Response of nitrogen mineralization dynamics and biochemical properties to litter amendments to soils of a poplar plantation

Understanding the impact of plant litters on soil nitrogen （N） dynamics could facilitate development of management strategies that promote plantation ecosystem function. Our objective was to evaluate the effects of different litter types on N mineralization and availability, microbial biomass, and activities of L-asparaginase and odiphenol oxidase （o-DPO） in soils of a poplar （Populus deltoides） plantation through 24 weeks of incubation experiments. The tested litters included foliage （F）, branch （B）, or root （R） of poplar trees, and understory vegetation （U） or a mixture of F, B, and U （M）. Litter amendments led to rapid N immobilization during the first 4 weeks of incubation, while net N mineralization was detected in all tested soils from 6 to 24 weeks of incubation, with zero-order reaction rate constants （k） ranging from 7.7 to 9.6 mg N released kg-1 soil wk-1. Moreover, litter addition led to increased （C） 49-128% and increased microbial biomass carbon MBC：MBN ratio by 5-92%, strengthened activities of L-aspaxaginase and o-DPO by 14-74%; Up to about 37 kg N ha-1 net increase in mineralized N in litter added soils during 24 weeks of incubation suggests that adequate poplar and understory litter management could lead to reduced inputs while facilitate sustainable and economic viable plantation production.

Dynamics of iron and aluminum storages in a subtropical forest headwater stream

The forest headwater streams are important hubs for connecting terrestrial and aquatic ecosystems,with plant litter and sediments as the major carriers for material migrations;however,until now we knew little about the dynamics of trace elements such as iron(Fe)and aluminum(Al)in forest headwater streams.Here,we quantitatively identified the spatiotemporal dynamics of Fe and Al storages in plant litter and sediments and their influencing factors in a subtropical forest headwater stream,and assessed the potential pollution risk.The results showed that:(1)the mean concentrations of Fe and Al in plant litter(sediments)were 5.48 and 8.46(7.39 and 47.47)g·kg^(-1),and the mean storages of Fe and Al in plant litter(sediments)were 0.26 and 0.43(749.04 and 5030.90)g·m^(-2),respectively;(2)the storages of Fe and Al in plant litter and sediments significantly fluctuated from January to December,and showed a decreasing pattern from the source to mouth;and(3)storages of Fe and Al had no significant correlation with riparian forest type and the present of tributary and the Fe and Al storages in plant litter were mainly affected by water temperature and water alkalinity,and their storages in sediments were mainly affected by water temperature and frequency of rainfall;and(4)there were no anthropogenic pollution in Fe and Al in the forest headwater stream.Our study revealed the primary factors of concentrations and storages of Fe and Al in plant litter and sediments in a forest headwater stream,which will improve our understanding of the role of headwater streams in forest nutrient storage and cycling along with hydrological processes.

Pool of Biological Resources for Potential Applications in Solid State Fermentation Obtained from a Forest Plantation of Pinus pseudostrobus Lindl, Mexico

A forest plantation, product of the reforestation of pine trees, represented a pool of biological resources for the implementation of a solid state fermentation process. The trees were identified as Pinus pseudostrobus Lindl from which lignocellulosic material in the form of pine needles was collected. Soil fungi, responsible for plant litter decomposition, were cultured at laboratory conditions and tested for their ability to grow on cellulose and hemicellulose as the sole carbon sources. A fungal strain, belonging to the genus Penicillium, was selected for growing it on pine needles as the substrate in a solid state culture. After following the culture for six days, the newly isolated strain exhibited a much higher capacity for spore production and holocellulose degradation, compared to a purchased strain of Penicillium chrysogenum and two control conditions. This work marks the beginning of future studies focused on commercial applications and represents the first report of a biotechnological process based on pine needles and their degradation by an ascomycetes species belonging to the genus Penicillium.

