Carex Meadow Research Articles

It takes two to Tango: Plant height and nutrient level determine the diet selection of wintering geese in Poyang Lake, a Ramsar wetland

In Poyang Lake, the largest and one of the most important wintering sites in the East Asian-Australasian Flyway, Carex (Carex cinerascens Kük) meadows provide the primary food source for the wintering geese. However, due to intensified river regulation and more frequent extreme climatic events such as drought, observational evidence suggests that the synchrony of geese migration and Carex phenology could not be maintained without human interventions, imposing a great risk of food shortage during the wintering period. Consequently, the current conservation priority in this Ramsar site is shifted to wet meadow improvement to ensure optimal food quality. Understanding the food preferences of wintering geese is the key for effective wet meadow management. As the growth stage and nutrient level of food plants are the decisive factors influencing the diet selection of herbivores, in this study, we sampled the preferred food items by tracking the foraging paths of the Greater White-fronted Goose (n = 84) and Bean Goose (n = 34) to quantify the “foraging window” in terms of plant height,protein level, and energy content. Further, we established relationships between the above three variables of Carex based on in-situ measurements. The results show that the geese prefer plants with height ranging from 2.4 to 25.0 cm, with protein content from 13.9 to 25.2 %, and energy content from 1440.0 to 1813.6 KJ/100 g. While plant energy content increases with height, the height-protein level relationship is negative. The opposite growth curves signify a conservation challenge to maintain the delicate balance between the quantity and quality requirements of wintering geese. Carex meadow management, such as mowing, should focus on optimizing the timing of action to maximize energy supply while maintaining the right protein level for the long-term fitness, reproduction and survival of the birds.

Vegetation Dynamic in a Large Floodplain Wetland: The Effects of Hydroclimatic Regime

Floodplain wetlands are among the most dynamic ecosystems on Earth, featuring high biodiversity and productivity. They are also sensitive to anthropogenic disturbances and are globally threatened. Understanding how flow regime drives the spatiotemporal dynamics of wetland habitats is fundamental to effective conservation practices. In this study, using Landsat imagery and the random forest (RF) machine learning algorithm, we mapped the winter distribution of four wetland habitats (i.e., Carex meadow, reedbed, mudflat, and shallow water) in East Dongting Lake, a Ramsar wetland in the middle to lower Yangtze Basin of China, for 34 years (1988–2021). The dynamics of wetland habitats were explored through pixel-by-pixel comparisons. Further, the response of wetland habitats to flow regime variations was investigated using generalized additive mixed models (GAMM). Our results demonstrated the constant expansion of reedbeds and shrinkage of mudflats, and that there were three processes contributing to the reduction in mudflat: (1) permanent replacement by reedbed; (2) irreversible loss to water; and (3) transitional swapping with Carex meadow. These changes in the relative extent of wetland habitats may degrade the conservation function of the Ramsar wetland. Moreover, the duration of the dry season and the date of water level withdrawal were identified as the key flow regime parameters shaping the size of wetland habitats. However, different wetland vegetation showed distinct responses to variations in flow regime: while Carex meadow increased with earlier water withdrawal and a longer dry season, reedbed continuously expanded independent of the flow regime corresponding to the increase in winter rainfall. Our findings suggested that flow regime acts in concert with other factors, such as climate change and sand mining in river channels, driving wetland habitat transition in a floodplain landscape. Therefore, effective conservation can only be achieved through diverse restoration strategies addressing all drivers.

Soil characteristics and response thresholds of salt meadow on lake beaches of the Ordos platform

Salt meadow on lake beaches is the most dynamic plant community. Studying its soil characteristics and response threshold allows us to understand the external driving forces of vegetation stable-state maintenance and dynamic changes, and provide a theoretical basis for the utilization and ecological restoration of lake beach wetland resources. In this study, the community diversity, physical and chemical properties of soil, and ecological response thresholds of key soil indexes of four groups of meadows are discussed: (I) succulent salt-tolerant plant meadow, (II) Carex meadow, (III) grass meadow, and (IV) weed grass meadow. The major findings are as follows. First, Group I is easy to form a single-optimal community in the inland salt marsh beach, with patchy distribution. Group II has a lot of associated species, and most of them grew in clusters. Group III often has obvious dominant species, and the populations and individuals are evenly distributed in the community. The dominant species of Group IV are diverse, and the distribution is the most uniform. Second, there are significant differences in water content, salinity, nutrient and particle size composition of the four types of salt meadows. For Groups I-IV, the soil water content (WC) follows I > II > IV > III; the total salt content (TS) of soil follows I > III > II > IV; the pH value follows III > II > IV > I. Third, the diversity of salt meadow plants in lake beaches is closely related to the contents of WC, TS, Na+, HCO3−, particle size, available potassium (AK), alkali hydrolyzable nitrogen (AN) and available phosphorus (AP) in soil. The vegetation of the four formation groups shows different ecological response threshold intervals. Fourth, the response thresholds of salt meadow vegetation to water content, salt content and sand content of soil are inherently related (but the response threshold to nutrients in soil is unclear).

