Baohua Guan

China's Natural Wetlands: Past Problems, Current Status, and Future Challenges

Abstract Natural wetlands, occupying 3.8% of Chinas land and providing 54.9% of ecosystem services, are unevenly distributed among eight wetland regions. Natural wetlands in China suffered great loss and degradation (e.g., 23.0% freshwater swamps, 51.2% costal wetlands) because of the wetland reclamation during Chinas long history of civilization, and the population pressure and the misguided policies over the last 50 years. Recently, with an improved understanding that healthy wetland ecosystems play a vital role in her sustainable economic development, China started major efforts in wetland conservation, as signified by the policy to return reclaimed croplands to wetlands, the funding of billions of dollars to restore degraded wetlands, and the national plan to place 90% of natural wetlands under protection by 2030. This paper describes the current status of the natural wetlands in China, reviews past problems, and discusses current efforts and future challenges in protecting Chinas natural wetlands.

Effects of nutrient levels in surface water and sediment on the growth of the floating-leaved macrophyte Trapa maximowiczii: implication for management of macrophytes in East Bay of Lake Taihu, China

Trapa maximowiczii is a floating-leaved macrophyte common in China. The plant population in East Bay, Lake Taihu, has been expanding rapidly in recent years. In order to better understand the mechanisms controlling the population dynamics in this species, two outdoor experiments were conducted from 9 May to 8 July 2007, evaluating the effect on the growth of T. maximowiczii of different nutrient levels in water column and sediment. Results showed that high concentration of nutrients (nitrogen and phosphorous) in water led to significant increases in rosette diameter and plant dry weight, dry weight of aquatic roots and anchoring roots, but had no effect on plant height or main stem node count. Phosphorus enrichment resulted in increases in plant dry weight and seed number. However, no such difference was observed between the nitrogen enrichment treatment and the control. Sediment fertility had significant effects on plant growth. Plant height, plant dry weight, dry weight of aquatic and anchoring roots, and maximum rosette diameter were significantly greater in high-nutrient sediment than those in low-nutrient sediment. This study suggests that eutrophication of water (especially increasing phosphorus loading) and accumulated nutrients in sediment may be among the causes leading to increasing biomass of the floating-leaved macrophyte T. maximowiczii in East Bay of Lake Taihu.

Submerged macrophytes facilitate dominance of omnivorous fish in a subtropical shallow lake: implications for lake restoration

Biomanipulation based on removal of coarse fish, piscivorous fish stocking and sometimes also planting of submerged macrophytes has been used to restore temperate eutrophic shallow lakes. However, in warmer lakes, omnivorous fish are more abundant and apparently less well controlled by the piscivores. We investigated the food web structure and energy pathways of fish in the restored part of subtropical Lake Wuli, China, using gut contents analysis (GCA) and the IsoSource model based on stable isotope analysis (SIA) data. We found that omnivores dominated the fish community in terms of numbers. GCA showed that cyclopoid copepods constituted the main food item for the planktivores, while all adult omnivorous fish fed mainly on macrophytes. The IsoSource SIA model supported these results. Furthermore, piscivores consumed shrimps rather than juvenile omnivores, and the SIA analysis revealed no trophic links between piscivores and adult omnivores or zooplanktivores. We conclude that macrophytes constituted an important food item for omnivores, potentially promoting population growth of omnivores as control by piscivores was weak. This may yield a high predation pressure on both zooplankton and on macrophytes, possibly preventing the establishment of a stable macrophyte state following restoration of eutrophic lakes unless the fish density is regularly controlled.

Wetlands of Northeast Asia and High Asia: an overview

This review reports background information on wetlands in the Northeast Asia and High Asia areas, including wetland coverage and type, significance for local populations, and threats to their vitality and protection, with particular focus on the relationship of how global change influenced wetlands. Natural wetlands in these areas have been greatly depleted and degraded, largely due to global climate change, drainage and conversion to agriculture and silviculture, hydrologic alterations, exotics invasions, and misguided management policies. Global warming has caused wetland and ice-sheet loss in High Asia and permafrost thawing in tundra wetlands in Northeast Asia, and hence induced enormous reductions in water-storage sources in High Asia and carbon loss in Northeast Asia. This, in the long term, will exacerbate chronic water shortage and positively feed back global warming. Recently, better understanding of the vital role of healthy wetland ecosystems to Asia’s sustainable economic development has led to major efforts in wetland conservation and restoration. Nonetheless, collaborative efforts to restore and protect the wetlands must involve not only the countries of Northeast and High Asia but also international agencies. Research has been productive but the results should be more effectively integrated with policy-making and wetland restoration practices under future climatic scenarios.

Fragment propagation and colonization ability enhanced and varied at node level after escaping from apical dominance in submerged macrophytes.

Aquatic plants develop strong fragment propagation and colonization ability to endure the natural disturbances. However, detailed research of ability to endure the natural disturbances has been lacking to date. Therefore, reproduction (shoot) and colonization (root) of shoot fragments of Potamogeton crispus L. with or without apices were investigated for the effect of apical dominance, and the growth of decapitated shoot fragments at three lengths (2, 4, 6 cm) was compared. Meanwhile, fragment propagation at levels of bud position was studied for bud position effect after escaping from apical dominance. The results showed significant increases occurred in the outgrowth of lateral branches on fragments decapitated compared with the fragments with apices, implying that apical dominance exists. Different lengths of fragments showed little difference in biomass allocations, but significant differences were noted in their propagation. Meanwhile, the effect of bud position was verified, due to the significant difference of average reproduction per node among the three length groups. Thus, the present study has made progress in the current understanding of aquatic plant dispersion among natural systems and contributes to improve methods of in vitro propagation for re-implantation purposes.

