03239nas a2200313 4500008004100000245011900041210006900160300001400229490000700243520231400250100002002564700001702584700001402601700002002615700002402635700001602659700001702675700002402692700001702716700001602733700001502749700001902764700001502783700001502798700001702813700001702830700001602847856006202863 2017 eng d00aPushing precipitation to the extremes in distributed experiments: recommendations for simulating wet and dry years0 aPushing precipitation to the extremes in distributed experiments a1774-17820 v233 a

Intensification of the global hydrological cycle, ranging from larger individual precipitation events to more extreme multiyear droughts, has the potential to cause widespread alterations in ecosystem structure and function. With evidence that the incidence of extreme precipitation years (defined statistically from historical precipitation records) is increasing, there is a clear need to identify ecosystems that are most vulnerable to these changes and understand why some ecosystems are more sensitive to extremes than others. To date, opportunistic studies of naturally occurring extreme precipitation years, combined with results from a relatively small number of experiments, have provided limited mechanistic understanding of differences in ecosystem sensitivity, suggesting that new approaches are needed. Coordinated distributed experiments (CDEs) arrayed across multiple ecosystem types and focused on water can enhance our understanding of differential ecosystem sensitivity to precipitation extremes, but there are many design challenges to overcome (e.g., cost, comparability, standardization). Here, we evaluate contemporary experimental approaches for manipulating precipitation under field conditions to inform the design of ‘Drought-Net’, a relatively low-cost CDE that simulates extreme precipitation years. A common method for imposing both dry and wet years is to alter each ambient precipitation event. We endorse this approach for imposing extreme precipitation years because it simultaneously alters other precipitation characteristics (i.e., event size) consistent with natural precipitation patterns. However, we do not advocate applying identical treatment levels at all sites – a common approach to standardization in CDEs. This is because precipitation variability varies >fivefold globally resulting in a wide range of ecosystem-specific thresholds for defining extreme precipitation years. For CDEs focused on precipitation extremes, treatments should be based on each site's past climatic characteristics. This approach, though not often used by ecologists, allows ecological responses to be directly compared across disparate ecosystems and climates, facilitating process-level understanding of ecosystem sensitivity to precipitation extremes.

1 aKnapp, Alan, K.1 aAvolio, M.L.1 aBeier, C.1 aCarroll, C.J.W.1 aCollins, Scott., L.1 aDukes, J.S.1 aFraser, L.H.1 aGriffin-Nolan, R.J.1 aHoover, D.L.1 aJentsch, A.1 aLoik, M.E.1 aPhillips, R.P.1 aPost, A.K.1 aSala, O.E.1 aSlette, I.J.1 aYahdjian, L.1 aSmith, M.D. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.1350401778nas a2200325 4500008004100000245012500041210006900166300001300235490000700248520081800255100001701073700001601090700001801106700001601124700002201140700001701162700001701179700001801196700002401214700001601238700002001254700001301274700001301287700001201300700001601312700001601328700001801344700001901362856007101381 2013 eng d00aCoordinated distributed experiments: an emerging tool for testing global hypotheses in ecology and environmental science0 aCoordinated distributed experiments an emerging tool for testing a147 -1550 v113 a

There is a growing realization among scientists and policy makers that an increased understanding of today's environmental issues requires international collaboration and data synthesis. Meta-analyses have served this role in ecology for more than a decade, but the different experimental methodologies researchers use can limit the strength of the meta-analytic approach. Considering the global nature of many environmental issues, a new collaborative approach, which we call coordinated distributed experiments (CDEs), is needed that will control for both spatial and temporal scale, and that encompasses large geographic ranges. Ecological CDEs, involving standardized, controlled protocols, have the potential to advance our understanding of general principles in ecology and environmental science.

1 aFraser, L.H.1 aHenry, H.A.1 aCarlyle, C.N.1 aWhite, S.R.1 aBeierkuhnlein, C.1 aCahill, J.F.1 aCasper, B.B.1 aCleland, E.E.1 aCollins, Scott., L.1 aDukes, J.S.1 aKnapp, Alan, K.1 aLind, E.1 aLong, R.1 aLuo, Y.1 aReich, P.B.1 aSmith, M.D.1 aSternberg, M.1 aTurkington, R. uhttps://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/11027901977nas a2200265 4500008004100000245015800041210006900199300001500268490000700283520111400290100002001404700002001424700001601444700001501460700001701475700001801492700001901510700001801529700001601547700001701563700001901580700001901599700001601618856007701634 2012 eng d00aThe effect of experimental warming and precipitation change on proteolytic enzyme activity: positive feedbacks to nitrogen availability are not universal0 aeffect of experimental warming and precipitation change on prote a2617 -26250 v183 a

Nitrogen regulates the Earth's climate system by constraining the terrestrial sink for atmospheric CO2. Proteolytic enzymes are a principal driver of the within-system cycle of soil nitrogen, yet there is little to no understanding of their response to climate change. Here, we use a single methodology to investigate potential proteolytic enzyme activity in soils from 16 global change experiments. We show that regardless of geographical location or experimental manipulation (i.e., temperature, precipitation, or both), all sites plotted along a single line relating the response ratio of potential proteolytic activity to soil moisture deficit, the difference between precipitation and evapotranspiration. In particular, warming and reductions in precipitation stimulated potential proteolytic activity in mesic sites – temperate and boreal forests, arctic tundra – whereas these manipulations suppressed potential activity in dry grasslands. This study provides a foundation for a simple representation of the impacts of climate change on a central component of the nitrogen cycle.

