A hypergeometric model is proposed instead of two previous stochastic tree distribution models (the Poisson model and Neyman-A model) to describe the topological relationship of trees and the influences of the exclusion distance on the GF and CI of the forest plantation canopies. The results show that: (1) the hypergeometric model is more suitable than the Poisson model and Neyman-A model for describing the topological relationship of trees in forest plantations; (2) the exclusion distance has strong impacts on GF and CI: there are significant differences between the results of the hypergeometric model and the Poisson model. Larger RASD causes lower GF and larger CI. The simulations are verified by field measurements in four forest plantation stands. Similarly, impacts of RASD on GF and CI are also found for other two crown shapes (prolate and oblate ellipsoids).

     

New insights into the history of domesticated and wild apricots and its contribution to Plum pox virus resistance

Studying domesticated species and their wild relatives allows understanding of the mechanisms of population divergence and adaptation, and identifying valuable genetic resources. Apricot is an important fruit in the Northern hemisphere, where it is threatened by the Plum pox virus (PPV), causing the sharka disease. The histories of apricot domestication and of its resistance to sharka are however still poorly understood. We used 18 microsatellite markers to genotype a collection of 230 wild trees from Central Asia and 142 cultivated apricots as representatives of the worldwide cultivated apricot germplasm; we also performed experimental PPV inoculation tests. The genetic markers revealed highest levels of diversity in Central Asian and Chinese wild and cultivated apricots, confirming an origin in this region. In cultivated apricots, Chinese accessions were differentiated from more Western accessions, while cultivated apricots were differentiated from wild apricots. An approximate Bayesian approach indicated that apricots likely underwent two independent domestication events, with bottlenecks, from the same wild population. Central Asian native apricots exhibited genetic subdivision and high frequency of resistance to sharka. Altogether, our results contribute to the understanding of the domestication history of cultivated apricot and point to valuable genetic diversity in the extant genetic resources of wild apricots.     

Rotavirus-encoded virus-like small RNA triggers autophagy by targeting IGF1R via the PI3K/Akt/mTOR pathway

Rotaviruses are double-stranded RNA viruses that are a major cause of viral diarrhea in infants. Examining virus–host cell interaction is important for elucidating mechanisms of virus proliferation in host cells. Viruses can create an environment that promotes their survival and self-proliferation by encoding miRNAs or miRNA-like molecules that target various host cell. However, it remains unclear whether RNA viruses encode viral miRNAs, and their regulation mechanisms are largely unknown. We previously performed deep sequencing analysis to investigate rotavirus-encoded miRNAs, and identified the small RNA molecule Chr17_1755, which we named RV-vsRNA1755. In our present study, we determined that RV-vsRNA1755 is encoded by the rotavirus NSP4 gene and that it targets the host cell IGF1R, which is part of the PI3K/Akt pathway. We further explored the biological characteristics and functions of RV-vsRNA1755.Our results suggest that rotavirus adapts to manipulate PI3K/Akt signaling at early phases of infection. RV-vsRNA1755 targets IGF1R, blockading the PI3K/Akt pathway and triggering autophagy, but it ultimately inhibits autophagy maturation. A mechanism through which rotavirus encodes a virus-like small RNA (RV-vsRNA1755) that triggers autophagy by targeting the host cell IGF1R gene was revealed. These data provide a theoretical basis for therapeutic drug screening targeting RV-vsRNA1755.     

Gammaproteobacterial Diversity and Carbon Utilization in Response to Salinity in the Lakes on the Qinghai–Tibetan Plateau

The Gammaproteobacteria are widely and abundantly distributed in various environments, and they play important roles in the geochemical cycles of biogenic elements (e.g., C, N and S) in the ecosystems. Previous studies showed that Gammaproteobacteria dominate in saline and hypersaline lakes. However, little is known on how salinity influences gammaproteobacterial community composition and their ecological functions (i.e., organic carbon degradation). In this study, we investigated the gammaproteobacterial diversity and carbon utilization and their response to salinity in six saline/hypersaline lakes and one freshwater lake on the Qinghai–Tibetan Plateau (QTP). The results indicated that the gammaproteobacterial community composition was mainly influenced by the salinity of the studied QTP lakes. Salinity was also a key environmental factor influencing the carbon utilization ability of Gammaproteobacteria: within one genus (e.g., Halomonas, Pseudoalteromonas, Vibrio) the strains retrieved from low-salinity environments had stronger carbon utilization ability than their counterparts from high-salinity environments; within one genus, the strains isolated from lakes with different salinity shared similar carbon utilization preference, indicating that species belonging to the same genus may execute similar ecological functions in the environments regardless of salinity.     

A case report of spontaneous staphylococcal meningitis in a cynomolgus monkey

This report describes a suppurative meningitis in a young cynomolgus. The animal had neutrophil aggregation in the subarachnoid space and hemorrhage in bilateral adrenal glands. Staphylococcus was identified by FISH in brain. To our knowledge, this is the first case of staphylococcal meningitis with Waterhouse‐Friderichsen syndrome in a cynomolgus monkey.