Interactive effects of soils,local environmental conditions and herbivores on secondary chemicals in tallow tree

Plants produce secondary chemicals that may vary along with latitude due to changing abiotic and biotic stress gradients and local environmental conditions.Teasing apart the individual and combined effects of these different abiotic,such as soil nutrients,and biotic factors,such as soil biota and herbivores,on secondary chemicals is critical for understanding plant responses to changing environments.We conducted an experiment at different latitudes in China,using tallow tree(Triadica sebifera)seedlings sourced from a population at 31°N.These seedlings were cultivated in gardens located at low,middle and high latitudes,with either local soil or soil from the original seed collection site(origin soil).The seedlings were exposed to natural levels of aboveground herbivores or had them excluded.Plant secondary chemicals(both foliar and root),aboveground herbivores and soil characteristics were measured.Results showed that most leaf and root secondary metabolites depended on the interaction of the experimental site and soil type.Leaf and root phenolic and tannin concentrations were higher at the middle latitude site,especially in the origin soil.Root and foliar flavonoid concentrations increased when aboveground herbivores were excluded.Microbial communities depended strongly on soil treatment.The different responses of tannins versus flavonoids suggest that these two chemical classes differ in their responses to the varying abiotic and biotic factors in these sites along latitudes.Taken together,our results emphasize the importance of considering the interactive effects of local environmental conditions,soil properties and herbivory in regulating plant chemical defenses.

外来入侵物种在青藏高原的入侵性和生态影响不一致

在全球变化背景下,管控入侵物种是一项具有挑战性的工作。这主要由于从入侵物种的入侵性推断它们的生态危害存在很大的不确定性。更确切地说,入侵性和生态危害的关系可能依赖于所研究的生态系统,同时这种关系还没有在像青藏高原这样独特的高寒生态系统中被研究过。在这项研究中,我们在青藏高原东南部的一个样带上调查了32种入侵植物。我们将这些入侵物种的生态危害分解为分布范围(R)、局部丰度(A)和个体对本地植物群落的影响(E)3个组分,并研究了植物性状对这些组分的相对贡献。研究结果表明,入侵植物的入侵性(R×A)和其所产生的危害(R×A×E)没有相关性。这表明这些入侵植物的入侵性不能反映它们对本地群落生态危害的严重性。在青藏高原,R和A共同驱动了入侵性,而R单独驱动了生态危害。植物性状并没有通过这3个组分驱动入侵性和生态危害,只有果实类型(主要是浆果)影响了E。我们的结果表明,驱动入侵性和生态危害的组分的不匹配导致了入侵植物的入侵性不能反映它们的生态危害。因此,关于入侵物种的管控应该优先考虑那些分布广泛的物种或者已经被证实会对本地物种产生负面影响的物种。

Soil Respiration and Litter Decomposition Increased Following Perennial Forb Invasion into an Annual Grassland

Exotic plant invasions may alter ecosystem carbon processes, especially when native plants are displaced by plants of a different functional group. Forb invasions into grasslands are common, yet little is known about how they impact carbon cycling. We conducted a field study over 2 years from April 2010 to March 2012 in China to examine changes in soil respiration （Rsoil） following invasion of exotic perennial forb species （Alternanthera philoxeroides or Solidago canadensis） into an annual grassland dominated by a native annual graminoid （Eragrostis pilosa）. Measurements of Rsoil were taken once a week in stands of the native annual graminoid or one of the forb species using static chamber-gas chromatograph method. Aboveground litterfall of each of the three focal species was collected biweekly and litter decomposition rates were measured in a 6-month litterbag experiment. The monthly average and annual cumulative Rsoil increased following invasion by either forb species. The increases in cumulative Rsoil were smaller with invasion of Solidago （36%） than Alternanthera （65%）. Both invasive forbs were associated with higher litter quantity and quality （e.g., C：N ratio） than the native annum graminoid. Compared to the native annual graminoid, the invasive forbs Altevnanthera （155%） and Solidago （361%） produced larger amounts of more rapidly decomposing litter, with the litter decay constant k being 3.8, 2.0 and 1.0 for Alternanthera, Solidago and Eragrostis, respectively. Functional groups of the invasive plants and the native plants they replaced appear to be useful predictors of directions of changes in Rsoil, but the magnitude of changes in Rsoil seems to be sensitive to variations in invader functional traits.

