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Weixin Cheng

Bio: Weixin Cheng is an academic researcher from University of California, Santa Cruz. The author has contributed to research in topics: Rhizosphere & Soil organic matter. The author has an hindex of 49, co-authored 111 publications receiving 8685 citations. Previous affiliations of Weixin Cheng include Chinese Academy of Sciences & San Diego State University.


Papers
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Journal ArticleDOI
TL;DR: The results suggest that litter placement can strongly influence the com- position of decomposer communities and that the resulting trophic relationships are important to determining the rates and timing of plant litter decomposition and N dynamics.
Abstract: We conducted field experiments to test the general hypothesis that the com- position of decomposer communities and their trophic interactions can influence patterns of plant litter decomposition and nitrogen dynamics in ecosystems. Conventional (CT) and no-tillage (NT) agroecosystems were used to test this idea because of their structural sim- plicity and known differences in their functional properties. Biocides were applied to ex- perimentally exclude bacteria, saprophytic fungi, and microarthropods in field exclosures. Abundances of decomposer organisms (bacteria, fungi, protozoa, nematodes, microar- thropods), decomposition rates, and nitrogen fluxes were quantified in surface and buried litterbags (Secale cereale litter) placed in both NT and CT systems. Measurements of in situ soil respiration rates were made concurrently. The abundance and biomass of all microbial and faunal groups were greater on buried than surface litter. The mesofauna contributed more to the total heterotrophic C in buried litter from CT (6-22%) than in surface litter from NT (0.4-1/1%). Buried litter decay rates (1.4-1.7%/d) were -2.5 times faster than rates for surface litter (0.5-O.7%/d). Ratios of fungal to bacterial biomass and fungivore to bacterivore biomass on NT surface litter generally increased over the study period resulting in ratios that were 2.7 and 2.2 times greater, respectively, than those of CT buried litter by the end of the summer. The exclusion experiments showed that fungi had a somewhat greater influence on the decomposition of surface litter from NT while bacteria were more important in the de- composition of buried litter from CT. The fungicide and bactericide reduced decomposition rates of NT surface litter by 36 and 25% of controls, respectively, while in CT buried litter they were reduced by 21 and 35% of controls, respectively. Microarthropods were more important in mobilizing surface litter nitrogen by grazing on fungi than in contributing to litter mass loss. Where fungivorous microarthropods were experimentally excluded, there was less than a 5% reduction in mass loss from litter of both NT and CT, but fungi- fungivore interactions were important in regulating litter N dynamics in NT surface litter. As fungal densities increased following the exclusion of microarthropods on NT surface litter, there was 25% greater N retention as compared to the control after 56 d of decay. Saprophytic fungi were responsible for as much as 86% of the net N immobilized (1.81 g /m2) in surface litter by the end of the study when densities of fungivorous microarthropods were low. Although bacteria were important in regulating buried litter decomposition rates and the population dynamics of bacterivorous fauna, their influence on buried litter N dynamics remains less clear. The larger microbial biomass and greater contribution of a bacterivorous fauna on buried litter is consistent with the greater carbon losses and lower carbon assimilation in CT than NT agroecosystems. In summary, our results suggest that litter placement can strongly influence the com- position of decomposer communities and that the resulting trophic relationships are im- portant to determining the rates and timing of plant litter decomposition and N dynamics. Furthermore, cross placement studies suggest that the decomposer communities within each tillage system, while not discrete, are adapted to the native litter placements in each.

