Bioturbation of Burrowing Crabs Promotes Sediment Turnover and Carbon and Nitrogen Movements in an Estuarine Salt Marsh

Ecological functions of bioturbation in ecosystems have received increasing attention over the recent decades, and crab burrowing has been considered as one of the major bioturbations affecting the physical and chemical processes in salt marshes. This study assessed the integrated effects of crab excavating and burrow mimic trapping on sediment turnover and vertical C and N distributions in a Chinese salt marsh in the Yangtze River estuary. Crab burrowing increased soil water content and the turnover of carbon and nitrogen and decreased bulk soil density. Vertical movement of materials, nutrient cycling and reuse driven by crab burrowing might be obstructed by vegetation (Phragmites australis and Spartina alterniflora communities). The amount of soil excavated by crab burrowing was higher than that deposited into burrow mimics. In Phragmites marshes, Spartina marshes and unvegetated mudflats, net transport of soil to the marsh surface was 171.73, 109.54, and 374.95 g m⁻² d⁻¹, respectively; and the corresponding estimated soil turnover time was 2.89, 4.07 and 1.83 years, respectively. Crab burrowing in salt marshes can mix surface and deeper soil over a period of years, accelerating litter decomposition and promoting the efficient reuse of nutrients by plants. Therefore, bioturbation affects soil physical processes and functioning of ecosystems, and needs to be addressed in ecosystem management.     

The validity of burrow counting in estimating the densities of Chiromantes dehaani and Ilyoplax deschampsi in tidal flat at Yangtze Estuary

It has been confirmed that the crabs play significant roles in the structure and function of coastal wetland ecosystems, such as mangroves and salt marshes. However it is not easy to estimate the abundance and density of burrowing crabs effectively, thus a further understanding of roles of crabs in these ecosystems has been lagged. Some studies have discussed the suitability of several census techniques, such as burrow counting method in estimating crab density in mangroves. The validities of burrow counting method and other census techniques in estimating crab density, however, has not been tested in salt marshes, especially where vegetation are dense. In this study, we tested the validity of burrow counting method in estimating the densities of Chiromantes dehaani and Ilyoplax deschampsi in tidal flat with dense vegetation of Phragmites australis and Zizania aquatica at Yangtze Estuary through comparing densities estimated by the burrow counting method and the excavation. Burrow counting averagely underestimated the density of C. dehaani by 15% and the degree of underestimation varied among vegetations and habitats (from an overestimate by 23% to underestimate by 41%). Burrow counting averagely overestimated the density of I. deschampsi by 43% and the degree of overestimate varied from 0% to 133% depending on the vegetations and habitats. The percentage of occupied burrows and the number of crabs sharing one burrow were important factors influencing the validity of estimating crab density through burrow counting method.     

The validity of burrow counting in estimating the densities of Chiromantes dehaani and Ilyoplax deschampsi in tidal flat at Yangtze Estuary

It has been confirmed that the crabs play significant roles in the structure and function of coastal wetland ecosystems, such as mangroves and salt marshes. However it is not easy to estimate the abundance and density of burrowing crabs effectively, thus a further understanding of roles of crabs in these ecosystems has been lagged. Some studies have discussed the suitability of several census techniques, such as burrow counting method in estimating crab density in mangroves. The validities of burrow counting method and other census techniques in estimating crab density, however, has not been tested in salt marshes, especially where vegetation are dense. In this study, we tested the validity of burrow counting method in estimating the densities of Chiromantes dehaani and Ilyoplax deschampsi in tidal flat with dense vegetation of Phragmites australis and Zizania aquatica at Yangtze Estuary through comparing densities estimated by the burrow counting method and the excavation. Burrow counting averagely underestimated the density of C. dehaani by 15% and the degree of underestimation varied among vegetations and habitats (from an overestimate by 23% to underestimate by 41%). Burrow counting averagely overestimated the density of I. deschampsi by 43% and the degree of overestimate varied from 0% to 133% depending on the vegetations and habitats. The percentage of occupied burrows and the number of crabs sharing one burrow were important factors influencing the validity of estimating crab density through burrow counting method.     