UV-B has larger negative impacts on invasive populations of Triadica sebifera but ozone impacts do not vary

Aims Abiotic stresses may interact with each other to determine impacts on plants so that their combined impact is less than or more than additive.Increasing UV-B radiation and surface ozone(O3)are two major components of global change that may have such interactive impacts.Moreover,invasive and native populations of plants may respond differently to stresses as they can vary in primary and secondary metabolism.Methods Here,we conducted a factorial field experiment with open-top chambers assigned to an ozone treatment(ambient,100 ppb,or 150 ppb)and UV-B treatment(ambient or increased 20%).We grew seedlings of native and invasive populations of Triadica sebifera in these chambers for one growing season.Important Findings Invasive plants grew faster than native plants in ambient UV-B but they did not differ significantly in elevated UV-B.Litter production of invasive plants was especially sensitive to UV-B in a way that increased with UV-B for native plants but decreased for invasive plants which may be important for nutrient cycling.In ambient UV-B,total mass decreased as ozone increased.Total mass was lower with elevated UV-B but there was no additional impact of increasing ozone.Leaf area did not decrease with UV-B so SLA and LAR were lowest at ambient ozone levels.These results suggest that the effects of ozone will depend on UV-B conditions perhaps due to changes in foliar traits.The traits that allow invasive populations of plants to be successful invaders may make them especially sensitive to UV-B which may reduce their success in future climatic conditions.

Tallow tree allocates contrasting secondary chemicals in response to varying environments along elevational gradients

Aims Understanding how tree species regulate multiple types of secondary chemicals along elevational gradients is critical for elucidating the physiological and ecological strategies of plants in response to varying biotic and/or abiotic environments.This study aims to examine how Chinese tallow tree(Triadica sebifera)allocates resources to the production of different secondary chemicals in response to varying environments across elevational gradients.Methods We conducted field surveys of different herbivore feeding guilds and their damage rates on Chinese tallow trees along an elevational gradient in China and measured secondary chemicals(tannins and flavonoids)in damaged and undamaged leaves.Important Findings The odds of a leaf being damaged(chewing or scarring)decreased with elevation.Flavonoid concentrations increased with elevation in undamaged leaves but decreased with elevation in damaged leaves,with quercitrin contributing most strongly to this pattern,likely as results of plant responding to changing biotic or abiotic stresses along elevational gradients.Tannin concentrations did not vary with elevation,so undamaged leaves had relatively lower tannin to flavonoid ratios at high elevation than at low elevation.Our study reveals variation in herbivory and contrasting trends in plant secondary metabolism along an elevation gradient and highlights the importance of simultaneously considering multiple types of secondary chemicals in plant physiological and ecological strategies.

Differences in seed properties and germination between native and introduced populations of Triadica sebifera

