Performing Department
(N/A)
Non Technical Summary
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;}
Animal Health Component
0%
Research Effort Categories
Basic
90%
Applied
10%
Developmental
0%
Goals / Objectives
The southwestern US is an N fixation hotspot in which woody N fixers represent a greater percentage of woody plant basal area than most other areas of the US. Many areas across Texas and the US southwest have experienced periods of major drought conditions in the past several decades; the frequency and severity of droughts such as these are predicted to increase in the future. Understanding the role that drought plays in controlling rates of N fixation is critical to understanding inputs of N into these ecosystems in the future, and to parameterizing the role of N fixation in maintaining critical ecosystem services in the rangelands of this region.The ecophysiology of N fixers strongly suggests that drought, and water availability in general, plays an important role in determining rates of N fixation, and thus rates of N input into ecosystems. Other work has investigated the interactions between N availability and light availability on N fixation rates, demonstrating the need to investigate variation in multiple environmental parameters concurrently. The next step in understanding how drought may affect N fixation rates is to examine how WUE efficiency in N fixers changes with changing water availability in conjunction with variability in other environmental parameters, specifically light and N availability.Objective 1: Quantify the relative effects of drought versus light limitation and excess soil N availability on N fixation, WUE, and drought tolerance across several N-fixing tree species.Objective 2: Quantify how woody N fixers affect ecosystem services (e.g., forage quality, plant biodiversity, and soil C) in rangelands across a precipitation gradient, and how these effects correlate with N-fixer WUE and proxies of N fixation.Objective 3: Quantify how the effects drought on N-fixation rates in Prosopis glandulosa are driven by local adaptation versus acclimation by growing seeds collected from across the rainfall gradient crossed with Rhizobia collected from across the rainfall gradient.
Project Methods
The overall goal of our study is to develop a mechanistic understanding of how N inputs from N-fixing trees will change in response to drought across a precipitation gradient. To address this goal, we will use a combination of two greenhouse experiments and field sampling. We will use the first greenhouse experiment to determine the relative effect of drought versus other environmental controls, as well as the interactive effects of these environmental controls, on N fixation and its relationship to tree WUE and drought tolerance. This will be evaluated across species adapted to climates that vary in precipitation. Our field sampling will focus largely on a single species to evaluate proxies of tree N fixation and the effects of an N-fixing tree on various ecosystem services across an East-West precipitation gradient. Our second greenhouse experiment will evaluate how adaptation of an N-fixing tree species, and its associated bacteria, from different points on the precipitation gradient mediate the effect of drought on N fixation.