Abundance changes of marsh plant species over 40 years are better explained by niche position water level than functional traits

Acknowledgements: This study was supported by the National Natural Science Foundation of China (grants No.41671109 and 41371107) and by the Natural Science Foundation of Jilin Province (grant No. 20190201281JC). We thank Xiaofeng Xu for the suggestions and Håkan Rydin for the comments on the manuscript.Peer reviewedPostprin

Plant–plant interactions vary greatly along a flooding gradient in a dam-induced riparian habitat

Plant–plant interactions under extreme environmental stress are still controversial. The stress gradient hypothesis (SGH) proposes that facilitation prevails under extreme environmental stresses, while an alternative view states that facilitation collapses or even switches back to competition at the extreme end of stress gradients. However, how the relationship between plant–plant interaction and periodic extreme flooding stress varies and its underlying mechanism are still unclear in a dam-regulated riparian ecosystem. We established a controlled experiment using two dominant species pairs (Cynodon dactylon–Cyperus rotundus and C. dactylon–Xanthium sibiricum) in the water level fluctuating zone of the Three Gorges Dam to examine their growth responses to the periodic extreme flooding stress. The results showed that as flooding stress increased, the competitive effect of C. dactylon on X. sibiricum shifted to facilitation, whereas the effect of X. sibiricum on C. dactylon maintained a strong inhibition. The plant height of X. sibiricum was the most important driver of the interaction between X. sibiricum and C. dactylon along the flooding gradient. The net effect of C. dactylon on C. rotundus shifted from neutral to negative, and the inhibitory effect of C. rotundus on C. dactylon became stronger at the extreme end of flooding stress. The root biomass of the two species was the key trait regulating their interaction with increasing flooding stress. Overall, the SGH was partially supported along our periodic extreme flooding stress gradient. Aboveground resource (light) might be the dominant factor driving the response of the interaction between annual plants and perennial clonal plants to periodic flooding stress, whereas belowground resource (water and nutrients) was probably the dominant factor for perennial clonal plants. Our study will help to further understand the environmental responses of plant–plant relationships and their regulatory mechanism, and the succession of riparian plant communities under extreme environmental changes, providing a basic theoretical basis and data support for the ecological restoration and management of riparian wetland vegetation

Response of Plant Height, Species Richness and Aboveground Biomass to Flooding Gradient along Vegetation Zones in Floodplain Wetlands, Northeast China.

Flooding regime changes resulting from natural and human activity have been projected to affect wetland plant community structures and functions. It is therefore important to conduct investigations across a range of flooding gradients to assess the impact of flooding depth on wetland vegetation. We conducted this study to identify the pattern of plant height, species richness and aboveground biomass variation along the flooding gradient in floodplain wetlands located in Northeast China. We found that the response of dominant species height to the flooding gradient depends on specific species, i.e., a quadratic response for Carex lasiocarpa, a negative correlation for Calamagrostis angustifolia, and no response for Carex appendiculata. Species richness showed an intermediate effect along the vegetation zone from marsh to wet meadow while aboveground biomass increased. When the communities were analysed separately, only the water table depth had significant impact on species richness for two Carex communities and no variable for C. angustifolia community, while height of dominant species influenced aboveground biomass. When the three above-mentioned communities were grouped together, variations in species richness were mainly determined by community type, water table depth and community mean height, while variations in aboveground biomass were driven by community type and the height of dominant species. These findings indicate that if habitat drying of these herbaceous wetlands in this region continues, then two Carex marshes would be replaced gradually by C. angustifolia wet meadow in the near future. This will lead to a reduction in biodiversity and an increase in productivity and carbon budget. Meanwhile, functional traits must be considered, and should be a focus of attention in future studies on the species diversity and ecosystem function in this region

The effect of temperature changes and K supply on the reproduction and growth of Bolboschoenus planiculmis

