Explore the vast range of titles available.

In California, water is a perennial concern. As competition for water resources increases due to growth in population, California’s tree nut farmers are committed to improving the efficiency of water used for food production. There is an imminent need to have reliable methods that provide information about the temporal and spatial variability of crop water requirements, which allow farmers to make irrigation decisions at field scale. This study focuses on estimating the actual evapotranspiration and crop coefficients of an almond and pistachio orchard located in Central Valley (California) during an entire growing season by combining a simple crop evapotranspiration model with remote sensing data. A dataset of the vegetation index NDVI derived from Landsat-8 was used to facilitate the estimation of the basal crop coefficient (Kcb), or potential crop water use. The soil water evaporation coefficient (Ke) was measured from microlysimeters. The water stress coefficient (Ks) was derived from airborne remotely sensed canopy thermal-based methods, using seasonal regressions between the crop water stress index (CWSI) and stem water potential (Ψstem). These regressions were statistically-significant for both crops, indicating clear seasonal differences in pistachios, but not in almonds. In almonds, the estimated maximum Kcb values ranged between 1.05 to 0.90, while for pistachios, it ranged between 0.89 to 0.80. The model indicated a difference of 97 mm in transpiration over the season between both crops. Soil evaporation accounted for an average of 16% and 13% of the total actual evapotranspiration for almonds and pistachios, respectively. Verification of the model-based daily crop evapotranspiration estimates was done using eddy-covariance and surface renewal data collected in the same orchards, yielding an R2 ≥ 0.7 and average root mean square errors (RMSE) of 0.74 and 0.91 mm·day−1 for almond and pistachio, respectively. It is concluded that the combination of crop evapotranspiration models with remotely-sensed data is helpful for upscaling irrigation information from plant to field scale and thus may be used by farmers for making day-to-day irrigation management decisions.

Climate change and biodiversity loss are two global challenges that can be addressed simultaneously through reforestation of previously cleared land. However, carbon markets can encourage reforestations that focus on maximizing carbon storage, potentially at the expense of biodiversity conservation. To identify opportunities to optimize reforestation design and management to meet both goals, we examined the forest stand features associated with carbon stocks in biomass and soil, as well as bird abundance and diversity, in remnant and restored riparian forest stands in central California, U.S.A. Within three decades of reforestation, both planted and naturally regenerating riparian forest stands provided significantly greater carbon storage and avian biodiversity benefits compared to baseline conditions. They were also similar to a remnant riparian forest stand. We identified a synergy between carbon storage and biodiversity benefits in their positive associations with understorey cover, but we also identified a trade‐off in their relationships to forest stand density. Biomass carbon stocks were strongly positively related to stand density, while bird density and diversity suffered at the highest stand densities. The variability in understorey cover across forest stands indicates an opportunity for further enhancement of carbon and biodiversity benefits in areas where understorey cover is low, while the variability in stand density suggests an opportunity to re‐examine reforestation goals and consider thinning to achieve those goals. Synthesis and applications. We identified synergies and trade‐offs between carbon storage and biodiversity in their relationships to forest stand features, indicating opportunities to optimize reforestation design and management to achieve multiple goals. Our approach can be adapted to other reforestation efforts intended to simultaneously address the global challenges of climate change and biodiversity loss. Foreign Language Resumen El cambio climatico y la pérdida de biodiversidad son dos problemas globales que se pueden enfrentar con la reforestación de tierras previamente degradadas. Sin embargo, los mercados de carbon promueven reforestaciones enfocadas en maximizar el almacenamiento de carbon, posiblemente a cuestas de la conservación de la biodiversidad. Para identificar oportunidades de diseño y gestión de programas de reforestación enfocados en estos dos objetivos, evaluamos las características de rodales de bosques que determinan las medias de carbon en la biomasa y en los suelos, y que también determinan la abundancia y diversidad de aves en rodales de bosques riparios remanentes y restaurados en el centro de California, Estados Unidos. En tres décadas de reforestación, los rodales de bosques riparios sembrados y regenerados naturalmente incrementaron de manera significativa el almacenamiento de carbono y los beneficios para la biodiversidad de aves comparado con condiciones de referencia. Los rodales de bosques riparios también mostraron características similares a un rodal de bosque ripario remanente. Hemos identificado una sinergia entre el almacenamiento de carbono y beneficios a la biodiversidad porque estan positivamente asociadas con la cobertura del sotobosque, pero también identificamos una compensación con la densidad del rodal de bosque. Las reservas de carbono en la biomasa demostraron una fuerte relación positiva con la densidad del rodal, mientras que la densidad y la diversidad de las aves sufrieron en las densidades más altas del rodal. La variabilidad en la cobertura del sotobosque en los rodales de bosque indica una oportunidad para augmentar beneficios de carbon y de biodiversidad en áreas donde la coberatura esté baja, mientras que la variabilidad en la densidad de los rodales sugiere una oportunidad para reexaminar las metas de reforestación posiblemente considerando el raleo para alcanzar las metas. Síntesis y aplicaciones. Identificamos sinergias y compensaciones entre el almacenamiento de carbono y la biodiversidad con las características de rodales de bosque, indicando oportunidades para optimizar el diseño y la gestión de programas de reforestación para lograr objetivos múltiples. Nuestro enfoque se puede adaptar a otros esfuerzos de reforestación dedicados a enfrentar simultáneamente los problemas globales de cambio climatico y la pérdida de biodiversidad. We identified synergies and trade‐offs between carbon storage and biodiversity in their relationships to forest stand features, indicating opportunities to optimize reforestation design and management to achieve multiple goals. Our approach can be adapted to other reforestation efforts intended to simultaneously address the global challenges of climate change and biodiversity loss.

