We asked whether 3–5 kg N y−1 atmospheric N deposition was sufficient to have influenced natural, otherwise undisturbed, terrestrial and aquatic ecosystems
of the Colorado Front Range by comparing ecosystem processes and properties east and west of the Continental Divide. The eastern
side receives elevated N deposition from urban, agricultural, and industrial sources, compared with 1–2 kg N y−1 on the western side. Foliage of east side old-growth Englemann spruce forests have significantly lower C:N and lignin:N ratios
and greater N:Mg and N:P ratios. Soil % N is higher, and C:N ratios lower in the east side stands, and potential net N mineralization
rates are greater. Lake NO3 concentrations are significantly higher in eastern lakes than western lakes. Two east side lakes studied paleolimnologically
revealed rapid changes in diatom community composition and increased biovolumes and cell concentrations. The diatom flora
is now representative of increased disturbance or eutrophication. Sediment nitrogen isotopic ratios have become progressively
lighter over the past 50 years, coincident with the change in algal flora, possibly from an influx of isotopically light N
volatilized from agricultural fields and feedlots. Seventy-five percent of the increased east side soil N pool can be accounted
for by increased N deposition commensurate with human settlement. Nitrogen emissions from fixed, mobile, and agricultural
sources have increased dramatically since approximately 1950 to the east of the Colorado Front Range, as they have in many
parts of the world. Our findings indicate even slight increases in atmospheric deposition lead to measurable changes in ecosystem
properties.
Received 16 November 1999; accepted 8 February 2000. 相似文献
Background: High-mountain ecosystems are centres of plant diversity that are particularly sensitive to land-use and climate change.
Aims: We investigated the ecological trends associated with land use and climate change since the 1950s in different vegetation types in high-mountain habitats in the central Apennines.
Methods: We analysed temporal changes in: Pinus mugo scrub, calcareous subalpine grasslands and alpine scree vegetation, comparing historical and recent vegetation records from vegetation plots from two periods (1955–1980 and 1990–2014) for their ecological indicator values (Landolt temperature and nutrient indicators) and structural traits (growth forms) over time using generalised linear models (GLMs).
Results: We observed significant temporal differences in the ecology and structure of the analysed habitats. In the Pinus mugo scrub we detected a reduction of subalpine and herbaceous species and in calcareous alpine screes we observed an increment of the lower montane, montane and subalpine species and of dwarf shrubs. Conversely, subalpine grasslands were stable over time.
Conclusions: Ecological changes that have occurred in the Central Apennines, following changes in type and intensity of land use and recent warming are consistent with those observed in other European mountains, for which climate and land-use changes are claimed as the main driving forces. 相似文献
AimsArundinella anomala and Miscanthus sinensis are dominant species in the subalpine meadow of Wugongshan Mountains. Here we studied the effects of climate warming on allometric relationships among different growth components in the two species through simulated warming in natural habitat. Methods The warming experiments were conducted with open-top chambers (OTCs) in natural habitat in a subalpine meadow community of Wugongshan Mountains. The two main Gramineae species, Arundinella anomala and Miscanthus sinensis, were selected as the study materials. Two sizes of OTCs were set up to create contrasting levels of warming (i.e. TD for low warming and TG for high warming). The morphological variables, such as the plant height and the basal diameter of shoots, were measured. Allometric analysis was conducted with the Smart Package in R software. Important findings Significant or highly significant correlations and significant allometric relationships were found between and among growth components in both species. The allometry of the growth in most morphological features was strengthened and modified by simulated warming. Stem diameter and plant height, and spike length in A. anomala and M. sinensis changed from isometric to allometric following warming. The relationship The synchronized growth between stem diameter and spikelet in A. anomala was weakened, but their allometry was enhanced with increased warming. The allometric relationship between plant height and leaf length in A. anomala transformed into isometric growth, but it was in reversed pattern in M. sinensis. Warming promoted the plant height and leaf sheath length in A. anomala, whilst higher warming changed the growth relationship between plant height and leaf sheath length in M. sinensis. Similar allometric relationships among the leaf traits were observed, but warming did not significantly impact their allometric exponents. The results suggested that climate warming could have varied effects on different plants, and the differences are often related to the adaptability of plants. 相似文献