Effect of available burrow densities of plateau pika (Ochotona curzoniae) on soil physicochemical property of the bare land and vegetation land in the Qinghai-Tibetan Plateau

The available burrow densities of plateau pika (Ochotona curzoniae) regulate the soil physicochemical property in alpine meadow. A field survey was conducted to investigate the effect of available burrow densities of plateau pika on soil physicochemical property of bare land (bare patch produced by burrowing behavior of plateau pika) and vegetation land (land covered with vegetation). This study indicated that the increase in available burrow of plateau pika caused the soil water content at 0–10 cm layer of bare land and that at 10–20 cm of vegetation land to reduce, and caused the soil water content at 10– 20 cm layer of bare land and that at 0–10 cm layer of vegetation land to firstly increase and then decline. In the increasing process of available burrow of plateau pika, the soil silt content firstly increased and then decreased, and soil sand content firstly decreased and then increased. With the increase of available burrow of plateau pika, the soil porosity at 0–10 cm layer of bare land and that at 10–20 cm layer of vegetation land decreased, while the soil porosity at 10–20 cm layer of bare land and that at 0–10 cm of vegetation land firstly increased and then decreased. Soil pH value, soil organic matter, total nitrogen and total phosphorus content firstly increased and then decreased, peaking at 14 available burrows per 625 m², while total soil potassium content did not respond to available burrow densities of plateau pika. This study suggested that the proper available burrows existing in the alpine meadow increased soil permeability, accelerated soil moisture to penetrate deeply, increased the proportion of soil silt, and improved the soil nutrient; however, this beneficial effect was strongly influenced by the available burrow density of plateau pika, implying that plateau pika did not benefit soil structure when its available burrow was over 34 number/625 m².     

Small- and large-scale effect of the SW Atlantic burrowing crab Chasmagnathus granulatus on habitat use by migratory shorebirds

Here we address the question of whether the presence of the burrowing crabs Chasmagnathus granulatus affects small- and large-scale habitat use by migrant shorebirds. This crab is the dominant species in soft bare sediments and vegetated intertidal areas along the SW Atlantic estuaries (southern Brazil 28°S to the northern Argentinean Patagonia 42°S). They generate very extensive burrow beds in soft bottom intertidal areas. Our information shows that this burrowing crab affects the small-scale habitat use by shorebirds, given that shorebirds never walk through the funnel-shaped entrances of burrows. Given that crab burrow entrances occupy up to 40% of the intertidal area, there is a large decrease of available shorebird habitat in crab beds, restricting their activity to the spaces between the burrows. The southern migratory shorebird Charadrius falklandicus maximize the use of these areas by foraging closer to the burrows than the other bird species. Neotropical migrants, such as Calidris fuscicollis, Pluvialis squatarola and Tringa melanoleuca, used foraging paths that tended to maximize the distance from burrows, especially the distance to larger burrows. A field experiment showed that this was not necessarily due to a decrease in the availability of polychaetes near the crab burrows. A combination of landscape measurements and satellite images showed that crab beds covered up to 40% of the intertidal area of the Mar Chiquita coastal lagoon (37°40′S, Argentina), and nearly 100% of the intertidal area of the Bahia Blanca estuary (38°48′-39°25′S, Argentina). These two estuaries are located along the migratory flyway of Neotropical migratory shorebirds, but the Bahia Blanca estuary (area∼110,000 ha) shows a much lower shorebird diversity than Mar Chiquita (area∼4500 ha). The most common species in Bahia Blanca is the two-banded plover C. falklandicus, the species least affected by crabs at Mar Chiquita and which prefers to use high-density crab areas as foraging sites. The oystercatcher Haematopus palliatus was also most abundant in high-density crab areas, but they used these areas for resting. The abundances of preys varied during the study period and between the crab density areas, indicating that the use of these areas by birds is independent of crab density. However, burrowing crabs affect the depth distribution of polychaete and thus their availability to shorebirds. We suggest that this shorebirds-burrowing organism interaction could be generalized for other intertidal estuarine habitats.     

Abiotic stress mediates top-down and bottom-up control in a Southwestern Atlantic salt marsh

Increasing evidence has shown that nutrients and consumers interact to control primary productivity in natural systems, but how abiotic stress affects this interaction is unclear. Moreover, while herbivores can strongly impact zonation patterns in a variety of systems, there are few examples of this in salt marshes. We evaluated the effect of nutrients and herbivores on the productivity and distribution of the cordgrass Spartina densiflora along an intertidal stress gradient, in a Southwestern Atlantic salt marsh. We characterized abiotic stresses (salinity, ammonium concentration, and anoxia) and manipulated nutrients and the presence of the herbivorous crab Neohelice (Chasmagnathus) granulata, at different tidal heights with a factorial experiment. Abiotic stress increased at both ends of the tidal gradient. Salinity and anoxia were highest at the upper and lower edge of the intertidal, respectively. Nutrients and herbivory interacted to control cordgrass biomass, but their relative importance varied with environmental context. Herbivory increased at lower tidal heights to the point that cordgrass transplants onto bare mud substrate were entirely consumed unless crabs were excluded, while nutrients were most important where abiotic stress was reduced. Our results show how the impact of herbivores and nutrients on plant productivity can be dependent on environmental conditions and that the lower intertidal limits of marsh plants can be controlled by herbivory.     

