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991.
A field experiment was established at 2000 m above sea level (asl) in the central Swiss Alps with the aim of investigating the effects of elevated ozone (O(3)) and nitrogen deposition (N), and of their combination, on above-ground productivity and species composition of subalpine grassland. One hundred and eighty monoliths were extracted from a species-rich Geo-Montani-Nardetum pasture and exposed in a free-air O(3)-fumigation system to one of three concentrations of O(3) (ambient, 1.2 x ambient, 1.6 x ambient) and five concentrations of additional N. Above-ground biomass, proportion of functional groups and normalized difference vegetation index (NDVI) were measured annually. After 3 yr of treatment, the vegetation responded to the N input with an increase in above-ground productivity and altered species composition, but without changes resulting from elevated O(3). N input > 10 kg N ha(-1) yr(-1) was sufficient to affect the composition of functional groups, with sedges benefiting over-proportionally. No interaction of O(3) x N was observed, except for NDVI; positive effects of N addition on canopy greenness were counteracted by accelerated leaf senescence in the highest O(3) treatment. The results suggest that effects of elevated O(3) on the productivity and floristic composition of subalpine grassland may develop slowly, regardless of the sensitive response to increasing N. 相似文献
992.
Jeffrey M. Klopatek 《Plant and Soil》2007,294(1-2):157-167
Litterfall and fine root production were measured for three years as part of a carbon balance study of three forest stands
in the Pacific Northwest of the United States. A young second-growth Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] stand, a second-growth Douglas-fir with red alder (Alnus rubra Bong.) stand, and an old-growth (∼550 years) Douglas-fir stand were monitored for inputs of carbon and nitrogen into the
soil from litterfall and fine root production, as well as changes in soil C and N. Fine root production and soil nutrient
changes were measured through the use of soil ingrowth bags containing homogenized soil from the respective stands. Litterfall
biomass was greatest in the Douglas-fir-alder stand (527 g m−2 yr−1) that annually returned nearly three times the amount of N as the other stands. Mean residence time for forest floor material
was also shortest at this site averaging 4.6 years and 5.5 years for C an N, respectively. Fine root production in the upper
20 cm ranged from 584 g m−2 in the N rich Douglas-fir-alder stand to 836 g m−2 in the old-growth stand. Fine root production (down to one meter) was always greater than litterfall with a below:above ratio
ranging from 3.73 for the young Douglas-fir stand to 1.62 for the Douglas-fir-alder stand. The below:above N ratios for all
three stands closely approximate those for biomass. Soil changes in both C and N differed by site, but the soil C changes
in the old-growth stand mirrored those obtained in an ongoing CO2 flux study. Results from the soil ingrowth bags strongly suggest that this method provides a simple, but sufficient device
for measuring potential fine root biomass production as well as soil chemical changes. 相似文献
993.
Competition for nitrogen between Pinus sylvestris and ectomycorrhizal fungi generates potential for negative feedback under elevated CO2 总被引:1,自引:0,他引:1
We investigated fungal species-specific responses of ectomycorrhizal (ECM) Scots pine (Pinus sylvestris) seedlings on growth and nutrient acquisition together with mycelial development under ambient and elevated CO2. Each seedling was associated with one of the following ECM species: Hebeloma cylindrosporum, Laccaria bicolor, Suillus bovinus, S. luteus, Piloderma croceum, Paxillus involutus, Boletus badius, or non-mycorrhizal, under ambient, and elevated CO2 (350 or 700 μl l−1 CO2); each treatment contained six replicates. The trial lasted 156 days. During the final 28 days, the seedlings were labeled
with 14CO2. We measured hyphal length, plant biomass, 14C allocation, and plant nitrogen and phosphorus concentration. Almost all parameters were significantly affected by fungal
species and/or CO2. There were very few significant interactions. Elevated CO2 decreased shoot-to-root ratio, most strongly so in species with the largest extraradical mycelium. Under elevated CO2, ECM root growth increased significantly more than hyphal growth. Extraradical hyphal length was significantly negatively
correlated with shoot biomass, shoot N content, and total plant N uptake. Root dry weight was significantly negatively correlated
with root N and P concentration. Fungal sink strength for N strongly affected plant growth through N immobilization. Mycorrhizal
fungal-induced progressive nitrogen limitation (PNL) has the potential to generate negative feedback with plant growth under
elevated CO2.
Responsible Editor: Herbert Johannes Kronzucker 相似文献
994.
