** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** THE SOUTHWESTERN UNITED STATES IS EXPECTED TO UNDERGO MORE FREQUENT AND SEVERE DROUGHT WITH CLIMATE CHANGE. THE AMOUNT OF PLANT GROWTH THAT CAN OCCUR IN RANGELANDS EXPERIENCING DROUGHT MAY BE HIGHLY DEPENDENT ON NITROGEN INPUTS. MOST NEW NITROGEN NATURALLY ENTERING AGROECOSYSTEMS (THAT IS, NOT FROM FERTILIZER ADDITIONS) IN THE SOUTHWESTERN UNITED STATES COMES FROM NITROGEN-FIXING PLANTS, PARTICULARLY TREES SUCH AS MESQUITE (PROSOPIS GLANDULOSA). NITROGEN IS CRITICAL FOR PLANT GROWTH, PARTICULARLY WITH DROUGHT, AS HIGHER NITROGEN CONTENT INCREASES WATER USE EFFICIENCY OF PLANTS. WE WILL CONDUCT TWO GREENHOUSE EXPERIMENTS COMBINED WITH FIELD SAMPLING TO UNDERSTAND THE EFFECTS OF DROUGHT ON RATES OF NITROGEN FIXATION INPUTS TO RANGELANDS, CONNECTING NITROGEN-FIXING TREES TO DROUGHT TOLERANCE TO RANGELAND ECOSYSTEM SERVICES. THE FIRST GREENHOUSE EXPERIMENT WILL EXAMINE HOW DIFFERENT ENVIRONMENTAL FACTORS (DROUGHT, LIGHT, AND NITROGEN) CONTROL HOW MUCH NITROGEN IS FIXED BY TREE SPECIES ADAPTED TO DIFFERENT LEVELS OF ARIDITY. NEXT, A FIELD STUDY WILL EXAMINE THE LINKS BETWEEN NITROGEN FIXATION BY MESQUITE TREES AND ECOSYSTEM SERVICES (FORAGE QUALITY, HERBACEOUS BIODIVERSITY, SOIL CARBON) ACROSS A RAINFALL GRADIENT IN TEXAS. THE SECOND GREENHOUSE EXPERIMENT WILL EXAMINE HOW SHORT- VS LONG-TERM CHANGES IN PLANTS AND SOIL BACTERIA CONTROL THE RATES OF NITROGEN FIXATION IN RESPONSE TO DROUGHT, USING MESQUITE SEEDS AND SOILS COLLECTED FROM RANGELAND SITES ACROSS THE RAINFALL GRADIENT. OUR OVERALL GOAL IS TO DEVELOP A PREDICTIVE UNDERSTANDING OF HOW DROUGHT WILL IMPACT NITROGEN FIXATION AND ECOSYSTEM SERVICES (FORAGE QUALITY, HERBACEOUS BIODIVERSITY, SOIL CARBON) ACROSS RANGELANDS IN THE SOUTHWESTERN UNITED STATES.@FONT-FACE{PANOSE-1:2 4 5 3 5 4 6 3 2 4;MSO-FONT-CHARSET:0;MSO-GENERIC-MSO-FONT-PITCH:VARIABLE;MSO-FONT-SIGNATURE:-536870145 1107305727 0 0 415 0;}@FONT-FACE{PANOSE-1:2 15 5 2 2 2 4 3 2 4;MSO-FONT-CHARSET:0;MSO-GENERIC-MSO-FONT-PITCH:VARIABLE;MSO-FONT-SIGNATURE:-536859905 -1073732485 9 0 511 0;}P.MSONORMAL, LI.MSONORMAL, DIV.MSONORMAL{MSO-STYLE-UNHIDE:NO;MSO-STYLE-QFORMAT:YES;MSO-STYLE-PARENT:;MARGIN:0IN;MSO-PAGINATION:WIDOW-ORPHAN;;MSO-ASCII-MSO-ASCII-THEME-FONT:MINOR-LATIN;MSO-FAREAST-MSO-FAREAST-THEME-FONT:MINOR-LATIN;MSO-HANSI-MSO-HANSI-THEME-FONT:MINOR-LATIN;MSO-BIDI-MSO-BIDI-THEME-FONT:MINOR-BIDI;MSO-FONT-KERNING:1.0PT;MSO-LIGATURES:STANDARDCONTEXTUAL;}P{MSO-STYLE-NOSHOW:YES;MSO-STYLE-PRIORITY:99;MSO-MARGIN-TOP-ALT:AUTO;MARGIN-RIGHT:0IN;MSO-MARGIN-BOTTOM-ALT:AUTO;MARGIN-LEFT:0IN;MSO-PAGINATION:WIDOW-ORPHAN;;MSO-FAREAST-}.MSOCHPDEFAULT{MSO-STYLE-TYPE:EXPORT-ONLY;MSO-DEFAULT-PROPS:YES;MSO-ASCII-MSO-ASCII-THEME-FONT:MINOR-LATIN;MSO-FAREAST-MSO-FAREAST-THEME-FONT:MINOR-LATIN;MSO-HANSI-MSO-HANSI-THEME-FONT:MINOR-LATIN;MSO-BIDI-MSO-BIDI-THEME-FONT:MINOR-BIDI;}DIV.WORDSECTION1{PAGE:WORDSECTION1;}