Soils account for the largest terrestrial pool of carbon and have the potential for even greater quantities of carbon sequestration. Typical soil carbon (C) stocks used in global carbon models only account for the upper 1 meter of soil. Previously unaccounted for deep carbon pools (>1 m) were generally considered to provide a negligible input to total C contents and represent less dynamic C pools. Here we assess deep soil C pools associated with an alluvial floodplain ecosystem transitioning from agricultural production to restoration of native vegetation. We analyzed the soil organic carbon (SOC) concentrations of 87 surface soil samples (0–15 cm) and 23 subsurface boreholes (0–3 m). We evaluated the quantitative importance of the burial process in the sequestration of subsurface C and found our subsurface soils (0–3 m) contained considerably more C than typical C stocks of 0–1 m. This deep unaccounted soil C could have considerable implications for global C accounting. We compared differences in surface soil C related to vegetation and land use history and determined that flooding restoration could promote greater C accumulation in surface soils. We conclude deep floodplain soils may store substantial quantities of C and floodplain restoration should promote active C sequestration.

The annual dynamics of whole mature almond tree nutrient remobilization in spring and the accumulation of nutrients in perennial tissues during the year were determined by sequential coring, tissue sampling, nutrient analysis, whole tree excavation and biomass estimation for trees grown under four nitrogen rate treatments 140 kg ha−1 N (N140), 224 kg ha−1 N (N224), 309 kg ha−1 N (N309), and 392 kg ha−1 N (N392) over 2 years. Whole tree perennial organ N content was greatest in dormancy then declined through bud swell, flowering and fruit set, achieving the lowest total whole tree nutrient content of perennial organs by March 12 [12–14 days after full bloom (DAFB)] coincident with 60–70% leaf expansion. During this period no net increment in whole tree N content (annual plus perennial N) was observed indicating that tree demand for N for bud break, flowering, fruit set and leaf out was met by remobilized stored N and that there was no net N uptake from soil. Remobilizable N increased with increasing N application up to N309 and was maximal at 44.4 ± 4 kg ha−1 and 37.5 ± 5.7 kg ha−1 for the optimally fertilized N309 in 2012 and 2013 respectively. Net increases in perennial organ N (stored N) commenced 41 DAFB and continued through full leaf abscission at 249 DAFB. Total annual N increment in perennial organs varied from 25 to 60 kg ha−1 and was strongly influenced by N rate and tree yield. N remobilized from senescing leaves contributed from 11 to 15.5 ± 0.6 kg ha−1 to perennial stored N. Similar patterns of nutrient remobilization and storage were observed for P, K, and S with maximal whole tree perennial storage occurring during dormancy and remobilization of that stored P, K, S to support annual tree demands through to fruit set and 70–100% leaf development. Net annual increment in perennial organ P, K, S commenced 98 DAFB and continued through full leaf abscission at 249 DAFB. Organ specific contribution to remobilizable and stored nutrients changes over the growing season are presented. Details of the pattern of perennial organ nutrient allocation, storage, and remobilization provides a framework for the optimal management of nutrients in almond with relevance for other deciduous tree species.

