摘要:

AbstractQuercus roburL. saplings were exposed in an outdoor experiment to supplemental levels of UV‐8 (280–315 nm) radiation using treatment arrays of cellulose diacetate‐filtered fluorescent lamps that also produce UV‐A (315–400 nm) radiation. Saplings were also exposed to UV‐A radiation alone using control arrays of the same lamps filtered with polyester and to ambient levels of radiation, using arrays of unenergized lamps. The UV‐B treatment was modulated to maintain a 30% elevation above the ambient level of UV‐B radiation, measured by a broad‐band sensor weighted with an erythemal action spectrum. Saplings exposed to UV‐B radiation beneath treatment arrays developed thicker leaves than those beneath ambient and control arrays. Despite the fact that supplemental levels of UV‐A radiation were only a small percentage of ambient levels, apparent UV‐A effects were also recorded. Significant increases in sapling height, lammas shoot length and herbivory by chewing insects were observed under treatment and control arrays, relative to ambient, but there were no differences between the responses of saplings under treatment and control. These data imply that supplemental UV‐A radiation or other effects associated with energised lamps can significantly affect plant growth parameters and herbivory in outdoor studies. We conclude that the results from current outdoor UV‐B supplementation experiments that lack control exposures using polyester‐filtered lamps need to be interpreted with caution and that future supplementation experiments should

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1996.tb00083.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractA new modulated lamp system is described. This system has successfully provided an ultraviolet‐B (UV‐B) supplement in proportion to ambient UV‐B. The modulated system was used to simulate the UV‐B environment resulting from an annual mean reduction of 15% in the stratospheric ozone under UK field conditions, but taking account of seasonal variation in depletion. The effects of this enhanced level of UV‐B on the growth, physiology and yield of four cultivars of pea were assessed.Enhanced UV‐B resulted in small reductions in the number of stems and total stem length per plant (respectively 4.7 and 8.7%). There were also significant decreases in the dry weight of peas (10.1%), pods (10.3%) and stems (7.8%) per plant. UV‐B treatment had no effect on the number of peas per pod or average pea weight, but did significantly reduce (12.1%) the number of pods per plant. This decrease in pod number was partly due to enhanced abscission of pods during the final month of plant growth. UV‐B treatment had no significant effect on chlorophyll fluorescence characteristics or CO2assimilation rate per unit leaf area. These results are consistent with previous controlled environment experiments, and suggest that reduction in yield may be due to direct effects of UV‐B on plant growth rather than a decrease in photosynthetic capacity p

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1996.tb00084.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The phenology ofFagus sylvaticawas unaffected by exposure to an atmosphere of elevated CO2(600 μL L‐1) after two years of fumigation. Non‐significant changes in nitrogen and phenolic content of the leaves decreased the nutritional status of beech for female larvae in elevated CO2such that they responded by eating in a compensatory manner; males were unaffected. Rates of development, mortality and adult biomass ofRhynchaenus fagiwere no different from those in ambient CO2concentrations (355 μL L‐1). It is possible that, with the changes in leaf chemistry affecting the females, fecundity will be altered, with important consequences for populations of beech

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1996.tb00085.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractA model of the daily carbon balance of a black spruce/feathermoss boreal forest ecosystem was developed and results compared to preliminary data from the 1994 BOREAS field campaign in northem Manitoba, Canada. The model, driven by daily weather conditions, simulated daily soil climate status (temperature and moisture profiles), spruce photosynthesis and respiration, moss photosynthesis and respiration, and litter decomposition. Model agreement with preliminary field data was good for net ecosystem exchange (NEE), capturing both the asymmetrical seasonality and short‐term variability. During the growing season simulated daily NEE ranged from ‐4 g C m‐2d‐1(carbon uptake by ecosystem) to + 2 g C m‐2d‐1(carbon flux to atmosphere), with fluctuations from day to day. In the early winter simulated NEE values were + 0.5 g C m‐2d‐1, dropping to + 0.2 g C m‐2d‐1in mid‐winter. Simulated soil respiration during the growing season (+ 1 to + 5 g C m‐2d‐1) was dominated by metabolic respiration of the live moss, with litter decomposition usually contributing less than 30% and live spruce root respiration less than 10% of the total. Both spruce and moss net primary productivity (NPP) rates were higher in early summer than late summer. Simulated annual NEE for 1994 was ‐51 g C m‐2y‐1, with 83% going into tree growth and 17% into the soil carbon accumulation. Moss NPP (58 g C m‐2y‐1) was considered to be litter (i.e. soil carbon input; no net increase in live moss biomass). Ecosystem respiration during the snow‐covered season (84 g C m‐2) was 58% of the growing season net carbon uptake. A simulation of the same site for 1968–1989 showed = 10–20% year‐to‐year variability in heterotrophic respiration (mean of + 113 g C m‐2y‐1). Moss NPP ranged from 19 to 114 g C m‐2y‐1; spruce NPP from 81 to 150 g C m‐2y‐1; spruce growth (NPP minus litterfall) from 34 to 103 g C m‐2y‐1; NEE ranged from +37 to ‐142 g C m‐2y‐1. Values for these carbon balance terms in 1994 were slightly smaller than the 1969–89 means. Higher ecosystem productivity years (more negative NEE) generally had early springs and relatively wet summer