1 aBrozostek, E.R.1 aBlair, John, M.1 aDukes, J.S.1 aFrey, S.D.1 aHobbie, S.E.1 aMelillo, J.M.1 aMitchell, R.J.1 aPendall, E.S.1 aReich, P.B.1 aShaver, G.R.1 aStefanskii, A.1 aTjoelker, M.G.1 aFinzi, A.C. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2486.2012.02685.x02905nas a2200313 4500008004100000245013800041210006900179300001500248490000700263520198500270100001202255700001502267700001702282700001702299700001302316700001302329700001502342700001402357700001402371700001502385700001602400700001502416700001702431700002002448700001502468700001602483700001502499856007702514 2008 eng d00aModeled interactive effects of precipitation, temperature, and CO2 on ecosystem carbon and water dynamics in different climatic zones0 aModeled interactive effects of precipitation temperature and CO2 a1986 -19990 v143 a

Interactive effects of multiple global change factors on ecosystem processes are complex. It is relatively expensive to explore those interactions in manipulative experiments. We conducted a modeling analysis to identify potentially important interactions and to stimulate hypothesis formulation for experimental research. Four models were used to quantify interactive effects of climate warming (T), altered precipitation amounts [doubled (DP) and halved (HP)] and seasonality (SP, moving precipitation in July and August to January and February to create summer drought), and elevated [CO2] (C) on net primary production (NPP), heterotrophic respiration (Rh), net ecosystem production (NEP), transpiration, and runoff. We examined those responses in seven ecosystems, including forests, grasslands, and heathlands in different climate zones. The modeling analysis showed that none of the three-way interactions among T, C, and altered precipitation was substantial for either carbon or water processes, nor consistent among the seven ecosystems. However, two-way interactive effects on NPP, Rh, and NEP were generally positive (i.e. amplification of one factor's effect by the other factor) between T and C or between T and DP. A negative interaction (i.e. depression of one factor's effect by the other factor) occurred for simulated NPP between T and HP. The interactive effects on runoff were positive between T and HP. Four pairs of two-way interactive effects on plant transpiration were positive and two pairs negative. In addition, wet sites generally had smaller relative changes in NPP, Rh, runoff, and transpiration but larger absolute changes in NEP than dry sites in response to the treatments. The modeling results suggest new hypotheses to be tested in multifactor global change experiments. Likewise, more experimental evidence is needed for the further improvement of ecosystem models in order to adequately simulate complex interactive processes.

1 aLuo, Y.1 aGerten, D.1 aLe Maire, G.1 aParton, W.J.1 aWeng, E.1 aZhou, X.1 aKeough, C.1 aBeier, C.1 aCiais, P.1 aCramer, W.1 aDukes, J.S.1 aEmmett, B.1 aHanson, P.J.1 aKnapp, Alan, K.1 aLinder, S.1 aNepstad, D.1 aRustad, L. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2486.2008.01629.x02411nas a2200313 4500008004100000245010500041210006900146300001000215490000700225520152600232100001501758700001201773700001701785700001701802700001501819700001301834700001401847700001401861700001501875700001601890700001501906700001701921700002001938700001501958700001601973700001501989700001602004856007702020 2008 eng d00aModelled effects of precipitation on ecosystem carbon and water dynamics in different climatic zones0 aModelled effects of precipitation on ecosystem carbon and water  a1 -150 v143 a

The ongoing changes in the global climate expose the world's ecosystems not only to increasing CO2 concentrations and temperatures but also to altered precipitation (P) regimes. Using four well-established process-based ecosystem models (LPJ, DayCent, ORCHIDEE, TECO), we explored effects of potential P changes on water limitation and net primary production (NPP) in seven terrestrial ecosystems with distinctive vegetation types in different hydroclimatic zones. We found that NPP responses to P changes differed not only among sites but also within a year at a given site. The magnitudes of NPP change were basically determined by the degree of ecosystem water limitation, which was quantified here using the ratio between atmospheric transpirational demand and soil water supply. Humid sites and/or periods were least responsive to any change in P as compared with moderately humid or dry sites/periods. We also found that NPP responded more strongly to doubling or halving of P amount and a seasonal shift in P occurrence than that to altered P frequency and intensity at constant annual amounts. The findings were highly robust across the four models especially in terms of the direction of changes and largely consistent with earlier P manipulation experiments and modelling results. Overall, this study underscores the widespread importance of P as a driver of change in ecosystems, although the ultimate response of a particular site will depend on the detailed nature and seasonal timing of P change.

1 aGerten, D.1 aLuo, Y.1 aLe Maire, G.1 aParton, W.J.1 aKeough, C.1 aWeng, E.1 aBeier, C.1 aCiais, P.1 aCramer, W.1 aDukes, J.S.1 aEmmett, B.1 aHanson, P.J.1 aKnapp, Alan, K.1 aLinder, S.1 aNepstad, D.1 aRustad, L.1 aSowerby, A. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2486.2008.01651.x