The headwater loss of the western plateau exacerbates China's long thirst

Abstract China is a country poor in water resources, with an annual 2800 km3 of freshwater storage and 2300 m3 of water availability per capita. Both the water shortage and low use efficiency make modern China thirsty. Furthermore, the loss of glaciers and wetlands in the western plateau that feed the major rivers of China as their headwaters will exacerbate this thirst in the future. Although groundwater might be tapped as a resource, most regions already use their aquifers excessively. China needs to focus on its urgent water-shortage problems to safeguard its booming economy and to contribute more to world development.

Photosynthetic parameters of Mosla hangchowensis and M. dianthera as affected by soil moisture

We compared the photosynthetic traits in response to soil water availability in an endangered plant species Mosla hangchowensis Matsuda and in a weed Mosla dianthera (Buch.-Ham.) Maxim. The highest diurnal mean net photosynthetic rate (PNmean), stomatal conductance (gs), and water use efficiency (WUE) of both species occurred at 60 % soil water holding capacity (WHC), while the lowest values occurred at 20 % WHC. The PNmean, gs, and chlorophyll (Chl) a and b contents of M. hangchowensis were lower than those of M. dianthera, while the physiological plasticity indices were higher than those of M. dianthera. M. hangchowensis had strong adaptability to the changing soil water status but weak extending population ability in its habitats because of the low PNmean, which may be one of the causes of its endangerment.

Phenotypic plasticity of Mosla chinensis and M. scabra (Labiatae) response to soil water status

The growth and architectural plasticity of Mosla chinensis Maxim. in response to soil water status were compared with the congeneric plant, Mosla scabra (Thunb.) C. Y. Wu et H. W. Li. Two-week-old seedlings were exposed to five levels of soil water for a 6-week period. The results indicated that: an individual’s total mass, root mass, apical height, basal diameter, accumulative branch length and branch fresh weight/dry weight ratio (FW(subscript B) /DW(subscript B)) of both species had high plasticity in response to soil water content (p＜0.05), and the plasticity of these traits in M. scabra is mostly higher than in M. chinensis. The leaf mass ratio (LMR), specific leaf area (SLA), root mass ration (RMR), and root/shoot ratio (R/S) of both species had low plasticity. Furthermore, leaf mass, branch mass, branch mass ratio (BMR). and branch length ratio (BLR) had high plasticity (P＜0.05) in M. chinensis but not in M. scabra (P＞0.05) while branch number exhibited contrary trends. In response to soil water, M. scabra adjusted the traits of total mass and size, in terms of a bigger PI, more than M. chinensis while M. chinensis only adjusted partial branch and root traits, such as BMR, BLR, FW(subscript B)/DW(subscript B), RMR and R/S, more than M. scabra. The optimum water niches (OWN) of both M. chinensis and M. scabra are from 40% soil water holding capacity (WHC) to constant saturation, but M. chinensis is only found in relatively dry environments while M. scabra is distributed from dry to wet environments in the field, so the actual water niche (AWN) was separated from the OWN in M. chinensis, but not in M. scabra. Mosla chinensis grew slower and remained smaller than M. scabra and other neighbor species in the field, and it therefore had no competitive superiority in the community. Mosla scabra was very competitive because of its higher yield and taller growth.

Photosynthetic characteristics and growth of Mosla hangchowensis and M. dianthera under different irradiances

The photosynthetic and growth characteristics of Mosla hangchowensis, an endangered species and M. dianthera, a weed, were compared under three irradiances (PPFD) similar to shaded forest understory, forest edge and open land. Both species grown at lower PPFD had lower PPFD-saturated photosynthetic rate (Pmax), saturation PPFD, compensation PPFD, apparent quantum yield, total mass and root/shoot ratio and higher specific leaf area, leaf area ratio and height ratio. At the same PPFD treatment, however, specific leaf area and leaf area ratio of M. hangchowensis were higher than those of M. dianthera, other above parameters were lower than those of M. dianthera. Water use efficiency did not differ between M. hangchowensis and M. dianthera, but it reached its maximum at 70 % of full PPFD. These results suggested the optimum habitat of M. hangchowensis is the forest edge.

Influence of Substrate Phosphorus Concentration and Plant Density on Growth and Phosphorus Accumulation of Alternanthera philoxeroides

ABSTRACT We investigated the effects of three substrate phosphorus concentration and three plant density on the phenotypic plasticities of the invasive plant, alligator weed (Alternanthera philoxeroide, Amaranthaceae). Phosphorus concentration affected mainly the plant tissue phosphorus accumulation, while plant density affected mainly growth traits, especially those of the stem. The greatest stem mass and stem basal diameter occurred with the combined treatment of medium substrate phosphorus concentration and high plant density (64 ind. m−2), while the greatest stem length and internode number occurred with medium phosphorus concentration and low plant density (16 ind. m−2). Alligator weed had highest leaf, stem, and root phosphorus concentrations with treatment of high phosphorus concentration and low plant density (16 ind. m−2). These results suggest that alligator weed has plasticity in response to substrate phosphorus and plant density and adapts to high phosphorus by accumulating more phosphorus into plant tissues and to high plant density by producing larger but less vegetative individuals, these are strategies that might facilitate invasiveness in eutrophic shallow waters.