Browsing by Author "Zou, Jianwen"

Now showing 1 - 4 of 4
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    Chinese Tallow Trees (Triadica sebifera) from the Invasive Range Outperform Those from the Native Range with an Active Soil Community or Phosphorus Fertilization
    (Public Library of Science, 2013) Zhang, Ling; Zhang, Yaojun; Wang, Hong; Zou, Jianwen; Siemann, Evan
    Two mechanisms that have been proposed to explain success of invasive plants are unusual biotic interactions, such as enemy release or enhanced mutualisms, and increased resource availability. However, while these mechanisms are usually considered separately, both may be involved in successful invasions. Biotic interactions may be positive or negative and may interact with nutritional resources in determining invasion success. In addition, the effects of different nutrients on invasions may vary. Finally, genetic variation in traits between populations located in introduced versus native ranges may be important for biotic interactions and/or resource use. Here, we investigated the roles of soil biota, resource availability, and plant genetic variation using seedlings of Triadica sebifera in an experiment in the native range (China). We manipulated nitrogen (control or 4 g/m2), phosphorus (control or 0.5 g/m2), soil biota (untreated or sterilized field soil), and plant origin (4 populations from the invasive range, 4 populations from the native range) in a full factorial experiment. Phosphorus addition increased root, stem, and leaf masses. Leaf mass and height growth depended on population origin and soil sterilization. Invasive populations had higher leaf mass and growth rates than native populations did in fresh soil but they had lower, comparable leaf mass and growth rates in sterilized soil. Invasive populations had higher growth rates with phosphorus addition but native ones did not. Soil sterilization decreased specific leaf area in both native and exotic populations. Negative effects of soil sterilization suggest that soil pathogens may not be as important as soil mutualists for T. sebifera performance. Moreover, interactive effects of sterilization and origin suggest that invasive T. sebifera may have evolved more beneficial relationships with the soil biota. Overall, seedlings from the invasive range outperformed those from the native range, however, an absence of soil biota or low phosphorus removed this advantage.
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    Decomposition of Phragmites australis litter retarded by invasive Solidago canadensis in mixtures: an antagonistic non-additive effect
    (Macmillan Publishers Limited, 2014) Zhang, Ling; Zhang, Yaojun; Zou, Jianwen; Siemann, Evan
    Solidago canadensis is an aggressive invader in China. Solidago invasion success is partially attributed to allelopathic compounds release and more benefits fromAMfungi, which potentially makes the properties of Solidago litter different from co-occurring natives. These properties may comprehensively affect litter decomposition of co-occurring natives. We conducted a field experiment to examine litter mixing effects in a Phragmites australis dominated community invaded by Solidago in southeast China. Solidago had more rapid mass and N loss rate than Phragmites when they decomposed separately. Litter mixing decreased N loss rate in Phragmites litter and increased that of Solidago. Large decreases in Phragmites mass loss and smaller increases in Solidago mass loss caused negative non-additive effect. Solidago litter extracts reduced soil C decomposition and N processes, suggested an inhibitory effect of Solidago secondary compounds. These results are consistent with the idea that nutrient transfer and secondary compounds both affected litter mixtures decomposition.
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    Non-Native Plant Litter Enhances Soil Carbon Dioxide Emissions in an Invaded Annual Grassland
    (Public Library of Science, 2014) Zhang, Ling; Wang, Hong; Zou, Jianwen; Rogers, William E.; Siemann, Evan
    Litter decomposition is a fundamental ecosystem process in which breakdown and decay of plant detritus releases carbon and nutrients. Invasive exotic plants may produce litter that differs from native plant litter in quality and quantity. Such differences may impact litter decomposition and soil respiration in ways that depend on whether exotic and native plant litters decompose in mixtures. However, few field experiments have examined how exotic plants affect soil respiration via litter decomposition. Here, we conducted an in situ study of litter decomposition of an annual native grass (Eragrostis pilosa), a perennial exotic forb (Alternanthera philoxeroides), and their mixtures in an annual grassland in China to examine potential invasion effects on soil respiration. Alternanthera litter decomposed faster than Eragrostis litter when each was incubated separately. Mass loss in litter mixes was more rapid than predicted from rates in single species bags (only 35% of predicted mass remained at 8 months) showing synergistic effects. Notably, exotic plant litter decomposition rate was unchanged but native plant litter decomposition rate was accelerated in mixtures (decay constant k = 0.20 month-1) compared to in isolation (k = 0.10 month-1). On average, every litter type increased soil respiration compared to bare soil from which litter was removed. However, the increases were larger for mixed litter (1.82 times) than for Alternanthera litter (1.58 times) or Eragrostis litter (1.30 times). Carbon released as CO2 relative to litter carbon input was also higher for mixed litter (3.34) than for Alternathera litter (2.29) or Eragrostis litter (1.19). Our results indicated that exotic Alternanthera produces rapidly decomposing litter which also accelerates the decomposition of native plant litter in litter mixtures and enhances soil respiration rates. Thus, this exotic invasive plant species will likely accelerate carbon cycling and increase soil respiration even at intermediate stages of invasion in these annual grasslands.
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    Shifts in traits of the invasive plant Sapium sebiferum and their effects on ecosystem carbon and nitrogen processes
    (2007) Zou, Jianwen; Siemann, Evan
    The evolution of increased competitive ability (EICA) hypothesis posits that release from natural enemies favors exotic plants evolving traits associated with faster-growth and lower herbivore-resistance in the introduced range. Given a trade-off between resistance and tolerance, decreased resistance may translate into increased tolerance to herbivory by invasive plants compared to conspecifics in the native range. These genetic shifts in traits of invasive plants may also have effects on soil and ecosystem processes. To test the EICA hypothesis, we conducted experiments in the native range of Sapium sebiferum using seeds from populations in the native Chinese range (native ecotype) and the invasive North American populations (invasive ecotype). Plants from invasive populations showed greater competitive ability, reduced resistance but increased tolerance to herbivory than those from native populations of Sapium sebiferum when they were competing against each other in the presence of native herbivores. Despite that native specialist beetles Aphthonomorpha collaris preferred invasive populations over native populations of S. sebiferum when beetles had a choice between them in a bioassay trial, plants from invasive populations compensated for leaf damage more efficiently than those from native populations. These results suggest that invasive S. sebiferum has become a faster-growing, less herbivore-resistant and more herbivore-tolerant plant in the introduced range compared to conspecifics in the native range. A greenhouse study showed that invasive North American populations of S. sebiferum differed genetically from native Chinese populations in most plant functional traits. Of 13 measured plant variables, the root to shoot ratio (RSR), total leaf area (TLA) and net CO2 assimilation (A) were identified as powerful traits that contributed the most to the genetic difference between native Chinese and invasive North American population types. These shifts in functional traits resulted in higher soil-plant system CO 2 and N2O emissions for invasive ecotypes than for native ecotypes of Sapium in an outdoor pot experiment. Compared with native ecotypes, invasive ecotypes accelerated soil carbon and nitrogen processes and promoted more nitrogen uptake through soil-plant direct interactions. The results of this study suggest that shift in traits of invasive plants and their effects on ecosystem processes may have implications for their invasiveness.