Growth and Physiological Adaptation of Salix matsudana Koidz. to Periodic Submergence in the Hydro-Fluctuation Zone of the Three Gorges Dam Reservoir of China

Submergence-tolerant trees are essential for vegetation restoration of the hydro-fluctuation zone of the Three Gorges Dam Reservoir (TGDR) area. Thus, it is of great significance to select the submergence-tolerant plant species by conducting in situ studies. To restore degraded riparian vegetation under the circumstances of dynamic impoundment of the TGDR, Salix matsudana Koidz., a flooding-tolerant native tree species, was introduced to conduct an in situ practical study to test its performance in re-vegetating and restoring the hydro-fluctuation zone of the TGDR. Effects of periodic moderate submergence (MS) and deep submergence (DS) on photosynthesis and growth of Salix matsudana Koidz. were investigated after three water cycles compared to a control (i.e., shallow submergence, abbreviated as SS) in order to specifically assess its application prospects in vegetation restoration under such extreme environment. Results showed that net photosynthetic rate (Pn), intrinsic water use efficiency (WUEi) and limiting value of stomata (Ls) of S. matsudana were significantly reduced in DS. However, pigment content had no significant change in all submergence treatments. Diameter at breast height (DBH) and tree height of S. matsudana were significantly decreased in both MS and DS when compared to that of SS, respectively. In contrast, the primary branch number of S. matsudana was significantly increased as submergence increased. In addition, relative diameter and height growth rates of S. matsudana were also reduced under submergence. Considering the sustained growth of this species, S. matsudana saplings are tolerant to long-term periodic submergence and can be applied to the vegetative restoration of the hydro-fluctuation zone of the TGDR region

Baseline data on tree height and diameter at breast height (DBH) of <i>T</i>. <i>distichum</i> and <i>T</i>. <i>ascendens</i> saplings prior to planting in 2012 (means ± S.E., n = 9).

<p>Baseline data on tree height and diameter at breast height (DBH) of <i>T</i>. <i>distichum</i> and <i>T</i>. <i>ascendens</i> saplings prior to planting in 2012 (means ± S.E., n = 9).</p

Submergence depth and duration of the treatments at different elevations during the three water cycles.

<p>Submergence depth and duration of the treatments at different elevations during the three water cycles.</p

Relative growth rates in DBH (RDGR) and height (RHGR) of <i>T</i>. <i>distichum</i> and <i>T</i>. <i>ascendens</i> saplings after experiencing three water level change cycles (means ± S.E., n = 9).

<p>Relative growth rates in DBH (RDGR) and height (RHGR) of <i>T</i>. <i>distichum</i> and <i>T</i>. <i>ascendens</i> saplings after experiencing three water level change cycles (means ± S.E., n = 9).</p

Genetic variability and population divergence of Rhododendron platypodum Diels in China in the context of conservation

Genetic diversity in endangered species is of special significance in the face of escalating global climate change and alarming biodiversity declines. Rhododendron platypodum Diels, an endangered species endemic to China, is distinguished by its restricted geographical range. This study aimed to explore genetic diversity and differentiation among its populations, gathering samples from all four distribution sites: Jinfo Mountain (JFM), Zhaoyun Mountain (ZYM), Baima Mountain (BMM), and Mao’er Mountain (MEM). We employed 18 pairs of Simple Sequence Repeat (SSR) primers to ascertain the genetic diversity and structural characteristics of these samples and further utilized 19 phenotypic data points to corroborate the differentiation observed among the populations. These primers detected 52 alleles, with the average number of observed alleles (Na) being 2.89, the average number of effective alleles (Ne) being 2.12, the average observed heterozygosity (Ho) being 0.57, and the expected heterozygosity (He) being 0.50. This array of data demonstrates the efficacy of the primers in reflecting R. platypodum’s genetic diversity. SSR-based genetic analysis of the populations yielded Ho, He, and Shannon index (I) values ranging from 0.47 to 0.65, 0.36 to 0.46, and 0.53 to 0.69, respectively. Notably, the ZYM population emerged as the most genetically diverse. Further analysis, incorporating molecular variance, principal component analysis, UPGMA cluster analysis, and structure analysis, highlighted significant genetic differentiation between the Chongqing (BMM, JFM, ZYM) and Guangxi (MEM) populations. Morphological data analysis corroborated these findings. Additionally, marked genetic and morphological distinctions were evident among the three Chongqing populations (BMM, JFM, and ZYM). This suggests that, despite the observed regional differentiation, R. platypodum’s overall genetic diversity is relatively constrained compared to other species within the Rhododendron genus. Consequently, R. platypodum conservation hinges critically on preserving its genetic diversity and protecting its distinct populations