608 citations

Journal ArticleDOI
TL;DR: In this article, the effects of shading wheat plants on rhizosphere respiration and root priming of soil organic matter decomposition were investigated by using a natural abundance 13C tracer method and 14C pulse labeling simultaneously.
Abstract: The effects of shading wheat plants on rhizosphere respiration and rhizosphere priming of soil organic matter decomposition were investigated by using a natural abundance 13C tracer method and 14C pulse labeling simultaneously. Seven days with strongly reduced photosynthesis (12/60 h day/night period) resulted in only half of the total CO2 efflux from soil compared to the treatment with a 12/12 h day/night period. The CO2 efflux from unplanted soil amounted to only 12 and 20% of the total CO2 efflux from the soil with non-shaded and shaded plants, respectively. On average 75% of total CO2 efflux from the planted soil with prolonged night periods was root-derived. Rhizosphere respiration was tightly coupled with plant photosynthetic activity. Any factor affecting photosynthesis, or substrate supply to roots and rhizosphere microorganisms, is an important determinant of root-derived CO2 efflux, and thereby, total CO2 efflux from soils. Clear diurnal dynamics of the total CO2 efflux intensity indicate the existence of an endogenous control mechanism of rhizosphere respiration. The light-on events after prolonged dark periods lead to strong increases of root-derived and therefore of total CO2 efflux from soil. After 14C pulse labeling, two maxima of the root-derived 14CO2 efflux were measured (6 and 24 h). This result demonstrated the diurnal dynamics of the rhizosphere respiration of recently-assimilated C in both the normal light conditions and shaded plants as well. The total amount of root-derived C respired in the rhizosphere was 17.3 and 20.6% of the total assimilated C for non-shaded and shaded plants, respectively. Both methods used, 13C natural abundance and 14C pulse labeling, gave similar estimates of root-derived CO2 during the whole observation period: 1.80±0.27 and 1.67±0.37 mg C kg−1 h−1 (±SD), respectively. Both tracer methods show that the cultivation of wheat led to the increasing decomposition intensity of soil organic matter (priming effect). Additionally, 13C natural abundance allows tracing of the dynamics of the priming effect depending on the light-on events.

462 citations

Journal ArticleDOI
TL;DR: This work demonstrates that a shift in microbial metabolic response to different substrate inputs from plants is a plausible mechanism leading to positive or negative RPEs and suggests that the RPE may have resulted from an evolutionarily stable mutualistic association between plants and rhizosphere microbes.
Abstract: Summary Therhizosphereprimingeffect(RPE)isamechanismbywhichplantsinteractwithsoilfunctions. The large impact of the RPE on soil organic matter decomposition rates (from 50% reduction to 380% increase) warrants similar attention to that being paid to climatic controls on ecosystem functions. Furthermore, global increases in atmospheric CO2 concentration and surface temperature can significantly alter theRPE. Our analysis using agame theoretic model suggests that the RPE may have resulted from an evolutionarily stable mutualistic association between plantsandrhizospheremicrobes.Throughmodelsimulationsbasedonmicrobialphysiology,we demonstratethatashiftinmicrobialmetabolicresponsetodifferentsubstrateinputsfromplants isaplausiblemechanismleadingtopositiveornegativeRPEs.InacasestudyoftheDukeFree-Air CO2 Enrichment experiment, performance of the PhotoCent model was significantly improved by including an RPE-induced 40% increase in soil organic matter decomposition rate for the elevated CO2 treatment - demonstrating the value of incorporating the RPE into future ecosystemmodels.Overall,theRPEisemergingasacrucialmechanisminterrestrialecosystems, which awaits substantial research and model development.

396 citations

Journal ArticleDOI
TL;DR: The magnitude of therhizosphere effect ranged from 0% to as high as 383% above the decomposition rate in the no-plant control, indicating that the rhizosphere priming can substantially intensify decomposition.
Abstract: Plant species and soil fertility presumably control rhizosphere effects on soil organic matter (SOM) decomposition, but qualitative and quantitative descriptions of such controls are still sparse. In this study, rhizosphere effects of soybean [Glycine max (L.) Merr.] and spring wheat (Triticum aestivum L.) on SOM decomposition were investigated at four phenological stages under three levels of fertilization in a greenhouse experiment using natural 13 C tracers. The magnitude of the rhizosphere effect ranged from 0% to as high as 383% above the decomposition rate in the no-plant control, indicating that the rhizosphere priming can substantially intensify decomposition. The rhizosphere priming effect was responsible for a major portion of the total soil C efflux. Cumulative soil C loss caused by rhizosphere effects during the whole growing season equated to the amount of root biomass C for the soybean treatment, and 71% of root biomass C for the wheat treatment. Different plant species produced significantly different rhizosphere priming effects. The overall rhizosphere priming effect of soybean plants was significantly higher than for wheat plants. Plant phenology significantly influenced the rhizosphere priming effect. Little rhizosphere effect occurred in both wheat and soybean treatments initially. The priming effect of the wheat rhizosphere reached 287% above the no-plant control at the flowering stage and declined significantly afterward. The priming effect of the soybean rhizosphere peaked at 383% above the no-plant control during the late vegetative stage and remained at high levels onward. Contrary to many published reports, NPK fertilization did not significantly modify the rhizosphere priming effect.