Increased nutrient supply facilitates acclimation to high-water level in the marsh plant Deyeuxia angustifolia: The response of root morphology

Both water level and nutrient availability are important factors influencing the growth of wetland plants. Increased nutrient supply might counteract the negative effects of flooding on the growth of the fast-growing species. Experimental evidence is scarce and the mechanism is far from clear. The aim of this study is to identify the role of nutrient availability in acclimation to high-water level by investigating the growth and root morphology of the marsh plant Deyeuxia angustifolia, one of the dominant species in the Sanjiang Plain, China. Experimental treatments included two water levels (0 and 10 cm, relative to soil surface) and three levels of nutrient supply (0, 0.5 and 1 g fertilizer per container). High-water level usually led to decreased biomass accumulation, shoot mass and root mass, whereas biomass accumulation was unaffected by water level at the highest nutrient level, indicating that high-nutrient availability played a role in compensating for the growth loss induced by the high-water level. Increased nutrient supply led to decreased root length in 0 cm water-level treatments, but root length increased with nutrient supply in the 10 cm water-level treatments. High-water level usually led to a lower lateral root density, lateral root:main root length ratio and the diameter of main roots and laterals, whereas increased nutrient supply resulted in thicker main roots or laterals, and a higher total root length, lateral root density and lateral root:main root length ratio. These data indicate that the growth of D. angustifolia is restrained by high-water level, and that increased nutrient supply not only ameliorates root characteristics to acclimate to high-water level but also results in a high-total root length to facilitate nutrient acquisition.     

Activity patterns, feeding and burrowing behaviour of the crab Ucides cordatus (Ucididae) in a high intertidal mangrove forest in North Brazil

Activity patterns, feeding and burrowing behaviour of the economically important semi-terrestrial mangrove crab Ucides cordatus (Ucididae, L. 1763) was studied in a high intertidal Rhizophora mangle forest stand in Bragança, North Brazil. Video observations in the rainy and dry season were conducted over 24 h cycles at different lunar phases to investigate the behaviour of these litter-feeding crabs outside their burrows. During the rainy season, crabs stayed inside their burrows for 79% and 92% of the time during day and night, respectively. Time spent for feeding, burrowing and other activities outside their burrows was significantly longer during the day with 9.9% (night: 1.7%) and at waning and waxing moon with 9% (full and new moon: 0.9%). At neap tides (no tidal inundation) foraging and feeding activities outside burrows were clearly light-dependent, increasing at dawn and decreasing at dusk. Highest activities during daytime relate to the visual localisation of food. During the dry season, crabs spent less time inside burrows at neap tides than during the rainy season (80% and 91%, respectively). However, time spent for feeding activities was similar during both seasons. During almost all observation periods crabs collected leaf litter, but rarely fed on it outside burrows. At neap tides nearly all available litter was collected, suggesting that the U. cordatus population is litter-limited during these times. At spring tides (regular tidal inundation) the surface activity of U. cordatus was tide-dependent. Crabs closed their burrow entrances 2-3 h before flooding and re-emerged as soon as the tide retreated. During the day, burrow maintenance was the second most frequent behaviour after feeding. Agonistic interactions were regularly observed and were mainly related to burrow defence. The mean foraging radius of the crabs was only 19 cm (max: 1 m) underneath high Rhizophora mangle trees where crab densities were high. The results point to a high competition for burrows and show that U. cordatus is territorial. It is concluded that several exogenous factors, in particular light, leaf litter availability, flooding of burrows and the presence of conspecifics are important in controlling the crabs' activity patterns.     

