Partitioning of evapotranspiration using a stable isotope technique in an arid and high temperature agricultural production system

Agricultural production in the hot and arid low desert systems of southern California relies heavily on irrigation. A better understanding of how much and to what extent irrigated water is transpired by crops relative to being lost through evaporation would improve the management of increasingly limited water resources. In this study, we examined the partitioning of evapotranspiration (ET) over a field of forage sorghum (Sorghum bicolor), which was under evaluation as a potential biofuel feedstock, based on isotope measurements of three irrigation cycles at the vegetative stage. This study employed customized transparent chambers coupled with a laser-based isotope analyzer to continuously measure near-surface variations in the stable isotopic composition of evaporation (E, δE), transpiration (T, δT) and ET (δET) to partition the total water flux. Due to the extreme heat and aridity, δE and δT were very similar, which makes this system highly unusual. Contrary to an expectation that the isotopic signatures of T, E, and ET would become increasingly enriched as soils became drier, our results showed an interesting pattern that δE, δT, and δET increased initially as soil water was depleted following irrigation, but decreased with further soil drying in mid to late irrigation cycle. These changes are likely caused by root water transport from deeper to shallower soil layers. Results indicate that about 46% of the irrigated water delivered to the crop was used as transpiration, with 54% lost as direct evaporation. This implies that 28 − 39% of the total source water was used by the crop, considering the typical 60 − 85% efficiency of flood irrigation. The stable isotope technique provided an effective means of determining surface partitioning of irrigation water in this unusually harsh production environment. The results suggest the potential to further minimize unproductive water losses in these production systems

Municipal sewage sludge compost promotes Mangifera persiciforma tree growth with no risk of heavy metal contamination of soil

Application of sewage sludge compost (SSC) as a fertilizer on landscaping provides a potential way for the effective disposal of sludge. However, the response of landscape trees to SSC application and the impacts of heavy metals from SSC on soil are poorly understood. We conducted a pot experiment to investigate the effects of SSC addition on Mangifera persiciforma growth and quantified its uptake of heavy metals from SSC by setting five treatments with mass ratios of SSC to lateritic soil as 0%:100% (CK), 15%:85% (S15), 30%:70% (S30), 60%:40% (S60), and 100%:0% (S100). As expected, the fertility and heavy metal concentrations (Cu, Zn, Pb and Cd) in substrate significantly increased with SSC addition. The best performance in terms of plant height, ground diameter, biomass and N, P, K uptake were found i n S30, implying a reasonable amount of SSC could benefit the growth of M. persiciforma. The concentrations of Cu, Pb and Cd in S30 were insignificantly different from CK after harvest, indicating that M. persiciforma reduced the risk of heavy metal contamination of soil arising from SSC application. This study suggests that a reasonable rate of SSC addition can enhance M. persiciforma growth without causing the contamination of landscaping soil by heavy metals

The inflection point hypothesis: The relationship between the temperature dependence of enzyme-catalyzed reaction rates and microbial growth rates.

The temperature dependence of biological rates at different scales (from individual enzymes to isolated organisms to ecosystem processes such as soil respiration and photosynthesis) is the subject of much historical and contemporary research. The precise relationship between the temperature dependence of enzyme rates and those at larger scales is not well understood. We have developed macromolecular rate theory (MMRT) to describe the temperature dependence of biological processes at all scales. Here we formalize the scaling relationship by investigating MMRT both at the molecular scale (constituent enzymes) and for growth of the parent organism. We demonstrate that the inflection point (ᵢₙ) for the temperature dependence of individual metabolic enzymes coincides with the optimal growth temperature for the parent organism, and we rationalize this concordance in terms of the necessity for linearly correlated rates for metabolic enzymes over fluctuating environmental temperatures to maintain homeostasis. Indeed, ᵢₙ is likely to be under strong selection pressure to maintain coordinated rates across environmental temperature ranges. At temperatures at which rates become uncorrelated, we postulate a regulatory catastrophe and organism growth rates precipitously decline at temperatures where this occurs. We show that the curvature in the plots of the natural log of the rate versus temperature for individual enzymes determines the curvature for the metabolic process overall and the curvature for the temperature dependence of the growth of the organism. We have called this "the inflection point hypothesis", and this hypothesis suggests many avenues for future investigation, including avenues for engineering the thermal tolerance of organisms

Summer dry-down modulates the isotopic composition of soil CO2 production in snow-dominated landscapes