鄂尔多斯台地盐沼滩涂湿地土壤细菌群落结构及特征

PDF HTML阅读 XML下载 导出引用 引用提醒 鄂尔多斯台地盐沼滩涂湿地土壤细菌群落结构及特征 DOI: 10.5846/stxb202012313339 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41761102） Characteristics and distribution of soil bacterial of salt marsh tidal wetland in Ordos Platform Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:依据植被分类法将鄂尔多斯高原盐沼滩涂湿地划分为肉质耐盐草甸（B）、苔草草甸（C）、禾草草甸（D）和杂类草草甸（E）等4个植被亚型，并以盐沼裸地（A）为对照样地，共计5种盐沼滩涂湿地景观类型。运用高通量测序技术分别研究其土壤细菌群落结构特征、分布情况，以及土壤盐分与土壤细菌之间的关系。结果表明：（1）5种盐沼滩涂湿地的土壤细菌样品共12213条OTUs，属于45个门，122个纲，365个目，663个科，1375个属，2882个种。（2）变形菌门（26.19%）是盐沼滩涂湿地平均相对丰度最高的门，其次为放线菌门（17.15%），绿弯菌门（12.62%），芽单胞菌门（Gemmatimonadetes，11.23%），拟杆菌门（Bacteroidetes，9.38%），酸杆菌门（Acidobacteria，8.83%）厚壁菌门（Firmicutes，2.96%）；芽单胞菌纲中的未定细菌（norank_c_Gemmatimonadetes）是丰度最高的属，平均丰度为5.75%。（3）鄂尔多斯盐沼滩涂湿地自西南向东北，空间位置相近的土壤细菌群落结构具有更大的相似性，随着土壤盐分变化，变形菌门相对丰度存在先增大后减小的趋势，与异常球菌-栖热门菌的变化趋势相反，绿弯菌门、酸杆菌门相对丰度大致呈不断增大的趋势，拟杆菌门和厚壁菌门大体呈逐渐减少的趋势，芽单胞菌门和（Rokubacteria）的变化趋势上下波动，不稳定（4）不同盐沼滩涂湿地土壤细菌群落丰度与多样性的结果均表现为：苔草草甸>杂类草草甸>禾草草甸>肉质耐盐草甸>盐沼裸地。（5）在土壤盐分指标中，与鄂尔多斯盐沼滩涂湿地细菌群落相关性依次为TS> CO32-> Na+> Cl-> pH > SO42- >K+> Mg2+> Ca2+> HCO3-。此研究结果不仅可为揭示鄂尔多斯高原盐沼滩涂湿地土壤细菌区系组成及其对应的环境特征的变化规律提供理论依据，而且进一步探讨了土壤盐分与土壤微生物之间的关系，为高原盐沼地区的土壤修复及生境演替提供了参考。 Abstract:According to the vegetation classification method, the salt marsh tidal wetland in Ordos Plateau was divided into 4 vegetation subtypes, such as succulent salt-tolerant meadow (B), carex meadow (C), grass meadow (D) and forbs meadow (E). meanwhile, salt marsh bare land (A) was taken as the control plot, there are five landscape types of salt marsh tidal wetland designed. The structure characteristics and distribution of soil bacterial community and the relationship between soil salinity and soil bacteria were studied by high-throughput sequencing technique. The results showed that:(1) There were 12213 OTUs in the soil bacteria samples of 5 kinds of salt marsh tidal wetland, which belonged to 2882 species, 1375 genera, 663 families, 365 orders, 122 classes and 45 phyla. (2) Proteobacteria (26.19%) was the highest average relative abundance of salt marsh tidal wetland, followed by Actinobacteria (17.15%), Chloroflexi (12.62%), Gemmatimonadetes (11.23%), Bacteroidetes (9.38%), Acidobacteria (8.83%) and Firmicutes (2.96%); the undetermined bacterium (norank_c_Gemmatimonadetes) in Gemmatimonadetes was the most abundant genus with an average abundance of 5.75%. (3) The community structure of soil bacteria with close spatial positions had a greater similarity from southwest to northeast in Ordos salt marsh tidal wetland. With the change of salt content in soil, the relative abundance of Proteobacteria increased at first and then decreased, which was contrary to the change trend of Deinococcus-Thermus; the relative abundance of Chloroflexi and Acidobacteria showed an increasing trend. Bacteroidetes and Firmicutes generally showed a decreasing trend, and Gemmatimonadetes and Rokubacteria showed a fluctuating and unstable change trend. (4) The abundance and diversity of soil bacterial community in different salt marsh tidal wetlands were as follows:carex meadow > forbs meadow > grass meadow > succulent salt-tolerant meadow > salt marsh bare land. (5) The correlation between soil salinity and bacterial community in Ordos salt marsh tidal wetland from high to low was as follows:TS > CO32-> Na + > Cl-> pH > SO42-> K + > Mg2 + > Ca2+> HCO3-. The results of this study could not only provide theoretical basis for revealing the composition of soil bacterial flora in salt marsh tidal wetland of Ordos Plateau and the change law of its corresponding environmental characteristics, but also further explored the relationship between soil salinity and soil microorganisms, so as to provide reference for soil remediation and habitat succession in salt marsh areas of Ordos Plateau. 参考文献 相似文献 引证文献