PREMISE OF THE STUDY: Plant phenology influences resource utilization, carbon fluxes, and interspecific interactions. Although controls on aboveground phenology have been studied to some degree, controls on root phenology are exceptionally poorly understood. METHODS: We used minirhizotrons to examine the timing of grape root production over 5 yr in Fredonia, New York, USA, in a humid continental climate; and over 3 yr in Oakville, California, USA, in a Mediterranean climate. We used data from previous experiments to examine the relationship of root phenology with aboveground phenology. We compared interannual variability in root and shoot growth and determined the influence of abiotic factors on the timing of root initiation, peak root standing crop, peak root growth rate, and cessation of root growth. KEY RESULTS: Root phenology was not tightly coupled with aboveground phenological periods. Both sites typically had one yearly root flush and high interannual variability in root growth. Root phenology was more variable in California than in New York. In this and other published studies, interannual variation in root phenology was greater than variation in aboveground phenology. The three phenological phases of root growth—root initiation, peak root growth, and root cessation—were related to different suites of abiotic factors. CONCLUSIONS: Root phenology is highly variable among years. Analysis of potential controlling factors over several years suggest that belowground phenological phases should be analyzed separately from each other. If aboveground grape phenology responds differently than belowground phenology to changes in air temperature, global warming may further uncouple the timing of aboveground and belowground growth.

Background Quantifying terrestrial carbon (C) stocks in vineyards represents an important opportunity for estimating C sequestration in perennial cropping systems. Considering 7.2 M ha are dedicated to winegrape production globally, the potential for annual C capture and storage in this crop is of interest to mitigate greenhouse gas emissions. In this study, we used destructive sampling to measure C stocks in the woody biomass of 15-year-old Cabernet Sauvignon vines from a vineyard in California’s northern San Joaquin Valley. We characterize C stocks in terms of allometric variation between biomass fractions of roots, aboveground wood, canes, leaves and fruits, and then test correlations between easy-to-measure variables such as trunk diameter, pruning weights and harvest weight to vine biomass fractions. Carbon stocks at the vineyard block scale were validated from biomass mounds generated during vineyard removal. Results Total vine C was estimated at 12.3 Mg C ha −1 , of which 8.9 Mg C ha −1 came from perennial vine biomass. Annual biomass was estimated at 1.7 Mg C ha −1 from leaves and canes and 1.7 Mg C ha −1 from fruit. Strong, positive correlations were found between the diameter of the trunk and overall woody C stocks (R 2  = 0.85), pruning weights and leaf and fruit C stocks (R 2  = 0.93), and between fruit weight and annual C stocks (R 2  = 0.96). Conclusions Vineyard C partitioning obtained in this study provides detailed C storage estimations in order to understand the spatial and temporal distribution of winegrape C. Allometric equations based on simple and practical biomass and biometric measurements could enable winegrape growers to more easily estimate existing and future C stocks by scaling up from berries and vines to vineyard blocks.

Nitrogen fertilizer applied to soil is the primary source of the greenhouse gas (GHG) nitrous oxide (N 2 O). The assessment of N 2 O emissions, or net fluxes of the GHG methane (CH 4 ), are lacking for upland, arid agricultural ecosystems worldwide. In California, where rates of application for nitrogen (N) can exceed 300 kg per hectare for N-intensive fruit and nut crops (>2 million acres), liquid N fertilizers applied through microirrigation systems (fertigation) represent the predominant method of N fertilization. Little information is available for how these concentrated and spatially discrete N solution applications influence N 2 O emissions and net CH 4 fluxes (the sum of methanogenic and methanotrophic activity). In this study we examined soil N 2 O-N emissions and net CH 4 fluxes for drip and stationary microsprinklers, two of the most widely used fertigation emitters, in an almond orchard where 235.5 kg N/ha were applied during the season of measurement (2009-2010). We accomplished this by modeling the spatial patterns of N 2 O and CH 4 at the scale of meters and centimeters using simple mathematical approaches. For two applications of 33.6 kg/ha and three applications of 56.1 kg/ha targeted to the phenologic stages with highest tree N demand, the spatial patterns of N 2 O fluxes were similar to the emitter water distribution pattern and independent of temperature and fertilizer N form applied. Net CH 4 fluxes were extremely low and there was no discernible spatial pattern, but areas kept dry (driveways between tree rows) generally consumed CH 4 while it was produced in the microirrigation wet-up area. The N 2 O-N emissions for fertigation events at the scale of days, and over a season, were significantly higher from the drip irrigated orchard (1.6 ± 0.7 kg N 2 O-N ha −1 yr −1 ) than a microsprinkler irrigated orchard (0.6 ± 0.3 kg N 2 O-N ha −1 yr −1 ). N 2 O emissions and net CH 4 fluxes were only significantly correlated with soil water filled pore space and not with mineral-N. The correlation was much better for N 2 O emissions. Our results greatly improve our ability to scale N 2 O production to the orchard level, and provide growers with a tool for lowering almond orchard carbon and nitrogen footprints.