Behavioral plasticity of the soft-shell clam, Mya arenaria (L.), in the presence of predators increases survival in the field

Soft-shell clams, Mya arenaria, are sessile, suspension-feeding bivalves that are preyed upon by the exotic green crab, Carcinus maenas. Clams evade crab consumers by burrowing deeper into the sediment after perceiving a threat from a nearby predator. The purpose of this study was to determine the types of signals that M. arenaria use to detect predators and the types of behaviors clams use to avoid being eaten. In a field study, clams increased their burial depth in the presence of green crab predators consuming conspecifics that were caged nearby, and also increased burial depth after artificial tactile stimulation in the laboratory assay. These results indicate that clams can use chemical and mechanical cues to detect potential predatory threats. We performed a field study to examine the difference in survivability of clams that had burrowed deeper into the sediment in response to predators vs. control clams that were burrowed less deeply. Significantly higher survival rates were observed in clams that had initially burrowed more deeply, suggesting that increasing burial depth is a valid predator avoidance strategy. Some bivalves also alter their pumping rates in the presence of predators, making them less apparent and providing more structural defense by covering soft tissue, and we measured pumping time of soft-shell clams in the presence and absence of predators, when burrowing was not an option for escape. Soft-shell clams did not alter their pumping time in the presence of green crab predators, possibly because they employ a burrowing method called “hydraulic” or “jet-propelled” burrowing, where it is necessary for the clam to pump in order to burrow. Chemical signals and tactile cues instigated behavioral changes in M. arenaria, and this change in behavior (increasing burial depth) increased clam survival in the field.     

Phenotypic plasticity of the maize root system in response to heterogeneous nitrogen availability

Mineral nutrients are distributed in a non-uniform manner in the soil. Plasticity in root responses to the availability of mineral nutrients is believed to be important for optimizing nutrient acquisition. The response of root architecture to heterogeneous nutrient availability has been documented in various plant species, and the molecular mechanisms coordinating these responses have been investigated particularly in Arabidopsis, a model dicotyledonous plant. Recently, progress has been made in describing the phenotypic plasticity of root architecture in maize, a monocotyledonous crop. This article reviews aspects of phenotypic plasticity of maize root system architecture, with special emphasis on describing (1) the development of its complex root system; (2) phenotypic responses in root system architecture to heterogeneous N availability; (3) the importance of phenotypic plasticity for N acquisition; (4) different regulation of root growth and nutrients uptake by shoot; and (5) root traits in maize breeding. This knowledge will inform breeding strategies for root traits enabling more efficient acquisition of soil resources and synchronizing crop growth demand, root resource acquisition and fertilizer application during crop growing season, thereby maximizing crop yields and nutrient-use efficiency and minimizing environmental pollution.     

Growth and allocation of the arctic sedges Eriohorum angustifolium and E. vaginatum: effects of variable soil oxygen and nutrient availability

In arctic tundra soil, oxygen depletion associated with soil flooding may control plant growth either directly through anoxia or indirectly through effects on nutrient availability. This study was designed to evaluate whether plant growth and physiology of two arctic sedge species are more strongly controlled by the direct or indirect effects of decreased soil aeration. Eriophorum angustifolium and E. vaginatum, which originate from flooded and well-drained habitats, respectively, were grown in an in situ transplant garden at two levels of soil oxygen, nitrogen, and phosphorus availability over two growing seasons. In both species, N addition had a stronger effect on growth and biomass allocation than P addition or soil oxygen depletion. Net photosynthesis and carbohydrate concentrations were relatively insensitive to changes in these factors. Biomass reallocated from shoots to below-ground parts in response to limited N supply was equally divided between roots (nutrient acquisition) and perennating rhizomes (storage tissue formation) in E. angustifolium. E. Vaginatum only increased its allocation to rhizomes. In the flood-tolerant E. angustifolium, growth was improved by soil anoxia and biomass allocation among plant parts was not significantly affected. Contrary to our initial hypothesis, whole-plant growth in E. vaginatum improved in flooded soils; however, it only did so when N availability was high. Under low N availability growth in flooded soils was reduced by 20% compared to growth in the aerobic environment. Reduced biomass allocation to rhizomes and thus to storage potential under anaerobic conditions may reduce long-term survival of E. vaginatum in flooded habitats.     

Certain organism-substrate relationships affecting the distribution of Uca minax (Crustacea: Decapoda)

The involvement of substrate in the ecology of the fiddler crab Uca minax was investigated by means of both field and laboratory studies. These included determination of the oxygen-holding capacities of five types of substrates on which this organism lives, as well as experiments to determine if there is substrate selection. The effect of population density on burrowing was also studied to determine the optimum number of individuals needed in the selection experiments, and to delineate the mechanisms these organisms use for avoiding dispersion onto less favorable substrates. Results indicate that Uca minax prefers substrates with high organic content, although these were shown to contain the lowest substrate oxygen. This evidence suggests that Uca minax prefers substrates of high energy value, and explains the significance of this species' adaptation in withstanding low oxygen tensions. Population density experiments indicate that at high population densities these crabs reduce intraspecific encounter and competition by burrowing and subsequently covering their burrows. Seasonal monitoring of burrow temperatures indicate the stability of this microenvironment as compared with the surrounding air temperature. These data also demonstrate the significance of the adjacent water in the habitat ecology of Uca minax.     