Aims Seeds of many invasive plants germinate more quickly than those of native species,likely facilitating invasion success.Assessing the germination traits and seed properties simultaneously for introduced and native populations of an invasive plant is essential to understanding biological invasions.Here,we used Triadica sebifera as a study organism to examine intraspecific differences in seed germination together with seed characteristics.Methods We measured physical(volume,mass,coat hardness and coat thickness of seeds)and chemical(crude fat,soluble protein,sugar,gibberellins[GA]and abscisic acid[ABA]of kernels)properties of T.sebifera seeds collected in 2017 from 12 introduced(United States)populations and 12 native(China)populations and tested their germination rates and timing in a greenhouse experiment in China.Furthermore,we conducted an extra experiment in the United States using seeds collected in 2016 and 2017 to compare the effects of study sites(China vs.United States)and seed collection time(2016 vs.2017)on seed germination.Important Findings Seeds from the introduced range germinated faster than those from the native range.Physical and chemical measurements showed that seeds from the introduced range were larger,had higher GA concentrations and GA:ABA ratio,but lower crude fat concentrations compared to those from the native range.There were no significant differences in seed mass,coat hardness and coat thickness or kernel ABA,soluble protein or sugar concentrations between seeds from introduced vs.native ranges.Germination rates were correlated between United States and China greenhouses but germination rates for populations varied between collection years.Our results suggest that larger seeds and higher GA likely contribute to faster germination,potentially facilitating T.sebifera invasion in the introduced range.

Litter age interacted with N and P addition to impact soil N_(2)O emissions in Cunninghamia lanceolata plantations

Litter decomposition impacts carbon(C)and nutrient cycling.Nitrogen(N)and phosphorus(P)addition as well as litter age impact litter decomposition.Effects of nutrient addition and litter age on litter decomposition may impact emissions of soil nitrous oxide(N_(2)O),which is an important greenhouse gas.However,no study has examined the effects of interactions between litter age and nutrient addition on soil N_(2)O emissions,and explored the underlining mechanisms simultaneously,thus limiting our evaluation of litter decomposition effects on N_(2)O emissions.Litter with different age was collected from Cunninghamia lanceolata plantations experienced N and P addition treatments to examine the effects of nutrient addition and litter age on N_(2)O emissions by incubation study.Litter age generally increased N_(2)O emissions via a decrease in litter C:N ratio.While P addition decreased N_(2)O emissions,N addition increased them mainly by positive effects on soil enzymes as indicated by microbial functional genes associated with N_(2)O production and negative effects on litter C:N ratio.Litter age and nutrient addition interacted to impact soil N_(2)O emissions.In future forest management,both nutrient addition and litter age should be considered in evaluation of management effects on N_(2)O emissions,especially thinning or selectively cutting involving litter input with different age.

The effects of elevated ozone and CO_(2) on growth and defense of native,exotic and invader trees

Aims Elevated ozone and CO_(2) can differentially affect the performance of plant species.Variation among native,exotic and invader spe-cies in their growth and defense responses to CO_(2) and ozone may shape CO_(2) and ozone effects on invasions,perhaps in part also due to variation between native and invasive populations of invaders.Methods We manipulated ozone(control or 100 ppb)and CO_(2)(ambient or 800 ppm)in a factorial greenhouse experiment in replicated cham-bers.We investigated growth and defense(tannins)of seedlings of Triadica sebifera from invasive(USA)and native(China)populations and pairs of US and China tree species within three genera(Celtis,Liquidambar and Platanus).Important Findings Overall,ozone reduced growth in ambient CO_(2) but elevated CO_(2) limited this effect.T.sebifera plants from invasive populations had higher growth than those from native populations in control con-ditions or the combination of elevated CO_(2) and ozone in which invasive populations had greater increases in growth.Their perfor-mances were similar in elevated CO_(2) because native populations were more responsive and their performances were similar with elevated ozone because invasive populations were more suscep-tible.Compared to other species,T.sebifera had high growth rates but low levels of tannin production that were insensitive to vari-ation in CO_(2) or ozone.Both China and US Platanus plants reduced tannins with increased CO_(2) and/or ozone and US Liquidambar plants increased tannins with the combination of elevated CO_(2) and ozone.The growth results suggest that intraspecific variation in T.sebifera will reduce the effects of CO_(2) or ozone alone on inva-sions but increase their combined effects.The tannin results suggest that defense responses to CO_(2) and ozone will be variable across native and exotic species.The effects of CO_(2) and ozone on growth and defense of native and exotic species indicate that the benefit or harm to species from these global change drivers is an idiosyncratic combination of species origin and genus.