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1. Diurnal patterns of productivity of arbuscular mycorrhizal fungi revealed with the Soil Ecosystem Observatory

   https://doi.org/10.1111/nph.12393  

   Hernandez, Rebecca R. ; Allen, Michael F. ( July 2013 , New Phytologist)

   Arbuscular mycorrhizal (AM) fungi are the most abundant plant symbiont and a major pathway of carbon sequestration in soils. However, their basic biology, including their activity throughout a 24‐h day : night cycle, remains unknown.

   We employed thein situSoil Ecosystem Observatory to quantify the rates of diurnal growth, dieback and net productivity of extra‐radicalAMfungi.AMfungal hyphae showed significantly different rates of growth and dieback over a period of 24 h and paralleled the circadian‐driven photosynthetic oscillations observed in plants.

   The greatest rates (and incidences) of growth and dieback occurred between noon and 18:00 h. Growth and dieback events often occurred simultaneously and were tightly coupled with soil temperature and moisture, suggesting a rapid acclimation of the external phase ofAMfungi to the immediate environment.

   Changes in the environmental conditions and variability of the mycorrhizosphere may alter the diurnal patterns of productivity ofAMfungi, thereby modifying soil carbon sequestration, nutrient cycling and host plant success.

    

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2. Ecotypic variation in forage nutrient value of a dominant prairie grass across a precipitation gradient

   https://doi.org/10.1111/grs.12131  

   Gibson, David J. ; Donatelli, Juliette M. ; AbuGhazaleh, Amer ; Baer, Sara G. ; Johnson, Loretta C. ( September 2016 , Grassland Science)

   Ecotypic variation in forage nutrient value of a dominant grassland species,Andropogon gerardiiVitman (big bluestem), was quantified across a longitudinal precipitation gradient of theUSGreat Plains. Ecotypic variation ofA. gerardiihas been documented across this gradient, but the extent to which forage nutrient value differs among ecotypes is poorly known. Seven indicators of forage nutrient value (neutral detergent fiber [NDF], acid detergent fiber [ADF],in‐vitrodry matter digestibility [IVDMD], crude protein [CP], crude fat [CF], ash content) and relative feed value [RFV] were examined in 12 populations representing four ecotypes corresponding with distinct climate regions: eastern Colorado, central Kansas, eastern Kansas and southern Illinois. Vegetative material ofA. gerardiiwas collected from each population in July 2010. A greenhouse study tested the effect of watering regime on seedlings of the ecotypes from three of the precipitation regions grown under controlled conditions. Forage nutrient value indicators nitrogen andCPincreased, andADFdecreased east to west, whileIVDMDdecreased across the gradient corresponding with less annual precipitation. The greenhouse experiment showed that sampling before and after water treatment affected forage nutrient value measurements, with the exception ofNDFandCF. Nutrient value was most related to soil moisture and phenology, with smaller differences among ecotypes. Nutrient value of populations from the southern Illinois ecotype changed the least in response to variation in soil moisture. The southern Illinois ecotype will likely maintain forge nutrient value under variable precipitation projected to occur with climate change better than the ecotypes from more westerly parts of the range ofA. gerardii.

    

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3. Enhanced gross primary production and evapotranspiration in juniper‐encroached grasslands

   https://doi.org/10.1111/gcb.14441  

   Wang, Jie ; Xiao, Xiangming ; Zhang, Yao ; Qin, Yuanwei ; Doughty, Russell B. ; Wu, Xiaocui ; Bajgain, Rajen ; Du, Ling ( October 2018 , Global Change Biology)

   Woody plant encroachment (WPE) into grasslands has been occurring globally and may be accelerated by climate change in the future. This land cover change is expected to alter the carbon and water cycles, but it remains uncertain how and to what extent the carbon and water cycles may change withWPEinto grasslands under current climate. In this study, we examined the difference of vegetation indices (VIs), evapotranspiration (ET), gross primary production (GPP), and solar‐induced chlorophyll fluorescence (SIF) during 2000–2010 between grasslands and juniper‐encroached grasslands. We also quantitatively assessed the changes ofGPPandETfor grasslands with different proportions of juniper encroachment (JWPE). Our results suggested thatJWPEincreased theGPP,ET, greenness‐relatedVIs, andSIFof grasslands. Mean annualGPPandETwere, respectively, ~55% and ~45% higher when grasslands were completely converted into juniper forests under contemporary climate during 2000–2010. The enhancement of annualGPPandETfor grasslands withJWPEvaried over years ranging from about +20%GPP(~+30% forET) in the wettest year (2007) to about twice as muchGPP(~+55% forET) in the severe drought year (2006) relative to grasslands without encroachment. Additionally, the differences inGPPandETshowed significant seasonal dynamics. During the peak growing season (May–August),GPPandETfor grasslands withJWPEwere ~30% and ~40% higher on average. This analysis provided insights into how and to what degree carbon and water cycles were impacted byJWPE, which is vital to understanding howJWPEand ecological succession will affect the regional and global carbon and water budgets in the future.

