Mechanism Underlying the Spatial Pattern Formation of Dominant Tree Species in a Natural Secondary Forest

<div><p>Studying the spatial pattern of plant species may provide significant insights into processes and mechanisms that maintain stand stability. To better understand the dynamics of naturally regenerated secondary forests, univariate and bivariate Ripley’s <i>L(r)</i> functions were employed to evaluate intra-/interspecific relationships of four dominant tree species (<i>Populus davidiana</i>, <i>Betula platyphylla</i>, <i>Larix gmelinii</i> and <i>Acer mono</i>) and to distinguish the underlying mechanism of spatial distribution. The results showed that the distribution of soil, water and nutrients was not fragmented but presented clear gradients. An overall aggregated distribution existed at most distances. No correlation was found between the spatial pattern of soil conditions and that of trees. Both positive and negative intra- and interspecific relationships were found between different DBH classes at various distances. Large trees did not show systematic inhibition of the saplings. By contrast, the inhibition intensified as the height differences increased between the compared pairs. Except for <i>Larix</i>, universal inhibition of saplings by upper layer trees occurred among other species, and this reflected the vertical competition for light. Therefore, we believe that competition for light rather than soil nutrients underlies the mechanism driving the formation of stand spatial pattern in the rocky mountainous areas examined.</p></div

Mechanism Underlying the Spatial Pattern Formation of Dominant Tree Species in a Natural Secondary Forest - Fig 1

<p>Spatial distributions of trees of different DBH classes (small (a), medium (b), large (c)) and height classes (sapling (d), medium (e), tall (f)).</p

Characteristics of the four dominant species in the secondary forest within the survey area covering 4ha.

<p>Characteristics of the four dominant species in the secondary forest within the survey area covering 4ha.</p

Univariate analyses of trees of different DBH classes.

<p>Univariate functions <i>L</i>(r) (dotted lines) are shown with the simulation intervals (shadow areas). L: large (DBH = 1-15cm); M: middle (DBH = 15-30cm); S: small (DBH> = 30cm).</p

Statistics of trees in each DBH and height interval and the corresponding relationship between DBH and height (embedded) for the four dominant species.

<p>Statistics of trees in each DBH and height interval and the corresponding relationship between DBH and height (embedded) for the four dominant species.</p

Bivariate analyses exploring the association of intra- and interspecies relationships between trees of different height ranks.

<p>The classification of height classes was the same as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0152596#pone.0152596.g004" target="_blank">Fig 4</a>. U: upper layer, M: middle layer; S: sapling. Grey bars: repulsion; yellow bars: attraction; void: independence.</p

Spearman’s rank correlation coefficients (P level) of tree distribution and the spatial pattern of soil nutrients, i.e. correlation between the number of individuals of different DBH/height classes and the soil condition indices.

<p>The correlation is significant if P<0.05.</p

Spatial distribution of soil physical and chemical indices.

<p>Spatial distribution of soil physical and chemical indices.</p

Descriptive statistics of soil traits from samples across the 4-ha plot area.

<p>Descriptive statistics of soil traits from samples across the 4-ha plot area.</p

Susceptibility of Overweight Mice to Liver Injury as a Result of the ZnO Nanoparticle-Enhanced Liver Deposition of Pb²⁺

The prevalence of the applications of nanomaterials in consumer products and water treatment facilities increases the chance that humans will be exposed to both nanoparticles and environmental pollutants such as heavy metals. Co-exposure to nanoparticles and heavy metals may adversely affect human health, especially in susceptible populations such as overweight subjects. To evaluate the impact of such co-exposures, we orally administered zinc oxide nanoparticles (ZNPs; 14 or 58 nm) and/or Pb­(Ac)₂ at tolerable doses to both healthy overweight and healthy normal weight mice. The ZNPs enhanced the deposition of Pb in all major organs in the overweight mice compared with that in the normal mice. As a result, higher levels of hepatic reactive oxygen species, pro-inflammatory cytokines, and liver injury were observed in the overweight mice but not in the normal weight mice. Our findings underscore a potentially enhanced risk of nanoparticle/heavy metal co-exposure in the susceptible overweight population