Contrasting habitat use and conservation status of Chinese-wintering and other Eurasian Greater White-fronted Goose (Anser albifrons) populations

BackgroundGPS/GSM tracking data were used to contrast use of (i) habitats and (ii) protected areas between three Arctic-nesting Greater White-fronted Geese (Anser albifrons, GWFG) populations throughout the annual cycle. We wished to demonstrate that the East Asian Continental Population (which winters on natural wetlands in the Chinese Yangtze River floodplain and is currently declining) avoids using farmland at multiple wintering sites. We also gathered tracking evidence to support general observations from two increasing population of GWFG, the North Sea-Baltic (which winters in Europe) and the West Pacific (which winter in Korea and Japan) winter mostly within farmland landscapes, using wetlands only for safe night roosts.MethodsWe tracked 156 GWFG throughout their annual cycle using GPS/GSM transmitters from these three populations to determine migration routes and stopover staging patterns. We used Brownian Bridge Movement Models to generate summer, winter and migration stopover home ranges which we then overlaid in GIS with land cover and protected area boundary at national level to determine habitat use and degree of protection from nature conservation designated areas.ResultsData confirmed that 73% of European wintering GWFG homes ranges were from within farmland, compared to 59% in Japan and Korea, but just 5% in China, confirming the heavy winter use of agricultural landscapes by GWFG away from China, and avoidance of farmland at multiple sites within the Yangtze River floodplain. The same GWFG used farmland in northeast China in spring and autumn, confirming their experience of exploiting such habitats at other stages of their annual cycle. Chinese wintering birds showed the greatest overlap with protected areas of all three populations, showing current levels of site safeguard are failing to protect this population.ConclusionsResults confirm the need for strategic planning to protect the East Asian Continental GWFG population. While the site protection network in place to protect the species seems adequate, it has failed to stop the declines. Buffalo grazing could serve as one simple strategy to improve the condition of feeding habitats at Dongting Lake and Poyang Lake in the Yangtze, where vast Carex meadows exist. In addition, while we warn against pushing GWFG to winter farmland feeding in China because of the long-term potential to conflict with agricultural interests, we recommend experimental sacrificial, disturbance-free farmland within designated refuge areas adjacent to the Yangtze River floodplain wetland reserves as a manipulative experiment to improve the conservation status of this population in years when natural food sources are limited.

Effects of hydrological environment on litter carbon input into the surface soil organic carbon pool in the Dongting Lake floodplain