    

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4. Contrasting ecosystem CO 2 fluxes of inland and coastal wetlands: a meta‐analysis of eddy covariance data

   https://doi.org/10.1111/gcb.13424  

   Lu, Weizhi ; Xiao, Jingfeng ; Liu, Fang ; Zhang, Yue ; Liu, Chang'an ; Lin, Guanghui ( August 2016 , Global Change Biology)

   Wetlands play an important role in regulating the atmospheric carbon dioxide (CO₂) concentrations and thus affecting the climate. However, there is still lack of quantitative evaluation of such a role across different wetland types, especially at the global scale. Here, we conducted a meta‐analysis to compare ecosystemCO₂fluxes among various types of wetlands using a global database compiled from the literature. This database consists of 143 site‐years of eddy covariance data from 22 inland wetland and 21 coastal wetland sites across the globe. Coastal wetlands had higher annual gross primary productivity (GPP), ecosystem respiration (R_e), and net ecosystem productivity (NEP) than inland wetlands. On a per unit area basis, coastal wetlands provided largeCO₂sinks, while inland wetlands provided smallCO₂sinks or were nearlyCO₂neutral. The annualCO₂sink strength was 93.15 and 208.37 g C m⁻²for inland and coastal wetlands, respectively. AnnualCO₂fluxes were mainly regulated by mean annual temperature (MAT) and mean annual precipitation (MAP). For coastal and inland wetlands combined,MATandMAPexplained 71%, 54%, and 57% of the variations inGPP,R_e, andNEP, respectively. TheCO₂fluxes of wetlands were also related to leaf area index (LAI). TheCO₂fluxes also varied with water table depth (WTD), although the effects ofWTDwere not statistically significant.NEPwas jointly determined byGPPandR_efor both inland and coastal wetlands. However, theNEP/R_eandNEP/GPPratios exhibited little variability for inland wetlands and decreased for coastal wetlands with increasing latitude. The contrasting ofCO₂fluxes between inland and coastal wetlands globally can improve our understanding of the roles of wetlands in the global C cycle. Our results also have implications for informing wetland management and climate change policymaking, for example, the efforts being made by international organizations and enterprises to restore coastal wetlands for enhancing blue carbon sinks.

    

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5. Nutrients associated with terrestrial dissolved organic matter drive changes in zooplankton:phytoplankton biomass ratios in an alpine lake

   https://doi.org/10.1111/fwb.12847  

   Kissman, Carrie E. H. ; Williamson, Craig E. ; Rose, Kevin C. ; Saros, Jasmine E. ( November 2016 , Freshwater Biology)

   Dissolved organic matter (DOM) is increasing in many lakes due to climate change and other environmental forcing. A 21‐day microcosm experiment that manipulated terrestrialDOMwas used to determine the effect ofDOMon zooplankton:phytoplankton biomass ratios (z:p). We predicted that ifDOMadditions increase the amount of fixed carbon available for higher trophic levels through stimulation of the microbial loop and hence zooplankton, the z:p will increase. However, ifDOMadditions increase other nutrients besides fixed carbon, we predict stable or decreasing z:p due to nutrient stimulation of phytoplankton that subsequently enhances zooplankton.

   The effects of experimental additions of terrestrially derivedDOMon zooplankton, phytoplankton, z:p and zooplankton net grazing were assessed in microcosms (sealed bags) incubated in the epilimnion (shallow; 1.5 m) and hypolimnion (deep; 8.0 m) strata of an alpine lake.

   DOMaddition treatments (DOM+) had a 6.0‐ to 7.5‐fold increase in phytoplankton biomass relative to controls, but only a 1.3‐ to 1.5‐fold increase in zooplankton biomass, on day 21 of the experiment. The z:p was, thus, lower in theDOM+ treatments (ratios: 2.3 deep and 4.4 shallow) than in the control treatments (ratios: 13.4 deep and 17.5 shallow), providing evidence thatDOMadditions provide nutrient subsidies besides fixed carbon that stimulate phytoplankton biomass accumulation.

   The increase in zooplankton biomass during the experiment was similar in magnitude to the total amount of dissolved organic carbon (DOC) in theDOMadded in the sealed bags at the beginning of the experiment, which suggests zooplankton biomass stimulation due to increased phytoplankton biomass, and not fromDOMthrough the microbial loop, which would have greater trophic transfer losses. The consumer net grazing effect in theDOM+ treatments was reduced by 2.8‐fold in the shallow stratum and by 2.9‐fold in the deep stratum relative to the control treatments, indicating that zooplankton were unable to exert strong top–down control on the primary producers.

   The role of nutrients needs to be considered when examining the response of pelagic ecosystems to inputs of terrestrialDOM, especially in lakes with lowerDOCconcentrations.

    

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