Search

• Exotic plant invasions can alter ecosystem processes, particularly if the invasive species are functionally different from native species. We investigated whether such alterations can be explained by differences in functional traits between native and invasive plants of the same functional group or by differences in functional group affiliation. • We compared six invasive forbs in Europe with six native forbs and six native graminoids in leaf and whole-plant traits, plasticity in response to nutrient supply and interspecific competition, litter decomposition rate, effects on soil nutrient availability, and allelopathy. All traits were measured in a series of pot experiments, and leaf traits additionally in the field. • Invasive forbs differed from native forbs for only a few traits; they had less leaf chlorophyll and lower phosphorus (P) uptake from soil, but they tended to have a stronger allelopathic effect. The invasive forbs differed in many traits from the native graminoids, their leaves had lower tissue densities and a shorter life span, their litter decomposed faster and they had a lower nitrogen-use efficiency. • Our results suggest that invasive forbs have the potential to alter ecosystem properties when invading graminoid-dominated and displacing native graminoids but not when displacing native forbs., (© 2010 The Authors. New Phytologist © 2010 New Phytologist Trust.)

Shifts from nitrogen (N)- to phosphorus (P)-limited growth due to high N deposition may alter the functioning of wetland vegetation. This experiment tested how N vs P deficiency affects the growth and nutrient use of wetland sedges. Five wetland Carex species were grown at nine N : P supply ratios (0.6-405) with two absolute levels of N and P. Biomass and nutrient concentrations were determined after one and two growing seasons. Shoot biomass was maximal at N : P supply ratios of 15-26 after one season but 5-15 after two seasons. Photosynthesis after the first season, second-year growth, leaf longevity, and the fraction of nutrient supply retained by plants over two seasons were all negatively related to N : P supply ratios, with small effects of absolute supply. The five Carex species responded similarly to N : P ratios but differed in nutrient resorption efficiency and biomass allocation. Plants treated with high N : P ratios appeared to lose nutrients below ground. Such losses may reduce plant performance in P-limited wetlands affected by high N deposition.

Question How does pioneer vegetation of acid inland dunes respond to addition of nitrogen (N) and phosphorus (P)? Location Two inland dune reserves in The Netherlands with low and high N deposition. Methods During 2.5 yr, N and P addition (control, N, P, NP) took place in three different vegetation types of inland dunes ( Polytrichum piliferum mats, Campylopus introflexus mats and lichen-dominated vegetation). In each site, changes in the vegetation were recorded in three replicate quadrats of 1 m × 1 m per treatment. Differences in element content of grasses and lichens were recorded, together with vegetation parameters, including cover and height of grasses, bryophytes and lichens. Results In the site with high N deposition, grasses were taller, had higher N:P ratios and a generally lower lichen cover than in the low-deposition area. Experimental N application resulted in higher N and lower base metal concentrations in grasses and an increase in grass cover and size. In contrast, lichens showed a general decline in the N treatment and the lichen:grass ratio decreased. The effect of N addition was larger in the low-deposition area. The P treatment had an opposite effect: lichens increased in size and cover and overgrew grasses, especially when reindeer lichens were present. This suggests that the cryptogam layer was P-limited even in the low N deposition site. Conclusions Pioneer vegetation in inland dunes is susceptible to N and P addition. The results provide evidence for a decrease in lichen cover due to increased N deposition. [ABSTRACT FROM AUTHOR]

1. Nitrogen and phosphorus supply influences the rate of litter decomposition and nutrient dynamics during decomposition. Besides the total amount of N and P available to decomposers, their relative supply (N : P ratio) might be important, e.g. through an influence on the composition and activity of microbial communities. 2. We carried out two experiments using laboratory microcosms to test that (i) N : P ratios (in either litter or the environment) determine whether N or P limits the rate of decomposition, (ii) the ‘critical’ N : P ratio between N and P limitation depends on overall nutrient availability, (iii) litter colonization by fungi and bacteria depends on the N : P ratio, and (iv) N : P ratios determine if proportionately more N or P is retained or immobilized by the litter. 3. In one experiment, cellulose as a nutrient-free litter analogue was incubated on sand fertilized with varying N : P supply ratios, whereas in a second experiment, Carex leaf litter with varying N : P ratios was incubated on nutrient-free sand. 4. Results essentially support our hypotheses. Cellulose decomposition was N- or P-limited depending on the N : P supply ratio. The shift from N to P limitation occurred at N : P supply ratios of 1·7–45, depending on overall nutrient supply. Bacteria were most abundant on cellulose at low N : P supply ratios, when decomposition was N-limited, while fungi were relatively more important at high N : P ratios, when decomposition was P-limited. The amounts of mineral N and P immobilized on cellulose and those released from litter, both in absolute terms and relative to supply, depended on the type of nutrient limitation (N vs. P). 5. The N : P ratio of nutrients available to decomposers appears to be an important determinant of plant litter decomposition, the relative importance of fungi and bacteria in litter-associated microbial communities, and litter nutrient dynamics. [ABSTRACT FROM AUTHOR]