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1996.tb00086.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractWe present a simple theoretical analysis of the long term response of forest growth and carbon allocation to increased atmospheric [CO2] and N deposition. Our analysis is based on a recent model which predicts that plant light‐use efficiency increases with [CO2] but is independent of plant N supply. We combine that model with simple assumptions for nitrogen fluxes in the soil. A quasi‐equilibrium analysis of the short term tree and soil pools is then used to develop a simple graphical depiction of the long term carbon and nitrogen supply constraints on total growth, stem growth and foliar allocation.Our results suggest that long‐term growth responses to [CO2] and N deposition depend strongly on the extent to which stem allocation and foliage allocation are coupled. At one extreme (‘no coupling’), when stem allocation is fixed and independent of foliage allocation, there is no response of total growth or stem growth to increased [CO2] unless N deposition increases. At the other extreme (‘linear coupling’), when stem allocation is proportional to foliage allocation, there is a significant long‐term increase in total growth following a doubling of [CO2], even when N deposition is unchanged, but stem growth decreases because of a long‐term decrease in foliage allocation. For both types of coupling, total growth and stem growth increase with increasing N deposition. In the case of linear coupling, however, the N deposition response of stem growth is significantly larger than that of total growth, because of a long‐term increase in foliage allocation. We compare our results with those obtained previously from an alternative model of canopy light‐use efficiency involving a dependence on the foliar N:C ratio in addition to [CO2].Our results highlight the need for more experimental information on (i) the extent to which canopy light‐use efficiency is independent of N supply, and (ii) the relationship between foliage allocat

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1996.tb00087.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractAtmospheric carbon dioxide enrichment and increasing nitrogen deposition are often predicted to increase forest productivity based on currently available data for isolated forest tree seedlings or their leaves. However, it is highly uncertain whether such seedling responses will scale to the stand level. Therefore, we studied the effects of increasing CO2(280, 420 and 560 μL L‐1) and increasing rates of wet N deposition (0, 30 and 90 kg ha‐1y‐1) on whole stands of 4‐year‐old spruce trees (Picea abies). One tree from each of six clones, together with two herbaceous understory species, were established in each of nine 0.7 m2model ecosystems in nutrient poor forest soil and grown in a simulated montane climate for two years. Shoot level light‐saturated net photosynthesis measured at growth CO2concentrations increased with increasing CO2, as well as with increasing N deposition. However, predawn shoot respiration was unaffected by treatments. When measured at a common CO2concentration of 420 μL L‐137% down‐regulation of photosynthesis was observed in plants grown at 560 μL CO2L‐1. Length growth of shoots and stem diameter were not affected by CO2or N deposition. Bud burst was delayed, leaf area index (LAI) was lower, needle litter fall increased and soil CO2efflux increased with increasing CO2. N deposition had no effect on these traits. At the ecosystem level the rate of net CO2exchange was not significantly different between CO2and N treatments. Most of the responses to CO2studied here were nonlinear with the most significant differences between 280 and 420 μL CO2L‐1and relatively small changes between 420 and 560 μL CO2L‐1. Our results suggest that the lack of above‐ground growth responses to elevated CO2is due to the combined effects of physiological down‐regulation of photosynthesis at the leaf level, allometric adjustment at the canopy level (reduced LAI), and increasing strength of below‐ground carbon sinks. The non‐linearity of treatment effects further suggests that major responses of coniferous forests to atmospheric CO2enrichment might already be under way and that future resp

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1996.tb00088.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractWe investigated the responses of model calcareous grassland communities to three CO2concentrations: 330, 500, and 660 μL L‐1, The communities were composed of six species,Bromus erectusHudson,Festuca ovinaL.,Prunella vulgarisL.,Prunella grandiflora(L.) Scholler,Hieracium pilosellaL., andTrifolium repensL., that are native to the calcareous grasslands of Europe. Genotypic variation in CO2response was studied inBromus erectusandFestuca ovina.Plants were harvested after c. 126 days of growth. We found that:At the community level, there were marginally significant (0.1≥P>0.05) increases in leaf and litter dry weight with increasing CO2concentration.There were significant differences between species in CO2response, including both negative and positive responses.Prunella vulgarishad a significant negative response;Hieraciunt pilosellaandFestuca ovinahad significant positive responses;Prunella grandiflorahad a marginally significant positive response; andBromus erectusandTrifotium repensdid not have significant responses.There was significant variation among genotypes in the response to elevated CO2inBromus erectus, but not inFestuca ovina.Based on the observed species‐ and genotype‐level variation in CO2response of calcareous grassland plants in this and other studies, we speculate that increasing atmospheric CO2concentrations will alter community structure in calcareous gr

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1996.tb00089.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractA 1100‐year long record of lake ecosystem response to climate and catchment change with precise chronological control is reported. Diatom and pollen assemblages of an annually laminated (varved) sediment from a northern Swedish lake (Kassjön, Våsterbotten) were used as records of lake diatom communities and catchment vegetation. These data were compared with summer temperature estimates based on tree‐ring records of the same geographical area to identify the effects of climate change and catchment disturbance on diatom assemblages in the lake. In a canonical ordination, 23% of the variability in the total diatom assemblages for the period AD1040–1804 was accounted for by changes in pollen data which reflect agricultural development in the catchment. Diatom species richness, however, exhibited a stronger relationship with summer temperature and, significantly, declined with the lower temperatures associated with the Little Ice Age minimum (early 17th century). Summer temperature accounted for 23% of the variability in diatom species richness 20 years later. The mechanism behind this time‐lag is unclear, but may be related to catchment‐mediated effects, given recent evidence for lags in the response of boreal‐forest vegetation regeneration cycles to climatic variability. These results suggest that climate‐related effects on lakes occurring over medium timescales can be resolved in lake sediments. Moreover, it is possible to identify these effects despite cultural‐related signals, but as the latter become more extreme in the late 20th century the climate s

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1996.tb00090.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY