An official website of the United States government
Climate models predict that water limited regions around the world will become drier and warmer in the near future, including southwestern North America. We developed a large-scale experimental system that allows testing of the ecosystem impacts of precipitation changes. Four treatments were applied to 1600 m2 plots (40 m × 40 m), each with three replicates in a piñon pine (Pinus edulis) and juniper (Juniper monosperma) ecosystem. These species have extensive root systems, requiring large-scale manipulation to effectively alter soil water availability.  Treatments consisted of: 1) irrigation plots that receive supplemental water additions, 2) drought plots that receive 55% of ambient rainfall, 3) cover-control plots that receive ambient precipitation, but allow determination of treatment infrastructure artifacts, and 4) ambient control plots. Our drought structures effectively reduced soil water potential and volumetric water content compared to the ambient, cover-control, and water addition plots. Drought and cover control plots experienced an average increase in maximum soil and air temperature at ground level of 1-4° C during the growing season compared to ambient plots, and concurrent short-term diurnal increases in maximum air temperature were also observed directly above and below plastic structures. Our drought and irrigation treatments significantly influenced tree predawn water potential, sap-flow, and net photosynthesis, with drought treatment trees exhibiting significant decreases in physiological function compared to ambient and irrigated trees.  Supplemental irrigation resulted in a significant increase in both plant water potential and xylem sap-flow compared to trees in the other treatments. This experimental design effectively allows manipulation of plant water stress at the ecosystem scale, permits a wide range of drought conditions, and provides prolonged drought conditions comparable to historical droughts in the past – drought events for which wide-spread mortality in both these species was observed. Water potential measurements were used to monitor the water stress of the two target species across the four treatment regimes.  Sampling for water potentials occurred twice daily.  One set of samples was collected hours before dawn and another set was collected at mid-day.  The predawn readings provided the “least-stressed†tree water content values as they were collected after the trees had returned to equilibrium over the evening and had yet to start transpiring.  The mid-day values, collected after tree-level respiration had been occurring for hours and when the daily temperatures were highest, represented the opposite “most-stressed†scenario. To gauge the effect of the irrigation treatment on the water content of the trees, we sampled water potentials just before and just after irrigation events.  Â
more »
« less
This content will become publicly available on April 1, 2026
Sunflower and Sunn Hemp Potential as Summer Cover Crops in Southern Texas
The strategic incorporation of low-cost management practices, such as cover crops (CCs), to citrus production in southern Texas could add valuable ecosystem services that increase trees’ resilience to changing climatic conditions. To provide insight into how producers can manage CCs to optimize ecosystem services, we conducted a study in controlled conditions to examine the potential of adding three annual summer CCs species: common buckwheat (Fagopyrum esculentum), sunflower (Helianthus annuus L.), and sunn hemp (Crotalaria juncea L.) as monocultures growing in two representative soil types of the citrus region in Texas, and receiving one of these irrigation volumes based on calculated daily water losses [i.e., evapotranspiration (ET)] corresponding to 100, 75, 50, and 25% field capacity replenishment. Sunflower and sunn hemp produced the highest aboveground dry matter, which was on average 338 and 342% greater than buckwheat. Sunn hemp emerged faster than the other CCs, and mortality was relatively uniform across CCs, but buckwheat exhibited the highest sensitivity to drought and heat distress. Sunn hemp exhibited superior aboveground biomass accumulation, height, and chlorophyll content. All CCs performed similarly in both experimental soils, under native fertility conditions, and without the addition of mineral fertilizers. Irrigation at 75 and 100% ET levels were conducive to enhanced plant growth, which indicates that a minimum of 86.4 mm (75% ET) is required during CCs lifespan, but sunn hemp and sunflower were also capable of tolerating medium (50% ET) drought stress. Overall, our findings suggest that sunflower and sunn hemp exhibited traits desirable for incorporation as CCs to a perennial citrus production system. The primary benefit was the addition of organic matter with minimum management; however, both CCs’ performance was dependent on planting timing, successful early establishment, and favorable environmental conditions.
more »
« less
- Award ID(s):
- 1914745
- PAR ID:
- 10591261
- Publisher / Repository:
- MDPI
- Date Published:
- Journal Name:
- Agronomy
- Volume:
- 15
- Issue:
- 4
- ISSN:
- 2073-4395
- Page Range / eLocation ID:
- 986
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Citrusspp. trees are not fully dormant during the winter months in the northern hemisphere; therefore, they are susceptible to sporadic freeze events of various magnitudes that could decline tree productivity or be lethal. In Feb 2021, winter storm Uri produced freezing air temperatures for nearly 72 hours, which created several degrees of injuries to citrus orchards in southern Texas. Producers in the area implemented combinations of multiple horticultural practices aimed at remediating injuries from the cold spell to stimulate root and tree recovery. However, there is a gap in our understanding of how practices such as compost application (CA) combined with varying rates of nitrogen (N) might facilitate tree recovery. Therefore, we conducted a 2-year field experiment using two CAs as soil amendments in combination with three N rates (112, 168, and 224 kg·ha−1N) to evaluate fruit yield and internal quality, root growth, and recovery of ‘Rio Red’ grapefruits (Citrus×paradisiMacf.) and ‘Marrs’ sweet oranges (Citrus sinensis). The yields of both crops exhibited modest improvement with CA in 2022; however, it was nonsignificant. Moreover, CA elicited more beneficial effects than N rates alone when rehabilitating trees and improving fruit internal quality after freezing events. Grapefruit brix was 4% higher in fruits harvested from trees treated with compost, and grapefruit roots exhibited a two-fold dry weight increment with CA. Sweet oranges from trees in the CA treatment had 22% lower acidity compared with that of untreated trees. Overall, our results indicate that citrus producers in southern Texas and other subtropical citrus-producing regions might facilitate the rehabilitation of tree injuries attributed to mild to moderate freeze events with moderate financial gains with the timely application of compost, which enhanced tree fitness and ameliorated fruit productivity declines during subsequent harvests.more » « less
-
Abstract Evapotranspiration (ET) is co‐regulated by subsurface water availability, atmospheric demand for water, and radiation. Spatial differences in the limiting factors on ET that emerge along the soil‐plant‐atmosphere continuum result in distinct ecohydrological regimes with differing sensitivities to atmospheric and subsurface drivers. However, different components of the soil‐plant‐atmosphere continuum are not equally well understood. Deep subsurface water access is particularly difficult to measure and model, but can sustain ET under drought conditions when shallow soil moisture appears to be acutely limiting. Here, we exploited this principle to identify ecosystems that rely on deep subsurface water availability. We first used a plant hydraulic model to determine the expected ET behavior for plants with deep water access. We then examined 19 flux towers and found that responsiveness of ET to atmospheric conditions during dry periods was indicative of some ecosystems with deep water access. We used the divergent sensitivities of ET to vapor pressure deficit, radiation, and shallow soil moisture to identify distinct ecohydrological regimes in gridded data covering the continental U.S. We diagnosed deep water usage in ecosystems where ET remained sensitive to atmospheric conditions despite being insensitive to shallow soil moisture variability. Further, we found that drought stress, plant hydraulic traits, and ecosystem biophysical variables mediated the sensitivity of ET to aboveground and belowground conditions.more » « less
-
Abstract Climate variability and periodic droughts have complex effects on carbon (C) fluxes, with uncertain implications for ecosystem C balance under a changing climate. Responses to climate change can be modulated by persistent effects of climate history on plant communities, soil microbial activity, and nutrient cycling (i.e., legacies). To assess how legacies of past precipitation regimes influence tallgrass prairie C cycling under new precipitation regimes, we modified a long‐term irrigation experiment that simulated a wetter climate for >25 years. We reversed irrigated and control (ambient precipitation) treatments in some plots and imposed an experimental drought in plots with a history of irrigation or ambient precipitation to assess how climate legacies affect aboveground net primary productivity (ANPP), soil respiration, and selected soil C pools. Legacy effects of elevated precipitation (irrigation) included higher C fluxes and altered labile soil C pools, and in some cases altered sensitivity to new climate treatments. Indeed, decades of irrigation reduced the sensitivity of both ANPP and soil respiration to drought compared with controls. Positive legacy effects of irrigation on ANPP persisted for at least 3 years following treatment reversal, were apparent in both wet and dry years, and were associated with altered plant functional composition. In contrast, legacy effects on soil respiration were comparatively short‐lived and did not manifest under natural or experimentally‐imposed “wet years,” suggesting that legacy effects on CO2efflux are contingent on current conditions. Although total soil C remained similar across treatments, long‐term irrigation increased labile soil C and the sensitivity of microbial biomass C to drought. Importantly, the magnitude of legacy effects for all response variables varied with topography, suggesting that landscape can modulate the strength and direction of climate legacies. Our results demonstrate the role of climate history as an important determinant of terrestrial C cycling responses to future climate changes.more » « less
-
Abstract The relationship between diversity and stability remains a key question in ecology and has important consequences for understanding the sustainability (and profitability) of bioenergy cropping systems; yet to date, little work has been done to examine these relationships in agricultural systems directly. In this study, we evaluated the relationship between biodiversity (in number of planted species) and the stability of biomass production in four experimental bioenergy cropping systems established in Wisconsin and Michigan. Species composition and aboveground production were monitored at all sites for 8–10 years (2010–2019) allowing us to evaluate the temporal stability of biomass yield (defined as the temporal mean divided by the temporal SD) in these cropping systems. A major regional drought in 2012 also allowed us to evaluate resistance and resilience. Although three of the cropping systems were established with the same seed mixtures and were managed in the same way, species composition differed markedly between sites. This limited our ability to attribute differences within cropping systems across sites to the abundance of specific species. Overall, there was no clear relationship between planted species richness and yield stability in biomass production at these sites. At both sites, the lowest diversity system (switchgrass monoculture) had the highest interannual stability in production and was equivalent to that of the highest diversity treatment (prairie). Resilience to the drought was high in all treatments and did not differ among the four cropping systems; however, resistance to drought differed among systems and was highest in the switchgrass monocultures at both sites. The abundance of perennial C4grasses increased over time in all cropping systems, except for the successional plots. The persistence of annual species in the successional treatments at both sites likely contributed to low stability and high interannual turnover in this system. We found no evidence that increasing the diversity of planted species in bioenergy cropping systems enhances stability in aboveground biomass production; nor was there any difference in resistance or resilience to drought. The higher costs of establishing more diverse bioenergy cropping systems may be warranted if other ecosystem services, such as supporting diverse pollinator and predator insect species at the landscape scale, are desired from bioenergy crops in addition to biomass production.more » « less