Litter carbon is the main source of the surface soil organic carbon pool (S-SOCP). However, the impact of changes in the hydrological environment of natural wetlands on litter input to S-SOCP remains unclear. In the present study, the effects of hydrological changes (soil water content [SWC] and days of flooding [DF]) on the litter decomposition process and S-SOCP were investigated from January 2018 to November 2019 in the Dongting Lake floodplain of China. Furthermore, the contribution of litter to the S-SOCP in Carex meadow and Reed wetland were calculated. The results showed that a large part of litter (approximately 50%–70%) decomposed annually, especially during the flooding season. Litter contributed 283.68 g C m−2 a–1 to the S-SOCP in the Carex meadow and 275.24 g C m−2 a–1 to the Reed wetland. In the Carex meadow and Reed wetland, the belowground litter contribution was higher than the aboveground litter during the non-flooding season. In contrast, during the flooding season, the aboveground litter contribution in the Carex meadow is higher, whereas the belowground litter dominates in the Reed wetland. The SWC indicated a positive correlation with soil organic carbon (SOC) and a negative correlation with the microbial biomass carbon (MBC) and dissolved organic carbon (DOC) in the Carex meadow. However, SWC shows a negative correlation with SOC and a positive correlation with MBC in the Reed wetland during the non-flooding season. During the flooding season, the variation of DOC during the flooding season (ΔDOC) is positively correlated with DF in the Carex meadow and Reed wetland. SWC and DF are the main drivers of litter decomposition into the S-SOCP in non-flooding and flooding seasons, respectively. Therefore, the construction of microhabitat with prolonged flooding and relatively higher soil water content are essential ways to improve the carbon sequestration potential in floodplains.

Phenological mismatch caused by water regime change may explain the population variation of the vulnerable lesser white-fronted goose in east Dongting Lake, China

Phenological mismatches between migratory birds and food availability driven by global warming have been found to influence the fitness and population dynamics of several herbivorous goose species in Arctic breeding sites. However, the effect of phenological mismatches at wintering sites have been inadequately studied. We used long-term data to explore the consequences of water regime changes on phenological mismatch (i.e., days between arrival of geese and timing of the optimal Normalized Difference Vegetation Index [NDVIopt]) and detect the relative role of the mismatch as a driver of annual variations in abundance and distribution of the Lesser White-fronted Goose Anser erythropus (a vulnerable species on the IUCN Red List) in East Dongting Lake, which is the one of this species’ largest wintering sites worldwide. The NDVI of the Carex meadow (i.e., the dominant vegetation in East Dongting Lake wetland and also the major food resource for the geese) was used as the phenology metric. Results showed that the water recession pattern greatly influenced food conditions when geese arrived at the site. Early water recession led to significantly higher NDVI, whereas late water recession led to significantly lower NDVI than did the optimal water recession. However, the suitable habitat area was significantly larger under the optimal water recession pattern. Both early and late water level recessions caused greater mismatches and resulted in lower geese abundance and a more concentrated distribution. NDVI was positively correlated with aboveground biomass and negatively correlated with N% of Carex spp. High biomass and low N% related to high NDVI caused by early water recession may indicate unfavorable food conditions at the time that geese arrive and reduced sustainable food availability in mid-winter, while a low NDVI and limited habitat area caused by late water recession may indicate an insufficient food supply. In conclusion, non-optimal water recession led to a greater phenological mismatch and resulted in limited habitat quality (e.g., lower leaf N%) under early water recession but limited habitat quantity (e.g., smaller habitat area and lower aboveground biomass) under late water recession, and ultimately threatened the Lesser White-fronted Goose. Our results contributed to explaining the decline of the Lesser White-fronted Goose population in this wintering site.

Changes in Methane Emission and Community Composition of Methane-Cycling Microorganisms Along an Elevation Gradient in the Dongting Lake Floodplain, China

Methane (CH4) emission and environmental controls of CH4-cycling microorganisms are unclear in inland floodplains. Here, we examined soil CH4 emissions and the community composition of CH4-cycling microorganisms under three vegetation types—mudflat (MF, no vegetation cover), Carex meadow (CM, mainly Carex brevicuspis), and reed land (RL, mainly Miscanthus sacchariflorus)—from water-adjacent areas to higher-elevation land in the Dongting Lake floodplain, China. The results showed that CH4 emission is the highest in CM, while significant absorption was observed in the RL site. The abundance ratio of methanogen/methanotroph was the highest in CM, intermediate in MF, and lowest in RL. The Methanosarcinaceae family represented the dominant methanogens in the three sampling sites (41.32–75.25%). The genus Methylocystis (60.85%, type II methanotrophs) was dominant in CM, while Methylobacter and Methylosarcina (type I methanotrophs) were the dominant genera in MF (51.00%) and RL (50.24%), respectively. Structural equation model analysis showed that methanogen and methanotroph abundance were affected by water table depth, soil water content, and pH indirectly through soil organic content, total nitrogen, microbial biomass carbon, and microbial biomass nitrogen. These results indicated that the Dongting Lake floodplain may change from a CH4 source to a CH4 sink with vegetation succession with an increase in elevation, and the methanogen/methanotroph ratio can be used as a proxy for CH4 emission in wetland soils. The continuous increase in reed area combined with the decrease in Carex meadow may mitigate CH4 emission and enhance the CH4 sink function during the non-flood season in the Dongting Lake floodplain.

