Summary• Plant invasion potentially alters ecosystem carbon (C) and nitrogen (N) cycles. However, the overall direction and magnitude of such alterations are poorly quantified.• Here, 94 experimental studies were synthesized, using a meta-analysis approach, to quantify the changes of 20 variables associated with C and N cycles, including their pools, fluxes, and other related parameters in response to plant invasion.• Pool variables showed significant changes in invaded ecosystems relative to native ecosystems, ranging from a 5% increase in root carbon stock to a 133% increase in shoot C stock. Flux variables, such as above-ground net primary production and litter decomposition, increased by 50-120% in invaded ecosystems, compared with native ones. Plant N concentration, soil and concentrations were 40, 30 and 17% higher in invaded than in native ecosystems, respectively. Increases in plant production and soil N availability indicate that there was positive feedback between plant invasion and C and N cycles in invaded ecosystems.• Invasions by woody and N-fixing plants tended to have greater impacts on C and N cycles than those by herbaceous and nonN-fixing plants, respectively. The responses to plant invasion are not different among forests, grasslands, and wetlands. All of these changes suggest that plant invasion profoundly influences ecosystem processes.Key words: carbon and nitrogen pools and fluxes, litter quality, meta-analysis, plant invasion, soil nitrogen availability.New Phytologist (2008) 177: 706-714

Because the flowering and fruiting phenology of plants is sensitive to environmental cues such as temperature and moisture, climate change is likely to alter community-level patterns of reproductive phenology. Here we report a previously unreported phenomenon: experimental warming advanced flowering and fruiting phenology for species that began to flower before the peak of summer heat but delayed reproduction in species that started flowering after the peak temperature in a tallgrass prairie in North America. The warming-induced divergence of flowering and fruiting toward the two ends of the growing season resulted in a gap in the staggered progression of flowering and fruiting in the community during the middle of the season. A double precipitation treatment did not significantly affect flowering and fruiting phenology. Variation among species in the direction and magnitude of their response to warming caused compression and expansion of the reproductive periods of different species, changed the amount of overlap between the reproductive phases, and created possibilities for an altered selective environment to reshape communities in a future warmed world.climate change ͉ global warming ͉ precipitation P henology is a sensitive biosphere indicator of climate change (1, 2). Long-term surface data and remote sensing measurements indicate that plant phenology has been advanced by 2-3 days in spring and delayed by 0.3-1.6 days in autumn per decade (3-6) in the past 30-80 years, resulting in extension of the growing season. An extended growing season leads to increased production in terrestrial and marine ecosystems (7,8), widens amplitudes of the annual CO 2 cycle in the atmosphere (9), and prolongs production of allergic pollens (10). Although changes in vegetative phenology have considerable consequences for ecosystem functioning, we lack information on responses of reproductive phenology due to climate change, especially in a community setting (11,12). Reproductive events usually determine population and community dynamics in future generations, affecting evolutionary processes. Because the flowering and fruiting phenology of plants is very sensitive to environmental cues such as temperature, moisture, and photoperiod (13), it is imperative to understand the impact of climate change on reproductive phenology.Reproductive phenology of assembled species in a plant community is often staggered in an unbroken progression over the growing season (14-17). This temporal distribution of community-level reproductive events is largely generated by the different developmental trajectories and life forms of the different species and may be shaped by their resource needs during reproduction and ecological sorting (18). Phenological differences in reproductive events among species over the growing season may reduce competition by spreading primary resource use over different temporal pools (19)(20)(21). Differential changes in phenology and growth between species in response to climate change could lead to new patterns of spec...

Global warming potentially alters the terrestrial carbon (C) cycle, likely feeding back to further climate warming. However, how the ecosystem C cycle responds and feeds back to warming remains unclear. Here we used a meta-analysis approach to quantify the response ratios of 18 variables of the ecosystem C cycle to experimental warming and evaluated ecosystem C-cycle feedback to climate warming. Our results showed that warming stimulated gross ecosystem photosynthesis (GEP) by 15.7%, net primary production (NPP) by 4.4%, and plant C pools from above- and belowground parts by 6.8% and 7.0%, respectively. Experimental warming accelerated litter mass loss by 6.8%, soil respiration by 9.0%, and dissolved organic C leaching by 12.1%. In addition, the responses of some of those variables to experimental warming differed among the ecosystem types. Our results demonstrated that the stimulation of plant-derived C influx basically offset the increase in warming-induced efflux and resulted in insignificant changes in litter and soil C content, indicating that climate warming may not trigger strong positive C-climate feedback from terrestrial ecosystems. Moreover, the increase in plant C storage together with the slight but not statistically significant decrease of net ecosystem exchange (NEE) across ecosystems suggests that terrestrial ecosystems might be a weak C sink rather than a C source under global climate warming. Our results are also potentially useful for parameterizing and benchmarking land surface models in terms of C cycle responses to climate warming.

Summary• Anthropogenic nitrogen (N) addition may substantially alter the terrestrial N cycle. However, a comprehensive understanding of how the ecosystem N cycle responds to external N input remains elusive.• Here, we evaluated the central tendencies of the responses of 15 variables associated with the ecosystem N cycle to N addition, using data extracted from 206 peer-reviewed papers.• Our results showed that the largest changes in the ecosystem N cycle caused by N addition were increases in soil inorganic N leaching (461%), soil NO 3 ) concentration (429%), nitrification (154%), nitrous oxide emission (134%), and denitrification (84%). N addition also substantially increased soil NH 4 + concentration (47%), and the N content in belowground (53%) and aboveground (44%) plant pools, leaves (24%), litter (24%) and dissolved organic N (21%). Total N content in the organic horizon (6.1%) and mineral soil (6.2%) slightly increased in response to N addition. However, N addition induced a decrease in microbial biomass N by 5.8%.• The increases in N effluxes caused by N addition were much greater than those in plant and soil pools except soil NO 3 ), suggesting a leaky terrestrial N system.

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