Bork, E. W.

Cahill, J. F.

Chang, S. X.

Proctor, H. C.

Wilson, S. D.

English

University of Kentucky

University of Kentucky UKnowledge International Grassland Congress Proceedings 21st International Grassland Congress / 8th International Rangeland Congress Interactions between Defoliation, Warming, and Drought in a Native Northern Grassland in Alberta, Canada J. F. Cahill University of Alberta, Canada E. W. Bork University of Alberta, Canada S. X. Chang University of Alberta, Canada H. C. Proctor University of Alberta, Canada S. D. Wilson University of Regina, Canada Follow this and additional works at: https://uknowledge.uky.edu/igc  Part of the Plant Sciences Commons, and the Soil Science Commons This document is available at https://uknowledge.uky.edu/igc/21/8-1/5 The 21st International Grassland Congress / 8th International Rangeland Congress took place in Hohhot, China from June 29 through July 5, 2008. Proceedings edited by Organizing Committee of 2008 IGC/IRC Conference Published by Guangdong People's Publishing House This Event is brought to you for free and open access by the Plant and Soil Sciences at UKnowledge. It has been accepted for inclusion in International Grassland Congress Proceedings by an authorized administrator of UKnowledge. For more information, please contact UKnowledge@lsv.uky.edu. 　 Multifunctional Grasslands in a Changing World 　 Volume Ⅰ 　 瞯 ]873　 瞯Grasslands/Rangelands Resources and Ecology ——— Climate Change and Impact on Grasslands/RangelandsInteractions between defoliation , warming , and drought in a native northern grassland inAlberta , CanadaJ .F . Cahill1 , E .W . Bork 2 , S .X . Chang3 , H .C . Proctor 1 , S .D . W ilson41 Department o f Biological Sciences , University o f A lberta , Edmonton , A lberta , Canada T6G 2E9 , E‐mail : j c .cahill＠ualberta .ca , 2 Department o f A griculture , Food and Nutritional Sciences , University o f A lberta , Edmonton , A lberta ,Canada T6G 2P5 , 3 Dep artment o f Renew able Resources , University o f A lberta , Edmonton , A lberta , Canada T6G 2E3 , 4Department o f Biology , University o f Regina , Regina , Saskatchew an . Canada S4S 0A2Key words : climate change , carbon and nitrogen fluxes , rangeland function , plant community compositionIntroduction Canada contains ２２ M ha of land dedicated to range and forage production , where the majority of C is produced andstored belowground ( Steinaker and Wilson ２００５) . A healthy rangeland stores equivalent C mass per ha as forested ecosystems ,and because this C is primarily belowground , it is at lower risk of release during fires . Consequently , healthy grasslandecosystems may play a significant role in mitigating global climate change . Overgrazing has been documented on up to half of allrangelands in the region , and through a potential decline in root biomass , may reduce soil carbon storage . Coupled withpredictions of climate change , these disturbances are likely to further change range health . Improvement of rangeland conditionprovides direct economic benefits , and because native rangelands store more C than annual croplands , this should also lead toincreased C storage , with implications for feedback to climate systems both locally and globally . We however have a relativelypoor understanding of how range management practices such as grazing intensity and the predicted future climate ( which maybecome warmer and drier in some regions) interact to affect the function of the native northern temperate grassland ecosystems( Zhou et al . ２００６) .Materials and methods We used a randomized complete block design with ５ blocks for a ２ ( warming vs . non‐warming ) x ３ ( twointensities of clipping to simulate grazing vs . no clipping ) × ２ ( drought vs no drought) factorial experiment for the full studywhich began in spring ２００７ . The warming treatment was applied using open‐top chambers ( OTC , ４０ cm high and ２ m indiameter) that can increase the near surface air temperature by ２‐４ ℃ . As the size of OTCs precluded the use of actual ungulategrazing , simulated grazing was achieved through manual clipping of vegetation in and around ( buffer ) each plot . Simulatedgrazing of low and high intensity treatments consisted of clipping to a stubble height of approximately ７ .５ m and ２ .５ cm , whichroughly corresponded to the removal of ３０％ and ８０％ of standing current annual biomass . Drought treatments were appliedusing shelters that intercepted ７０％ of natural precipitation . In each plot , near surface air temperature , soil temperature andsoil moisture content were measured continuously , plant community compositional responses were assessed at peak biomass ,soil N availabilities were measured using the Plant Root Simulators ( PRS) probes , and fluxes of CO２ and N２O were determinedusing a static gas chamber‐gas chromatograph system . Rates of N mineralization were determined using the buried‐bag method .Microbial biomass C and N were measured using the fumigation‐extraction method . Soil microbial functional diversity andcomposition were studied using the Biolog and phospholipid fatty acid ( PLFA ) techniques . A mini‐rhizotron was used toestimate belowground primary productivity and carbon flow .Results Preliminary results from a pilot study conducted in ２００６‐０７ showed that the combined warming by defoliation treatmentproduced an additional increase in soil (０‐５ cm) temperature of about ２ °C relative to all other treatments during August ２００６ .Soil moisture content exhibited high temporal variability throughout the growing season of ２００６ likely reflecting fluctuations inrainfall during this period . Plant community species richness and diversity remained relatively stable throughout the growingseason in ２００６ and differences among the treatments were relatively minor . Due to warming , rough fescue ( Festuca hallii )increased in canopy cover , but towards the end of the growing season had fewer tillers . Warming also altered the morphology ofmany‐flowered aster ( A ster f alcatus ) and bastard toadflax ( Commandra umbellata) . Few treatment effects were observed forsoil microbial biomass C and N , but both parameters had large seasonal variations . In June ２００６ , the warming treatmentresulted in greater ammonification , and defoliation decreased the net nitrification rates , both in the ０‐５ cm soil layer .Nitrification was the dominant process in the transformation of organic N to inorganic form in the system . We have so farobserved few other significant differences caused by the treatments .Conclusions These northern temperate fescue grasslands appear rather resilient to changes in the climatic conditions andmanagement practices in the first year of a pilot study . However , we predict that over the longer‐term ( e .g . , up to threeyears) , the grassland ecosystem under study will respond to sustained changes in climate and management treatments in a muchmore significant way , as changes in plant grow th will have cascading effects on ecosystem processes .ReferencesSteinaker DF , Wilson SD ( ２００５) Belowground litter contributions to nitrogen cycling at a northern grassland‐forest boundary .Ecology ８６ : ２８２５‐２８３３ .Zhou XH , Sherry RA , An Y , Wallace LL , Luo YQ ( ２００６ ) Main and interactive effects of warming , clipping , and doubledprecipitation on soil CO２ efflux in a grassland ecosystem . Global Biogeochemical Cycles ２０ , GB１００３ .

Interactions between Defoliation, Warming, and Drought in a Native Northern Grassland in Alberta, Canada

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Interactions between Defoliation, Warming, and Drought in a Native Northern Grassland in Alberta, Canada

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