The occupation of artificial burrows by Helice tridens (De Haan) and the length of its stay

The mud-crab Helice tridens (De Haan) influences the cycling of matter in salt-marsh ecosystems through its burrowing activity. If the crabs occupy and stay in their burrows for a short time, their burrowing activity will be great, since they will continuously construct new burrows. Therefore, investigation of the relation between the crabs and their burrows is considered to be important. In the present study, the relation between pipes as a form of artificial burrow and their occupation by the crab was analyzed. A close relationship was recognized between the diameter of the pipe opening and the carapace width of the crab which occupied the pipe, while pipes with a length shorter than the depth of the crab burrows were hardly occupied. These results indicate that the diameter and length of an artificial burrow affects the likelihood of its occupation by this species of crab. The length of the crab's stay in this type of artificial burrow was generally 1 day. This result may be related to the field observation that newly made burrows frequently collapse due to water current occurring through tidal action after the crabs have left.     

Effects of plateau pika (Ochotona curzoniae) on net ecosystem carbon exchange of grassland in the Three Rivers Headwaters region, Qinghai-Tibet, China

Background and aim

Because the indigenous burrowing lagomorph plateau pika (Ochotona curzoniae) is considered to have negative ecological impacts on alpine meadow steppe grasslands of the Headwaters Region of the Yellow, Yangtze and Mekong Rivers we investigated its effects on ecosystem productivity and soil properties, and especially net ecosystem carbon flux.

Methods

We measured net ecosystem CO₂ exchange (NEE) and its components gross ecosystem productivity (GEP) and ecosystem respiration (ER) at peak aboveground biomass by the chamber method with reference to plant and soil characteristics of areas of alpine meadow steppe with different densities of pika burrows.

Results

Higher burrow density decreased NEE, GEP and ER. Above-ground biomass, species number, plant cover and leaf area index decreased with increasing pika density. Higher burrow density was associated with lower soil moisture and higher soil temperature. Responses of NEE were related to changes of abiotic and biotic factors affecting its two components. NEE was positively related to soil moisture, soil ammonium nitrogen, plant cover, leaf area index and above-ground biomass but was negatively correlated with higher soil nitrate nitrogen.

Conclusion

Decrease of NEE by plateau pika may reduce the carbon sink balance of Qinghai-Tibet plateau grassland. Such effects may be influenced by grazing pressure from domestic livestock, population levels of natural predators, and climate change.     

Burrow structure and foraging costs in the fossorial rodent,Thomomys bottae

Summary A model for calculating the energy cost of burrowing by fossorial rodents is presented and used to examine the energetics of foraging by burrowing. The pocket gopher Thomomys bottae (Rodentia: Geomyidae) digs burrows for access to food. Feeding tunnels of Thomomys are broken into segments by laterals to the surface that are used to dispose of excavated soil. Energy cost of burrowing depends on both soil type and on burrow structure, defined by the length of burrow segments, angle of ascent of laterals, depth of feeding tunnels, and burrow diameter. In a desert scrub habitat, Thomomys adjust burrow segment length to minimize cost of burrowing. Observed segment lengths (mean=1.33 m) closely approximate the minimum-cost segment length of 1.22 m. Minimizing energy expended per meter of tunnel constructed maximizes efficiency of foraging by burrowing in the desert scrub. Burrow diameter and cost of burrowing increase with body size, while benefits do not, so foraging by burrowing becomes less enconomical as body size increases. Maximum possible body size of fossorial mammals depends on habitat productivity and energy cost of burrowing in local soils.     

The SW Atlantic burrowing crab Chasmagnathus granulatus Dana affects the distribution and survival of the fiddler crab Uca uruguayensis Nobili

In this paper, we address the question of whether the presence of the burrowing crab Chasmagnathus granulatus affects the habitat use of the fiddler crab Uca uruguayensis. Field samples showed that the species have a disjoint spatial distribution. Male fiddler crab density decreased in zones with C. granulatus, however, female density increased. Male fiddler crabs avoided feeding on sediment affected by C. granulatus and were more preyed. Predation was higher during the fiddler crab reproductive season and, probably due to predation risk, males showed lower reproductive display in shared zones. Field experiments shows that when C. granulatus were excluded, densities of U. uruguayensis increased mainly due to an increase in density of males. Habitat differentiation of these species may be because C. granulatus affects U. uruguayensis in several ways, including direct predation, disturbance and behavioural changes associated to predation risk. Males and females are affected differentially probably because of the extreme sexual dimorphism of this crab species. Coloration on enlarged claw and waving activities are all factors that increase predation risk for male and the presence of only one feeding claw may increase sediment-mediated effects.     