299 citations

Journal ArticleDOI
TL;DR: Investigating the RPE of two plant species grown in two soil types and sampled at two phenological stages over an 88-day period shows that root–soil–microbial interactions can stimulate soil C and N mineralization through rhizosphere effects, providing clear evidence for the microbial activation hypothesis of RPE.
Abstract: Living roots and their rhizodeposits affect microbial activity and soil carbon (C) and nitrogen (N) mineralization. This so-called rhizosphere priming effect (RPE) has been increasingly recognized recently. However, the magnitude of the RPE and its driving mechanisms remain elusive. Here we investigated the RPE of two plant species (soybean and sunflower) grown in two soil types (a farm or a prairie soil) and sampled at two phenological stages (vegetative and mature stages) over an 88-day period in a greenhouse experiment. We measured soil C mineralization using a continuous 13C-labeling method, and quantified gross N mineralization with a 15N-pool dilution technique. We found that living roots significantly enhanced soil C mineralization, by 27–245%. This positive RPE on soil C mineralization did not vary between the two soils or the two phenological stages, but was significantly greater in sunflower compared to soybean. The magnitude of the RPE was positively correlated with rhizosphere respiration rate across all treatments, suggesting the variation of RPE among treatments was likely caused by variations in root activity and rhizodeposit quantity. Moreover, living roots stimulated gross N mineralization rate by 36–62% in five treatments, while they had no significant impact in the other three treatments. We also quantified soil microbial biomass and extracellular enzyme activity when plants were at the vegetative stage. Generally, living roots increased microbial biomass carbon by 0–28%, β-glucosidase activity by 19–56%, and oxidative enzyme activity by 0–46%. These results are consistent with the positive rhizosphere effect on soil C (45–79%) and N (10–52%) mineralization measured at the same period. We also found significant positive relationships between β-glucosidase activity and soil C mineralization rates and between oxidative enzyme activity and gross N mineralization rates across treatments. These relationships provide clear evidence for the microbial activation hypothesis of RPE. Our results demonstrate that root–soil–microbial interactions can stimulate soil C and N mineralization through rhizosphere effects. The relationships between the RPE and rhizosphere respiration rate and soil enzyme activity can be used for explicit representations of RPE in soil organic matter models.

293 citations


Cited by
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Journal ArticleDOI
TL;DR: Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols used xiii 1.
Abstract: Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

14,171 citations

Journal ArticleDOI
TL;DR: The results from this review may provide the most plausible estimates of how plants in their native environments and field-grown crops will respond to rising atmospheric [CO(2)]; but even with FACE there are limitations, which are discussed.
Abstract: Contents Summary 1 I. What is FACE? 2 II. Materials and methods 2 III. Photosynthetic carbon uptake 3 IV. Acclimation of photosynthesis 6 V. Growth, above-ground production and yield 8 VI. So, what have we learned? 10 Acknowledgements 11 References 11 Appendix 1. References included in the database for meta-analyses 14 Appendix 2. Results of the meta-analysis of FACE effects 18 Summary Free-air CO2 enrichment (FACE) experiments allow study of the effects of elevated [CO2] on plants and ecosystems grown under natural conditions without enclosure. Data from 120 primary, peer-reviewed articles describing physiology and production in the 12 large-scale FACE experiments (475–600 ppm) were collected and summarized using meta-analytic techniques. The results confirm some results from previous chamber experiments: light-saturated carbon uptake, diurnal C assimilation, growth and above-ground production increased, while specific leaf area and stomatal conductance decreased in elevated [CO2]. There were differences in FACE. Trees were more responsive than herbaceous species to elevated [CO2]. Grain crop yields increased far less than anticipated from prior enclosure studies. The broad direction of change in photosynthesis and production in elevated [CO2] may be similar in FACE and enclosure studies, but there are major quantitative differences: trees were more responsive than other functional types; C4 species showed little response; and the reduction in plant nitrogen was small and largely accounted for by decreased Rubisco. The results from this review may provide the most plausible estimates of how plants in their native environments and field-grown crops will respond to rising atmospheric [CO2]; but even with FACE there are limitations, which are also discussed.

