Effects of Water Level on Three Wetlands Soil Seed Banks on the Tibetan Plateau

<div><p>Background</p><p>Although the effect of water level on germination in soil seed banks has been documented in many ecosystems, the mechanism is not fully understood, and to date no empirical studies on this subject exist. Further, no work has been done on the effect of water level on seed banks of drying and saline-alkaline wetlands in alpine areas on the Tibetan Plateau.</p><p>Methodology</p><p>We examined the effects of water level (0 cm, 5 cm and 10 cm) on seed germination and seedling establishment from soil seed banks at 0–5 cm and 5–10 cm depths in typical, drying, and saline-alkaline wetlands. We also explore the potential role of soil seed bank in restoration of drying and saline-alkaline wetlands.</p><p>Principal Findings</p><p>Species richness decreased with increase in water level, but there almost no change in seed density. A huge difference exists in species composition of the seed bank among different water levels in all three wetlands, especially between 0 cm and 5 cm and 0 cm and 10 cm. Similarity of species composition between seed bank and plant community was higher in 0 cm water level in drying wetland than in the other two wetlands. The similarity was much higher in 0 cm water level than in 5 cm and 10 cm water levels in all three wetlands. Species composition of the alpine wetland plant community changed significantly after drying and salinization, however, species composition of the seed bank was unchanged regardless of the environment change.</p><p>Conclusions/Significance</p><p>Water level greatly affects seed bank recruitment and plant community establishment. Further, different water levels in restored habitats are likely to determine its species composition of the plant community. The seed bank is important in restoration of degraded wetlands. Successful restoration of drying and salinization wetlands could depend on the seed bank.</p></div

Two-dimensional nonmetric multidimensional scaling (NMDS) ordination of species composition of seed banks and plant community in wetlands with 0, 5, and 10 cm water levels on the Tibetan Plateau.

<p>Data for each wetland (T =  Typical wetland; D =  Drying wetland; S =  Saline-alkaline wetland) were analyzed separately. In addition, the seed banks and plant community of three wetlands were compared among each other (bottom-right). Ordination was based on relative abundance data. Different symbols represent different seed bank and plant community types. There were five sites for each seed bank, 10 plots for typical and saline-alkaline wetland plant communities and 6 plots for the drying wetland plant community. Location of ordination points within each diagram indicates degree of similarity between each one.</p

The proportion of life forms in three water levels and vegetation at different wetlands in Tibetan Plateau (Black bar: perennial species, gray bar: biennial species, and white bar: annual species).

<p>T =  Typical wetland; D =  Drying wetland; S =  Saline-alkaline wetland.</p

Species richness and seed density of 0–5 and 5–10 cm soil depths per plot (n = 5) changes in 0 cm, 5 cm and 10 cm water levels in three habitats.

<p>Seed density comparisons were carried out using log-transformed data. Different letters indicate significant differences (ANOVA, Tukey range test) of mean values of each soil depth. T =  Typical wetland; D =  Drying wetland; S =  Saline-alkaline wetland.</p

Seasonal dynamics of the plant community and soil seed bank along a successional gradient in a subalpine meadow on the Tibetan Plateau.

BACKGROUND: Knowledge about how change the importance of soil seed bank and relationship between seed mass and abundance during vegetation succession is crucial for understanding vegetation dynamics. Many studies have been conducted, but their ecological mechanisms of community assembly are not fully understood. METHODOLOGY: We examined the seasonal dynamics of the vegetation and soil seed bank as well as seed size distribution along a successional gradient. We also explored the potential role of the soil seed bank in plant community regeneration, the relationship between seed mass and species abundance, and the relative importance of deterministic and stochastic processes along a successional gradient. PRINCIPAL FINDINGS: Species richness of seed bank increased (shallow layer and the total) and seed density decreased (each layer and the total) significantly with succession. Species richness and seed density differed significantly between different seasons and among soil depths. Seed mass showed a significant negative relationship with relative abundance in the earliest successional stage, but the relationships were not significant in later stages. Seed mass showed no relationship with relative abundance in the whole successional series in seed bank. Results were similar for both July 2005 and April 2006. CONCLUSIONS: The seed mass and abundance relationship was determined by a complex interaction between small and larger seeded species and environmental factors. Both stochastic processes and deterministic processes were important determinants of the structure of the earliest stage. The importance of seed bank decreased with succession. The restoration of abandoned farmed and grazed meadows to the species-rich subalpine meadow in Tibetan Plateau can be successfully achieved from the soil seed bank. However, at least 20 years are required to fully restore an abandoned agricultural meadow to a natural mature subalpine meadow