In mountainous landscapes, soil moisture is highly dynamic due to the effects of topography and the temporal variability imposed by seasonal precipitation, including rainfall and snow. Soil moisture is known to affect ecosystem carbon exchange both aboveground and belowground, as well as the stable isotopic composition of exchanged CO 2 . In this study we used an extensive suite of measurements to examine the effects of seasonal changes in soil moisture on the isotopic composition of soil CO 2 production at the landscape level. We show that the seasonal decline in soil moisture (i.e., summer dry-down) appeared to impose a trend in the δ 13 C of soil CO 2 production (δ P ) with more negative δ P early in the growing season when soils were wet, and more positive δ P as the growing season progressed and soils dried out. This seemingly generalizable pattern for a snow-dominated watershed is likely to represent the variability of recently assimilated C, tracked through the plant-soil system and imprinted in the respired CO 2 . Thus, our observations suggest that, at least for mountainous environments, seasonal changes in δ P are largely mediated by soil moisture and their spatial variability is partially organized by topography

A comprehensive assessment of anthropogenic and natural sources and sinks of Australasia\u27s carbon budget

Regional carbon budget assessments attribute and track changes in carbon sources and sinks and support the development and monitoring the efficacy of climate policies. We present a comprehensive assessment of the natural and anthropogenic carbon (C-CO2) fluxes for Australasia as a whole, as well as for Australia and New Zealand individually, for the period from 2010 to 2019, using two approaches: bottom-up methods that integrate flux estimates from land-surface models, data-driven models, and inventory estimates; and top-down atmospheric inversions based on satellite and in situ measurements. Our bottom-up decadal assessment suggests that Australasia\u27s net carbon balance was close to carbon neutral (−0.4 ± 77.0 TgC yr−1). However, substantial uncertainties remain in this estimate, primarily driven by the large spread between our regional terrestrial biosphere simulations and predictions from global ecosystem models. Within Australasia, Australia was a net source of 38.2 ± 75.8 TgC yr−1, and New Zealand was a net CO2 sink of −38.6 ± 13.4 TgC yr−1. The top-down approach using atmospheric CO2 inversions indicates that fluxes derived from the latest satellite retrievals are consistent within the range of uncertainties with Australia\u27s bottom-up budget. For New Zealand, the best agreement was found with a national scale flux inversion estimate based on in situ measurements, which provide better constrained of fluxes than satellite flux inversions. This study marks an important step toward a more comprehensive understanding of the net CO2 balance in both countries, facilitating the improvement of carbon accounting approaches and strategies to reduce emissions

Urban outdoor water use and response to drought assessed through mobile energy balance and vegetation greenness measurements

Urban vegetation provides many highly valued ecosystem services but also requires extensive urban water resources. Increasingly, cities are experiencing water limitations and managing outdoor urban water use is an important concern. Quantifying the water lost via evapotranspiration (ET) is critical for urban water management and conservation, especially in arid or semi-arid regions. In this study, we deployed a mobile energy balance platform to measure evaporative fraction throughout Riverside, California, a warm, semi-arid, city. We observed the relationship between evaporative fraction and satellite derived vegetation index across 29 sites, which was then used to map whole-city ET for a representative mid-summer period. Resulting ET distributions were strongly associated with both neighborhood population density and income. By comparing 2014 and 2015 summer-period water uses, our results show 7.8% reductions in evapotranspiration, which were also correlated with neighborhood demographic characteristics. Our findings suggest a mobile energy balance measurement platform coupled with satellite imagery could serve as an effective tool in assessing the outdoor water use at neighborhood to whole city scales

Seasonal soil moisture.

<p>Weekly averaged soil moisture in upland and riparian soil plots during the 2013 growing season.</p

Summer dry-down modulates the isotopic composition of soil CO₂ production in snow-dominated landscapes

<div><p>In mountainous landscapes, soil moisture is highly dynamic due to the effects of topography and the temporal variability imposed by seasonal precipitation, including rainfall and snow. Soil moisture is known to affect ecosystem carbon exchange both aboveground and belowground, as well as the stable isotopic composition of exchanged CO₂. In this study we used an extensive suite of measurements to examine the effects of seasonal changes in soil moisture on the isotopic composition of soil CO₂ production at the landscape level. We show that the seasonal decline in soil moisture (i.e., summer dry-down) appeared to impose a trend in the δ¹³C of soil CO₂ production (δ_P) with more negative δ_P early in the growing season when soils were wet, and more positive δ_P as the growing season progressed and soils dried out. This seemingly generalizable pattern for a snow-dominated watershed is likely to represent the variability of recently assimilated C, tracked through the plant-soil system and imprinted in the respired CO₂. Thus, our observations suggest that, at least for mountainous environments, seasonal changes in δ_P are largely mediated by soil moisture and their spatial variability is partially organized by topography.</p></div