L'taief B Sifi B Zaman-Allah M Drevon JJ Lachaâl M 《Journal of plant physiology》2007,164(8):1028-1036
Nodule conductance to O2 diffusion has been involved as a major factor of the inhibition of N2 fixation by soil salinity that severely reduces the production of grain legumes. In order to determine the effect of this constraint on the nodule conductance, oxygen uptake by the nodulated roots of Cicer arietinum was measured by recording the concentration of O2 as a function of pO2 in a gas-tight incubator. After germination and inoculation with the strain Mesorhizobium ciceri UPMCa7, the varieties Amdoun 1 and INRAT 93-1 were hydroponically grown in a glasshouse on 1L glass bottles filled with nutrient solution containing 25 mM NaCl. Salinity induced a marked decrease in shoot (30% versus 14%), root (43% versus 20%), and nodule biomass (100% versus 43%) for Amdoun 1 relative to INRAT 93-1. Although salinity completely prevented nodule formation in the sensitive variety Amdoun 1, nodule number and biomass were higher in the first than in the second variety in the absence of salt. This effect was associated with a significantly higher O2 uptake by nodulated root (510 versus 255 micromol O2 plant(-1)h(-1)) and nodule conductance (20 versus 5 microm s(-1)) in Amdoun 1 than in INRAT 93-1. Salinity did not significantly change the nodule conductance and nodule permeability for INRAT 93-1. Thus, the salt tolerance of this variety appears to be associated with stability in nodule conductance and the capacity to form nodules under salt constraint. 相似文献
995.
996.
Anthemis cotula is a widespread invasive alien species in Kashmir Himalaya. Being a winter annual, the species reproduces entirely by achenes and synchrony between germination requirements of the species and the habitat conditions must be of critical importance in its invasiveness. To examine how the achenes of different ages respond to different environmental cues, two laboratory experiments were performed wherein effects of different nitrogen applications and growth hormones under continuous light and dark conditions were explored. Results show that the achenes are positively photoblastic and have requirement for after‐ripening. Nitrogen applied either as potassium nitrate or as thiourea significantly improved achene germination both under continuous light and dark conditions. Although kinetin (6‐furfurylaminopurine) did not influence achene germination, gibberellic acid (GA3) applied at 1.0 mM concentration had the most significant effect on the final percentage germination under both light and dark conditions. These results suggest that the achenes have an elaborate mechanism of sensing the habitat conditions that helps them to synchronise their germination with favourable environmental conditions – a strategy that aids the species in ensuring recruitment, survival and its spread in Kashmir Himalaya. 相似文献
997.
998.
Rivas R Laranjo M Mateos PF Oliveira S Martínez-Molina E Velázquez E 《Letters in applied microbiology》2007,44(4):412-418
AIMS: To identify several strains of Mesorhizobium amorphae and Mesorhizobium tianshanense nodulating Cicer arietinum in Spain and Portugal, and to study the symbiotic genes carried by these strains. METHODS AND RESULTS: The sequences of 16S-23S intergenic spacer (ITS), 16S rRNA gene and symbiotic genes nodC and nifH were analysed. According to their 16S rRNA gene and ITS sequences, the strains from this study were identified as M. amorphae and M. tianshanense. The type strains of these species were isolated in China from Glycyrrhiza pallidiflora and Amorpha fruticosa nodules, respectively, and are not capable of nodulating chickpea. These strains carry symbiotic genes, phylogenetically divergent from those of the chickpea isolates, whose nodC and nifH genes showed more than 99% similarity with respect to those from Mesorhizobium ciceri and Mesorhizobium mediterraneum, the two common chickpea nodulating species in Spain and Portugal. CONCLUSIONS: The results from this study showed that different symbiotic genes have been acquired by strains from the same species during their coevolution with different legumes in distinct geographical locations. SIGNIFICANCE AND IMPACT OF THE STUDY: A new infrasubspecific division named biovar ciceri is proposed within M. amorphae and M. tianshanense to include the strains able to effectively nodulate Cicer arietinum. 相似文献
999.
L. DA S. PONTES J.-F. SOUSSANA† F. LOUAULT D. ANDUEZA‡ P. CARRÈRE 《Functional ecology》2007,21(5):844-853
1000.
We investigated the responses of photon-saturated photosynthesis rate (P
sat) and its simultaneous acclimation of anatomy and nitrogen use patterns of current needles of Korean pine (Pinus koraiensis) seedlings grown under factorial combinations of two nitrogen levels and irradiances. Although N supply resulted in a significant
increase of N content in needles under both irradiances, the increase of P
sat tended to be suppressed only in shade (S). The significant increase of P
sat in full sunlight (O) was associated with the increase of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) and chlorophyll
(Chl) contents. In contrast, small increase of Chl content and no increase of RuBPCO content were found in S (90 % cut of
full irradiance), which would result in a small increase of P
sat. This result suggests that extra N is stocked in needles under shade for the growth in next season. With N supply, a significant
decrease of specific leaf area (SLA) was detected only in O. This decrease of SLA was due to the increase of density of needle.
Furthermore, the increase of needle density was not due to the increased number and size of mesophyll cells, but the increased
density of each mesophyll cell. Therefore, although SLA changed in O, the change did not involve anatomical adaptation to
use increased N effectively, at least observable by light microscopy. Hence, even though the SLA would change, N deposition
will improve the photosynthetic capacity of Korean pine seedlings, not through the development of needle anatomy but through
improvement of the allocation of N in both irradiances. 相似文献