Morphological and physiological responses to sediment type and light availability in roots of the submerged plant Myriophyllum spicatum

BACKGROUND AND AIMS: Both sediment and light are essential factors regulating the growth of submerged macrophytes, but the role of these two factors in regulating root morphology and physiology is far from clear. The responses of root morphology and physiology to sediment type and light availability in the submerged plant Myriophyllum spicatum were studied and the hypothesis was tested that a trade-off exists in root growth strategy between internal aeration and nutrient acquisition. METHODS: Plants were grown on two types of sediment (fertile mud and an infertile mixture of mud and sandy loam) and under three levels of light availability (600, 80 and 20 micro mol m(-2) s(-1)) in a greenhouse. KEY RESULTS: The significantly higher alcohol dehydrogenase (ADH) activity in root tissues indicated that oxygen deficiency existed in the plants growing in fertile mud and low (or high) light environments. Significantly, low plant N and P concentrations indicated that nutrient deficiency existed in the mixed sediment and high light environment. As a response to anoxia, plants did not change the porosity of the main roots. The effect of sediment type on root morphology was insignificant under higher light environments, whereas root diameter generally decreased but specific root length (SRL) increased with decreasing light availability. Both low light and fertile mud jointly led to lack of second-order laterals. More biomass was allocated to lateral roots in infertile environments, whereas mass fractions of laterals were lower in low light and mud environments. CONCLUSIONS: These data indicate that this plant can achieve the trade-off between internal aeration and nutrient acquisition by adjusting the structure of the root system and the pattern of biomass allocation to different root orders rather than root morphology and root porosity.     

Ecosystem engineers activate mycorrhizal mutualism in salt marshes

Theory predicts that ecosystem engineers should have their most dramatic effects when they enable species, through habitat amelioration, to live in zones where physical and biological conditions would otherwise suppress or limit them. Mutualisms between mycorrhizal fungi and plants are key determinants of productivity and biodiversity in most terrestrial systems, but are thought to be unimportant in wetlands because anoxic sediments exclude fungal symbionts. Our field surveys revealed arbuscular mycorrhizal associations on salt marsh plant roots, but only in the presence of crabs that oxygenate soils as a by-product of burrowing. Field experiments demonstrate that fungal colonization is dependent on crab burrowing and responsible for nearly 35% of plant growth. These results highlight ecosystem engineers as ecological linchpins that can activate and maintain key mutualisms between species. Our findings align salt marshes with other important biogenic habitats whose productivity is reliant on mutualisms between the primary foundation species and micro-organisms.     

高原鼠兔有效洞穴密度对高寒草甸优势植物叶片和土壤氮磷化学计量特征的影响

采用有效洞穴密度代替高原鼠兔(Ochotona curzoniae)活动强度的方法,研究了高原鼠兔有效洞穴密度(10、15、21和31个/625 m~2)对高寒草甸优势植物高山嵩草(Kobresiapygmaea)、垂穗披碱草(Elymus nutans)、小花草玉梅(Anemone rivularis)叶片和土壤氮(N)磷(P)化学计量特征的影响。结果表明,3种优势植物叶片N含量随有效洞穴密度增加而显著增加(P0.05),但叶片P含量却出现分异,表现为高山嵩草和垂穗披碱草叶片P含量随有效洞穴密度增加而先增加后降低(P0.05),小花草玉梅叶片P含量逐渐增加(P0.05);高山嵩草叶片N:P随有效洞穴密度增加先降低后增加(P0.05),垂穗披碱草叶片N:P逐渐增加,小花草玉梅叶片N:P则先增加后降低。土壤0-10 cm和10-20 cm土层N含量随有效洞穴密度增加无明显变化;0—10cm土层P含量随有效洞穴密度增加先降低后增加,10—20 cm土层P含量逐渐降低;0—10 cm土层N:P随有效洞穴密度增加元明显变化,而10-20 cm土层N:P则逐渐增加。优势植物叶片N、P、N:P与土壤N、P、N:P的相关性受植物根系分布特征和生存微环境的约束。