UNIVERSITY OF CALIFORNIA, MERCED Climatic Controls on Critical Zone Nutrient Biogeochemistry in Semiarid and Mediterranean Ecosystems A dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Environmental Systems by Morgan E. Barnes Committee in charge: Dr. Stephen C Hart, Co-Chair Dr. Asmeret Asefaw Berhe, Co-Chair Dr. Peggy O’Day Dr. Robert Young 2020 ã Morgan E. Barnes, 2020 All rights reserved The Dissertation of Morgan E. Barnes is approved, and it is acceptable in quality and form for publication on microfilm and electronically: _________________________________ Peggy O’Day _________________________________ Robert Young _________________________________ Asmeret Asefaw Berhe, Co-Chair _________________________________ Stephen C. Hart, Co-Chair University of California, Merced 2020 iii Table of Contents List of Tables...................................................................................................................vii List of Figures..................................................................................................................ix Acknowledgements..........................................................................................................xi Curriculum Vitae............................................................................................................xii Abstract of Dissertation..............................................................................................xviii 1 Introduction..............................................................................................................1 1.1 References.........................................................................................................3 2 Soil Phosphorus Stock and Speciation with Regolith Development: Does the Walker and Syers Model Apply to Dryland Climatic Gradients?...................... 9 2.1 Abstract............................................................................................................ 9 2.2 Introduction.................................................................................................... 10 2.3 Methods.......................................................................................................... 13 2.3.1 Study Sites.................................................................................... 13 2.3.2 Climate Parameters....................................................................... 14 2.3.3 Field Collection............................................................................. 14 2.3.4 Laboratory Analyses..................................................................... 15 2.3.5 Chemical Index of Weathering..................................................... 15 2.3.6 Phosphorus Stock.......................................................................... 16 2.3.7 Phosphorus Speciation.................................................................. 17 2.3.7.1 XANES............................................................................. 17 2.3.7.2 31P NMR............................................................................ 18 2.3.8 Statistical Analyses....................................................................... 20 2.4 Results............................................................................................................. 21 2.4.1 Changes in Weathering Intensity with Climate and Depth........... 21 2.4.2 Changes in P Concentration and stock with Climate and Deptth..21 2.4.3 XANES P Speciation.................................................................... 22 2.4.4 31P NMR Speciation...................................................................... 23 2.4.5 Changes in P Speciation with Climate.......................................... 24 2.4.6 Changes in P Speciation with Depth............................................. 24 2.4.7 Changes in P Speciation with Climate and Soil Properties.......... 25 2.5 Discussion....................................................................................................... 25 2.5.1 Climate-Driven Soil Weathering Intensity................................... 25 2.5.2 Walker and Syers Model Comparison.......................................... 27 2.5.2.1 P Concentration and Stock Changes with Climate........... 27 2.5.2.2 P Speciation Changes with Climate.................................. 29 2.5.3 P Speciation Changes with MAP, MAT, and Soil Properties....... 31 2.5.4 Implications for Ecosystem Productivity in a Changing Climate. 32 2.6 Summary......................................................................................................... 33 iv 2.7 References....................................................................................................... 34 2.8 Tables.............................................................................................................. 49 2.9 Figures............................................................................................................. 50 2.10 Supplementary Information...................................................................... 59 2.10.1 XANES......................................................................................... 59 2.10.2 31P NMR........................................................................................ 59 2.10.3 XANES Reference Compounds.................................................... 60 2.10.4 Supplementary Tables................................................................... 61 2.10.5 Supplementary Figures................................................................. 68 2.10.6 References..................................................................................... 75 3 Precipitation Controls Ecosystem C:N:P Stoichiometry Across Soil Horizons in Temperate Drylands.............................................................................................. 76 3.1 Abstract........................................................................................................... 76 3.2 Introduction..................................................................................................... 77 3.3 Methods........................................................................................................... 80 3.3.1 Study Sites.................................................................................... 80 3.3.2 Climate Parameters....................................................................... 81 3.3.3 Sample Collection......................................................................... 81 3.3.4 Laboratory Analyses..................................................................... 81 3.3.4.1 Soil Total Elemental Concertation.................................... 82 3.3.4.2 Microbial Biomass............................................................ 82 3.3.4.3 Soil Enzyme Activity........................................................ 83 3.3.4.4 Foliage and Root Total Elemental Concentration............ 83 3.3.5 Data Analyses............................................................................... 84 3.4 Results............................................................................................................. 85 3.4.1 Ecosystem C, N, and P Concentrations and Stoichiometry with MAP.............................................................................................. 85 3.4.2 Direct and Indirect Effects of MAP and MAT............................. 86 3.4.3 C, N, and P Concentrations and Stoichiometry with Depth......... 86 3.4.4 Comparison to Terrestrial Global Averages................................. 87 3.5 Discussion...................................................................................................... 87 3.6 Conclusion...................................................................................................... 92 3.7 References....................................................................................................... 92 3.8 Tables............................................................................................................ 107 3.9 Figures........................................................................................................... 110 3.10 Supplementary Tables............................................................................. 120 3.11 Supplementary Figures........................................................................... 125 4 The Median Isn’t the Message: Elucidating Nutrient Hot Spots and Hot Moments in a Sierra Nevada Forest Soil........................................................... 130 4.1 Abstract......................................................................................................... 130 4.2 Introduction................................................................................................... 131 4.3 Methods......................................................................................................... 133 4.3.1 Site Descriptions......................................................................... 133 4.3.2 Sampling Design......................................................................... 133 4.3.3 Laboratory Analyses................................................................... 135 v 4.3.4 Calculations................................................................................. 135 4.3.4.1 HS-HM Identification..................................................... 135 4.3.4.2 HS-HM Magnitude........................................................