Hydrological regime change and its ecological responses in East Dongting Lake, China

Extent, frequency and duration of lake water level fluctuations (WLF) are dominant forces controlling the functioning of lake ecosystems, especially in the lake's littoral and aquatic-terrestrial interface processes. In East Dongting Lake, Carex life history synchronize the arrival of overwintering birds, Carex meadow provide vital wintering ground for migratory waterbirds, especially for the Lesser White-fronted Geese. However, significant changes had taken place in the hydrological regime of East Dongting Lake and our research showed it caused chiefly by sediment deposition in the lake basin and the replenishment of the Three Gorges Dam. The annual lowest water level of the East Dongting Lake had gradually risen and the annual water level amplitude had decreased obviously over the past 60 years. Since the operation of the Three Gorges Dam, the average water level increased significantly from January to June. The Three Gorges Dam holder the incoming water from late September to late October that the status will change from flood control limited water level to normal water level, meanwhile the water level of East Dongting Lake declined significantly through the same duration, especially in October. The operation of the Three Gorges Dam decreased flooding days in the areas above 22-m elevation, resulting in lowering of the minimum elevation of vegetation-covered area and synchronous downward movement of vegetation distribution pattern. As the timing of water level recession at elevations of 24–27 m were 12, 17, 19 and 16 days earlier than that in 1981–2002, the optimum elevation for Carex growth decreased from 25–26 m to 24–25 m. After the operation of the Three Gorges Dam, the annual reversal times of water level increased significantly, which is not conducive to the formation of stable habitat and the utilization of resources by organisms.

The effects of flooding regimes and soil nutrients on lakeshore plant diversity in a pristine lake and a human managed lake in subtropical China

The hydrological regimes of many freshwater lakes have been dramatically changed by human activity. Nevertheless, few studies have reported the effects of human water management on the formation mechanisms of lakeshore plant communities. In this study, we investigated the effects of flooding and soil nutrients on the plant diversity of lakeshore Carex communities fringing a pristine lake (Poyang Lake) and a human managed lake (Shengjin Lake), two adjacent floodplain lakes in the middle and lower reaches of the Yangtze River. Over time, the Carex meadow at Shengjin Lake experienced a lower flooding frequency and a smaller amplitude of water level fluctuations in comparison with those obtained at Poyang Lake, but similar flooding durations were found for both sites. Soil total nitrogen (TN), total phosphorus (TP) and the ratio of TN to TP in study plots at Shengjin Lake tended to be higher than those in the plots at Poyang Lake at the 0–100 cm soil depth except for soil TP at the 0–10 cm soil depth. A total of 23 plant species were recorded in the Carex communities at the two lakes. Artificial water management increased plant diversity but had no effect on plant biomass in the Carex community. The primary factor in determining plant diversity changed from the flooding regime to the concentrations of soil nutrients as the water regime underwent management. Flooding regimes had strong direct impacts on the plant communities, while imposing few indirect effects on plants by changing soil nutrients in the pristine lake. Our results represent essential information for enhancing the robustness of management efforts for these large and important freshwater lakes.

Methane emissions from the littoral zone of Poyang lake during drawdown periods

Several studies have shown that lake littoral zones often support high methane (CH4) emissions. In this study, we measured CH4 emissions from two vegetation meadows in the littoral zone of Poyang Lake, China, from October 2014 to May 2015. CH4 emissions in the meadow dominated by Carex cinerascens were 11.27 ± 11.29 mg CH4 m−2 h−1, which were significantly higher than emissions in the meadow dominated by Artemisia selengensis (2.99 ± 1.67 mg CH4 m−2 h−1). Between-species differences in CH4 emission were caused by differences in belowground biomass. The results also showed distinct seasonal variation in CH4 emissions in this area; fluxes reached a maximum at the peak of the growing season and reached a minimum after the summer flood, when plants began to germinate. There were two peak values in the Carex meadow, and belowground biomass controlled the seasonality of CH4 emissions. Our results suggest that plant biomass may be a key factor controlling CH4 emissions in the littoral zone of Poyang Lake, highlighting that CH4 fluxes vary with vegetation type in littoral wetlands and demonstrating that spatial variation in CH4 emissions must be considered when estimating regional CH4 emissions in Poyang Lake. Considering climate change and the operations of a proposed hydraulic engineering project, changes to the hydrologic regime in this region may significantly affect CH4 emissions.