Host plant height explains the effect of nitrogen enrichment on arbuscular mycorrhizal fungal communities.

Nitrogen (N) enrichment is widely known to affect the root-associated arbuscular mycorrhizal fungal (AMF) community in different ways, for example, via altering soil properties and/or shifting host plant functional structure. However, empirical knowledge of their relative importance is still lacking. Using a long-term N addition experiment, we measured the AMF community taxonomic and phylogenetic diversity at the single plant species (roots of 15 plant species) and plant community (mixed roots) levels. We also measured four functional traits of 35 common plant species along the N addition gradient. We found divergent responses of AMF diversity to N addition for host plants with different innate heights (i.e. plant natural height under unfertilized treatment). Furthermore, our data showed that species-specific responses of AMF diversity to N addition were negatively related to the change in maximum plant height. When scaling up to the community level, N addition affected AMF diversity mainly through increasing the maximum plant height, rather than altering soil properties. Our results highlight the importance of plant height in driving AMF community dynamics under N enrichment at both species and community levels, thus providing important implications for understanding the response of AMF diversity to anthropogenic N deposition

Does a Moderately Warming Climate Compensate for the Negative Effects of UV-B Radiation on Amphibians at High Altitudes? A Test of Rana kukunoris Living on the Qinghai&ndash;Tibetan Plateau

Both the warming climate and ultraviolet-B radiation (UVBR) are considered to be notable environmental factors affecting amphibian population decline, with particular effects on tadpole development. However, the phenotypes of tadpoles living at high altitudes may be improved by moderately warming temperatures, reducing or eliminating the negative effects of oxidative damage caused by cool temperatures or strong UVBR at high altitudes. To verify this hypothesis, Rana kukunoris tadpoles, which live at high altitudes, were used to test the effect of the interaction of temperature and UVBR on their development and antioxidant systems in a fully factorial design. The tadpoles were exposed to UVBR and UVBR-free environments at 14 (cool temperature) and 22 &deg;C (warm temperature), respectively. UVBR and a warm temperature had opposite influences on several traits of the tadpoles, including their survival, developmental rate, individual size, preferred body temperature, thermal tolerance temperature, oxidative damage, and enzymatic and nonenzymatic antioxidant systems. The moderate temperature could compensate for or override the negative effects of UVBR by increasing the tadpoles&rsquo; preferred body temperature and critical tolerance temperature, thus enhancing the locomotion ability and thermal sensitivity of their antioxidant systems. Furthermore, the dark skin coloration and aggregation behavior of R. kukunoris tadpoles may also be effective strategies for allowing them to resist UVBR and helping them to better adapt to a warming environment with stronger UVBR. Thus, it is possible that a moderate degree of warming may increase the capacity of living organisms to adapt to environmental changes and thus have positive effects on the development of tadpoles living at high altitudes

The relationship between relative abundance and seed mass during succession in the vegetation (top row) and seed bank (botton row) of a Tibetan Plateau subalpine meadow (2005 – left; 2006- right).

<p>The Kendall's tau-b correlation coefficient (r) is shown in each figure. Significant relationships (P<0.05) are denoted with solid lines.</p

Descriptions of the habitat types investigated.

<p>All habitats have same slope, exposure, altitude, annual mean temperature (2.4°C) and annual mean precipitation (531.6 mm).</p

Species richness (left) and cover (right) (per quadrat, mean±SE) changes in vegetation along a successional gradient in the subalpine meadow of Tibetan Plateau.

<p>Letters indicate significant differences (ANOVA, Tukey range test).</p