Simultaneous measurements of CO2and O2fluxes from wheat (Triticum aestivum) shoots indicated that short-term exposures to elevated CO2concentrations diverted photosynthetic reductant from NO3 -or NO2 -reduction to CO2fixation. With longer exposures to elevated CO2, wheat leaves showed a diminished capacity for NO3 -photoassimilation at any CO2concentration. Moreover, high bicarbonate levels impeded NO2 -translocation into chloroplasts isolated from wheat or pea leaves. These results support the hypothesis that elevated CO2inhibits NO3 -photoassimilation. Accordingly, when wheat plants received NO3 -rather than NH4 +as a nitrogen source, CO2enhancement of shoot growth halved and CO2inhibition of shoot protein doubled. This result will likely have major implications for the ability of wheat to use NO3 -as a nitrogen source under elevated CO2.

Nitrous oxide (N2O) is a key atmospheric greenhouse gas that contributes to global climatic change through radiative warming and depletion of stratospheric ozone. In this report, N2Oflux was monitored simultaneously with photosynthetic CO2and O2exchanges from intact canopies of 12 wheat seedlings. The rates of N2O-N emitted ranged from <2 pmol·m-2· s-1when NH4 +was the N source, to 25.6 ± 1.7 pmol·m-2· s-1(mean ± SE, n = 13) when the N source was shifted to NO3 -. Such fluxes are among the smallest reported for any trace gas emitted by a higher plant. Leaf N2Oemissions were correlated with leaf nitrate assimilation activity, as measured by using the assimilation quotient, the ratio of CO2assimilated to O2evolved.15N isotopic signatures on N2Oemitted from leaves supported direct N2Oproduction by plant NO3 -assimilation and not N2Oproduced by microorganisms on root surfaces and emitted in the transpiration stream. In vitro production of N2Oby both intact chloroplasts and nitrite reductase, but not by nitrate reductase, indicated that N2Oproduced by leaves occurred during photoassimilation of NO2 -in the chloroplast. Given the large quantities of NO3 -assimilated by plants in the terrestrial biosphere, these observations suggest that formation of N2Oduring NO2 -photoassimilation could be an important global biogenic N2Osource.

We studied bacterial abundance and community structure of five soil cores using high-throughput sequencing of the 16S rRNA gene. Shifts in the soil bacterial composition were more pronounced within a vertical profile than across the landscape. Soil organic carbon (SOC) and nitrogen (N) concentrations decreased exponentially with soil depth and revealed a buried carbon-rich horizon between 0.8 and 1.3 m across all soil cores. This buried horizon was phylogenetically similar to its surrounding subsoils supporting the idea that the type of carbon, not necessarily the amount of carbon was driving the apparent similarities. In contrast to other studies, Nitrospirae was one of our major phyla with relatively high abundances throughout the soil profile except for the surface soil. Although depth is the major driver shaping soil bacterial community structure, positive correlations with SOC and N concentrations, however, were revealed with the bacterial abundance of Acidobacteria, one of the major, and Gemmatimonadetes, one of the minor phyla in our study. Our study showed that bacterial diversity in soils below 2.0 m can be still as high if not higher than in the above laying subsurface soil suggesting that various bacteria throughout the soil profile influence major biogeochemical processes in floodplain soils.