Hydrologic and Edaphic Controls on Soil Carbon Emission in Dongting Lake Floodplain, China

AbstractWetlands play a critical role in mitigating carbon emission. However, little is known about soil carbon emission and their environmental controls from inland floodplain wetlands. This study aimed to determine the effects of hydrologic and edaphic controllers (water table depth [WTD], soil temperature [Ts], and soil water content [SWC]) on soil C emission in Dongting Lake wetland, China. One‐year emissions were measured in Carex meadow and mudflat using static chambers during 2013 to 2014, including nonflooded season (NFs) and flooded season (Fs). The results showed that soil C emission in the Carex meadow and mudflat was 307.8 and 264.3 g C·m−2·year−1, respectively, and 50–66% of soil C were emitted during NFs. Compared with NFs, CO2 emission was significantly decreased by 57% but CH4 emission was significantly increased by 38 times during Fs in the Carex meadow. Stepwise regression combined with structural equation model analysis showed that CO2 and CH4 flux were mainly influenced by Ts during NFs, and they were controlled by water temperature (Tw) during Fs. During NFs, CO2 flux increased with increasing Ts and SWC but decreased significantly when SWC was over 66% and 52% in the Carex meadow and mudflat, respectively. CH4 flux showed an emission pulse at SWC and Ts of 65% and 17.2 °C, respectively. These results indicate that flooding significantly inhibited soil CO2 emission but stimulated CH4 emission. The continuous decrease of flooding days caused by anthropogenic disturbances may induce soil C loss in Dongting Lake wetlands.

Effects of hydrological regime on development of Carex wet meadows in East Dongting Lake, a Ramsar Wetland for wintering waterbirds

Wet meadows are one of the most important ecological components in floodplain, and are among the most dynamic ecosystems. Understanding the development of wet meadows and contributing environmental factors can provide better support for wetland management. Carex meadows in East Dongting Lake National Nature Reserve (EDLNNR) provide vital wintering ground for thousands of migratory waterbirds, and their ecological functions are under threated due to hydrological alternation. We measured wet meadow expansion in EDLNNR from 1989 to 2014, and explored its responses to hydrological and climatic factors within the generalised additive models (GAM) framework. We found an overall expansion of wet meadows over the study period. However, in contrast to many previous studies, our results showed that water level fluctuations at the hydrologic indicator site had only limited impacts on their development. Instead, sampling year, timing of water level recession, and local rainfall exerted significant effects. The effects of sampling year reflected the changes in sedimentation within Dongting Lake; and effects of timing of water withdrawal might be explained by the life history of the dominant sedge species. Our study suggested that the impacts of large scale hydrological alternation on vegetation may operate indirectly through its effects on sediment balance.

Interactions among vegetation, climate, and herbivory control greenhouse gas fluxes in a subarctic coastal wetland

AbstractHigh‐latitude ecosystems are experiencing the most rapid climate changes globally, and in many areas these changes are concurrent with shifts in patterns of herbivory. Individually, climate and herbivory are known to influence biosphere‐atmosphere greenhouse gas (GHG) exchange; however, the interactive effects of climate and herbivory in driving GHG fluxes have been poorly quantified, especially in coastal systems that support large populations of migratory waterfowl. We investigated the magnitude and the climatic and physical controls of GHG exchange within the Yukon‐Kuskokwim Delta in western Alaska across four distinct vegetation communities formed by herbivory and local microtopography. Net CO2 flux was greatest in the ungrazed Carex meadow community (3.97 ± 0.58 [SE] µmol CO2 m−2 s−1), but CH4 flux was greatest in the grazed community (14.00 ± 6.56 nmol CH4 m−2 s−1). The grazed community is also the only vegetation type where CH4 was a larger contributor than CO2 to overall GHG forcing. We found that vegetation community was an important predictor of CO2 and CH4 exchange, demonstrating that variation in regional gas exchange is best explained when the effect of grazing, determined by the difference between grazed and ungrazed communities, is included. Further, we identified an interaction between temperature and vegetation community, indicating that grazed regions could experience the greatest increases in CH4 emissions with warming. These results suggest that future GHG fluxes could be influenced by both climate and by changes in herbivore population dynamics that expand or contract the vegetation community most responsive to future temperature change.