Changes in soil microbial biomass and community structure with addition of contrasting types of plant litter in a semiarid grassland ecosystem

Aims Elevated atmospheric CO_(2)has the potential to enhance the net primary productivity of terrestrial ecosystems.However,the role of soil microorganisms on soil C cycling following this increased available C remains ambiguous.This study was conducted to determine how quality and quantity of plant litter inputs would affect soil microorganisms and consequently C turnover.Methods Soil microbial biomass and community structure,bacterial community-level physiological profile,and CO_(2)emission caused by different substrate C decomposition were investigated using techniques of biological measurements,chemical and stable C isotope analysis,and BIOLOG-ECO microplates in a semiarid grassland ecosystem of northern China in 2006 and 2007 by mixing three contrasting types of plant materials,C_(3)shoot litter(SC_(3)),C_(3)root litter(RC_(3)),and C4 shoot litter(SC4),into the 10-to 20-cm soil layer at rates equivalent to 0(C0),60(C60),120(C120)and 240 g C m
2(C240).Important Findings Litter addition significantly enriched soil microbial biomass C and N and resulted in changes in microbial structure.Principal component analysis of microbial structure clearly differentiated among zero addition,C_(3)-plant-derived litter,and C4-plant-derived litter and among shoot-and root-derived litter of C_(3)plants;soilmicroorganismsmainly utilized carbohydrates without litter addition,carboxylic acids with C_(3)-plant-derived litter addition and amino acidswith C4-plant-derived litter addition.We also detected stimulated decomposition of older substratewith C4-plant-derived litter inputs.Our results showthat both quality and quantity of belowground litter are involved in affecting soil microbial community structure in semiarid grassland ecosystem.

Influence of evenness on the litter-species richness-decomposition relationship in Mediterranean grasslands

Aims Human impacts on natural ecosystems induce changes in their functioning through alterations in species richness,composition and evenness of plant communities.Most litter diversity–decomposition processes studies have only manipulated species richness,ignoring the role of evenness.Here,results from a field litterbag experiment are presented to test whether changes in evenness of species distribution in litter mixtures affected the strength of the litter-species richness–decomposition relationship.Methods Ten herbaceous species abundant in Mediterranean grassland communities and representative of different genera and functional groups were used.Species richness was directly manipulated to produce litter mixtures of three and six plant species,as well as litter of each individual species used.Each level of species richness was replicated several times such that each repeat had a different species composition.Three-and six-species litter mixtures were also treated to vary in evenness(three levels).Decomposition rate was assessed by percentage dry weight loss over the 90 days of the experiment.Important Findings Decomposition rate was positively related to the linear increase in litter-species richness and was affected by the composition of the litter-species mixture.Decomposition rates differed significantly between evenness treatments and moreover,the strength of the positive relationship between litter-species richness and decomposition rate decreased notably in the low-evenness treatment.The effects of evenness on decomposition rate,at different richness levels,were partially explained by the differences in the initial litter mixture’s carbon-to-nitrogen ratio within them.This study reveals that shortterm decomposition rate is positively affected by both components of Mediterranean grassland litter-species diversity.

Stream-dwelling fungal decomposer communities along a gradient of eutrophication unraveled by 454 pyrosequencing

Microbial decomposers,especially a fungal group called aquatic hyphomycetes,play a critical role in processing plant litter in freshwaters by increasing its palatability to invertebrate shredders.Traditionally,communities of aquatic hyphomycetes have been assessed through the identification of spores,which misses non-sporulating taxa.Among new technologies,454 pyrosequencing stands out as most promising for large-scale species identification.However,very few attempts have been made to validate its effectiveness for assessing the diversity of stream-dwelling fungal communities.We attempted to gain greater insight into the diversity of aquatic fungal communities in streams exposed to various degrees of eutrophication by using the 454 pyrosequencing technology.A total of 173,889 ITS2 pyrosequencing reads with hits for fungi were obtained from the 5 investigated streams.The majority of operational taxonomic units(OTUs)belonged to Ascomycota and the identification to the genus level was achieved for 169 OTUs.Of the total,135,257 reads(ca.78%)showed close affinities to aquatic hyphomycete species.Pyrosequencing showed declining fungal diversity in the most eutrophic streams,which was congruent with a reduced diversity found through spore identification.Dominance patterns revealed by connecting representative OTUs to ITS sequences from aquatic hyphomycetes were similar to those determined by traditional spore identification techniques.However,454 pyrosequencing provided a more comprehensive view of fungal diversity;it captured almost twice as many taxa as spore counts.This study vali-dates the effectiveness of 454 pyrosequencing for surveying the diversity of stream-dwelling fungal decomposer communities.Its application may accelerate the use of these communities for monitoring the integrity of freshwaters.