Aims Climate warming and agricultural non-point source pollution both resulting from anthropogenic activities have been projected to affect plant reproduction and growth in wetlands worldwide. In order to predict and mitigate impacts of these anthropogenic activities, it is important to investigate how marsh plants respond to such environmental changes. Methods In this study, Bolboschoenus planiculmis, a tuberous sedge with a wide distribution range in Eurasia, was selected to examine the effect of air temperature changes (15, 20 and 25 °C over 24 h; 20/10 and 30/15 °C, day/night) and K supply (0, 1, 3, 9 and 18 mmol/L) on its reproductive and growth traits in climate chambers. Important Findings We found that high constant temperatures (20 and 25 °C) were more beneficial for tuberization of B. planiculmis than high alternating temperatures (30/15 °C), whereas aboveground biomass and shoot height were generally largest at high temperatures (30/15 and 25 °C). Both reproductive and growth traits of B. planiculmis showed hump-shaped relationships with K supply, with an optimum K concentration of around 1–3 mmol/L. The combination of high constant temperatures and optimal K concentrations promoted reproductive traits the most, whereas the combination of higher temperatures (30/15 and 25 °C) and K concentrations up to 9 mmol/L increased growth traits only. We therefore conclude that population abundance of B. planiculmis might benefit from global warming and the additional K supply.温度变化和钾添加对扁秆藨草生长及繁殖的影响 人类活动导致的气候变暖和农业面源污染已被认为是影响湿地植物生长和繁殖的重要因素。为了预 测和缓解这些人类活动的影响，研究沼泽植物如何响应这些环境变化具有重要意义。本研究选取在欧亚 大陆广泛分布的莎草科球茎植物扁秆藨草(Bolboschoenus planiculmis)为研究对象，考察气温变化(恒温： 15、20、25 °C及交替温度：20/10和30/15 °C)和钾添加(0、1、3、9 和18 mmol/L)对其生长和繁殖性状 的影响。研究结果表明，高的恒温(20、25 °C)比高的交替温度(30/15 °C)更有利于扁秆藨草球茎的形成， 而地上生物量和株高一般在较高温度下(30/15、25 °C)达到最大值。扁秆藨草的繁殖和生长性状均与施钾量 呈驼峰型关系，最适施钾量在1–3 mmol/L K。高恒温效应和最适钾浓度的交互作用对繁殖性状的促进作 用最大，但是，较高的温度(30/15和25 °C)和0–9 mmol/L的钾浓度只促进了生长性状的生长。综上所述， 扁秆藨草的种群优势度可能受益于全球变暖和额外的钾添加。ISSN:1752-9921ISSN:1752-993

Multivariate stepwise regression analysis for species richness and aboveground biomass.

<p>Multivariate stepwise regression analysis for species richness and aboveground biomass.</p

The relationship between average plant height and water table depth for three dominant species ((A) <i>Carex lasiocarpa</i> (B) <i>Carex appendiculata</i> (C) <i>Calamagrostis angustifolia</i>).

<p>The relationship between average plant height and water table depth for three dominant species ((A) <i>Carex lasiocarpa</i> (B) <i>Carex appendiculata</i> (C) <i>Calamagrostis angustifolia</i>).</p

Wetland types, geographical location and the administration authority of the studied sites in Northeast China.

<p>Wetland types, geographical location and the administration authority of the studied sites in Northeast China.</p

Summary of general linear models for species richness and aboveground biomass.

<p>Summary of general linear models for species richness and aboveground biomass.</p

The relationship between aboveground biomass and water table depth. (A)–(C) are for <i>Carex lasiocarpa</i>, <i>Carex appendiculata</i>, and <i>Calamagrostis angustifolia</i> community, (D) is for all three communities combined.

<p>The relationship between aboveground biomass and water table depth. (A)–(C) are for <i>Carex lasiocarpa</i>, <i>Carex appendiculata</i>, and <i>Calamagrostis angustifolia</i> community, (D) is for all three communities combined.</p

The describe statistic of species richness and biomass for three herb marsh communities.

<p>The describe statistic of species richness and biomass for three herb marsh communities.</p