Plant-mediated methane and nitrous oxide fluxes from a carex meadow in Poyang Lake during drawdown periods

Plants have been suggested to have significant effects on methane (CH4) and nitrous oxide (N2O) fluxes from littoral wetlands, but it remains unclear in subtropical lakes. We conducted in situ measurement of CH4 and N2O fluxes for two years. To distinguish between the effects of shoots and roots, three treatments (i.e., intact plants as control, shoot clipping, and root exclusion) were used. Effects of plant biomass, temperature, and soil moisture on CH4 and N2O fluxes were analyzed. The mean ecosystem CH4 emission rate was 36 μg CH4 m−2 h−1 for drying periods, but 8219 μg CH4 m−2 h−1 for drying-wetting transition periods. CH4 fluxes were positively correlated with below-ground and total biomass, but not with above-ground biomass. Clipping did not significantly alter CH4 flux rate, but root exclusion decreased the CH4 flux by 116 % as compared to the control. N2O emissions were similar for both the drying and drying-wetting transition periods, with a mean rate of 20 μg N2O m−2 h−1. Both clipping and root exclusion significantly increased N2O fluxes as compared to the control. There was no significant correlation between CH4 and N2O fluxes. Roots dominated plant-mediated enhancement in CH4 fluxes, but played almost an equal role as shoots in plant-regulated suppression on N2O fluxes in this Carex meadow during drawdown periods.

Climate and vegetation since the Last Interglacial (MIS 5e) in a putative glacial refugium, northern Idaho, USA

There are very few terrestrial sediment records from North America that contain a nearly continuous sequence spanning from the Last Interglacial period to the present. We present stratigraphic records of pollen and several other proxies from a Carex-dominated wetland, Star Meadows, located 140 km south of the maximum extent of the Cordilleran Ice Sheet and near the current southern extent of interior mesic forests in northern Idaho. Many species in this region are disjunct by 160 km of arid steppe and dry forest from their more extensive distribution along the Pacific Northwest coast and may have survived in an interior refugium. The chronology for the upper 251 cm was determined by six radiocarbon dates and one tephra deposit, and the age of the remainder of the core (251–809 cm) was estimated by correlation with SPECMAP δ18O. Fluctuating water levels were inferred from alternating peat, biogenic silica, and aquatic pollen types. During MIS 5e the region was warmer and drier than today and was dominated by Pinus (likely Pinus contorta) mixed conifer forest surrounding a Carex meadow. A cool-moist climate (MIS 5b–5d) soon developed, and the site was inundated with deep water. Pollen indicated wetland vegetation (Betula glandulosa, Typhaceae, and Salix) developed around a lake with a Pseudotsuga/Larix and Picea forest on the surrounding slopes. During MIS 5a, a warmer climate supported a Pseudotsuga/Larix, Abies, and Picea forest on the surrounding hillsides and a Carex-dominated environment within a dry meadow. From MIS 4 to MIS 3, a cool and wet Pinus and Picea forest predominated. Water levels rose, enabling Nuphar to persist within a perennial lake while a sedge fen established along the lake margin. As climate transitioned into MIS 2, a cooler and drier climate supported a Pinus and Picea subalpine parkland, though water levels remained high enough to support Nuphar. During the Last Glacial Maximum the sediment was mainly silt and clay with high Artemisia and very poor pollen preservation. Glaciers descended to 500 m elevation above Star Meadows in adjacent drainages suggesting a periglacial environment occurred at the site. Lake level decreased through the Pleistocene–Holocene transition (ca. 11.7 ka) and the site returned to a sedge peatland surrounded by an open Pinus forest. The most striking vegetation change occurred in the middle to late Holocene with the first occurrence and then later dominance of Cupressaceae pollen, most likely Thuja plicata, which is a dominant species in modern interior mesic forests. The late Holocene vegetation was uniquely mesic in the context of the last 120,000 years, casting doubt on this region serving as a glacial refugium.

Ecosystem respiration and its components from a Carex meadow of Poyang Lake during the drawdown period

Little is known about the components of ecosystem respiration from a subtropical littoral wetland with dramatic annual inundation dynamics. In this study, we investigated ecosystem respiration and its components in a Poyang lake Carex meadow during the drawdown periods from May 2009 to June 2011. Both ecosystem respiration and its components showed clear temporal variation pattern, with temperature being the dominant control. Ecosystem respiration ranged from 98.01 to 1359.25 mg CO2 m−2 h−1. Shoot and root respiration contributed approximately 36% and 26% to the ecosystem respiration, respectively, whereas microbial respiration accounted for 38% of the ecosystem respiration. The ratio of total soil respiration to ecosystem respiration varied from 0.45 to 0.90, depending on growing season stages. Their Q10 values ranged from 1.72 to 2.51, with the maximum for shoot respiration and the minimum for microbial respiration. In addition, the Q10 values varied with time and among ecosystem respiratory components and hence could not be treated as a constant. None of the respiration measurements was significantly related to soil moisture, suggesting that soil moisture was not a limiting environmental factor for respiratory activity during the drawdown periods in this meadow. The Carex meadow acted as strong carbon sink during the drawdown periods due to double growing seasons, but the previous summer flood duration could substantially alter carbon sink intensity in the following drawdown period. The total carbon sink of the littoral zone of Poyang Lake during drawdown periods was estimated to be 0.17–0.59 Tg C yr−1.