Diel vertical migration (DVM) by the sexes and life history stages of the copepod Diaptomus novamexicanus (Herrick) was investigated during two summers in a subalpine lake (Castle Lake, California, USA). Migratory behavior was quantified repeatedly by 1300 and 21–2200 hr sampling in the epilimnion. Population density and vertical distribution were estimated routinely at 1300 hr and at 2200 hr on selected dates. Males had greater night to day biomass differentials and ratios than females. The sexes showed comparable DVM participation (% of total biomass migrating) and amplitudes of migration (distance of ascent). Copepodids displayed higher participation, night/day ratios and amplitudes than younger copepods, but adult participation differed only from that of nauplii. Active participation in high amplitude ascents thus increased with age and was greatest in adult males. Analysis suggests that such relative behaviors probably occur in most limnetic Diaptomus, and that the magnitude of ascent into the epilimnion is associated with daytime vertical distribution. 相似文献
Dissolved organic nitrogen (DON) concentrations were measured in meso-oligotrophic Castle Lake, California during the ice-free season in 1982, 1983 and 1984. No consistent relationships were found between DON and particulate-N, primary productivity rates or chlorophyll concentrations. However, increases in DON concentrations were observed in the early growing season of 1982 and 1984 when water temperature was rising and a diatom bloom was senescing. DON increased at a high rate (0.31 mg atom N m–3 day–1), and then rapidly disappeared. Sediment released appared to be the most important source of DON. Dissolved free amino acids were always less than 7.5% of the DON pool, and did not vary in the composition of specific amino acids during the growing season. 相似文献
Background: Seedling germination and survival is a critical control on forest ecosystem boundaries, such as at the alpine–treeline ecotone. In addition, while it is known that species respond individualistically to the same suite of environmental drivers, the potential additional effect of local adaptation on seedling success has not been evaluated. Aims: To determine whether local adaptation may influence the position and movement of forest ecosystem boundaries, we quantified conifer seedling recruitment in common gardens across a subalpine forest to alpine tundra gradient at Niwot Ridge, Colorado, USA. Methods: We studied Pinus flexilis and Picea engelmannii grown from seed collected locally at High (3400m a.s.l.) and Low (3060m a.s.l.) elevations. We monitored emergence and survival of seeds sown directly into plots and survival of seedlings germinated indoors and transplanted after snowmelt. Results: Emergence and survival through the first growing season was greater for P. flexilis than P. engelmannii and for Low compared with High provenances. Yet survival through the second growing season was similar for both species and provenances. Seedling emergence and survival tended to be greatest in the subalpine forest and lowest in the alpine tundra. Survival was greater for transplants than for field-germinated seedlings. Conclusions: These results suggest that survival through the first few weeks is critical to the establishment of natural germinants. In addition, even small distances between seed sources can have a significant effect on early demographic performance – a factor that has rarely been considered in previous studies of tree recruitment and species range shifts. 相似文献
随着全球大气氮沉降的明显增加,将有可能显著影响我国西部地区受氮限制的亚高山森林生态系统。土壤微生物是生态系统的重要组成部分,是土壤物质循环和能量流动的重要参与者。由于生态系统类型、土壤养分、氮沉降背景值等的差异,土壤呼吸和土壤生物量碳氮对施氮的响应存在许多不确定性。而施氮会不会促进亚高山森林生态系统中土壤呼吸和微生物对土壤碳氮的固定?基于此假设,选择了川西60年生的四川红杉(Larix mastersiana)亚高山针叶林为研究对象,通过4个水平的土壤施氮控制试验(CK:0 g m~(-2) a~(-1)、N1:2 g m~(-2)a~(-1)、N2:5 g m~(-2) a~(-1)、N3:10 g m~(-2)a~(-1)),监测了土壤呼吸及土壤微生物生物量碳氮在一个生长季的动态情况。结果表明:施氮对土壤呼吸各指标和土壤微生物碳氮都有极显著的影响,施氮能促进土壤全呼吸、自养呼吸、异养呼吸通量和土壤微生物生物量碳氮的增长,施氮使土壤呼吸通量提高了11%—15%,土壤微生物量碳提高了5%—9%,土壤微生物量氮提高了23%—34%。在中氮水平下(5 g m~(-2) a~(-1))对土壤呼吸的促进最显著。相关分析发现,土壤呼吸与微生物生物量碳氮和微生物代谢商极呈显著正相关,微生物量碳氮与土壤温度呈极显著的正相关,与土壤湿度呈极显著负相关。通过一般线性回归拟合土壤呼吸速率与土壤10 cm温湿度的关系,发现土壤呼吸速率与土壤温度呈极显著的正相关,与土壤湿度极显著负相关(P0.001),中氮水平下土壤温度敏感性系数Q_(10)值(7.10)明显高于对照(4.26)。 相似文献