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

Hysteresis of soil moisture spatial heterogeneity and the “homogenizing” effect of vegetation

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94935/1/wrcr12475.pd

Experimental landscape ecology

Abstract Experimentation in landscape ecology is widely conducted using diverse approaches to answer a broad range of questions. By assessing the response to controlled manipulations alternate hypotheses can be clearly refuted, model parameters quantified, and conditions are often ripe for unexpected insights. Results from landscape experiments complement the many well developed observational and modeling approaches more commonly used in landscape ecology. To better understand how landscape experimentation has been conducted and to identify future research directions, we reviewed and organized the diversity of experiments. We identified fifteen distinct landscape experiment types, which we categorized into four broad groups including (I) identifying landscape structure, (II) identifying how ecological processes vary within existing landscapes, (III) identifying how landscape structure influences ecological processes, and (IV) identifying landscape pattern formation factors. Experiment types vary along axes of scalable to real landscapes and generalizability, suitability for analysis through traditional experimental design and flexibility of experimental setup, and complexity of implementation and resource requirements. The next generation of experiments are benefiting from more explicit inclusion of scaling theories and tighter coupling between experiments and cyberinfrastructure. Future experimental opportunities for landscape ecologists include expanded collaborations among experiments, better representations of microbial-soil structure relationships at microscales, and direct evaluations of landscape interactions with global changes. The history, current practice, and future needs of landscape ecological research strongly support an expanded role of experimental approaches that complements the rich observational and modeling strengths of the field

Appendix C. Table of full statistical models presented in Figs. 1–3.

Table of full statistical models presented in Figs. 1–3

DataSheet_1_A global synthesis of reported urban tree carbon production rates and approaches.pdf

Trees are a prominent feature of urban ecosystems. Urban tree productivity is a key component of urban ecosystem energetics and has been identified as a possible pathway for reducing global greenhouse gas concentrations. Recently, extensive research has been directed to evaluating the carbon dynamics of urban trees in cities throughout the world. Here, we synthesize this research, using results from previous studies from 154 cities to identify the distribution of urban tree productivity globally and the basis for generating urban tree productivity estimates. Reported urban tree productivity shows a strong relationship with estimated tree carbon content and exhibits increases with both temperature and precipitation, with land cover differences influencing the degree of climate sensitivity. Compared with a reference productivity estimate, urban trees showed greatly reduced estimated rates of productivity and the magnitude of reduced productivity was inversely correlated with precipitation but was independent of temperature. Reported rates of productivity across all studies suggest climate restrictions that are more important with less intensively managed land covers. Scaling these results globally suggests a limited opportunity for urban trees to contribute to atmospheric carbon dioxide reductions, especially in the absence of major carbon emission reductions. We found that the majority of results are derived from tree inventories from a single period with rates of productivity estimate through quasi-empirical or allometric models. The majority of studies have been conducted in temperate biomes and North America. These results show that existing urban tree assessments have substantial methodological restrictions and regional biases. Future research of urban tree productivity should look toward improved methods and can use this synthesis as a baseline for comparisons and improvement.</p

Appendix B. Figures showing summer and winter soil temperature and moisture across the elevation transect.

Figures showing summer and winter soil temperature and moisture across the elevation transect

Appendix A. Table providing site descriptions of elevation transect.

Table providing site descriptions of elevation transect