Delayed flood recession in central Yangtze floodplains can cause significant food shortages for wintering geese: results of inundation experiment.

Carex meadows are critical habitat for wintering geese in the floodplains of the middle and lower reaches of Yangtze River, China. These meadows follow a growth cycle closely tied to the seasonal hydrological fluctuation: as water levels recede in the fall, exposed mudflats provide habitat for Carex spp. growth. The seasonal growth of Carex overlaps the arrival of wintering geese and provides an important food source for the migrants. Recent alterations to the Yangtze's hydrology, however, have disrupted the synchronous relationship between water levels, Carex growth and wintering geese at Dongting Lake. In October 2012, we carried out an outdoor mesocosm experiment to investigate potential impacts of delayed water recession on the germination and growth of Carex heterolepis, the dominant Carex species at Dongting Lake, to understand how changes in hydrology might impact wintering goose habitat. Results showed that the delayed flood recession exerted significant impact on the first growth cycle of Carex growth. Prolonged inundation significantly lowered the intrinsic growth rate (P = 0.03) and maximum growth rates (P = 0.02). It also took significantly longer time to reach the peak growth rate (P = 0.04 and 0.05 for number of shoot and biomass, respectively). As a result, biomass accumulation was reduced by 45, 62 and 90 % for 10-day, 20-day and 30-day inundation treatments, respectively. These results indicate a severe risk of food shortage for wintering geese when water recession delayed. This potential risk should be taken into consideration when operating any hydrological control structures that alter the flood regimes in Dongting Lake.

The benefits of being big: effects of body size on energy budgets of three wintering goose species grazing Carex beds in the Yangtze River floodplain, China

Herbivores of different body size vary in food selection because of their different metabolic requirements and abilities to harvest and digest food. Compared with smaller grazers, larger ones require higher food quantity but can tolerate poorer quality. This divergence may also explain habitat partitioning in the distribution of closely related species. By estimating daily energy expenditure (based on observed activity budgets) and energy intake (using the indigestible marker method in food and faeces), we compared the field energy budgets of three wintering herbivorous goose species differing in body size feeding on the same Carex meadows. Throughout the winter, the larger Bean Geese Anser fabalis serrirostris and Greater White-fronted Geese Anser albifrons maintained positive energy budgets grazing lower quality Carex, in contrast to the smaller Lesser White-fronted Geese Anser erythropus which failed to do so and could only maintain positive energy budgets by grazing high-quality Alopecurus, Cynodon and Eleocharis. However, all three species failed to maintain positive energy balance and lost mass in mid-winter. These results have important implications for explaining the divergent distribution patterns of these species on their wintering grounds in China.

How sedge meadow soils, microtopography, and vegetation respond to Sedimentation

The expansion of urban and agricultural activities in watersheds of the Midwestern USA facilitates the conversion of species-rich sedge meadows to stands of Phalaris arundinacea and Typha spp. We doc- ument the role of sediment accumulation in this process based on field surveys of three sedge meadows dominated by Carex stricta, their adjacent Phalaris or Typha stands, and transitions from Carex to these invasive species. The complex microtopography of Carex tussocks facilitates the occurrence of other native species. Tussock surface area and species richness were positively correlated in two marshes (r 2 5 0.57 and 0.41); on average, a 33-cm-tall tussock supported 7.6 species. Phalaris also grew in tussock form in wetter areas but did not support native species. We found an average of 10.5 Carex tussocks per 10-m transect, but only 3.5 Phalaris tussocks. Microtopographic relief, determined with a high-precision GPS, measured 11% greater in Carex meadows than Phalaris stands. Inflowing sediments reduced microtopographic vari- ation and surface area for native species. We calculated a loss of one species per 1000 cm 2 of lost tussock surface area, and loss of 1.2 species for every 10-cm addition of sediment over the sedge meadow surface. Alluvium overlying the sedge meadow soil had a smaller proportion of organic matter content and higher dry bulk density than the buried histic materials. We conclude that sedimentation contributes to the loss of native species in remnant wetlands.