3,140 citations

Book
01 Sep 2011
TL;DR: In this paper, the Ecosystem Concept is used to describe the Earth's Climate System and Geology and Soils, and the ecosystem concept is used for managing and sustaining ecosystems.
Abstract: I. CONTEXT * The Ecosystem Concept * Earth's Climate System * Geology and Soils * II. MECHANISMS * Terrestrial Water and Energy Balance * Carbon Input to Terrestrial Ecosystems * Terrestrial Production Processes * Terrestrial Decomposition * Terrestrial Plant Nutrient Use * Terrestrial Nutrient Cycling * Aquatic Carbon and Nutrient Cycling * Trophic Dynamics * Community Effects on Ecosystem Processes * III. PATTERNS * Temporal Dynamics * Landscape Heterogeneity and Ecosystem Dynamics * IV. INTEGRATION * Global Biogeochemical Cycles * Managing and Sustaining Ecosystem * Abbreviations * Glossary * References

3,086 citations

Journal ArticleDOI
TL;DR: The only way to eliminate Nr accumulation and stop the cascade is to convert Nr back to nonreactive N2, which leads to lag times in the continuation of the cascade.
Abstract: Human production of food and energy is the dominant continental process that breaks the triple bond in molecular nitrogen (N2) and creates reactive nitrogen (Nr) species. Circulation of anthropogenic Nr in Earth’s atmosphere, hydrosphere, and biosphere has a wide variety of consequences, which are magnified with time as Nr moves along its biogeochemical pathway. The same atom of Nr can cause multiple effects in the atmosphere, in terrestrial ecosystems, in freshwater and marine systems, and on human health. We call this sequence of effects the nitrogen cascade. As the cascade progresses, the origin of Nr becomes unimportant. Reactive nitrogen does not cascade at the same rate through all environmental systems; some systems have the ability to accumulate Nr, which leads to lag times in the continuation of the cascade. These lags slow the cascade and result in Nr accumulation in certain reservoirs, which in turn can enhance the effects of Nr on that environment. The only way to eliminate Nr accumul...

2,647 citations

Book ChapterDOI
TL;DR: The issues of nutrient-limited plant growth and nutrient uptake, with special emphasis on the importance of the uptake of nutrients in organic form—both by mycorrhizal and by non-mycorrhIZal plants—and the influence of symbiotic nitrogen fixation are treated.
Abstract: Publisher Summary In this chapter, the advances that have been made in understanding the ecology of the mineral nutrition of wild plants from terrestrial ecosystems have been reviewed. This chapter is organized along three lines. First, the issues of nutrient-limited plant growth and nutrient uptake, with special emphasis on the importance of the uptake of nutrients in organic form—both by mycorrhizal and by non-mycorrhizal plants—and the importance of symbiotic nitrogen fixation is treated. In addition, the influence of allocation patterns on mineral nutrient uptake is described. Next, a few of the nutritional aspects of leaf functioning and how nutrients are used for biomass production by the plant are explored. That is done by studying the nutrient use efficiency (NUE) of plants and the various components of NUE. Finally, the feedback of plant species to soil nutrient availability by reviewing patterns in litter decomposition and nutrient mineralization is investigated. The chapter concludes with a synthesis of the various aspects of the mineral nutrition of wild plants. The chapter ends with a conceptual description of plant strategies with respect to mineral nutrition.

2,552 citations